PRACTICAL GUIDE ON THE SELECTION OF PROCESS TECHNOLOGY FOR THE TREATMENT OF AQUEOUS ORGANIC EFFLUENT...

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PRACTICAL GUIDE ON THE SELECTION OF PROCESS TECHNOLOGY FOR THE TREATMENT OF AQUEOUS ORGANIC EFFLUENT STREAMS

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PRACTICAL GUIDE ON THE SELECTION OF PROCESS TECHNOLOGY FOR THE TREATMENT OF AQUEOUS ORGANIC EFFLUENT STREAMS CONTENTS 0 INTRODUCTION/PURPOSE 1 SCOPE 2 FIELD OF APPLICATION 3 DEFINITIONS

3.1 IPU 3.2 AOS 3.3 BODs 3.4 COD 3.5 TOC 3.6 Toxicity 3.7 Refractory Organics/Hard COD 3.8 Heavy Metals 3.9 EA 3.10 Biological Treatment Terms 3.11 BATNEEC 3.12 BPEO 3.13 EQS/LV 3.14 IPC 3.15 VOC 3.16 F/M Ratio 3.17 MLSS 3.18 MLVSS 4 DESIGN/ECONOMIC GUIDELINES



5 EUROPEAN LEGISLATION 5.1 General 5.2 Integrated Pollution Control (IPC) 5.3 Best Available Techniques Not Entailing Excessive Costs (BATNEEC) 5.4 Best Practicable Environmental Option (BPEO) 5.5 Environmental Quality Standards(EQS) 6 IPU EXIT CONCENTRATION 7 SITE/LOCAL REQUIREMENTS 8 PROCESS SELECTION PROCEDURE 8.1 Waste Minimization Techniques (WMT) 8.2 AOS Stream Definition 8.3 Technical Check List 8.4 Preliminary Selection of Suitable Technologies 8.5 Process Sequences 8.6 Economic Evaluation 8.7 Process Selection APPENDICES A DIRECTIVE 76/464/EEC - LIST 1 B DIRECTIVE 76/464/EEC - LIST 2 C THE EUROPEAN COMMISSION PRIORITY CANDIDATE LIST D THE UK RED LIST E CURRENT VALUES FOR EUROPEAN COMMUNITY ENVIRONMENTAL QUALITY STANDARDS AND CORRESPONDING LIMIT VALUES F ESTABLISHED TECHNOLOGIES G EMERGING TECHNOLOGY H PROPRIETARY/LESS COMMON TECHNOLOGIES J COMPARATIVE COST DATA



FIGURES 1 INTERMEDIATE PROCESS UNIT SYSTEM 2 AOS TREATMENT - SELECTION PROCEDURE (INLET CONCENTRATION) 3 AOS TREATMENT - SELECTION PROCEDURE (OUTLET CONCENTRATION) 4 LIQUID WASTE TREATMENT PROCESSES



0 INTRODUCTION/PURPOSE This Guide is one in the series of GBHE's Environmental Technical Practice Guides. Its purpose is to provide the practicing Process Engineer with: (a) A brief, simple environmental framework within which initial process design work handling aqueous organic streams (AOS) can proceed efficiently. (b) A structured selection procedure which will facilitate the generation of a small number of competing flowsheet schemes. These options will then be further refined prior to selection of the preferred process. (c) A summary of the commercially proven and emerging technologies for the treatment of Aqueous Organic Streams. 1 SCOPE This Guide presents in outline those key factors which need to be addressed by the chemical engineer when faced with the task of generating preliminary flowsheet schemes for the treatment of AOS. The guide does not present technical data to be used for design purposes, nor does it attempt to replicate detailed descriptions of alternate technologies. This information should be sought in Research reports, from in-house specialists, in the literature and from contractors. 2 FIELD OF APPLICATION This Guide is available to Process Engineers in GBH Enterprises Worldwide. 3 DEFINITIONS 3.1 IPU An Intermediate Process Unit utilizes any suitable technology to treat plant Aqueous Organic Streams in such a way that all water, surplus to production requirements, is exported from the plant as Product streams. Such streams may require further treatment prior to discharge to receiving waters. Further treatment may be on site or off site (e.g. a biological treatment unit), (see Figure1).



The IPU system will be designed to achieve the best overall economics while meeting environmental constraints focusing on: (a) Recycle of material back into the process either for reuse or destruction. (b) Technical and economic integration with any downstream biological unit, e.g. selective removal of those chemicals which are not to enter receiving waters but are impractical or more expensive to remove either by biological treatment or subsequent tertiary treatment. (c) Achievement of adequate quality control of the exported aqueous product stream.

All AOS should be listed as candidates for treatment by an IPU system. 3.2 AOS Aqueous Organic Streams are single phase, contain dissolved organics, and are surplus to process requirements, (see 8.3). 3.3 BODs The chemical oxygen demand is determined by a batch reactor test in which microbes are allowed to degrade organic matter in the presence of oxygen over a period of 5 days at 20°C. 3.4 COD The chemical oxygen demand is determined by a procedure in which a chemical oxidizing agent is added to the sample and refluxed for 2 hours. The amount of oxidizing agent destroyed in the test is proportional to the COD of the sample. The COD value will normally be higher than the BODs.



3.5 TOC Total organic carbon is measured by converting all of the carbon present in the sample into carbon dioxide by combusting the sample in a high temperature furnace and measuring the carbon dioxide formed by infrared spectroscopy. 3.6 Toxicity The definition of toxicity raises complex issues beyond the scope of this Guide. The considerable concern that waste waters can convey hazardous materials into the environment has led to legislation in virtually every country. In the EC and U.K., lists of dangerous substances (see 5.1) have been issued under legislation with selection based on considerations of toxicity, persistence and bio-accumulation. In the U.S.A. the situation is similar, but greater emphasis is placed on acute toxicity tests. The key test for acute toxicity is LC50 which means that approximately 50% of the aquatic species (usually fish) used in the test will die under the conditions of concentration and time given. The term TLm (Median Tolerance Limit) means that approximately 50% of the fish will show abnormal behavior (including death) under the conditions given. Legislation, which may be different from one country to another, is moving toward "toxicity based consent" based on identified species. In cases of discharges to municipal treatment plants, the toxicity of the discharged effluent to the microbes in the treatment process has to be determined. 3.7 Refractory Organics/Hard COD These are organic chemicals which resist biodegradation. Examples include some halogenated hydrocarbons and chlorinated pesticides. 3.8 Heavy Metals Any cation having an atomic weight greater than 23 should be considered to be a heavy metal. These are persistent and can be toxic/carcinogenic.



3.9 EA Environment Agency 3.10 Biological Treatment Terms "Equalization" is the provision of storage capacity for effluent in order to reduce the variability of waste water flow rates and composition to acceptable levels which protect the treatment plant from shock pollutants and hydraulic loadings. These variations may occur, for example, due to cyclical process operations, unsteady state process operation, spillage, plant maintenance operations, fire-water and storm-water. "Primary Treatment" means the first major operation in a waste water treatment works in which a substantial proportion of the suspended solids contained within the incoming waste water are removed, usually by sedimentation. "Secondary Treatment" means treatment by biological methods and is usually preceded by primary treatment. "Tertiary or Advanced Treatment" processes control specific organic and inorganic pollutants. The more common processes are used for the removal of nitrogen and phosphorus nutrients. Other more special- purpose processes include carbon adsorption, ion exchange and reverse osmosis. 3.11 BATNEEC Best Available Techniques Not Entailing Excessive Costs. 3.12 BPEO Best Practicable Environmental Option. 3.13 EQS/LV Environmental Quality Standards, this is usually expressed as an annual average. Limit Value.



3.14 IPC Integrated Pollution Control. 3.15 VOC Volatile Organic Compounds. 3.16 F/M Ratio Feed to biomass ratio usually expressed in (g/day)/g. 3.17 MLSS "Mixed-Liquor Suspended Solids"; the concentration of suspended solids in the "mixed-liquor", measured by filtration and drying. Beware: dissolved salts can lead to misleading results. The value includes active biosolids, inactive biosolids and inert non-biosolids. 3.18 MLVSS "Mixed-Liquor Volatile Suspended Solids"; the concentration of suspended solids in the "mixed-liquor" which are capable of being vaporized in at 500°C. Measured by filtration on ashless paper and incineration in a muffle-furnace. Commonly used to estimate (MLSS - inorganic inerts); not equal to active biomass. 4 DESIGN/ECONOMIC GUIDELINES During the design of any plant the following recommendations should be considered by the process engineer: (a) Check out the Project philosophy regarding "Cleaner Technology" and contribute to its formulation as appropriate. (b) Rigorously apply waste minimization techniques by avoiding the production of waste or reducing its rate of production



Note: AOS may contain material that could be profitably upgraded and sold as a byproduct. (c) Assess the selection of process technology/operating conditions and methods of process control with a view to eliminating/reducing AOS. (d) Assess the design of equipment with a view to minimizing AOS produced during start-up, shutdowns, product changes, plant maintenance and equipment cleaning operations. (e) The AOS produced in the process should not be flow sheeted to enter the site drainage system except where specific approval is given by Site Environmental Group. (f) AOS produced in a plant should not be mixed with each other unless there is a clear economic case for treating several AOS in a single IPU. In most cases, it is more economic to treat a concentrated stream at source. (g) All on-plot plant AOS, including intermittent discharges, should be piped above ground to an IPU, except where this can be shown to be unnecessary. (h) Special consideration should be given to the case for removing any volatile compounds contained in AOS in an IPU. (j) Each on-plot effluent stream leaving an IPU should have Product Status and therefore a specification to show that it meets the requirements of the Site Drainage system and the input conditions of any downstream biological treatment that may be required.



The specification should include definition of: (1) Flow Rate (2) Composition (3) Temperature (4) BOD/COD/TOC (5) pH (6) Volatiles (7) Color (8) Suspended/dissolved solids/salts (9) Toxicity (10) Metals (11) Stream availability/variability (k) Any project economic evaluation should include the cost involved in treatment of AOS to meet the Site and legal requirements. (l) Work on preliminary flowsheet schemes should assume that EA authorization will take into account the effect of any downstream treatment stages through which the plant effluent would pass. In consequence, the process engineer should make an early check on existing/planned on-site or off-site facilities and establish through the Project Team the technical basis on which these facilities could be utilized. 5 EUROPEAN LEGISLATION 5.1 General Most EC Directives relating to the discharge of "dangerous substances" to water are based on the framework Directive 76/464/EEC. The aim of this Directive is to cause a reduction in the level of pollution of Community water by defined "dangerous substances". The most harmful of these substances were selected on the basis of their toxicity, persistence in the environment and bio-accumulation and are included in List 1 of the Directive (Appendix A), known as the "Black List". The less harmful substances were selected because they have a deleterious effect on the aquatic environment and are included in List 2, the " Grey List" (Appendix B).



It should be understood that List 1 and List 2 contain both individual substances and families and groups of substances from which specific substances will be identified and characterized in subsequent daughter Directives but this is proving to be a slow process. Daughter Directives have been issued for mercury, cadmium plus some pesticides and chlorinated organic compounds. The European Commission has established a priority list of 132 substances (Appendix C) which are candidates for inclusion under the Directive. "The Red List" was defined in the United Kingdom North Sea Action Plan 1985-1995. The Trade Effluent Regulations 1989 and 1992 require special control of the discharge of Red List substances (plus carbon tetrachloride and trichloroethylene) to sewer. The Red List was used as a basis for defining prescribed substances to water under the Environmental Protection Act 1990. Appendix D is the original Red List. 5.2 Integrated Pollution Control (IPC) Release of prescribed substances is subject to integrated pollution control (IPC) measures as required by the Environmental Protection Act 1990 and in line with the EC Directive's requirement that any discharge of List 1 or List 2 substances into the aquatic environment should be subject to prior authorization. In practice, IPC covers the whole of the chemical industry. For the purposes of this guide its most important requirements are covered by 5.3 to 5.5. 5.3 Best Available Techniques Not Entailing Excessive Costs (BATNEEC) Ensure that best available techniques not entailing excessive costs (BATNEEC) will be utilized to: (a) Prevent the release of prescribed substances or, where that is not practicable, reduce the release of such substances to a minimum and sufficiently low level which is judged to be harmless. (b) Similarly render harmless any other substances which might cause harm if released.



5.4 Best Practicable Environmental Option (BPEO) Ensure that BATNEEC will be used for minimizing the pollution which may be caused by releases to the environment taken as a whole having regard to the best practicable environmental option (BPEO) available. 5.5 Environmental Quality Standards(EQS) Compliance with any Environmental Quality Standards(EQS) prescribed by the Secretary of State. Whereas the EQS (or quality objective in EC terminology) approach applies to List 2 substances throughout the European Community, Member States have a choice of two methods of control for discharges of List 1 substances. The U.K. favors the use of EQS which specify concentration limits in the receiving water. Therefore, the chemical engineer should seek guidance from the Site Environmental Adviser regarding the degree of dilution between the discharge point and the receiving water before using EQS. The alternative Limit Value (LV) approach utilizes fixed maximum emission quantities/concentrations which are specific to a given sector of industry. In consequence, these LVs can be used directly to arrive at an exit stream design specification. Unfortunately, from the viewpoint of the chemical engineer, the number of substances for which LVs have been issued is limited (see Appendix E). 6 IPU EXIT CONCENTRATION Determining for design purposes the quantity and composition of Product leaving each IPU is a complex exercise. The following factors should be taken into account: (a) Project Team directed discussion with GBHE has the expertise to advise on environmental matters. (b) Process definition and performance of BATNEEC. (c) Assessment of BPEO options. (d) Receiving waters - more than one option? (e) Downstream treatment options: (1) plant Works or Site bio unit; (2) municipal sewerage undertaker; (3) direct discharge to receiving waters; (4) tertiary treatment.



(f) Relevant Environmental Quality Standards and Limit Values (see!5.5). (g) Toxicological test results. (h) Existing and projected EA authorization and NRA/RPB consent requirements and conditions. 7 SITE/LOCAL REQUIREMENTS It is recommended that all project flowsheet proposals should be discussed at an early stage with: (a) Site Environmental Group. (b) GBH Enterprises In consequence, the Project Team may then decide to obtain further information from external sources as appropriate. In the case of projects not preceded by a research stage, these discussions should be part of the work undertaken to generate basic flowsheet options. All ongoing research projects should review their future work program periodically in this way as part of an environmental impact assessment. This may require some experimental evaluation of the specific toxicity of the individual components of the effluent stream which, together with the discharge rates, may be an important factor in the selection of treatment processes. 8 PROCESS SELECTION PROCEDURE The recommended procedure for selection of candidate processes for use by an IPU includes seven stages. See 8.1 to 8.7. 8.1 Waste Minimization Techniques (WMT) Apply WMT to achieve waste elimination, recovery and recycle within the process to minimize the size of an AOS. [See Ref 1].



8.2 AOS Stream Definition Define each AOS in terms of: (a) Chemical analysis/VOC (b) Toxicological tests (c) Temperature/pressure (d) pH, BOD, COD, TOC (e) Flow rate/availability pattern (f) Variability Once the composition and key toxic components are known, it is necessary to form an initial view of the allowable final emission levels from the IPU for each of the parameters listed above (see Clause 6). 8.3 Technical Check List 8.3.1 Parameters Apply the following technical check list. These parameters, if present in the AOS, can influence substantially the choice of treatment technology. (a) Foams (b) Emulsions (c) Suspended solids (d) Immiscible liquids (e) Azeotropes (f) Color (g) Volatile organics (h) Salts/Complexes



8.3.2 Other Factors In multi-step treatment processes the progressive change in AOS composition may cause problems to occur in subsequent stages e.g.: (a) A stream suitable for Bio-treatment may become unsuitable following extraction with a solvent which is toxic to the bio- organism. (b) A change in pH may precipitate some soluble organics or metals. (c) Acids may form during an oxidation step and cause corrosion. (d) The properties of a non-foaming liquid may be changed in such a way that it will generate frothing. 8.4 Preliminary Selection of Suitable Technologies 8.4.1 General Review the Established Technologies and Emerging Technologies listed in 8.4.2 and 8.4.3 and expanded in Appendices F and G respectively, then select a short list of technology options. This activity may be assisted by utilizing Figures 2 and 3 which differentiate treatment technologies by applying two criteria: (a) Initial concentration of dissolved Organics in the water (Figure 2). (b) The final concentration required (Figure 3). In addition, reference should be made to Appendix H and Figure 4 which categorize liquid waste treatment processes by application.



8.4.2 Established Technologies The technologies listed below are described in outline in Appendix F. (a) Bio Treatment: Aerobic: - Activated Sludge - VITOX - Deep Shaft - Bio Towers Anaerobic (b) Physical Separation (1) Coagulation/Flocculation (2) Distillation (3) Stripping (4) Steam Stripping (5) Air Stripping (6) Liquid/Liquid extraction (7) Adsorption: - General - Granular Carbon - Powder Carbon - Charcoal - Zeolites/polymeric - Ion exchange (c) Membrane processes - General - Microfiltration - Ultra filtration - Reverse Osmosis - Pervaporation - Electro dialysis (d) Chemical Oxidation - Wet Air Oxidation - U.V. Light - U.V. Light + H2O2 - Ozone - H2O2/Fe - Other (e) Thermal Oxidation - Total (Incinerators) - Partial (Oil-Gas process)



8.4.3 Emerging Technologies The technologies listed below are described in outline in Appendix G. (a) Supercritical Water Oxidation (b) Liquid Membranes (c) Reed Beds 8.5 Process Sequences In some cases it will not be possible or desirable to achieve the required design objective by using a single technology, and several treatment steps may have to be designed to operate in sequence. In addition, the most suitable options for treating each individual AOS can be listed as a basis for generating alternative process flow schemes which combine the several AOS in different ways. A comparative evaluation will then lead to a short list of preferred options. These should be assessed in more detail by following up appropriate references and discussion with GBHE specialists/contractors. 8.6 Economic Evaluation Economic evaluation data obtained from sources external to the Project Team should be treated with caution. In this first issue of the Guide no internally generated economic assessment data has been provided. However, some published comparative cost data has been appended (see Appendix J) which shows the variability of costs as a function of the specific chemical composition of each stream. An example of the type of problem commonly met in this area are cost comparisons which, when examined in detail, are found to apply to different technical definitions (e.g. items of equipment are omitted or feed/product qualities are different.)



8.7 Process Selection The main objective at this final stage is to identify those options which perform strongly when judged against the following criteria: (a) Compliance with legislation. (b) Compliance with GBHE rules and requirements. (c) Low capital cost. (d) Low operating cost. (e) High reliability. (f) Compatibility with existing and projected Site operations. The process engineer should then justify to the Project Team his/her selection of preferred options. It is likely that considerable Project effort will then be applied to refine the preliminary selection referred to here in order to select a preferred process. In some cases it may also be necessary to reassess other factors, for example, the chemistry of the process or the location of the plant.



APPENDIX A DIRECTIVE 76/464/EEC - LIST 1 List 1 contains individual substances which belong to the following families and groups of substances, selected mainly on the basis of their toxicity, persistence and bio-accumulation with the exception of those which are biologically harmless or which are rapidly converted into substances which are biologically harmless. (1) Organo-halogen compounds and substances which may form such compounds in the aqueous environment. (2) Organo-phosphorus compounds. (3) Organotin compounds. (4) Substances in respect of which it has been proved that they possess carcinogenic properties in or via the aquatic environment. (Where certain substances in List 2 are carcinogenic they are included in this category). (5) Mercury and its compounds. (6) Cadmium and its compounds. (7) Persistent mineral oils and hydrocarbons of mineral origin, and for the purposes of implementing Articles 2, 8, 9 and 14 of this Directive. (8) Persistent synthetic substances which may float, remain in suspension or sink and which may interfere with any use of the waters



APPENDIX B DIRECTIVE 76/464/EEC - LIST 2 List 2 contains: (a) Substances belonging to the families and groups of substances in List 1 for which the limit values referred to in Article 6 of the Directive have not been determined. (b) Certain individual substances and categories of substances belonging to the families and groups of substances listed below, and which have a deleterious effect on the aquatic environment, which can, however, be confined to a given area and which depend on the characteristics and location of the water into which they are discharged. Families and groups of substances referred to in the second indent: (1) The following metalloids and metals and their compounds: 1 Zinc 8 Antimony 15 Uranium 2 Copper 9 Molybdenum 16 Vanadium 3 Nickel 10 Titanium 17 Cobalt 4 Chromium 11 Tin 18 Thallium 5 Lead 12 Barium 19 Tellurium 6 Selenium 13 Beryllium 20 Silver 7 Arsenic 14 Boron (2) Biocides and their derivatives not appearing in List 1. (3) Substances which have a deleterious effect on the taste and/or smell of the products for human consumption derived from the aquatic environment, and compounds liable to give rise to such substances in water. (4) Toxic or persistent organic compounds of silicon and substances which may give rise to such compounds in water, excluding those which are biologically harmless or are rapidly converted in water into harmless substances. (5) Inorganic compounds of phosphorus and elemental phosphorus. (6) Non persistent mineral oils and hydrocarbons of petroleum origin. (7) Cyanides and fluorides.



(8) Substances which have an adverse effect on the oxygen balance, particularly: ammonia, nitrites.



APPENDIX F ESTABLISHED TECHNOLOGIES Table of Contents F.1 BIO TREATMENT: AEROBIC - ACTIVATED SLUDGE PROCESS F.2 BIO TREATMENT: AEROBIC - VITOX PROCESS F.3 BIO TREATMENT: AEROBIC - DEEP SHAFT F.4 BIO TREATMENT: AEROBIC - BIO-TOWERS F.5 BIO TREATMENT: ANAEROBIC PROCESSES F.6 COAGULATION/FLOCCULATION F.7 DISTILLATION F.8 STRIPPING F.9 AIR STRIPPING: PACKED COLUMNS F.10 AIR STRIPPING: HIGEE F.11 LIQUID/LIQUID EXTRACTION F.12 ADSORPTION - GENERAL F.13 ADSORPTION: GRANULAR CARBON F.14 ADSORPTION: POWDER CARBON F.15 ADSORPTION: BONE CHARCOAL F.16 ADSORPTION: POLYMERIC/ZEOLITES F.17 ADSORPTION: ION EXCHANGE F.18 MEMBRANE PROCESSES (GENERAL) F.19 MEMBRANE PROCESSES: MICROFILTRATION



F.20 MEMBRANE PROCESSES: ULTRAFILTRATION F.21 MEMBRANE PROCESSES: REVERSE OSMOSIS F.22 MEMBRANE PROCESSES: PERVAPORATION F.23 MEMBRANE PROCESSES: ELECTRODIALYSIS F.24 CHEMICAL OXIDATION: WET AIR OXIDATION (WAO) F.25 CHEMICAL OXIDATION: U.V. LIGHT F.26 CHEMICAL OXIDATION: U.V. LIGHT + H202 F.27 CHEMICAL OXIDATION: OZONE F.28 CHEMICAL OXIDATION: H2O2/Fe (FENTON'S REAGENT) F.29 CHEMICAL OXIDATION: OTHERS F.30 TOTAL THERMAL OXIDATION: INCINERATION F.31 PARTIAL THERMAL OXIDATION: OIL-GAS PROCESS



F.1 BIO TREATMENT: AEROBIC - ACTIVATED SLUDGE PROCESS F.1.1 Introduction Aerobic biological waste water treatment is the process by which microorganisms consume biodegradable organic compounds and free oxygen to produce cell growth, CO2 and water. Bio treatment can only destroy biodegradable compounds and therefore those chemicals which are not biodegradable (hard COD) will pass through and will require additional treatment. Not all the biodegradable material is oxidized and the BOD5 leaving the treatment beds depends on the design of the process, the technology employed and the residence time, and can vary from 5 to 40% of the original BODs. F.1.2 Process Description Several types of bio treatment processes have been operated over the years. Differentiation between these requires a careful assessment of cost and performance on a project by project basis. A bio treatment process may include the following additive stages: (a) Primary treatment: (1) An equalization stage to minimize concentration and temperature fluctuations (typical operating temperature 10 to 37°C) (2) A pH adjustment and nutrients dosing stage to prepare the feed for the process. (typical pH range 5.5 to 9). (3) A Suspended Solids removal stage. (b) Secondary treatment: (1) The aeration tanks which are agitated to maintain the biomass in suspension and where air or oxygen is injected. The sizes of the tanks depend on the stream mass flow, the type and concentration of chemicals present and the exit BOD/COD levels required (i.e. standards and legislation).



(2) A sedimentation stage to separate the biomass from the water and allow recycle of the biomass to the aeration tanks. (3) A sludge thickening stage. This is applied to surplus sludge to reduce its water content to a level suitable for further treatment or landfill. (c) Tertiary treatment: Removal of specific organic or inorganic pollutant such as hard COD/metals and excess nutrients (phosphorus and nitrogen compounds if they have not been removed in the nitrification/ denitrification section of a secondary treatment). (d) Sludge disposal: An appropriate sludge disposal stage: for example, landfill, land spread, incineration, digestion in aerobic or anaerobic digesters or Wet Air Oxidation. F.1.3 Process Requirements/Limitations (a) A substantial amount of land is required to locate the equipment, although it can be reduced by using Deep Shaft and similar "tower" processes. (b) Electric power is required to ensure adequate mixing/the ` suspension of the solids if necessary and oxygen/air mass transfer. There are several generic and proprietary methods for dispersing the air and maintaining solids suspension (e.g. surface aerators, liquid jet aerators, fine bubble diffusers, venting aerators, etc.). The total power requirement is one of the main factors in the choice of process. Typical values are 0.05 kW/m3 with an oxygen transfer capability of 2 kgO2/kW.h. (c) In the absence of a specific treatment stage: (1) Heavy metals will either remain dissolved in the water or will accumulate in the biomass and may create subsequent sludge disposal problems.



(2) The non-biodegradable chemicals will not be oxidized, and if allowed to remain in the effluent may result in toxic effect/COD problems in receiving waters. ] (d) The performance of a conventional activated sludge bio treatment plant can be improved by the addition of powdered activated carbon. This technology is well established and marketed as the PACT process by Zimpro Passavant. The main benefits derived from the combined adsorption/biological oxidation are: (1) It buffers the system against shock loads of biologically toxic or inhibitory compounds. (2) Improved removal of compounds which exhibit only partial or slow biodegradability. (3) Improved COD reduction and color removal by adsorption of Refractory Organics. (4) Increased hydraulic capacity of an existing facility. (5) Reduced VOC losses from the aeration basin. However, VOC could be present in the off-gas from the Wet Air Regeneration process. (6) Improved sludge settling capacity. The choice of carbon is important, but generally speaking the cheaper "low" activity waste water carbons are more commonly used. The economics and elegance of the PACT process may be improved by adopting Wet Air Regeneration (WAR) of the spent carbon contained in the surplus biomass. In this manner, excess biomass is oxidized (the high COD providing autogenous operation of the reactor) and contained carbon may be regenerated for recycle. Virgin carbon make-up is required to compensate for physical losses and deterioration of carbon activity on repeated regeneration.



(e) The amount of sludge produced per tonne of BODs is a function of the type of process used and the operating conditions [feed to biomass ratio (F/M)] but it ranges from about 0.5 tonne/tonne on a dry weight basis with F/M of 1.0 down to less than 0.1 tonne/tonne with F/M lower than 0.2. (f) During plant shutdown periods the biomass should be sustained by an alternative feed supply. In addition, the design should cater for the required turndown. (g) Start-up of a bio treatment system normally takes several days before BOD removal is effective. In consequence, its design usually incorporates protection against any identified risk to the biomass health. This is usually a combination of operating procedures and detection by analysis which enable unacceptable feed to be dumped into holding tanks/lagoons. This material can then be blended into the feed at an acceptable rate. (h) Temperature influences the rate of reaction but is limited to a maximum of 40°C in most cases. (j) The kinetic constants of the biological reactions become dependent on the mode of operation of the system, as well as the chemical nature of the waste, and should be determined experimentally. (k) Minor nutrient (e.g. Fe, K, Mg, Zn, Mn) are also required for optimum performance.



F.2 BIO TREATMENT: AEROBIC - VITOX PROCESS F.2.1 Introduction The VITOX process is a bio treatment process developed by BOC for the treatment of effluents. Its distinguishing feature is the use of oxygen instead of air. F.2.2 Process Description The operation of a VITOX process is very similar to the traditional activated sludge process. However, BOC makes several specific claims: (a) The use of oxygen allows the process to operate at a higher biomass concentration "M" and therefore a smaller size biological treatment tank is required for the same duty. (b) In the case of existing plants, the extra capacity can be used either to increase the overall treatment capability by maintaining the F/M ratio or, alternatively, to reduce the final DOB of the discharge by operating at a lower F/M. (c) If the process is operated at low F/M ratios, then the rate of production of excess biomass can be reduced. In some cases, this rate can be so low that it is possible to discharge the excess biomass mixed with the treatment effluent without exceeding the suspended solid specification of the receiving waters. F.2.3 Process Requirements/Limitations (a) It requires a supply of oxygen at a suitable price. (b) The VITOX process is normally designed to operate with a low F/M ratio, high "M" concentrations and a low rate of sludge export. (c) I t may need a larger clarifier because the high operating "M" can produce hindered settling. (d) The low sludge production may result in progressive build up of inert solids (e.g. metals and inorganic salts).



F.3 BIO TREATMENT: AEROBIC - DEEP SHAFT F.3.1 Introduction The Deep Shaft process is a specific aerobic process utilizing air as oxidant and developed by ICI for the treatment of effluents. Its main difference from a traditional activated sludge process is its design as a tower which is located underground and therefore it provides a very compact arrangement. F.3.2 Process Description Each shaft is divided into a down comer and a riser. Compressed gas is injected into the down comer to induce liquid circulation by an air lift effect, to create turbulence and supply oxygen to the microorganisms. (During start-up, air is injected into the riser to establish circulation). The good mixing, long bubble residence times and large hydrostatic head create a high oxygen transfer rate, and so with increased availability of nutrients the BOD degradation rate is maximized. As with conventional processes, a treatability study is commonly needed for detailed design purposes. Gas bubbles disengage in the head tank at the shaft top, and the clarifier feed is taken from here. Excess sludge is removed from the clarifier. There are several specific claims for the Deep Shaft process: (a) A very small land requirement for the biological bed. (b) An intensified process due to the high hydrostatic pressure generated at the bottom of the shaft which increases the oxygen transfer rate. (c) An enclosed system which can be located in sensitive areas like building basements and proximity to domestic housing. (d) Lower power input than traditional designs.



F.3.3 Process Requirements/Limitations To date, the Deep Shaft has been operated with air, and air/oxygen mixtures. Anti-froth agents may need to be added to avoid frothing in the head tank.



F.4 BIO TREATMENT: AEROBIC - BIO-TOWERS F.4.1 Introduction The bio-tower technology is an alternative to the conventional activated sludge plants which uses enclosed tanks of up to 30 m height instead of open basins. This results in a more compact design and, in some cases, lower capital and energy costs. F.4.2 Process Description The aeration is provided by the injection of air into the waste water stream. The mixture of air and waste water is then injected at several points at the bottom of the tower to achieve uniform distribution of the air. The height of the tower determines the hydrostatic pressure and the solubility of oxygen at the point of injection. This results in a much higher oxygen efficiency than that achieved by conventional activated sludge plants. Additional claims for the bio-tower design (compared with a conventional activated sludge process) are: Volume of air required 20% Energy required 40-50% Land area required 20% The closed tank design facilitates elimination of pollution by fumes and aerosols.



F.5 BIO TREATMENT: ANAEROBIC PROCESSES F.5.1 Introduction Anaerobic treatment is a biological process in which microorganisms convert organic compounds in the presence of water into methane, CO2, cellular materials and other organic compounds. Anaerobic processes do not require the introduction of air or oxygen. Some microorganisms are able to operate both under aerobic or anaerobic conditions while other are specifically anaerobic. F.5.2 Process Description There are three basic types of reactor systems: (a) Deep lagoons - often used as pretreatment but which can have an odor problem. (b) Enclosed vessels with suspended growth - with separation and recycle of the suspended solids. (c) Enclosed vessels with fixed growth - in which the microbial growth is attached to solid surfaces provided in the form of packing or particles in the case of a fluidized bed system. F.5.3 Process Requirements/Limitations Anaerobic treatment has the following characteristics: (a) Suitable for: (1) pretreatment of high strength waste streams; (2) waste water sludge destruction. (b) Low sludge production rate. (c) Energy potential of the off-gas produced.



(d) Reaction rate is slow compared with aerobic processes and needs higher temperatures. (e) Anaerobic treatment can destroy some chemicals which are not degradable by an aerobic process. (f) Effluent from anaerobic processes usually requires further treatment prior to discharge to receiving waters. (g) Very sensitive to variations in incoming effluent composition and flow rate. (h) Sulfates in the effluents are reduced to H2S which may require corrosion resistant materials of construction.



F.6 COAGULATION/FLOCCULATION F.6.1 Introduction Coagulation and flocculation are well established methods for removing soluble and insoluble organic compounds from water and are generically known as Physical - Chemical processes. They are mainly used prior to biological processes to partially remove suspended solids, colloidal particles and dissolved substances (dyes and other hard COD compounds). F.6.2 Process Description The treatment, which in most cases is specific to the organic compounds to be removed, requires the pH to be adjusted to insure the optimum performance of the coagulation and flocculation stages. The coagulation process involves the addition of a coagulant to the aqueous stream to destabilize the colloidal suspensions and allow the organic matter to come out of solution. In most cases a flocculant is also added to promote the formation of large flocs which can then be separated by settling. The most widely used coagulants are iron or aluminum salts although synthetic cationic polyelectrolyte's can also be used. The inorganic salts are generally used together with lime or caustic to produce a hydroxide precipitate. When using ferrous salts it is possible to use their reducing power to break the azoic link in some dye molecules and render them colorless. Coagulants are mainly synthetic organic polymers of acrylamide and acrylic acid and, depending on their composition, can be cationic, anionic or neutral. Natural organic polymers, starches and alginates and inorganic coagulants, activated silica, alumino silicates and clays are also used. The settling time required depends on the sedimentation rate of the flocs obtained. The clear liquid is separated from the top of the settling tank and the concentrated sludge is removed from the bottom and then further de- watered in a pressure filter before disposal by a suitable method; normally to landfill, depending on the toxicity of the chemicals present.



The size of the coagulation, flocculation and settling stages depends on the nature of the physical and chemical reactions taking place and the type, composition and quantity of the reagents used. F.6.3 Process Requirements/Limitations This process requires the addition of specific coagulating and flocculating chemicals which need to be identified and evaluated during laboratory trials. Depending on the coagulating chemicals used, the pH may need to be increased to 9 or 10 using caustic or lime and then neutralized with a mineral acid or CO2. In most cases, for economic reasons, the process is operated to achieve only a partial removal of the BOD and COD and is then followed by a Biological Treatment Stage to achieve the required discharge values.



F.7 DISTILLATION F.7.1 Introduction Distillation as a recovery technique is generally limited to separating compounds more volatile than water from water itself. F.7.2 Process Description A distillation column consists of two sections: (a) A stripping section below the feed entry which can be designed to control the final concentration of volatile organics in the aqueous product stream. (b) A rectifying section above the feed which, combined with the choice of reflux, allows control of the concentration of water in the recovered organic product stream. F.7.3 Process Requirements/Limitations (a) Distillation is used for the recovery of individual organic compounds or groups of compounds from aqueous streams only if: (1) their concentration is high enough to make economic sense, generally greater than 5%, and the water content of the recovered stream is acceptable either for recycle or subsequent processing or export; (2) it is the most cost effective process for removal of compounds which are highly toxic and have to be separated to facilitate subsequent treatment of the aqueous stream or for disposal as a concentrated stream (e.g. by incineration); (3) relative volatility of organics with water exceeds 1.2. Below 1.2, it is generally more economic to remove high concentrations of organics by liquid-liquid extraction (see F.11). (b) The overhead stream, mainly organics, may require further treatment or purification if it is to be returned to the process.



F.8 STRIPPING F.8.1 Introduction The stripping process is a variant of conventional distillation, utilizing either a reboiler for steam generation or direct injection of steam from an outside source. Even relatively high boiling compounds can be removed efficiently by this method, e.g. Phenol (Boiling point 182°C). F.8.2 Process Description A stripping column consists of one section below the feed designed to achieve the required low level of organics in the water. It can operate on a batch or continuous mode. F.8.3 Process Requirements/Limitations (a) The overheads are recovered as a mixture of organics in water which will separate into two phases if immiscible and the distribution of the organic compounds between the organic and the water layer will be determined by solubility levels. (b) Both layers may need to be further treated before disposal or recycle. In some cases the water layer can be recycled back to the column. (c) Removal of high boiling point components is assisted by operation under vacuum.



F.9 AIR STRIPPING: PACKED COLUMNS F.9.1 Introduction Air stripping is the countercurrent contacting in a column of an AOS with a gas stream usually air or N2, although natural gas has also been used to strip methanol from water. It is only useful for volatile organics, that is, compounds with a boiling point less than 100°C. It can reduce the final COD to less than 0.001ppm and can remove up to 99.9% of the organics present. F.9.2 Process Description Air stripping is performed in packed columns and requires a substantial volume of air which then has to be disposed of in an acceptable way to prevent the organics reaching the environment. F.9.3 Process Requirements/Limitations If the columns are operating continuously, the packing may get fouled and require a continuous or intermittent supply of biocide at a level of 50 to 500 ppm which will be discharged in the water. Batch operation may need 2 columns and regular cleaning to control fouling.



F.10 AIR STRIPPING: ICI HIGEE F.10.1 Introduction The Higee process intensifies mass transfer between a gas stream and a liquid stream by means of high "g" forces generated by rotation. For example, in this way the height of packing required to reach equilibrium for the EDC/water system is reduced from about 0.8 m per stage in a packed column to less than 0.06 m achieved in the Higee machine. F.10.2 Process Description The packing has the form of a hollow cylinder which rotates on its axis. The liquid is distributed on the inside surface and travels through the packing by centrifugal force. The stripping gas is fed to the outside of the rotating cylinder and travels through the packing counter currently with the liquid and is discharged from the centre. The thickness of the packing, and therefore the outside diameter of the rotor, is a function of the number of stages required (at about 50 to 70 mm per stage) and the axial length of the cylinder is determined by the liquid flow. The machine operates in the range of 100 to 1000 times terrestrial "g" and therefore a very small volume of packing is required when compared with a packed tower. The standard stacked rings Sherwood correlation for the calculation of flooding has been found to apply to the rotating packing. F.10.3 Process Requirements/Limitations Fouling of various types may develop in the packing.



F.11 LIQUID/LIQUID EXTRACTION F.11.1 Introduction Liquid/liquid extraction's main application is to remove organic components which are present in high concentration (1 to 25%) and the relative volatility to water is less than 1.2 (otherwise distillation may be more appropriate) An organic, low toxicity, preferably biodegradable solvent with very low water solubility is required. F.11.2 Process Description The process involves the countercurrent contact of the AOS with a water immiscible, selective organic solvent which is then phase separated from the treated water. The loaded organic solvent is then separated from the contained organics by distillation before recycling it to the extractor. A solvent purge is normally removed for purification. F.11.3 Process Requirements/Limitations The organic solvent will be present in small amounts in the treated water and, depending on its toxicity, solubility and cost, will have to be removed for recovery or destruction by a suitable treatment.



F.12 ADSORPTION - GENERAL F.12.1 Introduction Adsorption is a well established process for the removal of organic compounds from industrial waste waters and potable waters. Although a variety of adsorbents are available commercially, activated carbon is by far the most popular. This is a broad spectrum adsorbent with a wide pore size distribution which makes it very attractive for AOS treatment. Activated carbon is available in two basic forms, viz. powder (PAC) or granular (GAC). PAC is the cheapest, for example, at about $2/kg compared with $4-6/kg for a GAC of similar activity, and achieves a higher adsorption rate but is less amenable to regeneration. F.12.2 PAC Fresh PAC is normally added to the aqueous waste in the last stirred tank in a series. Then, after filtration at each stage, it is transferred through the remaining tanks countercurrent to the AOS to achieve maximum use of adsorptive capacity. Regeneration may not be cost effective. F.12.3 GAC The use of GAC in fixed beds requires less material handling than PAC. However, the moving bed version is likely to be more problematical in this respect. When the adsorption capacity of the carbon is exhausted, the spent GAC is usually discharged prior to regeneration/reactivation and the adsorber reloaded with active material. Spent GAC is usually regenerated and reactivated in large plant using multiple-hearth furnaces. Regeneration/reactivation losses are typically 5-10% and the reactivated carbon has different adsorption characteristics to virgin carbon in part due to enlarged pore sizes caused by the Pyrolysis step. A contract regeneration/reactivation service is available (e.g. Chemviron Carbons). Alternatively, it can be incinerated. If on-line regeneration is feasible, for example by steam stripping, then this may be preferred.



F.12.4 Key Points Adsorption is used mainly for the removal of dissolved organics that are present in small amounts and are difficult to remove by biological methods. For a given adsorbent/adsorbate system the adsorption capacity, as defined by the adsorption isotherm, is influenced by many factors including temperature, solubility, pH, size of adsorbate molecule, adsorbent pore structure, etc. but the most important factor is the adsorbate concentration in the aqueous phase. For example, the capacity of a GAC (expressed as weight adsorbate/weight adsorbent) is expected to be about 45% when in equilibrium with an aqueous solution containing 2000 ppm Aniline whereas at 1-10 ppm the capacity falls to less than 1%. The bed life will, however, be appreciable because the quantity of adsorbate present is so small. GAC is regenerated by four methods: (1) Steam Stripping - applied in situations where the molecular weight of the adsorbate (in situ) is generally less than 200; separation usually allows recycle of the organic layer with the aqueous layer discharged either to receiving waters or to biotreatment or recycled to adsorber feed. (2) Chemical - e.g. caustic washing to remove Phenol. (in situ) (3) Solvent Extraction - e.g. elution of dyestuffs. (in situ) (4) Thermal - is used principally at waste water treatment plants and usually includes multiple-hearth furnaces. The process includes drying, volatilization, Pyrolysis, and reactivation stages. GAC weight loss is typically 5-10%. Most modern units employ afterburners operating at 1200/1300°C to destroy any dioxins that may have been formed.



The bed size in terms of its length/diameter ratio is influenced by the shape of the adsorption profile through the bed and whether the bed is regenerated or used on a once-through basis. For example, the more favorable adsorption profile achieved by chlorobenzene allows the use of a lower L/D ratio than with dyestuffs while still achieving efficient utilization of the carbon bed. In the case of dyestuffs adsorption the bed should be sized for a minimum of two weeks operation on-line compared with only a few hours for chlorobenzene, depending on the regeneration time. Hydraulic loadings are usually in the range 1-6 m3/m2 with the lowest loadings selected for adsorbates that are slow to adsorb such as dyestuffs. Carbon adsorption is commonly used to treat AOS containing from a few ppb to 2000!ppm of dissolved organics. If the AOS contains suspended solids then the adsorption bed should be preceded by a filtration stage.



F.13 ADSORPTION: GRANULAR CARBON F.13.1 Introduction Granular carbon is a treatment process for the removal of small amounts of dissolved, refractory organic compounds from water. It is used when high quality process water is required for reuse or when the organic compounds are so toxic that they have to be removed before the effluent water is finally discharged to receiving waters.

F.13.2 Process Description Granular carbon is used in fixed packed beds which operate with continuous liquid feed until they are economically loaded, at which point they have to be taken off-line and the carbon either regenerated or replaced with fresh material. Various series/parallel equipment arrangements are needed to achieve the required technical performance and reliability. In most cases, granular carbon is only economic if the organic compounds can be removed and the carbon regenerated and reused several times. The most commonly used methods of regeneration are steam stripping, solvent extraction and partial combustion, or a combination of these. Laboratory tests are advisable since: (a) Some organic compound present in minor amounts in a stream may interfere with the adsorption of the key component and drastically reduce the efficiency of the beds.



(b) The presence of inorganic salts may cause an irreversible deactivation of the carbon which will then have to be replaced. (c) The reliable calculation of steady-state rate of carbon make-up to a specific adsorption/regeneration process requires the use of practical data. During regeneration there is always a mass loss due to attrition and partial combustion which needs to be compensated by addition of fresh carbon. However, a further purge and addition of carbon may be necessary to compensate any progressive irreversible loss of adsorption capacity. F.13.3 Process Requirements/Limitations Granular carbon is usually only suitable economically if it can be readily regenerated. The size of the bed has to be calculated so that it takes a reasonable time to achieve economic loading. F.13.4 Carbon Properties Data sheets on carbon properties can be obtained from the following suppliers:- NORIT CHEMVIRON SUTCLIFFE SPEAKMAN



F.14 ADSORPTION: POWDER CARBON F.14.1 Introduction Powder carbon is more active per unit mass than granular carbon and it can be used in both batch and continuous processes to remove impurities. However, it requires suitable filtration equipment to separate it from the treated liquid. For effluent treatment it is used mainly in activated sludge processes to adsorb the non-biodegradable components. F.14.2 Process Description PAC is used in stirred tanks followed by filtration to remove trace impurities. The spent PAC is then disposed of, according to the toxicity of the adsorbate, by such methods as landfill and incineration.



As part of an activated sludge process (PACT) the carbon is added to the unit and remains suspended with the sludge. Most of the carbon is recycled to the process from the primary clarifier together with the biomass. Treatment of the excess sludge and contained carbon in a Wet Air Oxidation process may enable the carbon to be recycled with benefit, in addition to destruction of the sludge. F.14.3 Process Requirements/Limitations The process requires the handling and disposal of carbon slurries.



F.15 ADSORPTION: BONE CHARCOAL F.15.1 Introduction Bone Charcoal, marketed as Brimac by Tate and Lyle, contains two separate components, an active carbon surface and a hydroxyapatite lattice. As a result of this surface activity, it is more commonly used for heavy metal recovery particularly lead, iron, manganese and zinc and is used by several U.K. water companies. F.15.2 Process Description It is available in granular form and is used on a once-through basis in equipment similar to that which utilizes GAC. The reactivation (if required) will have to be designed to remove any metals as well as the organic compounds present. F.15.3 Process Requirements/Limitations Other uses include color removal (e.g. humic acid and peat color) and trace organics, fluoride etc.



F.16 ADSORPTION: POLYMERIC/ZEOLITES F.16.1 Polymeric As well as the ion exchange resins (see F.17) a number of non-ionic polymeric media (e.g. polystyrene, polyacrylate) are commercially available for use as sorbents including the Amberlite XAD-x range from Rohm and Haas. These will absorb organic substances from aqueous streams. However, capacities tend to be low and the resins themselves are prone to attack by both microorganisms and aggressive media or conditions. Their utility is thus limited. F.16.2 Zeolites and other Molecular Sieves Traditional alumino silicate zeolites behave in aqueous media as cation exchangers. They will also extract some polar neutral organic molecules (e.g. sugars) by a complexation mechanism. The more recently discovered high silica zeolites and silica molecular sieve are hydrophobic at high Si/Al ratios and behave as solid organic solvents. The best known example is "Silicalite" (UOP Corporation). Such materials will extract organic molecules from aqueous solutions, the exact partition depending upon concentration, temperature, solubility and polarity. The unique fixed pore size combined with a choice of chemical composition and structure allows achievement of far higher selectivity's than activated carbon. Also, their thermal and oxidative stabilities mean that in most cases cleanly regenerable systems are possible. However, these materials are at present relatively new and expensive. It is anticipated that many more microporous inorganic sorbents will soon become available. F.16.3 Other Inorganic Sorbents Many simple inorganic compounds (e.g. oxides and hydroxides) have potential as agents for removal of organics from aqueous streams. The use of alumina to remove chlorinated hydrocarbons in this way is well known.



F.17 ADSORPTION: ION EXCHANGE Ion exchange resins are polymeric materials which contain specific chemical groups capable of reacting with cations and anions and with acidic or alkaline impurities. Of the many types of resins available, some may be appropriate for AOS application. However, the exchange process inevitably releases a new substance into the aqueous stream and regeneration usually creates further wastes except where recycle back into the chemical process is a practical option. This is a very specialized topic which is beyond the scope of this Guide. However, ion exchange should be evaluated for any application which requires the removal of small amounts of high value or toxic metals or strongly polar refractory impurities from aqueous organic streams.



F.18 MEMBRANE PROCESSES (GENERAL) F.18.1 Introduction Membrane processes utilize a solid semi permeable membrane which allows selected components of an AOS to pass through. The type of membrane and the operating conditions determine which components are allowed through. There are many types of membrane which individually or in combination can perform most of the common separations. The driving force for mass transfer is either pressure, concentration or an electric potential. The pressure driven processes are classified according to the pressure used: (a) Low pressure (0.1 to 3 bar ) for microfiltration (MF) (b) Medium pressure ( 2 to 10 bar) for ultrafiltration (UF) (c) High pressure (10 to 100 bar) for reverse osmosis (RO) F.18.2 Process Description In membrane processes the type of membrane chosen is only one component of the process technology which has to be developed and optimized specifically for each application taking into account the characteristics of each separation problem. The main steps (i.e. membrane selection, module design, plant hydraulic design, operating procedure, cleaning procedure, replacement procedure) are outlined as follows. F.18.2.1 Membranes The chemical composition and physical structure of the membrane is designed to be compatible with the fluid to be treated and the separation required.



F.18.2.2 Modules There are several types of module design: (a) Hollow fiber modules are assembled as a tube bundle with the AOS flowing within the hollow fibers and the clean water collected on the shell-side. (b) Spiral wound modules are similar in construction to spiral wound heat exchangers. (c) Plate and frame modules are similar to pressure filters. In all cases the mechanical design includes a method of accommodating the operating pressure across the membrane. F.18.2.3 Operating procedure The AOS to be treated is circulated at high rate and at the required pressure over the surface of the membrane. The solute then permeates through the wall of the membrane. This method of operation is called cross-flow and is designed to maintain high cross flow over the surface of the membrane to reduce the rate of fouling. F.18.2.4 Cleaning procedure Although most membrane systems operate under cross-flow conditions they still need cleaning at regular intervals. MF membranes with capillary pores in hollow fiber form can be cleaned by back-flushing with either the cleaned process liquid or a gas (air or N2). MF with tortuous pores, UF and RO membranes are usually cleaned by circulating proprietary cleaning agents in water, such as detergents, to remove the fouling layer. The rate of fouling determines the frequency and duration of the back- flushing operation.



Changes in properties and composition of the AOS will also have an influence on the frequency of cleaning. F.18.2.5 Replacement It is possible that degradation of the membrane may occur under operating conditions and therefore the economic operating life of alternative membranes should be determined by life cycle tests as an aid to selection. F.18.3 Process Requirements/Limitations Membranes are characterized by their rejection capability which is the % of the solute contained in the feed which remains after membrane separation. In most cases the membrane process has to be developed to meet the requirements of a specific AOS. This can be a lengthy and expensive development process. While there are hundreds of different types of membrane capable of performing thousands of separations there are very few off-the-peg commercial membrane processes available for treatment of industrial AOS. Most commonly used membranes are fabricated from organic polymers and therefore have an operating temperature limit and a chemical compatibility limit. Recent developments include the use of PEEK membranes which extends the operating temperature range to 140+°C and the chemical resistance. Metallic membranes made of sintered stainless steel are also available.



F.19 MEMBRANE PROCESSES: MICROFILTRATION F.19.1 Introduction Microfiltration is a low pressure process, (0.1 to 3 bar) which uses a porous membrane, suitable for the separation of suspended solids and colloidal matter and some viruses from liquid streams down to 0.2 microns in size. F.19.2 Process Description Although its main application is for product cleaning (e.g. wine or beer clarification) it can also be used to remove suspended BOD from an AOS to give a product water suitable for recycle. Other applications include: (a) Separation of oil-water emulsions. (b) Metal recovery as colloidal oxides or hydroxides. (c) Production of ultrapure water for the semiconductor industry. The process is normally operated under cross-flow conditions with regular back-flushing of the membranes using either compressed air or the filtrate.



F.20 MEMBRANE PROCESSES: ULTRAFILTRATION F.20.1 Introduction Ultra filtration is a medium pressure process (2 to 10!bar) which uses a non-porous or a very fine pore membrane to achieve the separation of suspended solids, colloidal matter and viruses from liquid streams down to 0.002 microns in size. F.20.2 Process Description Although similar in operation to microfiltration, because of the smaller size pores it allows the solvent and small solute molecules to pass through and rejects large solute molecules (Molecular Weight > 500). Ultra filtration membranes are usually characterized by their "molecular weight cut-off" (MWCO) which is the MW which has a retention of 90% under the test conditions. Although the actual performance is also a function of the pH, molecular structure and the pore size distribution of the membrane. It is used to separate oil-water emulsions down to 10 to 50!ppm of oil. However, if the initial oil concentration is more than 2% a centrifugal pretreatment is usual. The process is normally operated under cross-flow conditions with regular back-flushing.



F.21 MEMBRANE PROCESSES: REVERSE OSMOSIS F.21.1 Introduction Processes using reverse osmosis can separate water contained in an AOS by forcing this water through a membrane. The pressure applied is greater than the osmotic pressure of the AOS. The separated water is generally clean enough for recycle back into the process and the waste concentrated in the AOS can either be sent to the next treatment stage or recycled. The process operates at between 10 to 100!bar and ambient temperature and requires less energy than simple distillation to achieve a required degree of concentration. For organic molecules the degree of rejection varies according to the molecular weight, initial concentration and solubility. For example: Permasep B-9 polyamide membrane processing AOS with an initial concentration of 500 to 2000 ppm achieves: % rejection Methanol 0 Ethanol 28 n-Propanol 62 iso-Propanol 75 n-butanol 65 iso-butanol 95 F.21.2 Process Description The process is operated under cross-flow conditions and at pressures up to 100 bar and temperatures up to 70°C. Several stages may be used in series or parallel to achieve the required flow rate and final purity. It has been used to desalinate water and treat landfill leachate. The clean water stream produced from leachate is suitable for discharge or reuse and the concentrated stream can be recycled back to the landfill or disposed of in an appropriate manner.



De-ionized water for laboratory use is produced by reverse osmosis in preference to distillation. F.21.3 Process Requirements/Limitations The membranes are very sensitive to fouling, and pretreatment of the AOS is absolutely essential. This will include removal of fine particles, removal of sparingly soluble salts which might precipitate out as the water is removed and their concentration increases, and pH adjustment.



F.22 MEMBRANE PROCESSES: PERVAPORATION F.22.1 Introduction Pervaporation is the process of evaporation through a membrane of one or several components of an AOS into a vapor phase and it can be used for: (a) Removal of volatile organics from water (Benzene, CFC's). (b) Water reduction from AOS containing organic solvents (down to less than 1% water). (c) Separation of polar from non-polar compounds are being developed (e.g. Methanol from Toluene). It can be used as an alternative to, or in combination with, activated granular carbon, air stripping, or conventional distillation. F.22.2 Process Description The process is based on the preferential diffusion of a component of the AOS through a non-porous membrane. The driving force is due to the concentration difference provided by the evaporation of the components on the low pressure side of the membrane. The evaporation is effected by operating under vacuum or circulating a carrier gas which vaporizes the liquid from the surface and transports the vapor. The heat of vaporization has to be provided via the feed liquid and a condenser is required to condense the separated vapor. F.22.3 Process Requirements/Limitations There are several commercial installations which remove water from 80/20 ethanol/water mixtures by means of a pervaporation process (rather than the alternative method of azeotropic distillation). In this case, the flux is a function of the initial water concentration and can change from 1 kg/m2.h from a solution of 1% water in ethanol to almost zero at 0.1% water.



F.23 MEMBRANE PROCESSES: ELECTRODIALYSIS F.23.1 Introduction When a membrane is used to fabricate channels which separate an AOS into parallel streams and an electric field is applied, the ionic components of the AOS separate by migration through the membrane towards the respective electrode. Cation and anion transfer membranes are used in the same cell. F.23.2 Process Description The AOS is fed to an electrolytic cell containing alternate cation and anion membranes which are arranged to deliver two exit streams. The AOS is thereby separated into a dilute stream and a concentrate. The dilute stream could be suitable for discharge into receiving waters. The concentrate is either recycled or sent for further treatment. F.23.3 Process Requirements/Limitations Suitable cation and anion membranes are required.



F.24 CHEMICAL OXIDATION: WET AIR OXIDATION (WAO) F.24.1 Introduction WAO is a liquid phase oxidation process suitable for the treatment of concentrated waste water streams and waste water sludge's including pulp and paper industry waste liquors, biomass sludge, refinery waste caustic liquors and AOS. WAO can also be used to regenerate any powder activated carbon purged with the surplus sludge from bio treatment process. F.24.2 Process Description The AOS is treated in a reactor at high pressure (50 to 200!bar) and high temperature (200 to 350°C) with air or oxygen to achieve at least a partial cleavage of organic molecules present. It is an expensive processing step and should only be used to do that part of the oxidation which cannot be done economically using a biological process. The exit stream from the WAO process is normally treated in a biological process to arrive at the required final BOD suitable for discharge. F.24.3 Process Requirements/Limitations This process needs high pressure equipment and adequate controls for the temperature and oxygen or air input. The process generates organic acids which need to be neutralized to prevent corrosion. The off-gas produced contains CO which should be oxidized catalytically to CO2 before discharge to atmosphere. To minimize energy usage and achieve economic operation the concentration of organic compounds in the AOS should be high enough to achieve the required reactor temperature adiabatically.



F.25 CHEMICAL OXIDATION: U.V. LIGHT F.25.1 Introduction Ultraviolet (U.V.) light on its own is used as a tertiary treatment to destroy all microorganisms present in water. It is also used in those cases where chlorine is not acceptable. In addition, there is enhanced performance of U.V. light by the addition of either hydrogen peroxide, ozone or titanium dioxide. F.25.2 Process Description The water is irradiated by passing over a U.V. source. The intensity of the radiation and the residence time are controlled to achieve the required dose. The U.V. light is generated by one or several mercury vapor lamps assembled within a stainless steel shell. The U.V. intensity is measured and controlled and the tubes are replaced when they reach the end of their useful life (>200 h). In some cases the surface of the tubes gets coated with residues and it has to be cleaned. This can be done on-line using reciprocating scrapers which wipe over the surface at regular intervals, or off-line with an acid wash. F.25.3 Process Requirements/Limitations This process requires clean streams because the efficiency of the U.V. light transmission is greatly reduced by the presence of suspended or colloidal matter.



F.26 CHEMICAL OXIDATION: U.V. LIGHT + H202 F.26.1 Introduction The combination of U.V. light and H2O2 can destroy most organic molecules dissolved in aqueous streams including aliphatic chlorinated hydrocarbons, toxics and other hard COD. F.26.2 Process Description The process involves the addition of the required amount of H2O2 (typically a 5:1 molar excess) prior to irradiation with U.V. light. The hydroxyl radicals generated are powerful oxidizing agents which can in certain cases completely convert the organic compounds present into CO2, salts and water. F.26.3 Process Requirements/Limitations This process is suitable for treating aqueous streams having both a low solids content and a low organic content and can, therefore, be used either directly on an appropriate stream or as a tertiary treatment step. The process can produce a TOC free product stream and does not generate any other effluents. In some cases it has been found to be competitive with the alternative tertiary treatment processes like granular carbon adsorption or air stripping. Both of these need further treatment stages to deal with the secondary streams produced during operation or regeneration. All designs incorporate on-line cleaning of the U.V. tubes to maintain high light transmission efficiency.



F.27 CHEMICAL OXIDATION: OZONE F.27.1 Introduction Ozone is a powerful oxidizing agent which is used mainly as a tertiary treatment to destroy bacteria present in the water and in those cases where chlorine is not acceptable. It can also be used in conjunction with H2O2 to promote the formation of more powerful free radicals which can be used for the destruction of pesticides. In some cases, ozone has been used for the final oxidation of domestic sewage to produce disinfected water useful for irrigation or industrial use. F.27.2 Process Description The process includes the production of ozone which is a highly toxic and corrosive gas and therefore the equipment has to be designed accordingly. Ozone is never produced as a pure chemical but as a mixture in air or oxygen normally at a concentration of 3% w/w in air or 6% in oxygen. The main steps are: (a) Ozone production: by subjecting the oxygen in air to a high voltage silent electrical discharge. The air needs to be dried to less than 2!ppm of water (dew point - 70°C). (b) Ozone dispersion: due to its low solubility in water the appropriate agitation conditions have to be used to maximize mass transfer. (c) Excess ozone destruction:



due to its high toxicity the excess unreacted ozone (3 to 10% of the initial amount) has to be diluted or thermally decomposed before it is discharged into the atmosphere. F.27.3 Process Requirements/Limitations Good process control is required to insure optimum operation of the system and to minimize energy usage. The "Occupational Exposure Limit" for ozone is 0.1 ppm (calculated as an 8 hour time-average concentration). It may not be suitable for AOS containing VOCs which can be stripped out during the process.



F.28 CHEMICAL OXIDATION: H2O2/Fe (FENTON'S REAGENT) F.28.1 Introduction In circumstances where the AOS contains relatively low concentrations of COD (less than 2000 ppm) and recovery cannot be justified, then the use of peroxide/iron as a chemical oxidant may prove attractive. Work by FCMO, Zeneca has shown for a range of substrates derived from benzene/toluene/halogenated aliphatics, that: (a) Most of the aromatic substrates examined were amenable to removal by oxidation with peroxide/iron, under acid conditions. (b) Halogenated aliphatic substrates were resistant to oxidation. (c) Destruction of substrate was accompanied by a reduction in COD, typically by 30-75% of the starting value. The BOD also reduced substantially except in the case of benzene where the BOD approximately doubled. F.28.2 Process Description The peroxide charge required to achieve substantial removal of one mole of substrate is typically 5-10!moles, catalyzed by 0.15-0.5!moles ferrous iron. F.28.3 Process Requirements/Limitations The rate of substrate destruction is specific to its molecular structure and therefore should be determined by experiment.



F.29 CHEMICAL OXIDATION: OTHERS F.29.1 Chlorine Chlorine is a strong oxidant and the most commonly used reagent for the disinfection of water. Chlorine also reacts with any organic matter or ammonia/ammonium ion present. F.29.2 Chlorine Dioxide Chlorine dioxide is a strong oxidant. There are several commercial processes for making it, most of which use sodium chlorite as the starting point. It is used mainly as a bleaching agent but there are some environmental applications. One example is aqueous effluents containing between 100 and 1000 ppm of phenol. Unlike elemental chlorine, chlorine dioxide does not form organic chlorine compounds when it oxidizes organic compounds. The economics can be attractive where the need is for oxidation "on demand" on a modest scale. Degussa is one system supplier. F.29.3 Sodium Hypochlorite (4) Aqueous sodium hypochlorite is a well established process for the oxidation of organic matter in water. The main advantage is low cost - it's probably the cheapest oxidant, other than air. The main disadvantage is the tendency of this process to generate organic chlorine compounds. Scrubbing liquors from VOC and odor treatment plants can be treated this way. F.29.4 Lime, Caustic, Sulfides Lime, caustic, sulfides are commonly used in the precipitation of metals. F.29.5 Acids/Alkalies Acids/alkalies are used for the neutralization of waste water. This operation often turns out to be more difficult to achieve within budget than expected at first assessment and advice should be sought.



F.29.6 Aluminum Sulfate, Ferric Chloride, Lime, Sodium Aluminate Aluminum sulfate, ferric chloride, lime, sodium aluminate are used to precipitate phosphorus compounds from aqueous streams. F.29.7 Sulfur Dioxide Sulfur dioxide is used for the removal of chlorine from aqueous streams. F.29.8 OXISPEC OXISPEC is a process provided by JMC for the catalytically enhanced oxidation of AOS containing up to 1% w/w organics. The oxidants used are sodium hypochlorite, hydrogen peroxide, ozone and the catalyst is heterogeneous. Operating conditions are modest.



F.30 TOTAL THERMAL OXIDATION: INCINERATION F.30.1 Introduction Incineration is a well established method for the destruction of organic components. When the concentration of organics in an AOS is higher than 50%, the combustion is self-sustaining and it does not need supplementary fuel. To prevent excessive NOx formation, most modern incinerators operate with water injection into the low temperature second combustion chamber. In some cases very dilute solutions < 5% organic can be disposed of by injection into this chamber instead of water. F.30.2 Process Description The use of a custom-built incinerator for the destruction of a specific AOS is very expensive and should only be considered if no other practicable alternative is available. However, there are examples of the use of power plants, steam generators or fired process heaters to dispose of unwanted organic components and at the same time recover the calorific value. Such disposal requires very careful consideration. The main requirement is to make the AOS as near compatible with the capabilities of the existing equipment as is practicable. This may involve concentrating the AOS, or blending it with existing fuel supply, adding other fuels to achieve a homogeneous mixture. To minimize interference with the process heater operation it is common to design one of the burner guns to operate using the organic residues while the rest are operated with the normal fuel. The residues are stored in one or several tanks according to their composition and are then fired in campaigns when the rest of the plant is operating. Special waste may require custom designed incinerators to meet EA Authorization requirements. This is the case for chlorine containing organics which can form dioxins during incineration and require a second combustion stage operating at about 1200°C to insure complete destruction. NOx abatement may then be necessary.



F.30.3 Process Requirements/Limitations Rotary kilns can be used to incinerate liquids, sludge's and solids. The presence of metals in the feed may be a problem because they can react with the refractory lining and shorten its life. Heat recovery is sometimes implemented as part of the incinerator design in which case if the heat recovered in the incinerator is a substantial proportion of the process heat input it is very important that the reliability of the incinerator installation matches the process requirements. Most incinerator installations include particulate removal equipment to remove solids from the combustion gases. If present in the combustion gases, volatile metal compounds, P2O5, Br, SO2 etc. will probably have to be removed. This can be done using a wet or dry scrubber. Dry systems use a bag house for removal of particulates. For acid gas absorption, dry reagent is either blown directly into the bag house or injected as a slurry into a spray tower which precedes the bag house. Wet systems use a venturi scrubber for particulate removal and an acid gas absorber, typically a vertical counter flow packed tower to remove the acid gases. A back-up filtration or electrostatic precipitation stage is likely to be required. All these methods are likely to generate a need for further processing in order to minimize the ultimate disposal problem. In some locations the visible steam plume produced by the incinerator may also have to be removed either by reheating the combustion gases after scrubbing or by dilution with air/inert gas streams. Specific material recovery processes are available in which a combustion process is used to convert part of the AOS into its basic inorganic components which can then be used to reconstitute either the original material in a usable form or some other product. For example, the Acid Recovery Process in a methyl methacrylate plant uses oxygen to combust a dilute stream of waste sulfuric acid contaminated with organic impurities. The resulting SO2 is recovered from the combustion gases, reoxidized to SO3 and then absorbed in water to regenerate the sulfuric acid which is recycled within the process.



F.31 PARTIAL THERMAL OXIDATION: OIL- GAS PROCESS F.31.1 Introduction Partial oxidation is a well established process for the production of mixtures of CO and H2 by partial combustion of organic compounds in the presence of a limited amount of O2 and a moderator (either water or carbon dioxide). F.31.2 Process Description In the absence of a catalyst, the preheated feeds react adiabatically in the combustion section of the reactor at 30-100 bar and 1200-1500°C. The hot gas mixture produced is quenched either by direct contact with water or by indirect heat exchange. F.31.3 Process Requirements/Limitations Most liquid organic residues including those containing free water can be used as feed.



APPENDIX G EMERGING TECHNOLOGY Table of Contents G.1 SUPERCRITICAL WATER OXIDATION (SCWO) G.2 LIQUID MEMBRANES G.3 REED BEDS



G.1 SUPERCRITICAL WATER OXIDATION (SCWO) G.1.1 Introduction SCWO technology is used to totally oxidize all organics present in an AOS to CO2 and water. It operates in the supercritical region of water where all mixtures of water with organic compounds are completely miscible and react with the oxygen in less than one minute. G.1.2 Process Description AOS is heated under a pressure of 300 bar to a temperature in excess of 400°C with the addition of air. Heat integration is required to minimize energy consumption.



G.1.3 Process Requirements/Limitations This technology is expensive and its use will be restricted to the removal of hazardous, refractory materials.



G.2 LIQUID MEMBRANES G.2.1 Introduction Liquid membranes allow the removal of water soluble organics from AOS as an aqueous concentrate. This recovery technique can potentially be used when conventional solvent extraction of dilute AOS stream is uneconomic. The membrane system has to exist as a liquid phase and is specifically formulated so it can selectively extract the desired chemical(s) from one aqueous stream (the AOS waste water) and concentrate it in another aqueous phase (the strip phase). This enables the reuse or recycle of the extracted chemical or, alternatively, its disposal or treatment as a stream of lower volume. G.2.2 Process Description There are two types of liquid membrane: (a) Emulsion membranes In emulsion membranes, clean water is dispersed as micro-droplets in the organic continuous phase which forms the membrane. This emulsion membrane phase can be used as an extractant in equipment similar to traditional agitated liquid/liquid extraction plant. During the extraction of AOS, under the effect of the agitation the emulsion membrane splits itself into small droplets (still containing the water micro-droplets inside). The organic compounds contained within the AOS dissolve in the membrane organic phase and then transfer to the water micro-droplets. After the extractor the emulsion membrane is phase separated from the AOS. The emulsion is then broken to form an aqueous strip phase which is readily separated from the organic continuous phase either for disposal, recycle or further treatment. The membrane layer is then re-emulsified with clean water and reused.



(b) Fixed membranes The membrane is supported in a porous inert substrate (e.g. a hollow fiber). This is known as a Supported Membrane. Of the two types, the Emulsion Liquid Membrane has the most commercial potential because of the high surface area of membrane that can be achieved when forming and dispersing the emulsion (1000-3000 m2/m3). G.2.3 Process Requirements/Limitations The process requires: (a) A driving force for mass transfer. (b) Suitable emulsion stability, i.e. it does not coalesce when in contact with the feed phase and yet can subsequently be coalesced to release the strip phase. (c) The organics concentration in the AOS should be well below saturated solubility level. The process is limited by: (1) The presence of solids. (2) Entrainment of feed in the emulsion and osmosis of water into the emulsion. (Hence controlled contacting, good emulsion settling and short contact times are preferred). (3) Any accumulation of trace impurities in the liquid membrane which prevents the system from functioning properly. However, a purge could be removed and purified prior to reuse.



G.3 REED BEDS G.3.1 Introduction Reed beds are becoming accepted as an alternative to biological treatment and have been used in many small size communities and industrial applications for the destruction of biodegradable waste. G.3.2 Process Description The reed beds are constructed by removing the soil up to a depth of 1.5 m and installing an impermeable polypropylene membrane and refilling with suitable agricultural soil up to a height of 1 m. The reeds are then planted and allowed to grow. The AOS is percolated through the beds at such a rate that the effluent achieves the required specification. The feed liquid is distributed from an inlet manifold, passes through the reed bed and is then collected and discharged to receiving waters. The level is maintained at 20 cm below the surface to provide a non-flooded bed. Oxygen is transferred by the plants to the roots and supports the attached colonies of bacteria. The plant root system enables the flow of water through the bed.



APPENDIX H PROPRIETARY/LESS COMMON TECHNOLOGIES Table of Contents H.1 INTRODUCTION H.2 PRECIPITATION H.3 SOLIDIFICATION H.4 METEX H.5 BIOKOP H.6 A-B PROCESS H.7 BACTERIA - SPECIAL H.8 BIOSORPTION H.9 BIOBOR HSR H.10 BIOSTYR H.11 CAPTOR H.12 CARROUSEL H.13 LINDOX H.14 LINPOR H.15 OTTO AQUA-TECH HCR H.16 UNOX H.17 ACIMET H.18 ANTHANE/ANODEK H.19 BIOTHANE H.20 LARAN H.21 UHDE/SCHWARTING H.22 OXIDATION BY PERMANGANATE H.23 OXIDATION BY PHOTOCATALYSIS H.24 InTox .



H.25 KENOX H.26 MODAR H.27 ULTROX H.28 VerTech H.29 WINWOX AND WOX . H.30 ZIMPRO H.31 SPRAY ROASTING (SPRAY CALCINATION) H.32 PLASMA PROCESSING H.33 ELECTROCHEMICAL PROCESSES H.34 CRYSTALLIZATION



H.1 INTRODUCTION The information in this Appendix has been extracted from the document produced for GBHE. In the brief descriptions which follow, each technology/process is annotated with a number between (1) and (4) giving an indication of GBHE's current perception of the commercial status. The key is as follows: (1) At a development stage as far as the waste market is concerned. (2) Commercially available for up to a few years but not yet in widespread use for waste. (3) Commercially available for a considerable time but either never achieved widespread use or are in decline. (4) In widespread use. It should be emphasized that these numbers refer to waste treatment. For instance, a process identified as (1) or (2) might be in widespread use in another field such as potable water. The distinction between (2) and (3) is an attempt to identify within processes in limited commercial use those which could be emerging with a future as opposed to mature ones in decline. H.2 PRECIPITATION (4) Precipitation is usually achieved by addition of alkali to neutralize acidic waste, followed by filtration with dumping of the cake and discharge of the filtrate into sewer if possible. Flocculation as practiced in the water industry is a special case. Suitable for effluents from chemical and metallurgical operations - inorganic and organic acids and anions, metals and cyanides (e.g. Pickle liquors, metal finishing liquids). The main advantage is cheapness. Practiced for many years. A relatively recent development in flocculation is the use of a magnet to remove flocculant precipitates which have been caused to adhere to granules of magnetite (the Sirofloc process).



H.3 SOLIDIFICATION (3) Conversion of aqueous wastes to solids which can be land filled. Can vary from simple physical entrapment to more complex molecular caging. In the simpler concepts, proprietary additives are used, usually based on cement or silicates. Effluents should have neutral pH. Organic materials generally unsuitable. Some inorganics with high levels of dissolved salts also unsuitable as setting is inhibited. Developed since the 1960s, mainly in the U.S.A.. There are many doubts about the approach - particularly on softening with age with release of soluble constituents. In particular, the presence of organic compounds can weaken the solids. The commercial operating process is fairly widely used in Europe. (Over 80 techniques exist in the U.S.) H.4 METEX (2) A process for extracting heavy metals from industrial waste waters by adsorption on activated sludge under anaerobic conditions. It is operated in an upflow, cylindrical reactor having a conical separation zone at the top. Particularly suited to the removal of heavy metals from waste water with organic loads which are difficult to handle by conventional methods such as ion exchange or electrolysis. Sludge containing concentrated heavy metals has to be disposed of. Developed by Linde AG, originally for removing dissolved copper from winemaking wastes. Piloted on synthetic wastes containing other metals (Ni, Cr, Zn, Hg) and typical organics such as tartrate, citrate, and glycine. The Institute of Gas Technology, Chicago, has developed a similar process. H.5 BIOKOP (2) A process for treating liquid effluents containing wastes from organic chemical manufacture and also domestic sewage. It combines aerobic fermentation, in special reactors known as Biohoch reactors, with treatment by powdered activated carbon. Low space requirement with energy saving due to high oxygen utilization. More complex and needs more control than traditional technology. Developed originally for treating the effluent from the Griesheim works of Hoechst AG, it was engineered by Uhde GmbH and is now offered by that company.



H.6 A-B PROCESS (2) This process stands for Adsorptions-Belebungsverfahren, German, meaning Adsorption-Activation process. A two-stage, aerobic activated sludge process for treating sewage and industrial wastes. The first (A) stage is highly loaded, the second (B) low-loaded. Such a system can cope with sudden changes in the quantity and quality of effluent feed. Suitable for high BOD, non-biotoxic wastes, both municipal and industrial. A small land area is required and the capital cost is lower than that of conventional activated sludge plant because fewer stages are required. Relatively low energy consumption. Developed in 1983 by B Bohnke at the Technical University of Aachen and subsequently engineered by Esmil. H.7 BACTERIA - SPECIAL (3) Use of bacteria which are specially adapted to metabolizing particular substrates. Developed in the 1970s, to improve the performance of activated sludge plants when specific materials were present (e.g. hydrocarbons) which were difficult for the normal spectrum of microorganisms to metabolize. Often referred to as bioaugmentation. Have not achieved mainstream use. The economics are contentious. Usually supplied freeze-dried. Suppliers include International Biochemical's Ltd and a variety of importers of products from the US. H.8 BIOSORPTION (1) A process for removing metals and some organic compounds from aqueous solution by biosorption on suitable microorganisms. Biotechna Ltd has been prominent in this field. Development started in about 1984. First patents were filed in 1987. They work with Graesser Contactors and organisms are grown in a helical reactor called a "Biocoil". These include bacteria, algae, fungi and yeasts. Desulfovibrio, a sulfur reducing bacteria, is one example. More recently, Archaeus Technology Group has been promoting its Arcasorb range.



H.9 BIOBOR HSR (2) An intensification of the classic activated sludge aerobic approach. Uses compressed air into a tower with moving perforated disc internals. HSR stands for Hubstrahlreaktor which translates to reciprocating jet reactor. Closed reactor giving odor control. Agitation gives high rate of oxygenation. Short residence time/relatively small volume. Doesn't take up much space. Low surplus sludge production. Developed by Borsig GmbH and now being commercialized. A mobile test rig can be rented. Claimed to be economic for rigorous treatment of wastes with very high BOD/COD levels. H.10 BIOSTYR (2) An immersed biological filtration approach using a fixed biomass. The microbiological organisms are trapped within rigid, lighter-than-water porous polystyrene granules. The effluent flows upward through a bed of these granules and air is injected at the base of the bed. Suitable for both dilute and concentrated effluents containing dissolved non-toxic organic matter. Compact with high performance in a single stage and no final clarification needed. Developed in France by OTV S.A. and licensed in the U.K. through General Water Processes Ltd. H.11 CAPTOR (2) A modification of the activated sludge system in which the microorganisms are retained in a reticulated, flexible polyether foam. Excess sludge is periodically pressed out mechanically. Particularly suited to concentrated effluents with high BOD and COD from food processing plants and the like. Occupies only 20% of the land area occupied by conventional activated sludge plant. Invented at UMIST and now offered by Simon Hartley. H.12 CARROUSEL (2) An unconventional aerobic treatment system for sewage and industrial effluents, providing efficient oxygenation, mixing, and quiescent flow in an elliptical aeration channel fitted with baffles. Suitable for effluents with moderate loadings of non biotoxic organic materials. Capital cost lower than that of conventional activated sludge plant because fewer stages are required. Low power requirements. Claimed to provide buffer against shock loading. Developed in Holland by DHV and now licensed in the U.K. by Esmil Ltd.



H.13 LINDOX (3) A variation of the activated sludge process, using industrial oxygen (90- 98%) instead of air. The liquor passes through several closed tanks in series and the oxygen is absorbed through the surface of the liquor. Can treat wastes having high nitrogen contents, e.g. those from meat processing plants. Occupies less space than conventional activated sludge plants. Totally enclosed so no odors. More complex to operate and maintain than conventional plant. Developed by Linde AG in the 1970s and first operated at a meat rendering plant in Oberding in 1974. Closely related to the Unox process. Claimed to be viable for the more difficult and variable effluents, such as from the food industry, with very high oxygen demand and potential problems with sludge bulking. H.14 LINPOR (3) Uses an open-pore plastic foam for retaining the biomass. Suitable for high BOD, non-biotoxic effluents - particularly really concentrated ones. Its use enables the capacity of an activated sludge plant to be increased without adding extra tanks. Good results where sludge bulking might be a problem. More complex than conventional plant. Invented at the Technische Universitat, Munich, and further developed by Linde AG. Initiated by the demand for nitrification in the activated sludge process calling for large treatment volumes. H.15 OTTO AQUA-TECH HCR (2) An intensification of the classic activated sludge aerobic approach. HCR stands for high capacity reactor. Uses a vertical loop reactor aerated from the top by a two-phase air jet in conjunction with a sedimentation facility. Closed reactor giving odor control. The means of aeration is claimed to give very high mass transfer rates between microorganisms and the supplied substrate. Doesn't take up much space. Reduced surplus sludge. Total cost in use claimed to be lower than activated sludge. Fundamental research at the Institute for Thermic Processing at the Technical University of Clausthal-Zellerfeld. Developed and engineered by Otto. First commercial installation 1989. Eleven plants have now been installed in Germany and Italy on wastes from dairies, abattoirs, yeast processing, printing ink manufacture, olive oil refining and landfill leachate.



H.16 UNOX (3) A variation of the activated sludge process based on the use of oxygen instead of air, in closed reaction tanks. The preferred source of oxygen depends on the size of the plant; small plants use liquid oxygen; medium- sized plants use the pressure-swing process, and large plants have cryogenic generators. Occupies less space than conventional activated sludge plants. Totally enclosed, so no odors. Accepts large swings in oxygen demand. More complex than conventional activated sludge - needs higher standard of operation and maintenance. Capital costs lower and operating costs higher than conventional activated sludge plants. Developed by Union Carbide Corporation in the late 1960s and now licensed to a number of other companies including Wimpey Engineering in the U.K.. Similar to the Lindox process. H.17 ACIMET (1) A two-stage, anaerobic digestion process for treating municipal waste waters. In the first stage, organic matter is decomposed to a mixture of acids, aldehydes and alcohols. In the second, the carbon in this mixture is anaerobically converted to methane. Suitable for wastes containing large amounts of cellulose as well as municipal wastes. Designed primarily to produce gas for fuel. Invented in 1974 by S Ghosh and D L Klass at the Illinois Institute of Gas Technology, Chicago. First commercialized in 1991 by IGT and DuPage County, Illinois, at the Woodridge-Greene Valley Wastewater Treatment Plant. H.18 ANTHANE/ANODEK (3) A two-stage process for generating methane by the anaerobic fermentation of industrial organic wastes. The process is designed basically for producing a fuel gas and is said to be suitable for effluents containing up to 40 g/l COD. Higher loading rates and shorter hydraulic residence times than conventional digestion are claimed. Invented by the Institute of Gas Technology, Chicago. Engineered by the Studiebureau O. de Konickx, (ODK) Belgium, and commercialized since 1977. Now offered by ODK's U.S. affiliate VIMAG Inc.



H.19 BIOTHANE (4) An anaerobic digestion system for treating industrial organic wastes. The reactor contains an upflow sludge blanket and is operated at about 35°C, the heat being provided by burning some of the product gas which contains 70% methane. It is usually necessary to add nutrients such as urea and iron. Particularly suited to food industry wastes. Occupies a relatively small land area. Essentially a pretreatment usually followed by a secondary aerobic stage. Developed in the early 1970s in Holland by Centrale Suiker Maatschappij; in 1984, Gist-Brocades nv (Delft) acquired the rights and subsequently licensed the process in the U.K. to Esmil Ltd. In 1990, more than 70 units had been built, worldwide, for a variety of industries. H.20 LARAN (2) An anaerobic process for treating industrial waste waters, generating methane for use as fuel. The process uses a fixed-bed loop reactor. Shock loads can be accommodated. Short retention times and good nitrification are claimed. Developed by Linde AG, Munich, in the early 1980s. European patent 161,469. First piloted at a dairy in 1983. Viable as a pretreatment for wastes with a high level of organic pollution prior to an aerobic "polishing" step. H.21 UHDE/SCHWARTING (2) An anaerobic fermentation process for treating aqueous wastes containing high concentrations of organic materials. Two fermenters are used, operated at different temperatures and acidities. In the first, insoluble materials are brought into solution and most of the organic matter is converted to acids and alcohols. In the second, methane and carbon dioxide are produced. Developed in 1982 in Germany by Geratebau Schwarting AG and the Fraunhofer Institute for Boundary Layer Research; engineered and offered by Uhde GmbH. Three plants have since been built in Germany and one in Portugal, all for the food industry. As with anaerobic processes generally, the value of the gas generated is important.



H.22 OXIDATION BY PERMANGANATE (3) This is often used for removing trace colors and odors from potable water, so it could be considered for removing traces of toxic materials from effluents too. In general, oxidation by permanganate is between 2 and 3 times as expensive as oxidation by chlorine so it would not be economic for removing more than trace amounts except for very specific applications. H.23 OXIDATION BY PHOTOCATALYSIS (1) Photocatalysis, using titanium dioxide catalyst and sunlight. Will treat compounds that are hard to oxidize in other ways, e.g. dioxins, if present in very dilute form. The photocatalytic properties of titanium dioxide have been known for many years but it has only been seriously considered for practical use during the last ten. Sandia National Laboratories and the Solar Research Institute, U.S.A., have demonstrated its usefulness for treating groundwater containing chlorinated hydrocarbons and predict its commercial adoption by 1995. There has been a lot of academic research but only one, modest, device has been marketed. This is the Nulite reactor from Nutech Environmental in Canada. H.24 InTox (1) The InTox process uses established wet air oxidation principles in a pipe reactor autoclave (230-280°C, 120 bars). The pipe is 2-4 km long and 2.5- 10 cm in diameter. The technology is based on an aluminum extraction process developed in Germany in the 1960s by VAW and Lurgi. The process was promoted in the U.K. during 1991 for waste treatment by InTox Corporation Limited. This is believed to be a group of individuals basing their promotion on a unit operated by Chemcontrol A/S in Denmark - the unit pictured in InTox literature. InTox claimed a higher degree of waste destruction than other wet air oxidation variants and also relatively low capital and operating costs. However, InTox ceased its promotion in late 1991. Apparently, the Chemcontrol unit is no longer operational and has been dismantled. In 1995 no information on the InTox process or InTox Corporation could be found. Lurgi (UK) Ltd have no knowledge of the process.



H.25 KENOX (2) The Kenox wet air oxidation process is offered by the Kenox Corporation of Ontario. This is a small company formed by some individuals who came together in 1983 to develop a system using a different reactor design from that used by Zimpro. Kenox became part of Environmental Technologies Investments of Toronto in 1991. Kenox claims that its reactor operates in a much more dynamic regime with a high circulation rate giving very much higher mass transfer of oxygen. For a given duty, its operating temperature and pressure (250°C, 700 psi) are lower than those of Zimpro. Kenox also claims that, overall, corrosion is less, total operating costs dramatically less and that when items of plant have to be replaced they can easily be sourced locally whereas Zimpro requires various specialized items to be sourced directly from the company. Until recently, the only unit in operation was of 12 gallons per minute capacity dealing with the washing wastes from a large steel drum reconditioning plant in Toronto. A breakthrough for Kenox was an agreement with Leigh Environmental in 1991 giving Leigh exclusive rights to use and market the Kenox technology in the U.K.. Leigh announced a merchant facility which is being installed at Small Heath in the Midlands. This is designed for 50,000 tpa of difficult organic wastes from the pesticide, chemical and pharmaceutical industries. This is being commissioned now and Leigh has said that, upon the successful completion of this exercise it will build three more merchant units in different parts of the country. H.26 MODAR (2) Modar Supercritical Water Oxidation (SCWO) Technology was invented in 1980 by M Modell, a professor of chemical engineering at MIT. It was then developed through the 1980s being piloted at the SKF Laboratories in 1985 and then at CECOS, a waste treatment company in Niagara Falls, in 1986. A larger capacity plant for CECOS has been designed but has not yet gone ahead. SCWO should still be classed as an emerging technology. The principle is that water above its critical point is an effective solvent for organic compounds and also gases including oxygen are completely miscible. Hence, a homogeneous single phase results where the organic compounds and oxygen can react rapidly without interfacial mass transfer limitations. Particularly suitable for 1-30% toxic organics in water.



With operations at above the critical point of water (374°C and 22.13 MPa pressure) - typically 620°C and 23.5 MPa - the engineering and materials of construction challenges are severe. However, for more than two years the worldwide exclusive license has been in the hands of ABB Lumus Crest Inc which gives the potential for heavyweight support. Indeed, ABB Lumus Crest claims to have "invested" about $2 million over the past two years in the development of the technology and has now completed two basic engineering packages for modest sized plants of 5,000 and 20,000 gallons per day respectively. The potential prize for ABB Lumus Crest is a more acceptable alternative to incineration with operating costs which could be a tenth of those of conventional incineration. H.27 ULTROX (1) Combined UV-Ozone-Hydrogen peroxide oxidation approach. Effluents should be free from particles or cloudiness and fairly dilute - concentration of organic to be destroyed initially in the range 20-30,000 ppm. Reduces total organic carbon to low parts per billion and will treat compounds that are hard to oxidize in other ways, e.g. halogenated organics. End products are CO2 and halide ion. Developed since the 1970s by Ultrox International and demonstration tests on 15 various effluents published. Tested on large scale in California in 1989, results well documented. H.28 VerTech (2) VerTech Treatment Systems BV of the Netherlands is promoting a system which uses conditions in the typical wet air oxidation range (i.e. 270°C and 10 MPa). However, VerTech describes the system as subsurface oxidation since it relies on a vertical pipe about one mile deep with pressure being created at the bottom by the weight of the liquid above it. The vertical shaft is drilled conventionally and encased in cement after which two concentric special quality steel tubes are suspended in it. Oxygen rather than air is normally advocated as the oxidizing agent. Although the company says that there is potential use of the system for industrial organic waste, a large volume throughput is required - a minimum of the order of 100 gallons per minute. This rules it out of most industrial waste applications. VerTech is concentrating its promotion on sewage sludge treatment with large volume flows with up to 10% solids. The operating experience is based on a system installed at Longmont, Colorado in 1985. About a year ago, a unit for the Veluwe Water Board at Apeldoorn in the Netherlands was announced.



H.29 WINWOX AND WOX (2) Catalyzed oxidation by hydrogen peroxide. Winwox has been developed since 1987 by the Winfrith Technology Centre (part of the U.K. Atomic Energy Authority) as a method of destroying ion exchange resins containing radioactive isotopes. A pilot plant for handling 200 kg batches containing 300 g/kg solids was built in 1989. WOX has similarly been developed by ASEA Atom, Sweden. Now being promoted for hazardous aqueous/organic wastes more generally. Advantages are mild conditions, small amount of secondary effluent and ordinary materials of construction. Capital costs relatively low but hydrogen peroxide costs high, hence likely to remain specific to specialized hazardous wastes. H.30 ZIMPRO (4) The Zimpro wet air oxidation process was introduced by J F Zimmerman in the U.S.A.. in 1954 and for many years was known as the Zimmerman wet incineration process. It has had a somewhat chequered ownership history but latterly has been offered by Zimpro Passavant Environmental Systems Inc under the Zimpro name. Zimpro Passavant became part of the Black Clawson Company late in 1990. Over the last 35 years, more than 200 Zimmerman/Zimpro wet air oxidation units have been installed around the world. Many of these have been for the treatment of pulp and paper industry waste liquors, sewage sludge and refinery waste caustic liquors. Experience on general industrial aqueous effluents containing organics is clearly more recent but the accumulated generic engineering and operational experience on the 200+ units is unrivalled. Zimpro has to be regarded as the current market leader in wet air oxidation. Typically operates at 280°C and 1700 psi. Sterling Organics are installing a unit with a design flow of 30 gallons per minute in Northumberland. This will remove para amino phenol from waste water generated in paracetamol manufacture.



H.31 SPRAY ROASTING (SPRAY CALCINATION) (3) Injection of liquid waste into a hot combustion chamber which may or may not contain a fluidized bed of inert material. Suitable for aqueous wastes, which may be strongly acid or alkaline, containing dissolved organic and/or inorganic compounds, e.g. steel pickling liquor containing hydrochloric acid and ferrous chloride; liquor from limonite beneficiation; caustic waste from oil refineries. A established process, often associated with hydrochloric acid recovery. Suppliers of systems include Babcock Woodall, Duckham and Copeland Systems Inc. H.32 PLASMA PROCESSING (1) A plasma is a gas in which some of the gas molecules are ionized to form positive ion and electron pairs and thus conducts electricity. Thermal plasmas based on arc discharge operate at very high temperatures, typically greater than 5,000°C. Waste is injected into the plasma arc and dissociation takes place sometimes with incineration if additional air or oxygen is introduced. Suitable for effluents containing virtually any organics and some inorganics. Particular attention is needed to rapid quenching after the plasma Pyrolysis to prevent chemical re-combination. Westinghouse has made a big effort to commercialize plasma technology for waste destruction with little success. EA Technology at Capenhurst is developing a system. Other suppliers/ developers include Arc Technologies Co, U.S.A., CSIRO, Australia and Tetronics Ltd. H.33 ELECTROCHEMICAL PROCESSES (3) Such processes include both those where oxidation or reduction of the substrate occur at an electrode, and those where a particular metal ion in a particular valence state is an intermediary. In principle, any aqueous solute which can be oxidized or reduced can be considered as a candidate for such a process. Large scale electrochemical technology goes back almost a century in the chloralkali industry but other applications have been slow - held back by lack of electrochemical expertise, limited access until recently to "off the shelf" pilot reactors and general perception of high cost. EA Technology (former ERDC) has been successful with specific packages such as the Chemelec cell for recovering metal and the CEER process for regenerating etchant with copper recovery from printed circuit board production.



The use of Ag2+ (the so-called "silver bullet" process) arose from work at a European plant where this oxidant was used to solubilize plutonium dioxide. It was then discovered that this oxidant also oxidized cellulose tissues to carbon dioxide. Relatively exotic and still under development. The electrochemical approach is generally particularly suitable for dilute effluents. Very powerful oxidants can be produced (e.g. Ag2+). Electrochemical processes are generally regarded as expensive in energy and capital and the economics depend on recovered materials or other specific factors. Small reactors and general know-how are available from EA Technology and their licensee Electrocatalytic, and Electrocell AB. AEA Technology is promoting the "silver bullet" process. H.34 CRYSTALLISATION (2) Removal of solutes from water or organic solutions by crystallization, either by evaporation or by cooling. Cooling is sometimes done by adding a cold liquid such as petrol or liquid carbon dioxide. Suitable for "clean" solutions - complex mixtures can be hard to crystallize. Ideally there should be some value in the solute or solvent. Widely used in the chemical industry, e.g. to remove ferrous sulfate from sulfuric acid residues from the sulfate process for making titanium dioxide.



APPENDIX J COMPARATIVE COST DATA J.1 EXAMPLE 1 Aqueous stream containing 2 to 3% TOC including CN compounds, inorganic salts such as ammonium sulfate, methylene chloride, benzene as well as some solids and heavy metals.

REFERENCE: 4 ŧ Widely practiced in the U.S.A. However, it may not be acceptable in the future. § This process still requires further technical development.



J.2 EXAMPLE 2 Aqueous stream containing 200 to 500 ppm TOC including benzene, toluene, ethylbenzene and xylene.

REFERENCE: 4



J.3 EXAMPLE 3 Aqueous stream containing 5 to 10 ppm TOC including TCE and PCB's.

REFERENCE: 4 J.4 INDICATIVE COST DATA (1993) CAPITAL COST OF A BIO TREATMENT PLANT: $1.0M to 1M/(tonne/day) of BOD COST OF LANDFILL: $50 to $132/tonne COST OF CONTRACT INCINERATION: General Waste: $250 to $3,3000/tonne Laboratory Waste: up to $16,500/tonne (Cost expected to increase by a minimum of 30%/year)

PRACTICAL GUIDE ON THE SELECTION OF PROCESS TECHNOLOGY FOR THE TREATMENT OF AQUEOUS ORGANIC EFFLUENT...

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Transcript of PRACTICAL GUIDE ON THE SELECTION OF PROCESS TECHNOLOGY FOR THE TREATMENT OF AQUEOUS ORGANIC EFFLUENT...