Treatment of Waste

OVERVIEW

The following brief discussion applies to all types of treatments, be it for hazardous waste or refinery wastewater.

It should be remembered that:1.Most Waste Generated is Wastewater

e.g. 214 million tons of hazardous waste generated in U.S. annually – of which 97% is wastewater.

2.The constituents in wastewater must be either:– Treated prior to discharge to a wastewater treatment plant– Collected for disposal at a hazardous waste landfill– Collected for treatment off-site.

3.Common Constituents of Industrial Wastewater1. Suspended solids2. Soluble organics3. Toxic organics4. Heavy metals and cyanide5. Color and turbidity6. Nitrogen and phosphorus7. Refractory substances (resistant to biodegradation)8. Oil and floating material9. Volatile materials

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4.Treatment of Industrial Wastewater: Depends on Final Destination– Either sent to wastewater treatment plant – For additional

treatment– Or directed to the environment :

i. to surface water ii. groundwater iii. aquifer recharge iv. direct use

5.Prior to discharge "wastewater" to any place:

– Water must meet requirements developed by the local authority or your industrial facility

– Discharge limits typically listed in a permit.– Periodic sampling and analytical requirements are required.

Typical common limits set by authorities : Biochemical oxygen demand Chemical oxygen demand Suspended solids Fats, oils and grease Heavy metals

4.Direct Discharge to Water BodyThis requires a special permit and seldom given to any industry In this case effluent must meet strict standards , and "point of discharge to the receiver water" is usually set as well e.g. shallow vs.deep areas of water body.

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Types of Waste Treatment

Basically there are four types of treatment trains:i. CHEMICAL TREATMENTii. PHYSICAL TREATMENTiii. BIOLOGICAL TREATMENTiv. THERMAL (INCINERATION)

The most important principle for effective treatments is to choose correctly the required method of treatment. This correct choice depends on knowing:

i. Partitioning between water and air – Henry’s Law coefficientii. Partitioning between water and organics – Kow – octanol water

coefficientiii. Biodegradability – Biodegradation rate constantiv. Moisture content

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The following represents the basics of each type of treatments

I. Chemical Treatmentsi. Catalysisii. Electrolysisiii. Hydrolysisiv. Neutralizationv. Photolysisvi. Oxidation /Reductionvii. Precipitation

i. CatalysisBasically, catalysis increase of rate and mechanism of a chemical reaction

e.g.– complete air oxidation of cyanides– dechlorination of chlorinated hydrocarbons

ii. Electrolysis oxidation or reduction at an electrode surface immersed in a conductivesolution under the influence of an applied potential.

iii. HydrolysisIs a reaction of a salt with water to form an acid and a base

XY + Water ------> HY + XOH

iv. Neutralization

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Means the adjustment of the pH by addition of either an acid or a base.This is carried out in continuous or batch reactors

v. PhotolysisMeans the breakdown of chemical bonds under UV or visible light

vi. Oxidation / ReductionOxidation – Transfer of electrons from the chemical being oxidized to the oxidizing agent (Cl2, O3, H2O2,KMnO4).Reduction – transfer of electrons from the reducing agent tothe chemical being reduced, such as reduction of Cr+6 (hexavalent state) to Cr+3 (trivalent state) using sulfur dioxide

vii. Precipitation Change in the solubility of compounds by addition of :– alkaline agents (caustic soda or lime)– sulfides (hydrogen and sodium sulfide are used to precipitate heavy

metals)– sulfates (cyanide removal)– carbonates

Physical Treatment ProcessesTrying to achieve one or more of the following:

– Reduction of waste concentration– Reduction of waste volume– Separation of waste components

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Physical Treatment Processes include:i. Adsorptionii. Air Strippingiii. Centrifugationiv. Distillationv. Electro - dialysisvi. Evaporationvii. Filtrationviii. Flocculation,ix. Precipitation, and sedimentationx. Flotationxi. Freeze Crystallizationxii. Ion Exchangexiii. Solidification

i. Adsorption : a. Separates organics (and some inorganics) from an aqueous waste

streamb. attraction and accumulation of the adsorbate (the organic)

contained in water or some aqueous phase onto the surface of a rigid, solid phase (the adsorbent) such as activated carbon.

ii. Air Strippinga. Volatile components are transferred from a liquid mixture (water)

to a gas (air).b. Driving force is related to the departure of the vapor-liquid phase

concentrations from equilibrium with mass transfer in the direction of decreasing concentration.

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iii. Centrifugationa. Centrifugal force is used to separate liquid from the solid in

enclosed environs. b. Primarily used to dewater sludge resulting in a reduction of the

sludge volume.c. Reduce slurry volumesd. Results in an increased solids concentration in the waste streams.

iv. Distillationa. Nondestructive liquid phase separation processb. Used for organic component recoveryc. Based on differences in vapor pressure

v. Electrodialysisa. Separates ionic components of a waste streamb. Uses synthetic membranes and an electrical field

– membrane is a semi-permeable one, allowing either anions or cations to pass through it

– electric field causes separation of positive from negative ionsiv. Evaporation

a. Concentrates the waste and reduces its volume by heating the mixture in pipes, ponds

b. The vapor phase is not collected and/or condensed as in distillation.

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v. Filtrationa. Liquid passes through a porous media that traps the solidsTypical media: Sand, Porosilineb. Backwash to clean filter,

vi. Flocculation, Precipitation, and Sedimentationa. Removes suspended solids, colloidsb. Enhance conditions for floc formation

i. Changing solubility of metalsii. Settling chamber

c. Flocculating particles aggregate or coalesce thereby changing the particle size, shape, and even specific gravity.

vii. Flotation (Dissolved Air Flotation DAF)a. removes solids suspended in the waste

– via agitation– sometimes via chemical addition

b. Air bubbles reduce the solid density– Bubbles carry particles to the surface of the tank.

c. A froth or foam forms at the top and contains the solids– removed with a skimmer arm

viii. Freeze Crystallizationa. The waste water is cooled to form purified iceb. crystalsc. Remaining liquid will be more concentrated

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d. The process can be repeated on the same waste to further concentrate

ix. Ion Exchangea. A synthetic or natural resin materialb. Used to removed dissolved solidsc. Heavy metals and anions attach to the resin surface, exchanged

for other anions that were previously on the surfaced. Occurs quickly, unless/until all the exchange sites are filled

– “Breakthrough” – requires regeneration.

x. Solidificationa. Fixes or encapsulates the waste

Rendering the Hazardous Waste into a non-hazardous solid product

b. Solidifying agents:– Silicates– Cement-based (Portland is common; results in rock-like solid)– Lime-based– Thermoplastics– Organic polymers

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Biological Treatment

As the name implies, it uses microbes to decompose organic wastes. During the process of biodegradation, sorption and stripping also occur.

Types of Biological Treatment

1. Aerated lagoons2. Activated Sludge3. Anaerobic Digestion4. Composting5. Enzyme Treatment6. Trickling Filters7. Waste Stabilization Ponds

i. Aerated lagoonsThree types of lagoons 3-5 meters deep are used:

– Well mixed (all aerobic)– Facultative– Settling lagoons

The treatment efficiency depends on many factors:– Oxygen availability– Waste biodegradability– Nutrients (N & P)– Detention time

ii.Activated Sludge10

Similar to aerated lagoons in operation. Usually 2 stage process viz:– Aeration basin– Clarifier

Some microbes are wasted, others are returned to the system (“activated”)

iii. Anaerobic DigestionUses microbes that do not need oxygen to respireNot usually suitable for industrial wastes

iv. Composting Land reclamation, land-farming. Biodegradation of organics in the soil. Requires collection of leachate and runoff for groundwater

protection. Can aeration by turning the soil.

v.Enzyme Treatment An enzyme must be added for the process to start. Speed up degradation of the waste. Applicability limited to simple waste streams:

– Enzyme is specific to target wastes– Inhibited by some inorganics– pH sensitivity

vi. Trickling Filters

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Microbes are supported on a solid media structure (e.g., rock, plastic)

Wastewater is trickled over the media There is a biofilm layer consisting of:

– Aerobic outer layer– Inner layer may be anaerobic– Waste concentration changes within the biofilm

vii. Waste Stabilization Ponds Basically, the method dilutes industrial wastes and uses shallow

basins (1 to 2 meters) deep Wind provides limited aeration but at the bottom of deep ponds the

processes mainly are anaerobic at the bottom. Photosynthetic algae of surface

Post-Treatment: Equilization12

The object from post-treatment can be summarized in the following six points:

1. Prevents shock loading of biological systems by dampening organic fluctuations.

2. Enables better pH control, and can reduce chemical requirements for neutralization.

3. Minimizes flow surges to physical/chemical treatment systems.

4. Provides continuous feed to biological systems5. Enables controlled discharge of treated wastewater to end

points thus enabling even distribution of the wastewater load.6. Prevents high concentrations of toxics from entering the

biological treatment plant too rapidly.

I. Primary TreatmentThis basically a physical treatment – settling basinsIt uses gravity to remove suspended solidsIt also employs screens, grinders, grit removal…etc.

II. Secondary Treatment

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Standard type of a secondary treatment consists of: Biological Treatment– Aerobic type such as: Aerated lagoons Activated sludge Trickling filters– Anaerobic type such as: digesters

III. Tertiary/ Advanced Treatment

This takes secondary treatment further by filtration to remove solids from treated wastewater and removes nitrogen and phosphorous compounds. By this treatment treated wastewater can be converted to potable water. The use of ionexchage systems are widely used.

IV. Ultimate Disposal OptionsFollowing treatment, remaining wastes often disposed to land such

as:– Waste streams remaining from the wastewater treatment at

the industrial site– Solid wastes not discharged to sewer– Solids/sludge from the wastewater treatment plant

V. Land farming

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There are many options to get rid of solid organic waste. One such method is land farming. In this method ploughing land is carried out first, and then only organic degradable waste is sprinkled evenly. Ploughing is repeated till upper layers of soil are homogenized. This is a cheap, effective and simple disposal method. Above all, the method enhances soil. One should remember that degradation factors depend on:

– Waste Composition– Contact between the waste and the microbes– Soil Temperature– Soil pH– Oxygen– Inorganic Nutrients- N & P– Moisture Content

If the treated "waste" is liquid, then another method can be used, namely: Deep Well Injection. The method depends on transferring of liquid waste deep underground far away from freshwater sources.

Criteria for "waste" waters in this method are:– Low Volume, High Concentration Waste– Difficult to treat by other methods– Compatible with material in disposal zone– Biologically Inactive– Non corrosive

VI. Incineration

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Destruction of wastes by CombustionThe method is suitable for:

– Gases– Liquids– Slurries– Sludge wastes– Solids– Containerized

Incineration destroys molecular structure, thus molecules with more stable structures and stronger chemical bonds require longer residence times and/or higher temperatures.

Incinerator operating conditions must be monitored continuously. The following are some parameters affecting the efficiency of burning:

Combustion temperature Residence time Degree of mixing Presence of excess air

The type of incinerator required depends on the chemic and physical state of "waste" .Examples of incinerators:

Liquid injection

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– Any pumpable waste– Converts liquid waste to gas prior to combustion

Kilns– Used on solids, liquids, and gases– Many different types (e.g., rotary kilns, cement kilns, lime kilns,

aggregate kilns).Calcination or sintering

– 1800oC and atmospheric pressure.– Destroys organics; reduces the volume of inorganics

Incinerator Performance must be monitored, thus:Destruction and Removal Efficiency (DRE) must be determined. This done by "monitoring" organization. The higher the figure of DRE , the more efficient is the incinerator.DRE of 99.99% for all “principal organic hazardous constituents” (POHCs) is required.– Example: Wastes containing dioxins and furansrequires 99.9999% DRE Incomplete combustion – afterburners must be installed for exhaust

– Combust the exhaust at higher temperature than the combustion of primary waste stream. Example: dioxin and furan creation, more toxic than precursors

75 dioxin congeners; 135 furan congenersIncinerators usually produce particulates; thus particulate controls are important. Particulates can be removed by using bag-houses, and water scrubbersControl of acid formation is also important e.g. HCl from combustion of chlorinated organics. Acids corrode metals and form "acid precipitates", and acid rain.

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Landfill

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Recycling is important for several reasons.

1) Recycling conserves natural resources. i.e., they don’t get replaced as we pull them out of the ground. Once they’re gone, they’re gone forever.

2) Recycling conserves landfill space. Landfill space will last longer if we only put items that are not recyclable into them. It costs a great deal of money to build a landfill and we need to be careful how much and how fast we fill them up.

3) Recycling employs people. Recycling employs people who

i. Collect the recyclable material, ii. Process the material or get it ready to sell to a manufacturer,

iii. Transport the materials to factories where it will be turned into new products,iv. Take the material and manufacture it into new products, v. Manufacture equipment and products used by the recycling industry, and finally

vi. Manage recycling programs and private and non-profit recycling programs. 4) Recycling conserves energy. Without question, recycling conserves the energy that would be necessary to create the same product from its raw resource.

5) Recycling reduces our dependence on overseas natural resources. This is important in two very important ways:

i. It reduces our dependence on overseas oil and gas which has national security implicationsii. It reduces our foreign trade deficit which is important to the strength of our economy.

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(H enry's law can be put into mathematical terms (at constant temperature) as

where p is the partial pressure of the solute in the gas above the solution, c is the concentration of the solute and kH is a constant with the dimensions of pressure divided by concentration.[1] The constant, known as the Henry's law constant, depends on the solute, the solvent and the temperature.

Some values for kH for gases dissolved in water at 298 K include:

oxygen (O2) : 769.2 L·atm/molcarbon dioxide (CO2) : 29.41 L·atm/molhydrogen (H2) : 1282.1 L·atm/mol

Octanol-Water Partition Coefficient (KOW) - "An organic compound's octanol-water partition coefficient, KOW, is defined as the ratio of the compound's concentration in a known volume of n-octanol to its concentration in a known volume of water after the octanol and water have reached equilibrium ... Water solubility was found to be the major factor affecting the partition coefficient." – Smit

Biodegradability:What exactly does this mean? I would define it as being able to be broken down by natural processes, into more basic components. Products are usually broken down by bacteria, fungi or other simple organisms. By this definition, most chemicals are biodegradable; the only thing differing would be the amount of time it takes to break down. A piece of bread will break down rather quickly, whereas a piece of plastic will take decades and beyond.

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Volume reduction

Volume reduction includes those techniques that remove the hazardous portion of a waste from a non-hazardous portion. These techniques are usually to reduce the volume, and thus the cost of disposing of a waste material. The techniques that can be used to reduce waste-stream volume can be divided into 2 general categories:

1.source segregation and2.waste concentration.

Segregation of wastes is in many cases a simple and economical technique for waste reduction. Wastes containing different types of metals can be treated separately so that the metal value in the sludge can be recovered. Concentration of a waste stream may increase the likelihood that the material can be recycled or reused.

Methods include :

gravity and vacuum filtration, ultra filtration, reverse osmosis,

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freeze vaporization etc.

What Is Biological Oxygen Demand And How Does It Affect Water Quality?

Biochemical oxygen demand is a measure of the quantity of oxygen used by microorganisms (e.g., aerobic bacteria) in the oxidation of organic matter. Natural sources of organic matter include plant decay and leaf fall.

Chemical oxygen demand (COD) is used as a measure of oxygen requirement of a sample that is susceptible to oxidation by strong chemical oxidant. The dichromate reflux method is preferred over procedures using other oxidants (eg potassium permanganate) because of its superior oxidizing ability, applicability to a wide variety of samples and ease of manipulation. Oxidation of most organic compounds is 95-100% of the theoretical value. 

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Source of e-wastes

Constituent

Health effects

Solder in printed circuit boards, glass panels and gaskets in computer monitors

Lead (PB)

Damage to central and peripheral nervous systems, blood systems and kidney damage.

Affects brain development of children.

Chip resistors and semiconductors

Cadmium (CD)

Toxic irreversible effects on human health. Accumulates in kidney and liver. Causes neural damage.

Teratogenic.

Relays and switches, printed circuit boards

Mercury

(Hg)

Chronic damage to the brain.

Respiratory and skin disorders due to bioaccumulation in fishes.

Corrosion protection of untreated and galvanized steel plates, decorator or hardner for steel housings

Hexavalent chromium

(Cr) VI

Asthmatic bronchitis.

DNA damage.

Cabling and computer housing

Plastics including

PVC

Burning produces dioxin. It causes

Reproductive and developmental problems; Immune system damage;

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Interfere with regulatory hormonesPlastic housing of electronic equipments and circuit boards.

Brominated flame

retardants (BFR)

Disrupts endocrine system functions

Front panel of CRTs

Barium (Ba)

Short term exposure causes:

Muscle weakness;

Damage to heart, liver and spleen.

MotherboardBeryllium

(Be)

Carcinogenic (lung cancer) Inhalation of fumes and dust. Causes

chronic beryllium disease or beryllicosis.

Skin diseases such as warts.

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