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Training on Anaerobic Process for CDM Project

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WASTEWATER TREATMENT PLANT IN GENERAL

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Wastewater Constituents and Unit Operation and Processes for their Removal

Chemical scrubbers; Carbon adsorption; Biofilters;

Odors

Air stripping; Carbon adsorption; Advanced Oxidation;

Volatile organic compounds

Membranes; Chemical treatment; Carbon adsorption; Ion exchange

Colloidal and dissolved solids

Chlorine compounds; Chlorine dioxide; Ozone; Ultraviolet (UV) radiation.

Pathogens

Chemical oxidation; Suspended-growth nitrification and denitrification; Fixed-film nitrification and denitrification; Air stripping. Chemical treatment; Biological phosphorous removal; Biological nutrient removal

NutrientsNitrogenPhosphorousNitrogen and Phosphorous

Aerobic and anaerobic suspended growth variations; Aerobic and anaerobic attached growth variations; Lagoon variations; Advanced oxidation; Membrane filtration; Chemical oxidation.

Biodegradable Organics

Screening; Grit removal; Sedimentation; Clarification; Flotation; Chemical Precipitation; Surface Filtration.

Suspended Solids

Unit Operation or ProcessConstituent

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Typical Contaminants of Untreated Domestic Wastewater

Total Solids [TS]Dissolved [TDS] + Suspended [SS] + Settleable

Biochemical Oxygen Demand [BOD5]Total Organic Carbon [TOC]Chemical Oxygen Demand [COD] - Quantity of oxygen needed to oxidize the components of the sludge – primarily oxidized to CO2 and H2ONitrogen (total as N)

Organic + Ammonia + Nitrites + NitratesTotal Kjeldahl Nitrogen [TKN] = Organic + Ammonia

Phosphorous (total as P)Organic + Inorganic

ChloridesSulfateAlkalinityGreaseVolatile Organic Compounds [VOCs]

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Biological Process Systems

Anaerobic Process

Aerobic Process

Suspended Growth Systems

SBRsActivated Sludge

Low Speed AearatorsHigh Speed AeratorsDisc Aeration

OrbalVLRVertiCel

Brush Aeration (Mammoth Rotor)Diffusers

Coarse BubbleFine Bubble

JetAerationMBR

Fixed Film (Attached Growth) Systems

Trickling FilterRBCSuspended Media

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Physical Unit OperationsUsed for Wastewater Treatment

Primary clarifierHigh-rate clarifierGravity thickener

Removal of settleable solidsThickening of solids and biosolids

Sedimentation

Grit chamberVortex separator

Removal of gritRemoval of grit and coarse solids

Accelerated sedimentation

FlocculatorPromoting the aggregation of small particles into large particles to enhance their removal by gravity sedimentation

Flocculation

Rapid mixerBlending chemicals with wastewater and for homogenizing and maintaining solids in suspension

Mixing

Equalization tankTemporary storage of flow to equalize flow rates and mass loadings of BOD and suspended solids

Flow equalization

Screenings grinderMacerator

Grinding of solids removed by bar racks Side-stream grinding of coarse solids

Grinding/ maceration

ComminutorIn-stream grinding of coarse solids to reduce sizeComminutionMicroscreenRemoval of fine solids, floatable matter, and algaeScreening, micro

Fine screenRemoval of small particlesScreening, fine

Bar rackRemoval of coarse solids such as sticks, rags, and other debris in untreated wastewater by interception (surface straining)

Screening, coarseDeviceApplicationsOperations

2008Sakti Siregar

Physical Unit OperationsUsed for Wastewater Treatment

Packed towerRemoval of ammonia, hydrogen sulfide, and other gases from wastewater and digester supernatant

Air stripping

Microfilteration, ultrafiltration, nonofiltration, and reverse osmosis

Removal of suspended and colloidal solids and dissolved organic and inorganic matter

Membrane filtration

Discfilter®Cloth-Media Disk Filter ®

Removal of residual suspended solidsSurface filtration

Depth filtersRemoval of residual suspended solidsDepth filtration

Gas stripperDiffused-air and mechanical aeration

Removal of volatile and semivolatile organic compounds from wastewaters

VOC control

Diffused-air aerationMechanical aeratorCascade aerator

Addition of oxygen to biological process

Postaeration of treated effluent

Aeration

Dissolved-air floatation (DAF)

Introduced air flotation

Removal of finely divided suspended solids and particles with densities close to that of water; also thickens biosolidsRemoval of oil and grease

FlotationDeviceApplicationsOperations

2008Sakti Siregar

Anaerobic versus aerobic processes

Aerobic processesAdvantages :

wellknown, widely used, many types of installations for small up to high capacities.applicable for low concentrations of BOD or COD and low temperatures ( 5 - 30 C ).very shockresistant to loading fluctuations and toxic chemicals.can produces high quality effluent for direct discharge to surface waters.

Disadvantages :requires usually large areas for construction due to low load and large dimensions for aeration bassins and sedimentation tanks.relatively high energy consumption for air compressor or aeration equipment ( mixers, dissolver, surface aerators etc )large production of surplus solids ( primary sediments and secondary sludge ). Increasing problem to find acceptable solutions for the solids ( dumping, incineration, agricultural applications ). often 50% of total treatment costs are related to solids disposal.when shortage, then relatively high dosage of nutrients is required ( N, P, S, micro hutrients )often problems related to emissions ( stench, volatile solvents ) and hygienic risks ( disease germs ).not well suited for high concentrated effluents.

2008Sakti Siregar

Anaerobic versus aerobic processes

Anaerobic processesAdvantages :

applicable for concentrated effluents; BOD from 1000 mg/l and higher, and for medium to large volumes.produces valuable biogas ( 70 - 90 % CH4 )requires no energy for oxygenation, only low energy consumption for pumps ( possible for biogas compressor )compact construction ( high loading rate ), thus small areas required. Usually completely closed equipment preventing emission problems.produces only a fraction of excess secondary sludge. Sludge is well stabilized and often used in new installation ( starter culture ) or ready for agricultural application. Biomass granules have long term stability, ideally for use in campaign plants.when shortage, only low dosage of nutrients required ( N, P, S micronutrients )

Disadvantages :temperature of waste water should be 20 C to 35 C, may require preheating.rather sensible to toxic chemicals, may require special precautionseffluent is usually not suited for discharge to surface waters, requires aerobic posttretment and sedimentation to reach discharge limitsnot suitable, unless special precautions, for waste waters containing relatively high concnetrations of nitrate and/ or sulfate ions.

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ANAEROBIC PROCESS

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Theory

The anaerobic conversion of dissolved organic C compounds into CH4 and CO2 is a complex process, in which numerous micro organism play a role

Hydrolytic micro organisms break down large molecules ( polymers ) into smaller soluble molecules ( monomers ) through the action of enzymes.Hydrolysis usually proceeds rapidly. The COD concentration of the liquid does not change Acidifying microorganism convert the dissolved monomers into volatile fatty acids ( VFA ) and some H2 gas.Main products are :

Formic acid C1Acetic acid C2Propionic acid C3(iso) Butyric acid C4(iso) Valeric acid C5

Acetogenic micro organism, this group converts the higher fatty acid C3, C4 and C5 into acetic acid and H2 gas.Example for propionic acid :CH3 - CH2-COO- + 3 H2O CH3-COO- + H+ + 3H2 +76 kJThe H2 gas escape from the liquid phase, thus the COD concentration decreases; according to the following calculation.

Methanogenic micro organisms, this group converts the endproducts of the foregoing processes ( hydrogen, formic acid, methanol, methylamine and acetic acid ) into CH4 and CO2 )

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Anaerobic Process

M ultiphase nature of Anaerobic Digestion (W illkie & Coleran, 1988)

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Commonly Used Names for Methane­forming Bacteria Methanogenic bacteriaMethanogensMethane-forming bacteria Methane-producing bacteria

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SULFATE-REDUCING BACTERIA

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Respiration

Substrates Used by Methane-forming BacteriaAcetate CH3COOHCarbon dioxide CO2Carbon monoxide COFormate HCOOHHydrogen H2Methanol CH3OHMethylamine CH3NH2

CH3COOH CH4 + CO2CO2 + 4H2 CH4 + 2H2O

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Bacteria

ACETATE-FORMING BACTERIAAcetate-forming (acetogenic) bacteria grow in a symbiotic relationship with methane-forming bacteria. Acetate serves as a substrate for methane-forming bac­teria

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Trend in Anaerobic WWTP

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Typical PFD

DRAWN on WHITE BOARD

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Factor in Anaerobic Treatment

Physical factorsTemperature, 35 deg CHydraulic Retention TimeSolid Retention TimeOrganic LoadingMixing , 10 – 20 W/m3Solid ConcentrationSludge type

Chemical factorspH, 6.8 – 7.2Alkalinity , bicarbonate alkalinity 2500 – 5000 mg/l CaCO3Volatile Acids, 50 – 300 mg/lNutrients COD : N : P = 350 : 5 :1Trace ElementToxic Compounds

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Anaerobic lagoon

Descriptionthe anaerobic lagoon is the most simple type of anaerobic treatment. Wastewater is fed to a pond in which conversion to biogas takes place spontaneously. Modern lagoons are covered and the biogas is collected for further use.Lagoon depths vary from 2.5 to 6.0 m.Figure 2.1 Anaerobic LagoonOperation performanceHRT : 7 - 80 daysLoad : 0.15 - 0.3 kg COD/ m3.dCOD reduction usually < 80%AdvantagesSimple systemsCheapAlso degradation of SS.DisadvantagesLarge area requirementSmell for not covered lagoons

ApplicationAnaerobic lagoons are really primitive anaerobdigester. They were first used in the meat processing industry because the waste is peculiarly well adapted to this form of treatment. Meat processing wastes contain high concentrations of fats that form a scum on the pond surface. This scum often reaches a thickness of 2 cm or more and provides insulation and prevents the escape of large amount of reduced sulfide compounds. Insulation is important because methane fermentation, the critical step in anaerobic digestion or treatment, is extremely temperature sensitive.Two types of anaerobic ponds or lagoons are in use, those for sludge and those for soluble waste. Sludge lagoons have been used for over 70 years in municipal waste treatment systems and have been introduced as a manure disposal process for dairies, feedlots and chicken ranches. Most sludge lagoons are shallow ditches or ponds that are intermittently filled with sewage sludge or manure. No temperature control is provided. Nuisance odors are a common problem, and location of sludge lagoons can be expected to be well known to naone living nearby.

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ANAEROBIC LAGOON

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ANAEROBIC LAGOON

Process Flow Diagram

PretreatmentOil/ Water SeparatorCooling Water Pond

Anaerobic LagoonAcidification PondMethane Generation Pond

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ANAEROBIC LAGOON

Process EquipmentIncoming Flow MeterOil/ Water Separator

Oil SkimmerOil Launder/ Baffle

Cooling Water PondOil SkimmerOil Launder/ Baffle

Anaerobic LagoonFeed pumpMixer ( Submersible mixer, ejector, pump + perforated pipe )Dewatering pumpMembraneDesludging PipeSampling portPressure indicatorDegasser pipe

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ANAEROBIC LAGOON

FLARE

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Process : Alkalinity

When volatile acids accumulate, the following chemical reaction occurs :

HCO3- + HVA VA- H2O + CO2

Bicarbonate alkalinity is consumed, carbon dioxide production increase, and eventually the pH falls.

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Process : Failure

IndicatorsVolatile acids concentration increasesBicarbonate alkalinity dropspH fallsGas production rate dropsPercentage of CO2 in gas increase

Typical causes of process failure

Hydraulic overloadDilute feed Excessive sludge productionFrit and scum accumulationAlkalinity washout

Organic overloadIncrease in ww productionIncrease in ww concentrationChange in ww characteristicToo rapid startupInfrequent feeding

Toxic overloadHeavy metalsDetergentChlorinated organicsOxygenCationSulfides

SolutionsAdjust alkalinity using a supplementAdjust feed schedullePretreatmentClean Lagoon

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Thank You

Sakti SiregarWastewater Treatment Engineersakti-siregar@bdg.centrin.net.id