Download - Anaerobic Process For Cdm Project
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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
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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
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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.
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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