2004 Biological Wastewater Treatment Operators School Advanced Treatment Systems May 13, 2004 Dean Pond, Black & Veatch

Advanced Treatment Systems What are the forms of nitrogen found in wastewater?

What are the forms of nitrogen found in wastewater? TKN = 40% Organic + 60% Free Ammonia Typical concentrations: Ammonia-N = 10-50 mg/L Organic N = 10 – 35 mg/L No nitrites or nitrates Forms of nitrogen: Organic N Ammonia Nitrite Nitrate TKN Total N

Advanced Treatment Systems Why is it necessary to treat the forms of nitrogen?

Why is it necessary to treat the forms of nitrogen? Improve receiving stream quality Increase chlorination efficiency Minimize pH changes in plant Increase suitability for reuse Prevent NH4 toxicity Protect groundwater from nitrate contamination

Advanced Treatment Systems What are the effects of N and P in receiving waters?

What are the effects of N and P in receiving waters? Increases aquatic growth (algae) Increases DO depletion Causes NH4 toxicity Causes pH changes

Advanced Treatment Systems Why is it sometimes necessary to remove P from municipal wastewater treatment plants?

Why is it sometimes necessary to remove P from municipal WWTPs? Reduce phosphorus, which is a key limiting nutrient in the environment Improve receiving water quality by: Reducing aquatic plant growth and DO depletion Preventing aquatic organism kill Reduce taste and odor problems in downstream drinking water supplies

Advanced Treatment Systems How is P removed by conventional secondary (biological) wastewater treatment plants?

How is P removed by conventional secondary (biological) WWTPs? Biological assimilation BUG = C60H86O23N12P 0.03 lb P/lb of bug mass GROW BUGS, WASTE BUGS = REMOVE P

Advanced Treatment Systems Where in the treatment plant process flow could chemical precipitants be added?

Where in the treatment plant flow could chemical precipitants be added? At pretreatment Before primary clarifiers After aeration basins At final clarifiers Ahead of effluent filters Considerations: Effective mixing Flexibility Sludge production

Advanced Treatment Systems How is N removed or altered by conventional secondary (biological) treatment?

How is N removed or altered by secondary (biological) treatment? Biological assimilation BUG = C60H86O23N12P 0.13 lb N/lb of bug mass Biological conversion by nitrification and denitrification

Nitrification NH4+  Nitrosomonas  NO2- NO2-  Nitrobacter  NO3- Notes: Aerobic process Control by SRT (4 + days) Uses oxygen  1 mg of NH4+ uses 4.6 mg O2 Depletes alkalinity  1 mg NH4+ consumes 7.14 mg alkalinity Low oxygen and temperature = difficult to operate

Denitrification NO3-  denitrifiers (facultative bacteria)  N2 gas + CO2 gas Notes: Anoxic process Control by volume and oxic MLSS recycle to anoxic zone N used as O2 source = 1 mg NO3- yields 2.85 mg O2 equivalent Adds alkalinity  1 mg NO3- restores 3.57 mg alkalinity High BOD and NO3- load and low temperature = difficult to operate

Advanced Treatment Systems What are typical flow application rates in tertiary filters?

What are typical flow application rates in tertiary filters? Automatic backwash filters (1-2 ft media depth) = 2 to 4 gpm/sf Deep bed filters (4-6 ft media depth) = 4 to 8 gpm/sf

Advanced Treatment Systems What are typical backwash rates for a tertiary filter (in gpm/sf)?

What are typical backwash rates for a tertiary filter (in gpm/sf)? Automatic backwash filters 20 to 25 gpm/sf 5 to 10% of throughput Deep bed filters 15 to 20 gpm/sf 3 to 5% of throughput

Advanced Treatment Systems Define advanced treatment…

Define advanced treatment … Treatment that improves or enhances secondary treatment processes Further removal of organics, nutrients and dissolved solids

Advanced Treatment Systems Explain circumstances under which advanced treatment may be necessary…

Explain circumstances under which advanced treatment may be necessary… Limited assimilative capacity of stream Toxicity reduction / elimination Nutrient control Closed systems Water reuse

Advanced Treatment Systems Identify and explain the objectives of the following advanced treatment systems: Further removal of organics Further removal of suspended solids Nutrient removal (N and P) Removal of dissolved solids

Identify and explain the objectives of the following advanced treatment systems: Further removal of organics Reduce effluent BOD to reduce receiving stream DO depletion Improve disinfection Reduce effluent N to improve water quality Further removal of suspended solids Removing TSS removes BOD Removing TSS removes N and P (BUG = C60H86O23N12P) Protects stream  sediment oxygen demand Improves efficiency of disinfection

Removal of nutrients (N and P) Identify and explain the objectives of the following advanced treatment systems: Removal of nutrients (N and P) Reduce oxygen demand of receiving stream Control nutrients and algae Control taste and odor in downstream drinking water Suitability for reuse (examples: boiler water recycle, irrigation – N&P control of runoff, groundwater recharge)

Removal of dissolved solids Identify and explain the objectives of the following advanced treatment systems: Removal of dissolved solids Removal of specific pollutant – zinc, chromium, lead Pretreatment of industrial waste Control effluent toxicity Make suitable for reuse

Advanced wastewater treatment… Describe the purpose or procedure and mechanism by which it is done for each of the following: Activated carbon adsorption Chemical coagulation Flocculation Phosphorus removal Nitrogen removal Effluent Filtration Polishing lagoons Nitrification Denitrification Ammonia striping Alum or ion precipitation Lime precipitation Reverse osmosis (RO) Electrodialysis

Activated Carbon Adsorption Purpose Tertiary treatment Removal of low concentration organic compounds Application: Influent Primary Trt Biological Trt  Filtration Carbon Disinfection Many variations

Activated Carbon Adsorption Continued … Carbon Regeneration 5 to 10% loss Less capacity than new carbon Hot air @ 350oF Chemicals (sodium hydroxide) Fire / Explosion Carbon usually replaced after 5 regenerations Mechanism: Active sites “Activated Carbon” Molecular bonding Particles adhere to surface

Chemical Coagulation Purpose Application Chemical feed with rapid mix Enhanced removal of organics and fine particles Addition of lime, alum, iron, polymer to change ionic charge Application Chemical feed with rapid mix Ahead of final clarifiers Ahead of filtration

Chemical Coagulation Lime+ Heavy metals Alum+ SS removal Continued … Lime+ Heavy metals Alum+ SS removal SS removal P removal P removal Polymer + - SS control Iron+ SS removal Mechanism: Destabilization by ionic charge neutralization Reduce charge that keeps small particles apart Aluminum sulfate Ferric chloride Ferric sulfate Ferrous sulfate _ _ _ _ + + _ + + _ _ _ + + _ + + + + _ _ + _ _ + + + _ + + _ + + + + + + _ _ + _ _ + _ _ + + + + _ _ + _ _ _ _ _ + _ + + + + + +

Flocculation Purpose Application Produce larger, more dense floc particles that will settle or filter easily Application Gentle mixing after rapid mix (coagulation) Mixing – Mechanical or Aeration Q Infl Q Gentle Mix / Flocculation Rapid Mix / Coagulation Sludge

Flocculation Mechanism Continued … Mechanism Coagulated particles strung together into larger floc particles (snow flake floc) +

Phosphorus Removal Purpose Application / Mechanism Reduce effluent P Biological or chemical method Reduce nutrient load on stream Reduce algae growth Reduce oxygen depletion Application / Mechanism Biological Chemical

Phosphorus Removal Biological Continued … RAS WAS P Release Final Clarifier RAS WAS Effl Q P Release Anaerobic Zone Aerobic P Luxury Uptake P Removal

Phosphorus Removal Chemical Continued … Chemical Coagulant Chemical Primary Clarifier Aerobic Zone Effl Final Clarifier Q Chemical Coagulant Chemical Coagulant RAS WAS P Removal

Nitrogen Removal Purpose Application / Mechanism Reduce effluent N (ammonia and nitrates) Biological or chemical Reduce nutrient load on stream Reduce algae growth Reduce oxygen depletion Application / Mechanism Advanced Activated Sludge Processes Nitrification (remove ammonia) NH4  NO2  NO3

Nitrogen Removal Deep Bed Filtration Air Stripping Continued … Denitrification (remove nitrate) NO3  NO2  NO, N2O or N2 gas Deep Bed Filtration Anaerobic fixed film bacteria (denitrify) Air Stripping Removes ammonia Elevated pH 10.8 to 11.5 NH4 as gas Q Media 6-8’ Methanol (carbon) Q

Effluent Filtration Purpose Application Remove SS (usually after FC) Reduce BOD and insoluble P Application Deep Bed 4-6’ sand and gravel Large cells 10’ x 30’ Similar to WTP (batch backwash) hL = 4 - 6 ft $$$ 2. Traveling Bridge 1-2’ sand and anthracite Small cells 1’ x 14’ Contiuous backwash hL = 2 - 3 ft

Effluent Filtration Loading Rate Mechanism Backwash Continued … Loading Rate Backwash 2 – 4 gpm/sf Frequency depends on loading 20 – 25 gpm/sf 5 – 15% of throughput Must clean beds Air scour Mechanism Filtration by granular media

Polishing Lagoons Purpose Application To further treat or polish the effluent After final clarifier Facultative pond (aerobic and anaerobic) Application Typical volume = 1 day average flow i.e., 1 mgd plant = 1 mgd lagoon 24 hour detention time Surface aerators

Polishing Lagoons Mechanism Continued … Sunlight Surface Aerator Algae M Settling Aerobic Anaerobic Sunlight  Photosynthesis  Algae + Organics & Nutrients Organic Matter  Anaerobic Decomposition Mechanism Algae and bacteria grow in pond consuming organics and nutrients in FC effluent. Algae settles and degrades by anaerobic process. methane gas

Nitrification Purpose Application Mechanism Reduce ammonia on plant effluent High ammonia concentrations are toxic to streams Quickest impact on DO versus nitrates Application SRT > 3 days in activated sludge process Grow Nitrosomonas and Nitrobacter NH4  NO2 NO3 Mechanism Biological conversion of ammonia to nitrate

Denitrification Purpose Application Mechanism Reduce nitrate on plant effluent Usually in combination with nitrification to reduce Total N to the stream Application Activated Sludge Process Deep Bed Filters Mechanism Biological conversion of nitrate to N2 gas Q Anx Oxic FC Oxic Recycle RAS WAS

Ammonia Stripping Purpose Application / Mechanism Reduce ammonia either before or after biological treatment Not commonly used in the US Application / Mechanism Raise pH  10.8 to 11.5, usually by adding lime Move equilibrium point to ammonia gas @ 250C and pH 11 NH4 gas = 98%

Ammonia Stripping Continued … Break wastewater into droplets and strip off ammonia gas with air Freefall through tower that circulates a lot of air to remove ammonia to atmosphere NH4 Air Lime Q NH4 Stripper Floc Precip. Lime Sludge Air Q

Alum or Iron Precipitation Purpose To remove orthophosphate Application As a backup to Bio-P process As chemical P removal As chemical process Mechanism Al+ or Fe+ + PO4  Aluminum or Iron Phosphate Al+ or Fe+ Q Filtration Optional Q Precipitate Rapid Mix RAS WAS + Precipitate

Lime Precipitation Purpose Application Mechanism P removal before primary clarifier or following biological treatment Application As a backup to Bio-P process As chemical P removal As chemical process High pH can be a problem in effluent or in biological treatment Mechanism Chemical conversion of phosphorus to calcium phosphate is in pH range of 9.5 to 11.0

Reverse Osmosis (RO) Purpose Application Mechanism High quality removal of various salts – calcium, sodium, magnesium Application Water reuse AWT Mechanism Chemical separation / filtration across a semi-permeable membrane High pressure Tertiary process Used in Gulf War to treat sea water sodium removal

Electrodialysis Purpose Application Mechanism Removal of ionic inorganic compounds Application AWT Medical WTP Clinical Mechanism Apply electrical current between two electrodes Water passes through semi-permeable membranes (ion-selective) Alternate spacing of cation and anion permeable membranes Cells of concentrated and diluted salts are formed

Electrodialysis Purpose Application Mechanism Removal of ionic inorganic compounds Application AWT Medical WTP Clinical Mechanism Apply electrical current between two electrodes Water passes through semi-permeable membranes (ion-selective) Alternate spacing of cation and anion permeable membranes Cells of concentrated and diluted salts are formed Sludge – concentrated salt waste stream as process reject water Problems – plugging, fowling of membranes, MUST pretreat activated carbon, multi-media filtration _ + H20 Cl- H+ _ + OH- Na+ Bipolar Membranes

Advanced wastewater treatment… What would be the effect on sludge production for each of the following advanced treatment processes? Activated carbon adsorption Chemical coagulation Flocculation Phosphorus removal Nitrogen removal Effluent Filtration Polishing lagoons Nitrification Denitrification Ammonia striping Alum or ion precipitation Lime precipitation Reverse osmosis (RO) Electrodialysis

TANSTAAFL (tanstaffull) What would be the effect on sludge production for each of the advanced treatment processes? TANSTAAFL (tanstaffull) “There ain’t no such thing as a free lunch.” REMOVE MORE STUFF = GET MORE SLUDGE More BOD & TSS Removal  MORE SLUDGE Add chemicals  MORE SLUDGE N & P Removal  MORE SLUDGE Some processes produce more sludge than others: Electro/mechanical – some sludge Biological – more sludge Chemical – MOST sludge