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 = C 60 H 86 O 23 N 12 P 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 = C 60 H 86 O 23 N 12 P 0.13 lb N/lb of bug mass Biological conversion by nitrification and denitrification
Nitrification NH 4 + Nitrosomonas NO 2 - NO 2 - Nitrobacter NO 3 - Notes: Aerobic process Control by SRT (4 + days) Uses oxygen 1 mg of NH 4 + uses 4.6 mg O 2 Depletes alkalinity 1 mg NH 4 + consumes 7.14 mg alkalinity Low oxygen and temperature = difficult to operate
Denitrification NO 3 - denitrifiers (facultative bacteria) N 2 gas + CO 2 gas Notes: Anoxic process Control by volume and oxic MLSS recycle to anoxic zone N used as O 2 source = 1 mg NO 3 - yields 2.85 mg O 2 equivalent Adds alkalinity 1 mg NO 3 - restores 3.57 mg alkalinity High BOD and NO 3 - load and low temperature = difficult to operate
Advanced Treatment Systems 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)?
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…
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…
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 = C 60 H 86 O 23 N 12 P) Protects stream sediment oxygen demand Improves efficiency of disinfection
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)
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 Carbon Regeneration 5 to 10% loss Less capacity than new carbon Hot 350 o F Chemicals (sodium hydroxide) Fire / Explosion Carbon usually replaced after 5 regenerations Mechanism: Active sites Activated Carbon Molecular bonding Particles adhere to surface Continued …
Chemical Coagulation Purpose 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 SS removal P removal P removal Polymer + - SS controlIron + SS removal P removal Mechanism: Destabilization by ionic charge neutralization Reduce charge that keeps small particles apart Continued … Aluminum sulfate Ferric chloride Ferric sulfate Ferrous sulfate _ _ _ _ _ _ _ _ _ _ _ _ _ _ __ _ _ _ _ _ _ _ _ _ _ ___
Flocculation Purpose Produce larger, more dense floc particles that will settle or filter easily Application Gentle mixing after rapid mix (coagulation) Mixing – Mechanical or Aeration Rapid Mix / Coagulation Infl Q Q Sludge Gentle Mix / Flocculation
Mechanism Coagulated particles strung together into larger floc particles (snow flake floc) Continued …
Phosphorus Removal Purpose 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 … Final Clarifier RAS WAS Effl Q P Release Anaerobic Zone Aerobic Zone P Luxury Uptake P Removal
Phosphorus Removal Chemical Continued … Final Clarifier RAS WAS Effl Q Aerobic Zone Chemical Coagulant P Removal Primary Clarifier Chemical Coagulant
Nitrogen Removal Purpose Reduce effluent N (ammonia and nitrates) Biological or chemical Reduce nutrient load on stream Reduce algae growth Reduce oxygen depletion Application / Mechanism 1. Advanced Activated Sludge Processes Nitrification (remove ammonia) NH 4 NO 2 NO 3
Nitrogen Removal Denitrification (remove nitrate) NO 3 NO 2 NO, N 2 O or N 2 gas 2. Deep Bed Filtration Anaerobic fixed film bacteria (denitrify) 3. Air Stripping Removes ammonia Elevated pH 10.8 to 11.5 NH 4 as gas Continued … Q Methanol (carbon) Media Q 6-8
Effluent Filtration Purpose Remove SS (usually after FC) Reduce BOD and insoluble P Application 1. Deep Bed 4-6 sand and gravel Large cells 10 x 30 Similar to WTP (batch backwash) hL = ft $$$ 2.Traveling Bridge 1-2 sand and anthracite Small cells 1 x 14 Contiuous backwash hL = ft
Effluent Filtration 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 Continued …
Polishing Lagoons Purpose 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 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. Continued … Aerobic Anaerobic Settling Algae Sunlight M Surface Aerator methane gas
Nitrification Purpose 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 NH 4 NO 2 NO 3 Mechanism Biological conversion of ammonia to nitrate
Denitrification Purpose Reduce nitrate on plant effluent Usually in combination with nitrification to reduce Total N to the stream Application 1. Activated Sludge Process 2. Deep Bed Filters Mechanism Biological conversion of nitrate to N 2 gas AnxOxic FC Oxic Recycle RAS WAS Q
Ammonia Stripping Purpose 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 25 0 C and pH 11 NH 4 gas = 98%
Ammonia Stripping 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 Floc Lime Sludge Air Precip. Q Continued … Lime NH 4 Stripper Q NH 4 Air
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 + + PO 4 Aluminum or Iron Phosphate Rapid Mix RAS Q Al + or Fe + Q Filtration Optional WAS + Precipitate Precipitate
Lime Precipitation Purpose 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 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 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 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 OH - Cl - _ + H20H20 H+H+ 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
What would be the effect on sludge production for each of the advanced treatment processes? TANSTAAFL (tanstaffull) There aint 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