Advances in Nitrogen and Phosphorus Removal at Low DO Conditions Pusker Regmi Vail Operator Training Seminar 13 October, 2016
Wastewater Treatment and Energy The water quality industry is currently facing dramatic changes It is shifting away from energy intensive wastewater treatment towards low-energy, sustainable technologies The future needs to focus on how one could extract energy captured from the wastewater rather than just treating it. 2
Energy Content of Wastewater The potential energy available in the wastewater exceeds the electricity requirements of the treatment process significantly. Energy required for secondary wastewater treatment 1,200 to 2,400 MJ/1000 m3 Energy available in wastewater for treatment, using previous data 5,850 MJ/1000 m3 (@ COD = 500 mg/l) Energy available in wastewater is 2 to 4 times the amount required for treatment 3
Energy Balance of WRRF ET - thermal energy ES - syntheses energy EE - electricity Wett et al. (2007) 4
Energy Balance of WRRF The conundrum of aerobic treatment is that electrical energy is needed to destroy chemical energy Energy Input 110,000 MJ/d Energy Lost 226,000 MJ/d Q = 20 MGD COD = 500 mg/l TSS = 240 mg/l Energy = 610,000 MJ/d Primary Clarification Secondary Clarification COD = 30 mg/l TSS = 10 mg/l Energy = 47,000 MJ/d Q = 0.15 MGD TSS = 1.5% Energy = 215,000 MJ/d Q = 0.6 MGD TSS = 0.5% Energy = 122,000 MJ/d Total Energy Needed ~ 250,000 MJ/d Energy Generated thru CHP ~ 70,000 to 100,000 MJ/d 5
Energy Usage in WRRF Energy Usage in WRRF Based on the WERF Report ENER1C12 Major Electricity Using Processes Units Typical Best Energy Practice Influent and Effluent Pumping kwh/mg 420 296 Screening and Grit Removal kwh/mg 61 10 Odor Control kwh/mg 300 300 Nitrifying Activated Sludge kwh/mg 944 519 BNR Biological Reactor kwh/mg 1454 690 Final Clarifiers and RAS Pumping kwh/mg 106 77 Anaerobic Digestion kwh/mg 122 11 Tertiary Filtration kwh/mg 102 89 Other kwh/mg 273 87 6
Energy Usage in Activated Sludge Plants Carbonaceous Removal Nitrification Enhanced Nitrogen Removal 7
Low Energy technology: Simultaneous nitrification denitrification
Conventional Biological Nutrient Removal N and P removal generally are carried out with physically separated anaerobic, anoxic and aerobic zones N removal relies primarily on autotrophic nitrification and heterotrophic denitrification
Simultaneous Nitrification-Denitrification Biological process where nitrification and denitrification occur concurrently in the same aerobic reactor (or in the same floc) SND relies on achieving a dynamic balance between nitrification and denitrification SND depends on: Micro environment that affects oxygen diffusivity inside the flocs [floc size] Macro environment that is related to mixing [bioreactor configuration] Bulk DO concentration Carbon availability Presence of novel microorganisms Anoxic Zone Aerobic Zone Diffusion Layer Carbon NH3-N DO NO3-N 10
Simultaneous Nitrification-Denitrification COD, 11
Simultaneous Nitrification-Denitrification Potential Advantages Elimination of separate tanks and internal recycle systems for denitrification Simpler process design Reduction of carbon, oxygen, energy and alkalinity consumption Potential Disadvantages Limited controlled aspects of the process such as: floc sizes internal storage of COD DO profile within the flocs Sludge bulking; primarily because of the excessive growth of filamentous bacteria 12
Factors affecting SND for N removal
Effluent NO3-N (mg/l) Effect of Influent Carbon on SND To accomplish denitrification in any process, the availability of readily biodegradable organic carbon is essential 16 14 12 10 8 6 4 2 0 0 2 4 6 8 10 12 Influent BOD:TKN Ratio (mg BOD5/mg TKN as N) Jimenez et al. (2010) Jimenez et al. (2011) 14
Effect of DO on SND Control of bulk DO concentration in the system is essential for achieving a high degree of SND Jimenez et al. (2010) 15
Nitrification fundamentals DO constraints nitrification kinetics 16
Effect of DO on SND Constant Aeration Bulk DO Controlled to 0.5 mg/l 17
Effect of DO on SND Cyclical Aeration 18
Low DO Bulking in Plants Performing SND Low DO required for SND is considered more susceptible to sludge bulking This has been considered one of the main disadvantages for SND processes Many facilities being operated in SND mode produce mixed liquor with marginal settling characteristics BNR facilities with AN or AX selectors often produce SVI values (90 percentile) of less than 120 and 150 ml/g (Parker et al., 2004) Plant Process SVI (ml/g) Iron Bridge Bardenpho 115/165 Eastern Reg. Bardenpho 120/160 Snapfinger Single-Stage 200/300 Central Single-Stage 140/180 Winter Haven Bardenpho 130/190 Mandarin MLE 150/180 Marlay Taylor Single-Stage 170/280 Stuart Single-Stage 212/350 Smith Creek A 2 O 200/245 19
SVI (ml/g) Low DO Bulking in Plants Performing SND Bulking in SND plants has driven some plants to convert to more conventional BNR processes 450 400 350 300 250 200 150 100 50 SND Process - Extended Aeration with Mechanical Aerators Construction Period A/O Process - Anaerobic Selector and New Fine-bubble aeration 0 1/1/2004 1/1/2005 1/1/2006 1/1/2007 1/1/2008 1/1/2009 Date 20
Evaluation of SND Plants Performance at Selected Treatment Facilities Plant Location Capacity (m 3 /hr) Process SRT (days) Effluent TN (mg/l) N Removal (%) SVI (ml/g) Iron Bridge Orlando, FL 6,420 Bardenpho 15 2.0 96 115/165 Eastern Reg. Orange Co., FL 4,010 Bardenpho 12 2.6 89 120/160 Snapfinger DeKalb Co., GA 2,410 Single-Stage 20 3.8 80 200/300 Central Ft. Myers, FL 1,765 Single-Stage NA 5.5 84 140/180 Winter Haven Winter Haven, FL 1,205 Bardenpho 25 2.4 93 130/190 Mandarin Jacksonville, FL 1,205 MLE 18 4.0 90 150/180 Marlay Taylor St. Mary s Co., MD 965 Single-Stage 25 4.5 86 170/280 Northwest Reg. Hillsborough Co., FL 805 Bardenpho 12 2.7 93 NA Tarpon Springs Tarpon Springs, FL 645 Bardenpho NA 2.2 92 NA Stuart Stuart, FL 645 Single-Stage 18 5.5 86 212/350 Smith Creek Raleigh, NC 545 A 2 O 25 4.5 90 200/245 21
Evaluation of SND Plants Performance at Selected Treatment Facilities Facilities with BNR configurations exhibited TN removal efficiencies of 89 to 96 percent Facilities using a single-reactor configurations (without explicitly defined anoxic zones) realized TN removal efficiencies in the order of 80 to 86 percent 22
Concentration (mg/l) Iron Bridge WWTP, City of Orlando FL Anaerobic Anoxic Oxidation Ditch operated in SND Post Anoxic Post Aerobic Influent and RAS To FST 18 16 14 12 10 8 6 4 2 0 15.5 7.1 Mixed Liquor Recycle 0.95 1 0 0 0.3 0.2 0.5 0 0 0 0.35 0.140.4 Anaerobic Anoxic Oxidation Ditch DO NH3-N NO3-N Post-Anoxic Post-Aerobic 23
N Species (mg N/L) Iron Bridge WWTP, City of Orlando FL N Removal 10.00 1.00 TKN NOx-N TN 0.10 Nov-04 May-05 Dec-05 Jul-06 Jan-07 Aug-07 Feb-08 WERF, 2011 24
Conclusions The application of SND processes may be based and limited by: Influent C:N ratio Optimum bulk DO from 0.3 mg/l to 0.7 mg/l Sludge bulking issues due to the excessive growth of filamentous bacteria The operator has limited control over important parameters impacting SND 25
Introduction Water phase Enhanced Biological Phosphorus Removal (EBPR) Acetate and propionate NO 2-, or NO 3 -
Effect of Carbon Source on EBPR Performance EBPR is favorable with an COD:P ratio > 15 PAOs tend to dominate at COD:P ratios of 10-20 whereas GAOs tend to dominate at COD:P ratios >50 mg-cod/mg-p. COD must have a sufficient VFAs, or COD that ferments into VFAs (5 mgvfa/l per 1 mg/l of P to be removed) Seasonal variations in COD ratios and VFA content must be closely investigated preceding EBPR design.
Traditional Flow Diagrams for N and P Removal Barnard (2011)
Estimate of VFA and rbcod Requirements for EBPR
SRT, days Effect of MCRT & Temperature on EBPR 12 10 8 6 4 BPR only, No Nitrification Nitrification in Conventional AS 2 0 No BPR, No Nitrification 10 12 14 16 18 20 22 24 26 28 30 Temperature, º C Note: Incipient Washout Conditions with No Design Safety Factor on SRT
Effluent TP, mg/l MCES Metro WWTP, St. Paul MN Daily 3.0 2.5 2.0 1.5 1.0 0.5 0.0 Daily 30-DMA Annual Moving
Issues with Simultaneous EBPR and N Removal EBPR becomes less stable when applied in conjunction with N removal processes due: competition with GAOs introduction of nitrate/nitrite to anaerobic zone competition for carbon N removal via denitrification becomes carbon limited due to EBPR Supplemental carbon is added for denitrification and/or EBPR
Integration of EBPR and N Removal Anaerobic-Oxic Process Anaerobic-Anoxic-Oxic Process
Challenges Combined Nitrogen Removal and Phosphorus removal Competition for carbon between heterotrophs and polyphosphate accumulating organisms (PAOs) Introduction of nitrate/nitrite to anaerobic zone, thereby disrupting anaerobic carbon uptake Competition with glycogen accumulating organisms (GAOs) Carbon limited conditions makes it even more difficult!! Brown and Caldwell 34
Is low carbon combined shortcut nitrogen removal and BioP possible? 35
Brown and Caldwell 36
City of St. Petersburg Southwest WRF No Primaries Anaerobic digestion 37
City of St. Petersburg Southwest WRF A/O Process Rated Capacity = 20 MGD Total SRT = 5 days Aerobic SRT = 3.5 days HRT = 6 hrs COD:TKN = 6.0 8.0 Minimum Temp. = 22 degree C Maximum Temp. = 30 degree C Effluent nutrient limits (Florida Water Reuse requirements) Total N = 10 mg/l Total P = 1.0 mg/l 38
City of St. Petersburg Southwest WRF Screening Grit Removal Biological Reactors Secondary Clarification Tertiary Filtration GBT Sidestream Return Anaerobic Digestion BFP 39
DO and SRT Control Strategy 40
DO and SRT Control Strategy Control Parameter Condition Action Reduce SRT to limit NH + 4 removal and NH + 4 lower than 1.0 mg N/L keep the average DO to a minimum value of 0.1 mg/l. NH + Increase SRT to improve NH + 4 Control 4 removal and keep DO to a minimum value of 0.1 NH + 4 higher than 3.0 mg N/L mg/l. If SRT approaches 5 days, increase the DO to a maximum value of 0.3 mg/l until NH + 4 is reduced Decrease the DO to a minimum value of NO - NO - 3 Control 3 higher than 1.0 mg N/L 0.1 mg/l and monitor NO - 2 accumulation (profile) in the aeration basin NO - 3 lower than 1.0 mgn/l No action required NO - 2 Control Monitor effluent NO - 2 as surrogate measurement of shunt performance 41
Summary of Influent Characteristics Parameters (mg/l) Value (Standard Deviation) COD 300 (±65) Soluble COD 120 (±20) Readily Biodegradable COD 65 (±15) Unbiodegradable COD 20 (±8.5) VFAs 13 (±5) TSS 140 (±35) TKN 42 (±5.6) NH 3 -N 30 (±4.5) TP 3.9 (±0.75) PO 4 -P 2.4 (±0.30) Alkalinity (mg/l CaCO 3 ) 210 (±20) ph (SU) 7.1 (±0.22) 42
Inorganic Nitrogen Profile Unaerated DO = 0.02 ± 0.01 mg/l Aerobic 1 DO = 0.22 ± 0.15 mg/l Aerobic 2 DO = 0.12 ± 0.08 mg/l Aerobic 3 DO = 0.08 ± 0.05 mg/l 0.8
Final Effluent Inorganic Nitrogen
Reason for excellent N removal? Autotrophic Bacteria Aerobic Environment Nitritation 75% O 2 (energy) ~100% Alkalinity 25% O 2 (energy) 1 mole Nitrite (NO 2- ) Ammonia Oxidizing Bacteria (AOB) 1 mole Nitrate (NO 3- ) Nitrite Oxidizing. Bacteria (NOB) 1 mole Nitrite (NO 2- ) Heterotrophic Bacteria Anoxic Environment 40% Carbon (COD) 60% Carbon (COD) Denitritation 1 mole Ammonia (NH 3 / NH + 4 ) ½ mol Nitrogen Gas (N 2 ) Advantages: 25% reduction in oxygen demand (energy) 40% reduction in carbon (e - donor) demand 40% reduction in biomass production 45
Maximum Nitrification Rate Tests SNR # DO Batch Test SNH 3 RR SNO X PR SNO 3 PR SNO 3 PR/ (mg/l) MLVSS (mg/l) (mgn/gvss/h) (mgn/gvss/h) (mgn/gvss/h) SNO X PR 1 5 2443 0.96 0.94 0.25 0.27 2 5 2280 0.98 1.04 0.30 0.29 3 0.30 2217 0.91 0.51 0.21-4 0.10 2300 0 0 0-46
Mechanism of NOB out-selection Residual effluent ammonia >1 mg/l (Maximize AOB activity) Heterotrophs out-competing NOB for NO 2 -N at low DO conditions Maintaining aggressive SRT based on AOB activity Brown and Caldwell 47
What about Bio-P? 48
Soluble PO4-P Profile Unaerated DO = 0.02 ± 0.01 mg/l Aerobic 1 DO = 0.22 ± 0.15 mg/l Aerobic 2 DO = 0.12 ± 0.08 mg/l Aerobic 3 DO = 0.08 ± 0.05 mg/l 49
Stable High Temperature Bio-P
P Removal with NO 2 Under Low DO/ Anoxic Conditions Denitrifying PAOs???
What about settling??
Final Thoughts N removal is via nitrite-shunt - The low DO and short SRT operation resulted in significant NOB out-selection Effective SND was achieved in a simple AO process High temperature and low DO operation didn't adversely affect biological phosphate uptake (Large anaerobic volume and low NOx-N recycle could be helpful) Excellent settling at low DO operation Simple manual control strategy for DO and SRT was effective Low DO ammonia oxidation was key to this process 53
Future Work Molecular work Who is doing what? Modeling Simultaneous N and P removal at low DO And the ultimate goal would be to replicate this process elsewhere with better process understanding WERF Project: Understanding the Impacts of Low- Energy and Low-Carbon Nitrogen Removal Technologies on Bio-P and Nutrient Recovery Processes (Started this week) Carbon efficient WRRF Granules/flocs system Advanced aeration control for SND Low DO shortcut nitrogen removal Goal Improved bio-p with DPAOs Benefits Process intensification Increased C and P recovery potential Reduced energy and chemical input Brown and Caldwell 54
Presenter contact information Pusker Regmi Ph.D. Email: pregmi@brwncald.com 55