Metropolitan Water Reclamation District of Greater Chicago Brett Garelli Deputy Director of M&O September 12, 2013
Outline Enhanced Biological Phosphorus Removal Principles Implementation at SWRP Optimization Approach EBPR Results Limitations/Challenges Faced DO Nitrate/Carbon Recycle Streams Conclusions
EBPR 1 2 3 4 1. RAS w/ PAOs returned and mixed w/ primary effluent (mixed liquor) 2. PAOs break polyp bonds for energy, uptake VFAs and store as PHB. By breaking poly P, release ortho P which is carried across cell membrane by Mg and K 3. PAOs use DO to break PHB for energy for growth and maintenance. They store the excess energy created by uptaking PO4 from outside the cell walls in the wastewater forming polyp (luxury uptake) 4. PAOs settle out w/ other biomass in secondaries and removed from system net removal during treatment
Optimal Conditions for EBPR Parameter EBPR design range/target COD:TP anaerobic zone >40 50 BOD:TP anaerobic zone >20 VFA:TP anaerobic zone 7-10 NO 3 -N anaerobic zone (mg/l) 0 DO anaerobic zone (mg/l) 0 DO beginning of aerobic zone (mg/l) 1 2 ortho P beginning of anaerobic zone/ortho P end of anaerobic zone 4 ph anaerobic >5.5 ph aerobic >6.9 HRT anaerobic zone (hours) 0.5-1.5 HRT aerobic zone (hours) 4-5 SRT summer (days) ~4 SRT winter (days) ~10 MLSS (mg/l) 3,000-4,000 Qras/Qinf 0.25-1.0 Temperature ( C) 5 28
Stickney Battery D Demonstration PE P4 P3 P2 P1 Aerobic zone RAS Channel Mixing channel Anaerobic zone Feeding Channel Air lift Channel Anoxic zone RAS Turn down of coarse bubblers and diffusers in anoxic and anaerobic zone as much as possible minimize air input/do and maintain suspension
Optimizing EBPR Parameters Based on Current Infrastructure Phases based on changes Phase I: Baseline Phase II: Beginning of air optimization. Phase III: Increased MLSS, further air optimization in RAS channel & aerobic zone. Phase IV: Held primary sludge in preliminary tanks for longer to generate VFAs from sludge. Phase V: Future reduce flow of RAS returning to Battery D and subsequently NO3 N Likely last point of optimization with current infrastructure.
PARAMETER Battery D Effluent TP PHASE I (5/1 9/12) PHASE II (9/13 10/9) PHASE III (10/10 12/12) PHASE IV (1/28/ 8/22) 1.16 mg/l 1.42 mg/l 0.90 mg/l 0.43 mg/l Influent TP Conc. 4.91 mg/l 3.69 mg/l 4.17 mg/l 4.76 mg/l Influent TP Load 7,534 lb/day 3,485 lb/day 4,006 lb/day 6,262 lb/day SRT 6.14 9.58 16.1 11 Battery DInfluent Flow 193 MGD 112 MGD 133 MGD 176 MGD RAS Flow 173 MGD 139 MGD 128 MGD 152 MGD RAS/Total Flow 0.98 1.24 1.03 0.98 Anaerobic Zone HRT (with RAS 26 min 39 min 37 min 29 min flow) MLSS 3343 mg/l 2224 mg/l 3227 mg/l 3728 mg/l BOD Load 187,802 lb/day 94,093 lb/day 119,578 lb/day 193,489 lb/day BOD:TP 24.08 26.37 27.20 29.8 RAS NO3* 6.75 mg/l 6.72 mg/l 6.28 mg/l 5.77 mg/l RAS NO3 Load* 9,944 lb/day 7,389 lb/day 6,589 lb/day 7,297 lb/day
8 7 6 BATT D TP BATT A, B, & C OUTFALL PE WEIGHTED TP 5 TP (mg/l) 4 3 2 1 0
DO Limitations RAS Returned through airlifts. No alternative infrastructure in place. Anoxic Zone Coarse bubble diffusers. No mixers in place Must rely on small amounts of air to keep solids in suspension. Have periodically burst air through system to clean out. Anaerobic Zone Fine bubble diffusers. No mixers in place Must rely on small amounts of air to keep solids in suspension. Currently doing more targeted study to see if daily bursts of air will eliminate solids deposition.
4 PE 3 Continuous DO P4 P3 P2 P1 5 2 1 RAS MCC (1) MC_M (2) MCC_Begin (3) RAS_end (4) RAS_middle (5) 82% 18% min 0 0 0 0 4.32 1.84 max 0 0 0 0.77 7.07 7.07 average 0 0 0 0.28 6.47 5.92 Anoxic zone starts in the middle of mixing channel Turned off air in RAS channel for Phase III
PE Continuous DO monitoring-phase III P4 P3 P2 P1 2 1 RAS D4_P1 D4_P1E DO (mg/l) (1) (2) Diffuser Opp diffuser min 0.26 0.62 0.00 max 1.68 2.74 1.68 average 0.76 1.35 0.42 DO levels at beginning of aerobic zone not high enough increase air at end of pass 1 but avoid back mixing
Nitrate/Carbon Limitations SWRP is a nitrifying plant. Typical [NO3] RAS 6 mg/l Average RAS/PE Flow 1 Significant NO3 returned. Affects the carbon available for P removal Denitrifiers take up the most readily available carbon quickly. Can have a great COD:TP ratio from primary effluent and experience poor TP removal due to NO3. Anoxic zone does not truly end until the end of the anaerobic zone. Only 60% of time is NO3 depleted before anaerobic zone. Battery D Effluent TP (mg/l) 2 1.8 1.6 1.4 1.2 1 0.8 0.6 0.4 0.2 0 NO3 & TP Concentrations 0 2 4 6 8 10 RAS NO3 (mg/l)
VFA Load (lb/day) 18000 16000 14000 12000 10000 8000 6000 4000 2000 VFA BOD Began holding sludge, effectively wasting ½ as much sludge. Further increased SRT & decreased wasted sludge. Construction began causing a shutdown of the 10 of the preliminary tanks. 100000 90000 80000 70000 60000 50000 40000 30000 20000 10000 BOD Load (lb/day) 0 0 1/16/2013 1/26/2013 2/5/2013 2/15/2013 2/25/2013 3/7/2013 3/17/2013 3/27/2013 4/6/2013 4/16/2013 4/26/2013 Efforts to increase the available carbon Holding primary sludge longer in the preliminary tanks. Encourage fermentation in ML channels by complete elimination of air. Elimination of tanks in service tested through construction most effective way to increase BOD out of the 3.
Correlation between carbon available at beginning of anaerobic zone and effluent TP. Not all carbon in system is usable. Better correlations have been found using solcod concentrations, rather than BOD. However, still seems to be a residual solcod concentration around 25 40 mg/l from profile data and bench scale experiments. rbcod analysis to further determine what portion is bioavailable. rbcod/solcod 0.65 Battery D Effluent TP 3 2.5 2 1.5 1 0.5 0 Right Before Anaerobic Zone Phase III 0 5 10 15 20 25 30 solcod:orthop
Recycle Streams EBPR would prefer stability in system in terms of TP, carbon, etc. SWRP Recycle Streams Relatively Constant Pre digester centrifuges Gravity concentration tank overflow Post digester centrifuges Variable LASMA Lagoon Decant Decant from drying beds desilting pond SWRP. Holding decant in desilting pond to avoid sending back solids. Dewatering events typically lasted between a day and a week. Not previously charted & no flow measurements available.
Lagoon Decant Lagoon decant represented an average 11% of influent TP load. Operations adjusted to aim for a more constant return flow. Phase III Phase III Lagoon Decant Data [TP]BATTERIES A, B, C 1.72 1.34 [TP]BATTERY D 0.91 0.63 % Removal 53% 55%
Major Findings Air lifts and air distribution system making it difficult to establish anoxic and anaerobic conditions in channels and tank Affecting denitrification and causing some nitrification anoxic zone doesn t end when we want it to. A lot of carbon being used by denitrifiers not much left for PAOs Low VFAs in Imhoff effluent Recycle streams P shock loads negatively affecting performance Higher MLSS leads to better P removal Do see a higher abundance of PAOs in test battery
Questions? Email: Brett.Garelli@mwrd.org