OBG PRESENTS: At the Mercy of the Process Impacts of Nitrogen Removal Performance on WWTP Disinfection Ned Talbot, PE Tri-Association Conference 2018 8/30/18 9:00-9:30AM
AGENDA Overview of Plant Processes Martinsburg WWTP Biological Performance and Stresses Impacts on Disinfection Performance Operator Techniques for Disinfection Reliability 2
OVERVIEW OF PLANT PROCESSES Martinsburg WWTP 3
WRRF Project: Martinsburg, WV 3 MGD (12 MGD influent, 10 MGD peak to bio) 5 mg/l TN effluent limit 0.5 mg/l TP effluent limit Project Summary Demo: Trickling filters Nitrification tower Modifications: New headworks, biological, ballasted polishing Improve clarification, disinfection, anaerobic digestion New solids handling, operations building 4
Simplified Process Flow Diagram 1. Headworks 2. MBBR 4. Co-Mag 3. Disinfection Martinsburg WWTP Upgrade 5. Solids Handling 5
MBBR Overview Protected biomass on plastic media expands capacity and effluent quality Nutrients, peak flows, cold temps M B B R I F A S Moving Bed Biofilm Reactor Integrated Fixed-Film Activated Sludge Fixed Biofilm / IR / TN (and some TP) Removal Fixed Biofilm + SS / IR + RAS / TN + EBio-P 6
MBBR for Martinsburg Benefits Obstacles 7
New Plant: MBBR ANR Process Headworks Expanded and Optimized Chlorination Status: Constructed, Optimized 8
DISINFECTION PROCESSES Chlorination Sodium Hypochlorite (12.5% solution) 2NaOCl+2H 2 O 2NaOH+HOCl+OCl - +H Goal: free chlorine residual Optimization CFD model of flow / mixing process upgrades Online chlorine residual and ORP control Dechlorination Sodium bisulfite dosing at effluent v-notch 9
Optimization Goals CFD modeling Velocity Contour at El 380.75 (1.75 above floor) Eliminate low flow spots or short-circuiting Create highly turbulent injection points 30 min plug flow contact time at peak flow 10
BIOLOGICAL PERFORMANCE AND STRESSES Impacts on Disinfection Performance 11
Biological Treatment Stresses on Disinfection Before Upgrade: Trickling Filter Plant with Nitrification Tower Incomplete nitrification / residual ammonia swings Chlorine demand linked to tower performance Incomplete hypochlorite mixing / short circuiting After Upgrade: Advanced Nutrient Removal Ammonia fully converted; CCT optimized MBBR sometimes stressed Occasional effluent NH 3 / NO 2 NO 3 Swings in chlorine demand 12
Variable MBBR Influent Flow and Loading Unexplained Influent BOD Loading Variability Diurnal variations high ammonia in dewatering filtrate press 6am to 4pm, 5 days / week Wet weather 2018 MBBR Stresses 13
Interim Wastewater Treatment Influent BOD: NH 3 -N Higher than Design Parameter Unit Design Mass Balance Apr 2014- Apr 2015 % of Design Load Startup Data July 2016- Oct 2016 % of Design Load Flow MGD 3.0 2.46 82% 1.8 60% lb/d 5,655 2,724 48% 3,652 65% Inf BOD 5 mg/l 226 132 246 Eff BOD 5 mg/l 17 15.0 5.20 lb/d 4,579 1,942 42% 4,604 101% Inf TSS mg/l 183 95 310 Eff TSS mg/l 20 12.9 5.7 lb/d 463 257 56% 180 39% Inf NH 3 -N mg/l 18.5 12.5 12.1 Eff NH 3 -N mg/l 0.6 1.3 0.23 Design: 12:1 Startup: 20:1 14
MBBR Stresses Variable Influent BOD: Ammonia Loading Change in Average BOD:NH3 ratio 15
MBBR Stresses Wet Weather Flow Spikes Stress on MBBR Challenges Disinfection 16
Variable MBBR Influent Flow and Loading Unexplained Influent BOD Loading Variability Diurnal variations high ammonia in dewatering filtrate press 6am to 4pm, 5 days / week MBBR Stresses Stress on MBBR reactors led to nitrite spikes Winter Versus Summer Wet weather 2018 Temperature change Zone loading swing zone operation changes Aeration optimization 17
MBBR Biofilm by Zone Process Performance by Design Summer (more denitrification capacity) Diurnal Variation Solids Treatment Recycles Seasonal Flexibility Summer, Winter Mix, BOD 5, NO 3 -> Anoxic BOD 5,NO 3 NH 3 Mix, BOD 5, NO 3 -> Anoxic NH 3 Air NH 3, NO 3 Oxic NH 3, NO 3 Air NH 3, NO 3 Oxic NO 3 IR Mix, NO 3, Carbon -> Anoxic TN < 5 A i r BOD - Heterotrophs (H) Denitrifiers Heterotrophs- DN Nitrifiers Autotrophs (A) IR Control Match NO 3 to BOD 5 Winter (more nitrification capacity) Mix, BOD 5, NO 3 -> Anoxic BOD 5?, NH 3 Air, BOD 5?, NH 3 -> Oxic NH 3 Air NH 3, NO 3 Oxic NH 3?, NO 3 Air NH 3?, NO 3 Oxic NO 3 IR Mix, NO 3, Carbon -> Anoxic TN < 5 A i r 18
MBBR Stresses Stress on MBBR reactors challenges disinfection Operational and Temperature Changes Increased Ammonia in Effluent 19
Wastewater Constituent Impacts on Chlorine Dose and Residual Wastewater Characteristics Ammonia Biochemical Oxygen Demand Hardness, Iron, Nitrate Nitrite Ph Total Suspended Solids Temperature Organic and Inorganic Materials Effects on Chlorine Forms chloramines when combined with chlorine; 10:1 free chlorine demand factor Chlorine oxidizes BOD and becomes ineffective; 0.1:1 free chlorine demand factor TOC to chlorine Minor effect Nitrite oxidized to nitrate; 5:1 free chlorine demand factor Affects distribution between hypochlorous acid and hypochlorite ions and among the various chloramine species; Lower ph forms more hypochlorous acid than hypochlorite ion Shielding of embedded bacteria and chlorine demand Disinfection rate increases with higher temperature Chlorine oxidizes the organic and inorganic materials and becomes ineffective; 1.0:1 ratio of organic-n to chlorine 20
Operator Techniques for Disinfection Reliability 21
Operator Concerns with Chlorine Disinfection Chlorine Residual Sampling (Hach CL17) Not real time one sample every 3 minutes Slow response to changes in demand Difficult to adjust sample points to optimize system Sample pumps require accessible location Only 5 fecal excursions allowed in current permit 22
Operational Adjustments to Improve Disinfection Reliability Addition of ORP probes Grab samples of nitrite in MBBR effluent confirm stress DISINFECTION RELIABILITY Fine tuning ORP and chlorine residual chemical feed control (hypochlorite and bisulfite) Adjustment of dewatering timing 23
ORP Probes Initial startup Measure potential of solution to oxidize or reduce Oxidative = positive mv (Cl 2 ); Reductive = negative mv Initial ORP Targets: 380mV hypo; 180mV bisulfite After 6 months of operation Moved probe closer to feed pt Adjusted hypo probe ORP target: 500mV, then 400mV Alarms: Low @ hypo @300 High @ bisulfite @270 High ORP @ hypo feed indicates high oxidation potential, chlorine residual Low ORP @ hypo feed indicates low chlorine residual, warning of MBBR stress Frequent replacement of salt bridge; recalibration 24
Solids Handling Batch Cycles Draw / Fill SST s for Thickening and Dewatering 6AM to 4PM 25
Diurnal Influent Loading + Volute Dewatering Press Recycle Ammonia rise during dewatering 26
Impact of Dewatering Timing 27
Many Causes of Biological Stress Variable influent loading Intermittent plant recycles Wet weather peak flows / I/I Summary Change of seasons / process temperature Operational Strategies for Reliable Disinfection ORP probes in combination with chlorine residual analyzers Optimized chemical feed control strategies Secondary effluent nutrient sampling program Experience with the process is a clear path to reliability 28
OBG PRESENTS: THERE S A WAY Questions? Ned.Talbot@obg.com 301-731-1150
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Lessons Learned: MBBR Internal Recycle Slipstream Primary effluent MBBR bypass Accidental during loss of power No check valves limited space Added check on FM Interlocked pumps on fail 31
Evaluate existing system and identify limitations Eliminate low flow spots or short-circuiting Disinfection Optimization Goals Create highly turbulent injection point for 1 second complete mix 30 min plug flow contact time at peak flow Dosage high enough to overcome chlorine demand. Dosage is typically 5 to 20 mg/l. 32
Breakpoint Chlorination Medora Corporation Informational Bulletin http://www.medoraco.com 33
MBBR Biofilm by Zone Air Mix BOD - Heterotrophs (H) Denitrifiers Heterotrophs-DN Nitrifiers Autotrophs (A) The Wrong Mix or Type of Biofilm by Zone? Process Performance by Stage Phase 1 Planned H A A High Load, or Low Air H? H A H? H? A? H, A? Intermittent / Insufficient Air H A, DN? Phase 2 Planned H- DN Sw A A H? H, A A H- DN High Load, Low Air, or no Auto H- DN H? H? A? H, A? Intermittent / Insufficient Air H- DN? H A, DN? 34