PLANNING FOR NUTRIENT REMOVAL: WHAT STEPS CAN WE BE TAKING NOW?

Transcription

1 PLANNING FOR NUTRIENT REMOVAL: WHAT STEPS CAN WE BE TAKING NOW? LEONARD E. RIPLEY, PH.D., P.E., BCEE SENIOR PROCESS ENGINEER FREESE AND NICHOLS, INC.

2 General Action Categories 1. Collect wastewater characterization data. 2. Collect plant performance data. 3. Assess current available capacity. 4. Brainstorm process configurations. 5. Perform process calculations consider using a process simulation model. Leonard Ripley: Planning for BNR -- Slide 2

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4 Conventional Influent Parameters Parameters: BOD & COD total and soluble TSS & VSS Nitrogen TKN, ammonia-n ph and alkalinity Phosphorus TP Frequency depends on size of plant: Large plants daily Smaller plants consider periodic intensive surveys, with at least one week in each season of the year Leonard Ripley: Planning for BNR -- Slide 4

5 Unconventional Influent Parameters Volatile fatty acids (VFA) measure w/ wet chemistry Readily biodegradable COD (rbcod) Flocculated filtered COD (ffcod) flocculate before filtering to remove colloidal COD Estimation method: ffcod (truly soluble) -- Effluent COD (recalcitrant) = rbcod Leonard Ripley: Planning for BNR -- Slide 5

6 Partitioning of Influent COD SOLUBLE COLLOIDAL PARTICULATE READILY DEGRADABLE rbcod CAN BE REMOVED WITH FLOCCULATION CAN BE REMOVED WITH FILTRATION SLOWLY DEGRADABLE (COMPARATIVELY MINOR) NONDEGRADABLE (INERT) ESTIMATE FROM PLANT EFFLUENT Leonard Ripley: BNR Residuals -- Slide 6

7 Characterization Objectives 1. Develop estimate of BOD & ammonia loading for evaluating current plant capacity. 2. Develop a record of TP, TKN, and rbcod/tp and their variation. Leonard Ripley: Planning for BNR -- Slide 7

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9 In-Plant Parameters Parameters: BOD & COD total and soluble Nitrogen TKN, ammonia-n ph and alkalinity Phosphorus TP & ortho Locations: Primary effluent Secondary effluent prior to and after filters Primary sludge, WAS, and digested sludge Thickener & dewatering filtrates or centrates Leonard Ripley: Planning for BNR -- Slide 9

10 Effluent Parameters Parameters: BOD & COD total and soluble TSS & VSS Nitrogen TKN, NH 4, NO 3, NO 2 -N ph and alkalinity Phosphorus pre/post filtration Frequency depends on size of plant: Large plants daily Smaller plants consider intensive surveys, with at least one week in each season of the year Leonard Ripley: Planning for BNR -- Slide 10

11 Plant Testing Measure removal rates in specific unit processes: Profile BOD, NH 3, NO3+NO2, oxygen uptake rate (OUR) along length of aeration basin during different times of the day. Compare basins at different loadings. Measure maximum mixed liquor nitrification rates (μ max ) with spike or SBR testing in lab Leonard Ripley: Planning for BNR -- Slide 11

12 Plant Performance Data Collection Objectives 1. Assess extent of current nutrient removal, particularly nitrification/denitrification. 2. Understand magnitude of return flow contributions. 3. Describe flows of organic carbon and nutrients sufficiently to develop a mass balance for the current plant where inputs outputs. Consider implementing or expanding process instrumentation; also, fine-tune process control $$$ Leonard Ripley: Planning for BNR -- Slide 12

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14 35,000-ft Capacity Review Calculate current ADF capacity of each unit: Chapter 317: average BOD Chapter 217: average + one standard deviation Do the AB s have reserve capacity? Can AB s be uprated single-stage nitrification or high-rate? Backwash equalization, or peak-flow storage? Rule of Thumb: bio-p takes 25-33% of AB volume Leonard Ripley: Planning for BNR -- Slide 14

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16 Process Screening Key factors: Projected effluent limits Wastewater TP & TKN concentrations Wastewater rbcod concentration Available AB nitrification capacity Yard piping, particularly RAS Return flow management Ability to phase improvements -- stage anoxic zones to save energy? Leonard Ripley: Planning for BNR -- Slide 16

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18 Process Calculations First Cut Typical Modified UCT Process How much nitrification volume do you need? Clarifier Anaerobic 1-2 hr ( %) Anoxic 2-4 hr Anoxic 2-4 hr Aerobic 4-12 hr NRCY 2 (50 100%) RAS (80 100%) WAS Compare configurations based on TP/rbCOD and C/N ratios. Calculate typical volumes for each treatment zone. Calculate typical flow rates for RAS and NRCY streams.

19 Process Calculations First Cut Clarifier Anaerobic 1-2 hr ( %) Anoxic 2-4 hr RAS (80 100%) WAS Compare configurations based on TP/rbCOD and C/N ratios. Calculate typical volumes for each treatment zone. Calculate typical flow rates for RAS and NRCY streams.

20 Detailed Process Calculations Process simulation modeling: What if analysis for different configurations. Estimate achievable biological removal. Manage sidestream loads. Caveat: The model is only as good as the data that goes into it! Leonard Ripley: Planning for BNR -- Slide 20

21 Conclusions Implementation of nutrient removal will not be easy. Advance planning can ease the process and potentially reap short-term energy savings by phasing improvements - tighter DO control and anoxic zones. Process selection will be very plant-specific don t just assume that everyone will end up with a UCT or JSB process. KEY POINT: Data collection! Influent characterization: BOD, TP, TKN, and rbcod Return stream loadings: TP, NH 3 Leonard Ripley: Planning for BNR -- Slide 21

22 Additional Resources Leonard Ripley: Planning for BNR -- Slide 22

23 Leonard Ripley: Planning for BNR -- Slide 23