WRF Webcast Minimizing Waste Backwash Water from a Biological Denitrification Treatment System (project #4470)

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1 No part of this presentation may be copied, reproduced, or otherwise utilized without permission. WRF Webcast Minimizing Waste Backwash Water from a Biological Denitrification Treatment System (project #4470) November 6, 2014

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10 Minimizing Waste Backwash Water from a Biological Denitrification Treatment System WRF Tailored Collaboration Project 4470 Issam Najm, Ph.D., P.E. Los Angeles, California Webcast November 6, 2014

11 Acknowledgement Water Research Foundation Hsiao-Wen Chen Los Angeles County Dept. of Public Works, Waterworks Division Adam Ariki TJ Kim Clark Ajwani PAC Members Khadija Durbas LADWP Patrick Evans CDM Smith Joanne Silverstein UC Boulder WQTS Nancy Patania Brown Brian Gallagher Eric Seo Karl Gramith 11

12 Outline 1. Project Objectives 2. Los Angeles County, District Biological Denitrification 4. The impetus behind the project 5. Pilot plant configuration & testing results 6. Cost Projections 7. Conclusions & Observations 12

13 Project Objectives 1. Evaluate the feasibility of recovering waste backwash water from a biological denitrification treatment system 2. Evaluate the potential for Cr(VI) removal with biological denitrification 13

14 LA County Waterworks Division A division of the Los Angeles County Dept. of Public Works Supplies water to 200,000 residents in LA County Five Waterworks Districts District Established Connections Estimated Population District 21; Kagel Canyon District 29; Malibu ,120 District 36; Val Verde ,320 4,650 District 37; Acton ,390 4,330 District 40; Antelope Valley , ,440 14

15 District 37 District 37 approx. 4,330 people 3 wells, and purchased treated surface water All three wells contain nitrate at various levels No local sewer system 15

16 Nitrate in Well

17 Conventional Nitrate Treatment Proven Physical/Chemical processes include: 1. Ion-Exchange 2. Reverse Osmosis Both technologies are currently used for nitrate removal from groundwater The problem is that both generate a high-salinity waste stream that cannot be discharged to a municipal sewer unless the WWTP discharges into the ocean This greatly limits their application for the majority of water systems 17

18 Biological Denitrification 18

19 Basic Mechanism Electron Donor Methanol: CH 3 OH CO 2 + 6e Ethanol: C 2 H 5 OH CO e Acetate: CH 3 COOH CO 2 + 8e Not yet Cell Synthesis Energy Production New Biomass NO 3 + CO e C 5 H 7 O 2 N (Biomass) Electron Acceptor (1) O 2 + 4e H 2 O (2) NO 3 + 5e 0.5 N 2 (3) SO e S 2 19

20 Acetic Acid (HAc) Demand Oxygen Reduction to H 2 O ~ 1.4 mg HAc / mg O mg / mg O 2 NO 3 N Reduction to N 2 ~ 3.7 mg HAc / mg N 0.70 mg / mg N Example: DO = 8 mg/l & NO 3 = 15 mg/l as N HAc demand from DO = = 11 mg/l HAc HAc Demand from NO 3 = = 56 mg/l HAc Total HAc Demand = 67 mg/l, which is 27 mg/l Organic Carbon Total biomass generated = 13 mg Biomass/L (~7 mg/l Organic Carbon) The rest, about 20 mg/l of the organic carbon added, is converted to CO 2 and soluble microbial products (SMPs) 20

Chlorine Treatment Process Train Biological Contactor

bacterial count Air bacterial count bacterial count

21 Chlorine Treatment Process Train Biological Contactor Aeration Filtration Disinfection Acetic Acid & Phosphoric Acid High Nitrate Coag. Low Nitrate Low oxygen Excess nitrogen gas High bacterial count Air Low Nitrate Low oxygen Excess nitrogen gas High bacterial count Low Nitrate Low oxygen Excess nitrogen gas High bacterial count 21

22 Coagulant Chlorine Acetic Acid Phosphoric Acid without Washwater Recovery Off-gas Treatment Clearwell / Reservoir Well Pump Air Compressor Waste Washwater Tank Sewer or Septic System 22

23 Process Performance 23

24 Groundwater Quality Parameter Unit Ave. Value Nitrate mg/l as N 8.2 Dissolved Oxygen mg/l 8.2 ph Temperature o C 21 Alkalinity mg/l CaCO Hardness mg/l CaCO TOC mg/l

25 Nitrate Removal Acetic Acid Dose = mg/l MCL Intentional Shutdown of Acetic Acid Feed 25

26 Cr(VI) Removal (1) Reduction from Cr(VI) to Cr(III): Cr e Cr 3+ (2) Precipitation of Cr(III): Cr OH Cr(OH) 3(s) (3) Coagulation & Filtration of Cr(OH) 3(s) precipitate 26

27 General Operating Parameters Parameter Value Biological Contactor EBCT 10 min Filtration Rate 3.0 gpm/sf Runtime Between Backwashes hrs Unit Backwash Volume (each) ~200 gal/sf Water Wastage Rate 5% to 10% 27

28 Waste Backwash Water The washwater is mostly biomass, with no constituents of concern (unless metals are concentrated into the washwater as discussed later) But a 5% 10% wastage rate is higher than most treatment systems (aside from RO) A high sewer capacity is required to accommodate this wastage rate, even for a relatively small system For example, a 1000-gpm system would generate 50 to 100 gpm of waste washwater This is not a sustainable approach, and thus washwater recovery will be necessary for most systems 28

29 Coagulant Chlorine Acetic Acid Phosphoric Acid without Washwater Recovery Off-gas Treatment Clearwell / Reservoir Well Pump Air Compressor Waste Washwater Tank Sewer 29

30 Coagulant Chlorine Acetic Acid Phosphoric Acid with Washwater Recovery Off-gas Treatment Clearwell / Reservoir Well Pump Air Compressor Coag. & Cl 2 Waste Washwater Recovery Tank Sewer 30

31 Pilot Testing 31

32 Pilot Plant Configuration 32

33 Pilot Plant 33

34 Batch Washwater recovery from process backwash FeCl 3 & Cl 2 to Head of Plant to off-site disposal 34

35 Washwater Recovery System Operation Parameter Value Operating Mode Batch Coagulant Type Ferric Chloride Coagulant Dose (Bio. Contactor WBW) 75 mg/l Coagulant Dose (Filter WBW) 50 mg/l Clarification Time 2 hrs Return Flow (as % of Feed Flow) 10% to 15% 35

36 Ave. Return Washwater Quality Parameter Unit Biological Contactor Media Filter Turbidity NTU 23 3 Total Iron mg/l 14 5 Dissolved Iron mg/l Ferrous Iron mg/l Nitrate mg/l Chromium µg/l 16 4 HPC CFU/mL TOC mg/l DOC mg/l

37 Iron Profile 37

38 Filter Performance 38

39 Filtered Water Turbidity after steady-state conditions were reached 39

40 Odor? No quantifiable sulfide was present during normal operation However, there was a detectable odor in the water It was mostly due to stagnation of biomass in the washwater recovery system 40

41 Sludge Quality Analyzed after 25 days of batch accumulation Parameter Unit Biological Contactor Sludge Media Filter Sludge Chromium mg/l Iron mg/l 2,200 3,700 VSS mg/l 4,200 2,300 TSS mg/l 7,800 10,000 COD mg/l No Cr(VI) was being added during this period (raw Cr = 1.9 µg/l) When Cr(VI) was being added at 25 µg/l, Cr in sludge was as high as 7.4 mg/l All Cr removed is accumulated in the sludge 41

42 Cost Range? 42

43 Assumptions Influent nitrate = 11 mg/l as N (50 mg/l as NO 3 ) Dissolved Oxygen = 8 mg/l Plant Utilization Rate = 95% EBCT = 7.5 minutes Filtration Rate = 3.0 gpm/sf Pressure vessels are used for all unit processes Washwater recovery & sludge disposal to sewer Sewer connection fee & disposal cost based on Los Angeles area cost 43

44 Range of Probable Capital Cost Projected using WQTS In-house BDN Design & Cost Model Includes: $29M Design Construction $11M $6M $17M $9M $15M Permitting CM Startup support 44

45 Range of Probable Water Cost ($/AF) Projected using WQTS In-house BDN Design & Cost Model Cost is equally split between capital debt payment and annual O&M cost $1,030 $554 $742 $400 $638 $344 Includes: Amortized Capital Annual O&M Labor Chemicals Sewer Discharge Energy Analytical Maintenance 45

46 Range of Probable Water Cost ($/kgal) Projected using WQTS In-house BDN Design & Cost Model $3.2 $1.7 Cost is equally split between capital debt payment and annual O&M cost $2.3 $1.2 $2.0 $1.1 Includes: Amortized Capital Annual O&M Labor Chemicals Sewer Discharge Energy Analytical Maintenance 46

47 Conclusions & Observations 1. Removal of nitrate is the easiest aspect of a biological treatment system. 2. Washwater recovery is necessary considering the high water wastage rate. 3. Identifying the right chemical treatment conditions is time consuming, and requires the ability to discharge water to sewer for a potentially long startup period. 4. Key water quality challenge is biomass management. 5. Biomass should not be allowed to stagnate, or it will ferment and generate odors. 6. However, the biggest challenge facing the implementation of biological denitrification is cost, especially for small systems. 47

48 Thank you! Questions? 48