Overview of Leachate Treatment Technologies -Pros, Cons, Costs, Concerns IVAN A. COOPER, P.E., B.C.E.E. CIVIL AND ENVIRONMENTAL CONSULTANTS, INC.

Transcription

1 Overview of Leachate Treatment Technologies -Pros, Cons, Costs, Concerns IVAN A. COOPER, P.E., B.C.E.E. CIVIL AND ENVIRONMENTAL CONSULTANTS, INC.

2 Outline Overview of Select Conventional Treatment Technologies MBR Biological Treatment Technology summary Common operational challenges Selection Criteria and How to Select a Process? Costs

3 Aerobic Biological Treatment Technologies Commonly Used for Leachate Treatment Attached Growth Activated Sludge Suspended Growth Activated Sludge Static Fixed Film Dynamic Fixed Film Continuous Batch Trickling Filters Web Media BAF A2O Submerged Deep Bed Filters RBC Plastic Seaweed IFAS MBBR Oxidation Ditch Conventional AS Extended Aeration MBR Step Feed Timeswitch Bardenpho Ludzak Ettinger Sharon In-Nitri Bioaugmentation (BAR) Bioaugmentation Enhanced (BABE) UCT/MUCT SBR MBR

4 MBR Process Used at many landfills Equalization is VERY important Requires aeration and membrane separation In-Tank or External Membrane? System Control by wasting, aeration Sludge Production/Solids Management Maintenance needed on membranes High quality effluent

5 Membrane Biological Reactor (MBR) It is still activated sludge (yes it is true!!!) Replace clarifier with ultrafiltration (UF) membranes 0.01 to 0.10 micron filter Much higher biomass concentration o 10,000 to 15,000 mg/l VSS More work in smaller aeration tank volume No settling issues Hollow fiber/ceramic Membrane (in Tank) Modules submerged in tank Immersed in mixed liquor, permeate drawn through the tubes o Access issues o Desludging Tubular Membranes (out of Tank) Cross flow external filtration in modules o Membrane flux is higher

6 MBR Technology

7 Internal MBR

8 Internal MBR Operation Modes

9 Activated Sludge Basics AERATION TYPES Diffused aeration coarse bubble/fine bubble Jet aeration Turbine aeration Surface aeration Organic (COD) and nitrogen (ammonia) biodegradation Heterotrophic organisms - COD degraders Autotrophic organisms Ammonia degraders Importance of Bench/Pilot Scale test Toxicity? Oxygen Uptake Nitrification Rate Sludge production cell production vs. energy (heat released) Membrane flux rate Cleaning cycle frequency

10 Leachate Activated Sludge Basics Loading - F to M ratio (food to microorganism ratio) 0.10 to 0.40 (10 lbs of BOD (COD) / 100 lbs microorganisms) Sludge Age 10 to 50 days typical Avg. time solids are in the aeration system Sludge age and F to M ratio Inversely related Nitrifiers Minimum sludge age for nitrification? o What is the nitrification rate Varies!! ph (Very Important!!!!) o 7.5 to 7.8 Temperature-Even More Important o Autotrophic bacteria dieoff over ~100 degrees F

11 Leachate Activated Sludge Basics Single Stage AS COD and nitrogen removal in same system o COD/Ammonia ratio (Very important!!!!) What if influent COD/ammonia ratio changes? o COD: N increases over about 10 or 15:1, then Population of nitrifiers going down (nitrifiers get crowded out) Two Stage AS Two AS systems, two Membrane Systems o Separate sludge system o Different microbial populations in each stage More robust for leachate treatment

12 Free Ammonia Inhibition

13 Membrane Biological Reactor (MBR) Temperature Design Concerns Temperature Hot Too hot in the summer!!!! Heat of Biological Oxidation o 2,700 to 3,200 calories/g of COD oxidized o Max temp. for nitrifiers (< 38 o C) Design for heat removal o Surface aerator o Evaporative cooler o Heat exchanger and cooling towers Temperature Cold Too cold in the winter!!!!! o Heat of Biological Oxidation not enough? o Interim heating o Steam injection

14 Temperature Design Range Why mesophilic 68 F (20 C) and 113 F (45 C) versus thermophilic ( deg F)? Materials Of Construction Corrosion UF, other equipment shut down Foaming Speed of reaction Nitrification ( F)

15 Temperature Model for Design STEADY-STATE TEMPERATURE MODEL Modification of original temperature model developed by Y. Argaman and C. E. Adams, Jr., WEFTEC 2004 paper written by Victor J. Boero The model can be used for completely mixed basins, totally or partially above ground, covered or not, aerated (diffused air or surface aeration) or not, with steam addition or not. Based on steady-state heat and mass balances for air and water. This may control the design!!! Not process kinetics

16 Advantages / Disadvantages for MBR systems ADVANTAGES BOD removal high 90% Oxidation/Nitrification Biological phosphorous removal possible Temperature Dependent DISADVANTAGES No color removal possibly increase by forming colored intermediates Nutrient removal may require several stages/ May be Land Intensive based on design Heterotrophic versus autotrophic populations Energy intensive Close operation attention needed Cleaning/scale control/avoid plugging High WAS flows

17 Key Design Considerations Influent Parameter Variability Flow & Constituents? Organic and Nitrogen Loading Biological Treatment -Temperature Considerations Biological Treatment - Nutrient Deficiency Nitrogen and Phosphorus TDS Biological inhibition/oxygen transfer Effluent limits (future?) Corrosion Fouling/Scaling Odors Sludge processing Labor required

18 Pretreatment Process Flow

19 Jet Aeration Example MBR System Jet Aeration Systems Often Used for Leachate Treatment External Circulation Pumps Blowers (VFD)

20 Construction Progress March 2014 Aeration Tanks

21 Startup May 2014

22 Operator Training Foam Temperature Pump Issues Scaling Piping and UF Startup Challenges September 2014

23 Foaming Challenges Foaming Foaming varies with f/m Controls: o Spray water = more to UF o Harnessing a portion of the jet mix recycle as a continuous knockdown spray; o Incorporating a knockdown defoamer (antifoam) NON-SILICA BASED! injection into the continuous spray feed pipe; o functional foam level sensor incorporating to control the defoamer feed.

24 Biological Fouling of UF Fouling Solutions Mineral Scale Calcium carbonate scale Acid cleaning step Biofouling Caustic clean helps remove biofouling Two biological fouling mechanisms Soluble Microbial Product (SMP) o Cells Lysis release internal contents Extracellular Polymeric Substance (EPS) o Polysaccharides (Goo) Control by proper nutrients P/N/micronutrients Check lab vacuum filtration rates o Flux rate o Example reduced from 3 minutes to 10 seconds for 100 ml sample

25 Biological Treatment - Common Operational Problems What is the process control method? F to M, Sludge Age, Wasting, None? Rapid Loading Changes Remember Equalization? Foam Poor Flux Rate Track filtration time in lab Nutrient deficiency (phosphorus) Too high F to M (too much COD) Low dissolved oxygen (DO) Winter temperature The design basis (i.e., 25 o C)? No temperature control Free Ammonia Inhibition

26 Ultrafilter Operation External MBR Ultrafilters Excellent quality effluent Requires monitoring pressure drop and cleaning (120 psi 80 psi) Initially plant staff ran below recommended pressure drop; elements clogged. Additional system training helped operations Scale formation added soda ash addition to primary step to remove Ca hardness Membrane autopsy Calcium carbonate scale controlled by acid cleaning. Calcium sulfate more difficult to remove.

27 Effluent Acceptance by POTW BOD: 30,000 mg/l 34 mg/l = % removal COD 55,000 mg/l 2,200 mg/l = 96% removal Metals All under limits Metals Permit, mg/l Acceptance Test, mg/l Arsenic Chromium Copper Iron Lead Nickel Zinc

28 Comparative Options New leachate treatment methods Jude Ifeanyichukwu Madu, Sweden, 2008

29 Comparative Aerobic Technologies Comparison MBBR RBC Activated Sludge SBR IFAS MBR Capital Investment Low to medium High High Low Medium High Effluent Quality Good Fair Good Good Good Excellent Footprint Low High High Low Medium Medium Flow Tolerance Aeration Blowers Good Poor Poor Good Good Fair Required None Required Required Required Required Recirculation pumps Not required Not required Required Not required Required Required Chemical usage Low Moderate Moderate Low Low Moderate Operator difficulty Low Low High Low Moderate Moderate High

30 Leachate Disposal Costs Alternatives built on combination of technologies Very site dependent / Sewer or direct discharge / Residual management Costs from various sources CONSTRUCTION & O/M Air Stripping Constructed Wetlands Phytoremediation Chemical Treatment Conventional Activated Sludge (CAS) MBR/MBBR SBR (EPA 1998, adjusted) RO MBR + RO Conventional AS (CAS) + RO Evaporation AOP Hauling (distance/disposal) $0.01 $0.03/gal $ $0.03/gal $ $0.03/gal $0.02 -$0.05/gal $ $0.076/gal $0.04 $0.065/gal $ $0.054/gal $ $0.10/gal $0.095/gal $ $0.35/Gal $ $0.09/gal $ $0.07/gal $ $0.40/gal

31 Summary Leachate Key Parameters of Interest Overview of Select Aerobic Biological Treatment Technologies Overcome Design Challenges How to Address Operational Issues? Selection Criteria and How to Select a Process Costs

32 Questions & Discussion CIVIL & ENVIRONMENTAL CONSULTANTS, INC. (CEC) IVAN A. COOPER, PE, BCEE: