Overview of Leachate Treatment Technologies -Pros,...
Transcript of Overview of Leachate Treatment Technologies -Pros,...
Overview of Leachate Treatment Technologies -Pros, Cons, Costs, Concerns
IVAN A. COOPER, P.E., B.C.E.E. CIVIL AND ENVIRONMENTAL CONSULTANTS, INC.
Outline
► Overview of Select Conventional Treatment Technologies ► MBR Biological Treatment ▪ Technology summary ▪ Common operational challenges
► Selection Criteria and How to Select a Process? ► Costs
Aerobic Biological Treatment Technologies Commonly Used for Leachate Treatment
Attached Growth Activated Sludge
Static Fixed Film Dynamic Fixed Film
Suspended Growth Activated Sludge
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
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
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
MBR Technology
Internal MBR
Internal MBR Operation Modes
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
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
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
Free Ammonia Inhibition
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 (< 38oC)
▪ 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
Temperature Design Range
► Why mesophilic 68°F (20°C) and 113°F (45°C) versus thermophilic (125 – 150 deg F)? Materials Of Construction Corrosion UF, other equipment shut down Foaming Speed of reaction Nitrification (95-100°F)
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
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
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
Pretreatment Process Flow
Jet Aeration Example MBR System ► Jet Aeration Systems Often
Used for Leachate Treatment
► External Circulation Pumps
► Blowers (VFD)
Construction Progress – March 2014 – Aeration Tanks
Startup – May 2014
Startup Challenges – September 2014
► Operator Training ► Foam ► Temperature ► Pump Issues ► Scaling – Piping and UF
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.
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
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., 25oC) ? ▪ No temperature control
► Free Ammonia Inhibition
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.
Effluent Acceptance by POTW
► BOD: ▪ 30,000 mg/l 34 mg/l = 99.932% 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 0.4 0.0529 ▪ Chromium 5.0 0.0298 ▪ Copper 2.7 0.247 ▪ Iron 150 2.7 ▪ Lead 0.4 0.0082 ▪ Nickel 2.3 0.0359 ▪ Zinc 3.0 0.0595
Comparative Options
New leachate treatment methods Jude Ifeanyichukwu Madu, Sweden, 2008
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
Good Poor
Poor Good Good Fair
Aeration Blowers
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
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 $0.01 – $0.03/gal Constructed Wetlands $0.01 - $0.03/gal Phytoremediation $0.01 - $0.03/gal Chemical Treatment $0.02 -$0.05/gal Conventional Activated Sludge (CAS) $0.035 - $0.076/gal MBR/MBBR $0.04 – $0.065/gal SBR (EPA 1998, adjusted) $0.02 - $0.054/gal RO $0.02 - $0.10/gal MBR + RO 0.064 - $0.095/gal Conventional AS (CAS) + RO $0.07 - $0.35/Gal Evaporation $0.03 - $0.09/gal AOP $0.06 - $0.07/gal Hauling (distance/disposal) $0.10 - $0.40/gal
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
Questions & Discussion
CIVIL & ENVIRONMENTAL CONSULTANTS, INC. (CEC) IVAN A. COOPER, PE, BCEE: [email protected]