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Leachate Treatment Jae K. (Jim) Park

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1 Leachate Treatment Jae K. (Jim) Park
Dept. of Civil and Environmental Engineering University of Wisconsin-Madison

2 Background (1) A complex organic waste that changes with time
Problematic components Degradable & nondegradable organics Hazardous organics and inorganics Ammonia, nitrate, and nitrite Suspended solids Color and odor Pathogens Treatment experience Lab & pilot scale: good treatment, large data base Field scale: limited data base

3 Background (2) Leachate disposal can be costly.
Development of the disposal process should take into account several areas Regulatory requirements Nature of leachate Operational considerations Available disposal options Failure to solve a problem with all constraints can lead to High capital and operating costs Difficulty in operation Compliance related problems

4 Treatment Options Off-site On-site facility facility Partial Complete
Disposal • Effluents • Sludges etc.

5 Leachate Properties Affecting Treatment Flow Fluctuation
10 m3/ha∙day Flow Time, months Options Overdesign and treat peak flow Equalize flow in landfill (recycle) or storage tanks

6 Leachate Properties Affecting Treatment Contaminant Concentration Fluctuation
Some peak quickly and decline: e.g., BOD Some persist for long periods: e.g., NH3-N Daily and seasonal variations occur Options Same as for flow Modify treatment system

7 Leachate Properties Affecting Treatment Organic Contaminants
Young Leachate - Biological Treatment BOD in 10,000’s Mostly VFA Older Leachate - Carbon Adsorption BODs in 100’s; COD in 1,000’s Humic and fulvic acids Priority organics

8 Leachate Properties Affecting Treatment Nitrogen and Heavy Metals
Ammonia (NH3-N) - Air Stripping Organic (Org-N) - Chlorination Combined - 100’s mg/L - Biouptake, Biological Nitrification/Denitrification Heavy Metals - Chemical Precipitation Iron (Fe) mainly; Zn, Pb, Cu

9 Leachate Properties Affecting Treatment Conservative Ions and Acidic pH
Conservative Ions - Reverse Osmosis High TDS Chloride Sulfate Sodium Acidic pH - Neutralization

10 Planning Treatment and Disposal
Estimate leachate flow, Q WBM/HELP Variations with site age Estimate leachate contaminant conc., C Type Variations with age Identify treatment and disposal options with discharge standards and cost Select treatment and disposal system Introduce uncertainty Maintain flexibility Q t C t

11 Changes in Landfill Leachate Quality
Phase 4 Methanogentic Phase 5 Maturation Phase 1 Adjustment Phase 3 Acetogenic COD Phase 2 Transition pH Concentration NH3 Landfill age

12 Leachate Management Practices in the U.S.
On-site treatment/ sewer or POTW (3.8%) Evaporation (2.3%) POTW Disposal (39.9%) Private/industrial treatment(13.5%) On-site treatment (7.5%) Not collected (9.0%) Other (9.7%) Sewer discharge (14.3%) POTW: Publicly Owned Treatment Work

13 Constructed Wetland Uses Polishing treatment Complete treatment
Advantages Relatively inexpensive to build/operate Associated with ‘green’ technologies Wetlands credits Disadvantages Large land requirement Cold weather Mediocre results especially for complete treatment systems

14 Reed Bed for Effluent Polishing

15 Reed Bed

16 Reed Bed Configuration

17 Performance of Reed Bed

18 Performance of Reed Bed

19 Typical Performance of Chapel Farm Landfill Leachate Treatment Plant
Leachate Leachate Parameter Cell 1 Cell 2 Effluent pH Alkalinity (mg/L as CaCO3) 5,150 5, COD 10,600 10, BOD 4,100 4,200 3 TOC 3,070 2,980 80 Fatty acids (as C) 1,702 1,946 ND Acetic ND Propionic ,290 ND iso-Butyric ND n-Butytic ND iso-Valeric ND n-Valeric ND Ammonia (mg-N/L) Nitrate (mg-N/L) < Nitrite (mg-N/L) < 0.1 Sulfate (mg/L) Phosphate (mg/L) < 0.1

20 Typical Performance of Chapel Farm Landfill Leachate Treatment Plant
Leachate Leachate Parameter Cell 1 Cell 2 Effluent Chloride (mg/L) 4,670 2,180 3,870 Sodium (mg/L) 1,360 1,210 1,070 Magnesium (mg/L) Potassium (mg/L) Calcium (mg/L) 1,040 1,030 25 Chromium (mg/L) < 0.04 Manganese (mg/L) < 0.1 Iron (mg/L) Nickel (mg/L) Copper (mg/L) Zinc (mg/L) Cadmium (mg/L) < 0.01 Lead (mg/L) < 0.04 Arsenic (mg/L)

21 Leachate Treatment Removal by road tanker to sewage works
Off-Site Removal by road tanker to sewage works Removal via pipeline or sewer to POTWs Most common On-Site Biological Physical/Chemical Mixed

22 Off-Site Treatment Expected Treatment in POTW
Secondary Treatment Excellent Removal BOD, SS, coliforms Some removal Metals (Fe, Zn), organics, NH3-N Little Removal Metals (Ni, Al), solvents, Cl-, Na+

23 Off-Site Treatment Sewer Surcharges
Wisconsin (1986), 6 cities Flow ($/1000 gal) BOD ($/lb) Average Range 0.11~ ~0.25 Example: 50 acre site with 12” precipitation/yr, BOD - 10,000 mg/L, and average $ above; then ~ $150,000/yr

24 Off-Site Treatment Impact of Leachate on POTW
Little data available Lab co-treatment studies with sewage 2% by volume is OK But organic load is much higher (> 50%) Expect Increased oxygen and P required Sludge production: biomass, metal precipitates Foaming, Odors Effluent: TDS, NH3-N, resistant organic No adverse impact - Metro Toronto (1985)

25 Typical Performance of Chapel Farm Landfill Leachate Treatment Plant
Parameters Control % Leachate (V/V%) 0.2% 1% 10% 25% 50% Operating conditions Aeration time (hrs) Solids retention time (days) Mixed liquor temp. (°C) pH DO (mg/L) MLSS (mg/L) MLVSS/MLSS ratio F/M ratio (kg BOD/kg TS/day) Respiration rate (mg O2/mg VS/hr) Sludge volume index (mL/g) 6 7 225 7.30.4 8.00.2 1120136 0.63 0.31 17.2 6710 7.30.2 8.10.4 105037 0.38 15 747 7.20.2 7.90.5 1230106 0.45 15.6 656 25 114058 0.70 0.30 13.3 728 7.10.1 8.40.2 1390190.59 0.25 13.7 6.21.0 9.01.6 170095 0.24 9.8 506 Removal efficiencies BOD removal (%) COD removal (%) SS removal (%) TKN removal (%) Ammonia removal (%) 90 88 89 61 54 93 86 59 49 80 58 50 74 73 36 28 68 94 31 30 62 63 96 32 Color (Influent/Effluent) Dominant wave length (nm) Hue Luminance (%) Purity (%) 500~505 Green 84/84 3/3 76/77 79/79 575~580 Yellow 82/82 20/20 30/30 47/51 40/40 MLSS: mixed liquor suspended solids; MLVSS: ML volatile SS; F/M: food/microorganisms

26 On-Site Treatment Physical/Chemical Processes
Coagulation/flocculation/settlement pH control and aeration/air stripping Activated carbon adsorption Reverse osmosis Oxidation with hydrogen peroxide Oxidation with hypochlorite Degassing  Evaporation Biological ( Aerobic: trickling filter, activated sludge, aerated lagoon, rotating biological contactor, sequencing batch reactor (SBR) Anaerobic: submerged filter, upflow anaerobic sludge blanket (UASB) Anoxic: denitrification Mixed Land treatment Vegetated ditch/root zone treatment

27 Trickling Filter Plastic random packing Plastic cross-flow packing

28 Sequencing Batch Reactor (SBR)
Suspended growth system Completely mixed mode; batch mode with discontinuous flow Typical F/M = 0.05~0.1 (comparable to an extended aeration type process) 1 2 3 Influent Mixing Fill React Settle 4 5 Effluent Draw Idle

29 Aerated Lagoons Suspended growth system Comletely mixed mode
Contact time limited to hydraulic retention time due to no recycle of sludge Limited effluent quality Raw wastewater Effluent Surface aerator

30 Rotating Biological Contactor (RBC) (1)
Attached growth system Plug flow mode Design based on specific surface area Aeration provided by rotating disks Better performance than other fixed- film systems due to lower organic loading per mass of biomass, longer detention time, and little short-circuiting

31 Rotating Biological Contactor (RBC) (2)

32 Anaerobic Fixed Film Reactor
Sludge age: > 100 days VSS: > 20,000 mg/L Increased efficiency and rapid elution of toxic sludge Not good for wastes containing a large portion of particulates and/or carbohydrates due to clogging Possible to treat low strength waste at nominal temperatures economically Effluent recycle (sufficient alkalinity) to raise pH to 7 Possible buildup of nonbiodegradable solids in reactor Loading rate: 0.42~3.4 kg COD/m3·day at 25°C; 60~80% COD removal; e.g. Landfill leachate: pH 5.4, COD 54,000 mg/L, 45% fatty acids, loading 7.9 kg COD/m3·day  89% removal

33 Upflow Anaerobic Sludge Blanket (UASB) Reactor
High sludge age at high loadings with separation of gas from the sludge solids VSS: 20,000 ~ 150,000 mg/L Sugar-beet waste: reactor size 800 m3, loading 10 kg COD/m3·day, and HRT 4 hrs  treatment efficiency 80% Difficult to maintain low effluent SS levels and occasional unexplained biomass washout

34 Achievable Effluent Levels by Chemical Precipitation
Technology Achievable eff. conc. (mg/L) Metal Sulfide precipitation/filtration Carbon adsorption Ferric hydroxide co-precipitation 0.05 0.06 0.005 Arsenic Sulfate precipitation 0.5 Barium Hydroxide precipitation at pH 10-11 Co-precipitation with ferric hydroxide Sulfide precipitation 0.05 0.008 Cadmium Hydroxide precipitation Sulfide precipitation 0.02~0.07 0.01~0.02 Copper Sulfide precipitation Alum co-precipitation Ferric hydroxide co-precipitation Ion exchange 0.01~0.02 Mercury Hydroxide precipitation at pH 10 0.12 Nickel Sulfide precipitation 0.05 Selenium Hydroxide precipitation at pH 11 0.1 Zinc

35 On-Site Treatment Biological Treatment
Essential if BOD > 50 mg/L Expect BOD removal SS removal with sedimentation NH3-N and Org-N removal by biouptake and nitrification Metal removal by biosorption and precipitation at oxides and carbonates Priority organics removal

36 On-Site Treatment Biological Treatment Process Types
Biomass in Suspension No Biomass Recycle Facultative pond, aerated lagoon Biomass Recycle Activated sludge Biomass Attached RBC, packed bed filter, trickling filter

37 Leachate Biodegradation Phases
Phase 1: Removal of high M.W. humic carbohydrate-like organics - adsorption to microorganisms Phase 2: Removal of free volatile fatty acids - decrease in ORP, conductivity, and DO Phase 3: Formation of intermediates - excretion of high M.W. humic carbohydrate-like organics Phase 4: Removal of high M.W. humic carbohydrate-like organics

38 Composition of Biologically Treated Leachate Effluent (1)
Schmitzer and Kahn (1972) Polymerized waste product Inert material from lyzed cells 20~50% of effluent COD (M.W.: 500~30,000) Reduced removal of heavy metals due to chelation Reduced removal of pathogens Source of color

39 Composition of Biologically Treated Leachate Effluent (2)
Painter et al. (1961); Bunch et al. (1961) Humic material: 65~75% High molecular weight: 21~49% Rebhun and Manka (1971) Humic substances: 39~45% Hurst and Burges (1967) Refractory organics: humic acid (M.W ~100,000); fulvic acid (2,000~10,000)

40 Composition of Biologically Treated Leachate Effluent (3)
Barker and Somers (1970); Finch et al. (1972) Certain high M.W. carbohydrates alone or in combination with humic material are resistant to microbial attack, which were isolated from exocellular polysaccharides. High M.W. carbohydrates were excreted at the end of the logarithmic growth phase and appeared to help forming flocs by bridging of bacterial cells.

41 Leachate Treatment Performance R.F. Weston Inc. (1974)
Biological treatment No COD decrease after 184 hrs of aeration (COD/TOC=2.1; BOD/COD=0.03) Activated carbon 59~94% COD removal - impractical Good for old stabilized leachate treatment Ozonation 22% COD removal after four hour test Not promising because of strong resistance of fatty acids, especially acetic acids, to ozone

42 On-Site Treatment Biotreatability - Aerobic, Suspended
BOD (COD), mg/L Retention Source In Out Time, day Boyle & Ham 2, Uloth & Mavinc¶ 36, Chian & DeWalle (35,200) (1,030) 7 Spencer & Farqunar (15,200) (260) 10 pH Fe, mg/L % removal Zn, mg/L % removal Cd, mg/L % removal Pb, mg/L % removal Ni, mg/L % removal • Moderate inhibition in a few cases, 20~24°C, lime & PO4 added

43 Buckden South Landfill Site, Cambridgeshire

44 Gairloch Landfill Site, Northern Scotland
Bryn Posteg Landfill Site, Wales

45 On-Site Treatment Biological Treatment - Field Example (1)
Posteg Landfill, Wales, UK PO4 (nutrient) Aerated pond Lined HDPE V = 1,000 m3 HRT = 10 days F/M  0.25 Temp. = 4C Facultative pond Settling: SVI = 40 Sewer 0~150 m3/d Sludge to landfill

46 On-Site Treatment Biological Treatment - Field Example (2)
Posteg Landfill, Wales, UK Contaminant Influent Effluent Peak Ave. BOD5, mg/L > 10,000 3,700 24 NH3-N, mg/L >1, Fe, mg/L > pH Cost Capital - $120,000 (1985) O&M - $1/1000 gal Sewer surcharge without treatment - $9/1000 gal Savings - $68,000/yr

47 On-Site Treatment Biological Treatment - Field Example (3)
Grows Landfill, Tullytown, PA EPA supported demonstration project Data source: Steiner & Fungaroli (1979) Conditions: Landfill - 50 acre, 800 ton/day, 85% MSW Treatment to meet sewer standards Flow: variable, ave. 10~15 gal/min Operating problems: NH3-N toxicity PO4-P deficiency Winter: reactor temp. 35°F

48 On-Site Treatment Biological Treatment - Field Example (4)
Grows Landfill, Tullytown, PA CaO Chemical Treatment • Mixed reactor • Sedimentation HRT = 1 day pH 10.5 Metallic sludge Ammonia Stripping • Aerated pond HRT = 1.8 day NH3-N H3PO4 Activated Sludge • Biomass recycle pH = 7.5 F/M = 0.3 Biosludge Cl2 Chlorination N2 Sewer

49 On-Site Treatment Biological Treatment - Field Example
Grows Landfill, Tullytown, PA Efficiency (average) Parameter Concentration, mg/L % removal Standard Influent Effluent BOD , NH4-N SS Fe Cl- - 3,172 2,925 -

50 On-Site Treatment Aerobic Biological Treatment - Design
Loading: F/M < 0.3 kg BOD/kg VSS/day SRT > 10 days (20°C); 20 days (10°C) Sludge production: 1 kg TSS/kg BOD removed O2 supply: high for young leachates PO4-P supplement: usually required NH3-N conversion: biomass uptake at BOD:N:P = 100:5:1; nitrification may dictate design for old leachate, may be inhibitory at high conc. Recycle of biomass: not required for high strength leachate Precipitate formation: CaCO3 & Fe2O3 can coat pump impellers and aeration components Sequencing batch reactor (SBR): < 100 m3/day SRT: Solids retention time

51 On-Site Treatment Anaerobic Biological Treatment (1)
Comparison of Anaerobic vs. Aerobic If BOD5 > 1,000 mg/L, then No O2 required Lower biomass produced CH4 is useable Anaerobic Aerobic Remove NH3-N Increase BOD & SS removal

52 On-Site Treatment Anaerobic Biological Treatment (2)
Anaerobic Fixed Film Reactors (AFFR) Films better than digesters Biomass washout reduced Higher loading possible Kinetically better Experience Field - limited, WMI, Milwaukee Laboratory: support medium - granular carbon, plastic film, sand, plastic rings; COD removals - 90~97%

53 On-Site Treatment Composite System
SW: 700 ton/day; Leachate: 80 m3/day Raw Leachate A CaO Neutralize pH Precipitate metals Chemical Precipitation Sludge B PO4-P BOD removal, 32°C Plastic rings 4 kg COD/m3/day Anaerobic Fixed Film Reactor CH4 BOD removal 70 day HRT, 20°C Nitrification Aerated Lagoon C Facultative Pond SS removal 70 day HRT, 20°C Denitrification D Effluent

54 On-Site Treatment Composite System
Treatment Efficiency - Pilot Scale Type A B C D COD 22, BOD5 16, TOC 8, Humic Acid NH3-N Fe Zn Ca 1,740 2, Cl- 1, ,015 1,080 SO Alkalinity 3,850 4,200 2,563 1,800 TDS 15,300 19,200 4,220 4,215 pH

55 On-Site Treatment Anaerobic Upflow Filter
Omega Hills Landfill, Milwaukee, WMI (1987) Designed for discharge into a POTW V = 200,000 gal HRT = 2 days Mixer Holding Tank Heat Exchanger (Landfill/Filter Gas) V = 56,500 ft3; HRT = 7.4 day; Loading = 442 lb/day/1000 ft3; Media depth = 20 ft; T = 95°F; Dia. = 20 ft; Qr/Q = 10/1 Filter Media Dia. = 30 ft POTW Solids Contact Clarifier Dia. = 30 ft

56 Omega Hills Landfill Leachate
Treatment Facility

57 On-Site Treatment Omega Hills Landfill Operation
Design Conditions Field Conditions 100,000 gal/day (Flow) ,000~30,000 gal/day 38,000 mg/L (BOD) ,000 mg/L (ave.) 900 lb/day/1000 ft3 (Loading) lb/day/1000 ft3 Excellent Treatment Contaminant Influent Effluent BOD 3,700~24, ~700 TSS 2,500~15, ~500 Cd Cu Pb Ni Zn Seeded with manure Underloaded - needs other high strength organic wastes

58 On-Site Treatment Physical/Chemical Processes
Used with bioprocesses except for old leachate (BOD5 < 50 mg/L) and contaminated groundwater Processes For Removal of Carbon Adsorption Nonbiodegradable organics: solvents, pesticides, humic acids, etc. Chemical Precipitation Heavy metals: Fe, Zn, etc. Suspended solids Air Stripping NH3-N Volatile solvents Granular Filtration Suspended solids Membranes - Conservative: organics, irons: Cl reverse osmosis Na+, etc.

59 On-Site Treatment Physical/Chemical Processes
Addition of simple chemicals followed by a sequence of mixing, coagulation/flocculation, and settlement Chemicals tested: Hydrated lime Quick lime Sodium hydroxide Magnesium hydroxide Alum Ferric chloride Ferric sulfate Polymeric coagulant aids

60 On-Site Treatment Physical/Chemical Processes - Examples
Lime Influent Chemical Precipitation Precipitate metals Sedimentation Settle precipitates Sludge Backwash Clarify influent to carbon adsorption Granular Filtration Adsorb TOC and solvents Carbon Adsorption Carbon regeneration plus afterburner at 1200°C Destroy TOC and solvents Effluent

61 On-Site Treatment Reverse Osmosis
Leachate STORK-Wafilin,VAM, Wijster, NL 1,000,000 tons (1986) Waste disposal: mainly composting Tubular, cellulose- acetate Concentrate Ultrasil® - cleansing Oxonia® - disinfection Spiral wound, composite Costs Capital: $2.5 106 (US, 1988) Operating: 1.4¢/gal (US, 1989) Permeate Stream Landfill > 80% Liquid < 20% < 2% Contaminants > 98%

62 On-Site Treatment RO Performance (1989)
Parameter Leachate Permeate Concentrate (estimated) Flow , gpm (35) COD, mg/L 2,860 3 (15,000) BOD, mg/L (1,100) TKN, mg/L 955 5* (4,700) Cl, mg/L 3,160 7 (15,500) Zn, mg/L (3.0) Cu, mg/L (0.7) Ni, mg/L (3.5) AOX**, mg/L * Does not meet discharge standard ** Adsorbable Organic Halides Potential Concentrate Treatment • Evaporation (30% solids) + heat drying (96% solids)

63 Millersville Leachate Treatment Facility

64 Millersville Landfill Leachate Treatment Facility Design and Operating Parameters
Item Value Flow (gpd) 25,000 Reactor volume (gallons) 224,100 Hydraulic residence time (days) 2.48 Sludge age (days) 25 MLVSS (mg/L) 4,000 Loading (F/M) (g COD/g VSS/day) 0.2 Nutrients (COD:N:P) 100:2:0.38 Sludge yield (g VSS/g COD) 0.3 Aeration type Fine bubble

65 Projected Leachate Quality and Discharge Standards
Korean Leachate Treatment Facilities Constituent Influent Effluent (mg/L) (mg/L) COD BOD Ammonia Nitrogen Total nitrogen N/A 100 TSS N/A 30 Q = 6,500 m3/day

66 Proposed Leachate Treatment
Chemical Precipitation Equalization Tank Air Stripping Leachate Chemical Remove ammonia (optional) Equalize flow Remove heavy metals and solids (optional) Reed bed Chemical SBR Discharge Sludge wasting Polish the effluent Remove organics, ammonia, nitrite/nitrate, and toxic compounds

67 Cost Estimates No fertilizer Fertilizer No NH3 stripping Design Services 1. Preliminary $165,000 $165,000 $165, Final $636,000 $636,000 $636,000 Construction 1. Mechanical $34,000,000 $36,000,000 $32,500, Wet lands $6,000,000 $6,000,000 $24,300,000 Start-up & Training $124,000 $124,000 $124,000 Total Cost $40,955,000 $42,955,000 $57,755,000

68 Landfill Leachate Treatmen Decisions
New/Young Landfill Neutralization (NaOH, lime, pH = 7.5) Biological Treatment Anaerobic (UASB) Aerobic (long SRT) Activated Sludge Sequencing Batch Reactor (SBR) Nitrification/Denitrification Disinfection Membrane Process/Activated Carbon Old Landfill: eliminate UASB Biological Sludges & Concentrations: landfill, POTW POTW Land Large surface water Small surface water

69 Aerobic Landfill Bioreactor

70 Landfill as a Bioreactor
Measure of Success Faster landfill stabilization Increased air space Reduced leachate management costs Reduced gases and odors Reduced long-term care costs Possibly, mining to regenerate cover material - a perpetual landfill?

71 Leachate Recirculation (1)
Can be used during the early stages when leachate production quantities are low. Can be used in later stages to eliminate problems of off-site transport during peak production periods or during downtimes of the transport devices. Advantages Attenuation of leachate strength/quantity Increased rate of landfill stabilization Enhanced gas production rates Immobilization of metals from landfill material Improved landfill settling rates Increased compaction rates

72 Leachate Recirculation (2)
Disadvantages Ponding/localized accumulation of leachate Severe localized subsidence/side slope stability problems Other management requirement due to excess leachate production Selective attenuation of contaminants recirculation, thus further treatment required Mass/fluid transfer limitation


74 Leachate Recirculation (3)
Methods of Recirculation Spray irrigation Working face application Gravity well/trench Injection well/trench Infiltration ponds

75 Typically Proposed Recirculation Leachate Distribution System
Soil cover Pump Waste Clay/geomembrane liner system Leachate collection system

76 Spray Irrigation Advantages Good coverage
Moderate weather restrictions Subject to evapotranspiration Easily adjusted for settlement concerns Disadvantages Subject to plugging Sophisticated design and construction Subject to freezing Surface water contamination potential

77 Injection Needles Advantages Portable Good coverage
Moderate design, construction requirements Moderate weather restrictions Easily adjusted and maintained Disadvantages Potential crushing of pipes Subject to freezing Surface water contamination potential (thru pipe leaks), limited use after capping

78 Surface Application Advantages Simple design
Most evaporation potential Good coverage Low capital investment Least subject to plugging Easily accessed for maintenance Disadvantages Odor Weather restrictions (wind, rain) Health risk Surface water contamination risk

79 Vertical Wells Advantages Minimal weather restrictions No odor
Simple design Easily combined with horizontal distribution lines Disadvantages Poor coverage w/o horizontal distribution Susceptible to differential settlement damage Subject to plugging Subject to short circulating of leachate Difficult to maintain vertical levelness

80 Horizontal Wells/Trenches
Advantages Fair to good coverage Minimal weather restrictions Disadvantages More sophisticated design and construction required Susceptible to differential settlement damage Virtually impossible repair or maintenance

81 Leachate Recirculation
Refuse Kv < Kh → Vertical injection wells better Not good for well-compacted refuse with a substantial component of soils or waste of low K. Clogging may occur when leachate is recirculated through horizontal pipes beneath the cap. The leachate should be spread uniformly over the landfill surface through a network of piping. Leachate spraying (similar to spray irrigation) has caused problems of odor and blowing of leachate. Prewetting of refuse and surface ponding have been used with mixed success.

82 Full-Scale Leachate Recirculation Hydraulic Application Rates
Recirculation method Application rates Pre-wetting 48 gal/ton or 1000 lb/yd3 Vertical injection wells a. 1 to 2.5 gpm/2.5-inch diameter well 1.7 to 4.1 gpd/ft2 landfill area b. 20 to 200 gpm/4 ft diameter well 0.12 to 2.3 gpd/ft2 landfill area Horizontal trenches 25~50 gpd/ft of trench length at 60 to 100 gpm Surface ponds 0.13~0.19 gal/ft2/day Spray irrigation 18 gpd/ft2 of landfill area 0.025 to gpd/ft2 of landfill area Source: Reinhart, D.R. and Carson, D. (1993). “Experiences with Full-Scale Application of Landfill Bioreactor Technology,” Solid Waste Association of North America, Preprint, SWANA, Silver Spring, MD.

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