Formation Composition and Management of Leachate.

LeachateIt is the contaminated liquid generated by sanitary landfills.It is a liquid that has percolated through solid waste and has extracted, dissolved or suspended materials.Sometimes it consists of liquid that has entered the landfill from external sources like surface drainage, rainfall as well as liquid from decomposition of SW. Leachate is the liquid that accumulate at the bottom of the landfill

Composition and Properties of leachateThe amount of leachate generated depends uponWater availability precipitation, surface runoff, waste decomposition, liquid waste disposal.Landfill surface condition, Refuse stateCondition of surrounding strata.

Composition and Properties of leachateThe potential for formation of leachate can be assessed by preparing a water balance on the landfill.It involves summing the amount of water entering the landfill and subtracting the amount of water consumed in chemical reactions and the quantity leaving as water Vapour.

Composition and Properties of leachateL = I E aWL= free leachate retained at siteI = Total liquid inputE = evaporation lossesa = Absorption capacity of wasteW = weight of waste disposal.

Composition and Properties of leachateTotal liquid input WaterTotal liquid input is-Water entering the landfill cell from aboveMoisture in the solid wasteMoisture in the cover materialMoisture in the sludgeWater it is the water leaving the landfill as vapor along the landfill gas.

Composition and Properties of leachateWater in solid waste = water entering the landfill with waste material i.e moisture in SW, rainfall content .Water in cover material It depend upon Type and source of cover materialSeason

Composition and Properties of leachateWater from above.Precipitation percolated through cover material.Water lost in the form of landfill gasWater lost as water vapor it is related to mass of water contained per cubic feet of landfill gas.Water lost due to evaporation

Composition of leachate

When water percolates through SW that are undergoing decomposition, both biological material and chemical constituents are leached into solution.Chemical composition of leachate will vary depending upon age of the landfill.Biodegradability of leachate vary with time.

Composition of leachate

If leachate sample is collected during acid phase pH will be low, BOD, COD will be high.If leachate sample is collected during methane fermentation phase pH will be 6.5- 7.5.BOD,COD will be low.pH of leachate is not only depends on the acids but also depend on partial pressure of carbon dioxide in the landfill gas which is in contact with leachate.

Composition of leachate in new and mature landfills.

ConstituentNewLandfillMature LandfillRangeTypicalpH4.5-7.567.5-8BOD2ooo-30000mg/lit10000mg/lit100 200mg/litCOD3000-6000018000100-500Total organic carbon1500- 20,000600080-160organic nitrogen10-80020080-120Total suspended solids200- 2000500100-400

Composition of leachate in new and mature landfills

ConstituentNewLandfillMature landfillAmmonia nitrogen10-80020020-40Nitrate5-40255-10Total phosphorous5-100305-10Alkalinity1000-100003000200-1000Hardness3000-100003500200-500Calcium200-30001000100-400Magnesium50-150025050-200Potassium200-100030050-400Sodium200-2500500100-200Chloride200-300030020-50

Movement of leachate

Under controlled condition leachate is found at the bottom of the landfill.From there its movement in unlined landfills is through underlying strata.As leachate percolates through underlying strata, chemical, biological constituents originally contained in it will be removed by filtering and adsorptive action of the material strata.

Control of leachate in landfillsDue to potential risk involved in allowing leachate to percolate to ground water, its elimination /containment is the best practice.The best way to control leachate is through prevention.It is necessary to control liquid access.Surface water can be controlled and diverted away from landfill by proper grading.6-12% slope of daily cover will allow water to drain freely from the landfill.

Control of leachate in landfillsConcrete lined channels /drainage ditches can be constructed around the perimeter of the site to divert upland rainfall and to collect surface runoff from the site.

Final cover/cap at the top of completed landfill is constructed so that it is impermeable and prevents infiltration of rainwater directly on landfill areas.it is designed and graded to keep away from burried waste.

Control of leachate in landfillsThe cap typically consists of soil layer -24 inches thick with 3-5% slope. It should be underdrain by a sandy soil drainage layer and flexible membrane liner with low permeability soil layer.

Control of leachate in landfillsThere are two ways to prevent leachate problems at a landfill1. Intercept and channel surface runoff to prevent it from entering the landfill.2. Provide suitable type of impermeable barrier/liner between the waste and underlying aquifer.

Control of leachate in landfills

Leachate Collection

Leachate collection- Leachate is directed to low points at the bottom of the landfill through the use of an efficient drainage layer composed of sand, gravel or a geosynthetic material.Perforated pipes are placed at low points to collect leachate and are sloped to allow the moisture to move out of the landfill.It consists of landfill liners, leachate holding facilities, leachate removal faclilties.

Leachate Collection

Landfill liners The objective in the design of landfill liners is to minimize the infiltration of leahate into subsurface soils below the landfill to reduce the GW contamination.Natural liners These refer to compacted clay. These are generally less permeable, resistant to chemical attack and have good sorption properties.Disadvantage do not act true contaminant barriers as leachate migrates through them.

Landfill Liners

Landfill liners

Landfill liners

Landfill liners

Leachate collection

Leacahte Collection

Leachate collection

Leacahte Collection for Secure landfill

Landfill linersSynthetic (geo-membrane)liners These are made up of high density polyethylene(HDPE). Less permeable, easy to install, strong.Sometimes expand/shrink according to temperature and age.The composite liners made up of synthetic material over 600mm( 24in) clay.This forms impermeable barrier which prevents leachate from mixing with ground water.

Landfill LinersSynthetic (geo-membrane)liner Clay must have hydraulic conductivity less than 1 10mm/s.It means any water /leachate enters the clay will flow at a rate less than one millionth of mm/sec. ( 30mm/year)

Landfill linersMultilayer landfill liner It consists of clay layer, Geomembrane serves as a composite barriers to movement of leachate and landfill gas.The sand layer serves as collection and drainage layer for any leachate generated within the landfill.Geotextile layer is used to minimize the intermixing of soil and sand layers. It consists of synthetic membrane + net clothFinal soil layer is used to protect the drainage layer.

Construction of clay liners Great care must be exercised in the construction of clay layer.Most serious problem with the use of clay is its tendency to form cracks due to desiccation.The clay liners should be laid in 4-6 in. layer with adequate compaction between the placement of succeeding layers.Same type of clay must be used as cracking can oocur due to diferential swelling of different types of clay

Leachate collection facilities -It is accomplished by using series of slopes , terraces and system of collection pipes.Terraces are sloped so that the leachate accumulating on surface of terraces will drain to leachate collection channels.Perforated pipe placed in each leachate collection channel is used to convey the collected leachate to a central location from there it is removed for the treatment/ reapplication to the surface of landfill.

Leachate Collection Pipe

The slope of the terrace is 1-5% slope of drainage channels is 0.5-1% The design objective is not to allow the leachate to pond at the bottom of the landfill.The depth of flow in the perforated drainage pipe increases from upper reaches of drainage channels to lower reaches.

Leachate removal and holding facilitiesLeachate collection pipe is passed through sides of landfill.Seal where the pipe penetrates the landfill liner.Use of inclined collection pipe located within the landfill.Leachate collection facilities are used where the leachate is to recycle/ treated at central location.In some cases leachate is collected in holding tank.

Leachate ManagementLeachate recyclingLeachate evaporationTreatmentDischarge to municipal waste water collection system.

Leachate recyclingDuring early stages of landfill operation leachate will contain significant amount of TDS, BOD,COD.when it is recirculated simple organic acids in leachate will converted to methane and carbon dioxide.Additional benefit is the recovery of landfill gas.Rate of gas production is greater in leachate circulation system.

Leachate evaporationIt involves use of lined leachate evaporation ponds. Ponds are uncovered in summer.Storage and disposal by spray on nearby lands in summer.If enough land is available, spraying of effluent is carried out on continuous basis.

Leachate treatmentBiological treatmentIt removes BOD and ammonia.common methods are aerated lagoons, activated sludge process.Discharge sludge is recirculated and used for removal of BOD and ammonia.

Anaerobic treatment-Anaerobic filtersAnaerobic digesters.Physicochemical treatmentSeparation of flocks by sedimentation, AdsorptionReverse osmosis.