Leachate
The use of linings is now mandatory within the United States, Australia and the European Union except where the waste is deemed inert.
However, despite much stricter statutory controls, leachates from modern sites are often found to contain a range of contaminants stemming from illegal activity or legally discarded household and domestic products.
The physical appearance of leachate when it emerges from a typical landfill site is a strongly odoured black-, yellow- or orange-coloured cloudy liquid.
In a landfill that receives a mixture of municipal, commercial, and mixed industrial waste but excludes significant amounts of concentrated chemical waste, landfill leachate may be characterized as a water-based solution of four groups of contaminants: dissolved organic matter (alcohols, acids, aldehydes, short chain sugars, etc.
), inorganic macro components (common cations and anions including sulfate, chloride, iron, aluminium, zinc and ammonia), heavy metals (Pb, Ni, Cu, Hg), and xenobiotic organic compounds such as halogenated organics, (PCBs, dioxins, etc.).
Bisphenol A, valsartan and 2-OH-benzothiazole had the highest average concentrations in raw leachates, after biological treatment and after reverse osmosis, respectively.
In the UK, in the late 1960s, central Government policy was to ensure new landfill sites were being chosen with permeable underlying geological strata to avoid the build-up of leachate.
In the wake of European advancements, the United States increased its development of leachate retaining and collection systems.
There are many components to a collection system including pumps, manholes, discharge lines and liquid level monitors.
Natural and synthetic liners may be utilized as both a collection device and as a means for isolating leachate within the fill to protect the soil and groundwater below.
Subsurface water monitoring, leachate collection, and clay liners are commonly included in the design and construction of a waste landfill.
To effectively serve the purpose of containing leachate in a landfill, a liner system must possess a number of physical properties.
In the closing of landfills, geomembranes are used to provide a low-permeability cover barrier to prevent the intrusion of rain water.
Geosynthetic clay liners (GCLs) are fabricated by distributing sodium bentonite in a uniform thickness between woven and non-woven geotextiles.
The pipe dimensions, type, and layout must all be planned with the weight and pressure of waste, and transport vehicles in mind.
As liquid enters the landfill cell, it moves down the filter, passes through the pipe network, and rests in the sump.
Collection pipes typically convey the leachate by gravity to one or more sumps, depending upon the size of the area drained.
The design of landfill membranes is at such low volumes that they should never have a measurable adverse impact on the quality of the receiving groundwater.
The leachate may then be mixed with chemical reagents to modify the pH and to coagulate and settle solids and to reduce the concentration of hazardous matter.
Traditional treatment involved a modified form of activated sludge to substantially reduce the dissolved organic content.
Reverse osmosis applicability is limited by conductivity, organics, and scaling inorganic elements such as CaSO4, Si, and Ba.
This is because leachates contain very high ammoniacal nitrogen concentrations, are usually very acidic, are often anoxic and, if received in large volumes relative to the incoming sewage flow, lack the phosphorus needed to prevent nutrient starvation for the biological communities that perform the sewage treatment processes.
[citation needed] However, within ageing municipal solid waste landfills, this may not be a problem as the pH returns close to neutral after the initial stage of acidogenic leachate decomposition.
Many older leachate streams also contained a variety of synthetic organic species and their decomposition products, some of which had the potential to be acutely damaging to the environment.
All plants in Europe must now be assessed under the EU ATEX Directive and zoned where explosion risks are identified to prevent future accidents.
Where toxic metals and organics are present this can lead to chronic toxin accumulation in both local and far distant populations.
[13] A possible ecological threat for the aquatic environment due to the occurrence of organic micropollutants in raw and treated landfill leachates has also been reported.
Leachate can also be produced from land that was contaminated by chemicals or toxic materials used in industrial activities such as factories, mines or storage sites.
In the context of civil engineering (more specifically reinforced concrete design), leachate refers to the effluent of pavement wash-off (that may include melting snow and ice with salt) that permeates through the cement paste onto the surface of the steel reinforcement, thereby catalyzing its oxidation and degradation.
[15] A possible risk for the aquatic environment due to the occurrence of organic micropollutants in raw or treated landfill leachates has also been reported in recent studies.
