What would happen if we didn't collect and treat leachate?

Leachate is a liquid that has passed through a solid (semi-)permeable material and, in the process, has carried dissolved or suspended substances with it. Strictly in the field of waste management, leachate is the substance that has resulted from water passing (percolating) through a landfill. Water generates leachate but at the same time dilutes contaminants. The water thus entrains substances that are harmful to the environment, making it necessary to treat the leachate in special installations.

(credit: Construction Magazine)

What does levigate contain?

Leachate is the major source of wastewater generated by a municipal landfill. Leachate is made up of different organic and inorganic compounds that can be dissolved or suspended. Organic carbon, nitrogen and methane gas as well as heavy metals (Pb, Zn, Fe and Mn) precipitated in sludge are the main elements that make up leachate. Dissolved organic matter (alcohols, acids, aldehydes, sugars, etc.), inorganic components (sulphates, chlorides, ammonia, etc.), and certain halogenated organic compounds of the dioxin class are also found in the leachate.

What factors influence the composition of leachate?

The composition of the leachate is determined by several factors, but the main ones are the type of waste landfilled, the age of the landfill and the weather conditions. The leachate produced from the decomposition processes of municipal waste has a completely different composition from landfills with low organic matter content. New landfills also produce a leachate with a high, acidic pH, which decreases as the landfill ages. Of the environmental factors, rainfall and temperature are the most important.

How is leachate neutralized?  

Because of its content, leachate must be collected and treated. The most common treatment processes are: biological treatment (aerated lagoons, biofiltration, etc); chemical treatment (ozone oxidation, hydrogen peroxide oxidation, UV treatment); physico-chemical treatment (precipitation, coagulation, flocculation); membrane separation (reverse osmosis plants, nanofiltration plants). Also, if the leachate is discharged into the sewage system (a method used in the past, rarely found in modern landfills), treatment is carried out by the sewage and wastewater treatment plant.

How is leachate treated at the IRIDEX warehouse in Chiajna?

Iridex pays special attention to environmental protection. Thanks to the waterproofing system of the warehouse base and embankments, leachate infiltration into the soil/subsoil is totally prevented.

Leachate collection system consists of a network of drainage pipes, located in a washed river gravel gravel state, 450 cm thick. The installation of the absorbent drains was carried out after the sealing system had been executed, and the absorbent drains are connected to the collector pipes connecting to the homogenization basin. Further on, the collection sumps are sealed with geomembrane.

The compartments of the landfill (C1-C7) are provided with a waterproofing system of the landfill base and slopes composed of: compacted clay layer, HDPE geomembrane, protected with two layers of geotextile material inside the drainage layer of the synthetic seal, layer made of washed gravel.

The base of the landfill has been shaped in cones to allow the leachate to collect in drains located 40 m apart. The 200mm diameter absorbing drains are perforated over 2/3 of the surface at the top. The total length of the drains is 5,480 meters and in each compartment (C1 - C7) a collector drain was installed.

The leachate drainage and collection piping system ensures controlled discharge from the landfill compartments and transportation to the leachate treatment complex.

The treatment system for the raw leachate collected by the drainage systems provides transportation to three collection basins. Two of the basins are circular, with a useful storage capacity of approximately 25m3/basin (for the collection of leachate from compartments C1- C5). There is also a third tank, made of reinforced concrete, waterproofed with geomembrane, with a useful storage capacity of about 80 m3, for the collection of leachate from the active compartments C6 and C7.

Eventually, the leachate ends up in the Leachate treatment plant type PALL, which works on the principle of reverse osmosis in two stages and purifies 10m3/h of leachate. The plant can operate continuously or discontinuously. The process produces permeate - chemically and microbiologically clean water - which is discharged into a retention pond. The latter, with a surface area of 52 m2, only improves the water quality under the action of the sun's rays and existing vegetation. The concentrate from the reverse osmosis treatment plant, on the other hand, is disposed of in the waste storage compartments and used for daily cover.

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