Leachate generated from wastewater treatment plant sludge disposed off in landfills can be very hazardous and difficult to deal with, since it is in liquid form and it will travel underground right into our water source systems. Thus this pose a big problem if there is no proper planning in the first place during the construction and designing stage of the aforesaid landfill site.
Generally landfill should be located as far as possible away from the communities and residential areas. Once a suitable site has been identified, further studies involving subsurface drainage and percolation should be studied in order to find out whether leachate generation will pose a problem towards underground water pollution. Once this has been determined or if local regulatory bodies require that leachate generation be controlled, then the site will probably have to be lined with a liner in accordance with the requirements. Therefore, although this seems to be like an ideal solution to incorporate a lining system introduced to the site but normally, it can be avoided if the sludge is properly treated prior to disposal to the landfill.
Cross section of a sludge landfill dug with a sloped gradient and covered with a bottom liner plus network of collection pipes.
There are several ways that we can do to ensure that the sludge before transferring to the landfill has undergone the right processes to stabilize it and make it safe and environmental friendly before it is disposed off. Generally there are three main processes involved here, first is to make sure that more amount of water is reduced by using dewatering method, another is to subject it to heat treatment and lastly is to have it undergo decomposition. There are different characteristics of the sludge that will affect the leachate that comes out from the landfill such as organic content, nutrients, pathogens, heavy metals and other toxic compounds.
The common leachate generated from wastewater sludge landfill normally has high concentrations of nutrients mainly nitrogen and phosphorus content that are not entirely removed during the stabilization processes. In addition to that, wastewater sludge also contains trace metals and organic compounds which will carry over to the leachate and worst concern is when it comes to cadmium because it will accumulate in plants until level that is hazardous to humans. Pathogens are also another problem because if this is not properly controlled and managed, it will cause outbreak of disease spread through vectors going to humans.
Coming to the subject of leachate control, basically the most common approach other than using a liner is to have a proper collection mechanism installed complete with a piping network plus a pump to transfer out the liquid and return it back to the sewage system. From here, it can undergo the same wastewater treatment plant processes and have it treated for another round of removal of contaminants. Sometimes if the landfill site is located far away from available collection system, the most viable option is to construct a small treatment facility like a package plant close to the landfill. The generated treated wastewater can then be discharged while the sludge is again sent back for disposal.