A special landfill site has been designed in New Zealand to exclusively handle toxic wastes. The use of a unique leachate system helps in restricting the leakage of dangerous chemicals into surrounding water bodies
LANDFILL sites earmarked for toxic waste disposal cannot be treated like just any other landfill. The waste being disposed needs to be carefully handled. And once dumped, measures to decontaminate the site should be taken (Water Report, Vol 5, No 3).
Sridhar Susarla, a researcher at the ecological chemistry and microbiology division of the National Institute for Resources ~nd Environment, Tsukuba, Japan, studied an improved version of toxic waste landfill in New Plymouth, New Zealand. The problem of contari1i- nation in this particular case arose from the fact that chemicals from the waste deposited by Ivon- Watkins Dow limited -producing phenoxy herbicides ( those which contain organic compounds of the phenoxy group) and other The top layer prevents the entry of rain water; industrial chemicals - the bottom layer contains the chemicals within leached into the ground and surface water bodies after being buried for more than seven years. There were three such locations where seepage of this kind had occurred.
To contain the prob- lem, the company called in environmental consultants to study the situation and recommend possible solu- tions. A secure toxic waste landfill in New Zealand was constructed by D' Appolonia Engineers Incorporated of the USA, specialists in chemical waste disposal. The designers decided to adopt a plan that would contain the waste on the site itself rather than trartsporting it to another site.
The adsorption and desorption characteristics of phenoxyacetic acids (an organic chemical used in the pharmaceutical, pesti- cide and dye industry) and .chlorophenols (a substi- tuted phenol that exists in three isomeric forms - ortho, para and meta; all three are used for the manufacture of dyes.) contained in the landfill led Susarla to the conclusion that the chemicals could be treated by usinR water. By passing water at a certain temperature, having a certain PH, all the chemicals could be leached completely. In the present case, the chemicals in the landfill were all water soluble to varying degrees and could therefore be removed.
A landfill measuring 60 m X 40 in x 9.5 in in area was constructed. It's main features were a double, lining consisting of a synthetic material (HDPE, or high density polymer) and low permeability soil (clay) encompassing the waste; two leachate collection systems sandwiching the synthetic layer where the lower is a back-up in the case of failure of the synthetic layer, and a groundwater sampling system. Of the two leachate, systems, the primary one has eight 100 mm, diameter HDPE pipes*ith perforations on the lower half of the pipe, the total pipe area provided is 1,500 sq in. The main function of these leachate systems is the distribution of water throughout the contaminated soil for c flection of chemicals and further treatment. On the whole, both- the top and the bottom layers are designed specially to make the landfill as secure and leak-proof as possible. This landfill design has a lifespan of 25 years by which time degradation of the chemicals is almost complete. According to Susairla, a more secure landfill site solved the immediate environmental problem, but the chemicals, remained for a long time.
Investigations were also conducted on the possibility of biological degradation of the chemicals. For the purpose, a mixed natural microbial population of Psuedomonas .- a fungal species - was obtained, from Soil inoculum. The results wCre positive because both the 'chemicals (phenoxyacetic acid and chlorophenol) degrade in the presence of the culture. In the aerobic process which was used at the site, there was a 92 per cent reduction in the toxicity of the leachate. The results of the activated sludge system - which was tried out in the laboratory - showed low concentration& of residual organic and inorganic ions, rendering the leachate non-hazardous. But, the best remediation method for leachates, both' environmentally and economically, is the activated sludge system followed by activated carbon absorption treatment. once the concentration of chemicals reaches the regulatory limit, it is legally safe for, the industry to abandon the site.
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