A fill of wastes

-- 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.