Development of a code of practice for co-disposal to obviate inimical environmental impacts of generated gases and leachates.
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Date
1996
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Abstract
Despite its phasing out in numerous countries, such as Germany and the U.S.A.,
co-disposal of hazardous waste with municipal solid waste continues to be widely practised
in South Africa. Co-disposal utilises properties and microbial activities in the refuse to
attenuate the hazardous waste and thus obviate its environmental impact potential. All
landfill operations require careful planning in not only site selection criteria but also the
type and amount of various wastes accepted for disposal. It is clear, however, that the
practice of co-disposal requires special precautions and management as the methods
employed in the landfill operation determine to a large extent the environmental effects
and, thus, the public acceptability of the operations.
Although co-disposal is not suitable for all industrial wastes the results of recent
research efforts, conducted mainly in the U.K., have indicated that, when properly
managed, co-disposal can be regarded as a safe and efficient disposal option for many
hazardous wastes. Environmental awareness in many European countries ensures that
numerous hazardous compounds are either recycled or recovered. Unfortunately, in South
Africa the lack of similar concern has resulted in increased concentrations of toxic
compounds being co-disposed on a regular basis. Since fundamental studies of this
technology, pertaining to South African conditions, have been lacking laboratory
models/microcosms were built to address this paucity.
Model. To effect the separation of species habitat domains of component species of
growth rate-dependent interacting microbial associations responsible for terminal catabolic
processes of the refuse fermentation, with retention of overlapping activity domains, and so
facilitate examination of species in isolation without violating the integrity of each
association, multi-stage models were constructed. The accidental overgassing of the culture
with liquid petroleum gas (LPG) effected interesting fermentation balance changes which
also emphasised the need for an Anaerobic Bioassay Test to assess the impacts of specific
perturbants. Evidence of differential susceptibility of the component species to phenol was
demonstrated in this study.
Microcosm. A total of 42 refuse packed single-stage glass column bioreactors were
commissioned and subjected to phenol and/or anaerobically digested sewage sludge codisposal.
The effects of four different operational modes: leachate discard (single elution);
leachate recycle; batch; and simulated rain on the co-disposals as well as refuse catabolism
per se were examined.
The results of these studies indicated that protracted periods of adaption to phenol (1000
and 2000 mg l -1) could have resulted from nutrient (elemental) limitation. Circumstantial
evidence was also gained which indicated that the nitrate- and sulphate-reducing bacteria
(SRB) were particularly sensitive to the added xenobiotic. Further, without the effective
participation of the nitrate- and SRB the active and total fermentation of both the phenol
and refuse components were depressed. It was also determined that the operating regime
employed was a key factor in refuse degradation although with time, and especially
following the phenol resupplementations, the operating conditions played a less significant
role. In general, the single elution operated columns demonstrated increased phenol
removal rates which were, unfortunately, coincident with low pH values and increased
leachate residual phenol concentrations. Leachate recycle, on the other hand, unlike the
batch operated columns, facilitated increased pH values and methane evolutions. The
simulated rain columns were characterised by rapid washout of the added phenol as well as
methanogenic precursors.
The sewage sludge co-disposal experiments, likewise, demonstrated that, depending on
the sludge:refuse ratio, the operating regime was extremely important in optimising the
refuse degradation processes although, in general, leachate recycle appeared to be the most
favoured method of operation.
Description
Thesis (Ph.D.)-University of Natal, Pietermaritzburg, 1996.
Keywords
Waste disposal in the ground., Sanitary landfills., Refuse and refuse disposal., Environmental chemistry., Sewage disposal., Theses--Microbiology.