Browsing by Author "Daneel, Richard A."

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Development of a code of practice for co-disposal to obviate inimical environmental impacts of generated gases and leachates.
(1996) Daneel, Richard A.; Senior, Eric.
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.
Preliminary investigation of nutrient supplementation of, and heavy metal mobilization by, dual (phenol/activated sewage sludge) co-disposal with refuse.
(1999) Ehlers, George A. C.; Senior, Eric.; Daneel, Richard A.
Investigation of landfill co-disposal technology, with emphasis on nutrient supplementation and heavy metal mobilization, was made. For the purpose of this study, co-disposal is defined as the combined disposal of wastewaters and/or sludges with refuse. It is, currently, the most cost-effective method of waste treatment and disposal. To assess whether refuse could be characterized as nutrient limited and to determine the effects of nutrient additions on the refuse solid-state methanogenic fermentation, nutrient supplementations were made to refuse (control), co-disposal (activated sewage sludge with refuse) and dual co-disposal (activated sewage sludge plus phenol with refuse) microcosms. The results showed that the domestic refuse used was not nutrient limited. For the controls, previously reported solid-state fermentation patterns resulted. Self-generating redox gradients were established with concomitant reductions in leachate Chemical Oxygen Demand and initiation of sulphate reduction. Thus, hydrogen sulphide and methane were both evolved. In contrast, nutrient supplementation, particularly with macronutrients and macronutrients plus trace elements, effected fermentation imbalances such that protracted low pH values and high volatile fatty acid concentrations were apparent. Redox gradient generation was slowed which militated against sulphate reduction and the onset of methanogenesis. In the absence of nutrient supplementation, low residual phenol concentrations characterized the dual co-disposal microcosms whereas elevated concentrations persisted in the equivalent nutrient supplemented microcosms. To investigate the implications of heavy metal retention / mobility during landfill co-disposal operation, microcosms were packed with "young" synthetic refuse and/or activated sewage sludge at packing ratios of 4.1:1 (1) or 4.1:2 (2). The sludge was "spiked" with each of four heavy metals, Cr(3+), Cu(2+), Ni(2+) and Zn(2+), to a concentration of 100 mg ⌠(1) (refuse/sludge ratio 1) or 200 mg ⌠(1) (ratio 2) while the control received the same concentrations of metals dissolved in distilled water. The heavy metal concentrations were increased progressively to 800 mg ⌠(1) (ratio 1) and 1 600 mg ⌠(1) (ratio 2). For all the microcosms, including an unperturbated control, unbalanced fermentations (acidogenesis > acidotrophy) resulted as evidenced by the low pH values. Thus, heavy metal toxicity was not the sole cause. The leached metal concentrations were in a consistent order with high Zn and Ni concentrations detected compared with immobilized Cr and Cu. After 15 weeks of operation with the higher applied loading, despite extensive retention, increases in Cr, Ni and Zn were detected in the microcosm leachates. Due to the elevated redox potentials, precipitation of the metals as insoluble sulphides was not operable. After 28 weeks of operation, microcosm depth samples (15, 25 and 40 cm) were collected and analysed for immobilized metals. Chromium was characterized by maximum retention at a depth of 15 cm. In contrast, nickel concentrations were comparable throughout the refuse/sludge profile while no specific adsorption patterns emerged for Cu and Zn. The implications of these findings in relation to co-disposal landfill site operation are discussed.