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Dissertation
The effects of cyanide and chloroform toxicity on methane fermentation
Doctor of Philosophy (Ph.D.), Drexel University
1981
DOI:
https://doi.org/10.17918/00007571
Abstract
Methane fermentation has proven to be an effective wastewater treatment process. However this process is generally considered to be easily upset by many toxicants which occur occasionally or chronically in industrial wastewaters. This research is an investigation of the response of methane fermentation to toxicity and a direct challenge to the concept that the process cannot tolerate toxicity without process failure. Cyanide and chloroform were selected as sample toxicants for this study. The factors which affect the toxicity of cyanide and chloroform in the methane fermentation process were: type of toxicant, concentration of toxicant, SRT, biomass concentration, toxicant exposure time, cell age, toxicant administration pattern and temperature. The recovery patterns demonstrated that the methanogens could acclimate and recover from cyanide and chloroform concentrations which were heretofore considered lethal. Prolonged periods of no methane production were not indicative of ultimate process failure. With an increasing toxicant concentration pattern, methane fermentation could acclimate to 30 mg/l of cyanide or 15 mg/l of chloroform in CSTR systems. With chloroform toxicity, recovery was faster at the higher SRT levels associated with higher biomass concentrations than for lower SRT levels. The recovery of methane fermentation from cyanide and chloroform toxicity at 35(DEGREES)C was faster than at 25(DEGREES)C. With acclimation, the anaerobic filters could acclimate to 20 and 40 mg/l of cyanide or chloroform at an acetate utilization rate of 3 gm/l-day. One day slug doses of 500 mg/l cyanide and 200 mg/l chloroform were administered to acclimated anaerobic filters of one day hydraulic detention time (HRT). Severe inhibition of methane production resulted the following day, but complete recovery of methane production was observed four to ten days later. The anaerobic filter provides three major advantages over the CSTR when treating wastewaters containing toxicants: (1) higher inherent SRT, (2) higher biomass concentration and (3) a plug flow mode that can pass slug doses of toxicants quickly, resulting in shorter toxicant exposure time to the biomass. These three factors offered positive resistance to toxicity. Cysteine, hydroxylamine, thiosulfate and dithionite all reduced cyanide toxicity to methanogens. Activated carbon only temporarily relieved chloroform toxicity in methane fermentation. After acclimation, the kinetic coefficients for methanogens exposed to cyanide and chloroform were not significantly different from the kinetic coefficients of the controls. The fate of cyanide or chloroform in methane fermentation was mainly due to washout and washout and gas stripping respectively. The recovery of methane fermentation from cyanide or chloroform was mainly by microbial acclimation and was not correlated with any residual "threshold" concentration of cyanide or chloroform which existed in the liquid phase at the time of gas production recovery.
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Details
- Title
- The effects of cyanide and chloroform toxicity on methane fermentation
- Creators
- Chia-Hwa Joseph Yang
- Awarding Institution
- Drexel University
- Degree Awarded
- Doctor of Philosophy (Ph.D.)
- Publisher
- Drexel University; Philadelphia, Pennsylvania
- Number of pages
- xiii, 230 pages
- Resource Type
- Dissertation
- Language
- English
- Academic Unit
- Drexel University
- Other Identifier
- 991021888845204721