Experimental investigation of nutrient requirements : EPS production and VOC inhibition on methane oxidation in tropical landfill cover soils | |
| Author | Wilai Chiemchaisri |
| Call Number | AIT Diss. no. EV-00-2 |
| Subject(s) | Landfill gases Methane |
| Note | A dissertation submitted in partial fulfillment of the requirements for the degree of Doctor of Technical Science., School of Environment, Resources and Development |
| Publisher | Asian Institute of Technology |
| Abstract | Emission of methane from landfills has brought public awareness of its global warming effect due to the fact that the global warming potential of methane is about twenty times greater than that of carbon dioxide. The microbial activities in landfills are complex and interrelated, particularly within the cover soil layer in which the oxidation of methane takes place in the presence of naturally occurring methanotrophs. This natural microbial activity may be the alternative inexpensive way to control methane emission from landfills. Aims of this study emphasized the investigation of the interaction between methanotrophic activities and the soil environment for better understanding in designing a final cover of landfill especially in tropical regions. Simulation of actual landfill cover soil was conducted by purging a synthetic landfi II gas through a lab-scale soil column. Changes in the biochemical characteristic of soil profiles in lysimeter were studied. In addition, soils taken from the lysimeter were used in batch experiments. The batch experiments were performed in t\VO parts. Part one: investigation of biological activity in soil with methane oxidation in three aspects: 1) changes of soil characteristic and interrelated microorganisms; 2) extracellular polysaccharide (EPS) production by methanotrophic metabolisms in various conditions; and 3) effects of soil nutrient contents, organic matter contents and oxygen to methane ratios on the methane oxidation . activity (MOA). Part two: investigation of the effects of toxic compounds on the methane oxidation activity. The toxic compounds employed were trichloroethylene (TCE), perchloroethylene (PCE), benzene and dichloromethane (DCM). They are volatile organic compounds (VOCs) frequently found in landfill gas. In the lysimeter, profiles of methane gas inside the soil column substantiate the fact that there \·Vas a decline of methane oxidation efficiency during the experimental period. The methane oxidation capacity calculated for the 10111-month profile was 0.414 g/m2-d as compared to 6. 16 g/m2-d of the 211d-month profile. Soil constituents profiles showed that EPS was significantly accumulated in methane oxidation zone (I 0-35 cm) and highest content found nearly soil surface (0-10 cm). Methanotrophs may be the EPS producer. Methylomonas metlwnica was identified as the dominant type of methanotrophs growing inside the methane oxidation zone in the soil lysimeter. The microbial EPS served as the binding agents of soil particles, vvhich could cause soil aggregation and result in blockiog oxygen transfer from the atmosphere. Beside, elevated levels of ammonium contents and 10,;i.1 levels of nitrate contents were found in the soil column. An imbalance of N-nutrients might also affect the methane oxidation rate. Conceivably, the combined effect of EPS and N-nutrients might adversely affect the methane oxidation efficiency in landfill cover so il. In part one of batch experiments. It was found that total organic matter (TOC) and EPS in soil \·Vith methane oxidation were increased vvith time, comparing to normal soil, due to abundant growing of methanotrophs. Nitrifying bacteria had activities interrelated to methanotrophs since they could provide nitrate for methanotrophs during methane oxidation. However, Addition of ammonium or nitrate nutrients to soil with methane oxidation more than 30 ~Lg/g Ill dry soil showed negative effects on the methane oxidation activities. Amendment of organic matter did not effect the methane oxidation activities. Oxygen was found as an important factor in regulating methane oxidation activity. At the given methane concentration, a maximum rate of MOA was found at the oxygen to methane ratio (wt/wt) of 6.5. Increasing in oxygen to methane ratios above 6.5 resulted in reducing methane oxidation rate. The EPS production in soil with methane oxidation did not related to temperature (20-45°C) however, the EPS production depended on soil water content. High EPS production was found at 17% ,;vater content. Methane and oxygen concentrations could stimulate EPS production. Increase in methane concentration, provided more substrates for methanotrophs, which could increase the methane oxidation rate subsequent ,.vith high EPS production. High EPS production found in high oxygen concentration was due to the mechanism of methanotrophs to alleviate the unfavorable conditions. In part tv.ro of batch experiments. Increase in VOC concentrations resulted in increase in the reduction of methane oxidation rate. Hmvever, their effects on the reduction of methane oxidation rate were different. TCE and DCM shov.red greater inhibition to methane oxidation rate than benzene and PCE. The reduction of methane oxidation rate caused by benzene or PCE could be due to toxicity effect, whereas the inhibition by TCE and DCM might result from the co-metabolic competitive-inhibition to methane oxidation. The cornpetitiveinhibition mechanism gave high inhibition to the methane oxidation. Soils 'vith mixture of voes were found to have greater inhibition effect to methane oxidation as compared to the soils with single VOCs. ·The significant reduction of methane oxidation rate always results from presence of DCM. Transmission electron microscope examination of the culture of methanotrophs exposed to TCE and PCE suggested adverse effect on internal structure of methanotrophic cells. This research demonstrates that EPS production; accumulation of ammonium ions and VOC exposure had negative effects on methane oxidation. These factors are recommended to be minimized in the landfill operation for sustaining the methane oxidation in landfill final cover. |
| Year | 2000 |
| Type | Dissertation |
| School | School of Environment, Resources, and Development (SERD) |
| Department | Department of Energy and Climate Change (Former title: Department of Energy, Environment, and Climate Change (DEECC)) |
| Academic Program/FoS | Environmental Engineering (EV) |
| Chairperson(s) | Visvanathan, C.;Wu, J.S. |
| Examination Committee(s) | Samorn Muttamara;Bhattacharya, S.C.;Oanh, N.T. Kim;Ahlert, R.C. |
| Scholarship Donor(s) | Ministry of University Affairs Royal Thai Government |
| Degree | Thesis (Ph.D.) - Asian Institute of Technology, 2000 |