Molecular microbiological approach to the nitrogen cycle-related communities in the wetlands of the AIT wastewater treatment plant | |
| Author | Nguyen Tran Thien Khanh |
| Call Number | AIT Thesis no.EV-04-17 |
| Subject(s) | Sewage disposal plants Molecular microbiology |
| Note | A thesis submitted in partial fulfillment of the requirements for the degree of Master of Engineering, School of Environment, Resources and Development |
| Publisher | Asian Institute of Technology |
| Series Statement | Thesis ; no. EV-04-17 |
| Abstract | The study presents a pioneering effort in molecular microbiology of the natural treatment systems (NTS). The microbial mechanisms are partially elucidated with a view to understanding N-removing performance of the integrated free water surface flow constructed wetland of the AIT WWT plant. Fluorescence In Situ Hybridisation (FISH) was the main technique used as a tool in the present study. Though employed extensively in the activated sludge and anaerobic digestion research, it is still to receive its dues in the field of NTS. The study strives to address this imbalance. Analysis of the fate of the N species in the downstream and upstream wetland sections revealed an erratic pattern of the N-removal. On one hand, over the period from April to July 2004 the wetland system did not seem to perform satisfactorily in terms of decreasing amount of ammonia released from the system with the final effluent. On the other hand, it was observed that at least during the period, which appears to roughly coincide with the dry season (December 2003- April 2004) and characterized by a different hydraulic regime (HRTwetland = 5.0 days), the wetland system showed a markedly improved removal ofN. The FISH analysis employing 8 different probes have revealed profound changes occurring microbiologically when one moves downstream in the wetland sections, namely, from section A to B. It was observed that during the period coinciding with the dry season numbers of bacteria belonging to the major taxa a- and ,8-proteobacteria (comprising critical nitrification-related bacteria: ammonia-oxidizers, specific to the Nso1225 probe and nitrite-oxidizers, the NIT3 probe) decrease. This appears to indicate the progressively increasing environmental pressure on nitrification. Overall, it can be concluded that molecular microbiological profiling of the wetland appears to corroborate biogeochemical monitoring data and conclusively indicate that the free surface flow wetland which is due to its nature should be characterized by aerobic/anoxic conditions is in fact currently characterized by the anaerobic/oxic conditions. It was observed that the cattail plant biomass harvested irregularly at the wetland was left in the wetland channels where it has inevitably rotten and leads to a significant anaerobiosis. As a result plant organic matter protein decomposed with a concomitant sulfate reduction. The partial harvesting of cattail plants took place in late March and sporadically continued through April and May, which loosely coincided with marked decrease in nitrification. Nevertheless, irregular but sometimes fairly reasonable Nremoval takes place with overall 6.5 mg N/L removed from the influent (approx. 0.014 kg TN/m3/day). Analysis of the biogeochemical monitoring in conjunction with the molecular microbiological data lead us to a preliminary conclusion that one of the main factors contributing to the malfunction of the AIT wetland is improper harvesting of the vegetation in the wetland channels. It is strongly recommended in future to remove harvested vegetation from the wetland channels and it would be highly beneficial for the N-removal to clean the channels of the decaying biomass accumulated over the years of the wetland operation. The molecular microbiological data obtained will further our understanding of the free surface flow wetlands, the most complex of all the waste water treatment systems. |
| Year | 2004 |
| Corresponding Series Added Entry | Asian Institute of Technology. Thesis ; no. EV-04-17 |
| Type | Thesis |
| School | School of Environment, Resources, and Development (SERD) |
| Department | Other Field of Studies (No Department) |
| Academic Program/FoS | Environmental Engineering and Management (EV) |
| Chairperson(s) | Shipin, Oleg V. |
| Examination Committee(s) | Nguyen Cong Thanh; Satoh, Hiroyasu; Preeda Parkpian |
| Scholarship Donor(s) | AIT Fellowship |
| Degree | Thesis (M.Eng.) - Asian Institute of Technology, 2004 |