Toxin release and distribution from microcystis aeruginosa kützing in the Bang Phra Reservoir | |
| Author | Wang, Xiaofeng |
| Call Number | AIT Diss. no.EV-02-05 |
| Subject(s) | Toxins--Thailand--Bang Phra Reservoir Microcystic aeruginosa--Thailand--Bang Phra Reservoir |
| Note | A dissertation submitted in partial fulfillment of the requirements for the degree of Doctor of Technical Science, School of Environment, Resources and Development, Asian Institute of Technology; Inter-University Program on Environmental Toxicology, Technology and Management, Chulabhom Research Institute and Mahidol University |
| Publisher | Asian Institute of Technology |
| Series Statement | Dissertation ; no. EV-02-05 |
| Abstract | A series of field surveys for assessing cyanobacterial blooms and toxin production in reservoir water was conducted to better understand the possible causes of such water blooms. Further a lab-scale experiment was also conducted to develop a biofilm technique for toxin and algae removal from the water. Two types of bioreactors; batch bioreactor and fluidized bed bioreactor were employed in parallel to determine their removal capacity through biofilm generation. In both bioreactors, granular activated carbon (GAC) was incorporated as a seeded medium. The first experiment focused on an investigation of the three kinds of heptapeptide toxins, microcystin-RR, microcystin-YR and microcystin-LR, from Microcystis aeruginosa which was the dominant alga in the Bang Ph.ra Reservoir, Thailand, over a one year period from January 2000 to April 2001. The concentrations of three toxins were found to greatly vary with locations and sampling time. Relevant water quality parameters such as light intensity, temperature, pH, dissolved oxygen, suspended solid, chemical oxygen demand, dissolved organic carbon, total nitrogen, total phosphorus, ammonia, nitrate, phosphate, total dissolved nitrogen, total dissolved phosphorus and chlorophyll a were also measured in parallel with microcystin measurements of the water samples. The relationships between water quality parameters, toxins, and chlorophyll a were established. The toxin concentrations increased in prop01tion with the increasing trend of total phosphorus, fraction of dissolved phosphorus, but were inversely correlated with water pH. Other parameters monitored did not show a strong indication under this tropical reservoir. Significant relationships between chlorophyll a and suspended solid, phosphate, nitrate and ammonia were observed suggesting that nitrogen and phosphorus are the two major nutrients strongly responsible for the growth of algae in this reservoir. From this study, it was further suggested that algal production in couple with toxin concentration mainly depended on nutrient levels present in the water body, since both light intensity and temperature were not identified as a restricting factor but rather as favorable for algal growth in the tropical reservoir all year long. Low concentrations (from 1.45 μg/l to 0.096 μg/l) of microcystins were observed throughout the whole monitoring period and might be existed as such in the future. Because of this, a health risk to local people who use this water for drinking purpose might be developed. The second section was carried out microcystins removal using a batch bioreactor. Natural eutrophicated water obtained from a fish pond was used as tested water. The bioreactor unit was simulated close to natural field conditions. In this experiment, microcystin-YR was completely degradated within a short period by the interaction process of microanimal and bacterial communities attached on the biofilm. In addition, the SS, COD and DOC resulted from algal decomposition were simultaneously removed. Micro-animals, which are able to predate Microcystis aeruginosa, were evidenced under microscopic study. Observations by scanning electron microscope (SEM), the bacteria were observed suggesting that biofilm was developed on the GAC surface. In the biodegradation process, different temperature (15°C, 20°C, 30°C and 40°C), pH (5.0, 6.0, 7.3, 8.0 and 9.0) and initial algae concentration (chlorophyll a 1375.6 μg/l, 890.7 μg/l, 427.8 μg/l as well as 300.0 μg/l) were compared. The optimum conditions for removing microcystin-YR and enhancing both the bacterial as well as micro-animal growth were around 30°C at neutral pH. The higher initial input of toxin concentration resulted in an increase of the removal rate of microcystin-YR. Whereas, aeration had also helped improving efficiency of bioreactor than regular shaking with anaerobic condition. Toxin removal rate with the addition. This might be due to GAC promoting physical adsorption and biological processes. Large surface area of GAC is also known to stimulate the micro-animal and bacterial propagation. The third section was designed to investigate biodegradation of microcystin from natural algal bloom water using fluidized bed bioreactor. Before biofilm was developed on the GAC surface, GAC itself served as an adsorbent to remove certain amount of toxin. However, the adsorption process reached equilibrium over a ce11ain period of operation. The biofilm formed on the GAC surface, then biosorption would proceed continuously to remove toxin and algal biomass. Because of this, removal duration would become longer. In the same experiments, three kinds of GAC, GAC made by coconut, wood and coal were included for comparison with varying influent concentrations of toxin and changes of hydraulic retention time (HRT) of bioreactors. It was noted that GAC made by coconut shell obtained the lowest efficacy in removal of microcystin. Higher influent contents of toxin input resulted in an increase of the toxin removal rate. This result was similar with the previous batch reactors. The HRT of the bioreactors had strong effect on toxin removal. At the same time, chlorophyll a, SS and COD were effectively removed by the biofilm in the bioreactors. |
| Year | 2002 |
| Corresponding Series Added Entry | Asian Institute of Technology. Dissertation ; no. EV-02-05 |
| Type | Dissertation |
| School | School of Environment, Resources, and Development |
| 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) | Preeda Pakpian |
| Examination Committee(s) | Apisit Eiumnoh;Fukushi, Kensuke;Mathuros Ruchirawat;Fujimoto, Naoshi;Ladda Wongrat;Nishimura, Osamu |
| Scholarship Donor(s) | State Education Commission of P. R. China |
| Degree | Thesis (Ph.D.) - Asian Institute of Technology, 2002 |