| Formaldehyde is an important chemical solvent and raw material for chemical industry. It is widely used in many chemical industries such as medicine, paper-making,wood-processing, organic synthesis, plastic and resin production industry and so on.Thus wastewater contained formaldehyde was discharged to the environment and can cause pollution. The methods used to treat formaldehyde wastewater can be divided into three kinds, physical, chemical and biological methods. During them biological method attracts much more attention because of its economical and environmental features.However, as the carcinogenicity and teratogenicity of formaldehyde, it can be toxic to organisms especially at high concentration, traditional activated sludge treatment can deal with limited formaldehyde concentration. Thus the bioaugmentation which means the addition of effective microorganisms to the treatment system may become a feasible approach.The aim of the research is to improve the ability of formaldehyde wastewater biodegradation so the microorganisms that can metabolize formaldehyde were isolated and the degradation properties and bioaugmentation were studied.Two strains that can use formaldehyde as the sole carbon source were isolated from activated sludge contaminated by the polyformaldehyde wastewater and soil and were named strain J1 and P1 respectively. Through the morphological and molecule biology identification, J1 and P1 were identified as Candida maltosa and Pseudomonsa putida respectively.The formaldehyde degradation property of C. maltosa and P. putida indicated that the optimum temperature of formaldehyde degradation for C. maltosa and P. putida was30℃ both; the optimum p H was 5 for C. maltosa and 8 for P. putida and C. maltosa was less sensitive to p H meant a wider p H range of application. P. putida can totally biodegrade formaldehyde concentration below 1200mg/L within 48 h which significantly faster than the 120 h of C. maltosa. But the lag phase when biodegrade formaldehyde concentration exceed 1400mg/L of P. putida was longer than that of C.maltosa and the degradation rate become fast again after adapting. P. putida shows a good capacity of acclimation. The addition of glucose didn’t inhibit the formaldehyde degradation by both C. maltosa and P. putida. Instead, the addition of glucose promote the growth of microorganisms, so the degradation rate increased. The addition ofglucose not only improved the degradation rate but also the maximum formaldehyde concentration that C. maltosa and P. putida can stand. When formaldehyde was the sole carbon source, C. maltosa can achieve 62% degradtion rate within 168 h when degrade2000mg/L formaldehyde and P. putida can completely degrade 1800mg/L formaldehyde within 240 h. While the two strains can completely degrade 2000mg/L formaldehyde with the presence of glucose. The comparison of formaldehyde degradation with other microorganisms indicated that C. maltosa and P. putida isolated in this research had the high capability to degrade formaldehyde especially P. putida could degrade formaldehyde faster than many other bacteria.The preliminary research on the mechanism of formaldehyde degradation by C.maltosa and P. putida showed that formaldehyde dehydrogenase was existed in both C.maltosa and P. putida and it could be highly induced by formaldehyde.The results of bioaugmentation by P. putida showed that P. putida can successfully colonize in the activated sludge and reach almost totally removal of formaldehyde below 1060mg/L. The removal rate was significant improved by the bioaugmentation. The preferable formaldehyde concentration of bioaugmented reactor was 720mg/L and it is 300mg/L of the control reactor. The acceptable formaldehyde concentration of bioaugmented reactor was 1060mg/L and it is 420mg/L of the control reactor. Bioaugmentation improved the acceptable formaldehyde concentration of the reactor and the ability to suffer shock loading.The results of PCR-TGGE technology showed that the bioaugmentation by P.putida didn’t destroy the community structure of seed slugde, on the contrary it relieved high formaldehyde stress and helped keeping the diversity of community structure.Microorganisms belong to α- Proteobacteria, β- Proteobacteria and γ- Proteobacteria were the dominant population before and after the treatment of formaldehyde wastewater. It means these microorganisms can play an important role in the treatment of not only municipal but also toxic wastewater. |
