Studies On Characteristics And Function Of Biofilms In The Constructed Wetland And Urban Water Bodies

Constructed wetland is a very potential waste water treatment technology, although its main mechanisms have been known, the relative biological and chemical processes have not been understood completely. The purification capacity of constructed wetland is based on its unique and complex mechanisms, among them, biofilms play very important roles. Development of biofilm affects the treatment efficiency of constructed wetland directly. Biofilms occur in nature on almost any surface that is in contact with water. Adsorption and re-transfer of biofilms have important effect on transfer and end results of pollutants. In the paper, Spatial distribution, metabolism, development, degradation capability and pentachloropHenol removal of biofilms in the substrate of constructed wetland and urban water bodies were studied, the main results are as following: Studies of the biofilms in the substrate of integrated vertical-flow constructed wetland(IVCW) 1. Biofilms of substrate of IVCW developed well, and their biomass reached to 21.8mg/g. Biofilms were accumulated mainly in top layer of the substrate. Spatial distribution of biofilms was related to distribution of aerobic microorganism and root system of wetland plants. Biomass, thickness, respiration, dehydrogenase activities and degradation of organic carbon of biofilms in down-flow chamber were all higher than those in up-flow chamber, and down-flow chamber is the main purifying space of organic pollutants in wastewater. Organic matter of waste water have been removed layer by layer, the removal efficiencies in layers from top to deep in down-flow chamber are 26.93%, 6.19%, 11.33%, 8.25%, 9.96%, and 62.7% in total. 2. The activities of biofilms with various development stages were different, and degradation capability of organic carbon were also different. The degradation rate increased 5 times from 10th days to 70th days. In the early stages of constructed wetland, the key to improve treatment efficiency of the system is how to promote development and degradation capability of biofilms. The optimal biofilm thickness was 150μm. The biofilm thickness in the outmost surface of the substrate was 3-4 times of the optimal thickness. Excessive biofilms accumulation in outmost layer was not benefical to improvement of treatment efficiency and prone to cause clog of constructed wetland. 3. The vertical distribution of root weight of wetland plants in IVCW shaped like a "T"from top to deep layers. Contrary to the quantity distribution, root activity distribution shaped like a handstand "T". Activities of slim roots were 1.68 times higher than main roots, the average root activities of spring roots were 10 times of those of winter roots, and the high activity point moved deeper with the advance of growing stages. The plant root system in IVCW concentrated mainly within 30cm layer of the substrate, did not reach the bottom of the substrate. Roots below 30cm in the substrate were less than 1% of total amount, the distribution space of root system was about 30% of total amount of substrate. The results showed that the better purifying space in constructed wetland were about 0-20cm depth, the promotion of growth of root system could utilize fully the substrate and increase the effective purifying space of constructed wetland . 4. During one year run of IVCW of Lotus Lake, biofilms of substate in the system have a continuous accumulation. Biomass of biofilms increased 1.35 times. Removal efficiencies of pollutant increase greatly, and formation of biofilms was benefical to improvement of treatment efficiency and stable run of the system. In the different run period of constructed wetlands, biomass, thickness, distribution, formation time and dehydrogenase activities in the wetland of Donghu Lake were all higher than those inthe wetland of Lotus Lake, so were removal efficiencies of pollutants. The average biomass of biofilms in the wetland of Donghu Lake was 3.69 times of that in the wetland of Lotus Lake. 5. The results indicated that development of biofilms affected the treatment efficiencies of constructed wetland directly. Biofilms, as an integrated structure of combination of microorganism and organic and inorganic matter, could be used as the direct and key index to assess the development of constructed wetland. Studies of characteristics of biofilms during the process of ecological restoration in urban water bodies 1. All parameters of biofilms in the top layer of large river were higher than those of in bottom layer and light had great influence on growth of biofilms. 2. Formation of biofilms were relevant close to water quality, results showed that higher water nutrition level had more biofilm accumulation and faster growing speed. Biomass, thickness and Volatile suspend solid (VSS) of biofilms in the top layer of large sublake all were 11%-36% higher than those in small sublake. By through ecological restoration of Lotus Lake, water quality of small sublake was better than that of large sublake, and accumulation of biofilms also proved the achievement. Studies of adsorption and degradation of pentachlorophenol by biofilms 1. The average removal rates of pentachlorophenol (PCP) by the substrate of IVCW were 77.3%, and it was higher in down-flow chamber than that in up-flow chamber. Among them, 26.3% was contributed to biofilms. Growth of biofilms improved the treatment efficiencies of IVCW, and the PCP average removal efficiency was as high as 98% by different technology combination of IVCW. 2. Adsorption experiment showed that the substrate with or without biofilms both could adsorb PCP. Formation of biofilms improved the adsorption capacities of the substrate to PCP, and 17.5% was contributed to biofilms in average. 3. PCP can be degradated rapidly by biofilms in water. The degradation kinetics of PCP indicated that biofilms had strong appetency to PCP, supplemented with carbon source could enhance biodegradation of PCP. Biodegradation played main role in theprocess of PCP removal, its contribution percentage was about 58%. PCP removal was increased with increasing concentration of biofilms. High initial PCP concentration (22.71mg/l) had not inhibition to biofilms activities, and it could achieve high initial PCP degradation rate. In the adsorption experiment by ultraviolet radiation treatment, the contribution percentage of biofilms was 68%. 4. Biofilms of anaerobic sediment of waters had a high degradation efficiencies to PCP, PCP degradation rates within 2d were 81.59%, and the average degradation rates were 2.25 mg·L-1·d-1 . The degradation rates were slow down at aerobic operation, but the activities were kept because of the capacity of tolerance of O2. 5. PCP biofilm degradation of top and bottom of waters were quite different, it was related to microorganism communities. Different water layers had different environment, communities and physiological characteristics were also different, so its capacity of PCP degradation and reaction condition were different.