Study On Advanced Treatment Of Secondary Effluent From Wastewater Treatment Plant By Constructed Wetland

With the development of society and economy, the demand of environment becomes higher and higher, especially to water environment. In current, the water pollution is the most important issue to our country. To solve these environmental issues, a lot of wastewater treatment plants has been built in recent twenty years, the running of these plants have important role in improving water environment of our country. But, the effluent of these plants is not accorded with the demand of nitrogen and phosphorus because of using second treatment. The nitrogen and phosphorus can cause the eutrophication of water body. For guaranteeing the demand of nitrogen and phosphorus, the third treatment unit must be built after the second treatment unit. The easy management, low cost of running and powerful practicability are the characteristics of constructed wetland, It is very meaningful to research the constructed wetland as the third treatment unit.The article studies the treatment of effluent of constructed wetland on COD, NH4+-N, NO-2N, NO-3-N, TP by the experiment research of substrate, plant, and running style. The constructed wetland was built in wastewater treatment station of Shandong Jianzhu University as advanced treatement unit. The COD, NH4+-N, TP of raw second outlet was88.5-103.5mg/L,14.8-20.2mg/L,1.7-3.06mg/L respectively. The constructed wetland has run from2009to2012, the better effect of treatment has been gained by three years’running. The COD, NH4+-N, TP of raw advanced outlet was better than<Discharge standard for municipal sewage treatment plant>（GB18918----2002） first grade A.Some results have been acquired in research.1. To select the substrates. By the experiments of absorption and desorption, the shale ceramsite has been selected as substrate. The physical and chemical characteristics of ceramsite have been gained by SEM and energy spectrum analysis. The strong ability of adsorption to phosphorus about shale ceramsite is relation to its structure of micropore and the metal elements in itself.2. To select the plants. The Phragmites australis, Arundo donax L., Typhal atifolia L. convexutricle sedge herb and sedge have been selected from Nansi lake. The rhizospheric microorganisms and their relationship between the envi-ronment have been analysed by DGGE. The results show:the number of rhiz-ospheric microorganisms is Arundo donax L more than Phragmites australis m-ore than yphalatifolia L. more than convexutricle sedge herb more than sedge. By software of Quantity One and atlas of DGGE. The Affinity of Phragmites australis, Arundo donax L. and Typhalatifolia L.is closer, the rhizospheric micr-oorganisms has function of nitrogen and phosphorus removal, so, the three plan ts have been selected in constructed wetland.3. By simulate the experiment of constructed wetland in laboratory. The affect to HRT and DO has been analysed. When the HRT is5days, the removal rate of COD is respective41.2%and20.1%more than the removal rate about HRT is1day and2days. When the HRT is7.5days, the removal rate of COD is only5.2%more than the removal rate of HRT is5days. So, the HRT of5days is selected.4. The effect of DO to the removal rate of NH4+-N has been researched, when the DO lower than1.5mg/L, the NH4+-N transforms to NO₂-N, the partial nitrification is existed, when the DO higher than1.5mg/L, the NH4+-N transforms to NO-3-N, nitrification has important role in this condition.5. By the research of biomass about surface of ceramsite, the biomass is very good correlativity between DO. These have strong adsorption between biofilm and ceramsite. By energy spectrum analysis, there are lot of metal ions on surface of ceramsite, the protein and humic acid are easily combined with high valence ion, polysaccharide is easily combined with low valence ion. In this condition, the biofilm do not fall off easily.6. Three plants have been planted in sit, Phragmites australis, Arundo donax L. and Typhalatifolia L, the adsorption of nitrogen and phosphorus has been researched, the adsorption to nitrogen and phosphorus of Phragmites australis is best, but, there are not obvious difference between them. By analyzing the content of nitrogen and phosphorus in different parts of the plant, the rules are concluded that the content of nitrogen in leaf is more than in stem, and more than in root, the content of phosphorus in root is more than in leaf, and more than in stem.7.By running in site for long time, the accumulation of material in wetland has been studied, the TS, VS and hydraulic conductivity has been tested the conclusions were confirmed that the accumulation of material in front part is higher than in middle and end part, most SS has been removed in front part of the wetland. Energy dispersive spectrum （EDS） about accumulated material on surface of ceramsite was analyzed, some conclusions were found that the component of accumulated material was similar to he component of ceramsite, this conclusion illustrated that the accumulated material was composed by broken body from ceramsite. By researching about accumulation of material on surface of ceramsite in long time running about constructed wetland, one conclusion was found that the constructed wetland has good efficiency after three years’running, the blocking has not been happened when it was used as third treatment in wastewater treatment plant, the pilot was built in Shandong Jianzhu University, the wetland has been run from2010to2012, from April to November ever year, the COD、NH4+-N、TP of effluent were accorded with the demand of<Discharge standard for municipal sewage treatment plant>（GB18918----2002） first grade A.