Study On Sewage Treatment Based On Constructed Wetland-stabilization Pond System

The reclaimed water station of Rizhao Polytechnic mainly processes the sewage generated by the staff residential district of the college.In this station,A2/O process is used and the effluent is required to meet the level A emission standard.The tail water is discharged into Rizhao Polytechnic section of Shadun River,and used further as a green water and ecological water.Due to not being up to the emission standard at some time,the drainage can not be discharged directly into the river and must be discharged into the municipal pipe network for secondary treatment.In order to achieve a stable effluent water quality,reduce the risk of water eutrophication and realize the reuse of water,the treatment of the tail water is carried out.In this study,a wetland stable pond system was constructed.(1)Selecting of the suitable aquatic organisms for the systemThe COD,NH3-N and TP removal ability of some aquatic plants were compared.Basing on the COD removal rate of the compared aquatic plants,the order from high to low was hornwort,ulothrix,typha,reed,water chestnut,water hyacinth.By comparing the NH3-N removal rate between the these plants,the order from high to low was water hyacinth,water chestnut,hornwort,ulothrix,reed,and typha.The order from high to low of the aquatic plants according their TP removal rate was typha,water chestnut,reed,hornwort,Water hyacinth,and ulothrix.With the removal efficiency of pollutants,aquatic plant sources,transplanting difficulty,post transplant management,removal of aquatic plants and landscaping and other comprehensive factors,the four aquatic plants water hyacinth,typha,ulothrix,hornwort were choiced finally.(2)Constructing the wetland stable pond systemWater hyacinth plants were transplanted directly into the vertical flow constructed wetland.Typha plants were transplanted together with the attached mud of the roots into the horizontal flow constructed wetland.Ulothrix and hornwort plants were transplanted into the biological stabilization pond.With the construction of the system,the effluent COD values were between 7mg/L-13mg/L,the average removal rate of COD values was 67.54%;NH3-N concentration of the effluent was between 0.8mg/L-2.7mg/L,and the average removal rate of NH3-N was 70.51%.The effluent TP was between 0.1mg/L-0.4mg/L,and the average TP removal rate was 66.67%.It was concluded that effect of tail water treatment by the wetland stable pond system is obvious.(3)The effluent of the constructed wetland stable pond system is stable,meeting the requirement of discharge.In the long-term operation of the artificial wetland stable pond treatment system,the effluent COD value was between 7mg/L-13mg/L,the effluent NH3-N concentration was between 0.8mg/L-2.7mg/L.and the effluent TP is between 0.1mg/L-0.4mg/L.These three indicators had reached the "Pollution discharge standard of urban sewage treatment plants"(GB18918-2002)level A emission standards.Basing on these results,the trail water of Rizhao Polytechnic reclaimed water station could be discharged after being treated by the constructed wetland and stabilization pond treatment system.(4)Reduced the eutrophication risk of the receiving water originated by tail water discharged by wetland stable pond treatment systemIn this study,the removal rate of COD of the constructed wetland stable pond system is between 66.20%-69.23%,the average removal rate of NH3-N was between 47.47%-79.22%,and the average removal rate of TP was between 60.00%-84.62%.It could be concluded that eutrophication risk originated by tail water discharge decreased obviously after treatment by the constructed wetland stable pond system.(5)Realized the purpose of reclaimed water reuseIn this study,the effluent COD of the constructed wetland stable pond system is between 7mg/L-13mg/L,NH3-N content is 0.8mg/L-2.7mg/L,TP content is 0.1mg/L-0.4mg/L.According to the "urban sewage recycling and utilization of urban water quality"(18920-2002 GB/T)and“Water quality standard for urban wastewater reuse and landscape environment"(GB/T18921-2002),after treatment of the constructed wetland and stabilization pond treatment system,the main water quality indexes of the effluent are satisfied with the requirement of water reuse.The effluent could be used as campus greening water,and discharged to the Rizhao Polytechnic section of Shadun River as ecological water use.