Discussion And Practice On Municipal Wastewater Reuse Process In Thermal Power Plant

Taking the secondary effluent from a WW TP as source water,the combined process of biological oxidation tower,secondary filter with fiber bundles and sand filtration and reverse osmosis(RO) was used to construct an advanced wastewater treatment and reuse project in a Thermal Power Plant in Dalian,which have been using tap water treated by mixed bed process as industry water.The advanced treatment effluent is mostly used as circulating cooling water and boiler make-up water to release the fund pressure of water and high generation cost.The stability investigation of the process was carried out by chronically monitoring the relative water quality index of the effluent of the key units.The function and characteristics of the process were also investigated and some shortcomings are pointed out.Solutions for the problems found in the operation of the process and some improvement suggestions for the process were provided.The operation result indicates that using single membrane method without UF in pretreatment of RO is feasible for advanced wastewater treatment.The biological oxidation tower has significant removal efficiency.The COD/BOD₅/NH₄⁺-N removal rate of the effluent of the biological oxidation tower is over 60%,78%and 92%.The organic pollutants and inorganic pollutants can be further removed through fiber bundles and sand filtration process.The average COD_Mn of the effluent of sand filter is 2.8mg/L,and the turbidity is lower than 0.1NTU and the SDI fluctuated between 3.3 and 4.0,meeting the index requirement of influent of RO system.The conductivity of effluent of RO is 18.7μS/cm, all the other index of the effluent quality can meet the index requirements of reuse water of the thermal power plant.The biological oxidation tower can not only reduce the biodegradable organic pollutant, but also improve the sedimentation performance of the raw water,which can ease the burden of the coagulation process.The function mechanism of the whole process can be interpreted by screening principle.Based on experimental analysis in laboratory and investigation in the operating process, the following improvement suggestions of the process are put forward:improve the structure of medicining line of sedimentation tank;increase the backwash intensity of fiber bundle filter;retrofit the filtering layer of sand filter;move the adding point for NaClO forward.The combined process has advantages such as good treatment effect,stable operation, small investment,low operation cost and so on and is of good popularization and application value.Finally,taking the project as an example,the paper discussed the economic and environmental benefits obtained by reclaimed water reuse project on promoting the development of municipal wastewater treatment industry...