Sewage Treatment Plant Design Of Small Mountain Town And Its Operation Research

With the continuous development of economy and people environmentalawareness, the sewage treatment in small town is becoming a urgent problem to besolved. But several current conventional treatment processes need large infrastructureinvestment, high energy consumption, and complex operation and management,difficult to be applied in the small urban areas existing technical and economicweakness. Recently, various ecological technologies for wastewater treatment have beendeveloped, becoming the new economic choices for sewage treatment in some smalltown.In the present paper, Gaofeng town domestic sewage treatment engineering wasdesigned with an aerator gaining energy through the natural waterfall, where theconstructed rapid infiltration system (CRIS) was built according to the local soilcharacteristics and climate conditions, after comparing some treatment processes.Finally, an innovative combined process,"Anaerobic hydrolysis+Natural falling wateraeration+Constructed Rapid Infiltration System", was put forward. The recent designscale of sewage plant was800m~3/d, and the forward design scale of sewage plant was1400m~3/d. The designed water quality for chemical oxygen demand (COD), totalnitrogen (TN), ammonia nitrogen(NH4+-N) and total phosphorus (TP) was300mg/L,40mg/L,30mg/L,5mg/L respectively。After the treatment engineering finished, a long run research was presented, andthe result showed that the effluent water quality almost met the first level-B standard of" Pollutants discharge standards in the urban sewage treatment plant (PDS)(GB18918-2002), Chinese standards".After longtime monitoring in the plant, the pollutants removal rates and the impactof temperature on pollutants purification efficiencies were studied. The relationshipsbetween removal loadings and influent loadings for pollutants were also investigated inthis paper. The results indicated that the treatment plant had acceptable removal abilitiesfor pollutants and were adaptable to water quality fluctuations. There are significantrelationships between pollutants purification efficiencies and temperature, especially tochemical oxygen demand (COD) and ammonium (NH4+-N), except TP, where therelationship is significant. The relationships between removal loadings per unit area andinfluent loadings are approximate logarithmic for various pollutants. The removal abilities for chemical oxygen demand (COD), total nitrogen (TN),ammonia nitrogen(NH4+-N) and total phosphorus (TP) in the combined process was14.377t/a,2.915t/a,3.995t/a and0.347t/a, respectively, after stable treatment, and thesewage treatment plant picks out good environmental benefits. The economic analysisindicated that the infrastructure investment for every ton treated wastewater was2522.2RMB, which was only20%to50%of conventional sewage treatment processes. Therunning cost for every ton treated wastewater was0.18RMB and less than several timesto the conventional process, indicating an significant environmental benefit.In conclusion, this study showed that the combined process," Anaerobic hydrolysis+Natural falling water aeration+Constructed Rapid Infiltration System", hasacceptable and stable removal abilities for pollutants, with low infrastructureinvestments demand, simple maintenance and management, and low energyconsumption and sludge production. Although temperature and influent loadingsinfluenced the treatment efficiencies, the effluent water quality almost met the firstlevel-B standard of PDS. Thus, this combined process is suitable to the domesticwastewater treatment in small mountain town, and the design and operation experiencescan provide reference for similar urban sewage treatment plant.