The Process Design Of A Sewage Treatment Plant For Fuxin

Fuxin city called “the city of coal and electricity” in the past is located in the northwest of Liaoning Province.With the depletion of coal resources in Fuxin area,the original two pillar enterprise(Haizhou Lutian coal mines and Gaode mining industry)have been bankrupt,and their upstream and downstream enterprises have also closed down.In December 2001,the State Council made Fuxin city as the first pilot city of resource-based economy transformation: from traditional resource-based city to the new economic and sustainable development city.Taiping New District is the old industrial and mining areas in Fuxin,which contained more than 80% large and medium-sized industrial enterprises.After the depletion of urban resources,the economic transformation of Taiping New District has become the top priority of the economic transformation of Fuxin.And environmental protection has to been taken to take for the sustainable development of Fuxin city.The total population of Fuxin in 2013 was 0.631 million,and in 2020 will up to 0.829 million.Of them,the total population was palnned to be 0.0824 million in 2015 and 0.0532 million in 2020 in Taiping District.There are 5 sewage treatment plants in the city,but not in Taiping.With the development of the New District,a large number of industrial enterprises will settle into Taiping New District.Therefore,the emergent thing of Taiping is to design and construct a municipal sewage treatment plant in order to achieve the purpose of the sustainable development of the city.According to the actual situation of Fuxin Taiping district,through the sewage treatment plant of service area planning population prediction and planning land Taiping City comprehensive water use,to determine the size of the design of sewage treatment plant 2.0 ×104tons/day.Through investigate Fuxin City sewage treatment plant sewage comprehensive water quality and other typical sewage water quality indicators,to determine the incoming water sewage plant design;Design according to the requirement of local environmental protection department of the sewage plant effluent reach GB18918 level in the urban sewage treatment plant pollutant discharge standard(standard of A);According to the composition,concentration of pollutants in sewage water and effluent standard design,two sets of selected suitable for waste water treatment process of our factory: improved A~2/O process and SBR process.From the reliability of the process operation,convenience and economy of total project investment,operation and management,which covers an area of comparison,finally determine the improved A~2/O process as the core process.Sewage treatment process: Coarse grid-Fine grid-Swirl grit chamber-Improved A~2/O biochemical pool-Secondary settling tank-Depth treatment filter-Chlorine disinfection contact tank-Water.among them,Coarse grid trash rack width S=10mm,Grating gap b=20mm,Flow through the gate Q=0.177m3/s,The flow rate through the gate v=0.6m/s,Fine grid trash rack width S=10mm,Grating gap b=5mm,Flow through the gate Q=0.177m3/s The flow rate through the gate v=0.8m/s;Grit chamber residence time 40 s,The surface load 198m3/m2·h,diameter D=2.0m,Effective depth H=1.0m;Sewage treatment plant design scale is Q=2.0 ×104 m3/d,BOD5-Sludge load 0.06 kgBOD5/kgMLSS·d,MLSS=3200mg/L,Sludge retention time 10.5d,Sludge Production 0.6 kgVSS/kgBOD5,Oxygen demand 1.6 kgO2/kgBOD5,RSS=8000 mg/L,Internal reflux ratio 200%,Sludge return ratio 100%,SVI=110;Surface hydraulic load of the second settling tank is 0.77 m3/m2·h,solid loading is 40 kgMLSS/m2·d,Effluent weir load is 1.7 L/m·s,Settling time 4h.The sludge produced by wastewater treatment plants contain plenty of water,complex compositions.And the problems of heavy metals,harmful microorganisms and non-biological organic compounds in the sludge is still puzzle in the environment.Sludge thermal hydrolysis is a new technology to reduce the sludge,harmless,and improve the biodegradability of sludge.At present,it is just applied in engineering applications in the world,and China also began to pay attention to this technology to solve the sewage problems which have been plagued by sewage plants and environmental protection industry.After high temperature and high pressure,it could destroy the microbial cell wall effectively and remove the water in the cell,so that reduce the water content in the sludge greatly.Finally and the sludge reduction can be achieved.At the same time,by pyrohydrolysis which is difficult to biodegradation of organic matter,such as microbial extracellular polymers become relatively simple organic matter,in order to improve the biodegradability of organic matter in sludge,it is conducive to the subsequent digestion of sludge.Can also reduce the amount of biomass in the sludge,so as to reduce the degree of damage to the biological aspects of the biological,to a certain extent,realize the harmless sludge.Therefore,the sludge treatment process,on the basis of the traditional sludge treatment process,increase the pyrohydrolysis unit,in order to achieve the reduction of sludge and biological harmless: excess sludge-Concentrate-Thermal hydrolysis-Digestion-Dehydration.The water content of the sludge from the second sink is 99.2%,After treatment by the concentration tank,the thermal hydrolysis reaction system is in the process of the system,At the temperature of 180 ℃,the reaction is 30 minutes.After digestion and dehydration,Finally the water content of the mud is about 50%;Sludge thermal hydrolysis unit consists of two processes: Sludge preheating and thermal hydrolysis reaction,The pyrohydrolysis system is made up of preheating-pyrohydrolysis-flash.After the surplus sludge from the two settling tank is heated to a temperature of 80℃ in the preheating tank,enters the hot water tank solution,under high temperature and high pressure(temperature 180℃,pressure 2.0MPa)components of the sludge occurs hydrolysis reaction,heat generated from the sludge mixed liquor into flash tank down to 60℃,into the subsequent anaerobic digestion unit.In the flash tank,hot steam generated by heat mixing liquid is send to the preheating tank and boiler feed water,preheating of mud and water.The total investment the process is 41.0065 million yuan,and the first part of project investment is 31.4599 million yuan,which includes the construction project cost of 18.1984 million yuan,equipment cost of 9.9245 million yuan and installation project cost 3.337 million yuan.The second part of the project for others is 6.3714 million yuan,basic reserve 2.5170 million yuan and circulating 0.6582 million yuan.