Study On The Designing And Effect Of Domestic Sewage Treatment With Improved Septic Tank+Constructed Wetland Integration Facility For Rural Areas

Four grids system of traditional septic tank + constructed wetland has been widely used in rural domestic sewage treatment in recent years,as a combined process which has better treatment effect as well as economic and landscape value compared with single treatment process.But there are still some problems,such as the poor effluent quality.large occupation area,unreliable parameters and high cost.Therefore,the research is dedicated to design a modified combined treatment system with higher purification efficiency and more stable effluent water quality which can meet the?Standards for pollutant discharge from urban sewage treatment plants?,class B.The contents are as follows:Part I:Screening of optimal septic tanks.Six kinds of FPR(Fiber-reinforced plastic)septic tanks designed by three factors of fecal pipe,volume ration and vent pipe,are conducted to treat rural sewage at Shaoshan village for screening the optimal septic tanks.Those tanks are T1-modified vent pipe,T2-modified fecal pipe,T3-modified volume ratio,T4-modified vent and fecal pipe,T5-modified vent pipe and volume ratio,T6-modified fecal pipe and volume radio,TO-the traditional septic tanks as the control.After running for one month,the results show that:(1)T4 has the highest removal rates of CODcr,TN,NH3-N and TP,which are 50.88%,30.45%,60%and 40.02%higher than the traditional septic tank respectively.(2)The height of fecal pipe is the most important factor to contribute to the removal rate,followed by the vent pipe and volume ratio.(3)The AHP-based analysis demonstrated that T4 has the best comprehensive performance for removal CODcr,TN,NH3-N,TP.Above all,T4 can be selected as the optimal septic tanks for rural sewage.Screening of the Part ? Constructed Wetland Model:Three plants(Iris pseudacorus L,Thalia dealbata Fraser and Canna indica L)were orthogonally combined with three substrates(Ceramsite,Zeolite and Limestone)into nine configurations.Models are:S1-Ceramic+Iris,S2-Ceramic+Thalia,S3-Ceramic+Canna,S4-zeolite+Thalia,S5-Zeolite+ Thalia,S6-Zeolite+Canna,S7-Limestone +Iris,S8-Limestone+Thalia,S9-Limestone +Canna,used to treat domestic sewage,dynamically monitor the water quality of the inlet and outlet water for one year.The results are as follows:(1)The highest annual removal rate of CODcr and TN is S6-zeolite+canna,which is 69.75%and 65.92%,respectively.The highest annual removal rate of NH3-N is S5-Zeolite+Thalia,71.59%,The highest removal rate of TP was S-ceramic+ Thalia was 53.74%,and the highest annual removal rate of SS was S8-Limestone+Thalia was 95.1%.The matrix has a more critical role in the configuration combination than the plant.The comprehensive evaluation of the treatment effect by the membership function method shows that the S2-Ceramic+Thalia system is the optimal combination.(2)The removal rates of CODcr,TN and NH3-N are obviously affected by seasonal changes,and the removal rate shows a downward trend in winter(December-February),and an upward trend in spring and summer(February-June).However,TP was not significantly affected by the season,but in the later stages,reverse concentration release occurred.The average removal rate of CODcr in each system was not significant(P>0.05).(3)The contribution rate of plants to the average removal of TN in the system is only about 7.9%,of which 7.65%and 11.03%of thaliaance and Canna,respectively,and the lowest is 5.11%of Iris,the average removal rate of plant-to-system TP is 6.51%,yellow.The average contribution rates of Acorus calamus,thalia and Canna are 5.55%,5.04%and 8.94%,respectively.Part III combined treatment device treatment effect study:The three-dimensional septic tank and constructed wetland were combined into three four-level integrated devices of different heights(1.4m,1.2m,lm)to treat the domestic sewage of farmers for one month.The results are as follows:The integrated purification effect of the 1.4m height four-grids integrated device is optimal.The influent concentrations of CODcr,TN,NH3-N and TP are 265mg/L,35.66mg/L,75.69mg,5.5mg/respectively.At L,the effluent concentrations were 38.9 mg/L,20 mg/L,5.45 mg/L,and 0.671 mg/L,respectively,and the removal rates were 85.3%,43.9%,92.7%,and 87.7%,respectively.Which can meet the?Standards for pollutant discharge from urban sewage treatment plants?,class B.