Study On Domestic Wastewater Treatment Of Rural Area In Hunan Province By Using Septic Tank Coupled With Constructed Wetland

Based on septic tanks and constructed wetland in four villages in Hunan province,the quality of both influent and effluent in septic tanks and constructed wetlands is determined in six months.Results showed that:(1)Different kinds of septic tank lead to different effect on wastewater treatment.“Three–Grill–Mode”septic tanks have the best treatment efficiency among all kinds of septic tank in the survey.The chemical oxygen demand(CODCr),five – day biochemical oxygen demand(BOD5)and suspended solids(SS)removal efficiency range from about 50% to 70%,40% to 70%,50% to 75%.However,the total nitrogen(TN)and total phosphorus(TP)removal efficiency is low,ranging from 10% below and 25.4% to 42.3%.(2)Constructed wetland has good removal efficiency on the chemical oxygen demand(CODCr),five–day biochemical oxygen demand(BOD5)and total phosphorus(TP),ranging from 75.3% to 87.7%,72.2% to 85.2%,and 80% above.But the suspended solids(SS),ammonia nitrogen(NH3 – N),total nitrogen(TN)removal efficiency is low,ranging from 62.9% to 68.1%,61.60% to 86.17% and 44.19% to82.71%.The effluent of constructed wetland systems meets the Class ?B of Discharge Standard of Pollutants for Municipal Wastewater Treatment Plant(GB18918–2002)in most of time,except the SS.(3)After “Three–Grill–Mode”septic tanks pretreatment,the domestic wastewater biochemical performance is improved,and is conductive to follow – up biological treatment process.While the BOD5 / NH3–N ratio and the BOD5 / TP ratio is reduced at the same time,it is harmful for removing the nitrogen and the phosphorus.However,the study shows that it affects little for removing the nitrogen and the phosphorus in constructed wetland,since constructed wetland remove nitrogen and the phosphorus not only by micro–organism,but also by plant and matrix.(4)The “Grille – Sanitation – Biological oxidation – Mode” pretreatment units in constructed wetland system plays an important role on removing CODCr,BOD5 and SS.These pretreatment units can reduce pollutant loading for constructed wetland as well as improve the biochemical performance.Therefore,these pretreatment units should be well managed.On the one hand,aeration system should be operated in the biological oxidation tank for improving the pollutant removal,the other hand,the suspended solids settled down in sedimentation tank should be removed avoiding thematrix in constructed wetland clogged.