| Night soil wastewater volume increases rapidly along with the increase of flush toilet proportion in China, and it can no longer be utilized as fertilizer resources because of the reduction of solid content in wastewater and the changing of tillage management. So the reduction and harmlessness of night soil wastewater are concerned increasingly. Nowadays, night soil wastewater in city is transferred through drainage pipe to wastewater treatment plant and disposed there. But in suburb villages and towns where it's short of drainage pipe network or wastewater treatment facilities, night soil wastewater is only treated by three-grille-mode septic tank whose effluent can't reach discharge standard.In this study, an improved underground infiltration treatment technology is proposed, based on existing technology both at home and abroad. This technology is aimed at solving the clogging problem that happens frequently in existing systems. A novel artificial soil infiltration column system which was composed of soil, sand, polymer organic materials; etc was constructed and applied to the septic tank effluent wastewater treatment. After the optimization of process conditions filler components and its ratio, infiltration system effluent can reach first (A) class standard of"Discharge standard of pollutants for municipal wastewater treatment plant", and infiltration system's permeability and anti-clogging ability can also be improved.Results are as follows:○1 During the steady running process with 300mg/L loading CODCr concentration and 12.5cm/d loading rate, among the four infiltration systems, effluent of the three systems whose sand/soil ratio are 2:8 3:7 and 5:5 can reach first (A) class of discharge standard; effluent of the system without soil can't reach first class of discharge standard. System with a 2:8 sand/soil ratio has almost the same removal performance as system with a 3:7 sand/soil ratio, their removal rate of CODCr, TN, NH4+-N, TP and SS can be more than 95%, 90%, 94%, 99.9% and 90%. TN, TP removal rate of the system with a 5:5 sand/soil ratio is 90% and 99%, which is less than that of former two systems.○2 Hydrophilic material A has little effect on the removal performance of land infiltration system, but it can enlarge system saturated infiltration rate from 20cm/h to about 30cm/h, and significantly improve system permeability and anti-clogging ability.○3 Loading pollutant concentration (LPC) has different effect on different infiltration systems. LPC has little effect on pollutant removal performance of systems whose sand/soil ratio are 2:8 and 3:7, but concentration of effluent TN, NH4+-N from the other two system increases along with the increase of PLC. The loading CODCr concentration should be kept under 400mg/L in order to keep infiltration system working properly in a long run.○4 Hydraulic loading rate has little effect on pollutant removal performance of the four infiltration systems, which means the four systems have high resistance to hydraulic loading rate. But hydraulic loading rate should be no more than 25cm/d in order to keep the systems running steadily in a long term.○5 Ambient temperature has great effect on system pollutant removal performance. Infiltration system can work properly when ambient temperature is above 15℃, and the effluent quality remains stable. But the effluent quality deteriorates when ambient temperature is below 10℃.○6 System saturated infiltration rate increases along with the soil proportion decreases in the filler system, so does the system permeability. Among the four infiltration systems, the system with a 2:5:5:1 material A/sand/soil/scrap iron ratio has the best balance between pollutant removal performance and saturated infiltration rate, and its filler components ratio is the most suitable for septic tank effluent land infiltration treatment system.
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