Study On Treatment Of Wastewater From Small Township By A Constructed Rapid Infiltration System

The rapid development of small towns accelerates environmental pollution and water shortage in our country. Appropriate treatment and reuse of wastewater become a concern in rural modernization. The object of this study was to investigate the effect of the Constructed Rapid Infiltration System (CRIS) on small town wastewater treatment and the applicability of reclaiming the wastewater in vegetable planting.Pilot tests were performed to optimize the design and operation parameters of the CRIS. The cycles consisted of ten factorial combinations of three soil-quartz ratios (1:1,2:1 and 3:1), two filling thicknesses (80cm and 100cm), four operating-drying schedules (1:1,1:2, 1:3 and 1:5) and three operation durations(<1day,1day and 3days). And the effluents from the system are applied to vegetable planting. COD,TP,TKN and NH4+-N are tested regularly.Results are the followings:The Constructed Rapid Infiltration System is suitable for removing COD and TP in wastewater from small townships. The highest removing rates of COD and TP reached 73.19% ± 1.78 % and 94.30 % ± 2.31 % respectively. But the removing rates of TKN and NH4+-N were pretty low, less than 20%.The treated water can meet the needs of the new Standard for reusing Township Wastewater for Agricultural Irrigating which is under editing.The ratio of operating-drying schedule was critical to the system's performance. Under medium-cycle and long-cycle situations, the smaller the ratio, the higher the removing rate of COD. The same phenomenon were observed in phosphorus elimination.No significant difference was observed between soil-quartz ratio of 2:1 and 3:1 of COD and phosphorus removing.The operating cycle has great impact on the system's performance. Under the ratio of 1:1 and 1:2, with the increase of the cycle length, the removing rate of COD drops and that of phosphorus increases. Under the ratio of 1:3 and 1:5, the removing rate of COD and phosphorus increase with the increase of the cycle length except columns filled with soil and quartz sand at volume ratio of 2:1, which are hardly affected by the length of operating cycles.There are no significant differences between the yields and the contents of harmful substances of vegetables irrigated by effluent of the system and those by fresh water.Therefore it is feasible to use the effluents of the constructed rapid infiltration system for irrigating leave vegetables.