| Recently, the non-ponit source pollution has significant impacts on both Tailake eutrophication and sustainable developing. Rural domestic wastewater is one of the most important fractions of nonpoint sources and treatment of rural domestic wastewater have been put on the agenda.Soil infiltration system treating sewage is very adaptable to rural in unsewered areas, which has become a new hot spot of Land Treatment Techniques, because of its most desirable for the efficiency and economy, flexibility in operation and management.Both of the infiltration system and the modified infiltration system were constructed and used for treating rural domestic wastewater. Initially, the influences of hydraulic load, artificial reaeration and growing plants, pollutants loading rate on pollutants removal as well as the removal efficiency of COD, TN, NH3-N and TP for modified infiltration system were discussed. Subsequently, the porosity and the changes of earthworm number were investigated to explore the effect of the earthworm on the modified infiltration system for sewage treatment. Finally, enzyme activities were studied in the modified infiltration system and obtained the main results as follows:Although good removal of chemical oxygen demand (COD) and total phosphorus (TP), the infiltration system may not adequately remove nitrogen, particularly nitrate nitrogen (NO3-N) and total nitrogen (TN). The removal of COD, TN, NH3-N and TP were investigated by the condition of sewage treatment with use of modified infiltration system, respectively. The results showed that the removal efficiency of COD, TN, NH3-N and TP was 70%～80%,60%～80%,85%～90% and 90%～95%, respectively, which was satisfied with the requirements of disposal of sewage.The removal efficiency of COD was 80%～90% when the hydraulic loading reduced from 0.1 m3·m-2·d-1 to 0.02 m3·m-2·d-1. Combined with the real run condition, the modified infiltration system has better anti-impact capability and has 0.05 m3·m-2·d-1 as the most suitable range. The removal efficiency of TN and NH3-N was improved 60%～80% and 85%～90% after artificial reaeration. The removal efficiency of TP was 90%～95% because of adsorption of phosphorus in fillers. The results showed modified infiltration system was not only satisfied with the requirements of disposal of sewage, but also low in energy consumption, and easy in operation and maintenance.The influence of the number change and the existence of earthworm on the soil structure were investigated as well. The results showed that earthworm could increase the dissolved oxygen of the effluent (1.7～3.4 mg·L-1) and increase the removal efficiency of organic matter. There existed very large difference in porosity of soils in between 15cm and 5cm, which increased 60%. Besides, the soil porosity was proved with the addition of the earthworm. There were decreased 34% in the number of the earthworm under 5cm depth. Conversely, capillary infiltration provided a suitable condition for the existence and breeding of earthworm. In the depth of 10～20 cm, the number of earthworm increased quickly.Enzyme activities in the substrates were analyzed, and the results indicated that enzyme activities of soil were remarkably higher than that of sand and gravel. Urease activities were no obvious correlative with the TN removal, and there were no correlation between urease activities and the COD removal, between dehydrogenase activities and the removals of COD and TN, between phosphatase activities activities and the removals of COD and TN.There verified that the pilot scale test for the rural domestic sewage treatment had higher ability to remove pollutants. The results showed modified infiltration system was satisfied with the requirements of disposal of sewage to the national primary standard A. As well as, the modified infiltration system has significant potential and advantages for the removals of pollutants especially N and P, operating cost and maintenance management. Overall, the essay concluded that the process were feasible either from the technological or economy for treating rural domestic wastewater in the rural area tour having certain free land.
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