Pilot study of removing nitrogen from sewage in under ground-ditch-pattern soil treatment system
污水土地生态处理脱氮技术的中型试验研究

Underground-ditch-patter soil treatment is a procedure whereby sewage is treated through self-purification in conjunction with manual techniques in a small scale system. This process is a kind of fleet soil zoology treatment technology, which relies on the principles of diffusion and capillary action in soil. Under artificially controlled conditions, sewage was distributed into the designated system equipped with a series of devices composed of soil, sand, pebbles, and a soil-water-animalcule-filling system, and was gradually decomposed as a result of a series of physical, chemical and biological reactions in different pollutant loadings and HRT(retention time). Through the pilot plant of underground-ditch-patter soil zoology treatment system filled with soil mainly confected by yellow clay - the typical soil type found in Guizhou, this paper investigates the efficacy of such systems in removing nitrogen and the different factors that influence the rate of removal of nitrogen. Results showed that average removal rates of NH~ _4-N and TN were 84.7% and 70.7%, with average effluent concentrations of NH~ _4-N, TN being 14.0mg/L, 24.7mg/L respectively, which meets the standard for water reuse issued by the Ministry of Construction of China. Nitrogen transformation bacteria analysis revealed that there were abundant nitrogen transformation bacteria in the pilot system. 10~3~10~6cfug(soil,colony for ming unit), 10~3~10~6MPN/g(soil,most probable number), 10~4~10~6 MPN/g(soil), 10~3~10~6 MPN/g(soil), were obtained respectively for ammonifying bacteria, nitrite bacteria, nitrate bacteria, denitrifying bacteria. Nitrogen in the influent was mainly eliminated through biological removal via nitrification/denitrification processes. Improving the nitrification performance through alterations in the soil-water-animalcule-plant environment proved to be the key to enhancing nitrogen removal rate. Results showed that appropriate concentrations of C/N are necessary for the process of denitrification. Moreover, when the pilot system was implemented with HRT of 4.5h, the effluent concentrations of NH~ _4-N was 18.48mg/L and the removal rates of NH~ _4-N was 82.87%, which met the standard for wastewater emission control regulations II(<25 mg/L). Underground-ditch-patter soil zoology treatment system has much potential in disposal loadings. At a reduced cost compared to existing mechanisms and with easy operation and management, this technique has many opportunities for further research and development.