Study On Effects Of External Solid Carbon Source On Denitrification In Land Treatment System

Regional imbalance of the development of wastewater treatment has been observedin our country, wastewater treatment in rural areas have been neglected, which bringsserious environmental, public health and economical problems. In rural areas, domesticwastewater is mainly characterized by small amount and dispersion. In addition, in ruralareas there are restrictions of finance, technical and human powers. Wastewater landtreatment system is effective, with low cost, easily to be operated and managed. It issuitable for domestic wastewater treatment in rural areas. But wastewater land treatmentsystem is not effective enough for total nitrogen removing. High nitrate nitrogenconcentration has been determined in its effluent. This is mainly caused by incompletedenitrification process because of lacks in the necessary organic carbon source. Thesystem needs to add a carbon source in order to complete denitrification. The traditionalliquid carbon source has a high cost. It also could easily lead to secondary pollution.Recently the study to explore new safe natural solid carbon source has become popular.The study included two parts: first is a static test of carbon release of luffa andrecycled cotton. Second is a continuous-flow test. The two tests will help to find outcarbon sources’ characteristics of carbon-releasing and denitrification.During the static releasing test of solid carbon source, the effect of different sludgeconcentration has been studied. It has been found that the higher sludge concentrationhelps to enhance the organic carbon releasing of solid carbon source. In addition,temperature does have an influence on carbon releasing process, but it related to thesludge concentration at the same time. When temperature changes form25℃to30℃,the COD concentration increased in the sample of luffa with a sludge concentration of0g/L or1g/L, while it decreased with a sludge concentration of2g/L. Measured COD/TNratios in all the samples were always greater than2.86, as a conclusion luffa and recycledcotton could be used as external solid carbon source to complete denitrification.During th, ae continuous-flow testn external solid carbon source reactor was connected after the underground soil infiltration system simulation reactor. The influentof the wastewater land treatment system was prepared in laboratory, the quality of whichwas made close to domestic wastewater in rural areas. The water hydraulic loading wasalways fixed at0.4cm/d. All the effluents were measured once every two days. Thestart-up period of the entire system is very short. It only needed around8days to enter astable operation period. The underground soil infiltration system simulation reactor’sperformance in removing total nitrogen is not quite good, leading a high total nitrogenconcentration of its effluent. And total nitrogen remains in the form of nitrate nitrogen inthe effluent. After subsequent processing in the external carbon source denitrificationreactor, total nitrogen concentration has been reduced significantly, which was up to thenational plant effluent standard Class1B. The removal rate of total nitrogen has beenfound easily affected by temperature.