Study On Artificial Wetland System Solid Carbon Source To Strengthen Denitrification

There are less carbon and nitrogen in the wastewater after treating by anaerobic digestion and artificial wetland enhancement in Chinese rural pig free-range farms. In order to enhance the remove of total nitrogen, this study chose four kinds of common straw including rice straw, wheat straw, corn straw and sorghum straw as solid carbon source of denitrification to optimize the pretreatment conditions through the reducing sugar content during enzymatic hydrolysis reactions. In the flask experiments, we examined the denitrification performance when we pretreated the straws as solid carbon source. What’s more, we built two parallel artificial wetland operations to strengthen denitrification and compared the effluent using rice straw without pretreatment and pretreated by calcium hydroxide as carbon resources respectly. The influences of other process parameters incuding nitrate nitrogen, hydraulic load, temperature and so on were also studied to analyze the characteristics of organic matter removal performance. Then the microbial community structure of the artificial wetland were studied through high-throughput sequencing technologies. The main conclusions are as follows:(1)Four kinds of common straw including rice straw, wheat straw, corn straw and sorghum straw pretreated by water and calcium hydroxide soaking were used as solid carbon source of denitrification to optimize the pretreatment conditions through the reducing sugar content during enzymatic hydrolysis reactions. The result showed that the enzymolysis effect of the staws with alkali pretreatment was significant. In a saturated solution of calcium hydroxide at 30°C, the optimal pretreatment time of four kinds of straws was 3 days, the best solid-liquid ratio were 1:30.(2)The results of the flask experiments showed that four kinds of the straws have obvious effect on nitrogen removal in the first day with the concentrations of nitrate nitrogen less than 10 mg/L. The denitrification effect was stable during 15 days. Compared to denitrification rates of the straws with and without soaking using water, the denitrification rate of the straws using alkali for pretreatment has increased significantly. The denitrification rate of rice straw, wheat straw, corn straw and sorghum straw using alkali for pretreatment were 0.074 mg/( g.h), 0.056 mg/( g.h), 0.055 mg/( g.h) and 0.077 mg/( g.h), respectly. The long running experiment of flasks with rice straw showed that the denitrification performance reduced with the extension of time.(3)Comparing the effluent of two parallel artificial wetland operations using rice straw without pretreatment and perpetrating by calcium hydroxide as carbon resources, we obtained the denitrification rate of the alkali soaking rice straw system under were significantly higher than that of the system using water for soaking straw under different nitrate nitrogen concentration and hydraulic load.When the nitrate nitrogen of influent was about 150 mg/L(hydraulic loading was 120 L/d), the nitrate nitrogen concentration of adding the alkali and water for soaking the rice straw were 3.6 mg/L and 15.4 mg/L and the denitrification rate were 0.1562 kg/(m3, d) and 0.1447 kg/(m3, d).(4)Dissolved Organic Matter(DOM) were significantlyreduced after treating by two artificial wetland. The microbial bacteria of the rice straw system without soaking mainly attributable to the Bacteroidetes(22.46%) and Proteobacteria(48.68%). The dominant genus were Flavobacterium(4.49%)) and Hydrogenophaga(6.17%). The microbial bacteria of the rice straw system with alkali soaking mainly attributable to Bacteroidetes(35.28%) and Proteobacteria(42.33%) and the dominant genus was Saprospiraceae_uncultured(13.32%).