Study On Nitrogen Removal By Denitrification Of Wastewater Using Agricultural Straw Fermentation Liquid As Carbon Source

In order to solve the problem of insufficient carbon source for nitrogen removal by denitrification in municipal wastewater treatment plants and to explore the recycling use of agricultural straws,four kinds of agricultural straws,i.e.,rice straw&corn stalk&rape straw and sugarcane peel,were used for anaerobic fermentation at three different temperatures of 25℃,35℃and 55℃and the solid concentration of 5%,10%and 15%in this study.By measuring the values of the soluble chemical oxygen demand（SCOD）,volatile fatty acid（VFA）and lactic acid and total nitrogen（TN）,the suitable straws fermentation broth was chosen as the external carbon source for denitrifying in wastewater.Furthermore,to obtain the optimal addition amounts of straws fermentation broth in different seasons,the effects of denitrification were investigated by adding the straws fermentation broth as an external carbon source according to COD/TN ratios of 4,6,8 in spring&autumn,summer and winter.Then the nitrogen removal efficiencies of the practical wastewater under the process of the aerobic/anoxic/aerobic/anoxic multistage SBR at the different seasons were studied by adding the optimal amounts of straws fermentation broth as an external carbon source.The main research results were as follows:（1）The optimum anaerobic fermentation temperature of rice straw,corn stalk,rape straw and sugarcane peel were 35℃among 25℃,35℃and 55℃different temperatures.There was more the higher quality carbon source in the fermentation broth of corn stalk and sugarcane peel than in the one of rice straw and rape straw.Therefore,the fermentation broth of corn stalk and sugarcane peel have more potential as external carbon source.According to the ratio of the total concentration of VFA and lactic acid to TN concentration in the straw fermentation broth,the optimum fermentation conditions of corn straw and sugarcane peel were obtained as follows:the temperature of 35℃and the solid concentration of 5%,and the ratios were 47.2 and 91.9,respectively.（2）The optimal dosages of corn straw and sugarcane peel fermentation broth as external carbon source in different seasons were studied under the condition of three dosages of COD/TN为4,6,8.The results showed that in spring&autumn when the initial concentration of NO₃^-was 90mg/L,the optimal dosages of corn straw and sugarcane peel fermentation broth as carbon source were 6 and 8,respectively,and the removal rates of nitrate nitrogen were 97.3%and 100%respectively;When the initial concentration of NO₃^-was 180mg/L,the optimum dosages of corn straw and sugarcane peel fermentation broth were 4 and 6,respectively,and the removal rates of nitrate nitrogen were 95.0%and 99.0%,respectively.In summer,when the initial concentration of NO₃^-was 90mg/L and 180mg/L,the effect of nitrogen removal was the best when corn straw and sugarcane peel fermentation broth was used as the external carbon source,when the optimal dosages were COD/TN为4.The removal rates of nitrate nitrogen were in the range of 96.5%⁹9.9%and 96.9%⁹7.4%respectively.In winter,when the initial concentration of NO₃^-was 90mg/L,the optimum dosage of corn straw and sugarcane peel fermentation broth as carbon source was8,and the removal rate of nitrate nitrogen was 54.8%and 61.8%,respectively.When the initial concentration of NO₃^-was 180mg/L,the optimum dosage of corn straw and sugarcane peel fermentation broth as carbon source were 6 and 4,and the removal rate of nitrate nitrogen was 52.7%and 59.4%respectively.In winter,the denitrification efficiency of adding corn straw fermentation broth and sugarcane peel fermentation broth as the external carbon source was not high.After increasing the dosage,it was found that although the denitrification efficiency increased,the COD load increased greatly.（3）In spring&autumn and summer and winter,the nitrogen removal efficiency were 68.1%,87.0%and 77.7%respectively when the corn stalk fermentation broth was used as the external carbon source in the multi-stage SBR process.The nitrogen removal efficiency were68.3%,90.4%and 76.5%,respectively,when the sugarcane peel fermentation liquid was used as the external carbon source in the multi-stage SBR process.Two kinds of straw fermentation broth had the best nitrogen removal effects in summer,and the effect of nitrogen removal in winter was better than that in spring&autumn.