Promoting effects of corn straw and exceed sludge as carbon sources on denitrification of constructed wetlands

Abstract

As the low C/N ratio of effluent from wastewater treatment plant, the advanced treatment of constructed wetlands (CWs) on the effluent is often unsatisfactory, especially for the removal of N. In order to increase the N removal efficiency, this paper tested three kinds of carbon sources acid and alkali treated straw, alkali treated straw and exceed sludge for promoting the denitrification of CWs. The results showed that alkali treated straw performed the strongest carbon release ability (0.43mg?g-1?h-1) and the maximum C/N ratio (27.3). While acid and alkali treated straw's carbon release ability and C/N ratio were 0.37 mg?g-1?h-1 and 12.8, exceed sludge's carbon release ability and C/N ratio were 0.37 mg?g-1?h-1 and 8.4. In order to improve the C/N ratio in CWs to 5/1, 450g alkali treated straw and exceed sludge were added into tide flow wetlands (TFCWs) and subsurface flow wetlands (SSFWs) respectively to test the improvement of denitrification. Compared with the control groups, the N removal of CWs with carbon sources were significantly improved. CWs with alkali treated straw showed better removal effects of N than CWs exceed sludge. The analysis results of the first-order kinetic process suggested that the denitrification rate constants of TFCW control group, TFCW with exceed sludge and TFCW with alkali treated straw were 0.126, 0.262 and 0.345, respectively. The denitrification rate of TFCW with alkali treated straw was 2.74 times of TFCW control group, and 1.32 times of TFCW with excess sludge. This study has contributed to understand the possibility of straw and exceed sludge as the carbon sources to strengthen the denitrification in CWs.