Preliminary Study On Nitrogen-retention Treatment Of Small-town Sewage For Agricultural Use

In northern China where water resources are scarce,COD in sewage for agricultural use needs to be removed to meet the standard,but the nitrogen-based nutrients can be intentionally retained,not only reducing the cost of nitrogen removal,but also partially replacing fertilizer input to reduce non-point source pollution.This paper investigated the feasibility of using nitrification inhibitors to weaken the nitrification and denitrification of activated sludge,and provides a reference for the nitrogen retention treatment of sewage for agricultural use in water-scarce areas in northern China.Using simulated domestic sewage with a COD concentration of 215.3 mg/L and a C/N ratio of 4.6,an aerobic batch treatment test was carried out to compare the effects of a typical competitive nitrification inhibitor dicyandiamide(DCD)and a typical non-competitive nitrification inhibitor thiourea(TU)and its derivatives on the nitrification and pH change of activated sludge cultured under intermittent aeration.The aerobic batch test results at different temperatures and pH conditions showed that regardless of whether the pH was buffered or not,DCD acted as a competitive nitrification inhibitor at the rate of 2-4 mg/L had a weak nitrification inhibitory effect(<10%)on the aerobically activated sludge of normal concentration range(> 1.0 MLSS g/L);the non-competitive nitrification inhibitor thiourea showed a significant nitrification inhibitory effect at a low dose(0.125 mg/L)on activated sludge(> 45%),slowed down the pH drop,and its nitrification inhibitory effect was better than its derivatives propylene thiourea and succinylthiourea;compared with the use of thiourea alone,the combined use of DCD and thiourea did not show an enhanced nitrification suppression effect.Based on the results from the aerobic batch test,thiourea was selected as the nitrification inhibitor in order to improve the nitrogen-retention efficiency during intermittently aerated treatment of simulated wastewater by activated sludge in sequential batch reactor(SBR).The results show that the addition of thiourea at a concentration of 0.125 mg/L during weak intermittent aeration of activated sludge did not affect COD removal,but inhibited nitrification to significantly increase the concentration of ammonium nitrogen and reduced the concentration of nitrate nitrogen to lower nitrogen loss via denitrification,and overall increased the concentration of inorganic nitrogen in the effluent by more than 30%.Therefore,thiourea can be used as nitrification inhibitor in intermittently aerated treatment of sewage by activated sludge in SBR in water-scarce areas,which not only reduces the cost of sewage treatment,but also better meets the requirements for irrigation,but further study is needed on the long-term sustainability of thiourea as nitrification inhibitor for nitrogen-retention treatment of sewage for agricultural use.