Study On Municipal Wastewater Treatment Using Constructed Rapid Infiltration System With Pre-denitrification

Constructed Rapid Infiltration system ?CRI?,which is characterized with low cost, low energy, easy to operate and good effluent quality, in recent year has been widely researched and applied in China. The relevant studies have shown that the result of denitrification is not satisfying because of can't provide oxygen-deficient environment and organic carbon source for denitrifying bacteria at the same time. Therefore, more and more study focuses on reinforcing the ability of denitrification in CRI system.In order to simulate CRI system, two artificial sand columns was applied in the experiment. The efficacy of wastewater treatment of two-stages CRI with pre-denitrification was studied. The paper analyzes the removal efficiency and regularity of the organic matter and nitrogen, optimization CRI mode of operation improve the removal efficiency of nitrogen in CRI system, and gets the best operating parameters of reflux ratio. In the meanwhile, the theory in organic matter and total nitrogen removal was analyzed. Moreover, the derivation of the kinetic model as to the denitrification system was also conducted.The biofilm formation and start-up of the A/O CRI system were performed by natural biofilm formation which have two stages. Keep the reflux ratio is 100% and hydraulic load is 80cm /?cm2·d?,that is reflux effluent of O-CRI system. The start-up took 34 days to succeed in cultivation bio-film, and the removal ratio of TN ,NH4+-N, gets to 35% and 70% separately in A/O CRI system.When the A/O CRI system becomes stable, keep the reflux ratio is 100% and hydraulic load is 80cm /?cm2·d?. The removal rate of TN was 40.8%. Addition of organic carbon from wastewater and NO3--N from effluent of O-CRI system in A-CRI system can enhance the denitrification process and improve the nitrogen removal efficiency. The reflux ratio affect the nitrogen removal efficiency significantly but the COD and NH4+-N removal efficiency slightly.In order to improve the removal rate of TN by using the solubility of NO3--N,and re-distribute nitrification liquor recycling in O-CRI system for improve reaeration.Experiments showed that the removal rate of COD was 93%,the removal rate of NH4+-N was improved from 79.9% to 93%.At the same time as the the sewage leaching for NO3--N , the nitrate nitrogen back into the A-CRI system , would promote the removal efficiency of TN to 78%.The reflux ratio affect the nitrogen removal efficiency significantly. In this paper, the removal efficiencies of COD, ammonia and total nitrogen ?TN? were investigated under reflux ration of 50%,75%,100%,respectively.Results showed the removal efficiencies of TN were best at the optimal reflux ratio of 75%,with the hydraulic load is 80cm /?cm2·d?.When hydraulic loading rose from 60cm /?cm2·d? to 120cm /?cm2·d?,reflux ratio decreased from 100% to 50%,the average concentrations of TN were rose from 8.9mg/L to 19.0mg/L, with the average removal rate of TN fell to 77.4% from 50.8%.For the two-stage A/O CRI system with re-denitrification, the kinetic model of denitrification in the A-CRI system, based on Eckenfelder model, was illustrated asfollows: ?S_e?/?S₀?=e⁽?-3.4301H?/(q^2.2354)).