反硝化生物滤池反冲洗周期优化及水力特性

Optimization of backwashing cycle and hydraulic characteristics of denitrifying biofilter

为探究反硝化生物滤池(DNBF)的最适运行参数和反冲洗周期,分别以石英砂和火山岩构建起2套DNBF,优化了水力停留时间(HRT)和碳氮比(C/N);通过滤池的处理效果、停留时间分布(RTD)分析和水力模型拟合确定了最佳的反冲洗周期。结果表明:在DNBF稳定运行后,2种填料的滤池处理效果相近,当HRT和C/N分别为2 h和4∶1时,出水的化学需氧量(COD)和总氮(TN)分别是(28.3±1.2) mg·L-1和(2.5±0.3) mg·L-1,此时碳源利用率较高;由脱氮性能和RTD分析得出的最佳反冲洗周期为1 d,出水COD和TN可分别达到(17.9±1.4) mg·L-1和(1.8±0.2) mg·L-1;当反冲洗周期延长后,滤池出水COD上升,脱氮性能大幅度下降,RTD曲线出峰从1θ(标准化时间)提前到0.5θ处、1.25θ和1.5θ处出现沟流现象,滤池中的流态趋向于混流式的多釜串联模型。通过RTD实验揭示不同反冲洗工况下DNBF内部水力特性的变化,可用于优化滤池的反冲洗周期。

To explore the optimal operating parameters and backwashing cycle of denitrifying biofilters(DNBFs),two DNBFs were constructed with quartz sand and volcanic rock served as their respective filter material.Hydraulic retention time(HRT)and carbon/nitrogen ratio(C/N)of DNBFs were optimized.Then the optimal backwashing cycle was determined by the treatment effect,residence time distribution(RTD)and hydraulic model fitting.The results showed that two DNBFs had the similar performances after their stable operation.At 2 h HRT and 4:1 C/N ratio,chemical oxygen demand(COD)and total nitrogen(TN)of the effluent were(28.3±1.2)mg·L-1 and(2.5±0.3)mg·L-1,respectively,and a good carbon source utilization efficiency for denitrification was achieved.Through nitrogen removal performance and RTD analysis,the optimal backwashing period was determined as 1 d,then COD and TN concentrations in the DNBFs effluent reached(17.9±1.4)mg·L-1 and(1.8±0.2)mg·L-1,respectively.When the backwashing cycle was extended,the effluent COD concentration increased and the denitrification performance deteriorated.The time for peak appearance of the RTD curve moved forward from 1θ(normalized time)to 0.5θ,the channeling phenomena occurred at 1.25θand 1.5θ,and the flow regime in the DNBF approached a mixed-flow multi-tank series model.The study indicated that the RTD experiment could reveal the change of internal hydraulic characteristics of DNBFs under different backwashing conditions,which can be used to optimize the backwashing cycle of the filter.