Study On Inhibition And Recovery Of Biological Denitrification Activity By Cr(Ⅵ) Impact

Due to improper pretreatment measures in industrial enterprises and leakage of wastewater,the wastewater biological treatment system may be impacted by high concentrations of heavy metals,and the biological denitrification process may be inhibited,resulting in the effluent nitrogen content exceeding the standard,thus affecting the water quality.Therefore,it is of great significance to study emergency treatment methods for rapid recovery after denitrification process is inhibited.In this study,eight groups of traditional denitrification biofilm reactors were constructed as research objects,and the effects of Cr（Ⅵ）cascade impact and direct impact on denitrification effect of denitrification system were investigated.The effects of natural recovery method,basic accelerator,anthraquinone-2,6-disulfonate（AQDS）accelerator,humic acid（HA）accelerator and riboflavin（VB₂）accelerator on the activity recovery of the inhibited system were developed and explored.The changes of microbial community structure and functional genes in the system under different conditions were monitored by functional genes and microbial high-throughput sequencing technology.The impact results of Cr（Ⅵ）cascade experiments showed that under the condition of low Cr（Ⅵ）concentration（20～80 mg/L）,the removal effect of COD and NO₃^--N in denitrification system has no obvious change.When the concentration of Cr（Ⅵ）increased to 100～125 mg/L,the denitrification system was severely inhibited,and the removal rates of COD and NO₃^--N in the reactor were 7.8～10.4%and18.9～21.3%,respectively.The accelerant could quickly restore the activity of the inhibited system within 42 cycles（about 7 days）.The removal rates of COD and NO₃^--N in the effluent reach 96.0%and 99.6%,respectively.The system need 68cycles of natural recovery to reach the same recovery level.The direct impact test of Cr（Ⅵ）showed that the denitrification system had poor tolerance to direct impact of high concentration Cr（Ⅵ）,and the removal rates of COD and NO₃^--N decreased sharply,reaching 10.9%and 15.4%respectively.Four kinds of biological accelerators promoted the recovery of system activity,and the highest removal rates of COD and NO₃^--N were 95.0%and 99.7%.The recovery rates of the system under different recovery methods are in the order of AQDS accelerator>VB₂ accelerator>HA accelerator>Basic accelerator>Natural recovery.High throughput analysis of functional genes found that redox mediator accelerator could effectively improve the species richness and diversity of denitrifying bacteria,and the microbial population structure at genus level in the system changed greatly before and after the impact.The accelerator formula developed in this study can provide technical reference for emergency treatment and recovery of sudden heavy metal impact in biological treatment process in sewage treatment plant.