Evaluation of Advanced Nitrogen Removal from Coking Wastewater Using Sulfide Iron-containing Sludge as a Denitrification Electron Donor

Abstract

In general, it is difficult to reach the total nitrogen discharge standard in the effluent after municipal and industrial wastewater treatment. The problems hindering advanced denitrification include an unstable C/N ratio in the influent wastewater, increased hydraulic loading with increasing reflux ratio, reduced reaction kinetics, high energy consumption, and secondary pollution and high sludge yield resulting from addition of organic carbon sources. Therefore, deep denitrification with the advantages of energy savings and easy operation is urgently needed. To address these issues, chemical iron sulfide sludge, collected after the pretreatment of sulfur-containing industrial wastewater, was used as a solid-phase electron donor to perform advanced denitrification using autotrophic denitrifiers. In this study, the secondary biological effluent of coking wastewater was the influent for denitrification and the performance of denitrification, transformation of sulfide and iron in the sludge, and microbial community changes were investigated. The optimal reaction conditions and effect range of the technology for deep denitrification of wastewater were then calculated. When the concentrations of NO3--N and NO2--N in the influent were (74.54±0.57) and (1.11±0.19) mg·L-1, respectively, the corresponding concentrations in the effluent were reduced to (2.78±1.08) and (2.87±0.71) mg·L-1, respectively, with a hydraulic retention time (HRT) of 18 h. The removal rate of TON (NO3--N+NO2--N) was as high as 90.0%, of which the reduction rate of NO3--N and the accumulation rate of NO2--N were 12.06 and 7.74 mmol·(L·d)-1, respectively. This study showed that the use of chemical sulfide iron sludge as an electron donor for deep denitrification is of practical importance, as it could simplify the subsequent treatment of sulfur- and iron-rich chemical sludge, finally reaching the goal of resource utilization.