Submicron magnetite enhanced simultaneous denitrification and degradation of phenol and quinoline

A large amount of coking wastewater will be generated and discharged during the production process of the coke industry. Such a refractory organic industrial wastewater contains ammonia nitrogen, cyanide, phenols, nitrogen heterocyclic aromatic hydrocarbons (such as quinoline. etc.), and polycyclic aromatic hydrocarbons, etc. Common biological treatment technology is often faced with the problem that it is difficult to meet the discharge standard of COD and ammonia nitrogen at the same time, which will pose a huge threat to human health and the ecological environment. At present, the biological treatment of coking plant wastewater mainly includes anaerobic-anoxic-oxic (A(2)/O), sequencing batch reactor activated sludge process (SBR), biological aerated filter, etc. However. these conventional biological treatment processes usually lead to the higher concentration of COD and total nitrogen (TN) in the effluent. which is difficult to meet the discharge standards. As a result, some new technologies for enhanced biological treatment of coking wastewater have been derived. For example, adding an aerobic unit (A(2)/O process) after the traditional A(2)/O or adding bioenhanced technology of phenol degrading bacteria can also improve the removal rate of pollutants (such as COD and ammonia nitrogen) in coking wastewater. However, these enhanced biological treatment technologies have many disadvantages, such as the increase of structures. the difficulty of maintaining the effectiveness of adding bacteria for a long time, and the high cost of capital construction and operation. In recent years, magnetite has been widely used in biological wastewater treatment because of its low cost. good conductivity and magnetism, and the micro-oxygen system can maintain its long-term mediating effect. In order to enhance the denitrification biodegradation of phenol and quinoline, the Fe3O4/AS composite system (R2) was established by adding submicron (0.1-0.3 urn) magnetite to the micro-oxygen continuous activated sludge reactor (AS). And explore its mechanism of action. The results show that after 80 d of operation under microaerobic conditions (DO =0.5-1.0 mg/L), the iron minerals in R2 reactor mainly exist in the form of magnetite and goethite. and the concentration of Fe2+ in effluent was always kept at about 0.2 mg/L, which effectively alleviated the reduction and dissolution of magnetite. When the concentration of quinoline in influent was 55 mg/L, the removal rates of COD, phenol. quinoline, NO3-N, total organic carbon (TOC) and total nitrogen in R2 were 38%. 49%, 65%, 64%. 23% and 98% higher than those in the control group RI respectively. In addition R2 had the better capabilities of mineralization and denitrification, and its removal rate of TOC and TN was increased by 23% and 100% respectively than that of RI. realizing the complete mineralization and removal of most of the pollutants. The mechanism research showed that the abundance of bacteria (such as Denitratisoma and Azoarcus) related to denitrification and aromatic degradation in R2 increased significantly; the addition of magnetite improved the secretion of extracellular polymer substances EPS (about twice as much as RI) and the cohesiveness of sludge microorganisms. Moreover, the concentration of extracellular electron shuttles (heme c and humic acid) in the EPS and the activities of enzymes related to pollutant degradation and nitrogen reduction were significantly increased (the dehydrogenase, nitrate reductase and nitrite reductase activities in EPS of R2 were 3.1, 5.8 and 4.3 times respectively). The addition of Fe3O4 significantly improved the degradation of quinoline and the activity and recovery of microorganisms, achieved better denitrification and carbon removal performance.