亚微米磁铁矿强化反硝化降解苯酚和喹啉

Submicron magnetite enhanced simultaneous denitrification and degradation of phenol and quinoline

导电性磁铁矿(Fe3O4)已被证实能促进厌氧微生物直接种间电子传递.然而磁铁矿在厌氧水处理过程中会被铁还原菌利用而溶解,造成大量磁铁矿随出水流失,影响其长期介导作用.基于此,本研究在微氧连续运行的活性污泥反应器(activated sludge reactor, AS)中投加亚微米级(0.1~0.3μm)磁铁矿建立Fe3O4/AS复合体系(R2),以强化反硝化生物降解苯酚和喹啉,并探讨其作用机理.结果表明,在微氧条件下(DO=0.5~1.0 mg/L)运行80 d后, R2体系有效缓解了磁铁矿的还原溶解,反应器中铁矿物主要以磁铁矿和针铁矿形式存在,其出水Fe2+浓度始终保持在0.2 mg/L左右;当进水喹啉浓度为55 mg/L时, R2体系中化学需氧量、苯酚、喹啉、NO3-N、总有机碳和总氮去除率比对照组R1分别提高了38%、49%、65%、64%、23%和98%.机理研究表明, R2中与反硝化和芳烃降解有关的菌属(如Denitratisoma和Azoarcus)丰度显著提升;磁铁矿刺激了胞外聚合物(extracellular polymeric substances, EPS)的分泌(约为R1的2倍)和污泥微生物间的凝聚;磁铁矿的加入显著提高了EPS中胞外电子穿梭体(血红素c和类腐殖酸)浓度以及与污染物降解和氮还原相关的酶活性(R2 EPS中脱氢酶、硝酸盐还原酶和亚硝酸盐还原酶活性分别是R1的2.4、5.8和4.3倍),从而加快了芳烃降解菌与反硝化菌之间的电子传递速率,实现了Fe3O4/AS体系更好的脱氮除碳性能.

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(A2/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(A2/O2 process) after the traditional A2/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 μm) 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 R1 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 R1, 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 R1) 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.