Research On Enhancement Of Anaerobic/Aerobic Combined System For Dyeing Wastewater Treatment By Iron-Carbon Internal Electrolysis

Dyeing wastewater is generally hard to degrade under high influent loadings. Compared to anaerobic or aerobic treatment method, anaerobic-aerobic combined process has the advantages, such as high removal efficiency, stable operation and strong shock resistance. And it has proven effective for the elimination of both color and organic carbon. Anaerobic reactor can degrade the organic pollutants in wastewater to a certain extent with relatively low operating cost, saving a lot of energy consumption for the following aerobic treatment. Thus, anaerobic technology becomes the key of dyeing wastewater treatment by this process. Up-flow anaerobic sludge bed (UASB) reactor, the most widely used effective anaerobic reactor in recent years, has a feature of simple structure, high treatment load, without need of aeration and stir equipments, no sludge return system, stable operation and good treatment effect. But it is still limited by slow granulation. The main reason for this is the slow growth of methanogens that are very susceptive to some environment conditions, such as pH, DO, temperature and toxic substance.In this subject, a punched column with three layers of iron-carbon (ZVI/AC) was built in the UASB reactor. Iron-carbon internal electrolysis reaction could take place due to the reducibility of iron, which created anaerobic environment suitable for the growth of methanogens. Then the wastewater treatment efficiency of anaerobic/aerobic sequential reactor system was improved. Under the conditions of influent COD concentration5000mg L-1, initial azo dye concentration100mg L-1and hydraulic retention time (HRT) of the anaerobic stage24h, the following conclusions could be drawn:(1)The addition of iron-carbon layers to the UASB reactor improved the anaerobic environment. The pH maintained between6.3-6.8and the oxidation-reduction potential stayed below-300mV. These approached the optimum conditions for the growth of methanogens. As results, the sludge granulation was accelerated and the COD removal rate of the anaerobic stage was increased from60%to90%. The total HRT of the sequential treatment system with the addition of iron-carbon layers was shortened significantly when the final effluent reached the same COD concentration. As HRT of the aerobic stage was16h, the COD concentration of final effluent was decreased from230mg L-1to80mg L-1. (2) Fe2+generated by the iron-carbon internal electrolysis reaction not only enhanced sludge granulation but also oxidized to Fe3+in the aerobic stage. Fe3+interacted with dark-colored autoxidation products to produce flocculant precipitates, resulting in low final effluent color. As HRT of the aerobic stage was16h, the total decolorization efficiency was increased from94.82%to98.22%. In addition, some products of iron-carbon internal electrolysis reaction may be beneficial to the growth of nitrobacteria, which improved the NH4+-N removal rate. The mineralization of aromatic amines mainly occurred in the anaerobic stage, but not obviously influenced by internal electrolysis reaction.(3) Iron-carbon internal electrolysis reaction not only promoted the growth of methanogens in the anaerobic stage, but also favored the growth of the bacteria related to dye degradation.