Effect of Trace Elements on Anaerobic Digestion of Coking Wastewater

The pretreatment of coking wastewater using ASBR was conducted at 35° in this paper. The addition of trace elements to the anaerobic reactor has positive effect on the anaerobic treatment of coking wastewater, but too much or too little of it will have negative effect. At the same time the addition of trace elements will be a large cost in field scale anaerobic wastewater treatment. So it is necessary to assay the optimal addition of trace elements to either enhance the anaerobic treatment efficiency or save the cost of addition trace elements. As the coking wastewater is generated in the coal gas purification and by-product recovery processes, there will be some trace elements remain in wastewater, which can save the cost of addition trace elements to coking wastewater than other wastewater anaerobic treatment. After three months´ stable operation at the optimal conditions and with the general addition of trace elements in ASBR, the optimal addition of trace elements was conducted in this study. In the condition of the addition of 60% of general trace elements into ASBR reactor, the COD removal rate could reach as high as 67.8% and had a high biomass remain in the reactor. But too low concentration of trace elements resulted in poor treatment efficiency. When the amounts of trace elements added into the ASBR decreased from 100% to 60% of general addition, the configuration of granular turned looser and the dominant bacteria in the granular turned from Methanosarcina to Methanosaeta.