Complexity of water quality in landfill leachate seriously inhibits the anaerobic treatment process, though the anaerobic biological system is the primary process of leachate treatment. Studies have shown that moderate addition of trace elements effectively promotes the anaerobic process and alleviates toxicity effect of certain substances in leachate. In view of the poor performance of anaerobic treatment caused by the complicated characteristics of leachate, and the incomplete researches on the effects of trace elements on anaerobic process for leachate treatment, this study investigates the effects of Fe2+, Co2+, Ni2+, and their combinations on the anaerobic treatment of leachate from domestic waste landfill site in Guangxi, aiming to provide important basis for improving the treatment efficiency of leachate. The main research contents and conclusions of this paper are as follows:Results of single-factor batch assays show that the effects of Fe2+, Co2+and Ni2+on the anaerobic treatment of leachate present the Hormesis effect (defined as a stimulatory effect of sub-inhibitory concentrations of toxic substances). The addition of trace elements not only promotes the anaerobic microorganisms to utilize recalcitrant organic compounds in leachate, but also improves the specific methanogenic activity (SMA) of the sludge, which results in the increase of methane yield in system. Furthermore, due to the limitation of various ligands in leachate to the bio-availability of trace elements, the requirement of leachate anaerobic treatment to trace elements appears to be higher than other systems.Though the similar stimulations of respective trace elements with a certain concentration range are observed, results of orthogonal batch assays also show that Fe2+is the major factor on anaerobic process for landfill leachate. The combinations can effectively facilitate the anaerobic treatment for landfill leachate when the dosages of Fe2+, Co2+and Ni2+are5mg·L-1,0.5~3mg·L-1and0.5~3mg·L-1, respectively.The contrast operation test results of UASB indicate that the start-up of the reactor can be completed in36d by gradually changing the gradient concentration of leachate and improving the VLR. At steady operation stage, the COD removal rate and the biogas yield might achieve above60%and3000mL·d-1, respectively, when the HRT dropping to20~24h and the VLR reaching to3-6kg-COD/(m3·d). At impact-load stage, the sudden change of VLR adversely affects the reactor operation and simultaneously when the HRT fall to12h, the contact and reaction time of anaerobic microorganisms with the substrate appears to be insufficient. The addition of combined Fe2+, Co2+and Ni2+can promote the efficiency of leachate treatment using the UASB reactor, with the COD removal rate and biogas yield superior to the control group all through the operation stage. Furthermore, the application of trace elements prompts the sludge proliferation to be more apparent, and improves the sedimentation performance of sludge. Meanwhile, the distribution of Methanobacteriaceae in the granular sludge becomes more intensive, but the community composition has no significant variation compared with the control group. |