The Strengthening Effect Of Zero Valent Iron On Anaerobic Biodegradation Of 2,4,6-Trichlorophenol And Its Mechanism

In this paper, 2,4,6-trichlorophenol(2,4,6-TCP) was the target pollutants, a preliminary exploration on the degradation characteristics of 2,4,6-trichlorophenol in single sludge system and zero valent iron(Fe0)/acclimated sludge under anaerobic system. And factors that effected Fe0/anaerobic microbial combined system were investigated, on the base of above, the present study focused on the degradation of 2,4,6-trichlorophenol under different redox conditions, and the impact of different carbon sources under nitrate-reducing conditions. In order to reveal the complex mechanism of the combined system, it also discussed the reductive dechlorination of 2,4,6-trichlorophenol and the corrosive process of Fe0 and its effect on degradation efficiency in combined system at different initial pH values. The results showed that,(1)Glucose as co-substrate, in both single sludge system and Fe0/anaerobic microbial combined system, 2,4,6-TCP could be degraded effectively. The process of acclimation was sped up by adding zero-valent iron and the removal rate of 2,4,6-TCP was increased.(2)The optimum conditions of 2,4,6-TCP(the initial concentration of 25 mg/L) degradation in Fe0/anaerobic microbial combined system were as follows: inoculation quantity of anaerobic sludge, 289.0 mgVSS/L, Fe0 dosage, 1.0 g/L, initial pH value, 8.0, amount of glucose, 0.5 g/L.(3)The reductive dechlorination of 2,4,6-TCP was significantly inhibited under nitrate-reducing conditions, nitrate-reduction activity increased with the increasing of initial nitrate concentrations. The degradation products of 2,4,6-TCP at an initial concentration of 5 mmol/L were 2,4-DCP and 4-MCP, and the accumulation of 4-MCP was found in system.(4)In acclimated sluge, 2,4,6-TCP dechlorination bacteria was not denitrifier. while there have both 2,4,6-TCP and nitrate, nitrate is reduced in this system followed by the reductive dechlorination of 2,4,6-TCP.(5)Under nitrate-reducing conditions, with different carbon sources, the degradation of 2,4,6-trichlorophenol in Fe0/anaerobic microbial combined system was conformed to the first-order kinetic model, the order of the reaction rate constant was k(glucose)> k(acetate)> k(lactate)>k(without added carbon source)>k(formate). (6)Sulfate and the mixed reduction environment both went against the degradation of 2,4,6-TCP in Fe0/anaerobic microbial combined system.(7)The continuously corrosion of Fe0 could produce electrons in Fe0/anaerobic microbial combined system in different initial pH values. The opitimal initial pH value for the degradation of 2,4,6-TCP was 9.0 in single sluge system, while 8.0 in the combined system. The products of zero valent iron's corrosion, Fe2+ and Fe3+, showed inhabitory effect on the degradation of 2,4,6-TCP in some degree, which was enhanced with increasing of Fe3+ concentration.(8)Fe0 reduced the demand for microorganisms on organic matter, the removal rate of COD decreased. Residual concentration of 2,4,6-TCP had some relevance to electron transport system activity.(9)The major pathway of 2,4,6-TCP degradation in Fe0/anaerobic microbial combined system was: 2,4,6-TCP→2,4-DCP→4-CP, and the accumulation of 4-MCP was found in system.