The Reinforcement Effect Of Zero Valent Iron On Reductive Dechlorination Of 2,4-Dichloro Phenols And Its Mechanism

Batch laboratory tests were conducted through inoculating the anaerobic mixed microorganism, to examine the effect of anaerobic biodegradation of 2,4-dichloro phenol(2,4-DCP) by the addition of zero-valent iron (Fe0) co-substrate with glucose in the anaerobic system, several factors that affected combined system co-substrate with glucose were evaluated. In addition, the effect of several electron donors such as Fe0, glucose, sodium acetate on the reductive dechlorination of 2,4-DCP were investigated, and the optimum conditions and sustainability of Fe0 as electron donor on 2,4-DCP dechlorination were investigated. Moreover, we discussed the process of Fe0 accelerating the biodegradation of 2,4-DCP and the degradation pathway of contaminant. The results showed that, (1) The combined use of Fe0 and anaerobic microorganism accelerated the dechlorination of 2,4-DCP effectively compared to the individual use co-substrate with glucose. The optimum quantity of added Fe0, pH and inoculation was 0.5 g/L, pH=8.0 and 376.2 mgVSS/L co-substrate with glucose in the combined system, respectively. (2) Fe0+glucose enhanced the dechlorination of contaminant effectively compared to glucose. Sodium acetate, Fe0 and Fe0+sodium acetate were all effective electron donors , and Fe0 was the optimum electron donor, and the optimum initial pH, Fe0 doses and quantity of inoculation was 8.0, 2.0 g/L and 646.6 mgVSS/L, respectively. 4-CP was the mainly intermediate product for 2,4-DCP dechlorination. (3) Fe0 could support the electron for reductive dechlorination of 2,4-DCP continuously. In contrast, when sodium acetate as electron donor, the effect of dechlorination was inferior to Fe0 with the consumption of sodium acetate. (4) The combined systems could stimulate the degradation of 2,4-DCP effectively at different pH, and neutral or little alkaline conditions was superior to acidic. The OH- from Fe0 corrosion balanced the degraded pH caused by fermenting of glucose and enhanced buffered ability of system. (5) Compared to neutral or little alkaline conditions, the higher pressure of hydrogen caused by the corrision of Fe0 had a disadvantage for dechlorinators to the competition of hydrogen. (6) Anaerobic microorganisms played a dominant role in the combined system, and Fe0 accelerated the degradation of 2,4-DCP. Moreover, the degradation of contaminant was the cooperating effect between electron catalysis from Fe0 and biology in combined system. Ferrous ion was the main corrosive product from Fe0. (7) The degree of Fe0 corrosion in acid condition was higher than neutral or alkaline conditions, and ferrous ion was the main corrosive product from Fe0, the content of ferric ion was relatively lower. In addition, ferrous ion increased the degradation of contaminant slightly. (8) 4-CP and 4-methylphenol were the intermediate products of 2,4-DCP degradation in combined system, the 2,4-DCP degradation pathway was: 2,4-DCP→4-CP→4-methylphenol, and was mineralized to CH4 and CO2 eventually.