| Combined treatment approach using mixed anaerobic culture and zero valent iron is a new and effective bio-enhancing technology, several researches has explored adding Fe~0 could accelerate biological reductive dechlorination of Chlorinated Organic Pollutants. This paper reported the degradation efficiency of 2,4,6-trichlorophenol by integrated microbial-Fe~0 treatment system, and the optimum conditions for 2,4,6-TCP removal. The synergistic mechanisms of degradation of 2,4,6-TCP were investigated. The degradation efficiency of 2,4,6-trichlorophenol under different redox conditions were studied at the same time. The main conclusions were as follows:1) The degradation efficiency of 2,4,6-TCP in integrated microbial-Fe~0 treatment system is much higher than that in either Fe~0 or mixed anaerobic culture as a sole system, 2,4,6-TCP could be degraded effectively in integrated system. The optimum condition for 2,4,6-TCP removal in integrated system was achieved as follows: inoculation quantity of anaerobic sludge, 0.434 gVSS·L-1, Fe~0 dose, 15 g·L-1, initial pH value, 7.0-8.0; When initial concentration of 2,4,6-TCP was between 20-60 mg/L, the enhancement effect of Fe~0 on 2,4,6-TCP removal increases with the increases of initial concentration.2) 2,4-DCP and 4-CP was identified as main intermediates of 2,4,6-TCP degradation in the integrated microbial-Fe~0 treatment system and the sole microbial system, occupied more than 80 percent of the total degradation products; 2,4,6-TCP can be completely degraded via sequential reductive dechlorination to form 2,4-DCP and 4-CP; 2,4,6-TCP was removed mainly by adsorbent function and coagulative precipitation function of Fe~0 in the sole Fe~0 system.3) The speed and degree of reductive dechlorination in integrated microbial-Fe~0 treatment system was largely exceeded that in the sole microbial system. Biological reductive dechlorination plays a leading role in degrading 2,4,6-TCP by integrated microbial-Fe~0 treatment, Fe~0 have enhancement effect on biological reductive dechorination.4) Fe~0, glucose, acetate with the same equivalent electron used as electron donor were compared, the removal rate of 2,4,6-TCP from high to low were: Fe~0>glucose>acetate; Fe~0 could provided electron donor for reductive dechlorination continually and steadily by corrosion. For the system using Fe~0 as electron donor, the degradation efficiency of 2,4,6-TCP decrease when adding fermentable substrate such as glucose to the system, but increase when adding acetate to the system.5) When Fe~0 used as electon donor, the degradation efficiency of 2,4,6-TCP after 200 h in the Fe(Ⅲ) reducing environment is above 80 percent; Fe~0 is more suitable for used as electron donor for reductive dechlorination of 2,4,6-TCP in Fe(Ⅲ)– reducing environment than glouse. When Fe~0 and glouse used as electron donor, Fe(III)-citrate reduction led to a slight decrease in degradation efficiency of 2,4,6-TCP , FeOOH reduction has little influence on the 2,4,6-TCP removal.6) Sulfate, molybdate, sulfide ion and (sulfate+molybdate) all have inhibitory effect on 2,4,6-TCP degradation, the inhibitory effect from strong to weak was followed by: sulfide ion>(sulfate+molybdate)>Sulfate or molybdate. When glouse used as electron donor, the microbial community structure is more complex, inhibitory effect of sulfate etc. is much lower than that using Fe~0 as electron donor. Adding molydate to sulfate reducing system not only can not decrease the inhibitory effect of sulfate reduce to 2,4,6-TCP degradation, however, lead to further decrease of the 2,4,6-TCP degradation efficiency. |
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