| Chlorophenols (CPs), as important contaminants widely distributed in the naturalenvironment, are highly toxic and difficult to be biodegraded. In this paper,2,4-dichlorophenol (2,4-DCP) was selected as a typical representative of the CPs, andsulfate reducing bacteria (SRB) and dissimilatory iron reducing bacteria(DIRB) wasselected as original strain. A study was conducted on the effect of2,4-DCP on SRB’sand DIRB’s growth and metabolic activity under different concentrations by observingthe changes in cell concentration of SRB and DIRB, and sulfate and nitrate reductionrates and bacterial morphology. It was found that2,4-DCP concentration basically didnot change during the whole incubation, which showed that pure cultures of SRB andDIRB didn’t degrade2,4-DCP. However, the result also showed that2,4-DCP hadimportant influence on the growth and metabolic activity of SRB. When theconcentration of2,4-DCP was20mg/L, SRB’s growth and metabolism was inhibited; asthe concentration come to50mg/L, SRB was inactivated; However, while theconcentration achieved2mg/L,5mg/L, the growth rate of SRB was accelerated.Compared with the blank control, the maximum growth rate raised102.67%, andsulfate-reducing rate increased64.39%, and different concentrations of2,4-DCP allinhibit DIRB’s growth. This study added iron oxides and sulfate minerals into thesimulative anaerobic system to investigate the effect of different minerals on the2,4-DCP’s anaerobic degradation. The results showed that all the three minerals, namelygoethite, magnetite and gypsum couldn’t adsorb the2,4-DCP in the anaerobic system.The stoichiometric relationship between2,4-DCP and4-chlorophenol(4-CP)demonstrated that the way of reductive dechlorination contributed to the transformationof the2,4-DCP.4-CP was stable and would be persistent for a long time, at the end ofthe experiment, it still existed. The addition of goethite or magnetite promoted thereductive conversion of2,4-DCP. When the system contained iron oxides as well assodium acetate, the stimulating effect was more noticeable, and the reductivedechlorination rate could increase31.04%and36.41%respectively for the goethitegroup and the magnetite group. Adding gypsum strongly inhibited the transformation of2,4-DCP, and declined the transformation rate by66.88%. Then the study addeddifferent proportions of iron oxide minerals and sulfate minerals into the simulatedanaerobic reaction system to observe the effect of different mineral compositions on the anaerobic transformation of2,4-DCP. It was found that2,4-DCP was rarely adsorbed onto minerals in the anaerobic system.2,4-DCP can be converted stoichiometricly to4-CPwhich was not easily further degraded due to its stability and would be persistent for along time. The transformation of2,4-DCP was inhibited as adding different proportionsof goethite/gypsum (Gt/Gp) into the anaerobic system. When there was no externalcarbon source, the degradation of2,4-DCP would be completely inhibited. And in thesodium acetate groups,,the inhibitory effect on the transformation of2,4-DCP was grad-ually increased with the decrease of Gt/Gp. When the Gt/Gp were10,5,2and1, the2,4-DCP conversion rate would be decreased by38.88%,46.52%,51.78%and68.59%respectively compared with control groups. The addition of sodium acetate significantl-y improved the conversion efficiency of2,4-DCP and shorten the conversion time. Sulfa-te in mixed minerals mainly contributed to the inhibitory activities, and the mere existe-nce of sulfate in complex systems can inhibit the conversion of2,4-DCP.This result hasvery important significance to understand the effect of organic pollutants difficultlybiodegraded under anaerobic sedimentary environment on microbial metabolic activity.And these conclusions had crucial significance for understanding the migration andtransformation of refractory organic contaminants in natural anaerobic enviroments. |
