Evaluation of methanol effect on an anaerobic sludge using methanogenic activity measurements and fluorescent in situ hybridization

Abstract

Many kinds of solvents are discharged from industries such as refineries, paint and pharmaceutical manufacturers etc. Hundreds of organic and inorganic raw materials and many organic solvents used to dissolve the compounds are required in these processes. The most commonly used solvents are methanol, ethanol, acetone, and isopropanol. Moreover, methylene chloride, toluene, chloroform, chlorobenzene, chloromethane, cyanide, phenol, and benzene are also used. Defining effect of solvents on both microbial community structure and activity changes in anaerobic reactors can lead to improvements in the understanding of interactions in the bioreactors, thereby obtaining better reactor performance in terms of higher degradation capacity and biogas production. In this study, a lab-scale anaerobic batch reactor inoculated with a seed sludge taken from a full-scale EGSB reactor was operated during 47 days as a preliminary-study. At the end of the operational period, sludge taken from the reactor was used to evaluate the effect of methanol on methanogenic activity and microbial community using SMA tests and FISH, respectively. SMA test results showed that the maximum acetoclastic activity of methanol added sludge samples decreased from 437 mlCH4 /gVSS/day to 252 mlCH4 /gVSS/day compared to control reactor sludge. In addition, maximum overall methanogenic activity was found to be 221 mlCH4 /gVSS/day in methanol added sludge samples, showing a 55% decrease when compared to control. According to FISH results, acetoclastic methanogens, Methanosaeta spp. and Methanosarcina spp. were found to be predominant methanogens in both sludges from the full-scale EGSB and lab-scale anaerobic batch reactors. However, predominance of acetoclastics methanogens tended to change to hydrogenotrophic methanogens, especially Methanobacteriales spp. under inhibitory effect of methanol. This shows that Methanobacteriales spp. is more resistant to stress conditions like inhibitory effect of a common organic solvent, i.e methanol.