Microbial population dynamics in an anaerobic completely stirred tank reactor treating a pharmaceutical wastewater

Abstract

In this study, effects of a chemical synthesis based pharmaceutical wastewater on performance of an anaerobic completely stirred tank reactor (CSTR) and activity of acetoclastic methanogens, number and composition of methanogens and non-methanogens were evaluated. The CSTR was initially fed with glucose. After that, it was fed with preaerated pharmaceutical wastewater diluted by glucose at different dilution ratios and then with raw pharmaceutical wastewater diluted with pre-aerated wastewater to enable acclimization of acetoclastic methanogens to the wastewater which contains nonbiodegradable/ toxic compounds for the anaerobic treatment. At initial study with glucose, 92% soluble COD removal efficiency was achieved with the CSTR at an organic loading rate (OLR) of 6 kgCOD/m3.d corresponding to an FIM ratio of 0.43 with a HRT of 2.5 days. Methane yield was 0.32 m3CfLJkgCOD and specific methanogenic activity (SMA) was found to be 336 mICHJgTVS.d. After initial study with glucose, the CSTR was fed with several dilutions of pre-aerated pharmaceutical wastewater with glucose (10%, 30% and 70%) and then 100% pre-aerated pharmaceutical wastewater. Due to the deteriation in the performance and decrease in the activity of acetoclastic methanogens after feeding with 100% pre-aerated pharmaceutical wastewater, HRT was increased from 2.5 days to 3.5 days. 71% soluble COD removal efficiency was obtained with a HRT of 3.5 days where methane yield was 0.28 m3CH4/kgCOD. However, SMA value was found to be 166 mICHJgTVS.d indicating approximately 47% activity loss ofthe acetoclastic methanogens compared with the results of feeding with glucose. Finally, raw pharmaceutical wastewater diluted with pre-aerated wastewater was fed into the CSTR in increasing ratios of 10%, 30% and 60%. Although a slight decrease in the performance was seen at a dilution ratio of 10% raw wastewater, there was a decrease in all parameters including soluble COD removal efficiency, methane yield, activity test results and an increase in total VF A concentration at a dilution ratio of 60% raw phannaceutical wastewater. According to the results of the SMA test indicating poor activity of acetoclastic methanogens, the study was discontinued at this ratio. According to the microbiological studies, there were variations in the dominant species and the ratio of acetoclastic methanogens to total bacteria during the operation. Methanococcus like species and short rods were dominant species after the operation with glucose. Short rods and medium rods were dominant at the end of the operation with 100% pre-aerated wastewater while short rods remained most dominant species until the end of the study. The ratio of acetoclastic methanogens to the total bacteria decreased at the end of the operation with glucose from 38% to 30% when 60% raw phannaceutical wastewater was introduced to the CSTR.