Formation and Biodegradation of Toluene in the Anaerobic Sludge Digestion Process

Abstract

The formation of toluene in municipal anaerobic primary and secondary sludge digestion processes was investigated. Experiments were carried out in a large laboratory‐scale reactor using sludge from a primary settling tank of a municipal treatment plant. It was found that toluene was produced in the supernatant in relatively large concentrations for almost all cases tested. The concentration of toluene varied and was found to depend on the stage of the anaerobic process. During the acidity phase, which is the first stage of anaerobic digestion, an increase of toluene concentration was observed, while in the transition period, from the acidity phase to methanogenesis, the toluene concentration decreased. It was concluded that biosynthesis of toluene occurs in the acidogenic phase, while biodegradation was prevalent in the methanogenic stage. Depending on the type of experiments, an increase of toluene from a base value of approximately 200 μg/L up to 20 000 and 42 000 μg/L was measured in the first stage of anaerobic digestion. In the subsequent methane‐production stage of digestion, the estimated rate of toluene decrease (biodegradation) varied from 400 to 900 μg/L‐d.

Determination of toluene formed during fermentation of sewage sludge

“…The formation of toluene in the hipolimnion layer (the cold lower layer of water) of eutrophic lakes was described in 1986 [10]. This phenomenon was also observed in sludge obtained during sewage treatment process [18]. The authors observed a significant increase in the *Corresponding author.…”

“…Toluene is universally used in industry (mainly as a solvent and gasoline additive) and in domestic products. Therefore almost always it is present in effluents channelled to waste water treatment plants [18], but this compound is easily biodegraded during biological treatment. For that reason, information on a large content of the compound in sewage sludge samples and on the possibility of formation during the fermentation process seems to be very interesting.…”

Toluene inhibition on an anaerobic reactor sludge in terms of potential activity and composition of acetoclastic methanogens

“…Changes in COD removal rate of the SMA test reactors There are plenty of studies assessing the effect of toluene on anaerobic reactor sludges under sulfate reducing, nitrate reducing and methanogenic conditions. [21][22][23][24] It was reported that different toluene concentrations up to 100 mM can be degraded in anaerobic reactors and did not have a negative effect on organic matter removal in these reactors. However, effect of toluene on potential methanogenic activity was not assessed in those studies.…”

Forensic source attribution for toluene in environmental samples

“…Toluene has also been formed under anaerobic digestion of sewage sludge within waste-treatment plants (Mrowiec et al 2005;Marczak et al 2006). Thus, microbiological processes for the formation of toluene are possible, albeit under a specific engineered setting not representative of natural environmental conditions.…”