Inhibition of the acetoclastic methanogenic activity by phenol andalkylphenols

Abstract

Chemical and petrochemical industries are important sources of aromatic pollutants. Petrochemical processes like caustic washing of middle distillates produce the spent caustic liquors highly concentrated in phenol and alkyl phenols. The anaerobic technology is considered a feasible strategy for petrochemical wastewater pre-treatment although high concentrations of phenol could limit its efficiency. The goal of this work was to determine the toxicity of both selected alkyl phenols and a synthetic "spent-caustic phenols mixture" on the acetoclastic Specific Methanogenic Activity (SMA) of unadapted and phenol-adapted granular sludge. Alkyl phenols were responsible for 50% (IC50) and 100% (IC100) inhibition of the SMA at concentrations ranging from 1.6 to 5.0 mM and from 4.1 to 27.5 mM, respectively, for un-adapted granular sludge. In the case of phenol-adapted granular sludge, the inhibitory concentrations ranged from 1.7 to 14.9 mM and from 4.0 to 83.0 for IC50 and IC100, respectively, highlighting the impact of sludge acclimation. The inhibition produced by 2-ethylphenol was more acute compared to phenol and was not reduced by the phenol acclimation process. The IC50 and IC100 values obtained for the synthetic "spent-caustic phenols mixture" were 9.5 mM and 88.4 mM, respectively. The inhibitory concentrations of phenol compounds were closely correlated with compound apolarity (log P), indicating that the lipophilic character of the tested compounds was responsible for their methanogenic toxicity. An inhibition model is confirmed to estimate the IC50 and IC100.

Inhibition of biogas production and biodegradability by substituted phenolic compounds in anaerobic sludge

“…2). A linear toxicity/apolarity relationship may be suggested since it has also been observed with different chemicals [5,10]. However, Caffeic acid does not follow this behaviour due to the double bond substitution ( CH CH COOH).…”

“…This toxicity is thought to be due to molecular size [25], substitution in the aromatic ring [26] and apolarity of the molecule [5,10]. Phenols thus disturb the trophic chain established between microorganisms by affecting the production of fatty acids, hydrogen and, consequently, methane [26,27].…”

“…Among aromatics are phenols which are found in agricultural and industrial wastes. In this group, caffeic acid, gallic acid, tyrosol, 4-hydroxybenzoic, and protocatechuic acid are found in olive oil, red wine and tanning wastewaters and in the degradation products of lignin [3,4], while phenol and catechol are well known industrial pollutants [5]. All these compounds may inhibit microbial activity [6,7], and therefore cause difficulties in bioremediation and potentially reduce the ability to produce biofuels by biomass fermentation.…”

Anaerobic treatment of wastewater from used industrial oil recovery

“…However, some intermediate compounds were detected in the effluent, such as phenolic hydrocarbons as well as trace concentrations of acetate, propionate and ethanol, indicating incomplete anaerobic oxidation. The partial inhibition of biogas production and the decrease in biodegradability of the UIO wastewater can be caused by the presence of substituted phenolic compounds 22, 23…”

Extension of the anaerobic digestion model No. 1 (ADM1) to include phenol compounds biodegradation processes for simulating the anaerobic co-digestion of olive mill wastes at mesophilic temperature

“…Where I, TVFA and I, phenol are non-competitive functions added to take into account the inhibition of methanogenic steps by high TVFA and high phenol levels [20], respectively. Their expressions are as follows: …”