Anaerobic degradation of increased phenol concentrations in batch assays

Phenol is a wastewater contaminant depicting an environmental hazard. It can be found in effluents from various industrial processes and becomes even more common as a waste by-product of biomass-based bioenergy concepts. Because of its toxicity to anaerobic microorganisms, it can be recalcitrant during biogas production and anaerobic wastewater treatment. This study tested increased phenol loads (100 to 5000 mg L-1) as the sole carbon source in a semi-continuous mesophilic anaerobic adaption experiment using an unadapted microbial community from a standard biogas plant. Phenol was completely degraded at starting concentrations of up to 2000 mg L-1. At 5000 mg L-1, complete inhibition of the anaerobic community was observed. Lag times were reduced down to less than a day treating 2000 mg L-1 after 16 weeks of adaption to gradually increased phenol concentrations. Specific degradation rates increased consecutively up to 7.02 mg g(VS)(-1) day(-1) at 2000 mg L-1. This concentration was completely degraded within less than 12 days. The microbial community composition was assessed using 16S rRNA gene-based terminal restriction fragment length polymorphism (T-RFLP) analysis. In the bacterial community, no clear shift was visible. Clostridia were with the highest relative abundance of 27 %, the most prominent bacterial class. T-RFs representing Clostridia, Anaerolinaceae, Flavobacteria, and Bacteroidea appeared at similar relative abundance level throughout the experiment. The archaeal community, however, changed from a Methanosarcinales-dominated community (57 %) to a community with a nearly even distribution of Methanobacteriales (21 %) and Methanosarcinales (34 %) with increasing starting phenol concentration.