Effects of artificial overdosing of p-cresol and phenylacetic acid on the anaerobic fermentation of sugar beet pulp

The inhibitory effect of exogenous p-cresol and phenyl-acetic acid (PAA) on the anaerobic fermentation of sugar beet pulp was studied. Experiments were set up in 1 1 working volumes at mesophilic temperature (38 degrees C). The organic loading rate (OLR) was 9.88 g volatile solids (VS) l(-1) sludge d(-1) with the addition of continuously increasing amounts of p-cresol or PAA. The threshold levels of p-cresol and PAA were 500 mg l(-1) and 3000 mg l(-1) in the sludge, respectively, but their mode of action differed. Our results show that p-cresol inhibits acetogenic bacteria, while PAA decreased the pH of the sludge, which had a negative effect on methanogenesis. The stage of p-cresol inhibition directly corresponds to its concentration in sludge: 500-700 mg l(-1) reduced conversion efficiency and over 700 mg l(-1) caused process failure. (C) 2013 Elsevier Ltd. All rights reserved.