Acidogenic Fermentation and Anaerobic Co-digestion of Mechanically Sorted OFMSW and Polyethylene Glycol

Abstract

This study is focused on the anaerobic biological treatment of a polyethylene glycol (PEG)-rich industrial wastewater and mechanically sorted organic fraction of municipal solid wastes, called residual organic matter (ROM), in order to assess the effects of mixing these substrates to produce volatile fatty acids (VFA) through anaerobic co-fermentation or biogas through anaerobic co-digestion. As a consequence of the anaerobic co-digestion of PEG and ROM (PEG representing a 3.5% v/v), the specific methane production (SMP) reached 0.44 Nm3 CH4 kg−1 volatile solids (VS) in front of 0.30 Nm3 CH4 kg−1 VS of the anaerobic digestion (AD) control reactor, with just a 35% higher organic loading rate (OLR) on VS basis. The fast degradation of PEG implied that effluent quality was nearly the same of AD process, showing high stability with neither increase of VS nor significant variations in nutrients. Acidogenic fermentation was carried out in batch tests for several mixtures of PEG industrial wastewater and ROM, where the percentages of PEG-rich wastewater on VS basis were 0, 12.5, 25, 37.5 and 50%. The best results of VFA increase per unit of VS of co-substrate fed was obtained for the mixture with 12.5% of PEG wastewater at 5 days retention time. The same mixture was fed in an anaerobic fermenter under mesophilic conditions treating ROM at an HRT of 3.5 days and without modifying the OLR (VS basis). As a consequence of this co-fermentation, the production of VFA was increased by 14% (12.1 g VFA L−1) when compared with the values obtained in mono-fermentation. Moreover, the percentages of acetic acid + propionic acid (66.5%) was in the range than that obtained with mono-fermentation of ROM (64.6%).