Biogas pre-upgrading by adsorption of trace compounds onto granular activated carbons and an activated carbon fiber-cloth B. Boulinguiez and P. Le Cloirec ABSTRACT B. Boulinguiez (corresponding author) P. Le Cloirec Ecole Nationale Supe ´ rieure de Chimie de Rennes (ENSCR), UMR CNRS 6226—Sciences Chimiques de Rennes, Campus de Beaulieu, Avenue du Ge ´ ne ´ ral Leclerc, 35700 Rennes, France E-mail: benoit.boulinguiez@ensc-rennes.fr; pierre.le-cloirec@ensc-rennes.fr The study assesses the adsorption onto activated carbon materials of selected volatile organic compounds -VOCs- (dichloromethane, 2-propanol, toluene, siloxane D4) in a biogas matrix composed of methane and carbon dioxide (55:45 v/v). Three different adsorbents are tested, two of them are granular activated carbon (GAC), and the last is an activated carbon fiber-cloth (ACFC). The adsorption isotherm data are fitted by different models by nonlinear regression. The Langmuir-Freundlich model appears to be the adequate one to describe the adsorption phenomena independently of the VOC considered or the adsorbent. The adsorbents present attractive adsorption capacity of the undesirable compounds in biogas atmosphere though the maximum adsorption capacities for a VOC are quite different from each other. The adsorption kinetics are characterized through three coefficients: the initial adsorption coefficient, the external film mass transfer coefficient and the internal diffusion coefficient of Weber. The ACFC demonstrates advanced kinetic yields compared to the granular activated carbon materials whatever VOC is considered. Therefore, pre-upgrading of biogas produced from wastewater sludge or co-digestion system by adsorption onto activated carbon appears worth investigating. Especially with ACFC material that presents correct adsorption capacities toward VOCs and concrete regeneration process opportunity to realize such process. Key words | activated carbon fiber-cloth, biogas, nonlinear regression, siloxane, VOC, wastewater sludge INTRODUCTION During recent decades, achievements in wastewater treat- ment plant strategies were oriented by a continuous effort to improve water quality. Use of the potential green energy from anaerobic process remained second-priority compared to water quality; however, the latter need not to be excluded at the expense of the former by now. In wastewater treatment plants, considerable amount of organic sub- stances is treated by the common and widespread microbial process of cleaning sewage from municipal, agricultural or industrial origins. The organic substances, dissolved or suspended in water, are converted daily to a gas called biogas (composed of methane and carbon dioxide), solids (microbial biomass) and water itself. Actually, these organic substances represent a substantial source of energy through the production of biogas in the microbial anaerobic process and formation of methane, as the end product of the anaerobic metabolism. A further contribution to this energy potential in sewage purification comes from the biomass inherently produced during the primary sludge and secondary (microbiological) sludge (Rulkens 2008). Increasingly, agricultural products (Murphy & McKeogh 2006; Weiland 2006; Anhuradha et al. 2007; Rizk et al. 2007) or organic fraction of municipal solid waste (Del Borghi et al. 1999; Sosnowski et al. 2003; doi: 10.2166/wst.2009.070 935 Q IWA Publishing 2009 Water Science & Technology—WST | 59.5 | 2009 Downloaded from https://iwaponline.com/wst/article-pdf/59/5/935/436894/935.pdf by guest on 15 June 2020