Characterisation and cleaning of biogas from sewage sludge for biomethane production. (1st July 2018)

• Record Type: Journal Article
• Authors: Paolini, Valerio; Petracchini, Francesco; Carnevale, Monica; Gallucci, Francesco; Perilli, Mattia; Esposito, Giulio; Segreto, Marco; Occulti, Leandro Galanti; Scaglione, Davide; Ianniello, Antonietta; Frattoni, Massimiliano
• Is Part Of: Journal of environmental management. Volume 217(2018)
• Page Start: 288
• Page End: 296
• Publication Date: 2018-07-01
• Subjects: Biogas -- Sewage sludge -- Siloxanes -- Zeolite -- Pressure swing adsorption; Environmental policy -- Periodicals; Environmental management -- Periodicals; Environment -- Periodicals; Ecology -- Periodicals; 363.705
• DOI: 10.1016/j.jenvman.2018.03.113
• Languages: English
• ISSNs: 0301-4797

Abstract

Abstract: This study investigates the conversion of sewage sludge from wastewater treatment plants (WWTP) into biomethane for automotive fuel or grid injection. A prototype plant was monitored in Northern Italy, based on vacuum swing adsorption (VSA) on synthetic zeolite 13×: this biogas upgrading method is similar to pressure swing adsorption (PSA) and commonly used for other kinds of biomass. Measurements of biogas inlet, biomethane outlet and off-gas were performed including CH4, CO2, CO, H2, O2, N2, HCl, HF, NH3, H2 S and volatile organic compounds (VOCs). Critical levels were observed in the biogas for of H2 S and HCl, whose concentrations were 1570 and 26.8 mg m −3, respectively. On the other hand, the concentration of halogenated VOCs (including tetrachloroethylene and traces of perfluoroalkilated substances, PFAS) and mercaptans were relatively low. A simultaneous and reversible adsorption on 13× zeolite was achieved for H2 S and CO2, and carbon filters played a minor role in desulfurisation. The presence of HCl is due to clarifying agents, and its removal is necessary in order to meet the required biomethane characteristics: an additional carbon-supported basic adsorbent was successfully used to remove this contaminant. This study also highlights the interference of CO2 towards HCl if sampling is performed in compliance with the new EU standard for biomethane. High total volatile silicon (TVS) was confirmed in sewage sludge biogas, with a major contribution of siloxane D5: the suitability of this compound as an indicator of total siloxanes is discussed. Results demonstrate that volatile methyl siloxanes (VMS) do not represent a critical issue for the VSA upgrading methodology. Highlights: HCl in biogas from sewage sludge far exceeds biomethane standard limits. Clarifying agents are the source of HCl in biogas from sewage sludge. Siloxanes in biogas from sewage sludge are removed with zeolite and carbon filters. Siloxane D5 can be an indicator of total volatile silicon in sewage sludge biogas. Simultaneous H2 S and CO2 removal is achieved in vacuum swing adsorption.