Updates on biogas enrichment and purification methods: A review

Abstract

The market for biogas production has been increasing every year all over the world. The use of biogas as an energy vector is accomplished through the most diverse applications, such as direct burning (thermal energy), internal combustion engines, and fuel cells. Besides direct applications, biogas can be used as a raw material for producing high added-value products, such as molecular hydrogen and renewable hydrocarbons, through a new enterprise concept, the biorefineries. Purity and quality control are determinant factors that enable the decision-making regarding the end use of biogas. Physical, chemical, and biological methods can be used in biogas upgrading processes as well as a combination of different techniques. This review aims to deepen the knowledge about relevant technologies for biogas purification. It also addresses the most efficient and feasible methods, challenges to be overcome, and main demands for future studies. Therefore, the presentation, in a detailed way, of the synergistic effects caused by components contained in natural biogas and the combinatorial methods for removing these contaminants, differentiates this from other works that approach only the purification techniques but do not point out their problems and causes more comprehensively. Thus, studies related to the combined effects of contaminants would be interesting in future works.

Biogas Upgrading Using a Single-Membrane System: A Review

“…Considering the state of research into the biogas composition, it can be clearly indicated that the CO 2 concentration in biogas depends on several factors, such as (I) temperature, (II) pressure and (III) liquid content in the digester [41]. It is non-toxic gas; however, it decreases the calorific value of biogas, reduces its density, laminar flame speed and combustion efficiency [34,57,88]. This implies that its high content reduces the economic feasibility of direct biogas application [40] and limits its use mainly to heat and electricity generation.…”

“…In turn, the second step, called 'biogas upgrading', aims to separate CO 2 , typically down to 2% vol. Consequently, it allows to obtain biomethane with properties and a composition similar to those of natural gas [34] and meet the quality standards of natural gas grids [35]. It has been widely reported that effectively upgraded biogas, referred to as biomethane, should contain more than 95-97% CH 4 [14,[36][37][38][39][40][41].…”

“…The separation with the use of dense membranes is based on the solution-diffusion mechanism. It is clearly related to the affinity of molecules with the membrane material and the diffusion via the polymeric film [34]. Although this technology has several promising advantages [75][76][77], gas permeation is the most commonly used.…”

Analysis of energy return on investment of dry anaerobic digestion for low water alperujo with oxidative, thermal and alkaline pretreatments

“…ALP is currently considered a waste and occasionally it is transferred to other establishments, which generates an additional transportation cost, where the residual oil is extracted with solvents, or is conditioned for its correct final disposal, since it has a high polyphenol content (Roig et al, 2006; Solomakou & Goula, 2021). This, added to the high amount of waste generated after each olive oil campaign, has aroused interest in ALP valorization (Oliveira et al, 2023).…”

Are Si–C bonds formed in the environment and/or in technical microbiological systems?

“…Biogases, mixtures of mostly methane and carbon dioxide, are an upcoming power resource advantageous in terms of greenness, sustainability, and climate protection. There are three kinds of biogases (Rasi et al 2011 ), those from anaerobic digestion of wastewater treatment sludge (Bougrier et al 2006 ; Appels et al 2008 ; De Arespacochaga et al 2020 ), those released from landfills (Bolan et al 2013 ; Kuhn et al 2017 ; Li et al 2019 ; De Arespacochaga et al 2020 ; Braganca et al 2020 ; Wang et al 2020 ), and those produced from agricultural wastes (Rasi et al 2013 ; Akhavan et al 2014 ; Foppiano et al 2020 ; Oliveira et al 2022 ). Digester gas contains siloxanes that were adsorbed to sludge out of sewage, coming from use of personal care products containing, e.g., D 4 and D 5 .…”