Special Issue “Advances in Biogas Desulfurization”

Implementation of a Pilot-Scale Biotrickling Filtration Process for Biogas Desulfurization under Anoxic Conditions Using Agricultural Digestate as Trickling Liquid

A pilot-scale biotrickling filter (BTF) was operated in counter-current flow mode under anoxic conditions, using diluted agricultural digestate as inoculum and as the recirculation medium for the nutrient source. The process was tested on-site at an agricultural fermentation plant, where real biogas was used. The pilot plant was therefore exposed to real process-related fluctuations. The purpose of this research was to attest the validity of the filtration process for use at an industrial-scale by operating the pilot plant under realistic conditions. Neither the use of agricultural digestate as trickling liquid and nor a BTF of this scale have previously been reported in the literature. The pilot plant was operated for 149 days. The highest inlet load was 8.5 gS-H₂Sm^-3h^-1 with a corresponding removal efficiency of 99.2%. The pH remained between 7.5 and 4.6 without any regulation throughout the complete experimental phase. The analysis of the microbial community showed that both anaerobic and anoxic bacteria can adapt to the fluctuating operating conditions and coexist simultaneously, thus contributing to the robustness of the process. The operation of an anoxic BTF with agricultural digestate as the trickling liquid proved to be viable for industrial-scale use.

Markers for the Comparison of the Performances of Anoxic Biotrickling Filters in Biogas Desulphurisation: A Critical Review

The agriculture and livestock industry generate waste used in anaerobic digestion to produce biogas containing methane (CH4), useful in the generation of electricity and heat. However, although biogas is mainly composed of CH4 (~65%) and CO2 (~34%), among the 1% of other compounds present is hydrogen sulphide (H2S) which deteriorates engines and power generation fuel cells that use biogas, generating a foul smell and contaminating the environment. As a solution to this, anoxic biofiltration, specifically with biotrickling filters (BTFs), stands out in terms of the elimination of H2S as it is cost-effective, efficient, and more environmentally friendly than chemical solutions. Research on the topic is uneven in terms of presenting performance markers, underestimating many microbiological indicators. Research from the last decade was analyzed (2010–2020), demonstrating that only 56% of the reviewed publications did not report microbiological analysis related to sulphur oxidising bacteria (SOB), the most important microbial group in desulphurisation BTFs. This exposes fundamental deficiencies within this type of research and difficulties in comparing performance between research works. In this review, traditional and microbiological performance markers of anoxic biofiltration to remove H2S are described. Additionally, an analysis to assess the efficiency of anoxic BTFs for biogas desulphurisation is proposed in order to have a complete and uniform assessment for research in this field.

Simultaneous removal of ammonium from landfill leachate and hydrogen sulfide from biogas using a novel two-stage oxic-anoxic system

Anoxic biodesulfurization has been achieved in several bioreactor systems that have shown robustness and high elimination capacities (ECs). However, the high operating costs of this technology, which are mainly caused by the high requirements of nitrite or nitrate, make its full-scale application difficult. In the present study, the use of biologically produced nitrate/nitrite by nitrification of two different ammonium substrates, namely synthetic medium and landfill leachate, is proposed as a novel alternative. The results demonstrate the feasibility of using both ammonium substrates as nutrient solutions. A maximum elemental sulfur production of 95 ± 1% and a maximum H₂S EC of 141.18 g S-H₂S m^-3 h^-1 (RE = 95.0%) was obtained using landfill leachate as the ammonium source. Next Generation Sequencing (NGS) analysis of the microbial community revealed that the most common genera present in the desulfurizing bioreactor were Sulfurimonas (91.8-50.9%) followed by Thauera (1.1-24.2%) and Lentimicrobium (2.0-9.7%).