Microbial protein production from methane via electrochemical biogas upgrading

Abstract

Microbial protein (MP) can alleviate the increasing pressure of food demand on agriculture and our environment. For its sustainable production, feedstocks such as biomethane or (bio)hydrogen are needed. Here, we coupled biogas produced from agricultural waste directly with electrochemical biogas upgrading to subsequently produce MP from methane, hydrogen or a mixture thereof. Biogas was produced from co-digestion of pumpkin and pig manure at production rates of 0.73 ± 0.24 Lbiogas L -1 reactor day -1 (59 % CH4) and 0.59 ± 0.29 Lbiogas L -1 reactor day -1 (50% CH4). The biogas was directed to the cathode of an electrochemical cell. At current densities of 20 and 40 A m −2 , CO2 removal efficiencies of 88 ± 14 % and 99 ± 1 % were achieved. Enrichments of MP (hydrogen-and methane oxidizing bacterial cultures)were cultivated on either raw biogas or gases obtained from the cathode (CH4, CO2, H2) and anode (CO2, O2) in batch mode with external supplementation of O2 and H2 when required.The best performance was obtained when the cathode off-gas was used in terms of biomass concentration (0.585 g CDW L -1 ), yield (0.150 g CDW g -1 COD), efficiency of COD conversion to protein (17%) volumetric biomass productivity (0.226 g CDW L -1 day -1 ) and volumetric protein productivity (0.181 g protein L -1 day -1 ). The protein content was similar when using anode and cathode off-gases (66.3 ± 7.3 % of CDW) with raw biogas resulting in a 6 % lower protein content. This proof of concept demonstrated that electrochemical biogas upgrading enables steering MP production.

Technologies and perspectives for achieving carbon neutrality

“…Other novel biotechnology strategies include metabolic engineering to enable microbial utilization of using CO 2 , CH 4 , and other C1 feedstocks for the production of microbial proteins rich in essential amino acids. 139 , 140 These proteins can be used as substitutes for animal proteins. Current advances in biotechnology provide a powerful platform for the production of protein-rich feed or food additives in the form of fungal, algae, yeast, and bacterial cell biomass.…”

Conversion of biogas from anaerobic digestion to single cell protein and bio-methanol: mechanism, microorganisms and key factors - A review

“…For instance, edible sugars (Quorn TM , Marlow Foods Ltd, UK), natural gas [60][61][62], and agro-industrial wastes [63][64][65]. However, there are some challenges associated with the use of these feedstocks for SCP production: i) edible sugars-based SCP production process may be economically less viable, ii) the direct utilization of agro-industrial wastes may lead to accumulation of heavy metals in the SCP, which might hinder the consumption of this bio-product [66], and iii) natural gas-based SCP production processes are becoming less attractive because of reliance on the unsustainable fossil resources.…”

“…A challenging issue associated with the use of ADs as a culture medium for SCP production is that they contain high ammonium concentration [86, 87], e.g., 1000-3000 mg NH 4 + -N/L [85], which should be diluted to meet the desired ammonium concentration (below 150 mg [66,71]. This implies that a large volume of freshwater for the dilution process is required while going to produce SCP at a large scale.…”

“…The generated biomass is then processed for the protein extraction. In order to enable both CH 4 and CO 2 contribution to the production of SCP, a possible solution is the use of methanotrophs co-cultivated with autotrophic HOB in a single stage system [66] (Figure 1b). This process relies on O 2 and H 2 gases, which are expensive resources [54] as they are usually generated by electrolysis of water that is an energy-intensive method [58,89].…”

Lipid accumulation capability of typical non‐acclimated activated sludge microbial consortia using methane gas as secondary carbon source

“…8 In all cases of these commercial applications of methanotrophs-to-product systems, methane was used to grow the methanotrophs for later harvesting of the targeted cell constituents of value. 25 Several works on methane-utilizing bacteria have been published in the recent years: production of polyhydroxyalkanoates (PHAs) from anaerobic digester sludge [26][27][28] ; treatment of high-nitrogen wastewater 29 ; electricity production from simulated biogas 30 ; electrochemical production of microbial protein 31 ; photoautotroph-methanotroph culturing for CO 2 -CH 4 utilization 32 ; immobilized methane-utilizing bacteria 33 ; and bubble-column reactor design for poly-3-hydroxybutyrate (PHB) production from CH 4 34 ; and CH 4 to methanol via immobilized methane-utilizing bacteria. 35 The envisioned concept of this present work is that the methane within biogas generated at a municipal WWTP could be directly used or supplemented with natural gas for the production of lipids via wasted AS microbial cells.…”