In-situ biogas upgrading by bio-methanation with an innovative membrane bioreactor combining sludge filtration and H2 injection

Abstract

A bioreactor using membrane technologies was used to demonstrate the feasibility of in-situ bio-methanation coupled to industrial wastewater treatment for biogas upgrading. High biogas productivity (1.7 Nm 3 Biogas/m 3 Bioreactor/day) with high CH4 content (97.9%) was reached. In-situ bio-methanation did not affect the COD removal efficiency of anerobic digestion (>94%). Process resilience has been tested for both substrate overload and H2 intermittence injection. Recovery of high CH4 content after 7 days without H2 injection occurred within few hours. Influence of microbial community has been studied showing that both hydrogenotrophic and homoacetogenic-acetoclastic pathways were involved.

Potential for Biomethanisation of CO2 from Anaerobic Digestion of Organic Wastes in the United Kingdom

“…Accurate determination of H 2 concentrations can also be problematic and as noted, there are different ways of dealing with variability in experimental measurements, with some studies normalising gas composition to 100% and others not. In some cases, however, the observed MER is greater than the volumetric CO 2 production without CO 2 biomethanisation [21,30,33,45,66,68], strongly supporting an increase in VBP. A similar phenomenon of increases in VBP or VMP has been observed in other work on gas recirculation [83], though no clear mechanisms have been confirmed.…”

“…Other food industry substrates trialled include potato starch wastewaters [65] and bioethanol distillery effluents [66]. The former was tested in a thermophilic UASB reactor with different diffuser types and gas and liquid recirculation rates.…”

“…In CO 2 biomethanisation trials with potato starch wastewater in UASB reactors (Bassani et al, 2016), stable operation was reported at a pH 8.38 with a CO 2 content 10% in the output gas. For ethanol distillery wastewater treated in an anaerobic membrane bioreactor (AnMBR) [66], the pH had reached 7.9 at a biogas methane content of 97.9% CH 4 and 1.4% CO 2 , with a corresponding increase in SMP from 0.297 to 0.389 L CH 4 g −1 VS: values close to these can therefore be taken as the maximum for this substrate for modelling purposes.…”

“…Most studies that calculate ratios of this type also choose to ignore the very small amount of dissolved H 2 leaving in the digestate [1,77,82]. Intriguingly, in several cases, the introduction of CO 2 biomethanisation is associated with an increase in VBP [21,22,24,27,29,33,43,45,47,57,61,66,68,74], meaning a larger amount of CH 4 is being produced and/or there is more CO 2 to biomethanise, per unit of organic feed.…”

Biomethane and Biomethanation Technology in the Material Cycles Sector

“…8 * (国研)国立環境研究所 資源循環領域 連絡先：〒 305 -8506 茨城県つくば市小野川 16 -2 QH 2 in：水素供給速度 QCO 2 in：CO 2流入 (生成) 速度 QNut in：栄養液供給速度 QSub in：廃棄物等原料供給速度 QGas cir：ガス循環速度 QNut cir：栄養液循環速度 QGas out：ガス流出速度 QNut out：栄養液流出速度 QSub out：原料流出速度 N：攪拌速度 F：担体充填率 (比表面積も考慮) の気液間物質移動係数 (kLa) を向上させることに焦点 を当ててきた。 rT=22.414 kLa(H2 l*−H 2 l)( 2 )こ こ で，rT (L/ (L ･ d)) は 水 素 の 気 液 間 移 動 速 度， 22.414 (L/mol) は標準状態における mol あたりの水素 体積，kLa は水素の気液間物質移動係数 (/h)，H2 l* は 気相の水素分圧に平衡する溶存水素濃度 (mol/L)，H2 l は液相における溶存水素濃度 (mol/L) である。2. 1 で 述べたように，ガス循環，散気装置，大きな比表面積の 濡れ界面形成，膜等によって kLa の向上が試みられてき た。図 3B において, kLa との関係では有効容積 VW (と くに液深)，ガス循環速度 QGas cir, 攪拌速度 N, 担体充填 率 F が重要となってくる。表 2 に示すように，方式別 では in-situ 型と比較して ex-situ 型では明らかに高い kLa が得られている。Ex-situ 型の各方式においても， さまざまな因子によって kLa 水 素 の mol あ た り の メ タ ン 収 率 は そ れ ぞ り，中 温 域 に お い て は Methanobacteriales 目，Methasaetaceae 科[13][14][15][16] の，高 温 域 においては Methanothermobacter 属, Methanobacteriaceae 科6,10,11)…”