Progress of research on methanogenic microbial electrolysis cell

doi:10.11949/0438-1157.20190011

Abstract

Abstract:

Methanogenic microbial electrolysis cell (MEC) is a new technology that uses microorganisms as catalysts to convert CO₂ or organic pollutants into methane by using external input electrical energy. MEC can treat a variety of pollutants such as sewage, sludge, biogas residue and produce methane while realizing CO₂ treatment and energy conversion. It is considered as one of the important solutions with high energy conversion efficiency, low cost and environment-friendly for energy shortages and environmental pollution problems. In recent years, MEC has received extensive attention in methanogenic biocathode structure, electron transport pathways, and methanogenic microbial communities. At the same time, new methanogenic technologies formed by MEC coupled anaerobic digestion or other wastewater treatment systems have been gradually developed and become researche hotspot. In this paper, the progress of research on methanogenic biocathode and the methanogenic microbial community of methanogenic MEC were reviewed. Furthermore, the new systems of the MEC coupled anaerobic digestion or other systems for methane production were also introduced. Finally, the research direction of methanogenic MEC and the technical problems that still need to be solved in the practical process were summarized and analyzed.

Key words: microbial electrolysis cell, carbon dioxide, methane, anaerobic digestion, waste water

摘要：

微生物电解池（microbial electrolysis cell，MEC）产甲烷技术是以微生物为催化剂，利用外界输入的电能将CO₂或有机污染物转化为甲烷的新技术。MEC在实现CO₂处置与能量转化的同时，能够处理污水、污泥、沼渣等多种污染物并生产甲烷，具有能量转化率高、生产成本低、环境友好等特点，可望成为解决能源紧缺和环境破坏问题的重要途径之一。近年来，MEC在产甲烷生物阴极结构及电子传递途径、产甲烷微生物群落等方面得到了广泛关注，同时，MEC耦合厌氧消化或其他废水处理系统形成的产甲烷新技术也逐渐研发并成为研究热点。本文综述了产甲烷生物阴极、产甲烷微生物群落等方面的研究现状，介绍了MEC耦合厌氧消化或其他系统产甲烷新技术，总结并分析了MEC产甲烷技术的研究方向和实用化过程仍需解决的技术难题。

关键词: 微生物电解池, 二氧化碳, 甲烷, 厌氧消化, 废水

CLC Number:

X 511

Zhengzhong MAO, Yi SUN, Zhipeng HUANG, Chaochao LI, Haobin HUANG, Shao an CHENG. Progress of research on methanogenic microbial electrolysis cell[J]. CIESC Journal, 2019, 70(7): 2411-2425.

毛政中, 孙怡, 黄志鹏, 李超超, 黄浩斌, 成少安. 微生物电解池产甲烷技术研究进展[J]. 化工学报, 2019, 70(7): 2411-2425.

Figures/Tables 9

Fig.1 Schematic of methanogenic MEC

Fig.2 Example of a new electrode structure in methanogenic MEC

Fig.3 Summary of methanogenic biocathode electron transport pathways and properties(All chemical substances involved in the calculation of the theoretical electrode potential are 1 mol·L-1 or 0.1 MPa, pH 7 and temperature 298 K) [6,33]

Fig.4 Summary of metabolic pathways of methanogens[9,38,39]

Table 1 Main composition of archaea in methanogenic microbial electrolysis cell

Exp. Num.	Type	Voltage^①/V	Inoculum/substrate	vCH_4(v)/（L·L^-1·d^-1）	Location	Dominant archaea genus	Ref.
（1）	DC^②（20ml each）	0.7	ADS^③/acetate	-	anode	Methanobacterium (65%)	[10]
（2）	DC（20ml each）	0.7	ADS/propionate	-	anode	Methanobacterium(57%)	[10]
（3）	SC^④	0.6	raw waste sludge	0.083	anode	Methanocorpusculum(93%)	[13]
（4）	SC	0.6	alkali pretreatment of the waste sludge	0.1	anode	Methanocorpusculum(85%)	[13]
（5）	SC（15 L）	0.3	food waste leachate	0.34 L·g^-1TCOD_removed	bulk sludge	Methanosarcina(45%)	[53]
（6）	SC（20 L）	0.3	AD sludge FWTP	(0.34 ± 0.02) L·g^-1TCOD_removed	bulk sludge	Methanosarcina(24%), Methanobacterium(19%)	[54]
（7）	SC（0.8m³）	4	FTWW^⑤/ADS from winery WWTP^⑥	1.16 ± 0.06	matured sludge	Methanomassillicoccus(22%), Methanosphaerula(14%)	[15]
（8）	SC（0.8m³）(anaerobic effluent recycling of 200%)	4	FTWW /ADS from winery WWTP	2.01±0.13	matured sludge	Methanothrix(37.33%), Methanosphaerula(11.17%)	[15]
（9）	SC (Φ80×120 mm)	0.6	waste activated sludge	2.26±0.16	suspended sludge	Methanosaeta(74%)	[55]
（10）	DC （300 ml each bottle）	-0.8	CO₂	5 L·m^-2·d^-1	cathode	Methanobacterium(86.7%)	[1]
（11）	DC（800ml cathode working volume）continuous mode	-0.7	AGS/ethanol and organic acids	—	cathode	Methanobacterium(77%)	[56]
（12）	DC（800ml cathode working volume）batch mode	-0.7	AGS/ethanol and organic acids	—	cathode	Methanobacterium(84%)	[56]
（13）	SC	0.6	raw waste sludge	0.083	cathode	Methanocorpusculum(77%)	[13]
（14）	SC	0.6	alkali pretreatment of the waste sludge	0.1	cathode	Methanobacterium(98%)	[13]
（15）	SC（open circuit）	0	raw waste sludge	0.064	cathode	Methanosaeta(48.2%)	[13]

Fig.5 Statistics of MEC methanogenic archaea genus relative abundance

Fig.6 Statistics of MEC bacteria genus relative abundance

Table 2 Summary of MEC coupled other systems for methane production

Coupling system	Effective volume/L	OLR^①/(g TCOD·L^-1·d^-1)	HRT/d	Applied voltage/V	Current density/ (A·m^-2)	TCOD removal/%	Other contaminants removal indicators/%	Ce^②/%	CCE^③/%	vCH_4(v)^④/ (L·L^-1·d^-1)	Ref.
AD-MEC DW^⑤ treatment	3	0.08	1	1	—	50	—	95	80	0.012	[58]
AD-MEC	0.5	2.02	24	0.8	0.0501±0.0028	87.5±2.2	36.9±1.7(VSS)	56.37±3.31	>100	0.073±0.001	[65]
AD-MEC FWTP^⑥ wastewater treatment	20	3.0	20	0.3	—	76.1±3.3	73.2±2.1%(TVS^⑦)	—	—	(0.34±0.02) L·(g COD)^-1	[54]
AD-MEC SEOR^⑧ wastewater treatment	0.022	0.21	20	1.2	80 A·m^-3	95.8	—	—	—	0.133±0.0045	[61]
TP-AD-MEC(fermentate-digestate mixture, 55℃)	anode:0.86; cathode:0.86	1.5	20	anode: +0.2 V vs SHE	0.723±0.048 (830 cm²)	28±3	—	119±28(particulate COD)	51±1	0.111±0.010	[12]
UAR^⑨-MEC	0.6	1.5—2	1	0.8±0.01	8.6 mA	83	97%(carbohydrate) 62%(protein) 83%(TOC)	15	—	142.8 ml·(g COD)^-1	[23]
MEC-AnMBR^?	12000	5.88—7.85	10	0.6	—	88.8	72.1%(TN^⑩) 87.4%( $N H 4 +$ -N) 86.9%(BOD₅)	—	—	0.123	[75]
AD-MEC (PS^?treatment)	anode:0.5; cathode:0.1	0.89	9	anode:-0.03 V vs SHE	2	70±4	61±9 (VSS)	63	—	—	[79]
ABR^?-MFC-MEC fecal wastewater treatment	ABR:28;MFC:9.6; MEC:9.6	0.75	48	MFC output voltage:(452.5±10.5)mV	—	95.9	95%( $N H 4 +$ -N)	—	—	biogas components: CH₄:55%–65%	[77]
PEC^?-MEC	anode:0.08; cathode:0.15	—	3	galvanostatic electrolysis at 2.5 mA	3.33(7.5 cm²)	—	—	—	82±10	0.0391	[80]
PEC-MEC	anode:0.45;cathode:0.45	—	—	—	0.275(40 cm²)	—	—	—	96	(192.0 ± 3.6) μl·d^-1·cm^-2	[81]
MEC-UASB^?(pilot scale F-T^? wastewater treatment)	800	30.23±1.07	MEC：0.11 UASB:1.67	4.0	—	93.5±1.6	—	—	—	2.01±0.13	[15]
N-MEC^? （3 groups: M/C/N）	1	M:1.6 C/N:0.9	M:0.58 C/N:1	M:1.3 C/N:1	—	M:80.9±3 C/N:99	C: 65%±2.4% N: 83%±3% （ $N H 4 +$ -N）	—	—	M: 0.451	[74]
UT^?-UASB-MEC	UASB-MEC:35; UT:10	0.92±0.02	7	0.5	45 mA	71.4	37.86%(VSS/SS)	—	—	—	[82]

Table 2 Summary of MEC coupled other systems for methane production

Coupling system	Effective volume/L	OLR^①/(g TCOD·L^-1·d^-1)	HRT/d	Applied voltage/V	Current density/ (A·m^-2)	TCOD removal/%	Other contaminants removal indicators/%	Ce^②/%	CCE^③/%	vCH_4(v)^④/ (L·L^-1·d^-1)	Ref.
AD-MEC DW^⑤ treatment	3	0.08	1	1	—	50	—	95	80	0.012	[58]
AD-MEC	0.5	2.02	24	0.8	0.0501±0.0028	87.5±2.2	36.9±1.7(VSS)	56.37±3.31	>100	0.073±0.001	[65]
AD-MEC FWTP^⑥ wastewater treatment	20	3.0	20	0.3	—	76.1±3.3	73.2±2.1%(TVS^⑦)	—	—	(0.34±0.02) L·(g COD)^-1	[54]
AD-MEC SEOR^⑧ wastewater treatment	0.022	0.21	20	1.2	80 A·m^-3	95.8	—	—	—	0.133±0.0045	[61]
TP-AD-MEC(fermentate-digestate mixture, 55℃)	anode:0.86; cathode:0.86	1.5	20	anode: +0.2 V vs SHE	0.723±0.048 (830 cm²)	28±3	—	119±28(particulate COD)	51±1	0.111±0.010	[12]
UAR^⑨-MEC	0.6	1.5—2	1	0.8±0.01	8.6 mA	83	97%(carbohydrate) 62%(protein) 83%(TOC)	15	—	142.8 ml·(g COD)^-1	[23]
MEC-AnMBR^?	12000	5.88—7.85	10	0.6	—	88.8	72.1%(TN^⑩) 87.4%( $N H 4 +$ -N) 86.9%(BOD₅)	—	—	0.123	[75]
AD-MEC (PS^?treatment)	anode:0.5; cathode:0.1	0.89	9	anode:-0.03 V vs SHE	2	70±4	61±9 (VSS)	63	—	—	[79]
ABR^?-MFC-MEC fecal wastewater treatment	ABR:28;MFC:9.6; MEC:9.6	0.75	48	MFC output voltage:(452.5±10.5)mV	—	95.9	95%( $N H 4 +$ -N)	—	—	biogas components: CH₄:55%–65%	[77]
PEC^?-MEC	anode:0.08; cathode:0.15	—	3	galvanostatic electrolysis at 2.5 mA	3.33(7.5 cm²)	—	—	—	82±10	0.0391	[80]
PEC-MEC	anode:0.45;cathode:0.45	—	—	—	0.275(40 cm²)	—	—	—	96	(192.0 ± 3.6) μl·d^-1·cm^-2	[81]
MEC-UASB^?(pilot scale F-T^? wastewater treatment)	800	30.23±1.07	MEC：0.11 UASB:1.67	4.0	—	93.5±1.6	—	—	—	2.01±0.13	[15]
N-MEC^? （3 groups: M/C/N）	1	M:1.6 C/N:0.9	M:0.58 C/N:1	M:1.3 C/N:1	—	M:80.9±3 C/N:99	C: 65%±2.4% N: 83%±3% （ $N H 4 +$ -N）	—	—	M: 0.451	[74]
UT^?-UASB-MEC	UASB-MEC:35; UT:10	0.92±0.02	7	0.5	45 mA	71.4	37.86%(VSS/SS)	—	—	—	[82]

Fig.7 Schematic diagram of methane production from MEC coupled systems in the past three years

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