Bio-Electrochemical Enhancement of Hydrogen and Methane Production in a Combined Anaerobic Digester (AD) and Microbial Electrolysis Cell (MEC) from Dairy Manure

Amro Hassanein,Yong Liang,Stephanie Lansing,Ling Qiu,Freddy Witarsa

doi:10.3390/su12208491

Abstract

Anaerobic digestion (AD) is a biological-based technology that generates methane-enriched biogas. A microbial electrolysis cell (MEC) uses electricity to initiate bacterial oxidization of organic matter to produce hydrogen. This study determined the effect of energy production and waste treatment when using dairy manure in a combined AD and MEC (AD-MEC) system compared to AD without MEC (AD-only). In the AD-MEC system, a single chamber MEC (150 mL) was placed inside a 10 L digester on day 20 of the digestion process and run for 272 h (11 days) to determine residual treatment and energy capacity with an MEC included. Cumulative H2 and CH4 production in the AD-MEC (2.43 L H2 and 23.6 L CH4) was higher than AD-only (0.00 L H2 and 10.9 L CH4). Hydrogen concentration during the first 24 h of MEC introduction constituted 20% of the produced biogas, after which time the H2 decreased as the CH4 concentration increased from 50% to 63%. The efficiency of electrical energy recovery (ηE) in the MEC was 73% (ηE min.) to 324% (ηE max.), with an average increase of 170% in total energy compared to AD-only. Chemical oxygen demand (COD) removal was higher in the AD-MEC (7.09 kJ/g COD removed) system compared to AD-only (6.19 kJ/g COD removed). This study showed that adding an MEC during the digestion process could increase overall energy production and organic removal from dairy manure.

Highlights

Microbial electrolysis cell (MEC) is a bioelectrochemical technology that uses concepts from microbial fuel cell (MFC) research
Was the overall Chemical oxygen demand (COD) reduction higher, but the COD conversion efficiency to renewable energy was higher in the anaerobic digestion (AD)-MEC (7.09 kJ/g COD removed) compared to AD-only (6.19 kJ/g COD removed)
The additional total solids (TS) reduction in the last 10 days of digestion was higher in the AD-MEC treatment (35.2%) compared to AD-only (13.4%), and the additional volatile solids (VS) reduction was 41.9% for AD-MEC treatment compared to 19.0% for AD-only

Summary

Introduction

Microbial electrolysis cell (MEC) is a bioelectrochemical technology that uses concepts from microbial fuel cell (MFC) research. While MFCs use microbial decomposition of organic compounds to produce an electric current, in an MEC, an electric current is applied to reverse the reaction to convert organic material to hydrogen (H2) and/or methane (CH4). MECs have been explored as a clean energy source and a promising innovative technology for H2 production using bioelectrochemical properties. Hydrogen gas is formed in an MEC from two sources of energy: (1) bacterial oxidization of organic matter and (2) electric input [1,2,3,4]. During AD, the waste is converted into biogas, a renewable energy source that consists of 55–75% CH4, 45–25% CO2, and small amounts of hydrogen sulfide (H2S), hydrogen (H2), and other gases [7,8]. The microbial process in the AD process is divided into two main phases: acidogenic and methanogenic [6,9]

Methods

Results

Conclusion