Microbial electrolysis contribution to anaerobic digestion of waste activated sludge, leading to accelerated methane production

Abstract

14Methane production rate (MPR) in waste activated sludge (WAS) digestion processes is typically limited 15 by the initial steps of complex organic matter degradation, leading to a limited MPR due to sludge 16 fermentation speed of solid particles. In this study, a novel microbial electrolysis AD reactor (ME-AD) was 17 used to accelerate methane production for energy recovery from WAS. Carbon bioconversion was 18 accelerated by ME producing H 2 at the cathode. MPR was enhanced to 91.8 gCH 4 /m 3 reactor/d in the 19 microbial electrolysis ME-AD reactor, thus improving the rate by 3 times compared to control conditions 20 (30.6 gCH 4 /m 3 reactor/d in AD). The methane production yield reached 116.2 mg/g VSS in the ME-AD 21 reactor. According to balance calculation on electron transfer and methane yield, the increased methane 22 production was mostly dependent on electron contribution through the ME system. Thus, the use of the 23 novel ME-AD reactor allowed to significantly enhance carbon degradation and methane production from 24 WAS. 25 26 2 29 1. Introduction 30 The large amount of activated sludge generated during wastewater treatment poses a critical threat (when 31 not properly disposed) to ecological systems [1], while proper treatment and disposal of excess sludge is 32 quite expensive (Wei et al. 2003). On the other hand, anaerobic digestion (AD) is widely used for sludge 33 reduction as an energy saving and recovering method [2]. However, AD rate is substantially limited by the 34 first two steps (hydrolysis and acidogenesis) to convert complex organic compounds into suitable substrates 35 for methanogenesis, in raw sludge [3-5]. Commonly, it takes from 20 to 30 days to degrade 30-50% of the 36 total COD or volatile solids (VS) of raw WAS, under mild environmental conditions [6]. The pressure of 37 rapid human population growth and increasing energy demand have thus promoted further research on 38 development and improvement of an rate-accelerating AD process, in order to enhance biogas production 39 and achieve faster degradation rate from WAS [7, 8]. 40Recently, some researchers pointed out that bioelectrochemical systems have the ability to promote carbon 41 oxidation on anode and in-site CO 2 capture and reduction on cathode, thus providing additional CH 4 42 formation in an integrated AD system [9, 10]. Recently a direct interspecies electron transfer for 43 methanogenesis has been proved between Geobacter and Methanosaeta [11]. However, few efforts have 44 been made to better understand bioelectrochemical contributions to organic conversion or methane 45 promotion, which is very important to achieve viable reactor operations in the future. Lately, microbial 46 electrolysis cells (MECs) have been tested for their ability to convert waste organic compounds from 47 3 Therefore, in this study, a coupled system was tested, by putting a microbial electrolysis (ME) system into 59 an AD system, for raw waste activated sludge treatment at mild environmental conditions. The microbial 60 electrolysis system wa...

Biorefinery perspectives of microbial electrolysis cells (MECs) for hydrogen and valuable chemicals production through wastewater treatment

“…This revealed that the electroactive biofilm formed on the electrode surface must have enhanced the stability of the AD rather than the electrical current (De Vrieze et al, 2014). Similarly, Liu et al (2016) combined MEC and AD to form an MEC-AD system to improve CH4 production rate (MPR) from waste activated sludge. MPR was enhanced to 91.8 g CH4/m 3 reactor/d in the integrated MEC-AD reactor, compared to 30.6 g CH4/m 3 reactor/d in the AD alone .…”

Microbial electrolysis cell as an emerging versatile technology: a review on its potential application, advance and challenge

“…fabricated a three‐dimensional biphasic Ni 5 P 4 ‐NiP 2 nanosheet matrix to act as a cathodic tunnel for H 2 generation in a microbially catalyzed bioanode, and obtained a high H 2 production rate of 9.78 mL day −1 cm −2 . In the past decade, Pt covered carbon cloth has been widely applied as cathode catalyst in MECs, but it is difficult to apply in practical H 2 production due to its high cost and the lack of strength of the carbon cloth. Nickel foam with Pt as the catalyst promoted H 2 yield to 0.71 m 3 m −3 day −1 under the applied supply of 0.8 V .…”

“…The effect of the applied voltage on the enhancement of CH 4 production in five studies: R1, R2, R3, R4 and R5, which tested different types of organic matter as a substrate. R OC (open‐circuit), R CC (closed‐circuit, 0.8 V), and WAS (waste‐activated sludge).…”

Performance of low temperature Microbial Fuel Cells (MFCs) catalyzed by mixed bacterial consortia

“…Lately, the contribution of bacteria without the ability for anode respiration in bioelectrochemical systems has been discussed. It was found that the part of the microbial communities that did not participate in extracellular electron transfer was maintained in the anaerobic niche of electrode biofilms, where they could provide labile products for electrode-respiring bacteria (Liu et al, 2016a(Liu et al, , 2016b. The diversity of the community may be maintained through utilization of compounds excreted by electrogenic bacteria, or by growth on the biomass of other cells by nonacetate-utilizing bacteria (Liu et al, 2010).…”