Geobacter Dominates the Inner Layers of a Stratified Biofilm on a Fluidized Anode During Brewery Wastewater Treatment

Abstract

In this study, we designed a microbial electrochemical fluidized bed reactor (ME-FBR), with an electroconductive anodic bed made of activated carbon particles for treating a brewery wastewater. Under a batch operating mode, acetate and propionate consumption rates were 13-fold and 2.4-fold higher, respectively, when the fluidized anode was polarized (0.2 V) with respect to open circuit conditions. Operating in a continuous mode, this system could effectively treat the brewery effluent at organic loading rates (OLR) over 1.7 kg m-3NRV d-1 and with removal efficiencies of 95 ± 1.4% (hydraulic retention time of 1 day and an influent of 1.7 g-COD L-1). The coulombic efficiency values highly depended upon the OLR applied, and varied from a 56 ± 15% to 10 ± 1%. Fluorescence in situ hybridization (FISH) analysis revealed a relative high abundance of Geobacter species (ca. 20%), and clearly showed a natural microbial stratification. Interestingly, the Geobacter cluster was highly enriched in the innermost layers of the biofilm (thickness of 10 μm), which were in contact with the electroconductive particles of bed, whereas the rest of bacteria were located in the outermost layers. To our knowledge, this is the first time that such a clear microbial stratification has been observed on an anode-respiring biofilm. Our results revealed the relevant role of Geobacter in switching between the electrode and other microbial communities performing metabolic reactions in the outermost environment of the biofilm.

Stratified microbial structure and activity within anode biofilm during electrochemically assisted brewery wastewater treatment

“…The removal rate of the polarized system was maintained at 80.3–81.8%, significantly higher than that of the open‐circuit system (74.6–75.9%; p <.05). The anaerobic treatment of brewery wastewater could remove less than 75% of the COD, while a bioelectrochemical treatment can provide a COD removal rate higher than 80% (Corsino et al, 2017; Tejedor‐Sanz et al, 2018). The results of this and previous studies suggest that the electrode polarization considerably contributed to the removal of organic matter from brewery wastewater.…”

“…These results indicate that a higher proportion of COD was used for electricity generation during the initial stage of continuous flow operation and that most COD might be lost by fermentation or reducing alternative nonelectrode electron acceptors in the later stages. The CEs of BESs treating brewery wastewaters largely depend on the reactor design and operation parameters, but generally are in the range of 5–56% (Wen, Wu, Zhao, & Sun, 2010; Kim, Yang, & Logan, 2015; Tejedor‐Sanz et al, 2017; Tejedor‐Sanz et al, 2018). Even with a low CE of 8.0–19.1%, the electricity generated from brewery wastewater could be self‐sufficient for wastewater treatment in a 90‐L reactor in a previous report (Dong et al, 2015).…”

“…A brewery wastewater was used in this study because it contains various biodegradable organic matter such as sugar, ethanol, and organic acids, which are suitable resources for BES fueling (Tejedor‐Sanz et al, 2018). The wastewater and anaerobic sludge used in all BES experiments were collected from Guangzhou Zhujiang Brewery Co. Ltd. (Guangzhou, China) and anaerobically stored at 4°C with an oxygen‐free headspace before use.…”

“…The COD and organic removal rates were calculated as ( C i − C e )/ C i ×100%, where C e and C i are the substrate concentrations in the effluent and influent, respectively. The daily Coulombic efficiency (CE), which represents the percentage of substrate converted to electrical energy during 24hr, was calculated as Q i / Q t ×100%, where Q i is the charge harvested by the anode (calculated by integrating the current over time) and Q t is the theoretical charge that could be harvested from the removed COD (Liu, Cheng, & Logan, 2005; Tejedor‐Sanz et al, 2018).…”

“…These investigations are crucial to determine whether the cells inside the biofilms contribute to current generation. Using a fluorescence in‐situ hybridization analysis, Tejedor‐Sanz, Fernández‐Labrador, Hart, Torres, and Esteve‐Núñez (2018) have reported predominance of Geobacter spp. at the anode interface compared to the solution interface, which, for the first time, has suggested stratification of microbial structure in a mixed‐culture anode biofilm.…”