Selection and community analysis of halophilic mixed exoelectrogens from salt lake soils

A dual-function mixed-culture biofilm for sulfadiazine removal and electricity production using bio-electrochemical system

Sulfadiazine (SDZ) is frequently detected in environmental samples, arousing much concern due to its toxicity and hard degradation. This study investigated the electricity generation capabilities, SDZ removal and microbial communities of a highly efficient mixed-culture system using repeated transfer enrichments in a bio-electrochemical system. The mixed-culture biofilm (S160-T2) produced a remarkable current density of 954.12 ± 15.08 μA cm-2 with 160 mg/L SDZ, which was 32.9 and 1.8 times higher than that of Geobacter sulfurreducens PCA with 40 mg/L SDZ and without additional SDZ, respectively. Especially, the impressive SDZ removal rate of 98.76 ± 0.79% was achieved within 96 h using the further acclimatized mixed-culture. The removal efficiency of this mixed-culture for SDZ through the bio-electrochemical system was 1.1 times higher than that using simple anaerobic biodegradation. Furthermore, the current density and removal efficiency in this system gradually decreased with increasing SDZ concentrations from 0 to 800 mg/L. In addition, community diversity data demonstrated that the dominant genera, Geobacter and Escherichia-Shigella, were enriched in mixed-culture biofilm, which might be responsible for the current production and SDZ removal. This work confirmed the important roles of acclimatized microbial consortia and co-substrates in the simultaneous removal of SDZ and electricity generation in an electrochemical system.

Accelerating anaerobic digestion process with novel single chamber microbial electrochemical systems with baffle

A newly designed microbial electrochemical system (MES) with the addition of a baffle between the electrodes was integrated with the anaerobic digestion (AD) process for biogas upgradation. Novel MES configuration attained an increased methane production rate of 292.6 mL/L∙d and methane yield of 0.36 ± 0.006 [Formula: see text] /g_COD, which were higher than the values (185.3 mL/L∙d and 0.33 ± 0.009 [Formula: see text] /g_COD) from the MES operation without baffle, respectively. Moreover, the MES with baffle operation resulted in increased substrate removal (88.4 ± 0.5%) and less volatile fatty acids accumulation with a high energy efficiency of 99.6 %. Microbial community analysis revealed that acids metabolizing bacteria, Firmicutes, and Methanothrix were highly enriched in the cathode biofilm of MES with baffle. This study suggests that the baffle addition into the single chamber MES is beneficial to further improve the methanogenesis process for practical applications in the scaled-up MES-AD process.

Extremophilic electroactive microorganisms: Promising biocatalysts for bioprocessing applications

Electroactive microorganisms (EAMs) use extracellular electron transfer (EET) processes to access insoluble electron donors or acceptors in cellular respiration. These are used in developing microbial electrochemical technologies (METs) for biosensing and bioelectronics applications and the valorization of liquid and gaseous wastes. EAMs from extreme environments can be useful to overcome the existing limitations of METs operated with non-extreme microorganisms. Studying extreme EAMs is also necessary to improve understanding of respiratory processes involving EET. This article first discusses the advantages of using extreme EAMs in METs and summarizes the diversity of EAMs from different extreme environments. It is followed by a detailed discussion on their use as biocatalysts in various bioprocessing applications via bioelectrochemical systems. Finally, the challenges associated with operating METs under extreme conditions and promising research opportunities on fundamental and applied aspects of extreme EAMs are presented.

Granulation of halophilic sludge inoculated with estuarine sediments for saline wastewater treatment

As a solution of the sludge loss in the treatment of saline wastewater, the granulation of halophilic sludge was explored in this study. The inoculated estuarine sediment was granulated to an average diameter of 1155 ± 102 μm under the selective settling pressure in the airlift sequencing batch reactor (SBR) when the influent organic loading rate (OLR) was doubled to 0.36 g COD/L·day. The results indicated that the OLR doubled the amount of total extracellular polymeric substance (EPS) and that protein was predominant in the EPS (72.8 ± 2.0%). The correlation between aggregate size and protein content was better than that between aggregate size and polysaccharide content. The amount of alginate-like exopolysaccharides (ALE) increased linearly at the mature granular stage, co-occurring with the compact and elastic structure of the granules. According to the results of 16S rRNA high -throughput sequencing, the Shannon-Weaver index of mature granule decreased by >50% compared to the inoculated sediment. Bacteria of Propionibacteriaceae family constituted 34% of the population in granules and were in symbiotic relationship with halophiles of family Rhodocyclaceae, Vibrionaceae, Flavobacteriaceae, and Cryomorphaceae. The aerobic halophilic granular sludge showed COD removal efficiency of 90.9 ± 0.8% and ammonia removal efficiency of 72.6 ± 4.0% for 30 g/L saline wastewater. An average nitrite accumulation ratio of 94.5 ± 2.9% was observed during nitrification. Granulation of halophilic sludge provides an effective solution to the saline sludge loss problem, which is a step forward to realize the biological treatment of saline wastewater by halophiles.