Enhanced sulfur recovery and sulfate reduction using single-chamber bioelectrochemical system

Performance and mechanism of sulfamethoxazole removal from seawater in a single-chamber bioelectrochemical system

The aim of this study was to investigate the performance and mechanism of sulfamethoxazole (SMX) biodegradation in seawater using a single-chamber bioelectrochemical system (SCBES). With an initial SMX concentration varying from 1 to 10 mg/L, the SMX removal decreased from 99.1 ± 2.0% to 89.6 ± 8.0% in the SCBES within 120 h under an applied voltage of 0.8 V. The SMX removals could be fitted by the pseudo-first-order equation (R2 > 0.96), which had a kinetic constant of 0.031 h-1 in the SCBES at 1 mg/L SMX. The control tests with a dual-chamber BES showed that the cathodic biofilms had higher SMX removal (97.0 ± 9% vs. 67.4 ± 7%) and S2- accumulation from SO42- reduction (651 ± 65 vs. 427 ± 43 mg/L) than anodic biofilms within 120 h, respectively. Higher bacterial viability and biomass in the cathodic than anodic biofilms of the SCBES resulted in higher performance of the cathodic biofilms (9.1:1 vs. 7.5:1 and 194 ± 30 vs. 76 ± 11 mg·protein/g). The linear relationship between SO42- removals and SMX concentrations (R2 > 0.970) demonstrated that sulfate-reducing bacteria (SRB) could be crucial to the SMX degradation. Desulfuromusa and Desulfococcus as the dominant species were identified in the bacterial communities of the SCBES. The high performance of SCBES may be attributed to the integration of bioelectrochemical reactions with the synergy between electrochemically active bacteria and SRBs. Results from this study showed that SCBES could be a promising way for SMX biodegradation in seawater.

Electrode functional microorganisms in bioelectrochemical systems and its regulation: A review

Bioelectrochemical systems (BES) as environmental remediation biotechnologies have boomed in the last two decades. Although BESs combined technologies with electro-chemistry, -biology, and -physics, microorganisms and biofilms remain at their core. In this review, various functional microorganisms in BESs for CO2 reduction, dehalogenation, nitrate, phosphate, and sulfate reduction, metal removal, and volatile organic compound oxidation are summarized and compared in detail. Moreover, interrelationship regulation approaches for functional microorganisms and methods for electroactive biofilm development, such as targeted electrode surface modification, chemical treatment, physical revealing, biological optimization, and genetic programming are pointed out. This review provides promising guidance and suggestions for the selection of microbial inoculants and provides an analysis of the role of individual microorganisms in mixed microbial communities and its metabolisms.

Biogenic sulfur recovery from sulfate-laden antibiotic production wastewater using a single-chamber up-flow bioelectrochemical reactor

The high-concentration sulfate (SO42-) in the antibiotic production wastewater hinders the anerobic methanogenic process and also proposes possible environmental risk. In this study, a novel single-chamber up-flow anaerobic bioelectrochemical reactor (UBER) was designed to realize simultaneous SO42- removal and elemental sulfur (S0) recovery. With the carbon felt, the cathode was installed underneath and the anode above to meet the different biological niches for sulfate reducing bacteria (SRB) and sulfur oxidizing bacteria (SOB). The bio-anode UBER (B-UBER) demonstrated a much higher average SO42- removal rate (SRR) of 113.2 ± 5.7 mg SO42--S L-1 d-1 coupled with a S0 production rate (SPR) of 54.4 ± 5.8 mg S0-S L-1 d-1 at the optimal voltage of 0.8 V than that in the abio-anode UBER (control reactor) (SRR = 86.6 ± 13.4 mg SO42--S L-1 d-1; SPR = 25.5 ± 9.7 mg S0-S L-1 d-1) under long-term operation. A large amount of biogenic S0 (about 72.2 mg g-1 VSS) was recovered in the B-UBER. The bio-anode, dominated by Thiovirga (SOB genus) and Acinetobacter (electrochemically active bacteria genus), exhibited a higher current density, lower overpotential, and lower internal resistance. C-type cytochromes mainly served as the crucial electron transfer mediator for both direct and indirect electron transfer, so that significantly increasing electron transfer capacity and biogenic S0 recovery. The reaction pathways of the sulfur transformation in the B-UBER were hypothesized that SRB utilized acetate as the main electron donor for SO42- reduction in the cathode zone and SOB transferred electrons to the anode or oxygen to produce biogenic S0 in the anode zone. This study proved a new pathway for biogenic S0 recovery and sulfate removal from sulfate-laden antibiotic production wastewater using a well-designed single-chamber bioelectrochemical reactor.

Comparative study of the removal of sulfate by UASB in light and dark environment

At present, the application of sewage treatment technologies is restricted by high sulfate concentrations. In the present work, the sulfate removal was biologically treated using an upflow anaerobic sludge blanket (UASB) in the absence/presence of light. First, the start-up of UASB for the sulfate removal was studied in terms of COD degradation, sulfate removal, and effluent pH. Second, the impacts of different operation parameters (i.e., COD/SO42- ratio, temperature and illumination time) on the UASB performance were explored. Third, the properties of sludge derived from the UASB at different time were analyzed. Results show that after 28 days of start-up, the COD removal efficiencies in both the photoreactor and non-photoreactor could reach a range of 85-90% while such reactors could achieve > 90% of sulfate being removed. Besides, higher illumination time could facilitate the removal of pollutants in the photoreactor. To sum up, the present study can provide technical support for the clean removal of sulfate from wastewater using photoreactors.

Enhanced metronidazole removal in seawater using a single-chamber bioelectrochemical system

The aim of this study was to investigate the removal of metronidazole (MNZ) from seawater using a bioelectrochemical system (BES). Single-chamber BES (i.e., S-BES) and dual-chamber BES (i.e., D-BES) were constructed with carbon brush as the anode and cathode. With the inoculum of sea mud and 2 g/L of glucose as the substrate in seawater, S-BES and D-BES were acclimated to test the MNZ removal. Results showed that S-BES could remove almost 100 % of 200 mg/L MNZ within 120 h and remain stable within 10 cycles of operation (∼50 d) under the applied voltage of 0.8 V. The MNZ removal reached ∼100 % and 60.2 % in the cathodic and anodic chambers of D-BES fed by 100 mg/L MNZ under 0.8 V, respectively. The MNZ concentration of 200 mg/L significantly inhibited the sulfur metabolism, decreased the ratio of live to dead cells in the electrode biofilms, and thus reduced the SO42- removal in the S-BES. The MNZ degradation and S2- oxidation was mainly attributed to the cathodic and anodic biofilms of S-BES, respectively. Three degradation pathways of MNZ were proposed based on the identified intermediates and results of density functional theory calculations. The synergies among different genus species in the bacterial communities of biofilms, and between anodic and cathodic reactions could be responsible for the high performance of S-BES. Results from this study should be not only useful for the MNZ removal but also for effective MNZ inhibition of sulfate-reducing bacteria induced microbiologically influenced corrosion in seawater.

Autotrophic degradation of sulfamethoxazole using sulfate-reducing biocathode in microbial photo-electrolysis system

Sulfamethoxazole is a representative of sulfonamide antibiotic pollutants. This study aims to investigate the degradation pathways of sulfamethoxazole and the response of microbial communities using the autotrophic biocathode in microbial photo-electrolysis systems (MPESs). Sulfamethoxazole with an initial concentration of 2 mg L-1 was degraded into small molecule propanol within 6 h with the biocathode. Elemental sulfur (S0) was detected in the cathode chamber, accounting for 57 % of the removed sulfate. The conversion from sulfate to S0 indicated that autotrophic microorganisms might adopt a novel pathway for sulfamethoxazole removal in the MPES. In the abiotic cathode, sulfamethoxazole degradation rate was 0.09 mg L-1 h-1 with the electrochemistry process. However, sulfamethoxazole was converted to products that still contain benzene rings, including p-aminothiophenol, 3-amino-5-methylisoxazole, and sulfonamide. The microbial community analysis indicated that the synergistic interaction of Desulfovibrio and Acetobacterium promoted the autotrophic degradation of sulfamethoxazole. The results suggested that autotrophic microorganisms may play an important role in the environmental transformation of sulfamethoxazole.

Scaling up of dual-chamber microbial electrochemical systems - An appraisal using systems design approach

Impetus to minimise the energy and carbon footprints of evolving wastewater resource recovery facilities has promoted the development of microbial electrochemical systems (MES) as an emerging energy-neutral and sustainable platform technology. Using separators in dual-chamber MES to isolate anodic and cathodic environments creates endless opportunities for its myriad applications. Nevertheless, the high internal resistance and the complex interdependencies among various system factors have challenged its scale-up. This critical review employed a systems approach to examine the complex interdependencies and practical issues surrounding the implementation and scalability of dual-chamber MES, where the anodic and cathodic reactions are mutually appraised to improve the overall system efficiency. The robustness and stability of anodic biofilms in large-volume MES is dependent on its inoculum source, antecedent history and enrichment strategies. The composition and anode-respiring activity of these biofilms are modulated by the anolyte composition, while their performance demands a delicate balance between the electrode size, macrostructure and the availability of substrates, buffers and nutrients when using real wastewater as anolyte. Additionally, the catholyte governed the reduction environment and associated energy consumption of MES with scalable electrocatalysts needed to enhance the sluggish reaction kinetics for energy-efficient resource recovery. A comprehensive assessment of the dual-chamber reactor configuration revealed that the tubular, spiral-wound, or plug-in modular MES configurations are suitable for pilot-scale, where it could be designed more effectively using efficient electrode macrostructure, suitable membranes and bespoke strategies for continuous operation to maximise their performance. It is anticipated that the critical and analytical understanding gained through this review will support the continuous development and scaling-up of dual-chamber MES for prospective energy-neutral treatment of wastewater and simultaneous circular management of highly relevant environmental resources.