Evaluation of a continuous flow microbial fuel cell for treating synthetic swine wastewater containing antibiotics

Recent advances in swine wastewater treatment technologies for resource recovery: A comprehensive review

Swine wastewater (SW), characterized by highly complex organic and nutrient substances, poses serious impacts on aquatic environment and public health. Furthermore, SW harbors valuable resources that possess substantial economic potential. As such, SW treatment technologies place increased emphasis on resource recycling, while progressively advancing towards energy saving, sustainability, and circular economy principles. This review comprehensively encapsulates the state-of-the-art knowledge for treating SW, including conventional (i.e., constructed wetlands, air stripping and aerobic system) and resource-utilization-based (i.e., anaerobic digestion, membrane separation, anaerobic ammonium oxidation, microbial fuel cells, and microalgal-based system) technologies. Furthermore, this research also elaborates the key factors influencing the SW treatment performance, such as pH, temperature, dissolved oxygen, hydraulic retention time and organic loading rate. The potentials for reutilizing energy, biomass and digestate produced during the SW treatment processes are also summarized. Moreover, the obstacles associated with full-scale implementation, long-term treatment, energy-efficient design, and nutrient recovery of various resource-utilization-based SW treatment technologies are emphasized. In addition, future research prospective, such as prioritization of process optimization, in-depth exploration of microbial mechanisms, enhancement of energy conversion efficiency, and integration of diverse technologies, are highlighted to expand engineering applications and establish a sustainable SW treatment system.

Integrated system of electro-catalytic oxidation and microbial fuel cells for the treatment of recalcitrant wastewater

The emission of recalcitrant wastewater poses serious threats to the environment. In this study, an integrated approach combining electrocatalytic oxidation (EC) for pretreatment and microbial fuel cells (MFC) for thorough pollutant degradation is proposed to ensure efficient degradation of target substances, with low energy input and enhanced bioavailability of refractory organics. When phenol was used as the pollutant, an initial concentration of 2000 mg/L phenol solution underwent EC treatment under constant current-exponential attenuation power supply mode, resulting in a COD removal rate of 54.53%, and a phenol degradation rate of 99.83%. Intermediate products such as hydroquinone and para-diphenol were detected in the solution. After subsequent MFC treatment, only minor amounts of para-diphenol were left, and the degradation rate of phenol and its intermediate products reached 100%, with an output power density of 110.4 mW m-2. When coal chemical wastewater was used as the pollutant, further examination of the EC-MFC system performance showed a COD removal rate of 49.23% in the EC section, and a 76.21% COD removal rate in the MFC section, with an output power density of 181.5 mW m-2. Microbiological analysis revealed typical electrogenic bacteria (such as Pseudomonas and Geobacter), and specific degrading functional bacteria (such as Stenotrophomonas, Delftia, and Brevundimonas). The dominant microbial communities and their proportions adapted to environmental changes in response to the variation of carbon sources.

Fruit peel crude enzymes for enhancement of biohydrogen production from synthetic swine wastewater by improving biohydrogen-formation processes of dark fermentation

Biohydrogen is a promising clean fuel but with a low yield. This study aims to enhance biohydrogen production from synthetic swine wastewater by employing crude enzymes obtained from different fruit peels (orange, mandarin, and banana) to improve the biohydrogen-formation processes of dark fermentation. Results indicated that dosing with crude enzymes affected volatile fatty acids (VFAs) and biogas composition insignificantly, while increased biohydrogen yield from 1.62 ± 0.00 (blank) to 1.90 ± 0.08 (orange peel), 2.01 ± 0.00 (mandarin peel), and 1.96 ± 0.01 (banana peel) mol H₂/mol glucose, respectively. Banana peel crude enzyme was the most effective additive, with 1 g/L protein improving 97.41 ± 3.72 % of biohydrogen yield. The crude enzymes wielded less influence on acetic acid and butyric acid pathways but enhanced other biohydrogen production pathways. These observations demonstrated that fruit peel-based crude enzymes as additives are advantageous to improving biohydrogen yield towards higher biohydrogen production.

Gd-Co nanosheet arrays coated on N-doped carbon spheres as cathode catalyst in photosynthetic microalgae microbial fuel cells

Biocompatible, durable and high catalytic cathode is crucial for the performance of photosynthetic microalgae microbial fuel cell (PMMFC). In this study, gadolinium-cobalt (Gd-Co) nanosheet arrays were coated on N-doped carbon spheres (N-CSs) that were supported using nickel foam (NF), to form a unique 3D hierarchical architecture of Gd-Co@N-CSs/NF cathode material. The morphology and structure of Gd-Co@N-CSs/NF was investigated by physicochemical characterization. The electricity generation and stability of NF, N-CSs/NF, Co@N-CSs/NF and Gd-Co@N-CSs/NF were evaluated using a dual-chamber PMMFC system with Chlorella vulgaris (C. vulgaris) in the cathode chamber. Results showed that doption of Gd to the cathode material resulted in Gd-Co@N-CSs/NF exhibiting superior catalytic activity for the oxygen reduction reaction (ORR), with an ORR peak potential of 0.78 V (vs. RHE). The electron transfer number (n) of Gd-Co@N-CSs/NF was 3.906, indicating ORR was mainly realized via 4e^- transfer pathway. Gd-Co@N-CSs/NF achieved a maximum power density of 115.9 mW m^-2 and an open circuit voltage of 614.8 mV, higher than the other three cathode materials. Gd-Co@N-CSs/NF exhibited excellent stability during 360 h of the PMMFC process, only dropping 5.8 % of maximum voltage. The cell density of C. vulgaris (3.7 × 10¹⁰ cells L^-1) in Gd-Co@N-CSs/NF system was significantly higher than those of NF, N-CSs/NF and Co@N-CSs/NF. This study shows that Gd-Co@N-CSs/NF is a promising cathode material and may be highly beneficial for the enhancement of PMMFC systems.

Ammonia/ammonium removal/recovery from wastewaters using bioelectrochemical systems (BES): A review

This review updates the current research efforts on using BES to recover NH₃/NH₄⁺, highlighting the novel configurations and introducing the working principles and the applications of microbial fuel cell (MFC), microbial electrolysis cell (MEC), microbial desalination cell (MDC), and microbial electrosynthesis cell (MESC) for NH₃/NH₄⁺ removal/recovery. However, commonly studied BES processes for NH₃/NH₄⁺ removal/recovery are energy intensive with external aeration needed for NH₃ stripping being the largest energy input. In such a process bipolar membranes used for yielding a local alkaline pool recovering NH₃ is not cost-effective. This gives a chance to microbial electrosynthesis which turned out to be a potential alternative option to approach circular bioeconomy. Furtherly, the reactor volume and NH₃/NH₄⁺ removal/recovery efficiency has a weakly positive correlation, indicating that there might be other factors controlling the reactor performance that are yet to be investigated.

Mechanism, electrochemistry and biotoxicity analysis of the biodegradation of sulfadiazine on Nickel(Ⅱ)/Manganese(Ⅱ)-modified graphite felt bioanode

Sulfadiazine (SDZ) is one of the most representative sulfonamides antibiotics, and its biodegradation has become a research hotspot in recent years. The present study innovatively adopted a microbial fuel cells with a Nickel (Ⅱ) and Manganese (Ⅱ)-decorated graphite felt bioanode (Ni(Ⅱ)/Mn (Ⅱ)-MFCs) to remove SDZ. The results demonstrated that the Ni(Ⅱ)/Mn (Ⅱ)-MFCs exhibited improved electrochemical performance, with a higher power density (742.98 ± 58.33 mW/m²) compared to the control MFCs (678.34 ± 52.87 mW/m²), an overall lower anode potential, and a larger double layer area (cyclic voltammetry). After 5 months of operation, approximately 97.95% of 30 mg/L SDZ was degraded within 120 h, which was 11.46% higher than that of the control MFCs. Moreover, SDZ and its byproducts could be better mineralized in the Ni(Ⅱ)/Mn (Ⅱ)-MFCs than the control, and the biotoxicity of SDZ towards Escherichia coli and Vibro qinghaiensis sp. Q67 could be greatly decreased after treatment with the modified MFCs. Based on the metabolites, we hypothesized that the chemical reactions hydroxylation, ammoxidation, SO₂-extrusion, sulfur-reduction, etc. played a significant role in SDZ biodegradation. A microbial community analysis revealed that Dechloromonas (2.37%), Denitratisoma (5.32%) and Lentimicrobium (26.35%) were the dominant functional microbes in the Ni(Ⅱ)/Mn (Ⅱ)-MFCs. This study may provide insights and a theoretical basis for the biodegradation of sulfonamides and thus may facilitate further investigations and relevant findings.

Enhanced photodegradation of antibiotics based on anoxygenic photosynthetic bacteria and bacterial metabolites: A sustainably green strategy for the removal of high-risk organics from secondary effluent

Antibiotic residues in effluents discharged from wastewater treatment plants (WWTPs) have been considered high-risk organics due to biorefractory property and potential toxicity. Secondary pollution and unsustainability existed in advanced treatment of secondary effluent are currently in urgent need of improvement. In this study, a sustainably green strategy based on Rhodopseudomonas palustris (R.palustris) by regulating the structure of extracellular polymeric substances (EPS) was proposed for the first time to achieve efficiently removal of sulfadiazine (SDZ). Results showed that 0.2 V was the optimal external potential for R.palustris to efficiently remove SDZ, where the biodegradation rate constant obtained at this potential was 4.87-folds higher than that in open-circuit mode and a complete removal was achieved within 58 h in the presence of EPS extracted at this potential. Three-dimensional excitation-emission matrix (3D-EEM) spectra analysis suggested that tryptophan protein-like, tyrosine protein-like, humic acid-like and fulvic acid-like substances present in EPS were the main effective components which was responsible for the indirect photodegradation of SDZ. The quenching experiments showed that ³EPS* was the dominant reactive species which accounted for 90% of SDZ removal. This study provides new implications for the advanced treatment of secondary effluent organic matters by developing eco-friendly bioaugmentation technology and biomaterials.

Microwave-assisted continuous flow phytosynthesis of silver nanoparticle/reduced graphene oxide composites and related visible light catalytic performance

The creation of an environmentally friendly synthesis method for silver nanomaterials (AgNPs) is an urgent concern for sustainable nanotechnology development. In the present study, a novel straightforward and green method for the preparation of silver nanoparticle/reduced graphene oxide (AgNP/rGO) composites was successfully developed through the combination of phytosynthesis, continuous flow synthesis and microwave-assistance. Oriental persimmon (Diospyros kaki Thunb.) extracts were used as both plant reducing and capping agents for fast online synthesis of AgNP/rGO composites. The experimental parameters were optimized and the morphologies of the prepared materials were investigated. The characterization results reveal that spherical AgNPs were quickly synthesized and uniformly dispersed on rGO sheets using the proposed online system. Fourier transform infrared spectroscopy analysis confirmed that phenols, flavonoids, and other substances in the plant extracts played a decisive role in the synthesis of AgNP/rGO composites. Using sodium borohydride (NaBH₄) degradation of p-nitrophenol (4-NP) as a model, the catalytic activity of the prepared AgNP/rGO materials was evaluated. The complete degradation of 4-NP was achieved within 12 min through the use of AgNP/rGO materials, and the composite had a much better catalytic activity than the bare AgNPs and rGO had. Compared with the conventional chemical method, our online method is facile, fast, cost-efficient, and environmentally friendly.

A Review of Stand-Alone and Hybrid Microbial Electrochemical Systems for Antibiotics Removal from Wastewater

The growing concern about residual antibiotics in the water environment pushes for innovative and cost-effective technologies for antibiotics removal from wastewater. In this context, various microbial electrochemical systems have been investigated as an alternative to conventional wastewater technologies that are usually ineffective for the adequate removal of antibiotics. This review article details the development of stand-alone and hybrid or integrated microbial electrochemical systems for antibiotics removal from wastewater. First, technical features, antibiotics removal efficiencies, process optimization, and technological bottlenecks of these systems are discussed. Second, a comparative summary based on the existing reports was established to provide insights into the selection between stand-alone and hybrid systems. Finally, research gaps, the relevance of recent progress in complementary areas, and future research needs have been discussed.

Novel continuous up-flow MFC for treatment of produced water: Flow rate effect, microbial community, and flow simulation

Produced water (PW) is the main waste produced by oil and gas industry, and its treatment represents an environmental and economical challenge for governments and the industry itself. Microbial fuel cells (MFC) emerge as an ecofriendly technology able to harvest energy and remove pollutants at the same time, however high internal resistance is a key problem limiting their operating performance and practical application. In this work, a novel continuous up-flow MFC was designed and fed solely using PW under different flowrates. Effects of the different flowrates (0 mL/s, 0.2 mL/s, 0.4 mL/s, and 0.6 mL/s) in power production performance and pollutants removal were analyzed. Our results demonstrated the removal efficiency of all the pollutants improved when flowrate incremented from 0 to 0.4 mL/s (COD: 96%, TDS: 22%, sulfates: 64%, TPH: 89%), but decreased when 0.6 mL/s was applied. The best power density of 227 mW/m² was achieved in a flowrate of 0.4 mL/s. Similar to the pollutant's removal, the power density increased together with the increment of flowrate and decreased when 0.6 mL/s was used. The reason for the performance fluctuation was the decrement of internal resistance from 80 Ω (batch mode) to 20 Ω (0.4 mL/s), and then the sudden increment to 90 Ω for 0.6 mL/s. A flow simulation revealed that until 0.4 mL/s the flow was organized and helped protons to arrive in the membrane faster, but flowrate of 0.6 mL/s created turbulence which prejudiced the transportation of protons incrementing the internal resistance. Microbial community analysis of the biofilm found that Desulfuromonas, Desulfovibrio and Geoalkalibacter were dominant bacteria in charge of pollutant removal and electricity production. This study can be helpful in guiding the use of continuous-flow MFC for PW treatment, and to accelerate the practical application of MFC technology in oil industry.

Effect of hydraulic retention time on the denitrification performance and metabolic mechanism of a multi-chambered bio-electrochemical system

The effects of hydraulic retention time (HRT) on the denitrification performance of the multi-chambered bio-electrochemistry system and the metabolic mechanism of the microbial community were investigated. Results indicated that the NO₃^--N and NO₂^--N removal efficiency was up to 99.5% and 99.9%, respectively. The electricity generation performance of the system was optimum at 24 h HRT, with the maximum power density and output voltage of the fourth chamber to be 471.2 mW/m³ and 602.4 mV, respectively. With the decrease of HRT from 24 h to 8 h, the protein-like substance in extracellular polymeric substance (EPS) of granular sludge was reduced and the fluorescence intensities were weakened. Besides, the abundance of metabolism pathway was the highest at 50.0% and 49.9%, respectively, and the methane metabolism (1.8% and 2.0%, respectively) and the nitrogen metabolism (0.8% and 0.9%, respectively) in Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway played important roles in providing guaranteed stability and efficient removal of organic matter and nitrogen from the system.

Plant microbial fuel cell: Opportunities, challenges, and prospects

Microbial fuel cells (MFCs) are considered as greener technologies for generation of bioenergy and simultaneously treatment of wastewater. However, the major drawback of these technologies was, rapid utilization of substrate by the microbes to generate power. This drawback is solved to a great extent by plant microbial fuel cell (PMFC) technology. Therefore, this review critically explored the challenges associated with PMFC technology and approaches to be employed for making it commercially feasible, started with brief introduction of MFCs, and PMFCs. This review also covered various factors like light intensity, carbon dioxide concentration in air, type of plant used, microbial flora in rhizosphere and also electrode material used which influence the efficiency of PMFC. Finally, this review comprehensively revealed the possibility of future intervention, such as application of biochar and preferable plants species which improve the performance of PMFC along with their opportunities challenges and prospects.

Recent trends in upgrading the performance of yeast as electrode biocatalyst in microbial fuel cells

Microbial fuel cell (MFC) is an optimistic fuel cell technology that applies microorganism's biochemical catalytic activities in consuming organic substrate and produce electricity. In the past, several researchers have reported power generation from Saccharomyces cerevisiae, but nowadays, most of the studies are centred around bacterial biofilms (prokaryotes) as anode biocatalyst. Yeast (a eukaryote) has also been applied as a biocatalyst in MFCs as they are non-pathogenic, easy to handle and tolerant to various environmental conditions. Yeast strains such as Arxula adeninvorans, Candida melibiosica, Hansenula polymorpha, Hansenula anomala, Kluyveromyces marxianus and Saccharomyces cerevisiae have been utilized in MFCs. This review summarizes the application of yeast as an anode biocatalyst together with a discussion on the mechanism of electron transfer from yeast cells to the anode and highlights the techniques applied in improving the efficiency of yeast-based MFCs. The recent challenges and benefits of utilizing yeast in MFCs have been also encapsulated in this review.