Effectiveness of piggery waste treatment using microbial fuel cells coupled with elutriated-phased acid fermentation

Thirty years of experience in water pollution control in Taihu Lake: A review

Taihu Lake has suffered from eutrophication and algal blooms for decades, primarily due to increasing anthropogenic pollutants from human activities. Extensive research and widespread implementation of water pollution control measures have significantly contributed to the improvement of water quality of Taihu Lake. However, the relevant experience of Taihu Lake pollution control has not been well summarized to provide insight for future lake restoration. This review article seeks to address this gap by first providing a comprehensive overview of Taihu Lake's water quality dynamics over the past thirty years, characterized by two distinct stages: (I) water quality deterioration (1990s-2007); and (II) water total nitrogen (TN) improvement but total phosphorus (TP) fluctuation (2007-current). Subsequently, we conducted a thorough review of the experiences and challenges associated with water pollution control during these two stages. Generally, pollution control practices emphasized point source control but overlooked non-point sources before 2007, possibly due to point sources being easier to identify and manage. Accordingly, the focus shifted from industrial point sources to a combination of industrial point and agricultural non-point sources after 2007 to control water pollution in the Taihu Lake Basin. Numerous studies have delved into non-point source pollution control, including source control, transport intercept, in-lake measures, and the integration of these technologies. Taken together, this paper provides suggestions based on the needs and opportunities of this region. Further research is needed to better understand and model the underlying pollution processes, as well as to increase public participation and improve policy and law implementation, which will assist decision-makers in formulating better water management in Taihu Lake.

Sludge source-redox mediators obtainment and availability for enhancing bioelectrogenesis and acidogenesis: Deciphering characteristics and mechanisms

Anaerobic biological treatment was regarded as one of promising options for realizing concurrent WAS reduction, stabilization and bioenergy/bioresource recycle. But the relatively low treatment efficiency limited its spreading application toward larger scale considerably in China. Aimed at such barrier, this study offered a novel enhancing strategy for achieving high-efficiency of bioenergy/bioresource recycle from WAS anaerobic treatment via improving bioelectrogenesis/acidogenesis using sludge source-redox mediators (SSRMs). SSRMs not only facilitated bioeletrogenesis with an increasing efficiency of 36% for voltage output and 39% for bioelectricity bioconversion, but also enhanced acidogenesis of WAS with a mean elevating efficiency of 37.5% of volatile fatty acids (VFAs) production within 5 d Mechanistic investigations indicated that SSRMs had a potential influence on improving the protein and carbohydrate metabolisms-related genes' expression for enhancing bioelectrogenesis and acidogenesis. Moreover, SSRMs exerted roles of electrochemical "catalysts" or as terminal electron acceptors with affecting functional proteins of complexes of Ⅰ and Ⅳ in electron transfer chains for improving electron transfer efficiency. Meanwhile, the core members' abundance, microbial diversity and community distributive evenness were prompted concurrently for carrying out superior bioelectrogenesis and acidogenesis. A schematic illustration was established for demonstrating the mechanism of SSRMs for enhancing bioelectrogenesis and acidogenesis via changing microbial metabolism functions, enhancing electron transfer efficiency, and regulating functional genes' expression of functional proteins (up-regulating cytochrome c oxidase and down-regulating-NADH dehydrogenase). This study provided an effective enhancing strategy for facilitating WAS bioconversion to bioenergy/bioresource with well-process sustainability.

Contribution of configurations, electrode and membrane materials, electron transfer mechanisms, and cost of components on the current and future development of microbial fuel cells

Microbial fuel cells (MFCs) are a technology that can be applied to both the wastewater treatment and bioenergy generation. This work discusses the contribution of improvements regarding the configurations, electrode materials, membrane materials, electron transfer mechanisms, and materials cost on the current and future development of MFCs. Analysis of the most recent scientific publications on the field denotes that dual-chamber MFCs configuration offers the greatest potential due to the excellent ability to be adapted to different operating environments. Carbon-based materials show the best performance, biocompatibility of carbon-brush anode favors the formation of the biofilm in a mixed consortium and in wastewater as a substrate resembles the conditions of real scenarios. Carbon-cloth cathode modified with nanotechnology favors the conductive properties of the electrode. Ceramic clay membranes emerge as an interesting low-cost membrane with a proton conductivity of 0.0817 S cm^-1, close to that obtained with the Nafion membrane. The use of nanotechnology in the electrodes also enhances electron transfer in MFCs. It increases the active sites at the anode and improves the interface with microorganisms. At the cathode, it favors its catalytic properties and the oxygen reduction reaction. These features together favor MFCs performance through energy production and substrate degradation with values above 2.0 W m^-2 and 90% respectively. All the recent advances in MFCs are gradually contributing to enable technological alternatives that, in addition to wastewater treatment, generate energy in a sustainable manner. It is important to continue the research efforts worldwide to make MFCs an available and affordable technology for industry and society.

Advancements in Bioelectricity Generation Through Nanomaterial-Modified Anode Electrodes in Microbial Fuel Cells

The use of nanotechnology in bioelectrochemical systems to recover bioelectricity and metals from waste appears to be a potentially appealing alternative to existing established procedures. This trend exactly characterizes the current renewable energy production technology. Hence, this review focuses on the improvement of the anode electrode by using different functional metal oxide-conducting polymer nanocomposites to enhance microbial fuel cell (MFC) performance. Enhancement of interfacial bioelectrocatalysis between electroactive microorganisms and hierarchical porous nanocomposite materials could enhance cost-effective bioanode materials with superior bioelectrocatalytic activity for MFCs. In this review, improvement in efficiency of MFCs by using iron oxide- and manganese oxide-based polypyrrole hybrid composites as model anode modifiers was discussed. The review also extended to discussing and covering the principles, components, power density, current density, and removal efficiencies of biofuel cell systems. In addition, this research review demonstrates the application of MFCs for renewable energy generation, wastewater treatment, and metal recovery. This is due to having their own unique working principle under mild conditions and using renewable biodegradable organic matter as a direct fuel source.

Managing the Effluents of Anaerobic Fermentations by Bioprocess Schemes Involving Membrane Bioreactors and Bio-Electrochemical Systems: A Mini-Review

Anaerobic bioprocesses, such as anaerobic digestion and dark fermentation, provide energy carriers in the form of methane and hydrogen gases, respectively. However, their wastewater-type residues, that is, the fermentation effluents, must be treated carefully due to the incomplete and non-selective conversion of organic matter fed to the actual system. For these reasons, the effluents contain various secondary metabolites and unutilized substrate, in most cases. Only a fraction of anaerobic effluents can be directly applied for fertilization under a moderate climate. Conventional wastewater treatment technologies may be used to clean the remainder, but that approach leads to a net loss of energy and of potentially useful agricultural input materials (organic carbon and NPK fertilizer substitutes). The rationale of this paper is to provide an overview of promising new research results in anaerobic effluent management strategies as a part of technological downstream that could fit the concept of new-generation biorefinery schemes aiming towards zero-waste discharge, while keeping in mind environmental protection, as well as economical perspectives. According to the literature, the effluents of the two above processes can be treated and valorized relying either on membrane bioreactors (in case of anaerobic digestion) or bio-electrochemical apparatus (for dark fermentation). In this work, relevant findings in the literature will be reviewed and analyzed to demonstrate the possibilities, challenges, and useful technical suggestions for realizing enhanced anaerobic effluent management. Both membrane technology and bio-electrochemical systems have the potential to improve the quality of anaerobic effluents, either separately or in combination as an integrated system.

Microbial profiles associated improving bioelectricity generation from sludge fermentation liquid via microbial fuel cells with adding fruit waste extracts

This first-attempt study illustrated the microbial cooperative interactions related to bioelectricity generation from the mixture of sludge fermentation liquid (SFL) and fruit waste extracts (FWEs) via microbial fuel cells (MFCs). The optimal output voltages of 0.65 V for SFL-MFCs, 0.51 V for FWEs-MFCs and 0.75 V for mixture-MFCs associated with bioelectricity conversion efficiencies of 1.061, 0.718 and 1.391 kWh/kg COD were reached, respectively. FWEs addition for substrates C/N ratio optimization contributed considerably to increase SFL-fed MFCs performance via triggering a higher microbial diversity, larger relatively abundance of functional genes and microbial synergistic interactions with genera enrichment of Clostridium, Alicycliphilus, Thermomonas, Geobacter, Paludibaculum, Pseudomonas, Taibaiella and Comamonas. Furthermore, a conceptual illustration of co-locating scenario of wastewater treatment plant(s), waste sludge in situ acidogenic fermentation, fruit waste collection/crushing station and MFC plant was proposed for the first time, which provided new thinking for future waste sludge treatment toward maximizing solid reduction and power recovery.

Bio-electrocatalytic remediation of hydrocarbons contaminated soil with integrated natural attenuation and chemical oxidant

The present study aimed to assess the possibility of integrating natural attenuation (NA) and chemical oxidation (O) with the bio-electrocatalytic remediation (BET) process to remediate petroleum hydrocarbons contaminated soil. Six different reactors were operated, wherein in the first reactor was a NA system, and the second condition to the NA was supplemented with a chemical oxidant (NAO). These systems were compared with BET systems which were differentiated based on the position and distance between the electrodes. The study was performed by considering NA as a common condition in all the six different reactors viz., NA, NAO, NA + BET with 0.5 cm space amid electrodes (BET_H-0.5), NAO + BET with 0.5 cm space amid electrodes (BETO_H-0.5), NAO + BET with 1.0 cm space amid electrodes (BETO_H-1.₀), and NAO + BET with vertical electrodes at 1.0 cm distance (BETO_V-1.₀). The highest total petroleum hydrocarbons (TPH) degradation efficiency was observed with BETO_H-0.5 (67 ± 0.8%) followed by BETO_H-1.0 (62 ± 0.6%), BET_H-0.5 (60%), BETO_V-1.0 (56 ± 0.5%), NAO (46.6%), and NA (27.7%). In NA, the indigenous microorganisms remediate the organic contaminants. In the NAO system, KMnO₄ actively breakdown the carbon-carbon double bond functional group. Further, in BETO_H-0.5, an anodophilic bacteria enriched around the electrode reported enhanced treatment efficiency along with a maximum of 260 mV (1.65 mA). BET systems integrated with chemical oxidation processes were much more effective in the TPH removal process than an individual process. The BET method adopted here thus provides a good opportunity for bio-electrocatalytic remediation of TPH and resource recovery in the form of bioelectricity.

Facile one-pot microwave assisted synthesis of rGO-CuS-ZnS hybrid nanocomposite cathode catalysts for microbial fuel cell application

A reduced graphene oxide-copper sulfide-zinc sulfide (rGO-CuS-ZnS) hybrid nanocomposite was synthesized using a surfactant-free in-situ microwave technique. The in-situ microwave method was used to prepare 1-D ZnS nanorods and CuS nanoparticles decorated into the rGO nanosheets. The prepared hybrid nanocomposite catalysts were analyzed by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, elemental mapping analysis, and X-ray photoelectron spectroscopy. The effectiveness of the synthesized rGO-CuS-ZnS hybrid nanocomposite (rGO-CZS HBNC) was estimated using an innovative cathode catalyst in microbial fuel cell (MFC). MFCs were fabricated differently such as SL (single-layer), DL (double-layer), and TL (triple-layer) loading. Followed using cyclic voltammetry and impedance analyses, the electrochemical evaluation of the prepared MFCs was evaluated. Among the fabricated MFCs, the DL MFCs with rGO-CuS-ZnS cathode catalyst displayed higher power density (1692 ± 15 mW/m²) and OCP (761 ± 9 mV) than the other catalysts loadings, such as SL and TL. rGO-CZS HBNC are potential cathode materials for MFC applications.

Electro-fermentation for biofuels and biochemicals production: Current status and future directions

Electro-fermentation is an emerging bioporcess that could regulate the metabolism of electrochemically active microorganisms. The provision of electrodes for the fermentation process that functions as an electron acceptor and supports the formation and transportation of electrons and protons, consequently producing bioelectricity and value-added chemicals. The traditional method of fermentation has several limitations in usability and economic feasibility. Subsequently, a series of metabolic processes occurring in conventional fermentation processes are most often redox misaligned. In this regard, electro-fermentation emerged as a hybrid technology which can regulate a series of metabolic processes occurring in a bioreactor by regulating the redox instabilities and boosting the overall metabolic process towards high biomass yield and enhanced product formation. The present article deals with microorganisms-electrode interactions, various types of electro-fermentation systems, comparative evaluation of pure and mixed culture electro-fermentation application, and value-added fuels and chemical synthesis.

Linking microbial mechanism with bioelectricity production in sludge matrix-fed microbial fuel cells: Freezing/thawing liquid versus fermentation liquor

This first-attempt study elucidated the microbial mechanism associated with bioelectricity output in microbial fuel cells (MFCs) fed with sludge matrices of freezing/thawing (F/T) liquid versus fermentation liquor, while a novel schematic elucidation for exploring cooperative interactions in anodic microbial consortia of MFCs supplied with such two feeds toward electrogenesis was put forward. Moreover, the F/T liquid cultivated main genera of Azospira, Povalibacter, Thauera, Terrimonas, Alicycliphilus, Dokdonella and Simplicispira for dual organics degradation and electrogenesis with power density of 0.152 mW/m² and electrogenesis efficiency of 1.152 kWh/kg COD, while the fermentation liquor fostered higher diversity and medium evenness with the enrichment of Phenylobacterium, Cellulomonas, Edaphobacter, Burkholderia, Clostridium, Sphingomonas, Leifsonia and Microbacterium in anodic biofilm and causing larger power density of 0.182 mW/m² and 1.418 kWh/kg COD-electrogenesis efficiency. Comparative analysis results indicated that the anodic fermentative bacteria exert considerable influence on concurrent organics degradation and electricity production through the synergistic interactions with exoelectrogens toward stable running of MFCs. Besides, the higher anodic microbial diversity, relatively middling community evenness and larger abundance of functional genes associated with electrogenesis together played contributive roles on more power generation through MFCs for treating WAS matrix. This study was conducive to bring about some new microbial mechanism understanding on maximizing bioenergy recovery via MFCs in future sludge management.

Techno-economic assessment of various hydrogen production methods - A review

Hydrogen is a clean fuel that could provide energy incentives and reduce environmental impacts, if production platform is carefully selected and optimized. In specific, techno-economic and sensitivity analysis of the existing hydrogen production platforms and processes is need for an hour to boost the future hydrogen economical aspects. This will have greater impact on future hydrogen production project designs and developing new approaches to reduce the overall production costs to make it as cheaper fuel. The sensitivity analysis of various hydrogen production process such as pyrolysis, gasification, steam reforming of natural gas, dark fermentation, photobiolysis, water electrolysis and renewable liquid reforming were reviewed to evaluate their merits and demerits along with cost-effectiveness. On economic view point, steam reforming of natural gas is efficient, low cost and best methods for hydrogen production. A future research is required to reduce energy input and trapping carbon dioxide emission using membrane models.

Insights into redox mediators-resource harvest/application with power production from waste activated sludge through freezing/thawing-assisted anaerobic acidogenesis coupling microbial fuel cells

This first-attempted study demonstrated endogenous redox-mediators harvest/application from waste activated sludge (WAS) through freezing/thawing (F/T) pretreatment-enhanced anaerobic acidogenesis coupled with microbial fuel cells (MFCs). A total of 2.57 kWh electricity was produced from per kg soluble chemical oxygen demand (SCOD) via MFCs just in 2 d with about 90% organics removal, which contained 1.152 kWh/kg COD from F/T liquid together with 1.418 kWh/kg COD from fermentation liquid. The fermentation liquor-MFCs fostered higher anodic biodiversity and more power output as compared with the F/T liquid-MFCs. Essentially, the completely endogenous redox mediators-like substances with relatively high redox activities could be retained after MFC electrogenesis from F/T liquid and played electron shuttle-roles sufficiently in enlarging bio-energy production of MFCs, which seemed to be an effective option for harvesting endogenous redox mediators from sludge. This study might inspire progressive thinking toward aims of high-efficiency of resource recycle/bioenergy production from WAS.

Waste based hydrogen production for circular bioeconomy: Current status and future directions

The present fossil fuel-based energy sector has led to significant industrial growth. On the other hand, the dependence on fossil fuels leads to adverse impact on the environment through releases of greenhouse gases. In this scenario, one possible substitute is biohydrogen, an eco-friendly energy carrier as high-energy produces. The substrates rich in organic compounds like organic waste/wastewater are very useful for improved hydrogen generation through the dark fermentation. Thus, this review article, initially, the status of biohydrogen production from organic waste and various strategies to enhance the process efficiency are concisely discussed. Then, the practical confines of biohydrogen processes are thoroughly discussed. Also, alternate routes such as multiple process integration approach by adopting biorefinery concept to increase overall process efficacy are considered to address industrial-level applications. To conclude, future perspectives besides with possible ways of transforming dark fermentation effluent to biofuels and biochemicals, which leads to circular bioeconomy, are discussed.