Onset Investigation on Dynamic Change of Biohythane Generation and Microbial Structure in Dual-chamber versus Single-chamber Microbial Electrolysis Cells

Economic and environmental analysis: Straw biogas project operating at full load with dry yellow corn straw

Due to the unique straw raw materials in China, the current straw biogas project based on the "two-stage" process of wet anaerobic digestion still has problems such as deficient technology, low production capacity, and weak profitability. In this study, we improved the original process for the biogas project, aiming at increasing biogas yield and profit. The results show that the new process (NP) can effectively recover the "carbon" by anaerobic hydrolysis, solve the problems of scum and crust, and significantly improve the biomethane yield (141.3%-321.8%), net profit ($599,667-$772,004/year), and carbon emission reduction equivalent (2.7×107-4.6×107 kg CO2e/year). Based on the amount of dry yellow corn straw that can be collected annually for energy-oriented production, NP's potential economic and environmental value is estimated to be significant. This study provides reliable technical support for efficient utilization of agricultural resources and circular economy.

Zero-discharge, self-sustained 3D-printed microbial electrolysis cell for biohydrogen production: a review

Microbial fuel cell (MFC) and microbial electrolysis cell (MEC) technologies have been used recently in bench-scale bioenergy (electricity) generation, biohydrogen (H2) production, biosensing, and wastewater treatment. There are still a lot of obstacles to overcome in terms of commercialization and industrial settling. These difficulties include lengthy start-up times, intricate reactor designs for managing large reaction volumes, and expensive and time-consuming large-scale system fabrication procedures. Interestingly, combining three-dimensional (3D) printing with MFC and MEC technology appears to be a workable and promising way to get past these obstacles. Moreover, a rapid start-up with no delays in the current generation using MFC and MEC is possible with 3D printed bio-anodes. Furthermore, H2 can be generated from wastewater by powering a stacked MFC and MEC-coupled with electrochemical capacitor (ECC) system using 3D printing technology. To the best of the author's knowledge, this review paper is the first to explicitly highlight the use of 3D printing in creating a stacked MFC-ECC-MEC system in conjunction with a photobioreactor (PBR) to produce significant quantities of H2 and carbon dioxide (CO2) can be utilized for algae production. A notable feature of 3D printing technology is its reliable production capabilities, enabling MFC-ECC-MEC-PBR systems to be expanded by setting up numerous stacks of MFC-ECC-MEC-PBR units devoid of material waste and human error. The present review attempts to provide an update on the current status of the 3D printing application, that is meant to propel the MFC-ECC-MEC-PBR system forward.

Electro-mediated cathodic oxygen drives respiration chain electron transfer of electroactive bacteria to enhance refractory organic biological oxidation

In electro-mediated biological system (EMBS), biological anode and cathode components were incorporated into an anaerobic bioreactor, providing a small amount of oxygen to the cathode as an electron acceptor. Oxygen diffusion also impacts the anode's anaerobic ecological environment. This study unraveled how oxygen influences the metabolism and electron transport chain during the biological oxidation of refractory organics. Under the influence of electromotive force, the straight-chain model pollutant N,N-dimethylformamide (DMF) showed rapid degradation and better ammonification, with maximum rates reaching 0.53 h-1 and 26.6 %, respectively. Elevated electromotive force promoted the enrichment of functional electroactive bacteria on the anode and enhanced the availability of electron storage sites, thereby facilitating electron transfer at the anode-biofilm interface. Conversely, the anodic micro-aerobic environment disrupted the anaerobic microbial community structure, and the competitive interactions among fermentative bacteria and electroactive bacteria inhibited DMF degradation. Metagenomic analysis confirmed that cathodic oxygen up-regulated the pyruvate metabolism and the tricarboxylic acid (TCA) cycle to generate NADH and synthesize ATP. The electromotive force induced by cathodic oxygen accelerated the electron transfer in respiratory chains of electroactive bacteria, driving the oxidation of NADH and enhancing the degradation of organics. This study improves our understanding of the regulatory mechanisms governing metabolic pathways under the influence of cathodic oxygen. It offers potential for developing more efficient EMBS in industrial wastewater pretreatment, ensuring that oxygen is prevented from diffusing to the anode during micro-aeration at the cathode.

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.

Advantages of residual phenol in coal chemical wastewater as a co-metabolic substrate for naphthalene degradation by microbial electrolysis cell

The use of co-metabolic substrates is effective for polycyclic aromatic hydrocarbons (PAHs) removal, but the potential of the high phenol concentrations in coal chemical wastewater (CCW) as a co-metabolic substrate in microbial electrolysis cell (MEC) has been neglected. In this study, the efficacy of varying phenol concentrations in comparison to simple substrates for degrading naphthalene in MEC under comparable COD has been explored. Results showed that phenol as a co-metabolic substrate outperformed sodium acetate and glucose in facilitating naphthalene degradation efficiency at 50 mg-COD/L. The naphthalene removal efficiency from RP, RA, and RG was found to be 84.11 ± 0.44 %, 73.80 ± 0.27 % and 72.43 ± 0.34 %, respectively. Similarly, phenol not only enhanced microbial biomass more effectively, but also exhibited optimal COD metabolism capacity. The addition of phenol resulted in a stepwise reduction in the molecular weight of naphthalene, whereas sodium acetate and glucose led to more diverse degradation pathways. Some bacteria with the potential ability to degrade PAHs were detected in phenol-added MEC, including Alicycliphilus, Azospira, Stenotrophomonas, Pseudomonas, and Sedimentibacter. Besides, phenol enhanced the expression of ncrA and nmsA genes, leading to more efficient degradation of naphthalene, with ncrA responsible for mediating the reduction of the benzene ring in naphthalene and nmsA closely associated with the decarboxylation of naphthalene. This study provides guidance for the effective co-degradation of PAHs in CCW with MEC, demonstrating the effectiveness of using phenol as a co-substrate relative to simple substrates in the removal of naphthalene.

Revealing the roles of chemical communication in restoring the formation and electroactivity of electrogenic biofilm under electrical signaling disruption

Electrogenic biofilms in microbial electrochemical systems have played significant roles in simultaneous wastewater treatment and energy recovery owing to their unique extracellular electron transfer. Their formation has been shown to be regulated by electrical and chemical communication, but the interaction between these signal communication pathways has not been studied. This research investigated the coordination between intracellular c-di-GMP signaling and reinforced quorum sensing with or without exogenous HSL (a common quorum sensing molecule), on the formation of mixed-cultured electrogenic biofilm under electrical signaling disruption by tetraethylammonium (TEA, a broad-range potassium channel blocker). Intracellular c-di-GMP was spontaneously reinforced in response to TEA stress, and metagenomic analysis revealed that the dominant DGC (the genes for producing c-di-GMP) induced the eventual biofilm formation by mediating exopolysaccharide synthesis. Meanwhile, reinforced quorum sensing by exogenous HSL could also benefit the biofilm restoration, however, it alleviated the TEA-induced communication stress, resulting in the weakening of c-di-GMP dominance. Interestingly, suppressing electrical communication with or without HSL addition both induced selective enrichment of Geobacter of 85.5% or 30.1% respectively. Functional contribution analysis revealed the significant roles of Geobacter and Thauera in c-di-GMP signaling, especially Thauera in resistance to TEA stress. This study proposed a potential strategy for electrogenic biofilm regulation from the perspectives of cell-to-cell communication.

Fundamentals and recent progress in bioelectrochemical system-assisted biohythane production

Biohythane, a balanced mixture of 10%-30% v/v of hydrogen and 70%-90% v/v of methane, could be the backbone of an all-purpose future energy supply. Recently, bioelectrochemical systems (BES) became a new sensation among environmental biotechnology processes with the potential to sustainably generate biohythane. Therefore, to unleash its full potential for scaling up, researchers are consistently improving microbial metabolic pathways, novel reactors, and electrode designs. This review presents a detailed analysis of recently discovered fundamental mechanisms and science and engineering intervention of different strategies to improve the biohythane composition and production rate from BES. However, several milestones are to be achieved, for instance, improving electrode kinetics using efficient catalysts, engineered microbial communities, and improved reactor configurations, for commercializing this sustainable technology. Thus, a future perspective section is included to recommend novel research lines, mainly focusing on the microbial communities and the efficient electrocatalysts, to enhance reactor performance.

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.

R, Maitra S, Tarafdar A, Alphy MP, Kumar AN, Madhavan A, Sirohi R, Awasthi MK, Sindhu R, Varjani S, Binod P. Waste-Derived Fuels and Renewable Chemicals for Bioeconomy Promotion: A Sustainable Approach

Bio-based fuels and chemicals through the biorefinery approach has gained significant interest as an alternative platform for the petroleum-derived processes as these biobased processes are noticed to have positive environmental and societal impacts. Decades of research was involved in understanding the diversity of microorganisms in different habitats that could synthesize various secondary metabolites that have functional potential as fuels, chemicals, nutraceuticals, food ingredients, and many more. Later, due to the substrate-related process economics, the diverse low-value, high-carbon feedstocks like lignocellulosic biomass, industrial byproducts, and waste streams were investigated to have greater potential. Among them, municipal solid wastes can be used as the source of substrates for the production of commercially viable gaseous and liquid fuels, as well as short-chain fattyacids and carboxylic acids. In this work, technologies and processes demanding the production of value-added products were explained in detail to understand and inculcate the value of municipal solid wastes and the economy, and it can provide to the biorefinery aspect.