A novel operational strategy to enhance wastewater treatment with dual-anode assembled microbial desalination cell

Advancements in spontaneous microbial desalination technology for sustainable water purification and simultaneous power generation: A review

Population growth and rapid urbanization have put a lot of pressure on the already scarce freshwater around the globe. The availability of freshwater is not only limited but it is non-uniform also. Available desalination technologies help mitigate water shortage; however, these techniques are energy-intensive and unsustainable. Desalination technologies utilizing renewable energy and bio-electrochemical systems have been developed to achieve limited sustainability. With technological advancements, microbial desalination cell (MDC) has been developed which is capable of desalination, wastewater treatment, and power generation simultaneously. This review critically examined the performance of various MDC techniques concerning their stimulus parameters including COD removal, total desalination rate, total dissolved solids reduction rate, Coulombic efficiency, and power density. Limitations of MDCs have also been incorporated in the review. Work on MDC coupled with other robust desalination techniques offering advantages such as better desalination and more water recovery e.g. osmotic-MDC etc. has been included. Researchers have tremendously worked on MDCs with different electro-catalysts. Few of these are not sustainable and costly. Authors have reviewed critically with belief that it will pave a way for the commercialization of this eco-friendly technology.

Effect of internal and external resistances on desalination in microbial desalination cell

The green and cost-effective nature of the microbial desalination cell (MDC) make it a promising alternative for future sustainable desalination. However, MDC suffers from a low desalination rate that inhibits it being commercialized. External resistance (R_ext) is one of the factors that significantly affect the desalination rate in MDCs, which is still under debate. This research, for the first time, investigated the impact of R_ext on MDCs with different internal resistance (R_int) of the system to discover the optimal range of R_ext for efficient MDC performance. The results showed that the effect of R_ext on desalination rate (2.52 mg/h) was quite low when the R_int of MDC was high (200 Ω). However, operating the MDC with a low R_int (67 Ω) significantly improved the desalination rate (9.85 mg/h) and current generation. When MDC was operated with a low R_int the effect of variable R_ext on desalination and current generation was noticeable. Therefore, low R_int (67 Ω) MDC was used to select the optimum R_ext when the optimal range was found to be R_ext ≪ R_int, R_ext < R_int, R_ext ≈ R_int (ranging from 1-69 Ω) to achieve the highest desalination rates (10.41-8.59 mg/h). The results showed the superior effect of R_int on desalination rate before selecting the optimal range of R_ext in the outer circuit.

Pushing microbial desalination cells towards field application: Prevailing challenges, potential mitigation strategies, and future prospects

Microbial desalination cells (MDCs) have been experimentally proven as a versatile bioelectrochemical system (BES). They have the potential to alleviate environmental pollution, reduce water scarcity and save energy and operational costs. However, MDCs alone are inadequate to realise a complete wastewater and desalination treatment at a high-efficiency performance. The assembly of identical MDC units that hydraulically and electrically connected can improve the performance better than standalone MDCs. In the same manner, the coupling of MDCs with other BES or conventional water reclamation technology has also exhibits a promising performance. However, the scaling-up effort has been slowly progressing, leading to a lack of knowledge for guiding MDC technology into practicality. Many challenges remain unsolved and should be mitigated before MDCs can be fully implemented in real applications. Here, we aim to provide a comprehensive chronological-based review that covers technological limitations and mitigation strategies, which have been developed for standalone MDCs. We extend our discussion on how assembled, coupled and scaled-up MDCs have improved in comparison with standalone and lab-scale MDC systems. This review also outlines the prevailing challenges and potential mitigation strategies for scaling-up based on large-scale specifications and evaluates the prospects of selected MDC systems to be integrated with conventional anaerobic digestion (AD) and reverse osmosis (RO). This review offers several recommendations to promote up-scaling studies guided by the pilot scale BES and existing water reclamation technologies.

Resource recovery from wastewater can be an application niche of microbial desalination cells

Microbial desalination cells (MDCs) have been studied as an emerging technology to accomplish simultaneous wastewater treatment and saline water desalination. A good amount of effort has been invested to understand fundamental problems and develop functional systems of the MDC technology. However, a revisit of MDCs' desalination function reveals that the unique requirements like co-location of wastewater and saline water will greatly limit the application of this technology. In addition, the relatively low desalination rate of MDCs will result in a large reactor size and thus higher capital cost. Because of the need for wastewater (as a substrate for electricity generation), the MDC technology may have a promising niche of application for resource recovery from wastewater. A proper design of MDCs will allow the current-driven separation of ammonia, phosphorus, and volatile fatty acids (VFAs) from wastewater for further recovery. Based on the literature data, we conduct a case study analysis of mass flow for MDC-based resource recovery and demonstrate the potential of this function. Resource recovery can be a new function of interest to MDCs and worth further exploration of its technical and economic feasibility.

Construction of innovative 3D-weaved carbon mesh anode network to boost electron transfer and microbial activity in bioelectrochemical system

Bioelectrochemical system (BES) is promising technology to simultaneously treat wastewater and recover energy, and electrode material is important for the system performance. Microbial fuel cell (MFC) is one of typical BES to be applied in wastewater treatment. How to improve the electrode material is significant to improve wastewater treatment, energy recovery and cost effectiveness. In this study, 3D-weaved carbon electrode entity, assembled by multiple pieces of carbon mesh (CM), was proposed to combine all electrode components as entity to facilitate electron conduction and ionic migration, compared with carbon brush (CB) and granular activated carbon (GAC). The result showed that current density and internal resistance of MFC using 3D-weaved CM as horizontally extended inside anode (CM(T)) were 30.9 A m-3 and 4.5 Ω, respectively, with higher output than traditional GAC (22.6 A m-3 and 6.2 Ω). Though GAC had greater electrode filling and surface area for biomass growth, the electron transfer efficiency per unit electrode biomass was only at 0.0019 ± 0.0002 mol g-1 d-1, much lower than CM(T) at 0.0077 ± 0.0009 mol g-1 day-1. Higher ionic migration rate of CM(T) suggested the assisting effect of composite electrode to enhance ionic transportation towards the cathode. Microbial analysis further indicated that 3D-CM electrode network could simultaneously enhance Geobacter abundance and methanogen activity, suggesting the importance of electrode network on electricigens. Furthermore, CM(T) could obtain 10 times higher energy output efficiency than traditional GAC when applied inside anode chamber. This study proved that network construction of anode electrode could promote the electrode performance and cost effectiveness, suggesting the future development of reactor design of bioelectrochemical system.

Microbial fuel cell system: a promising technology for pollutant removal and environmental remediation

The microbial fuel cell (MFC) system is a promising environmental remediation technology due to its simple compact design, low cost, and renewable energy producing. MFCs can convert chemical energy from waste matters to electrical energy, which provides a sustainable and environmentally friendly solution for pollutant degradations. In this review, we attempt to gather research progress of MFC technology in pollutant removal and environmental remediation. The main configurations and pollutant removal mechanism by MFCs are introduced. The research progress of MFC systems in pollutant removal and environmental remediation, including wastewater treatment, soil remediation, natural water and groundwater remediation, sludge and solid waste treatment, and greenhouse gas emission control, as well as the application of MFCs in environmental monitoring have been reviewed. Subsequently, the application of MFCs in environmental monitoring and the combination of MFCs with other technologies are described. Finally, the current limitations and potential future research has been demonstrated in this review.