Photosynthetic microbial desalination cells (PMDCs) for clean energy, water and biomass production

Enhancing electrokinetics and desalination efficiency through catalysts and electrode modifications in microbial desalination cells

Microbial desalination cells (MDCs) are considered as a sustainable technology for water desalination, wastewater treatment, and power generation. However, this neoteric technology suffers from different challenges, including sluggish oxygen reduction reaction and poor electron transfer from microbes to electrodes, ultimately leading to less power generation and desalination efficiency. This review delves into the intricate roles of both abiotic and biocatalysts in enhancing performance of MDCs through ion removal and charge transfer mechanisms. Detailed discussions highlight the comparative advantages and limitations of different catalyst types and insights into electrode modifications to optimise catalytic activity and biofilm formation. Further, recent advancements in electrode engineering, including surface coatings and integration of nanomaterial, geared towards enhancing efficiency of MDC and performance stability are discussed. Finally, future recommendations are provided, focusing on innovative catalyst designs, material integration, and considerations for scale-up and commercialisation, thereby offering a comprehensive roadmap for the continued advancement of MDC.

Microalgae-bacteria nexus for environmental remediation and renewable energy resources: Advances, mechanisms and biotechnological applications

Microalgae and bacteria, known for their resilience, rapid growth, and proximate ecological partnerships, play fundamental roles in environmental and biotechnological advancements. This comprehensive review explores the synergistic interactions between microalgae and bacteria as an innovative approach to address some of the most pressing environmental issues and the demands of clean and renewable freshwater and energy sources. Studies indicated that microalgae-bacteria consortia can considerably enhance the output of biotechnological applications; for instance, various reports showed during wastewater treatment the COD removal efficiency increased by 40%-90.5 % due to microalgae-bacteria consortia, suggesting its great potential amenability in biotechnology. This review critically synthesizes research works on the microalgae and bacteria nexus applied in the advancements of renewable energy generation, with a special focus on biohydrogen, reclamation of wastewater and desalination processes. The mechanisms of underlying interactions, the environmental factors influencing consortia performance, and the challenges and benefits of employing these bio-complexes over traditional methods are also discussed in detail. This paper also evaluates the biotechnological applications of these microorganism consortia for the augmentation of biomass production and the synthesis of valuable biochemicals. Furthermore, the review sheds light on the integration of microalgae-bacteria systems in microbial fuel cells for concurrent energy production, waste treatment, and resource recovery. This review postulates microalgae-bacteria consortia as a sustainable and efficient solution for clean water and energy, providing insights into future research directions and the potential for industrial-scale applications.

Evaluating application of photosynthetic microbial fuel cell to exhibit efficient carbon sequestration with concomitant value-added product recovery from wastewater: A review

The emission of CO2 from industrial (24%) and different anthropogenic activities, like transportation (27%), electricity production (25%), and agriculture (11%), can lead to global warming, which in the long term can trigger substantial climate changes. In this regard, CO2 sequestration and wastewater treatment in tandem with bioenergy production through photosynthetic microbial fuel cell (PMFC) is an economical and sustainable intervention to address the problem of global warming and elevating energy demands. Therefore, this review focuses on the application of different PMFC as a bio-refinery approach to produce biofuels and power generation accompanied with the holistic treatment of wastewater. Moreover, CO2 bio-fixation and electron transfer mechanism of different photosynthetic microbiota, and factors affecting the performance of PMFC with technical feasibility and drawbacks are also elucidated in this review. Also, low-cost approaches such as utilization of bio-membrane like coconut shell, microbial growth enhancement by extracellular cell signalling mechanisms, and exploitation of genetically engineered strain towards the commercialization of PMFC are highlighted. Thus, the present review intends to guide the budding researchers in developing more cost-effective and sustainable PMFCs, which could lead towards the commercialization of this inventive technology.

Sustainable application of tubular photosynthesis microbial desalination cell for simultaneous desalination of seawater for potable water supply associated with sewage treatment and energy recovery

A sustainable approach for simultaneous desalination of actual seawater for potable water supply, and bioelectrochemical treatment of sewage associated with power generation was evaluated in a tubular photosynthesis desalination microbial fuel cell (PDMC) continually operated for 180 days. Anion exchange membrane (AEM) was used to separate the bioanode and desalination compartments, whereby, and cation exchange membrane (CEM) was used to separate the desalination and biocathode compartments. Mixed bacterial species and mixed microalgae were utilized for inoculation of the bioanode and biocathode, respectively. The results revealed that maximum and average desalination efficiencies of saline seawater fed to the desalination compartment were 80 ± 1 % and 72 ± 1.2 %, respectively. Maximum and average removal efficiencies of the sewage organic content in the anodic compartment were up to 99.3 ± 0.5 % and 91.0 ± 0.8 %, respectively associated with maximum power output of 430.7 ± 0.7 mW/m³. In spite of the heavy growth of the mixed bacterial species and microalgae as well, no fouling of AEM and CEM was observed during the entire period of operation. Kinetic study demonstrated that Blackman model described well the bacterial growth. Dense and healthy growth of biofilm and the microalgae in the anodic and cathodic compartments, respectively were clearly observed during the operation period. The promising outcomes of this investigation demonstrated that the suggested approach is a potential sustainable option for simultaneous desalination of saline seawater for potable water supply, biotreatment of sewage, and power generation.

Algae-Assisted Microbial Desalination Cell: Analysis of Cathode Performance and Desalination Efficiency Assessment

Algae-assisted microbial desalination cells represent a sustainable technology for low-energy fresh water production in which microalgae culture is integrated into the system to enhance oxygen reduction reaction in the cathode chamber. However, the water production (desalination rate) is low compared to conventional technologies (i.e., reverse osmosis and/or electrodialysis), as biocathodes provide low current generation to sustain the desalination process. In this sense, more research efforts on this topic are necessary to address this bottleneck. Thus, this study provides analysis, from the electrochemical point of view, on the cathode performance of an algae-assisted microbial desalination cell (MDC) using Chlorella vulgaris. Firstly, the system was run with a pure culture of Chlorella vulgaris suspension in the cathode under conditions of an abiotic anode to assess the cathodic behavior (i.e., cathode polarization curves in light-dark conditions and oxygen depletion). Secondly, Geobacter sulfurreducens was inoculated in the anode compartment of the MDC, and the desalination cycle was carried out. The results showed that microalgae could generate an average of 9–11.5 mg/L of dissolved oxygen during the light phase, providing enough dissolved oxygen to drive the migration of ions (i.e., desalination) in the MDC system. Moreover, during the dark phase, a residual concentration of oxygen (ca. 5.5–8 mg/L) was measured, indicating that oxygen was not wholly depleted under our experimental conditions. Interestingly, the oxygen concentration was restored (after complete depletion of dissolved oxygen by flushing with N2) as soon as microalgae were exposed to the light phase again. After a 31 h desalination cycle, the cell generated a current density of 0.12 mA/cm2 at an efficiency of 60.15%, 77.37% salt was removed at a nominal desalination rate of 0.63 L/m2/h, coulombic efficiency was 9%, and 0.11 kWh/m3 of electric power was generated. The microalgae-assisted biocathode has an advantage over the air diffusion and bubbling as it can self-sustain a steady and higher concentration of oxygen, cost-effectively regenerate or recover from loss and sustainably retain the system’s performance under naturally occurring conditions. Thus, our study provides insights into implementing the algae-assisted cathode for sustainable desalination using MDC technology and subsequent optimization.

Recent Progress in Solar-Induced Direct Biomass-to-Electricity Hybrid Fuel Cell Using Microalgae as Feedstocks

Microalgae, as potential biodiesel feedstocks, have been widely reported to accumulate oil via genetic engineering techniques, or environmental stress regulation. Recently, the utilization of fuel cell technology to convert biomass into electricity has attracted much more attention due to its high efficiency, low pollution, low noise by microalgae as feedstocks. Normally, platinum and analogous noble metals as catalysts have been already demonstrated although they still exist lots of shortcomings. This mini review presents an overview of various fuel cell technologies with phosphomolybdic acid as catalysts for sustainable energy by using microalgae. Trends from literatures demonstrate that algal-based fuel cells could efficiently generate electricity, and concurrently produce high value-added products. This critical review can provide guiding suggestions for future study of algal-based energy conversion by fuel cell techniques.

Prospects in Cadmium-Contaminated Water Management Using Free-Living Cyanobacteria (Oscillatoria sp.)

In this study, the removal of cadmium (Cd) by free-living Oscillatoria sp. was studied. Our results showed that maximal Cd removal efficiency (~60%) by the cyanobacterial culture was achieved within 12–24 h in the presence of 5.0 or 25.0 mg/L of Cd. The mechanisms underlying this phenomenon were explored by elemental analysis and FTIR-ATR spectroscopy. It was found that metal adsorption by negatively charged functional groups in the cyanobacterial biomass was the main mechanism used by Oscillatoria sp. to remove metal from the aqueous medium, followed by Cd bioaccumulation into living cells. Additionally, Cd-exposed microalgae showed increased oxidative stress (MDA formation), a decreased dehydrogenase activity, a higher amount of soluble carbohydrates and a decreased total carotenoid concentration, as compared to the control cells. These results suggest that Oscillatoria sp. improved its antioxidative defense system under stressful conditions, through carotenoid-mediated ROS quenching and induction of carbohydrate catabolism, in order to counteract the oxidative damage and preserve the photosynthetic machinery and cellular energetics. In fact, no significant reduction in Oscillatoria sp. cell density, total protein amount, and chlorophyll a content was observed after 24-h Cd exposure, even at the highest metal concentration tested (i.e., 25.0 mg/L). Hence, the presented results are the first to describe some new insights about the metabolic and physiological behavior of living Oscillatoria sp. during Cd remediation, and open up the possibility of finding an equilibrium that maximizes metal removal performance with an active cyanobacterial metabolism, to achieve a rewarding and sustainable management of industrial metal-polluted wastewater.

Simultaneous bioelectricity generation and water desalination using Oscillatoria sp. as biocatalyst in photosynthetic microbial desalination cell

Globally, the scarcity of drinking water has triggered the researchers towards the development of desalination techniques to turn up saline water into potable. Microbial Desalination Cell (MDC) is a novel green technology that shows potential approach for desalination along with electricity generation and wastewater treatment. However, the expensive catholyte/catalyst in the cathode side has limited the MDC for real time application. Hence, the main objective of this work was to investigate the electricity generation during dairy wastewater treatment and desalination efficiency using biocathode (Oscillatoria sp.) in the MDC. The results showed that the maximum open circuit voltage of 652 ± 10 mV, COD removal efficiency of 80.2 ± 0.5% and desalination efficiency of 65.8 ± 0.5%, were achieved respectively. The effect of saline water concentration was investigated and the performance of MDC was compared with real (sea) water. This study demonstrated that Oscillatoria sp. could be used as a potential biocatalyst in the cathode chamber for enhancing salinity removal along with electricity generation and wastewater treatment in the MDC.

Anodic metabolic activity regulates the desalination efficiency in microbial catalysed electrochemical system

Anodic metabolic rate showed regulatory influence on the desalination performance of microbial desalination cell (MDC) under open (OC) and closed circuit (CC) operations. In this study, three MDCs were tested for desalination with three different organic substrate loads 1500 ± 55 mg/L in MDC-A; 3500 ± 10 g/L in MDC-B; 4500 ± 12 g/L in MDC-C. Higher desalination and substrate removal rates were observed in CC than OC. Average desalination was MDC-C (51.4%-CC) > MDC-B (47.3%-CC) > MDC-A (45.3%-CC) and COD removal efficiencies were MDC-C (68.4%-CC) > MDC-B (64.4%-CC) > MDC-A (51.9%-CC). Increase in organic load resulted in higher desalination efficiency which was due to higher electrochemical and ionic gradient apart from anodic metabolic activity. The voltage and current density were observed to be maximum in MDC-C (685 mV; 2.16 mA/m²) followed by MDC-B (598 mV; 1.98 mA/m²) and MDC-A (501 mV; 1.76 mA/m²). This study demonstrated that the MDCs performance can be regulated by varying organic load and circuitry modes.

Anoxic-biocathode microbial desalination cell as a new approach for wastewater remediation and clean water production

Bioelectrochemical systems are emerging as a promising and friendly alternative to convert the energy stored in wastewater directly into electricity by microorganisms and utilize it in situ to drive desalination. To better understand such processes, we propose the development of an anoxic biocathode microbial desalination Cell for the conversion of carbon- and nitrogen-rich wastewaters into bioenergy and to perform salt removal. Our results demonstrate a power output of 0.425 W m^-3 with desalination, organic matter removal and nitrate conversion efficiencies of 43.69, 99.85 and 92.11% respectively. Microbiological analysis revealed Proteobacteria as the dominant phylum in the anode (88.45%) and biocathode (97.13%). While a relatively higher bacterial abundance was developed in the anode chamber, the biocathode showed a greater variety of microorganisms, with a predominance of Paracoccus (73.2%), which are related to the denitrification process. These findings are promising and provide new opportunities for the development and application of this technology in the field of wastewater treatment to produce cleaner water and conserve natural resources.

Accomplishing a N-E-W (nutrient-energy-water) synergy in a bioelectrochemical nitritation-anammox process

This study reports an investigation of the concept, application and performance of a novel bioelectrochemical nitritation-anammox microbial desalination cell (MDC) for resource-efficient wastewater treatment and desalination. Two configurations of anammox MDCs (anaerobic-anammox cathode MDC (AnA_moxMDC) and nitration-anammox cathode MDC (NiA_moxMDC)) were compared with an air cathode MDC (CMDC), operated in fed-batch mode. Results from this study showed that the maximum power density produced by NiA_moxMDC (1,007 mW/m³) was higher than that of AnA_moxMDC (444 mW/m³) and CMDC (952 mW/m³). More than 92% of ammonium-nitrogen (NH₄⁺-N) removal was achieved in NiA_moxMDC, significantly higher than AnA_moxMDC (84%) and CMDC (77%). The NiA_moxMDC performed better than CMDC and AnA_moxMDC in terms of power density, COD removal and salt removal in desalination chamber. In addition, cyclic voltammetry analysis of anammox cathode showed a redox peak centered at -140 mV Vs Ag/AgCl confirming the catalytic activity of anammox bacteria towards the electron transfer process. Further, net energy balance of the NiA_moxMDC was the highest (NiA_moxMDC-0.022 kWh/m³ >CMDC-0.019 kWh/m³ >AnA_moxMDC-0.021 kWh/m³) among the three configurations. This study demonstrated, for the first time, a N-E-W synergy for resource-efficient wastewater treatment using nitritation-anammox process.

Bio-electrochemical system (BES) as an innovative approach for sustainable waste management in petroleum industry

Petroleum industry is one of the largest and fast growing industries due to the ever increasing global energy demands. Petroleum refinery produces huge quantities of wastes like oily sludge, wastewater, volatile organic compounds, waste catalyst, heavy metals, etc., because of its high capacity and continuous operation of many units. Major challenge to this industry is to manage the huge quantities of waste generated from different processes due to the complexity of waste as well as changing stringent environmental regulations. To decrease the energy loss for treatment and also to conserve the energy stored in the chemical bonds of these waste organics, bio-electrochemical system (BES) may be an efficient tool that reduce the economics of waste disposal by transforming the waste into energy pool. The present review discusses about the feasibility of using BES as a potential option for harnessing energy from different waste generated from petroleum refineries.

Assessing potential cathodes for resource recovery through wastewater treatment and salinity removal using non-buffered microbial electrochemical systems

The present study evaluates relative functioning of microbial electrochemical systems (MES) for simultaneous wastewater treatment, desalination and resource recovery. Two MES were designed having abiotic cathode (MES-A) and algal biocathode (MES-B) which were investigated with synthetic feed and saline water as proxy of typical real-field wastewater. Comparative anodic and cathodic efficiencies revealed a distinct disparity in both the MES when operated in open circuit (OC) and closed circuit (CC). The maximum open circuit voltage (OCV) read in MES-A and MES-B was about 700mV and 600mV, respectively. Salinity and organic carbon removal efficiencies were noticed high during CC operation as 72% and 55% in MES-A and 60% and 63% in MES-B. These discrete observations evidenced ascribe to the influence of microbial electrochemical induced ion-migration over cathodic reduction reactions (CRR).

Biodesalination-On harnessing the potential of nature's desalination processes

Water scarcity is now one of the major global crises, which has affected many aspects of human health, industrial development and ecosystem stability. To overcome this issue, water desalination has been employed. It is a process to remove salt and other minerals from saline water, and it covers a variety of approaches from traditional distillation to the well-established reverse osmosis. Although current water desalination methods can effectively provide fresh water, they are becoming increasingly controversial due to their adverse environmental impacts including high energy intensity and highly concentrated brine waste. For millions of years, microorganisms, the masters of adaptation, have survived on Earth without the excessive use of energy and resources or compromising their ambient environment. This has encouraged scientists to study the possibility of using biological processes for seawater desalination and the field has been exponentially growing ever since. Here, the term biodesalination is offered to cover all of the techniques which have their roots in biology for producing fresh water from saline solution. In addition to reviewing and categorizing biodesalination processes for the first time, this review also reveals unexplored research areas in biodesalination having potential to be used in water treatment.

Mutual facilitations of food waste treatment, microbial fuel cell bioelectricity generation and Chlorella vulgaris lipid production

Food waste contains large amount of organic matter that may be troublesome for handing, storage and transportation. A microbial fuel cell (MFC) was successfully constructed with different inoculum densities of Chlorella vulgaris for promoting food waste treatment. Maximum COD removal efficiency was registered with 44% and 25 g CODL(-1)d(-1) of substrate degradation rate when inoculated with the optimal initial density (150 mg L(-1)) of C. vulgaris, which were 2.9 times and 3.1 times higher than that of the abiotic cathode. With the optimum inoculum density of C. vulgaris, the highest open circuit voltage, working voltage and power density of MFC were 260 mV, 170 mV and 19151 mW m(-3), respectively. Besides the high biodiesel quality, promoted by MFC stimulation the biomass productivity and highest total lipid content of C. vulgaris were 207 mg L(-1)d(-1) and 31%, which were roughly 2.7 times and 1.2 times higher than the control group.

CO2 Fixation, Lipid Production, and Power Generation by a Novel Air-Lift-Type Microbial Carbon Capture Cell System

An air-lift-type microbial carbon capture cell (ALMCC) was constructed for the first time by using an air-lift-type photobioreactor as the cathode chamber. The performance of ALMCC in fixing high concentration of CO2, producing energy (power and biodiesel), and removing COD together with nutrients was investigated and compared with the traditional microbial carbon capture cell (MCC) and air-lift-type photobioreactor (ALP). The ALMCC system produced a maximum power density of 972.5 mW·m(-3) and removed 86.69% of COD, 70.52% of ammonium nitrogen, and 69.24% of phosphorus, which indicate that ALMCC performed better than MCC in terms of power generation and wastewater treatment efficiency. Besides, ALMCC demonstrated 9.98- and 1.88-fold increases over ALP and MCC in the CO2 fixation rate, respectively. Similarly, the ALMCC significantly presented a higher lipid productivity compared to those control reactors. More importantly, the preliminary analysis of energy balance suggested that the net energy of the ALMCC system was significantly superior to other systems and could theoretically produce enough energy to cover its consumption. In this work, the established ALMCC system simultaneously achieved the high level of CO2 fixation, energy recycle, and municipal wastewater treatment effectively and efficiently.