• Energy Research

Abstract Petroleum refinery wastewater (PRW) contains a high concentration of pollutants and may pose serious environmental risks. Conventional treatment methods of PRW are energy intensive, and thus there is an urgent need to develop sustainable technologies. Microbial desalination cells (MDCs) represent a new energy-efficient technology for simultaneous treatment of PRW and seawater. In this study, PRW was for the first time treated in an MDC and the effects of salt concentration and catholyte were studied. The maximum COD removal was achieved by the MDC using an initial salt concentration of 20 g/L NaCl solution, and the COD removal increased slightly from 64.0% to 70.5% when the catholyte was changed from phosphate buffer solution (PBS) to acidified water. The maximum desalination efficiency of 19.9% was obtained by an MDC operated with real seawater and PBS. Acidified water was found to be an efficient catholyte in terms of specific energy production. When desalinating real seawater, the highest total energy produced was 32.6 W h/kg COD with respect to COD removal or 9.5 W h/m 3 with respect to the total volume of the desalinated water. These results demonstrated that complex PRW could be used as an anodic substrate in MDCs for electricity generation and seawater desalination.

In this study, a dual chamber MFC was constructed for simultaneous removal of organic matter and nitrogenous pollutants and bioelectricity generation from synthetic and complex industrial wastewaters and it was operated in batch and continuous mode. When the cell potential was stable after 16 days of batch mode operation, the MFC was converted to continuous mode (from batch mode) and operated for 125 days with different organic loading rates (OLR) and ammonia loading rates (ALR) and fixed hydraulic retention time (HRT) of 40 h. The OLR of 1.49 kg COD m(-3) d(-1) and ALR of 0.58 kg NH3(-) m(-3) d(-1), for anodic and cathodic chambers, respectively, gave the best results. The highest value of cell potential on these OLRs was 310 mV with current density of 85.11 mA m(-2), power density of 26.38 mW m(-2) and volumetric power density of 192.20 mW m(-3). During this period, COD reduction was 78-83% in the anodic chamber and the ammonia reduction was 36-38%. After stable operation with synthetic wastewater one case study was performed with complex industrial wastewater. Continuous mode operation was performed at two different OLR and HRT with a constant ALR. A stable power density and volumetric power density of 23.56 mW m(-2) and 112.50 mW m(-3), respectively were achieved after 24 days of continuous operation at an OLR of 0.35 kg COD/m(3) day with an ALR of 0.43 kg NH3(-) m(-3) day(-1) and corresponding HRT of 68 h. A maximum of 89% COD removal and 40% removal of ammonia was obtained after 50 days. A stable voltage of 300 mV was obtained across 1000 Ω resistance. These findings suggest that BMFC can be used for the treatment of industrial wastewater, with carbon removal in anodic chamber and electricity generation.

Among the various renewable energy sources, biohydrogen is gaining a lot of traction as it has very high efficiency of conversion to usable power with less pollutant generation. The various technologies available for the production of biohydrogen from lignocellulosic biomass such as direct biophotolysis, indirect biophotolysis, photo, and dark fermentations have some drawbacks (e.g., low yield and slower production rate, etc.), which limits their practical application. Among these, metabolic engineering is presently the most promising for the production of biohydrogen as it overcomes most of the limitations in other technologies. Microbial electrolysis is another recent technology that is progressing very rapidly. However, it is the dark fermentation approach, followed by photo fermentation, which seem closer to commercialization. Biohydrogen production from lignocellulosic biomass is particularly suitable for relatively small and decentralized systems and it can be considered as an important sustainable and renewable energy source. The comprehensive life cycle assessment (LCA) of biohydrogen production from lignocellulosic biomass and its comparison with other biofuels can be a tool for policy decisions. In this paper, we discuss the various possible approaches for producing biohydrogen from lignocellulosic biomass which is an globally available abundant resource. The main technological challenges are discussed in detail, followed by potential solutions.

A waste-based circular economy approach is proposed for the phycoremediation of an X-ray developer (XD) solution. The present study emphasizes the utilization of food waste (FW) and agri-compost media (ACM) as growth media for D. armatus for the subsequent bioremediation potential of XD solution-coupled lipid production. A 3:1 dilution (FW/ACM: XD.) was found to be suitable for the phycoremediation study of XD solution towards the % removal of biological oxygen demand (BOD), chemical oxygen demand (COD) and silver. The phycoremediation studies of diluted XD solution in FW demonstrated a 74.50% BOD removal, 81.69% COD removal, and 54.70% removal of silver. The growth of D. armatus in diluted XD solution in food waste was 1.37% lipid content. The phycoremediation of diluted XD solution with ACM resulted in 83.05% BOD removal, 88.88% COD removal and 56.30% silver removal with the concomitant lipid production of 1.42%. The optimal bioremediation coupled lipid production of D. armatus was observed on the 19th day of D. armatus cultivation in the developer effluent, along with food waste and agri-compost media, for 31 days. The study suggests a sustainable utilization of waste (FW and ACM) as a nutritive medium to scrutinize the phycoremediation of XD solution with a concomitant lipid production that can open up new avenues in phycoremediation coupled energy commodities production.

The aim of the present work was to characterize the impedance response of an air-cathode MFC operating in a continuous mode and to determine intrinsic properties that define its performance which are crucial to be controlled for scalability purposes. The limiting step on electricity generation is the anodic electrochemically-active biofilm, independently of the external resistance, Rext, utilized. However, for Rext below 3 kΩ the internal impedance of the bioanode remained invariable, in good correspondence to the power density profile. The hydraulic retention time (HRT) had an effect on the impedance of both the bioanode and the air-cathode and especially on the overall MFC. The lowest HRT at which the MFC was operable was 3h. Yet, the variation on the HRT did not have a significant impact on power generation. A two constant phase element-model was associated with the EIS response of both bioanode and air-cathode, respectively. Consistency was found between the CPE behaviour and the normal power-law distribution of local resistivity with a uniform dielectric constant, which represented consistent values with the electrical double layer, the Nernst diffusion layer and presumably the biofilm thickness. These results have future implications on MFC monitoring and control, as well as in providing critical parameters for scale-up.

Abstract Saline water such as seawater or brackish water is a potential source for drinking water or for non-potable applications, but the existing desalination techniques are energy intensive. Therefore, there is an urgent need to develop sustainable desalination methods. Microbial desalination cells (MDCs) hold great promise for energy-efficient saline water desalination. In MDCs, electrical energy from wastewater is extracted by taking advantages of microbial extracellular respiration and used to drive desalination. Herein, we have comprehensively reviewed and discussed the potential functions of MDCs, including seawater desalination, brackish water desalination, water softening, hydrogen and chemical production, and groundwater remediation along with wastewater treatment. The role of process parameters in improving the MDC performance was also analyzed. We expect to provide insight into the advantages and limitations of this emerging technology from the aspect of its functions, thereby encouraging more research efforts towards further development and commercialization of MDCs.