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.

The operation characteristics of air cathode Microbial Desalination Cell to treat oil refinery wastewater

This system [microbial desalination cell (MDC)] is considered an excellent sustainable process to treat wastewater by biological anaerobic oxidation of the organic material by electroactive bacteria, desalinate saltwater, and electrical power generation. In the present work, MDC was used for treating oil refinery wastewater in the anode chamber by anaerobic bacteria. Simultaneously, an air pump was used to provide the oxygen to the cathode chamber as an electron acceptor to generate bioelectricity power. The power density generated by this air cathode MDC with 1KΩ external resistance at the 1st experiment was 71.11 μW/m2. It increased to a peak value of 570.86 μW/m2 at the last experiment. The maximum chemical oxygen demand (COD) removal percent of oily wastewater was 96%. The higher salinity removal rate 150.39 ppm/h with a first salt concentration in a desalinating chamber of 35000 ppm.

Comparative Studies of Recirculatory Microbial Desalination Cell–Microbial Electrolysis Cell Coupled Systems

The recirculatory microbial desalination cell–microbial electrolysis cell (MDC–MEC) coupled system is a novel technology that generates power, treats wastewater, and supports desalination through eco-friendly processes. This study focuses on the simultaneous efficient removal of Fe2+ and Pb2+ in the MEC and ammonium ions in the MDC. It also evaluates the performances of dual-chambered MEC (DCMEC) and single-chambered MEC (SCMEC), coupled with MDC with Ferricyanide as catholyte (MDCF) in heavy metals (Pb2+ and Fe2+) removal, in addition to the production of voltage, current, and power within a 48-h cycle. The SCMEC has a higher Pb2+ (74.61%) and Fe2+ (85.05%) removal efficiency during the 48-h cycle than the DCMEC due to the simultaneous use of microbial biosorption and the cathodic reduction potential. The DCMEC had a higher current density of 753.62 mAm−2 than that of SCMEC, i.e., 463.77 mAm−2, which influences higher desalination in the MDCF than in the SCMEC within the 48-h cycle. The MDCF produces a higher voltage (627 mV) than Control 1, MDC (505 mV), as a power source to the two MECs. Stable electrolytes’ pH and conductivities provide a conducive operation of the coupled system. This study lays a solid background for the type of MDC–MEC coupled systems needed for industrial scale-up.

The Catholyte Effects on The Microbial Desalination Cell Performance of Desalination and Power Generation

A microbial desalination cell (MDC) is a new approach to bioelectrochemical systems. It provides a more sustainable way to electrical power production, saltwater desalination, and wastewater treatment at the same time. This study examined three operation modes of the MDC: chemical cathode, air cathode, and biocathode MDC, to give clear sight of this system's performance. The experimental work results for these three modes were recorded as power densities generation, saltwater desalination rates, and COD removal percentages. For the chemical cathode MDC, the power density was 96.8 mW/m2, the desalination rate was 84.08 ppm/hr, and the COD removal percentage was 95.94%. The air cathode MDC results were different; the power density was 24.2 mW/m2, the desalination rate was 86.11 ppm/hr, and the COD removal percentage was 91.38%. The biocathode MDC results were 19.91 mW/m2 as the power density, 88.9 ppm/hr as the desalination rate, and 96.94% as the COD removal percentage. The most efficient type of MDC in this study in power production was the chemical cathode MDC, but it is the lowest sustainable. On the other hand, the biocathode MDC was the best in desalination process performance, and both the air cathode and biocathode MDC are more sustainable and environmentally friendly, especially the biocathode MDC.

Construction and operation of the MIDES plant

This chapter presents the construction, operation, and validation of all the MIDES systems, including water pre-treatment, wastewater pre-treatment, the microbial desalination cell (MDC), low-pressure reverse osmosis (RO), and post-treatment (remineralization and disinfection). MIDES technology has been validated with different water sources: brackish water from Demo Site 1, (Racons Brackish Water Desalination Plant (BWDP), located in Denia, Spain) and seawater from Demo Site 2 (Fonsalía Seawater Desalination Plant (SWDP), located in Guía de Isora, Spain). In this chapter, the preparation of both demo sites for the reception and installation of the pilot plants is also presented.

Microbial desalination cell design & bioengineering assays: Main concepts

The main goal of this chapter is to present the main concepts and principles for the microbial desalination process. Also, a rational explanation of the electrochemical behaviour of the microbial desalination cell (MDC) setup under different experimental conditions is presented. The final section of the chapter shows the design and construction of an MDC pre-pilot unit, as well as the main results of desalination and water treatment capacity for the scaled-up device.