Microalgae at niches of bioelectrochemical systems: A new platform for sustainable energy production coupled industrial effluent treatment

Engineered nanomaterials for carbon capture and bioenergy production in microbial electrochemical technologies: A review

The mounting threat of global warming, fuelled by industrialization and anthropogenic activities, is undeniable. In 2017, atmospheric carbon dioxide (CO2), the primary greenhouse gas, exceeded 410 ppm for the first time. Shockingly, on April 28, 2023, this figure surged even higher, reaching an alarming 425 ppm. Even though extensive research has been conducted on developing efficient carbon capture and storage technologies, most suffer from high costs, short lifespans, and significant environmental impacts. Recently, the use of engineered nanomaterials (ENM), particularly in microbial electrochemical technologies (METs), has gained momentum owing to their appropriate physicochemical properties and catalytic activity. By implementing ENM, the MET variants like microbial electrosynthesis (MES) and photosynthetic microbial fuel cells (pMFC) can enhance carbon capture efficiency with simultaneous bioenergy production and wastewater treatment. This review provides an overview of ENMs' role in carbon capture within MES and pMFC, highlighting advancements and charting future research directions.

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.

Role of electrode and proton exchange membrane configurations on microbial fuel cell performance toward bioelectricity generation integrated wastewater treatment

In the present study, the effects of electrode surface area, proton exchange membrane area, and volume of the anodic chamber were investigated on the performance of five different dual chamber microbial fuel cells (MFC) using synthetic wastewater toward wastewater treatment coupled electricity generation. In the batch mode, the five different MFC's were operated with the anodic chamber volumes of 93-890 mL, 17.33-56.77 cm² electrode surface area, obtained volumetric power densities of 137.72-58.13 mW/m³, and unit area power densities ranging from 27.04 to 11.94 mW/m². Fed-batch studies were done with the MFC having 740 mL anodic chamber volume at different wastewater COD concentrations. The power density per unit area increased from 22.93 mW/m² to 36.25 cm² when the distance between electrodes was reduced from 10 to 6 cm. A maximum volumetric power density of 135.21 mW/m³ has been attained with a 6 cm electrode distance with the accomplished COD reduction of 93.21%. The presence of biofilm on the anode has been visualized through the SEM images. The higher COD concentration of wastewater and the fed-batch operation resulted in increased power output and wastewater treatment efficiency.

A comprehensive review on the use of algal-bacterial systems for wastewater treatment with emphasis on nutrient and micropollutant removal

The scarcity of water resources and environmental pollution have highlighted the need for sustainable wastewater treatment. Existing conventional treatment systems are energy-intensive and not always able to meet stringent disposal standards. Recently, algal-bacterial systems have emerged as environmentally friendly sustainable processes for wastewater treatment and resource recovery. The algal-bacterial systems work on the principle of the symbiotic relationship between algae and bacteria. This paper comprehensively discusses the most recent studies on algal-bacterial systems for wastewater treatment, factors affecting the treatment, and aspects of resource recovery from the biomass. The algal-bacterial interaction includes cell-to-cell communication, substrate exchange, and horizontal gene transfer. The quorum sensing (QS) molecules and their effects on algal-bacterial interactions are briefly discussed. The effect of the factors such as pH, temperature, C/N/P ratio, light intensity, and external aeration on the algal-bacterial systems have been discussed. An overview of the modeling aspects of algal-bacterial systems has been provided. The algal-bacterial systems have the potential for removing micropollutants because of the diverse possible interactions between algae-bacteria. The removal mechanisms of micropollutants - sorption, biodegradation, and photodegradation, have been reviewed. The harvesting methods and resource recovery aspects have been presented. The major challenges associated with algal-bacterial systems for real scale implementation and future perspectives have been discussed. Integrating wastewater treatment with the algal biorefinery concept reduces the overall waste component in a wastewater treatment system by converting the biomass into a useful product, resulting in a sustainable system that contributes to the circular bioeconomy.

Bioelectrochemical systems-based metal recovery: Resource, conservation and recycling of metallic industrial effluents

Metals represent a large proportion of industrial effluents, which due to their high hazardous nature and toxicity are responsible to create environmental pollution that can pose significant threat to the global flora and fauna. Strict ecological rules compromise sustainable recovery of metals from industrial effluents by replacing unsustainable and energy-consuming physical and chemical techniques. Innovative technologies based on the bioelectrochemical systems (BES) are a rapidly developing research field with proven encouraging outcomes for many industrial commodities, considering the worthy options for recovering metals from industrial effluents. BES technology platform has redox capabilities with small energy-intensive processes. The positive stigma of BES in metals recovery is addressed in this review by demonstrating the significance of BES over the current physical and chemical techniques. The mechanisms of action of BES towards metal recovery have been postulated with the schematic representation. Operational limitations in BES-based metal recovery such as biocathode and metal toxicity are deeply discussed based on the available literature results. Eventually, a progressive inspection towards a BES-based metal recovery platform with possibilities of integration with other modern technologies is foreseen to meet the real-time challenges of viable industrial commercialization.

Sustainable, Decentralized Sanitation and Reuse with Hybrid Nature-Based Systems

Nature (ecosystem) based processes for wastewater treatment include constructed wetlands (CWs), waste stabilization ponds, vegetated drainage ditches, buffer zones, instream or bankside river techniques, and mixotrophic systems, where light and CO2 are utilized, in addition to organic carbon compounds, by algal cultures. Algae-based systems can simultaneously remove organic matter, N, and P and may offer substantial energetic advantages compared to traditional biological treatment systems, require small spatial footprint, and contribute to biofuels production and CO2 emissions mitigation. Bioelectrochemical systems (BES) such as microbial fuel cells (MFCs) present characteristics compatible with the use in isolated realities for water and wastewater treatment with contextual energy recovery and may be combined with other nature-based process technologies to achieve good treatment and energy efficiencies. Despite that their application in real-scale plants has not been assessed yet, the most probable outcome will be the in situ/on site treatment (or pretreatment) of wastes for small “in house” plants not connected to the sewerage network. This paper focuses on the current practices and perspectives of hybrid nature-based systems, such as constructed wetlands and microalgae integrated phytoremediation plants, and their possible integration with microbial electrochemical technologies to increase recovery possibilities from wastes and positively contribute to a green economy approach.

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.

Performance of different macrophytes in the decontamination of and electricity generation from swine wastewater via an integrated constructed wetland-microbial fuel cell process

Plants constitute a major element of constructed wetlands (CWs). In this study, a coupled system comprising an integrated vertical flow CW (IVCW) and a microbial fuel cell (MFC) for swine wastewater treatment was developed to research the effects of macrophytes commonly employed in CWs, Canna indica, Acorus calamus, and Ipomoea aquatica, on decontamination and electricity production in the system. Because of the different root types and amounts of oxygen released by the roots, the rates of chemical oxygen demand (COD) and ammonium nitrogen (NH₄⁺-N) removal from the swine wastewater differed as well. In the unplanted, Canna indica, Acorus calamus, and Ipomoea aquatica systems, the COD removal rates were 80.20%, 88.07%, 84.70%, and 82.20%, respectively, and the NH₄⁺-N removal rates were 49.96%, 75.02%, 70.25%, and 68.47%, respectively. The decontamination capability of the Canna indica system was better than those of the other systems. The average output voltages were 520±42, 715±20, 660±27, and 752±26mV for the unplanted, Canna indica, Acorus calamus, and Ipomoea aquatica systems, respectively, and the maximum power densities were 0.2230, 0.4136, 0.3614, and 0.4964W/m³, respectively. Ipomoea aquatica had the largest effect on bioelectricity generation promotion. In addition, electrochemically active bacteria, Geobacter and Desulfuromonas, were detected in the anodic biofilm by high-throughput sequencing analysis, and Comamonas (Proteobacteria), which is widely found in MFCs, was also detected in the anodic biofilm. These results confirmed the important role of plants in IVCW-MFCs.

Prospects of integrating algae technologies into landfill leachate treatment

Landfilling of municipal waste, an environmental challenge worldwide, results in the continuous formation of significant amounts of leachate, which poses a severe contamination threat to ground and surface water resources. Landfill leachate (LL) is generated by rainwater percolating through disposed waste materials and must be treated effectively before safe discharge into the environment. LL contains numerous pollutants and toxic substances, such as dissolved organic matter, inorganic chemicals, heavy metals, and anthropogenic organic compounds. Currently, LL treatment is carried out by a combination of physical, chemical, and microbial technologies. Microalgae are now viewed as a promising sustainable addition to the repertoire of technologies for treating LL. Photosynthetic algae have been shown to grow in LL under laboratory conditions, while some species have also been employed in larger-scale LL treatments. Treating leachate with algae can contribute to sustainable waste management at existing landfills by remediating low-quality water for recycling and reuse and generating large amounts of algal biomass for cost-effective manufacturing of biofuels and bioproducts. In this review, we will examine LL composition, traditional leachate treatment technologies, LL toxicity to algae, and the potential of employing algae at LL treatment facilities. Emphasis is placed on how algae can be integrated with existing technologies for biological treatment of LL, turning leachate from an environmental liability to an asset that can produce value-added biofuels and bioproducts for the bioeconomy.

Biosensing capabilities of bioelectrochemical systems towards sustainable water streams: Technological implications and future prospects

Bioelectrochemical systems (BESs) have been intensively investigated over the last decade owing to its wide-scale environmentally friendly applications, among which wastewater treatment, power generation and environmental monitoring for pollutants are prominent. Different variants of BES such as microbial fuel cell, microbial electrolysis cell, microbial desalination cell, enzymatic fuel cell, microbial solar cell, have been studied. These microbial bioelectrocatalytic systems have clear advantages over the existing analytical techniques for sustainable on-site application in wide environmental conditions with minimum human intervention, making the technology irrevocable and economically feasible. The key challenges to establish this technology are to achieve stable and efficient interaction between the electrode surface and microorganisms, reduction of time for start-up and toxic-shock recovery, sensitivity improvement in real-time conditions, device miniaturization and its long-term economically feasible commercial application. This review article summarizes the recent technical progress regarding bio-electrocatalytic processes and the implementation of BESs as a biosensor for determining various compositional characteristics of water and wastewater.