Heavy metals removal by algae and usage of activated metal-enriched biomass as cathode catalyst for improving performance of photosynthetic microbial fuel cell

Application of a novel photosynthetic microbial fuel cell employing carbonized bamboo monolith as cathode coated with agro-waste biochar to improve overall performance efficacy

In recent decades, researchers have paid an increasing attention to self-sustainable and renewable bioenergy production due to the depletion of fossil fuels and the upsurge of other environmental issues. Algae-assisted photosynthetic microbial fuel cell (PMFC) has been developed to produce self-sustainable bioenergy along with sustainable wastewater treatment and recovery of other valuables. Inevitably, the fabrication cost and poor algal biomass productivity due to the usage of metal catalysts and other toxic compounds diminishes field-scale execution of this technology. Hence, organic product like carbonized bamboo was applied directly as an eco-friendly cathode due to its inherent porous structure and economic sustainability. The highest power density of 85.85 mW/m2 was achieved by MFC with a 4 cm × 4 cm of graphitised bamboo monolith as cathode, which was further increased by 7.57 times by applying MnO2-doped activated bamboo-leaf biochar (MABB) coated over bamboo cathode in comparison to carbon felt cathode. Moreover, the highest chemical oxygen demand removal of 84.0 % was demonstrated along with simultaneous algal biomass productivity of 0.56 g/L.d through this system with a bamboo cathode loaded with an MABB catalyst. Further, the estimated cost of MABB-coated bamboo monolith as cathode (4 cm × 4 cm) was estimated to be only INR 2.22 = 0.02 $/cm2 (Conversion factor 80 INR = 1 $). Hence, this simply graphitised nature-derived green cathode proved its ability to ameliorate the overall performance efficacy of PMFC in order to achieve higher power output in a cost-effective way.

The Strategies Microalgae Adopt to Counteract the Toxic Effect of Heavy Metals

Besides biomass production, some microalgae have been used to treat wastewater contamination. However, in general, high concentrations of heavy metals significantly inhibit algal growth. We thus need to find ways to promote the resistance of microalgae to heavy metals, increase their growth rate under stress, and achieve coupling of heavy metal removal and biomass production simultaneously. In this review, mechanisms for removal of heavy metals by microalgae are proposed. Effects of exogenous chemical additives (dissolved organic matters, formaldehyde, sulphate, phosphate, nitric oxide donors, etc.) on algal biosorption to heavy metals are summarized. Genetic manipulation and microalgal strain selection strategies are also introduced, especially for the acid-tolerant strains with high biosorption efficiencies to Cr(VI) and Cd2+ at low pH conditions. Recent advances in (semi)continuous heavy-metal-bioremediation and biomass-production coupled system with immobilized microalgae, as well as challenges and solutions to the commercialization and industrialization of the coupled system were discussed.

Biochar coupled with multiple technologies for the removal of nitrogen and phosphorus from water: A review

Water eutrophication caused by nitrogen (N) and phosphorus (P) has become a global environmental issue. Biochar is a competent adsorbent for removing N and P from wastewater. However, compared with commercial activated carbon, biochar has relatively limited adsorption capacity. To broaden the field scale application of biochar, biochar coupled with multiple technologies (BC-MTs) (such as microorganisms, electrochemistry, biofilm, phytoremediation, etc.) have been extensively developed for environmental remediation. Nevertheless, due to the fluctuations and differences in biochar types, coupling methods, and wastewater types, various techniques show different removal mechanisms and performance, hindering the promotion and application of BC-MTs. A systematic review of the research progress of BC-MTs is highly necessary to gain a better understanding of the current research status and progress, as well as to promote the application of these techniques. In this paper, the application of pristine and modified biochar in adsorbing N and P in wastewater is critically reviewed. Then the removal performance, influencing factors, mechanisms, and the environmental applications of BC-MTs in wastewater are systematically summarized. In addition, the cost analysis and risk assessment of BC-MTs in environmental applications are conducted. Finally, suggestions and prospects for future research and practical application are put forward.