Cascading Integration of Electrofermentation and Photosynthesis—Low‐Carbon Biorefinery in Closed Loop Approach

Abstract

Single‐chambered electrofermentation (EF) bioreactors are operated using spent wash to evaluate the effect of applied voltage (EF/AV; −0.6 V) against closed‐circuit (EF/CC; 100 Ω) and control (EF/C; no voltage/resistance) operations using deoiled microalgae biomass‐derived biochar electrodes (anode) on increasing acidogenesis rate/efficiency. Higher total volatile fatty acids (VFA) production (mg L−1) is observed in EF/AV (2866), depicting 31% and 57% increments than EF/CC (1984) and EF/C (1224), respectively. The VFA profiles (C2–C4) in EF/AV are higher with acetic/butyric/propionic acids (1922/704/240 mg L−1) and biogas co‐generation [H2 (22%) and CH4 (3%)] than EF/CC and EF/C. The applied voltage (EF/AV) helps in electron flux regulation for increasing substrates conversion and VFA generation. Residual VFA‐rich effluents from EF process is utilized as substrate to mixotrophic microalgae cultivation (nutrient‐ and stress‐phase) that resulted in biomass production with simultaneous wastewater treatment. EF/AV depicted higher biomass growth (0.72 g L−1; 4th day) and substrate removal (63%) than other operations. Integrations of electrofermentation with photosynthetic processes operated with the residual resources in effluents towards product valorization and wastewater polishing, accounts for low‐carbon economy.

Advances in Biological Wastewater Treatment Processes: Focus on Low-Carbon Energy and Resource Recovery in Biorefinery Context

“…[ 45 , 48 ]. These advanced integrative processes could increase the cumulative wastewater treatment with a stage-wise approach, reducing chemical/reagent usage along with lowering the costs for operational feasibility as compared to conventional AOPs [ 16 , 17 , 41 ]. Though electrochemical processes have benefits in industrial wastewater treatment, the need to optimize the operational parameters and electrode materials in specified combinations to design a reactor raises the estimated costs for application feasibility [ 10 ].…”

“…Electro-/bioelectro-/photo-chemical processes could also be effective in advanced wastewater treatment for recalcitrant/emerging pollutant removal. The integration of diverse biological treatment strategies with a broad scope of their individual advantages in a sequential and closed-loop pattern could be a sustainable approach [ 16 , 17 ]. These integrated biological/electrochemical/bioelectrochemical wastewater treatments can also benefit in energy and resource recovery, along with low-carbon generation [ 6 , 18 ].…”

“…Nanotechnology can offer novel materials, such as nanoparticles, nanofibers, or nanocomposites, that can enhance biological treatment processes by providing catalysts, carriers, sensors, or antimicrobials [ 26 , 27 , 28 , 29 ]. Integrated biological wastewater treatment strategies can efficiently degrade organic pollutants in wastewater while also recovering valuable resources, such as energy, nutrients, minerals, and salts [ 16 , 17 , 30 ]. These strategies aim to reduce the environmental impact and operational cost of wastewater treatment, as well as to contribute to the circular economy and carbon neutrality goals [ 16 ].…”

“…Integrated biological wastewater treatment strategies can efficiently degrade organic pollutants in wastewater while also recovering valuable resources, such as energy, nutrients, minerals, and salts [ 16 , 17 , 30 ]. These strategies aim to reduce the environmental impact and operational cost of wastewater treatment, as well as to contribute to the circular economy and carbon neutrality goals [ 16 ].…”

Carbon farming: a circular framework to augment CO2 sinks and to combat climate change

“…158 They are recognized as potential source for third-generation bioenergy/biofuels, offering a more efficient choice for carbon fixation compared to terrestrial plants due to their accelerated growth and quicker biomass production. 127,159 A study model conducted in the USA validated that the pure CO 2 generated from the corn ethanol production process could be employed in open pond algal cultivation. This approach has the potential to decrease GHG emissions, alleviate water stress, and eliminate the need for the energy-intensive carbon capture process in carbon capture and utilization (CCU).…”