The industrial emission of chlorinated volatile organic compounds (Cl-VOCs) is a serious environmental hazard and creates significant health risks for humans. The physicochemical methods currently applied for removing Cl-VOCs are unsustainable due to high cost, inherent complexity, and formation of secondary toxic metabolites. For several decades, biological treatment of wastes has been considered the panacea. In this light, it seems promising to extend the application of bioremediation to treat Cl-VOCs. The current review provides a comprehensive update on the use of bioreactors such as biofilters, biotrickling filters, rotating biological contactors, scrubbers, and membrane bioreactors for the remediation of Cl-VOCs-laden industrial fumes. The integration of physicochemical processes with bioreactors would aid in overcoming the limitations of any individual process and enhance the degradation rate while ensuring the long-term stability of the system. As microbes play a pivotal role in bioreactor systems, various species involved in the remediation of Cl-VOCs are discussed. The diversity of the microbes influences the stability and functioning of the community, which necessitates the incorporation of bacteria and fungi, even algae, rotifers, and nematodes in the bioreactors. The review concludes with suggestions for future research considering the current challenges in realizing the full potential of bioreactors for treating Cl-VOCs.

As energy consumption and waste generation from human activities continue to rise, the technology of anaerobic digestion (AD), which converts waste into bioenergy, has gained popularity. Biogas produced from AD commonly contains 60 % CH4, 40 % CO2 and a minor fraction of impurities. Currently, several anaerobic reactors have been designed to upgrade the biogas with biomethane content above 90 %. This review summarizes the current trends in the biological upgradation of biogas from a bio-circular economy perspective to achieve sustainable energy goals. Examples of applications reporting the latest advancements in treating industrial effluents using high-rate anaerobic reactors have been mentioned. The integrated anaerobic-aerobic hybrid reactor offers a solution to the limitations of traditional methods in treating diverse effluents. A special focus on biological upgradation techniques such as in-situ, ex-situ, and hybrid mechanisms have been briefed. The key advantage of hybrid upgradation is its ability to address the pH rise during in-situ process. Additionally, the applications of artificial neural networks and optimization to upgrade biogas production have been discussed. The review concludes with future research directives with emphasis on the economic viability of the approaches.