Bioprocesses for resource recovery from waste gases: Current trends and industrial applications

Air pollution is a topic of important global concern because it has contributed significantly to an increase in the earth's global warming potential and contributed to severe health and environmental impacts. In this review, the different bioreactor configurations commonly used for waste gas treatment, namely the biofilters, the bio-trickling filters and the bioscrubbers, and their industrial applications were compared in terms of the type of inoculum, the packing material/media, removal efficiency and elimination capacity. Typically, biofilters are operated under the following range of operating conditions: gas residence time = 15-60 s; gas flow rate = 50-300,000 m(3) h(-1); temperature = 15-30 ?degrees C; pH = 6.0-7.5; filter area = 100-3000 m(2); relative humidity > 95.0%; and removal efficiencies > 75.0% depending on the waste gas composition and concentration. The biotechnological approaches for resource recovery, i.e., the conversion of C1 gaseous compounds (CO, CO2 and CH4) to liquified value-added products or biofuels have been discussed. From this review, it was evident that the performances of different aerobic, anoxic and/or anaerobic lab, pilot and full-scale bioreactors for waste gas treatment and resource recovery depend on the composition, the individual concentration of pollutants present in the waste gas and the gas flow rate. Although most of the research on product recovery from waste gas is rather limited to lab/pilot-scale studies, there are some key commercialized technologies that have proven to be economical at the full-scale. Thus, this review, comprehensively presents a complete overview of the current trends and limitations of conventional waste gas treatment systems, the benefits of novel bioreactor configura-tions and their potential to be applied for resource recovery from waste gases.