Comparative Evaluation of a Biotrickling Filter and a Tubular Photobioreactor for the Continuous Abatement of Toluene

Abstract

Volatile Organic Compounds (VOCs) are among the gas pollutants with a higher detrimental impact on human health and the environment. The increasing awareness of the population on the importance of air quality and the enforcement of stricter environmental regulations regarding the anthropogenic emissions of these hazardous pollutants have triggered the development of cost-efficient, environmentally friendly off-gas treatment technologies. Biological technologies such as biotrickling filters have been consistently proven as well stablished technologies for the treatment of VOC emissions, although the low solubility of oxygen might limit the aerobic degradation when treating high concentrations of VOCs. In this context, the synergic effects between microalgae and bacteria represent a sustainable platform to promote the simultaneous abatement of VOCs and CO₂ by increasing the dissolved oxygen concentration as a result of the photosynthetic process. In this study, a conventional biotrickling filter (BTF) and an innovative tubular photobioreactor (TPBR) inoculated with a microalgal-bacterial consortium, and interconnected to an external absorption, column were comparatively evaluated for toluene removal. Operating parameters such as the gas residence time (GRT) and the mineral salt medium renewal rate were optimized in order to boost toluene removal. In this sense, both bioreactors were capable of achieving removals > 85 % at a GRT of 45 s and a medium renewal rate of 800 mL d^-1. Maximum toluene elimination capacities of ~21 g m^-3 h^-1 were recorded in both the BTF and the TPBR. Despite the satisfactory performance of both systems, the photobioreactor presented a competitive advantage due to the capacity of algal biomass to fix the produced CO₂, considerably reducing the emissions of this greenhouse gas, while increasing the concentration of dissolved oxygen in the cultivation broth up to 7.7 mg O₂ L^-1