Original Contributions to Reaction Engineering Theory for Continuous Flow Biodegradation of Persistent Organic Pollutants in a Novel Biofilm Airlift Reactor

Persistent organic pollutants including organochlorine pesticides and polychlorinated biphenyls deposited in soils from industrial and agricultural activities in South West Nigeria constitute long-term ecosystem risks for which continuous biological treatment systems lack adequate theoretical design frameworks, particularly for biofilm-based reactor configurations. This study makes original contributions to reaction engineering theory for continuous flow biodegradation of persistent organic pollutants in a novel biofilm airlift reactor configured to treat contaminated groundwater from an agro-industrial zone in Ogun State. Original theoretical contributions include the derivation of a new effectiveness factor for biofilm degradation of hydrophobic organic compounds that explicitly accounts for the coupled effects of external mass transfer, intra-biofilm diffusion with partitioning into the extracellular polymeric substance matrix, and substrate inhibition kinetics, producing a comprehensive dimensionless design number, the Biofilm Hydrophobic Compound Utilisation Number, which predicts transition between mass-transfer-limited and kinetics-limited degradation regimes. The theory is implemented in a steady-state biofilm airlift reactor model validated using experimental data from a purpose-built pilot reactor operated with hexachlorobenzene-contaminated synthetic groundwater, achieving greater than 99% hexachlorobenzene removal at a hydraulic retention time of 6 hours with mixed anaerobic-aerobic biofilm consortia. A parameter estimation methodology is developed for reliable extraction of biofilm kinetic parameters from transient reactor performance data. The study establishes the theoretical and experimental foundations for designing biofilm airlift reactor treatment systems for persistent organic pollutant contamination in Nigeria. Keywords: biofilm airlift reactor, persistent organic pollutants, reaction engineering, biofilm theory, Ogun State