Improved toluene vapor removal in a moving bed biofilm reactor (MBBR): Performance, microbial dynamics, and kinetic study

Toluene, a toxic volatile organic compound (VOC), poses significant environmental and health risks. This study evaluates the performance of moving bed biofilm reactor (MBBR) and bubble column reactor (BCR) systems for toluene biodegradation under varying operational conditions. Using returned activated sludge (RAS) as inoculum, the MBBR demonstrated superior performance, achieving a maximum elimination capacity (EC_max) of 347 g.m⁻³.h⁻¹ and removal efficiency (RE) of 73 %, compared to the BCR with EC_max of 370 g.m⁻³.h⁻¹ at a higher inlet loading rate (ILR), but with a lower RE of 44 %. Biofilm microbial analysis revealed enrichment of aromatic-degrading genera, especially Castellaniella (35 %) and Pseudomonas (7.2 %) in the MBBR, along with reduced microbial diversity. The Shannon index declined from 6.6 to 5.8, Chao1 richness from 871 to 584, and the Simpson index from 0.95 to 0.82. Kinetic modeling using the Haldane equation indicated substrate inhibition at higher toluene concentrations, with EC_max = 5000 g·m⁻³·h⁻¹, Kₘ = 18 g·m⁻³, and Kᵢ = 0.25 g·m⁻³. Stoichiometric analysis showed 20 % mineralization of toluene to CO₂. Overall, the MBBR demonstrated higher operational flexibility, microbial adaptability, and stability under variable loading, positioning it as a robust and scalable option for treating VOC-laden air streams, particularly those containing hydrophobic compounds like toluene.