A wastewater containing aromatic sulfonates was treated in a laboratory-scale biofilm airlift suspension (BAS) reactor. The general objective of the experiments was to assess the performance of a particle-based biofilm reactor in the biodegradation of refractory organic compounds under varying operating conditions. To this end, the reactor was inoculated with a mixed culture of biomass, adapted to grow on the leachate as the sole source of carbon, which colonized carrier particles in the reactor and formed stable and uniform biofilms. Depending on their degradation kinetics (characterized in independent experiments) and the fraction of specific degraders in the biofilms, aromatic sulfonates attain different degradation efficiencies in the BAS reactor, with more compex molecules (e.g., trisusbtituted naphthalene sulfonates and some bisubstituted naphthalene sulfonates) showing the lowest degradation efficiencies. The BAS reactor achieved high biomass concentration (12 g L-1) and an overall degradation efficiency of 67% based on COD measurements for loading rates up to 0.45 kg(COD) kg(vs)(-1) day(-1), corresponding to a specific degradation rate of 0.3 kg(COD) kgvs(-1) day(-1). For higher loading rates, the hydraulic retention time of leachate in the reactor proved to be insufficient for complete degradation of aromatic sulfonate with slow degradation kinetics, resulting in a decrease of overall degradation efficiency. The fast degradation rate of most aromatic sulfonates is attributed to the long biomass retention time and reactor biomass concentration, resulting in high concentrations of degraders for specific compounds.