Linear alkylbenzene sulfonate (LAS) is an anionic surfactant used in cleaning products, which is usually found in wastewaters. Despite the greater LAS removal rate related to a lower concentrations of volatile fatty acids (VFA), the influence of different ranges of VFA on LAS degradation is not known. LAS degradation was evaluated in upflow anaerobic sludge blanket (UASB) and expanded granular sludge bed (EGSB) reactors at different ranges of VFA concentrations. The reactors were fed with a synthetic wastewater containing LAS (14 mg/L). A greater LAS removal rate (40–80%) was related to the lower and narrower range of acetic acid concentration (1–22 mg/L) in the EGSB reactor. In the UASB reactor, the acetic acid concentrations presented a wider range (2–45 mg/L), and some low LAS removal rates (around 20–25%) were observed even at low acetic acid concentrations (<10 mg/L). The high recirculation rate in the EGSB reactor improved substrate-biomass contact, which resulted in a narrower range of VFA and greater LAS removal rate. •The degradation of linear alkylbenzene sulfonate was evaluated.•The EGSB reactor presented the greater LAS degradation rate.•The efficiency of the EGSB reactor was related to its higher recirculation rate.•A smaller concentration of acetic acid was found in the effluent from the EGSB reactor.