A lab-scale anaerobic filter process was operated for the treatment of purified terephthalic acid (PTA) wastewater, and the influences of organic loading disturbances on the process performance were investigated. After about 15 month operation, the COD removal efficiency was maintained at 79% under the volumetric loading rate of 5.05 kg-COD/m(3)/d and the hydraulic retention time (HRT) of 50 h. Interestingly, this performance Could be further enhanced over 85% by applying a step-increase/decrease of the HRT, which was mainly due to the increased p-toluate degradation. In the shock loading tests of four major pollutants (benzoate, acetate, terephthalate and p-toluate), it was found that the overall process performance was adversely affected by all the shock loadings, indicating that the syntrophic microbial consortium involved in the PTA wastewater treatment is highly sensitive to the organic loading disturbances. The complex inhibition effects of the benzoate and acetate on the terephthalate and p-toluate degradations were mainly responsible for this sensitivity. (c) 2008 Elsevier Ltd. All rights reserved