The effects of the co-existence of biodegradable substrates such as glucose and peptone on removal rate of concentrated refractory organic pollutants in a solid phase aerobic biological treatment process were investigated. The DOC removal rate with co-existence of glucose and peptone became constant around 4-6 kg-C/m(3) per day at the steady state. But, the DOC removal rate decreased from 5.0 to 3.5 kg-C/m(3) per day when p-phenol sulphonic acid (PSA) was fed as the sole organic substrate. This suggests that the co-existence of glucose and peptone accelerated the removal of PSA in the bioreactor. In addition, from the analytical results of microbial quinines a, remarkable change in the quinone profiles was observed along with increasing PSA loading. The dominant quinone in the solid phase bioreactor treating the mixture of GP wastewater and PSA were UQ-8 and menaquinone (MK)-6, and those treating the wastewater containing only PSA as a sole carbon source was MK-6 followed by MK-7 and UQ-8, suggesting that different microbes contributed to PSA degradation with the change of experimental conditions. (c) 2004 Elsevier Ltd. All rights reserved.