BACKGROUND: At concentrations higher than 1 mg L-1, 4-chlorophenol (4-CP) is very toxic to living organisms, and if ingested beyond the permitted concentration it causes health disorders such as cancer and mutation. This laboratory study investigates treatment of contaminated water laden with 4-CP using coconut shell charcoal (CSC) waste. Batch studies were conducted to study the effects of dose, pH, and equilibrium time on 4-CP removal. To improve 4-CP removal, surface modification of the adsorbent with TiO2, HNO3, and/or NaOH was undertaken. RESULTS: At an initial 4-CP concentration of 25 mg L-1 under optimized conditions (dose 13.5 g L-1, pH 2.0; agitation speed 150 rpm and 50 min equilibrium time), the NaOH-treated CSC demonstrated a greater removal of 4-CP (71%) than those oxidized with HNO3 (40%) and/or coated with TiO2 (52%). The adsorption capacity of the NaOH-treated CSC (54.65 mg g(-1)) was higher than those treated with HNO3 (23.13 mg g(-1)) or coated with TiO2 (48.42 mg g(-1)). CONCLUSION: Although treatment results using the NaOH-treated CSC alone were promising, the treated effluents were still unable to meet the required limit of less than 1 mg L-1. Therefore, subsequent treatments are still required to complement the removal of 4-CP from the wastewater. (C) 2010 Society of Chemical Industry