BACKGROUND: The effect of coupled biological and photochemical processes for treatment of bio-recalcitrant effluents from chlorination (C) and first alkaline extraction (E(1)) stages of soda pulp bleaching in an agro-residue based pulp and papermill has been investigated. RESULTS: The work aims to evaluate the coupled effect on the extent of degradation in terms of chemical oxygen demand (COD) reduction. Biological treatment of C and E(1) effluent resulted in 30% and 57% COD, respectively, after 1 day of treatment with acclimatized activated sludge. However, further increase in retention time did not show any significant change in degradation efficiency. Investigations on photocatalytic treatment (at 365 nm and 0.625 W) of C effluent resulted in 47% degradation under optimized conditions (3 g L(-1) TiO(2), pH 6.0 and 0.01 mol L(-1) NaOCl), and E(1) effluent showed 37% degradation under optimized conditions (2.5 g L(-1), pH 4.0 and 0.03 mol L(-1) NaOCl) after 6 h of UV irradiation. However, photocatalytic treatment of biotreated (1 day) effluents under similar optimized conditions significantly enhanced the degradation to 81% and 93% in C and E(1) effluent, respectively, after 2 h irradiation. CONCLUSION: Coupled biological treatment followed by photocatalysis is an effective method for the reduction of total organic carbon (TOC) of the test effluents and it would facilitate closed circuiting of water used for soda bleaching in an agro pulp and papermill. (C) 2011 Society of Chemical Industry