External dosing of sweetmeat waste (SMW) dosing into exhausted upflow packed bed bioreactor (PBR) resulted in prompt reactivation of SO42- removal. Different SMW concentrations in terms of chemical oxygen demand (COD)/SO42- ratios (1, 2, 4 and 8) were introduced into four identical PBR where process stability was found within 3 weeks of operation. SO42- removal was proportional to COD/SO42- ratios up to 4 at which maximum sulfate removal (99%) was achieved at a rate of 607 mg/d. The value of COD consumption:5042 removal was much higher at ratio 4 than 8 whereas, ratio 2 was preferred over all. Net effluent acetate concentration profile and total microbial population attached to the reactor matrices were corresponding to COD/SO42- ratio as 4> 8 > 2 >> 1. Sulfate reducing bacteria (SRB) population was found to be inversely proportional to COD/SO42- ratio in which acetate oxidizing SRB and fermentative bacteria were the dominant. (C) 2015 Elsevier B.V. All rights reserved.