A 'fixed film algal photobioreactor (FFAPBR)' was tested forsugar mill effluent (SME) treatment. This reactor was developed in-house using Chlorellavulgaris, an alga, that allowedto grow on weathered rooftop sheet made of Fiber-reinforced plastic (FRP).Experiments carried out in open sun light, in which SME of 80 L, pumped slowly @12 L -1 minuteatone end of thereactor, collected at another and re-circulated.To check the effectiveness of the treatment parameters pH, COD and BOD were studied. Reduction in chemical (COD) and biological oxygen demand (BOD) was >80% in just 12h of treatment.Treated water was diluted in a ratio of 1:1with tap water and tested for fish survival. All fishes survived 96 hours of observation period and beyond.