Decolourization and detoxification of pulp and paper mill effluent by Cryptococcus sp.

Three fungal strains were isolated from sediments of pulp and paper mill in which PF7 reduced colour (27%) and lignin content (24%) of the effluent on 5th day. PF7 was identified as Cryptococcus sp. isolate FIST3 on the basis of ITS1 and ITS2 region sequences. The process of decolourization optimized, in shake flask experiments, by Taguchi approach indicated optimum conditions: temperature (30–35 °C); shaking condition (125 rpm); dextrose (1.0% w/v); tryptone (0.1% w/v); inoculum size (7.5% w/v); pH (5) and duration (24 h). Overall evaluation criterion (OEC) value before optimization was 32.3. There was 38% improvement in the process with final OEC value, 44.6 ± 2.02, at optimum conditions. The colour content of the effluent reduced by 50–53% and lignin content 35–40% after treatment at optimum conditions. Variation in pH from 5 to 6 had most significant effect on decolourization (72%) while variation in temperature from 30 °C to 35 °C had no effect on the process. Treated effluent was further evaluated for toxicity by alkaline single cell (comet) gel electrophoresis (SCGE) assay using Saccharomyces cerevisiae MTCC 36 as model organism, indicated 45% reduction. The results showed significant reduction in colour, lignin and toxicity of the effluent and this process can be scale up to industrial level.