Biotreatment of paper mill effluent using alkaliphilic Rhizobium sp. NCIM 5590 isolated from meteoric alkaline Lonar Lake, Buldhana District, Maharashtra, India

Bacterial strain Rhizobium sp. was isolated from littoral soil of meteoric alkaline Lonar Lake and used to treat paper mill waste water. The bacterium was found to fix 125.7 nmol of C 2 H 4 formed ml −1 culture media in 72 hr by ARA (acetylene reduction assay). The optimum pH for its growth was 12, whereas the optimum temperature was 40°C. The bacterium could tolerate salt concentrations up to 4%. The collected paper mill effluent used two dyes in combination, namely Acid Orange 7 ( AO ) and Acid Yellow 17 ( AY ) to produce brown paper, eventually producing coloured effluent containing unbound AO and AY . Rhizobium sp. was found to be efficient for decolorization of both AO and AY individually, as well as in a mixture of AO and AY , suggesting the ability of this strain for treating paper mill effluent. The strain was found to be efficient in reducing up to 85% of the colour from undiluted paper mill effluent within 18 hr. In addition, biotreatment also was effective in reducing COD , metals and toxicity from the waste water. Induction in the enzymes azo reductase and DCIP reductase indicated their possible involvement in biotreatment of paper mill effluent. The effluent toxicity before and after treatment was studied using Allium cepa root cells, evaluating various biochemical parameters to assess the toxicity, including lipid peroxidation, protein oxidation, antioxidant enzyme status (catalase, superoxide dismutase) and genotoxicity assays using single cell gel electrophoresis ( SCGE ).