MICROBIAL DECOLOURISATION OF BIOMETHANATED DISTILLERY SPENT-WASH

摘要

The fungal strain of Aspergillus niger Um_2 isolated from decaying wood was tested for its efficiency to decolourise the effluent from biomethanated spent-wash plant. The culture of Aspergillus niger Um_2 when grown in media containing glycerol (6%), yeast extract (0.5%), KH_2PO_4 (0.1%), MgSO_4 7H_2O (.05%) and biomethanated effluent (50% v/v) pH4.5 brought about 80% reduction in colour at a wavelength 475 nm within 10 days. With other nitrogen sources like peptone, urea or carbon sources like glucose, sorbitol, raffinose, mannitol the percent decolourisation was to the same extent. However, there was variation in percent colour removal and COD reduction within different biomethanated plants. Reductions in phosphate, sulfate and chloride contents of the effluent after fungal treatment were recorded. Biomass based colour removal indicated the adsorption of colouring compounds on the cell wall. Transmission electron microscopic observations suggested initial adsorption of colouring compounds on cell wall followed by their absorption and intracellular degradation. The role of intracellular enzyme activity degrading the colouring compounds in presence of phosphate and magnesium ions at pH 6.0 has been discussed. Gel permeation chromatography of treated effluent revealed emergence of a low molecular weight species of colouring compounds, caramel, melanoidin and alkaline degradation products suggesting their microbial degradation. Immobilised fungal culture was more efficient in colour removal from effluent as compare to free cells. The ability of immobilised culture to grow in 50% (v/v) biomethanated effluent without any nitrogen source was remarkable.