Optimal conditions for scp production by mixed cultures of a. Niger and cr. laurentii grown in sugar cane vinasse medium

Abstract

Mixed cultures of Aspergillus niger and Cryptococcus laurenti grown in sugar cane vinasse medium under continuous agitation were studied in order to establish optimal conditions (carbon:nitrogen:phosphorus ratios; carbohydrate concentration; initial pH; incubation temperature; incubation period) for biomass production and biological depuration of vinasse, a waste product from the ethanol industry. Pure (singlespecies) cultures of each microorganism were also analysed. Addition of nitrogen and phosphorus to vinasse medium altered significantly biomass production, carbohydrate consumption and BOD reduction. Protein content of biomass was greatly increased and BOD reduction diminished at carbohydrate concentrations higher than 3 gl'1. Both initial pH and incubation temperature had little influence on BOD reduction (most levels at around 50%). Vinasse pH was always around 7.0 after 48h of incubation.*Mixed cultures of A. niger and Cr. laurentii in sugar cane vinasse medium modified for optimal growth (20: 3.0: 0.1 C:N:P ratio; 8 gl4 carbohydrate content; pH 4.6; 30°C) reached maximal biomass concentrations after 24 hours of incubation; best results for BOD reduction (around 80%) and protein yields (40%) were recorded after 72 h of culture. Compared to pure cultures, the optimized mixed cultures of A. niger and Cr. laurentii produced lower concentrations of biomass.