Isolation and identification of a bioflocculant-producing strain and optimisation of cultural conditions via a response surface model

Abstract

A bioflocculant-producing strain named MY6-2 was isolated from a mixed activated sludge by a nitrogen-free medium. Based on 16S rDNA sequence, biochemical and morphological characteristics, the strain MY6-2 was identified as Bacillus mucilaginosus. The chemical analysis indicated that the flocculant MY6-2 was mainly composed of extracellular polysaccharide. The result of the composition of the medium showed that MY6-2 was able to generate bioflocculant in a nutrient-poor medium that consisted of 5 g L−1 sucrose and no nitrogen source. Response surface methodology (RSM) was used to optimise the fermentation condition of MY6-2 for maximum flocculating activity by using central composite design (CCD). Based on the result, the optimum conditions were as follows: 100 mL of broth in a 250 mL Erlenmeyer flask, initial pH 8.0 and inoculum concentration 10%, respectively. The highest flocculating rate of 90% was achieved under these conditions by adding 0.5 mL fermentation supernatant to 95 mL of Kaolin suspension.