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.

Keywords:

• bioflocculant
• Bacillus mucilaginosus
• flocculating rate
• RSM
• fermentation conditions

Disclosure statement

No potential conflict of interest was reported by the authors.

Funding

This work was supported by The Opening Foundation of Shaanxi Key Laboratory of Exploration, Comprehensive Utilization of Mineral resources [grant number 2014HB003], Shaanxi Science and Technology Development Project [grant number 2015SF263] and The Fundamental Research Funds for the Central Universities [grant number 2014G1502030] and the Open Research Fund of Key Laboratory of Subsurface Hydrology and Ecological Effect in Arid Region of Ministry of Education [310850142030].