Isolation and characterization of extracellular bioflocculants produced by bacteria isolated from Qatari ecosystems

Abstract

Compared with conventional synthetic flocculants, bioflocculants has special advantages such as safety, strong effect, biodegradable and harmlessness to humans and the environment, so they may potentially be applied in drinking and wastewater treatment, downstream processing, and fermentation processes. To utilize bioflocculants widely in industrial fields, it is desirable to find various microorganisms with high bioflocculant-producing ability and improve the flocculating efficiency of the bioflocculant. In the present study, screening of new flocculant-producing microorganisms was carried out using samples collected from different Qatari ecosystems. The flocculating activity of the novel bioflocculants produced by isolated microorganisms was investigated. A total of 5 g/l Kaolin suspension was used to measure the flocculating activity. Isolated bioflocculant-producing bacteria were identified by 16S rDNA analysis, using PCR with universal primers. Comparative analysis of the 16S rDNA sequence (∼550 bp) in the GenBank database revealed that these bacteria are related to the genus Bacillus. FT-IR spectrometry analysis of the extracted bioflocculants indicated the presence of carboxyl, hydroxyl and amino groups preferred for the flocculation process. Influences of pH and bioflocculant dosage on the flocculation were also examined. The maximum flocculating rates were observed at pH 7, 7 and 3 of the bioflocculants derived from strains QUST2, QUST6 and QUST9, respectively. However, 20.0 mg/l was the dose that gave the highest flocculating rate with all examined bioflocculants. The elemental analysis of examined bioflocculants revealed the mass proportion of C, H, N and S. Carbon and nitrogen contents of examined bioflocculants were in the range of 42-48% and 11-12%, respectively.