The characteristics and flocculation mechanisms of SMP and B-EPS from a bioflocculant-producing bacterium Pseudomonas sp. XD-3 and the application for sludge dewatering

Abstract

In this study, a novel bacterium Pseudomonas sp. XD-3 with bioflocculant-producing capability was identified and characterized. Strain XD-3 produced two kinds of flocculating active substances, soluble microbial products (SMP) and bound extracellular polymers substances (B-EPS). The flocculation efficiency of SMP was about 79.3% and that of B-EPS was 79.9%. Charge neutralization, ion bridging and hydrogen bonding played important roles in the flocculation of SMP, while ion bridging and hydrophobic force dominated the flocculation in B-EPS. Spectral analysis revealed that –OH and –COO- in SMP and B-EPS provided abundant binding sites for ion bridging. The presence of CNH3+ in SMP participated in charge neutralization. The hydrophobic groups of C-(C/H) and OC contributed to the hydrophobic force of B-EPS. In addition, both SMP and B-EPS contained proteins secondary structures that were beneficial for bioflocculation, such as α-helix, three-turn helices, β-sheet and aggregated strands. B-EPS exhibited satisfied sludge dewatering effect, with a water content reduction from 93.66% to 83.9% and a specific resistance to filtration (SRF) reduction from 13.48 × 1012 m/kg to 7.74 × 1012 m/kg. The composite flocculant of B-EPS and Al2(SO4)3 further reduced the SRF to 1.54 × 1012 m/kg at pH 4, CaCl2 dosage 23.3 g/kg, B-EPS 0.93 g/kg and Al2(SO4)3 150 g/kg.