Production of a bioflocculant from marine Stenotrophomonas maltophilia and its application in wastewater treatment

Abstract

The lack of access to safe drinking water and the need for an environmentally friendly approach has prompted bioflocculants to be promising alternatives to chemical flocculants in water and wastewater treatment. This study assessed the production of a bioflocculant from a marine environment and evaluated its application in wastewater treatment. The 16s rDNA nucleotide sequence analysis of isolate H7 revealed 99% similarity to S. maltophilia and was deposited in the GenBank with the accession number MT291866.1. A statistically based experimental design matrix for the bioflocculant production was explored using Plackett Burman (PB) to screen the significant factors and response surface methodology (RSM) coupled with central composite design (CCD) to optimise the production medium. PB revealed that glucose (𝑝<0.0071), yeast extract (𝑝<0.0041), K2HPO4 (𝑝<0.0032) and (NH4)2SO4) (𝑝<0.009) exhibited a statistically significant influence on the production of the bioflocculant producing strain with the probability values less than 0.05. CCD demonstrated that glucose as a carbon source and yeast extract as a nitrogen source supported the maximum bioflocculant production from marine S. maltophilia. The optimal quantities of 16.25 g/l glucose, 1.61 g/l yeast extract, 1.1 g/l K2HPO4 and 3.5 g/l (NH4)2SO4) achieved a maximum flocculation activity of 96.05% and 4 g yield of the purified bioflocculant. Fourier transform infrared (FTIR) spectroscopy revealed the presence of hydroxyl and carbonyl groups and sugar derivatives. This confirmed that a polysaccharide is the major backbone of bioflocculant produced by S. maltophilia. A Thermogravimetric analyser (TGA) indicated that the bioflocculant produced is thermostable as it retained 85% of the weight when heated up to 500 ℃. The scanning electron microscope (SEM) analysis revealed clumped sheath layers and an irregular pattern. The energy dispersive x-ray (EDX) analysis affirmed the presence of carbon, oxygen, magnesium, sulphur and potassium, (49.42),(34.23),( 0.73), (7.78), (0.14) and (7.7) respectively. Compared to commercially available flocculants, the bioflocculant exhibited 84.5% flocculation activity (FA), while polyethyleneimine and polyacrylamide demonstrated 65.7% and 29.6% FA, respectively. The application of the produced purified bioflocculant was investigated by treating primary sludge from a wastewater conventional plant with a COD removal efficiency of 71.5%, the bioflocculant produced has the potential to serve as an alternative to traditional flocculants.