Production, Characterisation and Application of Bioflocculants from Pure Bacterial Strains and their Consortia Isolated from Sodwana Bay in Kwa-Zulu Natal, South Africa

Flocculation is the physical purification technique whereby destabilized colloidal particles are enhanced to agglomerate to form large and settleable flocs. Bioflocculants have been the center of attention in bioremediation because of their effectiveness, biodegradability, harmlessness and environmentally inert nature. This study aimed at producing, characterising and applying bioflocculants from pure marine bacteria and their consortia. The medium composition and culture conditions of previously isolated bioflocculant producing strains: Bacillus pumilus JX860616, Bacillus subtilis CSM5 and Alcaligenes faecalis HCB2 and their consortia were optimised. The produced bioflocculants were obtained through solvent extraction and purification. The physicochemical analyses of the bioflocculants were attained by scanning electron microscopy (SEM), elemental detector, Zetasizer Nano, Fourier transform infrared (IR) spectrophotometry, liquid chromatography-mass spectrophotometry and thermo gravimetric analyzer. The thermal, pH and salinity stabilities of bioflocculants were evaluated spectrophotometrically. Flocculation mechanism was assessed by Zetasizer Nano. The biosafety of the bioflocculants was determined by 3-(4,5-dimethylthiazol-2-)-2,5-diphenyl tetrazolium bromide (MTT) assay. The removal efficiencies of the bioflocculants on biochemical oxygen demand (BOD), chemical oxygen demand (COD), sulphur, nitrogen, calcium and aluminium were determined spectrophotometrically in water from the Nhlabane estuary, effluents from the Umhlathuzi and a local coal mine wastewater treatment plants. Bioflocculant production by all the three pure bacterial species and two bacterial consortia was obtained when the inoculum sizes were 2% (v/v) or less. Fructose was effectively utilized for production of crude bioflocculant by B. subtilis CSM5, while maltose was a good carbon source for the bioflocculant production by A. faecalis HCB2. Glucose was preferred for production of crude bioflocculant extracts by Bacillus pumilus JX860616, consortium of B. pumilus JX860616 and B. subtilis CSM5 and consortium of B. pumilus JX860616 and A. faecalis HCB2, respectively. Amonium sulphate was efficiently utilized for bioflocculant production by B. pumilus JX860616 and consortium of B. pumilus JX860616 and B. subtilis CSM5. Urea was the best nitrogen source for production of crude bioflocculants by B. subtilis CSM5 and A. faecalis HCB2, while yeast extract supported production of bioflocculant by consortium of B. pumilus JX860616 and A. faecalis HCB2. The bioflocculants were produced when in optimum culture conditions of: 20-30°C, 55 -165 rpm, after 60-72 hours in different initial medium pH. The extracted and purified bioflocculant yields from bacterial consortia were higher than those of pure strains. B. pumilus JX860616 produced 2.5 g/l, B. subtilis CSM5 had 1.5 g/l and A. faecalis HCB2 had 2.7 g/l). The consortium of B. pumilus JX860616 and B. subtilis CSM5 yielded 3.1 g/l while that of B. pumilus JX860616 and A. faecalis HCB2 gave 3.0 g/l. All purified bioflocculants were cation dependent and relatively effective at low dosage bioflocculants (≤ 0.8 mg/ml). The bioflocculants are anionic glycoproteins in nature and are predominantly composed of carbohydrates. They revealed the presence of elements such as: N, C, O, P, Ca, and Na. IR observations showed that biofloculant TMT was indicative of hydroxyl, vinyl, amide and amino groups. All other bioflocculants (TTT, TKT, TST and TPT) had similar functional groups; hydroxyl, amino and amide groups. The bioflocculants were stable in a wide range of pH and also showed saline and thermal stability. They demonstrated a margin of safety as they revealed insignificant cytotoxic effects. The flocculation process could be as a result of double layer compression by Ba2+, chemical reactions and bridging mechanisms. The bioflocculants were comparatively effectively to convesional flocculants in the removal of pollutants. The results of this study advise that the use of bacterial consortia can improve bioflocculant yields and that bioflocculants have potential to serve as an alternatives to conventional chemical flocculants.

Grantor dc:publisher.institution

University of Zululand

Year dc:date.issued

2018

Author dc:creator

• Maliehe, Tsolanku Sidney

• bioflocculants --bacterial strains --production --South Africabioremediation

Licence

• https://devspace.unizulu.ac.za/bitstreams/9e2baf90-aa3c-4bd8-bc4b-ca671eb4771f/download