Characterization of selected microbial species for bioflocculant producing potential and comparison with traditional flocculants in industrial waste water treatment
Flocculation is an effective method used to separate the suspended colloids in both domestic and industrial wastewater treatments. The process is achieved with the help of various flocculants such as natural and synthetic inorganic or organic flocculants. Synthetic flocculants are conventionally used due to their high flocculating efficiency and availability. However, their applications result in serious health problems such as cancerogenicity and neurotoxiciy. Consequently, bioflocculants appear to be an attractive alternative to synthetic flocculants because they are non toxic, eco-friendly and able to flocculate at a low concentration dosage. In this study, the production of a bioflocculants from Ochrobactrum oryzae (AB841138), Providencia rettgeri (KF534469), Bacillus megaterium were assessed and the bioflocculant yield quantified. The bacteria O. oryzae (AB841138) and P. rettgeri (KF534469) were previously isolated from sediments located at Mthunzini, north of KZN, Republic of South Africa. The 16S rRNA gene sequencing was used to identify the organisms. While B. megaterium was sampled from the marine deepsea at Sodwana Bay, northern KZN, (RSA) and was identified using morphological and physiological characteristics which was eazy to performed as compared to the other two isolates. The nutritional reguirements and growth conditions such as inoculum size, energy sources, cations, pH, temperature, shaking speed and time course of bioflocculant producing microorganisms were investigated and their flocculating activities (FA) determined by spectrophotometry. Furthermore, the bioflocculants were extracted using ethanol and purified with (5:7 v/v) chloroform and butanol mixture. Physiochemical properties were assessed through elemental detection and scanning electron microscopy (SEM). The functional groups were evaluated using FTIR while chemical composition were analysed using phenol-sulphuric method (sugar content), carbazole method (uronic acid) and Folin-Lowry method (protein). Factors that influence the flocculating activities of the crude bioflocculants such as dosage size, cations, pH and thermal stability and toxicity were determined. The purified bioflocculants were used to treat wastewater from Erwat treatment plant from (Gauteng Province) RSA and coal wash water from Tendele Coal Mine (Kwa-Somkhele, KZN, RSA). The results of nutritional requirements and growth conditions revealed optimum inoculum size of 3% (v/v) for O. oryzae (AB841138), P. rettgeri (KF534469) and 2% (v/v) for B. megaterium. The purified bioflocculants were ORY84, PRKF5 and BMBF.The best carbon source for all three bioflocculants production ORY84, PRKF5 and BMBF was starch, with high flocculating activity of 94%, 94% and 92% attained respectively. Casein was the preferred nitrogen source for both PRKF5 and BMBF production with 83% and 91%, while yeast extract favoured maximum production of 92% for bioflocculant ORY84. The initial medium pH for PRKF5 was 6 while ORY84 and BMBF were produced at pH of 7. After a 96 hrs cultivation period under optimal culture conditions, 3.768 g of purified ORY84, with a maximum flocculating activity of 94% was recovered from 1 L growth broth of Ochrobactrum oryzae AB841138. Furthermore, 3.5 g PRKF5 and 3.103 g BMBF yield of pure bioflocculants with the respective highest flocculating activities of 92% and 89% were also obtained from 1 L growth broth at 72 h. The bioflocculants ORY84, PRKF5 and BMBF, demonstrated thermal stability within a temperature range of 50 to 100 ºC, with flocculating activities of over 80% of a kaolin suspension. The bioflocculants were stable at a wide pH range of (3–11). A low concentration dosage of 2% - 3% was used in the presence of divalent cations (Ca2+ and Mn2+) to flocculate both kaolin clay suspension, Erwat and Tendele coal mine wastewater. The chemical composition analyses revealed both bioflocculants consist of glycoproteins with a predominantly heteropolysaccharide backbones. Fourier transform infrared spectroscopy (FTIR) spectrum showed a broad peak stretching at 3491 cm-1, 3262 cm-1 and 1645 cm-1 stretching weak peak. The peaks confirm the functional groups of hydroxyl, carboxyl and amide groups being present in the bioflocculants are ideal for flocculation process. A scanning electron microscope (SEM), revealed a hexagonal structural image for ORY84, tubular structure for PRKF5 and a longitudinal structure for BMBF. The elemental analyser showed the presence of carbon and oxygen amongst other elements for all purified bioflocculant. Treatment of Tendele and Erwat wastewater with purified bioflocculants ORY84, PRKF5 and BMBF presented pre-eminent reduction efficiency of above 90% on COD and BOD. The bioflocculants further showed removal efficacy of above 80% for nutrients and metal elements as comparable to chemical floccullants (ferric chloride and alum). Therefore, the results from this study show that the bioflocculants ORY84, PRKF5 and BMBF produced by these marine bacterial isolates have great potential to serve as a substitute for hazardous synthetic flocculants. Bioflocculants can stand as attractive candidates for future developmental research and upscale in industrial applications.
ochrobactrum oryzae --Providencia rettgeri --Bacillus megaterium --bioflocculants --flocculating activity --chemical oxygen demand --biochemical oxygen demand
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