The present work was targeted to develop flocculating agent from natural sources i.e. bacteria and plants which could be utilized for remediation of wastewater samples through bioflocculation process. A potent bacterial strain capable of producing bioflocculant as extracellular polymeric substance was isolated from soil sample and identified as Bacillus amyloliquefaciens TERI VB2. The bioflocculant from this bacterial strain was designated as BF-VB2 and was observed as extracellular production through SEM imaging. The production of bioflocculant by B. amyloliquefaciens TERI VB2 was further optimized through nutritional and process parameter amendments which lead to enhanced flocculation activity (98.94%) and 15.78-fold increase in yield (10.26 g/L). The final flocculation activity achieved after optimizing dosage and other flocculation assay parameters was 99.8%, which corresponds that one milligram of BF-VB2 effectively flocculates 1980.0 mg ± 5.0 mg of kaolin particles.
Mucilage from two selected plants i.e. Moringa oleifera (BF-MO) and Phyllanthus emblica (BF-PE) extracted through acetone precipitation were used for further investigation. Under optimum conditions of dosage, pH, and concentration of contaminant; BF-PE displayed notable activity over BF-MO, as 98.0% flocculation was achieved at 80.0 mg/L dosage and 40 minutes of sedimentation, in case of BF-PE while, it required 110.0 mg/L dosage and 60 minutes sedimentation time for BF-MO.
The bacterial bioflocculant BF-VB2 was characterized as polysaccharide with small amount of protein. The major functional groups of BF-VB2 responsible for flocculation were hydroxyl, carboxyl, amines, and halides. On contrary, active phytochemicals observed in BF-PE were tannins; alkaloids; and flavonoids while, BF-MO had phenols and flavonoids.
BF-VB2 effectively flocculated textile dyeing industrial wastewater by reducing dye color (82.78% ± 3.03%), COD (92.54% ± 0.24%), TSS (73.59% ± 0.71%), and chloride ions (81.90% ± 0.716%). The best-fit kinetic model was pseudo-first order. Bridging due to presence of negative surface charges have been proposed as flocculation mechanism.
Plant-based flocculants were efficient in treating sewage wastewater and the optimum dosage required for maximum turbidity (22.0 NTU and 12.5 NTU) and TSS (600.323 mg/L and 600.46 mg/L) removal were 300 mg/L and 150 mg/L (w/v), respectively by BF-PE and BF-MO. Therefore, the flocculation activity possessed by both the flocculants were 90.36±1.235% and 93.67±2.08% respectively. The biodegradability index (BOD5/COD ratio) for raw sewage wastewater was 0.37; which was enhanced to 0.6 (BF-PE) and 0.52 (BF-MO). These two flocculants were also anionic in nature and displayed polymer bridging.
An integrative approach using grafting technology was used to produce a concoction of bacterial and plant-based green graft copolymer bioflocculant. The microwave-initiated grafting was optimized at BF-VB2 concentration of 4.0 g, BF-PE concentration of 1.0 g, and microwave irradiation time 120 sec, at microwave power of 800 W. Under optimized conditions about 40.0 % of grafting efficiency was achieved and spectral analysis of this grafted copolymer represented that intended grafting was attained. The concoction was designated as Phyllanthus-g-BacPol and it exhibited flocculation activity of 99.16% at 3.5 mg/L concentration for synthetic wastewater, which was in between the dosage required by BF-VB2 and BF-PE.
Comparative analysis of all the three types of flocculants presented bacterial bioflocculant BF-VB2 to be superior over others. However, the concoction developed also holds greater prospects for industrial applications and could be explored further. This study therefore, puts forward an efficient way to treat wastewater samples through bioflocculation using eco-friendly flocculating agents (obtained from natural sources) with higher flocculation activities and yield.