Synthesis, characterization and application of polyacrylamide grafted bioflocculants (TMT-1-g-PAM 2 and TST-1-g-PAM 3)

A dissertation submitted to the Faculty of Science and Agriculture for the requirements of the Degree of Master of Science in the Department of Biochemistry and Microbiology at the University of Zululand, 2018.

Water pollution is one of the major problems in the world. It contributes to water scarcity. Grafted bioflocculants have been found to have excellent wastewater remediation capabilities. Therefore, they have become one of the main research focal points in recent times as flocculants. The high efficacy is owed to their unique characteristics, which include having a branched structure and a high molecular weight. Therefore, the aim of this research was to synthesise, characterize and apply polyacrylamide grafted bioflocculants to wastewater treatment. Bioflocculants (TMT-1 and TST-1) produced by Bacillus pumilus JX860616 and a consortium of Bacillus pumilus JX860616 and Bacillus subtilis CSM5, respectively, were grafted with acrylamide chains using a microwave initiated method. To optimize the synthesis of the grafted bioflocculants, irradiation time and acrylamide concentration were varied. Optimum grades (TMT-1-g-PAM 2 and TST-1-g-PAM 3) were then characterized by intrinsic viscosity, elemental analysis, scanning electron microscopy (SEM), Fourier transform infrared (FTIR) spectroscopy, X-ray diffractometry (XRD) and thermogravimetric analysis (TGA). Furthermore, these optimum grades’ biosafety (on human embryonic kidney 293 cells, HEK 293) were assessed by 3-(4,5-dimethylthiazol-2-)-2,5- diphenyl tetrazolium bromide (MTT) assay. The grafted bioflocculants were also screened for antibacterial activity, using micro-dilution assay. Their biodegradation was investigated by a composting method. The effects of dosage size, cations, pH, temperature and salinity on the flocculating activities of the grafted bioflocculants were also evaluated, spectrophotometrically. The flocculation mechanism was determined by evaluating zeta potentials using Zetasizer Nano. Spectrophotometric cell tests were utilized to assess COD, BOD, N, P and S removal on domestic and coal mine wastewater by the grafted bioflocculants. The optimum grade (TMT-1-g-PAM 2) was obtained when a concentration of 2.5 g of acrylamide was used for grafting on TMT-1 at irradiation time of 3 min.; while TST-1-g-PAM 3 was synthesized by using 7.5 g of acrylamide at irradiation time of 3 min. Changes observed in intrinsic viscosity, elemental analysis, SEM, FTIR, XRD and TGA confirmed that grafting was successful. HEK 293 cells displayed high viability (75% in TMT-1-g-PAM 2 and 85% in TST-1-g-PAM 3) when exposed to high concentrations (i.e. 200 μg/ml) of the grafted bioflocculants. Both grafted bioflocculants did not show any antibacterial activity against the tested species. The grafted bioflocculants were biodegradable. The flocculants’ dosage size of 0.2 mg/ml possessed flocculating activities of xiv 81% for TMT-1-g-PAM 2 and 90% for TST-1-g-PAM 3. Furthermore, the grafted bioflocculants showed stability over a wide pH range (3–11), displaying flocculating activities above 75%. They also demonstrated thermal stability, both giving flocculating activity of 81% at 100 °C. Moreover, they were able to flocculate saline water (35 g/l NaCl), giving flocculating activity of 63% (TMT-1-g-PAM 2) and 64% (TST-1-g-PAM 3). There was a decrease in zeta potentials with the presence of cations (Ca2+; TMT-1-g-PAM 2 and Ba2+; TST-1-g-PAM 3), implying that flocculation could be due to double layer compression by cations, chemical reactions and bridging mechanisms. The removal of COD, BOD, N and P, in domestic wastewater, by the graft copolymer TMT-1-g-PAM 2 reached 98%, 54%, 53%, and 57% respectively. Whereas, the removal of those parameters by TST-1-g-PAM 3 was as follows: 98%; COD, 73%; BOD, 74%; N and 17%; P. In the case of coal mine wastewater, the removal efficiency by TMT-1-g- PAM 2 was: 98%; COD, 93%; BOD, 59%; N and 83%; S. For TST-1-g-PAM 3, the removal efficiency from coal mine wastewater achieved the following results: 95%; COD, 62%; BOD, 89%; N and 57%; S. Considering the unique properties – such as many functional groups, high stability, biosafety and removal efficiencies of water pollutants – both flocculants attract a potential industrial applicability.

National Research Foundation