Bioflocculant production by aspergillus flavus using chicken viscera as a substrate

Abstract

The biodegradability and safety of the bioflocculants make them potential alternative to non-biodegradable chemical flocculants for wastewater treatment. However, low yield and production cost has been reported to be the limiting factor for large scale bioflocculant production. The sustainability and economics of bioflocculant production is dependent on the use of low-cost substrate at optimum culture conditions. This study focused on the optimization of culture conditions for Aspergillus flavus growth and its bioflocculant production using chicken viscera hydrolysate as substrate. The effects of culture conditions including pH, shaker speed, temperature and inoculum size on bioflocculant production were investigated and optimized via response surface method in accordance with the critical component design (CCD) package of design expert. The purified bioflocculant was characterized using physical and chemical analysis. The flocculation performance and effect of cations on the bioflocculant was investigated using jar testing and Kaolin clay suspension as wastewater model. Under optimized culture conditions, 6.75 g/L of crude bioflocculant was produced. The bioflocculation activity was mostly distributed in the cell free supernatant with optimum efficiency of 91.8% at dose of 4 mL/100 mL Kaolin suspension. The purified bioflocculant was an uneven, coarse EPS assemblage in netted texture consisting of 23.46% protein and 74.5% polysaccharide, including 46% neutral sugar and 2.01% uronic acid with zeta potential of -25.28 ± 2.7 mV at pH 6.2. The Fourier-transform infrared (FTIR) and X-ray photoelectron spectroscopy (XPS) analysis indicated the presence of carbonyl, amino, hydroxyl and amide functional groups and mass proportion of C, O and N at 63.46%, 27.87% and 8.86%, respectively. It had a minimum of 83.1% efficiency in flocculating 2-12 g/L Kaolin clay suspension over a wide temperature range (4 - 80°C) and function optimally at neutral pH. It effectively flocculated different suspended particles such as activated carbon (92%), soil solids (94.8%) and algae (69.4%) at varying concentrations. Addition of both Ca2+ and Mg2+ stimulated the efficiency of the bioflocculant at all the concentrations tested with optimum flocculation efficiency of 95% recorded with 5 mL 1% Ca2+. Lower concentrations (1-2 mL) of Al3+ also stimulated the bioflocculant to about 94%, K+ slightly enhanced the flocculation at 4 – 10 mL 1%, while Na+ and Fe3+ inhibited the flocculation. This study indicates high potential of cation dependent bioflocculant production from chicken viscera at appropriate culture conditions and stand as an attractive candidate for additional exploration and development for large-scale bioflocculant production and application.