Biopesticide production using Bacillus thuringiensis kurstaki by valorization of starch industry wastewater and effluent from aerobic, anaerobic digestion

Abstract

Unconventional alternatives such as aerobic and anaerobic effluent from starch industry contain essential nutrients for Btk active ingredient synthesis. Effluent from starch industry is rich in carbon and nitrogen and can replace expensive feedstock used during the fermentation process. The main objective of this study was to achieve a biopesticide formulation from starch industry wastewater (SIW) with high entomotoxicity (UI/ml) of larvae comparable to Foray 76B, which is a commercial biopesticide. Bacillus thuringiensis var kurstaki HD1 (Btk) strain was cultivated and sub-cultured to aerobic, anaerobic digested effluent and SIW. Pre-treatment was carried on these different substrates to enhance the residual carbon required for Btk growth and delta endotoxin synthesis. After 48 hours of fermentation, cells count and delta-endotoxin were determined. A biopesticide formulation containing fermented broth and adjuvants was fed to larvae to determine larvae mortality. Btk cell growth and sporulation profile in SIW media displayed a high total cell count and viable spores compared to btk growth in anaerobic or aerobic media after 48h fermentation. The maximum endotoxin concentration in the SIW medium was 435μg/mL, whereas, in anaerobic and aerobic effluent, the maximum concentrations were at 161 μg/mL and 136 μg/mL, respectively. When acidic treatment was performed at pH 2 for these substrates, entomotoxicity obtained from aerobic and anaerobic biopesticide formulations displayed significantly higher entomoxicity than the untreated ones. The entomotoxicity of SIW treated at pH 2 was equivalent to the standard Foray 76B which is 20,000 IU/μL. Anaerobic and aerobic effluent did not contain enough total organic carbon to augment Btk growth and entomotoxicity. Substrates pre-treated at pH 2 provided significant organic matter for Btk growth and resulted in larval mortality equivalent to the com ercial biopesticide Foray 76B.