Starch industry wastewater for production of biopesticides – ramifications of solids concentrations

Abstract

Total solids (TS) concentrations ranging from 15 to 66 g L−1 of starch industry wastewater (SIW) were tested as raw material for the production of Bacillus thuringiensis var. kurstaki HD‐1 (Btk) biopesticide in shake flasks and a 15 L bench‐scale fermenter. Shake flask studies revealed a higher delta‐endotoxin concentration of Btk at 30 g L−1 TS concentration and 2.5% (v v−1) volume of pre‐culture. The fermenter experiments conducted using SIW at 30 g L−1 TS concentration under controlled conditions of temperature, pH and dissolved oxygen showed higher spore count, enzyme production (protease and amylase) and delta‐endotoxin concentration as compared with those of SIW at 15 g L−1 TS concentration. The entomotoxicity, at the end of fermentation, with SIW at 30 g L−1 solids concentration (17.8 × 109 SBU L−1, measured against spruce budworm) was considerably higher as compared with entomotoxicity at 15 g L−1 solids concentration (15.3 × 109 SBU L−1) and semi‐synthetic medium (11.7 × 109 SBU L−1). The pellet, comprising spores and delta‐endotoxin complex obtained after centrifugation and followed by resuspension (in supernatant) in one‐tenth of the original volume, of SIW at 30 g L−1 solids concentration media registered the highest potential for application (to protect forests against spruce budworm) than other media in term of entomotoxicity.