Solid state fermentation of biogas residues for production of Bacillus thuringiensis based bio-pesticide

Abstract: Biogas residue is the main byproduct from the biogas process. It has been widely used in agriculture and stockbreeding for its rich content of nutriments and microelements. Bio-pesticides derived from Bacillus thuringiensis are the most well-known biological agents for selective control of pest insects. However, the high cost of raw materials is one of the key factors hindering their development speed and scale. Recently, some cheap raw materials such as maize starch, wheat bran, rice straw and wastewater sludge have been successfully substituted for more expensive media. Biogas residue is renewable, low-cost, and is composed of organic material that contains the necessary nutritional elements to sustain the growth of microbes. In this study, Biogas residues were used as a substrate for bio-pesticides production by solid state fermentation. Principal component analysis of biogas residue indicated that it was well suited for the growth of Bacillus thuringiensis in the experiments. The culture medium recipe was optimized by the orthogonal test. Brewer's grain, corn meal, soybean cake power and mixed ions were chosen to carry out the study.The results showed that brewer's grain had the biggest effects on the growth of Bacillus thuringiensis and then followed the growth effects of corn meal, soybean cake power and mixed ions. Ultimately, the optimum media were 50% biogas residues, 35% brewer's grain, 10% corn meal, and 5% soybean cake power. This article compared the fermentation process among conventional media, only biogas residues media and the optimum media, under the optimized conditions. Spore counts of 5.23×1010 CFU/g and entomotoxicity of 16100 IU/mg were obtained after 48h fermentation, while 2.55×1010 CFU/g spore counts and 12500 IU/mg entomotoxicity were obtained in the conventional medium, and 1.74×108 CFU/g spore counts and 6000 IU/mg entomotoxicity were found in the only biogas residue medium. At last, by comparing the cost between conventional medium and the optimum media, the cost could be lowered by 36.3%. The present study proved the feasibility of using kitchen waste for the production of bio-pesticides, and it seemed to be a promising alternative for the use of conventional mediums to reduce the costs.