Process optimization of brewers’ grains fermentation using photosynthetic bacteria to make fish feed

In order to get high-quality fish feed from brewers’ spent grains, an anaerobic fermentation installation was set up, and the brewers’ grains as raw material were pretreated by anaerobic photosynthetic bacteria separated from drainage ditch of brewers’ grains in a beer factory. The orthogonal experiments were conducted based on single factors to study the semisolid fermentation technique for anaerobic photosynthetic bacteria culture. The results showed that the satisfied fermentation effect was attained under the technical conditions of dry brewers’ grains/water 1:9 (mass fraction), inoculation amount 9%, illumination intensity 1100 Lx, fermentation time 5 d, fermentation temperature 30℃, and material thickness 3 cm. After fermentation, the real protein concentration of brewers’ grains increased from 17.0% to 41.6%, the cellulose concentration decreased from 15.3% to 7.0%, the crude fat concentration increased from 5.9% to 6.6%, the crude ash concentration increased from 3.8% to 4.1%, the total phosphorus concentration increased from 0.6% to 1.3%, and the water concentration of dried brewers’ grains was 9.8%. All the six indices satisfied the China standard of Grass Carp’s fingerling (SC/T 1024-2002). The results can provide references for making active photosynthetic bacteria fish feed from brewers’ grains.