Novel and sustainable valorization of biogenic waste into microbial protein based fish dietary ingredient in bioreactor: Process optimization and sustainable utilization

Waste valorization is the concept of sustainability, and microbial floc is the valorised product of sustainable aquaculture. It converts nitrogenous waste into nutritious microbial protein that can replace fish meal partially or completely as feed for aquatic animals. The current study focuses on optimizing the process of production of microbial protein using aquaculture waste in a bioreactor and its utilization as feed for genetically improved farmed tilapia (GIFT) reared in inland saline groundwater with various inclusion levels. The retention time, aeration, and microbial flocculant (chitosan) were optimized to intensify the reaction, using a response surface methodology approach based on a full factorial experimental design. The chosen responses for evaluation were crude protein (CP), crude lipid (CL), and floc volume (FV). The interaction between aeration and retention time was found to play a significant role in the percentage of crude protein and crude lipid of microbial floc (p<0.001). The floc volume was significantly influenced by retention time and chitosan concentration (p<0.05). The process was optimized with 4 days of retention time, 30 ppm of chitosan concentration, and intermittent aeration (0.5 hr aeration and 0.5 hr no aeration), which resulted good quality microbial floc with a maximum CP of 24.74 %, a maximum CL of 2.13 %, and a FV of 13.75 ml. A completely randomized design with the inclusion of 0 %, 10 %, 20 %, and 30 % microbial floc (produced in a bioreactor) in feed was followed to evaluate the growth performance of GIFT. Among these, microbial flocs with a 20 % inclusion level showed a good growth trajectory. This study has shown that 20 % microbial floc meal in the diet is optimum for the growth of GIFT in inland saline groundwater. This study sustainably supports the waste valorization concept with microbial protein production in a bioreactor that is a suitable feed for GIFT.