Innovative biorefinery concept for biogas-based digestate with rice bran protein-rich feed ingredient for tilapia production

Abstract

This study evaluated the nutritional value and amino acid profiles of digestate from a biogas plant, as a substitute for rice bran, in tilapia feed and measured its effects on fish yields and production costs. Four isonitrogenous (24% crude protein) diets were formulated, using digestate at levels of 0%, 10%, 20%, and 30%, with respective reductions in rice bran content (31%, 24%, 17%, and 9%). The experiment was a triplicated, completely randomized design (CRD), starting with 140 fish fry per cage (3.0 × 3.0 × 2.0 m). The fish were fed to satiation twice per day for 180 days. Digestate was more nutritious than rice bran, with 15.3% crude protein and exceptionally high lysine (1872 mg/100 g). Differences in the diets tested had no significant effects on fish survival rates, growth and yield, and food conversion efficiency. The present findings strongly suggest that farmers could adopt tilapia growing systems with cheap and increase aquaculture production in order to meet the fish protein need and food security. Consequently, the least expensive diet was the most cost-effective.