Biological Conversion of Agricultural Wastes Into Microbial Proteins for Aquaculture Feed

Abstract

The growing world population will comprise 9 billion people by 2050 and protein consumption will be 50% higher in 2030 compared to 2000. To prepare for this increase, new sources of protein must be sought to replace the non-environmentally sustainable animal and plant proteins that are currently produced. Insects or microbial proteins can indeed be an economic and nutritious alternative not only for animal feed, but also as supplements for human consumption. Our study aimed at assessing the production of microbial proteins destined to aquaculture feed, using as starting material agricultural and animal wastes, in order to tackle at the same time the problem of waste disposal. A bioreactor was feed with the fluid obtained from the acidogenic fermentation of zootechnical and agricultural waste, containing a mixture of VFAs of which acetic acid was the most abundant (43.8 %). The highest productivity (1.6-2.0 gMLVSS/L per day) was obtained with an HRT of 2 days and an ORL of 22 gCOD/L per day. The produced bacterial biomass was analyzed to determine its suitability as fish feed, showing a crude protein content of 73 % over the MLVSS, of which glutamic and aspartic acid were the most abundant. These amounts are higher than what is found in most commercial fish feeds, suggesting that the bacterial biomass has potential to be used as aquaculture feed. PHAs accumulation tests on part of the biomass recovered from the bioreactor showed concentration of PHAs up to 62.2 % over cell dry weight, a positive result since PHAs have the potential to enhance fish growth.