Conventional ruminant production systems are often characterized by inefficient feed utilization and the generation of large volumes of agro-food byproducts (AFBs), which are frequently disposed of as waste. Some biorefineries, such as anaerobic digestion (AD), can produce value-added products like volatile fatty acids (VFAs). This study aimed to produce and evaluate a bio-based VFAs mixture from AFBs as a sustainable feed ingredient for ruminants, hypothesizing that it could partially replace conventional feed, improve rumen fermentation, and maintain feed intake. A semi-continuous immersed membrane bioreactor (MBR) was applied to bioconvert apple pomace and potato protein liquor and recover VFAs at an optimal organic loading rate of 3.7 gVS/L.day (28.6 g/L VFAs). The MBR achieved long-term performance (114 days) with a maximum of 40 g/L total solids but fouling hindered further operation. This study demonstrates the technical feasibility of using MBRs to produce VFAs from AFBs, offering a potentially more sustainable alternative to conventional VFAs production methods. In vitro studies, including a modified Menke gas method and the Rumen Simulation Technique (RUSITEC), demonstrated that the VFAs mixture did not negatively change rumen fermentation key parameters such as pH and redox potential. It significantly reduced methane production in RUSITEC when replacing 20% of concentrate energy. 

Subsequently, a pilot-scale MBR continuously produced feed-grade VFAs for 105 days, yielding 35 liters of the mixture daily. This mixture was then evaluated in an in vivo trial with 24 Suffolk lambs, where it was partially mixed with concentrate in the diet at two inclusion levels. Importantly, VFAs supplementation did not negatively affect feed intake, growth performance and altered rumen VFAs profiles, suggesting improved rumen fermentation.  

These findings suggest that industrial-scale production of sustainable bio-based VFAs from AFBs is technically feasible. This VFAs mixture shows promise as a feed ingredient for ruminants, capable of partially replacing concentrate’s energy, not disrupting the normal function of rumen fermentation, and potentially reducing enteric methane emissions.