Sustainable valorization of slaughterhouse solid waste: A review of characterization, conditioning, hydrolysis and biotransformation strategies

The meat processing industry generates significant quantities of waste, including solid animal by-products (ABPs) and slaughterhouse wastewater (SWW). For instance, based on global meat production in 2020 (approximately 250 million tons), slaughterhouse activities can generate up to 2,250 million m³ of SWW and around 375 million tons of ABPs annually. While SWW is typically treated on-site using conventional technologies, ABPs are managed in external facilities employing traditional methods such as incineration, landfilling or rendering. These practices not only intensify environmental and health issues but also hinder the potential of valorization of ABPs into high-value products. Recent advancements in biological processes have explored the transformation of ABPs into valuable products, such as biogas through anaerobic digestion (AD), predominantly at lab-scale. However, the hydrolysis of ABPs remains a critical bottleneck due to their complex composition and high organic content, requiring extended processing times and large reactor volumes, which limit industrial-scale applications. This review evaluates current and emerging practices for the treatment and valorization of slaughterhouse waste, with a focus on transforming these residues into high-value products, promoting sustainability in the meat industry. The study identifies and characterizes ABP fractions suitable for biological processes and emphasizes the role of waste conditioning and hydrolytic strategies aimed at enhancing the efficiency of biological based processes. Key factors influencing hydrolysis performance are discussed alongside the integration of pretreated waste in industrial AD process. The review provides a critical analysis of existing methods, highlighting their gaps, and identifies opportunities to optimize biological waste conversion for sustainable and high value bioproduct generation. • Methods for protein and lipid characterization remain unstandardized • Waste conditioning typically involves size reduction or dilution prior to hydrolysis. • Hydrolysis lacks consistent protocols, limiting reproducibility and scale-up. • The enzymatic-chemical hydrolysis synergy remains scarcely explored in ABPs. • Similar AD yields in pretreated and untreated waste highlight process limitations.