Effect of ultrasound and addition of bacterial product on hydrolysis of by-products from the meat-processing industry

Abstract

The hydrolysis efficiency of ultrasound (US) and bacterial product (BP; Liquid Certizyme 5™) was studied as a pre-treatment for anaerobic digestion (AD) of four animal by-products (ABP) from the meat-processing industry (digestive tract content + drumsieve waste, dissolved air flotation (DAF) sludge, grease trap sludge and the mixture of these). The change in volatile solids (VS) based hydrolysis parameters was screened using different specific US energy (Es) inputs (1000–14,000 kJ/kg of total solids (TS)) and durations of BP treatment (3–48 h). The Es of 6000–8500 kJ/kg TS increased most extensively the soluble chemical oxygen demand (CODsol) and VS ratio, by 45–290%, and soluble nitrogen (Nsol) by 44–99%. Simultaneously, the average particle size (APS) decreased by 45–75%, from the original value. With BP, the highest increases in CODsol/VS (29–130%), Nsol (35–63%) and decline in APS (40–70%) depended on the raw material (digestive tract content + drumsieve waste: 3 and 24 h; DAF sludge: 3 and 6 h, mixture: 12 and 48 h). BP apparently was more effective at hydrolyzing smaller cellulose particles, while US appeared to enhance the degradation of grease-containing cells.