An on-site pilot-scale experiment was conducted to investigate the performance of a multi-staged UASB (MS-UASB) reactor by feeding with a food processing wastewater containing high strength of lipid and protein. The reactor was operated at a thermophilic condition (55°C) for a period of 600 days. The reactor finally achieved 50 kgCOD·m−3ád−1 with a soluble COD removal of 90% (based on the influent total COD versus the effluent filtered COD), while the overall COD removal (based on the effluent COD-total) was considerably unsatisfactory at around only 60–70%. The presence of high strength of lipid and protein along with high concentration of Mg and Ca ions in the raw wastewater caused a severe scum and/or insolubilized substance formation within the UASB sludge bed, resulting in hindering the contact efficiency between substrate and sludge. The replacement of active microbial granules in the sludge bed with the insolubilized protein and lipid brought about deterioration of sludge methanogenic activity.

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