An on-site pilot-scale experiment was conducted to investigate the process performance of our newly proposed multi-staged UASB reactor by feeding with a food industrial wastewater containing high strength of lipid and protein. The reactor was operated at a thermophilic condition (55°C) for a period of 300 days. The reactor accomplished finally 50 kgCOD·m-3·L-1 at a soluble COD removal of 90%(corresponding to the influent COD strength of 7, 000 mgCOD·L-1 and HRT of 3.4 h), while the overall COD removal (based on the effluent COD-total) was considerably unsatisfactory at only around 50%. The presence of lipid, protein along with Mg and Ca ions in the raw wastewater caused a severe scum formation in the pre-acidification tank and UASB sludge bed, resulting in lessening the contact efficiency between substrate and sludge. Replacement of granules in the sludge bed by insolubilized lipid and protein caused deterioration of sludge methanogenic activity. The most optimum operational mode we established through 300 days experiment was to intentionally reject the retainment of insoluble lipid and protein fractions from UASB reactor by imposing a relatively high liquid velocity. It is recommended that for treatment of a kind of wastewater as used in this study the UASB process should serve as pretreatment for elimination of soluble organic fractions, and the subsequent activated sludge process serve as post-treatment for removal of remaining insoluble lipid/protein fractions.
