Treatment of dairy wastewater using an Upflow Anaerobic Sludge Blanket reactor

Wastewater coming from cheese-producing industries in Greece is high in organic matter (about 40-60 g/l Chemical Oxygen Demand, GOD) since it generally contains discarded cheese-whey as well. This wastewater is rich in easily biodegradable carbohydrates and has a relatively low content in suspended solids (1-5 g/l). Because of the high organic content of dairy wastewater, anaerobic digestion is essentially the only viable treatment method. An Upflow Anaerobic Sludge Blanket (UASB) reactor is a high rate treatment system, especially feasible for treating soluble (containing low solids) wastewaters. A well-performing UASB reactor is characterized by highly flocculated, well-settling, compact methanogenic sludge granules, resulting in a very high biomass content. The aim of this work is the study of a UASB reactor treating dairy wastewater. A UASB reactor of 101 useful volume was constructed and inoculated with anaerobic mixed liquor from dairy wastewater and glucose fed digesters. The digester efficiency of treating dairy wastewater at various organic loading rates was studied and its performance was assessed by monitoring pH, dissolved chemical oxygen demand (COD), biogas production and composition. Operation at an organic loading rate of 6.2 g COD/ld was found to be safe and could be increased to a maximum of 7.5 g COD/ld. A draw and fill digester fed with non-diluted wastewater was also studied in parallel for comparison purposes. The advantages of using a UASB reactor versus a conventional digester become questionable for the high COD (>42 g/l), non-diluted dairy wastewater case. (C) 1999 Silsoe Research Institute.