Reduction of scum accumulation through the addition of low-cost enzymatic extract in the feeding of high-rate anaerobic reactor

This work evaluates the reduction of scum accumulation on the top surface of upflow anaerobic sludge blanket (UASB) reactors by the addition of hydrolytic enzymes in their feed. For over 1 year, two UASB reactors of 1.4 L were maintained at 30 °C and continuously fed with synthetic domestic wastewater (containing 150 mg/L of soybean oil) under a hydraulic retention time of 10 h. The Control reactor was only fed with synthetic wastewater. Beginning at the 226th day of operation, low-cost hydrolytic enzymes (obtained by solid-state fermentation of Aspergillus terreus, a fungus isolated from a primary sewage sludge) were added into the feed of the other reactor (Test) for a lipase activity of 24 U/L, considerably reducing the formation of scum. In the Test reactor, the scum showed oil and grease (O&G) concentration between 0.8 and 1.3 g/L and an accumulation rate of 20 to 27 mg O&G/d. In the Control reactor, the scum had values twice as high (1.5–2.5 g/L and 34–51 mg O&G/d, respectively) and there were more operational problems. During the entire period of operation, both reactors presented high chemical oxygen demand removal (>80%), with no loss of effluent quality due to the addition of the enzymes.