Effect of aeration rate on nutrient removal from slaughterhouse wastewater in intermittently aerated sequencing batch reactors

The effect of aeration rate on nutrient removal from slaughterhouse wastewater was examined in two 10-L laboratory-scale sequencing batch reactors (SBRs-SBR1 and SBR2) operated at ambient temperature. The contaminants in the slaughterhouse wastewater had average concentrations of 4,000 mg chemical oxygen demand (COD) L(-1), 350 mg total nitrogen (TN) L(-1) and 26 mg total phosphorus (TP) L(-1). The duration of a complete SBR operation cycle was 8 h and comprised four operational phases: fill (7 min), react (393 min), settle (30 min) and draw/idle (50 min). During the react phase, the reactors were intermittently aerated four times at 50-min intervals, 50 min each time. DO, pH and oxidation-reduction potential (ORP) in the reactors were real-time monitored. Four aeration rates-0.2 L air min(-1) in SBR1 for 70 days, 0.4 L air min(-1) in SBR1 for 50 days, 0.8 L air min(-1) in SBR2 for 120 days and 1.2 L air min(-1) in SBR1 for 110 days-were tested. When the aeration rate was 0.2 L air min(-1), the SBR was continuously anaerobic. When the aeration rate was 0.4 L air min(-1), COD and TP removals were 90% but TN removal was only 34%. When the aeration rates were 0.8 and 1.2 L air min(-1), average effluent concentrations were 115 mg COD L(-1), 19 mg TN L(-1) and 0.7 mg TP L(-1), giving COD, TN and TP removals of 97%, 95% and 97%, respectively. It was found that partial nitrification followed by denitrification occurred in the intermittently aerated SBR systems.