Nutrient removal from slaughterhouse wastewater in an intermittently aerated sequencing batch reactor J.P. Li, M.G. Healy, X.M. Zhan * , M. Rodgers Department of Civil Engineering, National University of Ireland, Galway, Ireland Received 6 August 2007; received in revised form 31 January 2008; accepted 1 February 2008 Available online 21 March 2008 Abstract The performance of a 10 L sequencing batch reactor (SBR) treating slaughterhouse wastewater was examined at ambient tempera- ture. The influent wastewater comprised 4672 ± 952 mg chemical oxygen demand (COD)/L, 356 ± 46 mg total nitrogen (TN)/L and 29 ± 10 mg total phosphorus (TP)/L. The duration of a complete cycle was 8 h and comprised four phases: fill (7 min), react (393 min), settle (30 min) and draw/idle (50 min). During the react phase, the reactor was intermittently aerated with an air supply of 0.8 L/min four times at 50-min intervals, 50 min each time. At an influent organic loading rate of 1.2 g COD/(L d), average effluent con- centrations of COD, TN and TP were 150 mg/L, 15 mg/L and 0.8 mg/L, respectively. This represented COD, TN and TP removals of 96%, 96% and 99%, respectively. Phase studies show that biological phosphorus uptake occurred in the first aeration period and nitrogen removal took place in the following reaction time by means of partial nitrification and denitrification. The nitrogen balance analysis indi- cates that denitrification and biomass synthesis contributed to 66% and 34% of TN removed, respectively. Ó 2008 Elsevier Ltd. All rights reserved. Keywords: Intermittent aeration; Nutrient removal; Partial nitrification; Sequencing batch reactor; Slaughterhouse wastewater 1. Introduction In Ireland, there are currently 306 licensed slaughter- houses comprising 270 slaughterhouses licensed for the domestic market and 36 approved bovine export slaughter- houses (Howlett et al., 2005). Slaughterhouses produce high-strength wastewater (European Commission, 2005; Irish EPA, 2006). The amount of wastewater generated per cow is approximately 2 m 3 per day and mainly origi- nates in the rendering department and holding yards of slaughterhouses (Johns et al., 1995). In pig slaughter- houses, 1.6–8.3 m 3 of water per tonne of carcase is gener- ated (EC, 2005). Depending on whether preliminary treatment is carried out and its efficiency, the concentra- tions of contaminants in slaughterhouse wastewater can be variable, with suspended solids (SS), chemical oxygen demand (COD), total nitrogen (TN), and total phosphorus (TP) concentrations ranging 250–5000 mg/L, 1000– 20,000 mg/L, 150–10,000 mg/L and 22–217 mg/L, respec- tively (Fuchs et al., 2003; Cassidy and Belia, 2005; Del and Diez, 2005; Merzouki et al., 2005; Mittal, 2006). A ser- vice fee is normally charged for the treatment of slaughter- house wastewater in local municipal wastewater treatment plants. For large-scale slaughterhouses, on-site biological treat- ment is recommended by the European Commission to remove organic carbon (C) and nutrients before the waste- water is discharged to surface waters or local wastewater treatment plants (EC, 2005). The emission standards in Ire- land for slaughterhouse wastewater are: COD P 75% removal or 125–250 mg/L in the effluent; TN P 80% removal or 15–40 mg/L in the effluent; and TP P 80% removal or 2–5 mg/L in the effluent. The European Com- mission also recommends that sequencing batch reactors (SBRs) be amongst the best available techniques (BATs) for slaughterhouse wastewater treatment, as SBRs are capable of removing organic C, nutrients and SS from 0960-8524/$ - see front matter Ó 2008 Elsevier Ltd. All rights reserved. doi:10.1016/j.biortech.2008.02.001 * Corresponding author. Tel.: +353 91 395239; fax: +353 91 494507. E-mail address: xinmin.zhan@nuigalway.ie (X.M. Zhan). Available online at www.sciencedirect.com Bioresource Technology 99 (2008) 7644–7650