Modelling temperature effects on ammonia-oxidising bacterial biostability in chloraminated systems Dipok Chandra Sarker a , Arumugam Sathasivan a, b, ⁎, Cynthia A. Joll c , Anna Heitz c a Department of Civil and Construction Engineering, Curtin University, GPO Box U1987, Perth WA 6845, Australia b School of Computing, Engineering and Mathematics, University of Western Sydney, Locked Bag 1797, Penrith NSW 2751, Australia c Curtin Water Quality Research Centre, Curtin University, GPO Box U1987, Perth WA 6845, Australia HIGHLIGHTS ► Exponential curve does not fit the variation of specific growth rate with temperature. ► A model proposed by Ratkowsky et al. (1982) is adopted for sub-optimal temperature. ► A quadratic equation describes the specific growth rate beyond sub-optimal temperature. ► A biostable residual concentration greatly varies with temperature. ► The relationship was validated against full and laboratory scale results between 13-30 °C. abstract article info Article history: Received 4 October 2012 Received in revised form 10 February 2013 Accepted 16 February 2013 Available online 26 March 2013 Keywords: Temperature effects Free ammonia Ammonia-oxidising bacteria Nitrification Biostability curve Biostability The biostability concept has been successfully used to predict the onset of nitrification in drinking water dis- tribution systems, but in certain cases deficiencies have been observed in the predictions, indicating that modifications to parameters were needed. At the biostable disinfectant residual concentration (BRC), the rate of ammonia-oxidising bacterial (AOB) growth due to the substrate (free ammonia) and the rate of inac- tivation due to the disinfectant are balanced. Growth and inactivation rates vary greatly with temperature, but temperature is yet to be considered in the biostability equation. In this paper, two separate novel models are proposed which take into account the temperature effects on the biostability equation. First, a novel model of specific growth rate variability with temperature was shown to be valid for different bacterial spe- cies. Then, the biostability model was modified and validated for ammonia-oxidising bacterial activity using data collected from laboratory and full-scale distribution systems. The proposed model has two important uses: while the specific growth rate model and biostability model can be widely adopted for many microbes, the biostability model for AOB also has the potential to aid water utilities in disinfectant residual manage- ment throughout yearly temperature variations. © 2013 Elsevier B.V. All rights reserved. 1. Introduction Microbial chloramine decay, including that due to nitrification, presents a major challenge to water utilities in the management of chloraminated distribution systems. Nitrification, a microbial conver- sion of ammonia to nitrite, by ammonia-oxidising bacteria (AOB), and then to nitrate, by nitrite-oxidising bacteria (NOB), occurs over a pH range of 6.6 to 9.7 (Odell et al., 1996). Nitrification usually occurs at temperatures above 15 °C, but it can also occur at lower temperatures (Lipponen et al., 2004; Wilczak et al., 1996) in chloraminated distri- bution systems. Once nitrification commences, controlling or overcoming it is very difficult even by increasing the chloramine concentration up to 8.0 mg-Cl 2 L -1 through re-chloramination (Cunliffe, 1991; Skadsen, 1993). Chloramine decays at a much faster rate under nitrification conditions (Sathasivan et al., 2008) which may be due to soluble mi- crobial products produced after the onset of nitrification (Bal Krishna and Sathasivan, 2010; Bal Krishna et al., 2012). It is therefore impor- tant to understand the mechanism of nitrification and the point at which the onset of nitrification occurs, so that appropriate measures can be taken in advance. The onset of nitrification has been defined differently by different authors. Pintar et al. (2005) suggested that chloramine concentration was an appropriate indicator to judge the start of this process. Sathasivan et al. (2008) reported that a sudden increase in the concentration of nitrite, a drop in chloramine residual Science of the Total Environment 454–455 (2013) 88–98 ⁎ Corresponding author at: School of Computing, Engineering and Mathematics, Univer- sity of Western Sydney, Locked Bag 1797, Penrith NSW 2751, Australia. Tel.: +61 02 4736 0941; fax: +61 02 47360833. E-mail addresses: d.sarker@postgrad.curtin.edu.au (D.C. Sarker), a.sathasivan@uws.edu.au (A. Sathasivan). 0048-9697/$ – see front matter © 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.scitotenv.2013.02.045 Contents lists available at SciVerse ScienceDirect Science of the Total Environment journal homepage: www.elsevier.com/locate/scitotenv