BANDANA MAHTO is pursuing her Ph.D. from Indian Institute of Technology, Kharagpur. She is currently working as Assistant Professor in the department of Civil Engineering, B.I.T. Mesra, Patna campus, India. SUDHA GOEL is currently Associate professor, Department of Civil Engineering, I.I.T. Kharagpur, India. She has completed her MSE and Ph.D. in Environmental Engineering from The Johns Hopkins University, Baltimore, USA.
Cases of coliform growth have been reported in drinking water distribution systems (Fass et al. 1996; Sibille et al. 1998; Boualam et al. 2002; Mahto and Goel, 2008). Iron and magnesium as important inorganic nutrients are known to affect bacterial growth and survival under oligotrophic conditions (Goel and Bouwer, 2004). Corrosion of pipes can lead to elevated levels of iron in the system while magnesium is present in fairly high concentrations in ground waters. E. coli were grown in 1:100 nutrient broth solution and examined for the effect of varying iron and magnesium concentrations on bacterial growth and response to chlorine disinfection in the oligotrophic environments of drinking water distribution systems. Growth rates of E. coli increased with increase in concentration of inorganic nutrients such as Fe3+ and Mg2+. However, no growth of E. coli was observed in the presence of Fe3+ at a concentration of 0.05 mM. Growth and inactivation rates were negatively correlated for both inorganic nutrients tested, i.e., Fe3+ and Mg2+ implying that bacteria grown in the presence of inorganic nutrients are more resistant to chlorine disinfection and can survive in oligotrophic environments like drinking water distribution systems. Natural die-off rates also correlated negatively but strongly with growth rates (R2 > 0.9) implying that higher growth rates resulted in lower natural die-off rates. Correlation co-efficient values for growth and inactivation rate of E. coli in presence of Fe3+ ion and Mg2+ ion were found as r > 0.9 and r > 0.7 respectively.