ORIGINAL ARTICLE Disinfection of Waterborne Coliform Bacteria by Neem Oil Robert L. Matthews, 1 Michael R. Templeton, 2, * Sabitri K. Tripathi, 3 and Kiran Bhattarai 4 1 Water and Health Research Centre, Department of Civil Engineering, University of Bristol, Bristol, United Kingdom. 2 Department of Civil and Environmental Engineering, Imperial College London, London, United Kingdom. 3 Department of Science and Humanities; 4 Department of Civil Engineering; Nepal Engineering College, Bhaktapur, Nepal. Received: February 10, 2009 Accepted in revised form: June 5, 2009 Abstract This study assessed the ability of Neem oil to disinfect an Escherichia coli isolate in pure laboratory-grade water and total and fecal coliform bacteria in two unfiltered surface waters. Neem oil doses as low as 2.13 g  L 1 with 5 min of mixing time achieved high levels of inactivation of the E. coli in pure laboratory-grade water (>99% inactivation). However, the disinfection of total and fecal coliforms in the unfiltered surface waters was variable and limited to <70% inactivation typically. Increasing the Neem oil dose and mixing time generally resulted in an increase in the mean inactivation of total coliform bacteria but not always of fecal coliform bacteria. The inactivation of total coliforms was consistently greater than the inactivation of fecal coliforms, suggesting a potential range of sensitivities to Neem oil among coliform bacteria. Reduced effectiveness of the Neem oil in the unfiltered surface waters compared to the pure laboratory-grade water suggests a possible interference by natural water constituents (e.g., suspended particles, dissolved organic matter), which may inhibit the anti- bacterial potential of Neem oil, or that naturally occurring bacteria are more resistant to the antimicrobial effects of Neem oil. Overall, Neem oil was found to be insufficient on its own for use as a disinfectant of potable water; however, further investigation is recommended into the performance of Neem oil disinfection when combined with pretreatment steps (e.g., sand or cloth filtration) and into methods for concentrating the active antimicrobial ingredients of Neem oil to form more potent disinfectant solutions. Key words: disinfection; coliform; Neem; essential oils; drinking water; bacteria Introduction T he Moringa oleifera seed is an example of a naturally occurring material that is effective as a means for treating water and has been successfully adopted for use in develop- ing countries (e.g., Sudan) (Sutherland et al., 1989). The seed contains substances that act as a coagulant and thereby assist to settle out particles and pathogens from water. In India, lentils and seeds from the Tamarind tree and several other plants have also been proven as effective coagulants for wa- ters with high turbidity (Schulz and Okun, 1984). Comparatively little is known about the potential existence of natural disinfectants (i.e., substances with the ability to kill=inactivate pathogenic micro-organisms), even though many herbs and plant extracts are used in traditional medi- cine and as pesticides in developing countries (Ketkar et al., 1995; Ross, 1999). One such plant, the Neem tree (Azadirachta indica), was selected as the focus of this study; however, there are many other natural essential oils that have been reported to have antimicrobial properties (e.g., tea tree oil, eucalyptus, thyme) (Hammer et al., 1999; Lambert et al., 2001). The Neem tree grows widely in arid tropical and sub- tropical areas around the world (Schmutterer, 1995). The medicinal properties of components of the Neem tree have been known in India for thousands of years; it is referred to in Sanskrit texts as ‘‘Arishtha,’’ the reliever of sickness (Ketkar et al., 1995). Traditional medical uses of Neem products have covered a vast range of illnesses, from leprosy to intestinal worms. Neem leaf tea is also often used as a treatment for the symptoms of malaria and for diarrhoea (Shultz et al., 1992). Extracts from dried leaves have been reported to be effective in the treatment of skin infections such as ringworm and scabies (Biswas et al., 2002). A substantial number of antibacterial active compounds have been isolated from various parts of the Neem tree. The most active compound with regard to pest and insect control is thought to be azadirachtin (Schmutterer, 1990; Eppler et al., 1995), while nimbidin extracted from seed oil has been re- ported to exhibit strong antibacterial properties (Biswas et al., 2002). The antimicrobial components of essential oils gener- ally consist of a large group of mainly terpenoid compounds, *Corresponding author: Department of Civil and Environmental Engineering, Imperial College London, London, United Kingdom, SW7 2AZ. Phone: þ44(0)2075946099; Fax: þ44(0)2075946124; E-mail: m.templeton@imperial.ac.uk ENVIRONMENTAL ENGINEERING SCIENCE Volume 26, Number 9, 2009 ª Mary Ann Liebert, Inc. DOI: 10.1089=ees.2009.0058 1435