Contents lists available at ScienceDirect Journal of Water Process Engineering journal homepage: www.elsevier.com/locate/jwpe Performance verification of the photocatalytic solar water purification system for sterilization using actual drinking water in Thailand Nobuaki Negishi a, ⁎ , Chamorn Chawengkijwanich b , Nuttaporn Pimpha b , Siriporn Larpkiattaworn c , Tawatchai Charinpanitkul d a National Institute of Advanced Industrial Science and Technology, Onogawa 16-1, Tsukuba 305-8569, Japan b National Nanotechnology Center, 111 Thailand Science Park, Phahonyothin Road, Khlong Nueng, Khlong Luang, Pathum Thani 12120, Thailand c Thailand Institute of Scientific and Technological Research, 35 Mu 3 Tambon Khlong Ha, Amphoe Khlong Luang, Changwat, Pathum Thani, 12120, Thailand d Chulalongkorn University, 254 Phyathai Road, Patumwan, Bangkok 10330, Thailand ARTICLE INFO Keywords: Photocatalyst Solar Water purification Field test Bacteria ABSTRACT Evaluation of a simple photocatalytic solar water purification system to explore its feasibility as well as problems in purifying raw water under actual conditions was carried out in Chaing Ja Sai village, Chiang-Rai Province, Thailand. The maximal contamination level of bacteria in drinking water (water source is spring water without treatment) in the village was around 400 cfu/mL. We constructed the portable type solar water purification system with TiO 2 -coated silica gel packed in a series of connected Pyrex glass tubes with total 13-meter length. Water was fed into the purification system in one-passing at a flow rate of 2.5 L/hr under gravity from 8 A.M. to 5 P.M. and sampled every hour. Consecutive field tests were carried out over three days under solar irradiation. Significantly, the coliform and general bacteria contents in the water decreased from several hundred to a few cfu/mL under sunny conditions. The fluctuation profile of the coliform and general bacteria was observed to be approximately analogous to the UV-A intensity profile. These results show that the photocatalytic solar water purification system could be effectively employed to eliminate coliform and general bacteria, resulting in the reduction of the risk of infectious diseases due to contaminated drinking water. 1. Introduction Improvement of drinking water conditions is a pressing issue throughout the developing world. Presently, 800 million people worldwide do not have access to safe water and a solution to this problem is urgently required [1–3]. Thus far, various water purification systems and technologies have been proposed, however, the means to obtain a safe supply of drinking water generally requires great cost and labor. The main problem in developing countries is contamination of drinking water by bacteria. At present, membrane technologies such as a microfiltration membrane (MF), ultrafiltration membrane (UF) and reverse osmosis membrane (RO) to eliminate bacteria are considered the most practical from the reason of high and stable performance [4]. However, the initial and running costs for such membrane systems are high, and it is difficult that low-income group purchases these mem- brane filtration systems in developing countries. In recent years, rela- tively low-cost membrane filtration systems for developing countries have been employed with notable results [5,6]. On the top of that ceramic filters have also been applied for such filtration systems although they themselves are not able to separate bacteria so that Ag is loaded onto the filter [7]. However, one of the problems of these membrane system is the lifetime of the products such as fouling. In contrast to the high cost of membrane technology is the low-cost SODIS (solar disinfection) method which is considered the most facile ster- ilization technique. The principle behind the SODIS method depends on irradiation of PET-bottled water by the UV light in sunlight to increase its temperature [8]. However, a long solar irradiation time is required and users have had difficulty with its implementation [9]. Against these backgrounds, photocatalytic drinking water purification technology is focused on. The idea of photocatalytic water purification exists from long ago and many research results have been reported from 1980 to 1990 [10–13]. Subsequent research on drinking water sterilization by pho- tocatalysis [14,15] and references on photocatalytic sterilization in the aqueous phase targeting drinking water purification have also been published [16]. Photocatalytic water purification technology looks ex- cellent technology because the light source is possible to use solar light, and the theoretical life-time of TiO 2 photocatalyst is almost eternal. https://doi.org/10.1016/j.jwpe.2019.100835 Received 12 February 2019; Received in revised form 3 April 2019; Accepted 13 April 2019 ⁎ Corresponding author. E-mail address: n-negishi@aist.go.jp (N. Negishi). Journal of Water Process Engineering 31 (2019) 100835 2214-7144/ © 2019 Elsevier Ltd. All rights reserved. T