New measurement principle and basic performance of high-sensitivity turbidimeter with two optical systems in series

An outbreak of Cryptosporidium infection from tap water has triggered the implementation of stricter controls for the turbidity of filtered water in Japan. Accordingly, a growing number of water purification plants have begun to measure the number of particles, which is more closely correlated to this kind of protozoan than turbidity. With this background we have developed a high-sensitivity turbidimeter based on the particle counting method that supports both turbidity measurement and particle counting to realize a compact and low-cost monitoring system of filtered water. This paper explains the basic principles of the turbidimeter, which uses both forward-angle light scattering and light obscuration methods in series and determines the turbidity from particle counting by applying Mie's theory of light scattering. In basic experiments on turbidity standards such as kaolin solution and formazine solution, we verified that the turbidimeter could determine the particle counts and turbidity of filtered water with sufficient accuracy.