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.

Microcolumn test and model analysis of activated carbon adsorption of dissolved organic matter after precoagulation: effects of pH and pore size distribution.

Microcolumn adsorption experiments were conducted to generate breakthrough profiles of dissolved organic matter (DOM) remaining after coagulation treatment of a naturally colored surface water for three coal-based activated carbons (ACs) and four water pH levels. A plug-flow homogeneous surface diffusion model was applied to determine the intraparticle surface diffusivities of the DOM at different AC-pH combinations. It was found that, for all three ACs, the removal of DOM increased as pH decreased and the increasing extent changed with the ACs used. The pH dependency of the column performance seemed to be attributed more apparently to pH's capability in changing the zeta potential of AC particles. In addition, at all pH levels, the column performance varied markedly with the ACs used. Correlation analyses of the accumulated amounts of DOM onto all three ACs with corresponding pore volumes in several divided pore size regions clearly indicated that pores with sizes 30-100 A were more effective in adsorbing organic macromolecules. Furthermore, based on model simulations, the sensitivity of bed performance to equilibrium and kinetic parameters was quantified by conducting variance analyses with a four-way classification method.

Factors affecting the adsorption capacity of dissolved organic matter onto activated carbon: modified isotherm analysis.

Effects of aqueous phase Ca(II) concentrations and pH levels on the adsorption capacity of dissolved organic matters (DOMs) as well as the capacity dependency on the sources and types of DOMs and activated carbons (ACs) were examined. The Ca(II) effect was studied for three coal-based ACs having different pore size distributions (PSDs) and for three DOMs contained in three water samples. For each water sample, four working solutions prepared by adding different dosages of Ca(II) (0-1.5 mM) were used. For the water sample whose adsorption capacity was least affected by Ca(II), the effect of pH was subsequently examined for four water pH levels (pH = 5.5-10) and these three ACs. Isotherm data were analyzed in terms of a modified isotherm model selected from three models developed for normalizing isotherms of heterogeneous organic mixtures. The Ca(II) effect depended obviously on the DOMs used. For all three ACs, increasing Ca(II) greatly enhanced the adsorption capacity of a commercial humic acid. However, the capacity of the DOM in a naturally colored surface water source was much less affected and that of the DOM remaining after precoagulation was not affected. The DOM-Ca(II) interactions, rather than the AC-Ca(II) interactions, seemed to be the predominant mechanism that controlled the extent of the Ca(II)'s impact. Water pH greatly affected the adsorption of the surface water DOM remaining after precoagulation. This effect seemed to be attributed to pH's capability in changing ACs' charge characteristics reflected by zeta-potentials. The adsorption capacity increased as the water pH decreased and was well correlated as a function of pH and the volume of AC pores in sizes of 30-100 A. ACs having more pores in this size region generally exhibited larger adsorption capacities.