Grain-size distributions of both the underflow and overflow from the hydrocyclone circuit with hydrocyclones C1 and C3 are studied both in the full-scale plant and bench-scale plant. The separation performance of a hydrocyclone is expressed by a separation curve representing the probability of a particular particle ending up in either the underflow or the overflow. A particular configuration of a hydrocyclone circuit with C1 and C3 can benefit both separation performance and production of clean, good quality sand to minimize misplacement of fine particles between sand and sludge (fine fraction). After the first cycloning step, the separated flow with fine particles (C1 overflow) may still contain sand particles which increase an amount of residue. Cyclone C3 is included in the cycloning process to remove any sand fraction still present in the sludge. This can considerably reduce further the landfill cost.
A mathematical model was developed to simulate the steady-state grain-size distribution of the C1 underflow (UFC1), which represents the clean sand, in the hydrocyclone circuit with C1 and C3. It was shown that the grain-size distribution of UFC1 is better described by the presented model, which helped determine an amount of clean sand and the cost of soil washing for contaminated soil. The concept and numerical formulas of the presented model are introduced and discussed.

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Bromate ions exist in drinking water are by-products of ozonation of bromide-containing water and are also found in sodium hydrochlorate which is used as a disinfectant. Bromate ions cause the renal cell tumors in rats fed within aqueous bromate. In this paper, we present an overview of bromate ion concentrations in the Tama area of Tokyo, Tama River water, sewage treatment water and drinking water. Several samples of surface water and sewage treatment water were analyzed for bromate ion content from November 2002 to March 2003. Bromate ions were not detectable in the upper part of the mains tream and two tributary streams of the Tama River. However, in the mid-regions of the Tama River, the bromate ion concentration increased to 0.7-1.8 μg·l^-1. Sewage treatment water samples from six treatment plants had bromate ion concentrations of approximately 0.1-6.3 μg·l^-1, and we calculated that 0.7-1.7 kg of bromate ion flow into the Tama River daily. We also determined the concentrations of bromate ions in 449 drinking water samples provided by the Bureau of Waterworks of Tokyo, other waterworks in the Tama area and water supplies for individual use. Among these samples, bromate ions could not be detected at concentrations greater than 10μg·l^-1.

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The chemical composition of fine fractions (<63μm) of street dust in Nagoya City, central Japan, is examined to obtain information on the nonpoint pollution load of river and sewer systems in urban areas. The results show that the fine fractions of street dust have more C, Fe, Mn, Ca, Mg, P, Cr, Zn, Sb, As, Hf, and Au than hypothetical background level. Additionally, Ti and Co are also derived significantly from anthropogenic sources. Among these “enriched elements”, C, Ca, P, Zn and Ti are likely derived from tire and asphalt dusts, whereas Fe, Mn, Co and possibly Cr appear to be incorporated into street dust as iron alloy particles. These metallic iron particles are also considered to be derived from parts of vehicles such as their bodies and brake disks.

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