[pp.135-140]

‹Research Report›Effect of Treated Sewage Effluent on the Dissolved Zinc Concentration in Urban Rivers in

Hiromi KOBORI and Young-Sik HAM （Musashi Institute of Technology）

Abstract:
In order to clarify the effect of treated sewage effluent (TSE) on Zn concentration of urban rivers, this study has statistically analyzed Zn concentrations at 72 points of 4 main urban rivers (Tsurumi, Sakai, Katabira and Ohka Rivers) and 14 points of entry of TSE in Yokohama City, Central Japan. Although the Zn were undetectable levels in Katabira and Ohka Rivers without TSE, Zn concentrations in the Tsurumi and Sakai Rivers ranged from 0 to 0.04 mg L−1, partly exceeding the maximum allowable level (0.03 mg L−1) for Zn according to the ecological water quality criteria of Japan. Zn concentrations upstream of TSE entry points were significantly different from concentrations downstream of these entry points in both the Tsurumi and Sakai Rivers. In addition, the Zn concentrations downstream in both rivers were strongly correlated with the Zn concentrations of TSE. By testing to determine which parameter (Zn of TSE, downstream pH, COD or temperature) had more significant effects on downstream Zn concentrations, we developed a highly useful model pairing multiple regression analyses (MRA) with adjusted coefficient of multiple determination (R2) of 0.667 (F4,10 = 6.002, P = 0.027). This model estimates that the Zn concentration of downstream was significantly affected by that of TSE with a standardized regression coefficient of 0.820 (P = 0.024).

Key Word:
ecological water quality criteria, treated sewage effluent, urban river, zinc

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