低濃度残留塩素時の海生生物付着事例について

Abstract

Cooling efficiency at coastal industrial plants with seawater-based cooling systems is often reduced due to water flow blockage caused by marine biofouling. Maintenance of a residual chlorine concentration of 0.1–0.3 mg/L for 18 h/day is known to be an effective countermeasure, but it is often impossible to maintain so high a concentration because of chlorine-induced corrosion and/or environmental considerations. There have been only a few reports examining the effects of low concentrations of residual chlorine, so we carried out a study to evaluate the marine biofouling potential at residual chlorine concentrations of 0.05 mg/L or less, and to identity any related problems. The study was conducted at a factory on the shore of Ise Bay, Japan, at which no residual chlorine was detected in the discharge water. For 63 days (27 Apr. to 29 Jun. 2010) we regularly observed the extent of marine biofouling on a coarse-mesh vinylon net placed parallel to the water flow inside a cooling-water pipe through which seawater with a total residual chlorine concentration averaging 0.055 mg/L (range: 0.02–0.12 mg/L) was run continuously. We also checked the condition of the net on 6 Dec. 2010 after 30 days of uninterrupted exposure to the water flow. In both cases, much biofouling was observed on the test net. Thus, low levels of residual chlorine, even when applied continuously, appear insufficient to prevent biofouling and an attendant reduction in cooling efficiency.