LSI characteristics based on seasonal changes at water treatment plant of Korea

Abstract

Corrosion indices have a historical as well as practical relevance in assessing drinking water treatment systems. The Langelier saturation index (LSI) is commonly used as a corrosive index for drinking water. The systematic regulations including LSI as guideline for reducing corrosion have been established in Korea since 2011. However, studies in terms of seasonal changes are still required even though there are data to analyze corrosion indices. In this paper, LSI, Ryznar stability index (RSI), and aggressiveness index (AI) values of water produced by Seongnam water treatment plant (S. WTP) were analyzed and compared. RSI gives information on corrosion progress and scale in the pipe. AI is a simplified index of LSI, and both indices are based on calcium carbonate saturation. Two-stage control of the LSI value as a measure of the corrosive tendency of water is an alternative proposal. Temperature, pH, alkalinity, calcium hardness, and TDS were measured to evaluate water corrosiveness. Results for one-year period (2009) show that LSI varies in the ranges from –1.3 to –1.8, RSI varies from 10.2 to 10.9 while AI varies from 10.1 to 10.8. LSI increased by 4.3 times during the rainy season (July–September) but not during other seasons. During the same period, RSI increased up to 4.5%, while AI decreased to 3.1%. These values show that the water produced at S. WTP is very corrosive. One potential reason for the increase in LSI is that alkalinity and calcium hardness decrease to 20 and 9%, respectively, during heavy rainfall.