Development and implementation of a corrosion control algorithm based on calcium carbonate precipitation potential (CCPP) in a drinking water distribution system

摘要

Water corrosiveness depends mainly on the chemical factors of pH, alkalinity, Ca~(2+) concentration, dissolved oxygen, and total dissolved solids (TDS), and on the physical factors of temperature and flow velocity as well as pipe materials. The calcium carbonate precipitation potential (CCPP) control process and a simulated water distribution system (SWDS) were installed for a pilot-scale advanced water treatment process. The system was operated for 2 years. The CCPP control algorithm for anti-corrosion of a pipeline was developed and validated. The target CCPP value could be controlled by manipulating the pH and alkalinity with additions of sodium carbonate (Na_2CO_3) and carbon dioxide (CO_2) where enough calcium was present. The CCPP range of 0 ～ 4 mg L~(-1) was controlled reasonably to induce a calcium carbonate (CaCO_3) film on the surface of the pipeline, which provided the anti-corrosion effect. The proper range required of pH and alkalinity used to manipulate the range of 0 ～ 4 mg L~(-1) of CCPP was 8.0 ～ 8.3,70 ～ 100 mg L~(-1) as CaCO_3 when the Ca~(2+) concentration was in the range of 60 ～ 80 mg L~(-1) as CaCO_3, respectively, in this research. The effect of corrosion control was demonstrated by reduced iron and zinc concentrations released from the pipe material. This result might indicate the presence of the CaCO_3 film and the efficacy of its anti-corrosion effect. However, the simple proportional integral derivative (PID) controller's sensitivity seemed to be in need of further improvement.