A study of the effects of ozonation and flow on the corrosion of cement mortar lined ductile iron water pipe.

摘要

The objective of this study was to identify the effects of ozone and flow on corrosion of cement-mortar lined ductile iron pipe. Considerable research has been devoted to understanding the effects of water-chemistry on iron pipe corrosion and fouling. Less emphasis has been placed on the erosive effects of flow.;This research is focused on the effects of two factors, ozone addition and flow rate, on pipe corrosion. A two factor, three-level, design of experiment containing nine test levels was run. The base line of factors such as pH, hardness and fluoride concentration were determined at the beginning of each test run. Temperature was controlled in the range of 20 +/-5°C (degrees centigrade) during each test run.;A closed recycle system was used to observe changes over time and to simulate actual field conditions. The circulating pump and ozone generator run times were set to simulate normal water usage in a distribution system, 12 hours on and 12 hours off during a 24 hour period. Each test point was run for two weeks and then replicated for a second two weeks.;Corrosion was observed by the analysis of dissolved iron in the system. Hardness, measured as calcium carbonate, fluorine, and chlorine levels were measured at the beginning and end of each run. Visual inspection of the pipe was performed at the end of the test series.;Iron corrosion increased with the increased addition of ozone. The significance of corrosion was assessed using ANOVA. Flow was observed to enhance the effect of corrosion at the rates studied. The increase in dissolved iron was attributed to the corrosive effects of co-products such as NOx and ammonia, produced by the ozone generator. Both ammonia and nitrite appeared to be rapidly oxidized to nitrate with a lowering of pH in the system.;Results of this work show that co-products of ozone generation, such as nitrate, need to be evaluated when ozone is used for pretreatment or disinfection. In addition boundary layer thickness should be calculated as a means of evaluating erosion effects. As a result of this study, both ozone and flow were found to have statistically significant effects on iron corrosion. This study has tied together the areas of ozone chemistry and flow dynamics with a practical experimental design.