Research Of Iron Release Forecast Model Based On Oxidation Reduction Potential

As a common measurement in water treatment, oxidation reduction potential (ORP) is used to characterize the oxidation capacity of solution. It has many advantages such as easy to develop, low cost, simple operation method, and rapid and accurate test results.The object of this paper is to complete the theory systems of iron release from corroded iron pipes in drinking water distribution systems, and set up a forecast model about iron release. Relationships between ORP and iron release was investigated. Then a new ORP mechanism of iron release was analyzed and presented, and a new iron release prediction model based on the mechanism was established. Eventually the prediction model was validated in pilot-scale drinking water distribution systems.At present iron release can be divided into oxic and anoxic conditions. However, by lack of quantitative research, it doesn't establish the corresponding mathematical model and it isn't used to predict iron release. This paper examined correlations between iron release and ORP under different factors and levels (such as dissolved oxygen, free chlorine, monochloramine, pH, temperature, chloride, sulfate) using bench-scale pipe reactor made of two different service age corroded pipes. And according to results, iron release prediction model based on ORP was established. Meanwhile, relationship between influence of iron bacteria on iron release and ORP was investigated.Results indicate that:1. ORP correlates with iron release, ORP would decease by the amount of released iron increasing; it also can identify oxic and anoxic conditions of iron release.2. This correlation isn't affected by changes of pipe scales and water quality.3. Consequently, ORP can assess risks of iron release under complex conditions. When ORP is below100mV, iron release seriously; However when ORP is greater than300mV, iron release is governed well.4. The effect of iron bacteria on iron release is influenced by ORP. When ORP is greater than100mV, the influence of iron bacteria on iron release is negligible. However, for ORP values lower100mV, iron bacteria would increase iron release. Based on these results and previous work, this paper puts forward the ORP mechanism of iron release. The ORP mechanism indicates that:1. The rate of reaction rate of ferrous to ferric is decided directly by ORP; Increasing ORP can enhance the reaction rate and reduce amount of iron release.2. If ORP is lower than the critical value, ferrous will not be oxide, iron release will be in anoxic conditions.3. Iron concentrations increasing would reduce ORP values. According the ORP mechanism the ORP prediction model of iron release was set up. The model that iron release and ORP accords with exponential model. And the risk of iron release could be evaluated by ORP values.The model was verified in pilot-scale drinking water systems. The results indicate that the accuracy of model is well validated in different factors such as seasons, pipes, locations and flow conditions.