Online Control Of Chlorite In Chlorine Dioxide Byproducts In Drinking Water

Due to more and more organic substances and algae in the raw water,which increase the load on traditional water treatment processes,resulted in deterioration of effluent water quality.Pre-oxidation treatment units are usually necessary added to solving the problem for meeting drinking water quality standards.Chlorine dioxide pre-oxidation technology is favored for its high efficiency and broad spectrum.However,the inorganic byproducts?chlorite and chlorate?limited its widespread use.Therefore,it was critical for controlling inorganic by-products through the application of chlorine dioxide pre-oxidation technology.Recently,the research on the control of inorganic by-products is mainly focus on post-generation removal and combining other disinfectants to removing.However,there is little research on timely and effective control methods.Therefore,this research intends to study the relationship between the production of inorganic by-products of chlorine dioxide and the quality of raw water,in order to achieve a new technical solutions which through controlling the formation of inorganic by-products by online dosing chlorine dioxide based on the quality of raw water and to control the formation of inorganic by-products of chlorine dioxide.The precursors generated by chlorine dioxide by-products were screened by beaker experiments.The results showed that Fe²⁺,Mn²⁺,organic matter(characterized by UV₂₅₄)and algae?characterized by chlorophyll a?in the raw water were the main substances that caused the formation of inorganic by-products.The main matter of inorganic by-products was chlorite.Chlorite production occured mainly during the first 10 minutes of reaction contact.When the concentration of ferrous ions in the water is more than 0.5 mg/L,the concentration of chlorophyll a is more than 150?g/L,or the UV₂₅₄is greater than 0.143,there is a possibility that the effluent standard exceeds the maximum limit?700?g/L?.The two-factor factorical analysis was performed on the precursors of the selected inorganic byproducts.The results showed that there was no significant interaction between other factors on generating chlorite except Fe²⁺and Mn²⁺.Above,the chlorine dioxide dosage and the chlorite production prediction model?reservoir correction?were constructed:[ClO₂]_??=1.22[Mn²⁺]+1.32[Fe²⁺]+0.33[COD_Mn]+0.009[Chla]+0.35&[ClO₂^-]=897.14[Mn²⁺]+894.52[Fe²⁺]+221.96[COD_Mn]+4.20[Chla]+87.06.The modified model linearly fits the predicted and measured values of the reservoir water and the water in the plant to determine the coefficient R²>0.9,which mean better prediction effect than before.According to the model established,an on-line control system for chlorine dioxide by-products was built and applied to the pilot process.The results showed that compared with the conventional system?based on Remaining carbon dioxide?,the on-line control system had more lower dosing the amount of chlorine dioxide,which was reduced by10.7%,and the produced chlorite,which was reduced 12.1%.There was a little difference in removing conventional pollutants.The predicted value of the system model for the generation of chlorite after pre-oxidation was higher than the measured value.The linear relationship between the two coefficients of determination R²=0.85,after the correction R² achieving 0.92,which mean having a good predictive effect.It showed that this system can be applied to actual water bodies such as surface Class III water represented by the source water of Shenzhen.The relevant water quality indicators were:ammonia nitrogen content 0¹ mg/L,permanganate index 0⁶ mg/L,chlorophyll a content 0⁵0?g/L,pH from 6 to 9,the turbidity is from 1 to 22 NTU,and UV₂₅₄is 0 to 0.05 in surface waters.