Formation regularity of the inorganic by-product chlorite in killing algae with chlorine dioxide

This paper aims to study the generating regularity of the inorganic by-product chlorite in the algae preoxidation with chlorine dioxide in drinking water processing.For this purpose,we have made an investigation over the generating regularity of chlorite under the conditions of different dosages of chlorine dioxide,contact time and pH.We have also studied the other influencing factors related to water quality,such as algal initial concentration,organic substances and ammonia nitrogen concentration on the generation of the by-product chlorite.The testing and investigation results show that the by-product chlorite increases with the increase of the dosage of chlorine dioxide.In addition,it is found that time is the key factor to influence the generation of chlorite.Actually,large amounts of chlorite would be resulted in 30 minutes.Two hours later,we may find that there would be generated chlorite which is 10 to 30 percent of chlorine dioxide,with an initial pH value beginning to generate the chlorite.The longer the contact time,the lower the initial pH would be.30 minutes later after a 10 minute reaction,the initial pH value would increase to 6.However,70 minutes later,the initial pH value would turn to be 3.9.Furthermore,the chlorite would gradually increase in the acidity condition while the pH value would change from low to high.Nevertheless,when the pH changes from neutral to alkalinity,little increase would be found of the chlorite in final analysis.But,when the algal chlorophyll-a concentration remains below 14.93 μg/L,no variation of the amount of by-product chlorite could be found with the initial algal concentration.However,when the algal chlorophyll-a concentration is greater than 14.93 μg/L,the chlorite tends to increase with the increase of the algal initial concentration.Though the organic matter is likely to promote the formation of chlorite,the chlorite wouldn't be found increasing with the increase of the concentration of the organic matter,which demonstrates a decreasing trend with the increase of the ammonia nitrogen concentration.And the residual chlorine dioxide is found decreasing with the time prolonging in the process of the formation of chlorite.Based on the regression analysis of the experimental data,the relation between the residual chlorine dioxide and the time to be elapsed seems to be a function of the power series in the generation of the by-product chlorite.