Methods of optimizing chlorammoniation processes on the basis of online water quality monitoring (experience of SUE «Vodokanal of St. Petersburg»)

Summary

Disinfection of water with chlorine, along with the filtration at water treatment facilities has been historically the oldest and therefore routine technological process. The practice of disinfection process control that has been developed at the facilities over many years is often based on not exactly justified, and sometimes on erroneous, decisions made in the past. The main reference points, as a rule, are only regulated parameters, i. e., residual chlorine concentration and microbiological indicators at the outlet of the facilities. Meanwhile, the location of the chemical injection points, initial concentrations of chemicals and the dosing rate are of key importance from the point of view of the technology efficiency, reliability and safety. Accuracy and efficiency of chemical concentration control, control of the chlorine binding efficiency in the process of water ammoniation are the decisive factors in the process automation. Traditionally and formally, production control programs are based on the laboratory methods developed back in the early twentieth century. At the same time, progress in analytical instrumentation provides for monitoring the process parameters of disinfection in real time mode. The results of pilot tests of optimizing chlorammoniation processes based on online water quality monitoring are presented. The tests were carried out at the Southern Water Treatment Plant of SUE «Vodokanal of St. Petersburg». The analysis of the laboratory methods for monitoring the concentration of active chlorine and nitrogen-containing substances from the point of view of ensuring a reliable assessment of the physicochemical processes of chlorammoniation has been carried out. An assessment of the capabilities of modern analyzers for improving the efficiency, accuracy and safety of methods for controlling the chlorammoniation process is given. Some significant events in the history of the development of water disinfection technology in Russia and in the world are given in the Introduction.

Key words

disinfection , free ammonium , chlorination by-products , chlorine demand , chemical concentration , optimal parameters and process efficiency , flow-through analyzer , online monitoring , automatic dosing system

Optimization of drinking water chlorammoniation process

Summary

Water disinfection is the most important function of the public water supply. Chlorammoniation used for this purpose has a number of advantages compared to the traditional chlorination. However, it sets raised requirements to the analytical control instruments which limit the automation potential. Different control parameters are considered in relation to their possible application for the automation of the disinfection process. It is shown that the best parameter indicative of the optimal conditions of the process is the concentration of free ammonium. To choose a method of measuring free ammonium under the conditions of chlorammoniation at the existing water supply facilities tests on monitoring free ammonium by different methods were carried out. The limitations of some laboratory techniques are shown together with the advantages of the method using a gas-selective electrode, particularly in automatic analysis. The method of free ammonium monitoring with the use of an automatic analyzer with a gas-selective electrode has a number of advantages: a clear criterion of the optimal process conditions; the lowest absolute error of the measurements; possible use of the method for the automation of chlorine (ammonium) dosing. The operational tests showed the efficiency of the given method of the process control, reliable operation of the analyzer and good repeatability in relation to the laboratory data.

Key words

water disinfection , chlorammoniation , free ammonium , gas-selective electrode , automatic analysis