Combined waters need special treatment

Mixing groundwater and surface water affects the disinfection process and needs careful monitoring, says Michael Strahand, general manager of ATI Europe

As global warming increases pressure on the world's water reserves, it is necessary to regulate water consumption - and in some cases limit water use altogether.

Recently, authorities worldwide have imposed limits on the use of groundwater, proposing increases in the use of surface water. Although this is an effective method of conserving water sources, the combination of ground and surface water can significantly affect the water disinfection process.

The most common method used for water disinfection is the use of either free chlorine or chloramine. With the recent introduction of limits on the use of groundwater, it is necessary to develop new techniques of monitoring water quality and in particular obtaining reliable measurements of ammonia, chlorine and chloramines.

Groundwater provides about one-third of public water supplies across England and Wales. Governments and environmental agencies are now investigating the current and future availability of groundwater, and have introduced a range of initiatives to limit over-consumption.

In addition to concerns over the availability of groundwater, there are significant issues with water quality when groundwater and surface water are mixed. In Europe, most drinking water production companies use chlorine as a disinfectant. It is added to water as chlorine gas, calcium hypochlorite or sodium hypochlorite. For drinking water preparation from surface water, chlorine is used as a primary disinfectant in most cases. But chloramine is often used for the disinfection of groundwater for drinking water.

When groundwater and surface water mix in the distribution system, the chlorine and chloramine disinfectants combine to form a residual substance which contains ammonia, free chlorine and monochloramine. As a result of the rise in the use of combined surface water and groundwater, it is essential that water treatment plants are able to carry out accurate monitoring of these chemicals in water to avoid any potential health consequences.

The increasing level of concern over water quality has affected the use of chloramines in the water disinfection process. Chloramine levels are already carefully monitored. But added concerns over mixing chloramines with free chlorine have resulted in the increased need to obtain reliable measurements of chlorine and ammonia in drinking water.

Water sources
This means that both incoming and outgoing water sources are monitored at each water storage facility to determine the concentrations of ammonia, monochloramine, and free chlorine.

Ammonia monitoring has traditionally been undertaken by automated versions of ammonia-selective ion electrodes, but these methods are geared towards laboratory applications. These conventional systems generally use expensive, complex and labour-intensive instruments, which are difficult to maintain, and often require external service contracts.

When using older monitors, it is often necessary to install a sanitary sewer at each treatment location to treat the reagents added during the monitoring process, which required safe removal and generated a significant cost. Due to the expense and unreliable nature of old monitoring systems, the need for reliable, safe, accurate instruments has never been higher. The development of new technology has enabled a completely new approach to simultaneous online monitoring of chloramines and ammonia in water which is simpler, cheaper and more stable than conventional monitoring equipment. With this technique, measurements of both ammonia and chloramine can be carried out on one instrument.

These new systems provide users with a monitor which is both simple to operate and economical to purchase. This technique has been adopted by Analytical Technology Inc (ATI) with the development of the new Q45N Dissolved Ammonia Monitor.

This system uses reaction chemistry to convert ammonia in a solution to a stable monochloramine compound, equivalent in concentration to the original ammonia level. The chloramine concentration is then measured with an amperometric sensor that responds linearly to chloramines, while eliminating interface from excess free chlorine in solution.

ATI says it is cheaper than conventional monitors, and that the new technology has the advantage of allowing direct re-injection of the water withdrawn for monitoring purposes back into the distribution system without the need for additional sewers.

According to the company, maintenance of the new monitors is simple and easily managed by local people. The new Q45N monitor can also be used with ATI's free-chlorine monitor to provide measurement of free chlorine, chloramines, free ammonia and total ammonia.

The Q45N system consists of a wall-mounted chemistry system, and an electronic display and alarm package. The chemistry system contains the necessary metering pumps to provide chemical addition to the sample and delivery of the sample to the sensing element. The electronic display and alarm package provides the user interface to the system. Ammonia concentration is displayed on a large-format LCD display with secondary display for other operating variables.

Governments worldwide
Authorities and governments worldwide are now investigating levels of water usage, and a range of initiatives are being developed in order to regulate and reduce water consumption. Concerns over the quality of groundwater and surface water have motivated water treatment companies to look for more reliable and effective methods of analysis, in order to avoid unsafe and unstable concentrations of chloramines, ammonia and chlorine levels in drinking water.

New technologies have led to the introduction of simple and accurate monitors for the effective measurement of these potentially unsafe by-products of water disinfection. These new technologies provide water treatment plants worldwide with a cost-effective alternative to conventional systems by lowering overall service costs, while maintaining high standards of drinking water quality.

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