WHY ACCURATE DISSOLVED ORGANICS MEASUREMENT MATTERS FOR OPTIMUM DRINKING WATER QUALITY
Natural Organic Matter (NOM) exists in all sources of fresh water and, if not properly removed, can affect the effi ciency of potable water treatment and the quality of the treated water. In this article, Julian Edwards, Product Manager for Continuous Water Analysers for ABB Measurement & Analytics in the UK, explains why the removal of NOM is crucial for optimizing process effi ciency and personal safety. He also looks at for the best ways to accurately measure NOM levels throughout the potable water treatment cycle.
What is NOM and why is it a problem?
NOM is caused when decayed vegetation mixes with water. It’s a problem that must be closely monitored and controlled throughout potable water treatment processes to ensure the end result meets the highest levels of quality and safety for human use and/or consumption.
Most NOM is comprised of humic and fulvic substances that in most cases not in involving industrial pollution originates from soil coupled with decomposing plants and animals that enter streams, rivers, and lakes as well as aquifers. These substances are responsible for turning water from yellow to brown. They also provide an environment for bacteria and fungi to thrive in a way that can add to microbial growth in a water distribution system. Failure to adequately remove these NOM can increase the risk of pathogen-induced diseases, unpalatable taste and oppressive odor.
The importance of effective treatment
The central challenge for water utilities is their ability to accurately detect the wide variations of potential issues in the vast quantities of water passing through their plants to enable effective treatment. To protect people from the harmful effects of trihalomethanes (THMs), there must be highly accurate detection methods in place. Previously, to detect THMs required costly and time -consuming laboratory tests.
Various NOM elements are usually removed during the coagulation, fl occulation, and fi ltration stages of the water treatment process prior to the fi nal chlorination treatment. It is particularly important to remove humic substances in particular prior to chlorination because any remaining NOM can chemically react with the added chlorine to create undesirable disinfection by-products (DBPs) such as. THMs are known as possibly carcinogenic by-products that can be formed when organic material in water reacts with chloramines. Therefore, if pH and temperature conditions combine in the right recipe, a reaction
with the disinfectant used to make the water safer can potentially have the opposite effect of making it more detrimental to health.
For example, the presence of THMs in drinking water has been linked to heart, lung, kidney, liver, central nervous system damage and bladder or colorectal cancer. Several studies have also associated high levels of THMs in drinking water with an above average risk of miscarriages. Because of this, THM levels in public water supplies are strictly controlled and the controls are getting even tighter to ensure that THM levels in public water supplies remain within demonstrably safe limits.
To achieve that, water treatment processes must be able to maximize the removal of NOM safely, effi ciently, and consistently from water sources. To minimize the risk of DBP formation, utilities use modifi ed conventional processes such as enhanced coagulation and softening to ensure that organic materials are dissolved and reduced to levels that fall within indisputably safe limits. Many processes also use an activated carbon stage as an additional means capturing any dissolved organic matter that may escape processing during the coagulation stage.
The benefi ts of continuous online monitoring
Any issues with water treatment must be caught and resolved early to ensure public safety and health. Continuous on-line monitoring is essential to provide early warnings of any changes
AV400
to the treatment process, enabling timely and well-informed decision-making. Until recent years this testing was done using manual means, either in the fi eld or at processing facility. Quality control was broadly maintained, but any issues were slow to materialize until a potential hazard had been identifi ed through visual inspection or an incidence of ill health. This level of manual process control is not sustainable given today’s demands Potentially important events that must be identifi ed and rectifi ed immediately to preserve safety can be missed, and any manual test results will only be indicative of a particular moment in time rather than the present circumstances.
Tests done in the present must offer immediate and accurate results. And when it comes to detecting the presence of dissolved organics in raw water throughout the range of potable water treatment processes, there are two methods that can be used, specifi cally colour and UV detection.
Colour monitoring
Colorimetric measurement is, as the word suggests, the observation of colour as a measurement of a chemical in a solution. Colour determines the levels of either the absorption or concentration of a certain chemical based on the degree of colour depth and change and the ability of light to pass through it. With the exception of organics monitoring, many of the substances that need to be measured are colourless because
12TH & 13TH OCTOBER | TELFORD, UK
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