ISO TS 24522:2019 pdf free download – Event detection process: Guidelines for water and wastewater utilities.
A.4.1 Examples primarily for drinking water
A.4.1.1 General
There are a number of instruments and measurement methods that can provide useful information in event detection. The following examples are not exhaustive and others could be used.
A.4.1.2 Toxicity monitoring
The purpose of a toxicity monitoring system is not to detect each chemical substance, but to monitor the safety of drinking water in a holistic manner. Continuous biological monitoring enables rapid detection of toxic substances in water and can provide a real-time, online, early warning of contamination.
Toxicity is the ability of a substance to cause a living organism to undergo adverse effects upon exposure. These effects can include negative impacts on survival, growth, behaviour and reproduction. Toxicity tests are an attempt to measure toxicity in a sample by analysing the results that exposure produces on standard test organisms.
Toxicity testing in the realm of event detection can be a useful tool due to its ability to detect a wide variety of potential hazards. A variety of organism-based, enzyme system and other toxicity measuring systems are available.
— Toxicity tests are fairly adept at detecting chemical toxins, but they are, for the most part, ineffective against biological agents such as bacteria and viruses.
— Organism maintenance can be problematic.
— All toxicity-testing methods require knowledge of a baseline. Determining what the baseline is so that deviations can be detected requires time and effort.
— Some toxicity methods can be too sensitive when testing in the drinking water distribution network. Water treatment chemicals or simply common constituents of drinking water, such as trace metals that are not toxic to humans, can adversely affect them.
— The variable environment at the site of monitoring can be problematic in toxicity monitoring.
— Toxicity tests can be difficult to interpret.
A.4.1.3 Bulk parameter monitoring
Bulk parameter monitoring is the method of monitoring a number of common event parameters and then looking for anomalies that can be indicative of an event. These measurements can be compiled in the lab, in the field or with online instrumentation. A variety of instrument manufacturers have developed multiple-parameter performance monitors for both source water and water in the drinking water system. These systems encompass a diverse selection of different sensors and can be tailored to meet monitoring needs. Locally developed systems comprised of a few or many different sensors can be constructed and can be used in conjunction with results from other monitoring systems in an event detection system.
Decisions on which parameters to include in such a system are a matter of individual water utility choice. Parameters that are commonly part of such systems can include disinfectant residual (chlorine, where appropriate), pH, conductivity, turbidity and TOC (either conventional digestion or UV methods). Other parameters can be included if they fit the needs and capabilities of the water utility and address their concerns.
A.4.1.4 Gas chromatography
Gas chromatography methods are traditionally thought of as laboratory methods. Various manufacturers have modified gas chromatography methods to be online tools that work in a batch mode. Small, portable, gas chromatography methods are also available. One of the main benefits of this type of method is that, unlike toxicity and bulk parameter monitoring, it is not inferential in nature, but gives a true identification of the compounds present.
A drawback to this technique is the limited scope of compounds that are detected. Only volatile organics are amenable to being analysed by this method.
A.4.1.5 Ultraviolet absorbance and fluorescence
The tendency of various compounds to absorb light in the UV spectrum, and for some materials to fluoresce when exposed to this light, can be utilized as a detection mechanism.
Simple measurements of absorbance and fluorescence can be used, but various manufacturers have developed instruments that use algorithms to interpret the incoming absorption spectra to determine when a contaminant is present. These systems can detect organics that have an absorption or fluorescence signal in the wavelength range being monitored. The identification of a single substance or group of substances is limited to those that are detectable in the monitored spectrum and implemented in the set-up procedure.