Surface World December 2018 Surface World Magazine December 2018 - Page 68

PRODUCTS & PROCESSES The role of total organic carbon analysis in water treatment By Peter Morgan - Technical Sales Specialist - Elementar UK When treating water, it is important to identify the state and condition of the substances beforehand, as contaminated water can have serious consequences for the ecosystem and can cause illness in humans. Contaminants come in a variety of guises, including organic, non-organic and synthetic compounds. Total organic carbon analysis (TOC) is a way of determining what organic contaminants are present in water. Here, we will explain TOC analysis, the instruments used in analysis and the methods of analysing a water sample. Using TOC analysis in wastewater Before analysing TOC in wastewater, total inorganic carbon (TIC) has to be removed. It can be present in large quantities and may include dissolved carbon dioxide from bedrock and material from the erosion of the surrounding land. Removing TIC is a simple process, performed by adding acid to the water sample and purging out the resulting carbon dioxide with an inert gas such as nitrogen. TOC analysis explained Water can contain both natural and synthetic organic matter, which can be measured through TOC analysis. Examples of natural organic matter include amine, urea and faecal matter, while synthetic contaminants include - but are not limited to - pesticides, detergents and synthetic fertilisers. TOC refers to the amount of carbon that is found in any organic compound. Detecting levels of TOC has a wide range of applications, including checking water 66 quality, identifying contaminants within soil, and identifying the cleanliness of pharmaceutical equipment. A TOC instrument can typically perform the following tests: Total carbon (TC) Inorganic carbon (IC) Total organic carbon (TOC) Purgeable organic carbon (POC) Non-purgeable organic carbon (NPOC) Measuring TOC is a mandatory requirement for organisations operating in the water treatment sector across the world. Businesses that discharge wastewater into water courses, or into other parts of the water system, will need to ensure they monitor TOC levels and report these figures to the appropriate regulatory organisations. Water contaminated with any of the materials mentioned above can interact and cause reactions with one another, encourage microorganisms to grow, or make the water toxic for humans and animals. When discharging this contaminated water into the ecosystem, it can have catastrophic results, including damage to the ecosystem, sickness in animals and humans and, in some cases, death. The TOC process A TOC analysis consists of three distinct parts: sampling, oxidation and detection. Studies are completed using a TOC analyser. The TOC analysis process is as follows: Sampling - to ensure high-level performance, instruments used in TOC analysis should offer automatic sampling, acidification and sparging functionality, as this reduces errors and improves reproducibility and sample throughput. Oxidation - in order to identify TOC levels in a water sample, organic carbons must be oxidised. There are numerous techniques to achieve this, including using combustion analysers and the wet chemical technique. Detection - as samples go through oxidation, gases are released, which are detected by specially designed detectors. Results from the analysis are recorded by the technician conducting the experiment. DECEMBER 2018 As mentioned above, there are two methods used to measure TOC. Both have distinct applications and, as such, are useful for specific circumstances. Wet chemical - sometimes referred to as the UV oxidation/sodium persulphate method, this technique involves instrumentation that adds sodium persulphate to the water sample before applying UV light. This forms hydroxyl radicals and organic compounds are then converted to carbon dioxide, which is detected using a non-dispersive infrared detector (NDIR). Combustion analysers - combustion analysers measure TOC in a water sample by combusting it at a temperature above 680°C with a catalyst. Once combusted, the sample is fully oxidised and converted to carbon dioxide. As with the wet chemical approach, gases are detected by NDIR. Each method has its own benefits, so the choice of which technique to use will depend on the intended outcome. The combustion method oxidises solid particles in a sample, so it is very useful for dirty samples, such as those found in heavily polluted areas like the River Thames in London or wastewater for treatment. However, the wet chemical method is much more suited to testing drinking water or other clean water samples, as it has a lower overall detection limit for TOC and can also be more reproducible. TOC is often overlooked, but has an extremely important role when we consider how we deal with water. It provides a quick, easy and inexpensive way of checking water samples for contaminants. Alternative methods are usually more expensive or take longer than TOC, which would result in a slower response to contamination events that may disrupt drinking water supplies. Visit for more information: read online: