Natural Organic Matter
Natural Organic Matter (NOM), also known as Background Organic Matter (BOM) is the organic matter present in all sources of fresh water. Most natural organic matter comes from the decay or breakdown of vegetation, animal life, bacteria and algae that enter streams, rivers, lakes, and aquifers.
NOMs are made up of many different humic and fulvic compounds of which only a small percentage can be identified. Since they typically cannot be individually identified, they are often measured as a group in several different ways. These include as total organic carbon (TOC), dissolved organic carbon (DOC), ultraviolet adsorption at 254nm (UV254), and oxidisability or permanganate value.
The composition of NOM will vary substantially depending on the geography and geology of where the water is sourced. In particular, groundwaters, because of their natural purification, have low concentrations of organic matter, with typically less than 2mg/l measured as DOC. In contrast, surface waters generally have higher and more variable concentrations of organic matter with a typical DOC of 4mg/l.
Removal of Natural Organic Matter
The NOM is often referred to as ‘background’ when considering the removal of specific compounds with activated carbon. This is because the background organic level will compete with the specific contaminants for the available adsorption sites on the activated carbon.
Most natural organic matter is usually removed during the coagulation, flocculation, and filtration stages of the water treatment process before chlorination. The level of natural organic matter may also affect the efficiency of the drinking water plant operations and the quality of the treated water.
Activated carbon is widely used as an additional means to capture any dissolved organic matter that may escape processing during the coagulation stage. These are usually in a primary or roughing filter with coarse bed activated carbon types to avoid pressure drop build up.
Natural organic matter needs to be effectively reduced in drinking water for several reasons:
- NOM is generally the source of unpalatable taste and odour forming compounds found in drinking water – see following section
- Colour in drinking water is made up of a wide range of varying molecules, often of very high molecular weight, which will vary in different waters. NOM can be responsible for turning water yellow or brown.
- NOM can be a substrate for bacteria and fungi to survive in a way that aids microbial growth in a water distribution system.
- It is important to remove humic substances prior to chlorination, as NOM will also react with chlorine to form undesirable toxic disinfection by-products such as trihalomethanes (THM).
The updated Drinking Water Directive (EU) 2020 (2020/2184) protects the quality of drinking water and forms part of the regulation of water supply and sanitation in the European Union.
Taste and Odour Removal
Tastes and odours in water are due to the presence of very low concentrations of mainly natural compounds which are often in the nanogram per litre (ng/l) concentration range. It is therefore often very difficult to determine which specific molecules are responsible for the specific taste and odour. The most well-known natural compounds are geosmin and 2-methylisoborneol.
Since the compounds forming tastes and odours are difficult to analyse, a dilution number may be used. This is the number of times a sample of water has to be diluted with odour and taste free water until taste and odour can no longer be detected.
Common sources of taste and odour issues can include blue-green algae and actinomyces. These are a complex group of facultative anaerobic bacteria present in soil which can form terpenoids and pyrazines often associated with drinking water off-flavours. However, significant algal blooms and scum forming blue-green algae or cyanobacteria can release algal toxins such as microcystin. These can be particularly harmful to humans and animals if drinking or in contact with algal laden water.
Taste, Odour, and Organic Matter Removal on Activated Carbon
The original use of activated carbon in many water treatment works was primarily for taste and odour removal.
For short or periodic (seasonal) taste and odour problems, powder activated carbon is effective when added to the water, mixed, and removed by decantation or filtration. Where the problem becomes persistent, granular activated carbons beds are usually installed with relatively short contact times. Also, organic molecules with carbon-sulphur bonds often smell and taste bad, these are often preferentially adsorbed onto activated carbon.
Activated carbon is effective to some extent in reducing the colour of water, but its performance can vary significantly from one water to another and the nature of the colour. Test work is normally recommended in this application to determine the performance.
Granular activated carbon is one of the most recognised solutions for the removal of a wide range of organic contaminants from drinking water, since its first application over 50 years ago. When granular activated carbon was shown to have a proven efficiency at organic contaminant removal, contact times were extended for its further application for THM, pesticide, POPs and now PFAS removal.
What Organic Matter Can Be Removed Using Activated Carbon?
Activated carbon, primarily in granular or powder form, therefore have excellent adsorption capacity for the removal of a wide range of organic compounds in drinking water. Some of those substances that can be effectively removed with activated carbon technology are noted in the tables below:
| Algae Toxins | Humic Acid | Pesticides |
| Colour | 2- Methylisoborneol (MIB) | Taste |
| Disinfection By-Products (DPBs) | Microcystin | Terpenoids |
| Fulvic Acid | Natural Organic Matter (NOM) | Total Organic Carbon (TOC) |
| Geosmin | Odour |
For information on pesticides, POPs, and chlorinated organic removal, please see our article.
For information on Disinfection Byproducts or THM removal, please see our article.
For information on PFAS removal pesticides, please see our article.
How can Chemviron help?
Each water source is unique, often with different types of taste & odour compounds present. It is therefore sometimes appropriate to carry out a laboratory test on a representative water sample to understand the likely effectiveness of activated carbon use.
The most effective carbon to be used may depend on the nature of the organic contaminant, the level of their concentrations and the overall treatment steps involved. Chemviron help our existing and potential customers all over Europe with the most efficient ways to use activated carbon.
Performance Evaluation to Ensure the Most Effective Solution is Selected
Isotherm testing to evaluate the removal of organics using activated carbon can be used to determine the likely TOC effluent and so the likely effectiveness of GAC. Bench scale or site pilot testing are always considered much more effective at indicating likely carbon usage. Chemviron can provide support and advice with our pilot units which include our range of smaller mobile carbon filters.
In addition, Chemviron have an extensive reference library of performance data to help provide an appropriate technical solution.
Activated Carbons Proposed for Effective Performance
Chemviron provide a wide range of powder and granular activated carbons for these applications. The PULSORB® powder activated carbons and our CARBSORB® and FILTRASORB® granular activated carbons have been widely used for many years to remove taste and odour forming compounds.
FILTRASORB® carbons, in particular, are the most widely used granular activated carbons for drinking water treatment. This is primarily due to their excellent adsorption capacity, proven performance lifetime, and high durability for multiple reactivation cycles. FILTRASORB® activated carbons are produced from selected grades of bituminous coal, by a twin-stage process that re-agglomerates the product before steam activation.
With our depth of experience in this field, Chemviron can work with you to advise on the appropriate carbons for your specific application and how to ensure its effective use. This includes practical site support such as for backwashing which is required to ensure an even flow through the bed.
Spent Carbon Recycling and Mobile Carbon Filters for Sustainability and Cost Savings
Granular activated carbon that has been installed in water works can be recycled by thermal reactivation. The reactivated carbon may then be returned to the water works from which it was collected and put back into use for several more years. Thermal reactivation involves treating the spent carbon in a high-temperature furnace where the undesirable organics on the carbon are thermally destroyed. Recycling activated carbon by thermal reactivation is a sustainable and environmentally friendly technology that meets all our objectives to minimise waste and reduce CO2 emissions.
If the application is required for a groundwater, temporary or peak treatment, why not consider using mobile carbon filters that are available for rental. These are activated carbon filters that can be used on-site as both a water purification vessel and then transported to and from the site without needing any on-site carbon exchange.
Chemviron has a range of units of different sizes and capabilities including smaller mobile carbon filters which may be used as pilot units. If a mobile carbon filter was being used, the spent carbon may be easily returned in the mobile carbon filter to our reactivation centre for processing.
If you need technical support to evaluate the treatment proposed, help with the choice of activated carbon, our reactivation service, the use of our mobile carbon filter service or just some further advice, please contact us – contact our technical team.