Disinfection By-Products and Natural Organic Matter
Natural organic matter is present in all sources of fresh water and comes from the breakdown of organic matter, such as algae and vegetation. During the disinfection step in drinking water treatment, this organic matter may react with chlorine, ozone, chlorine dioxide or other disinfectants, to form undesirable toxic disinfection by-products (DBPs). These can include both organic compounds such as trihalomethanes (THMs) or inorganic compounds such as the bromate ion.
Trihalomethanes are essentially a byproduct of the water treatment process but pose potential health risks and so are included in water control regulations.
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.
Reducing the level of the natural organic matter, or so-called precursors, such as humic acids, is an effective way to decrease the formation of trihalomethanes in the final water. Less total organic carbon in the water before the final chlorination step means there will be less organic matter to react with the chlorine and so a lower formation of THMs.
Normally most natural organic matter is removed in the stages prior to chlorination, but this is not always the case. Therefore, a media filter such as granular activated carbon can be used to further reduce the organic matter.
Groundwater applications are typically lower in total organic carbon than surface waters and so generally will have lower DBP concentrations.
Trihalomethane (THMs) Removal
Trihalomethanes are formed when natural organic matter, such as humic acids – called precursors, react with chlorine used to treat the water. The bromine compounds are formed from bromide naturally present in the water reacting with the chlorine. These are considered as environmental pollutants and so THM levels in public water supplies are strictly controlled.
THMs are organic chemicals in which three of the four hydrogen atoms of methane (CH4) are replaced by halogen atoms. Trihalomethanes with all the same halogen atoms are called haloforms.
THMs and halocarbons vary from weakly- to strongly adsorbing onto activated carbon. The higher the chlorine substitution in a molecule, the more strongly it is adsorbed onto carbon, as carbon-chlorine or carbon-bromine compounds are better adsorbed than carbon-hydrogen compounds.
Chloramine removal
The chlorination of drinking water can also result in the formation of chloramine by-products in the water. These compounds exist in water in three forms: monochloramine (NH2Cl, at pH>7), dichloramine (NHCl2, at pH 4.4-7) or trichloramine (NCl3, at pH <4.4).
Because of the pH range, monochloramine is the most common. Chloramines, especially trichloramine, are mainly responsible for most of the “chlorine smell” of pools and are an irritant.
In the past, this compound was the quite difficult to remove using activated carbon. However, Chemviron’s CENTAUR® carbon has catalytic properties as well as adsorption properties, which makes CENTAUR® particularly effective for monochloramine removal. Consequently, the removal of all types of chloramine is feasible and cost-effective.
Where the water treatment process has struggled with DBP levels, then chloramine can be used instead of chlorine in the disinfection step. However, although chloramine reduces the formation of THMs and HAAs, it will form other DBPs such as halo nitriles and halo nitromethanes.
Haloacetic Acids (HAAs)
These are the next most common halogenated compounds and are thought to be more toxic than THMs but are usually in lower concentrations. However, they have a high solubility making them less easily adsorbed onto activated carbon.
What Disinfection By-Products Can Be Removed Using Activated Carbon?
Activated carbon, in granular or powder form, is one of the best available technologies for the removal of a wide range of organic contaminants from drinking water.
Granular activated carbon is also widely used as an additional means to capture 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. For such installations, existing rapid gravity filters can be retrofitted to take activated carbon. However, although these may have short empty bed contact times, they still may have sufficient capacity to reduce the organic load.
The adsorption of contaminants onto the carbon is governed primarily by diffusion kinetics. It is not an instantaneous process and so requires sufficient contact time and the right activated carbon to achieve the desired treatment objective.
Some of those substances including Disinfection By-products that can be effectively removed with activated carbon technology are noted in the table below:
| Bromodichloromethane | Dichloramine | Monochloroacetic acid |
| Bromoform | Disinfection By-Products (DPBs) | Monochloramine |
| Chlorodibromomethane | Haloacetic Acids (HAAs) | Natural Organic Matter (NOM) |
| Chloroform (Trichloromethane TCM) | Haloacetonitriles (HAN) | Nitrosoamines |
| Chlorophenols | Haloforms | Total Organic Carbon (TOC) |
| Colour | Haloketones | Trichloroacetic acid |
| Dibromochloromethane | Halomethanes | Trichloramine |
| Chloroform (Trichloromethane TCM) | Halonitriles | 2,4,6 Trichlorophenol (TCP) |
| Dichloroacetic acid | Halonitromethanes | Trihalomethanes (THMs) |
For information on pesticides, POPs, and chlorinated organic removal, please see our article.
For information on taste and odour removal, please see our article.
For information on PFAS removal pesticides, please see our article.
How can Chemviron help?
The most effective carbon to be used may depends on the nature of the organic contaminant, the level of their concentrations and the overall treatment steps involved.
Since each water source is different, it is sometimes appropriate to carry out a laboratory test on a representative water sample to assess the effectiveness of activated carbon use.
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.
Alternatively, the Accelerated Column Test (ACT), which was developed by our company, is an improved technique that combines the speed of an isotherm test, with the accuracy of a pilot column. The ACT is a bench-scale procedure that simulates a full-scale system to provide breakthrough test data for the removal of organic impurities in water but in a much shorter time.
In addition, Chemviron have an extensive reference library of performance data to help provide an appropriate technical solution.
Activated Carbons for High Performance
Chemviron provide a wide range of powder and granular activated carbons for these applications. The FILTRASORB® granular activated carbons have been widely used worldwide for many years to remove disinfection by-products and trihalomethane compounds.
FILTRASORB® carbons 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.