Chloramine is now becoming a common disinfectant for drinking water supplies replacing Chlorine in many capital cities including Sydney, Melbourne and Brisbane. This rollout will continue in the future with more and more towns and cities moving to this form of disinfectant. The main reason for this is the considerably reduced level of carcinogenic by-product trihalomethanes (THM’s) formed when using chloramines and it stays in the water much longer, a much higher residual.
The most common form is Monochloramine with concentrations ranging from 1.5 to 2.5 mg/L. Typical residual in Australia is 0.5 mg/L with a maximum of 3 mg/L. It is less effective than chlorine and therefore needs a higher initial dose and longer contact time. Unlike chlorine, monochloramines do not add any taste or smell to the water.
Types of Chloramine
There are 3 forms of inorganic Chloramine; monochloramine, dichloramine and trichloramine. All of these can be formed when water containing or injected with ammonia is chlorinated. The pH and the ammonia/ chlorine ratio determine which kind of chloramines is formed. At a pH <3 mainly trichloramine is formed, at pH 4-7 mainly dichloramines is formed while at a neutral pH >7 or above monochloramine is the main form produced.
The ammonia component of chloramines is also different depending upon the pH of the water. At pH levels >7 ammonium hydroxide is formed, <7, ammonium ion is formed. The ammonium ion is readily removed by cation resin (softener resin) or mixed bed resin however water hardness can substantially affect this. Ammonia is removed preferentially to sodium by cation resin but is displaced by calcium and magnesium (water hardness). Therefore a resin filter will remove ammonia initially but will then release the ammonia when it becomes exhausted with hardness. This could lead to an ammonia spike in the treated water.
Due to the low molecular weight, chloramines and in particular monochloramines are difficult to remove from water by reverse osmosis (RO), distillation, water softeners or resin filters. Distillation or evaporation does not remove chloramines effectively as the chloramines are volatilized and carried over to the product water (distillate). Pre-treatment is required for RO systems to remove chloramines prior to reaching the membrane with specialised carbon filters.
Standard activated carbon (GAC), carbon block or enhanced carbon filters do not remove chloramines. The carbon in these types of filters, whether it be coal, coconut shell or wood based carbon does not absorb chloramines. It removes or reduces them to some degree through a reduction-reaction, its ability to act as a catalyst for the chemical decomposition or conversion of chloramines to chloride (salt) in water. This reaction converts the chloramines into chloride salt and ammonia. This reaction releases the ammonia allowing it to pass through RO membranes and other filters excluding resin. The ability of resin to remove it is dependent upon the pH and other contaminants in the water. The free ammonia can also come in contact with other contaminants in the water and form undesirable Nitrates and Nitrites.
Granular activated carbon (GAC) filters can be used to remove/ convert chloramines however long contact times and low flow rates are required to achieve >95% removal. The cartridge rated capacity will also need to be reduced to 12-25% of the rated chlorine removal capacity for chloramines removal. This is dependent upon the cartridge manufacturer, type of GAC etc. Standard carbon block filters have very low removal/ conversion rates and are not recommended. These filters will not remove the ammonia from the water. For this reason we do not recommend the use of these carbon filters and suggest the use of chloramines reduction cartridges for cities such as Sydney, Melbourne and Brisbane where chloramines are currently used.
Potassium or sodium metabisulphite can also be used for chloramines removal.
Chloramines Reduction Filters
Specialised Chloramines reduction cartridges are manufactured specifically to remove chloramines and ammonia in one. They use a specially developed catalytic carbon to absorb and bond the chloramines. These cartridges need to be installed before or in place of any other carbon cartridges to be effective.
The main manufactures of these filters are; Omnipure Chloramine Reduction, Pentek Chlor Plus, and Filtrex Chloraguard. These are all high quality US made cartridges with a proven track record and available specification sheets.