Nitrates are compounds of nitrogen and oxygen, naturally present in the environment. Their concentrations in drinking water can increase significantly due to human activities like agricultural runoff and septic system discharge.
Elevated nitrate levels in drinking water pose a health concern, particularly for vulnerable populations. Infants under six months old are especially susceptible to methemoglobinemia, or “blue baby syndrome.” This occurs when nitrates convert to nitrites in the body, interfering with red blood cells’ ability to carry oxygen. Symptoms include bluish skin discoloration, shortness of breath, and lethargy; in severe cases, it can be fatal.
Common Home Water Treatment Options
Several effective methods remove nitrates from drinking water, with some practical for residential use. Reverse osmosis (RO) systems significantly reduce nitrate levels. This process forces water under pressure through a semi-permeable membrane, trapping larger molecules and dissolved solids like nitrates, while allowing purified water to pass.
RO systems are highly efficient, removing between 90% and 98% of nitrates. They often include pre-filters to remove sediment and chlorine, protecting the membrane and extending its lifespan. While effective, RO systems generate wastewater as concentrated contaminants flush away, and they require sufficient water pressure.
Distillation offers another effective approach to nitrate removal, mimicking Earth’s natural hydrologic cycle. Water is heated to its boiling point, converting it into steam. Inorganic compounds, including nitrates, and many other contaminants are left behind as water vaporizes. The purified steam then cools and condenses back into liquid water.
Distillation removes virtually all waterborne contaminants. However, this method is energy-intensive and has a slow output. Certain organic compounds that boil at lower temperatures than water could re-contaminate the distilled water if not properly addressed by post-filtration.
Ion exchange systems provide a third common method for residential nitrate removal. These systems contain specialized resin beads that exchange nitrate ions for other, less harmful ions. As nitrate-contaminated water passes through the resin, nitrate ions bind, and chloride ions are released.
Ion exchange units are effective, with nitrate-selective resins removing approximately 90% of nitrates when properly maintained. These systems require periodic regeneration, using a concentrated salt solution to flush accumulated nitrate ions off the resin. The process produces a saline waste stream and can lead to a slight increase in the water’s chloride content.
Advanced and Larger-Scale Removal Technologies
Beyond home applications, complex, large-scale technologies are employed for nitrate removal, often in municipal or industrial settings. Biological denitrification utilizes specific microorganisms to transform nitrates into harmless nitrogen gas. This process occurs under anaerobic (oxygen-free) conditions, where bacteria use nitrates as an electron acceptor.
Biological denitrification is often implemented in bioreactors or constructed wetlands. It offers an environmentally sound treatment method, converting a water contaminant into a naturally occurring atmospheric gas. The process requires a carbon source, such as methanol, to support bacterial growth. While effective and sustainable, managing the biological process can be complex.
Chemical reduction methods use chemical agents to convert nitrates into other nitrogen compounds. These techniques are not suitable for residential use due to the need for precise chemical handling and potential undesirable byproducts. For instance, some processes may use nano zero-valent iron (nZVI) to reduce nitrates to ammonia, requiring further oxidation. Such methods are integrated into sophisticated water treatment plants.
Adsorption is another technology that removes nitrates by attracting and holding nitrate ions onto certain materials. Various adsorbents have been investigated, including activated carbon, modified zeolites, and specific resins. The effectiveness of adsorption depends on the material’s properties, water chemistry, and the presence of other competing ions.
Adsorption systems have limitations, as the adsorbent material eventually saturates with nitrates and loses effectiveness. Regular regeneration or replacement is necessary to maintain performance. The presence of other anions, such as sulfate, phosphate, and chloride, can compete with nitrates for binding sites, reducing removal efficiency.
Selecting the Right Removal Method
Choosing an appropriate nitrate removal method involves considering several factors, beginning with comprehensive water testing. Professional water analysis is essential to accurately determine nitrate levels and identify other contaminants. The U.S. Environmental Protection Agency (EPA) has set a maximum contaminant level (MCL) for nitrates in drinking water at 10 milligrams per liter (mg/L) as nitrogen.
The cost of a removal system is a significant consideration, encompassing initial purchase, installation, and ongoing operational expenses. These costs can include energy consumption, regular filter replacements, and the purchase of salts for regeneration in ion exchange systems. Maintenance requirements vary between technologies. Some systems, like reverse osmosis, require periodic filter changes, while ion exchange systems need regular regeneration cycles.
Efficiency and effectiveness are paramount; it is important to select a system proven to achieve the desired nitrate reduction. Reverse osmosis and distillation offer very high removal rates, often exceeding 90%. Ion exchange systems also provide good performance when properly maintained. The scale of use is another factor, with point-of-use (POU) systems treating water at a single tap, such as a kitchen sink, and point-of-entry (POE) systems treating all water entering the home.
Methods That Do Not Work
Some commonly perceived methods of water treatment are ineffective at removing nitrates and can even worsen the problem. Boiling water, for instance, does not remove nitrates. As water evaporates during boiling, the nitrates remain behind, leading to a higher concentration of nitrates in the reduced volume of water.
Standard activated carbon filters, such as those found in pitcher filters or refrigerator dispensers, are generally ineffective for nitrate removal. These filters are designed to address contaminants like chlorine and some organic chemicals but do not capture nitrate ions. Relying on these methods for nitrate-contaminated water would not provide adequate protection.