Water treatment processes are critical in protecting public health. Many people associate clean and healthy water with water that has the best taste and smell. This is such a prevalent conception that many water treatment sites will compete in “best tasting water” competitions.
However, taste and odor problems are rarely linked to health effects. Water treaters will treat taste and odor to improve customer satisfaction.
Water treaters conduct a threshold odor test and a flavor profile analysis to determine the various types of odors and smells that are present in the water supply. This analysis helps set the path forward to eliminate the foul taste and odor in drinking water.
These blooms present in raw water can be a major contributor to foul taste and odor in treated water. Furthermore, various compounds derivative of industrial waste can impart foul odor and taste as well.
Industrial compounds such as phenols, hydrocarbons may exhibit foul odors as indicated by the threshold odor test at very low concentrations. Additionally, metals such as copper and zinc will yield a foul taste however not be present in the threshold odor test.
The flavor profile analysis will indicate specific tastes and odors that are present in the water supply. These flavors and odors are correlated to specific types of algae or pollution that lead to that result. Understanding the cause helps determine the chemical dosing path forward.
In order to control odor problems and improve taste, chemical dosing of oxidants is widely used. Oxidation is one of the most effective methodologies to remove foul tastes and odors. Various types of oxidants, such as potassium permanganate, ozone, hydrogen peroxide, and chlorine dioxide, are the most prevalent.
In other cases, sodium hypochlorite (also referred to as chlorine) is used to improve the taste. As this chemical is also prevalently used for disinfection, a proper dose of the chemical is critical. To use chlorine for taste and odor control, a higher chlorine dose than what is used for disinfection is required. This process is known as super chlorination.
While this process can help remove grassy or fishy tastes and smells, it can make some odors worse. For example, super chlorination will negatively impact those odors linked to phenols. Once super chlorination takes place, the excess chlorine is typically removed through the use of carbon.
Accurate dosing pumps should be utilized to ensure the proper amount of chlorine is added to prevent residual taste and odor. Dosing accuracy minimizes chemical use and helps optimize the process.
Additionally, certain geographical areas may have hydrogen sulfide in the groundwater, which in turn is found in well water. Hydrogen sulfide in the water supply creates a sulfur (“egg-like”) water smell. In these cases, chemical feed pumps are used to add chemicals to the water system to eliminate the odor.
Powder activated carbon (PAC) or granular activated carbon (GAC) are two different types of carbon treatments used. These carbon treatments bind to contaminants in the water, which can then be removed downstream in the process. These processes are known as adsorption. GAC adsorption methodologies are used when odor and flavor profiles are the most severe.
In addition to chemical dosing, aeration improves taste and odor caused by volatile organic compounds (VOCs) such as methane and hydrogen sulfide. Hydrogen sulfide is a common problem and is also removed via aeration.
Aeration is very effective at removing VOCs, dissolved gasses, and hydrogen sulfide; therefore, very efficient at removing their associated foul tastes and odors. This process primarily takes place prior to other treatment processes and has the benefit of removing this material before additional treatment processes need to occur.
It is important to ensure that the water is not over nor under aerated because improper aeration could lead to additional treatment challenges downstream in the process. While aeration is very effective at removing Hydrogen Sulfide, aeration does not remove foul odors and tastes associated with various types of algae, requiring chemical treatment.
Water treaters also must prevent foul odors and tastes that may manifest after treatment. Foul tastes and odors may arise based on the distribution system of the water after it leaves the treatment plant. In order to combat this, water treatment plants may maintain a chlorine residual, and the pH of the water may be adjusted.