Total Organic Carbon (TOC) refers to the amount of carbon atoms present in organic compounds within a water sample. It serves as a general indicator of water quality. Organic carbon occurs naturally in aquatic environments but can also be introduced through human activities. Assessing TOC levels is important for water purity, particularly in drinking water and industrial applications.
Where Organic Carbon in Water Comes From
Organic carbon in water originates from natural or anthropogenic sources. Natural organic matter (NOM) includes decaying vegetation like leaves and wood, and byproducts from aquatic organisms such as algae and bacteria. Runoff from soil, rich in humic and fulvic acids, also contributes to natural TOC in surface waters.
Human activities introduce additional organic carbon. Agricultural runoff, containing pesticides and fertilizers, and industrial discharges are anthropogenic sources. Wastewater effluent and urban runoff also contribute a range of synthetic organic compounds.
Why Monitoring TOC is Essential
Monitoring Total Organic Carbon is important for water quality and public health. TOC indicates organic contamination.
A primary concern is the formation of disinfection byproducts (DBPs). When organic matter in water reacts with disinfectants like chlorine, commonly used in water treatment, it can create potentially harmful DBPs such as trihalomethanes (THMs) and haloacetic acids (HAAs). Long-term exposure to these byproducts has been associated with health risks, including an increased risk of certain cancers, liver, kidney, or central nervous system problems. Water treatment facilities monitor TOC to minimize the formation of these compounds.
High TOC levels can also negatively affect water treatment processes. They increase disinfectant demand, potentially leading to higher chemical costs and operational challenges. Organic matter can also cause fouling of membranes in advanced treatment systems and promote microbial regrowth within water distribution networks. Some organic compounds can impart undesirable tastes and odors to drinking water.
How TOC is Assessed and Managed
Assessing Total Organic Carbon involves converting organic carbon into carbon dioxide (CO2) for measurement. This process begins by removing inorganic carbon through acidification and purging. The remaining organic compounds are oxidized using high-temperature combustion, heated persulfate, or ultraviolet (UV) light combined with persulfate, to transform them into CO2. The resulting CO2 concentration is quantified using a non-dispersive infrared (NDIR) detector.
Managing and reducing TOC involves several treatment strategies. Common approaches include coagulation and flocculation, where chemicals are added to clump organic particles for removal through sedimentation and filtration. Activated carbon adsorption is another method, where organic compounds adhere to the porous surface of activated carbon.
Advanced oxidation processes, which generate highly reactive hydroxyl radicals, can break down organic molecules. Ion exchange, reverse osmosis, and nanofiltration also remove dissolved organic matter. The primary goal of these techniques is to reduce organic precursors before disinfection, minimizing DBP formation and improving water quality.