Humic substances in our water resources originate from the soil or from degradation of plants, and effects drinking water purification process. Humic substances may have, in themselves, favourable effects on human health. They can form complexes with metals, resulting in better metal intake, and can behave as antioxidants. On the other hand, their presence in raw water represents one of the main problems in drinking water purification. In the course of disinfection by chlorine, humic materials may turn into carcinogenic substances such as trihalomethanes. Different technologies are available for removing humic materials from drinking water, which is, obviously, an important measure.
Humic substances are acidic polymers of various size and complicated structure, possessing different kinds of functional groups like aromatic groups, phenolic and alcoholic hydroxyl groups, carboxyl groups, and amino groups. Humic substances in the drinking water resources originate from the soil or from degradation of plants, and may have, in themselves, favourable effects on human health.
Due to their physico-chemical properties humic acids can bind and remove heavy metals from the organism (because of their high cation exchange capacity), and they also act as antioxidants and have antimutagenic effects. They accelerate cellular metabolism and make utilizable minerals and nutrients. Humic acids can form complexes with inorganic metal ions which then can be easily transported through membranes. Humic substances may adsorb mutagenic compounds and decrease their effects.
On the other hand, the presence of humic substances in the raw water represents one of the major problems of drinking water purification. In their original form they are not toxic, but in a disinfection process using chlorine humic materials are transformed to dangerous carcinogens such as trihalomethanes (THMs) and chlorinated phenol compounds. The most typical disinfection by-products are trichloromethane, dichloroacetic acid, and trichloroacetic acid. Concentration of THMs depends on the amount and quality of natural organic matter in the water. Removing humic materials from drinking water has obvious importance in cancer prevention. Different technologies are available: membrane filtration, activated carbon adsorption etc. According to the valid Hungarian regulation on quality requirements and control of drinking water (201/2001. (X.25.) Governmental Decree) the limit of THMs is 50 mg/dm3.
The concentration of humic materials can be followed by UV-VIS spectrophotometry (at 254 nm), furthermore by COD, TOC measurements and colourimetry (at 436 nm). Reactions of organic matter with chlorine and the forming of THM can be investigated by FT-IR and NMR spectroscopy. The possibility of humic materials reacting with chlorine and the potential of generating disinfection by-products are shown by the ratio of UV absorbance at 253 and 203 nm wavelengths (A253/A203). Higher A253/A203 ratio means more THMs after disinfection. Activated carbon adsorption is a widely used method in drinking water plants for removing organic materials from water.
The aim of our research was to determine the efficiency of removing humic materials by granulated activated carbon (GAC) and predict the likelihood of forming THMs from different humic substances. You may get detailes about this research in CEJOEM.