Treatment of microcontaminants in drinking water

Most of the challenges in drinking water treatment arise out of contaminants that are present in extremely low concentrations and have physical/chemical properties that make them extremely difficult to be removed by conventional treatment methods. This study tries to look at the treatment of two such microcontaminants---Perchlorate and MIB (Methyl Isoborneol)/Geosmin.Perchlorate (ClO4-) is a major inorganic contaminant in drinking water and has been detected in a number of public drinking water systems across the country and has serious health impacts associated with it. A complete and critical review on this intriguing contaminant is presented including a detailed discussion on sources of contamination, the policy aspects including regulation and the available treatment technologies and their feasibility. Although some technologies have become more established than the others, it is clearly evident that a single technology cannot be directly applied to a drinking water treatment system for compete removal of perchlorate and it is highly likely that a combination of these technologies that would have to be employed to overcome this challenge.Although some of the removal technologies such as ion exchange are effective for perchlorate, they invariable results in brines highly concentrated in perchlorate that pose further challenges due to disposal. Hence a destruction technology that completely reduces perchlorate to harmless chloride is preferred. This study investigates the potential removal of perchlorate ion in drinking water by combining electrochemical reduction with zero-valent iron reduction. The use of zero-valent iron in the process is expected to enhance electrochemical reduction of the perchlorate ion and the effectiveness of this technology will serve as a basis to further develop the proposed methodology to purify surface or ground water in target zones at a larger scale.Geosmin (trans-1,10-dimethyl-trans-9 decalol-C12H 22O) and MIB (2-methyl isoborneol-C11H20O) are organic semi-volatile chemicals that can seriously influence the finished quality of drinking water by imparting taste and odor to it even at extremely low concentrations. A critical review of these two taste and odor causing compounds in drinking water is presented with emphasis on their sources, health and regulatory implications and recent developments in their analysis. The relevant treatment alternatives are described in detail focusing on their respective advantages and problems associated with their implementation in a full-scale facility. Although some of these technologies are more effective and show more promise than the others, much work remains to be done in order to optimize these technologies so that they can be retrofitted or installed with minimal impact on the overall operation and effectiveness of the treatment system.Studies have shown that activated carbon adsorption is the most effective technology currently available for treatment of these compounds. The impact of adsorbent pore size distribution on activated carbon adsorption of MIB and geosmin was evaluated through single solute and multicomponent adsorption of these compounds on three types of activated carbon fibers (ACFs) and one granular activated carbon (GAC). The effect of the presence of natural organic matter (NOM) on MIB and geosmin adsorption was also studied for both the single solute and binary systems. The single solute adsorption isotherms fit Myers and Freundlich equations reasonably well and pore size distribution significantly influenced adsorption on the ACFs and GAC. It was also seen that presence of NOM significantly reduced its adsorption capacity due to competitive adsorption.The binary adsorption of MIB and geosmin on ACFs and GAC was well defined by the ideal adsorbed solute theory (IAST), which is a well established thermodynamic model for multicomponent adsorption. There were no significant differences in the binary isotherm between the oxic and anoxic conditions, indicating that adsorption was purely through physical adsorption and no oligomerization was taking place. Binary adsorptions in the presence of NOM did result in deviation from IAST behavior in case of two adsorbents.