Removal of Humic Substances and Thm Precursors By Activated Carbon: Effects of Heterogeneity, Chemical Pretreatment, and System Characteristics.

This research has investigated the removal of humic substances from water by activated carbon and the associated reduction of THM formation. Several operational conditions and process configurations are examined to quantify their respective impacts on the efficiencies of adsorption for removal of humic substances. Application of resulting concepts to water treatment system design and operation--in particular, integration with other treatment processes such as lime softening and alum coagulation have been examined. Some of the major conclusions drawn from this work were, (1) A portion of almost all humic materials tested was found to be essentially non-adsorbable. This fraction was generally not affected by alum and lime pretreatment processes. (2) Alum coagulation and lime softening treatments resulted in humic solutions which adsorbed differently than solutions which had not been subjected to these pretreatments. The extent of these effects depends on the type of humic material involved and on certain critical system characteristics. (3) For all humic solutions examined in this work, a significant fraction of TOC (at least 70 percent) had to be removed by activated carbon adsorption in order to accomplish a significant change in the THM formation potential of the residual. (4) To properly control the formation of THMs in a water treatment system utilizing alum or lime treatment either alone or in conjunction with activated carbon, the entire scheme of treatment should be optimized, rather than maximized for TOC removal. Many of the effects observed in the course of this work are attributable to the fact that humic substances are mixtures of compounds, and that their adsorption therefore involves differential and competitive multicomponent processes. This has been confirmed through analyses by gel permeation chromatography of the molecular weight distribution of untreated and treated humic solutions. Despite the heterogeneous nature of the humic systems, a simplified single-component adsorption model was found to provide reasonable simulations for both batch and fixed-bed reactor configurations.Ph.D.Engineering, Sanitary and MunicipalUniversity of Michiganhttp://deepblue.lib.umich.edu/bitstream/2027.42/160543/1/8512439.pd