This paper discusses the use of a two-stage clarification process to remove total organic carbon (TOC) from waterapproaching 0º C in temperature. The process utilized was a high-rate, 2-stage, clarification systemconsisting of a tube clarifier followed by an adsorption clarifier (AC). The tube clarifier uses externalsludge re-circulation and typically operates at a velocity of 4-5 gpm/ft2 of gross clarifier basin area. Itremoves in the range of 50% to 90% of the solids in the raw water, depending on the water quality.The AC typically operates at a velocity of 12-15 gpm/ft2 of gross clarifier basin area and removes inthe range of 65% to 85% of the solids entering the AC. The net production can be as high as 95% forthis 2-stage system.In treating cold river water such as this water, a 2-stage process is more accommodating to theapplied chemistry as well as economical for the application as compared to a traditional single stagesolids contact clarifier. The comparatively "slower" tube stage allows for the reaction kinetics to go intocompletion, while the comparatively "faster" AC stage allows for optimal separation efficiency. Further,river water typically carries a high fraction of the ready to coagulate humic acid content as shown bythe high SUVA values seen in this water, countering the negative effect created by the cold water.The average SUVA for this water was 4.24 L/mg C.m<sup>-1</sup>.The results showed that the 2-stage system removed in excess of 21% of TOC and dissolved organic carbon (DOC). Thereduced SUVA value of 2.85 L/mg C.m<sup>-1</sup> in the AC effluent indicates acceptable water for downstream processes. Solids removal in terms of turbidity was 52% across the tubes, 84% across the ACand 92% across the 2-stage system. Future evaluation of this 2-stage system on the same sourcewater under warm water conditions will provide valuable comparison data for future plant design withthis type of system.This 2-stage system can also provide pretreatment for granular media filter systems. Includes tables, figures.
