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Pilot-scale experiments were performed to investigate the effectiveness of enhanced coagulation in removing particles and trihalomethane (THM) precursors from two surface source waters: California ...

The efficiency of arsenic removal from source waters and artificial freshwaters during coagulation with ferric chloride and alum was examined in bench-scale studies. Arsenic(V) removal by either ferric chloride or alum was relatively insensitive to variations in source water composition below pH 8. At pH 8 and 9, the efficiency of arsenic(V) removal by ferric chloride was decreased in the presence of natural organic matter. The pH range for arsenic(V) removal with alum was more restricted than with ferric chloride. For source waters spiked with 20 μg/L arsenic(V), final dissolved arsenic(V) concentrations in the product water of less than 2 μg/L were achieved with both coagulants at neutral pH. Removal of arsenic(III) from source waters by ferric chloride was both less efficient and more strongly influenced by source water composition than removal of arsenic(V). The presence of sulfate (at pH 4 and 5) and natural organic matter (at pH 4 through 9) adversely affected the efficiency of arsenic(III) removal by ferric chloride. Arsenic(III) could not be removed from source waters by coagulation with alum.

Fouling experiments of thin film composite and cellulose acetate reverse osmosis membranes by aluminum oxide colloids are reported. Membrane fouling was investigated at various solution chemistries under fixed hydrodynamic conditions. Results show that the fouling rate increases with an increase in the ionic strength of the solution. Fouling was significant at high ionic strengths, including in the presence of background dissolved organic matter, resulting in a gradual decrease in product water flux. Under the chemical conditions tested, colloidal fouling was found to be reversible, thus indicating that pore blockage is not an important factor in colloidal fouling of reverse osmosis membranes. The role of chemical-colloidal interactions in colloidal fouling of reverse osmosis membranes is elucidated. Fouling is controlled by particle-membrane and particle-retained particle interactions, which, in turn, are determined by solution chemistry, chemical properties of colloids and membranes, and the magnitude of permeation drag.

A novel optical technique is used to investigate the dynamics of coagulation of particle suspensions with aluminum salt. The relative size of aggregates formed during coagulation, expressed as a “coagulation index,” can be continuously measured by this technique. Coagulation of clay particles with aluminum sulfate is examined at various aluminum concentrations, solution pH, and mixing intensities. Results indicate that the coagulation index provides valuable information about aggregate dynamics and coagulation mechanisms with aluminum salts.

Conventional water filtration methods cannot be generalized for use in direct wastewater filtration for drip (trickle) irrigation systems. Effluents from an oxidation ponds‐reservoir system and from an activated sludge plant were filtered through granular beds and filter screens, for the purpose of evaluating particle filterability. The granular beds remove particles larger than 10μm with an efficiency of 40 to 85%, depending on the existence of surface straining and effluent type, whereas smaller particles (1-2μm in size) are hardly removed, suggesting that minimum transport theory applies. The removal ratio for all particles measured increases with grain size and with bed depth, and decreases with filtration velocity, affecting the lower particle size range more. Filter screens clog very rapidly even though they remove only about 1–2% of the total suspended solids (TSS). Both turbidity and TSS are inferior to particle size distribution measurements for filterability evaluation of wastewater effluents.