Demonstration testing of alum recovery by liquid ion exchange

Abstract

A 0.63-L/s sludge flow liquid ion exchange alum recovery plant was tested at the Tampa (Fla.) water filtration plant. Two equipment setups were tested: one providing a rapid mix of sludge and solvent and the other a slow mix. Both were able to recover more than 90 percent of the aluminum and to reduce the dry weight of the sludge as predicted by acidification.Operating costs for a full-scale system were estimated at about the same as the value of the recovered alum. The economic considerations for installation would be based on treatment costs for the original sludge compared to those for the alum-free residual.Following extensive laboratory development'~' of the liquid ion exchange alum recovery process (outlined in Figure l), a demonstration plant was built at Tampa, Fla. The project was sponsored by the American Water Works Association Research Foundation, and funding for the demonstration plant was received from the foundation, the city of Tampa, Michigan State University, and RTR, SA. The objective of the demonstration plant was to determine scale-up efficiencies, to provide long-term operating data, and to evaluate process economics. This paper presents the results obtained at this plant. Previous papers should be consulted for details on process development, chemistry, the background of liquid ion exchange, and the rationale behind alum recovery. It should be emphasized that two different equipment setups were tested in Tampa. The first used a mixer-settler for extraction; the second used a contactor.*The city of Tampa's Hillsborough River water treatment plant is a 247.ML/d (65-mgd) conventional coagulation plant that treats a highly colored raw water. At the time of this project, Tampa utilized alum coagulation with sodium silicate addition as a settling aid (polymer has now replaced the sodium silicate). The sludge from the sedimentation basins had about a 0.3 percent suspended solids concentration, which can be gravity thickened to a suspended solids concentration of from 1 percent to 1.5 percent. Between 60 percent and 90 percent of the suspended solids are acid dissolvable. (See reference 3 for details on the characteristics of this sludge.) The Tampa sludge was chosen for the demonstration plant for two reasons: The 20 t/d (22 tons/d) of alum used at the plant made coagulant recovery an attractive treatment method. Because of the large amount of organic matter present in the *RTL, Lngano. Switzerland. 326 RESEARCH AND TECHNOLOGY sludge, it was felt that treating this sludge would be a demanding test of the liquid ion exchange process.

Coagulant recovery and reuse for drinking water treatment

“…2). This corroborates previous results of applying granular activated carbon for DOC removal from recovered alum sludge (Cornwell et al, 1981). The relative gradients of the isotherm plot (Fig.…”

Coagulant Recovery from Water Treatment Residuals: A Review of Applicable Technologies

“…More detailed research for full-scale LIE plants supports the positive outcomes of bench-scale studies, with alum recoveries still in excess of 90% (Cornwell et al, 1981). Coagulant performance, in terms of THM precursor concentrations, color and turbidity removals, was comparable to commercial coagulants at the same dose.…”

“…Increasing these two parameters was shown to increase operating cost savings (Cornwell et al, 1981). Criticism aimed at the inability of LIE to concentrate recovered aluminum seems unfounded (Sengupta and Prakash, 2002).…”

“…Criticism aimed at the inability of LIE to concentrate recovered aluminum seems unfounded (Sengupta and Prakash, 2002). No concentration takes place during the extraction phase but four-fold concentration increases have been reported in the stripping phase, producing recovered alum concentrations above 30,000 mg/L as Al (Cornwell et al, 1981).…”

“…There is potential for entrainment of organic solvent in the coagulant during the stripping stage and contamination of the treated water (Prakash and Sengupta, 2003), although an activated carbon polishing stage was originally suggested to prevent this (Cornwell et al, 1981). Similar techniques are used in extractive hydrometallurgy, where these limitations are less important.…”