EFFECTIVENESS OF USING AN ULTRAFILTRATION (UF) SYSTEM IN BATCH AND CONTINUOUS MODES TO RECONCENTRATE CYCLODEXTRIN

A full scale remediation project was conducted using a solution of cyclodextrin to enhance the recovery of DNAPL. Although the cost of cyclodextrin is similar compared to other chemical agents used for enhanced remediation, significant cost savings can be obtained by recycling the cyclodextrin solution. An ultrafiltration (UF) system was implemented at the site to reconcentrate the recovered cyclodextrin flushing solution. The main design criterion of the UF system required an increase of the recovered cyclodextrin solution from 5% to 20% (wt/wt). Multiple tests were conducted to establish the most effective method of operation, i.e. batch and continuous tests were performed. The batch method relayed on the UF system’s internal storage tank and permitted the cyclodextrin solution to recalculate multiple times through the UF membranes. During continuous operation, cyclodextrin solution passed through the UF’s internal membrane filter only once. The ultrafiltration tests demonstrated that it is possible to reconcentrate cyclodextrin solution. However, a few problems were encountered during these tests. Flow rates during continuous operation were to low to permit steady extraction/injection of the flushing solution. The efficiency of the membrane decreased over time during both, continuous and batch tests because of the formation of a hydrodynamic layer (cyclodextrin cake) on the membrane surface. The results of our field demonstration indicate that a larger membrane would decrease the effect of hydrodynamic layer formation and would have facilitated the flow rates needed to perform full scale operations. Compared to the continuous operation, the operation in batch mode proved the most effective and permitted reconcentration of the cyclodextrin solution to the desired concentration of 20%.