Removal of dissolved organic carbon from surface water by anion exchange and adsorption: Bench-scale testing to simulate a two-stage countercurrent process

The goal of this research was to use bench-scale testing to simulate a two-stage countercurrent sorption process for the removal of dissolved organic carbon (DOC) using a variety of sorbents including magnetic ion exchange (MIEX) resin, anion exchange resin (AER), granular activated carbon (GAC), and powdered activated carbon (PAC). Preliminary experiments used surface water from the St. Johns River (SJR), FL, USA with raw water DOC of 7.4-27.5 mg/L. Preliminary experiments investigated each sorbent at four different mixing speeds and five different contact times. MIEX resin, AERs, GACs, and PAC showed 54%, 20-30%, 5-10%, and 20% DOC removal at a 30 min contact time in preliminary kinetic experiments. DOC removal by the AERs and activated carbons was lower than by the MIEX resin even though the AERs and activated carbons had higher capacity than the MIEX resin. MIEX resin, PFA444 AER, and F400 GAC were selected for additional testing using the SJR water and a surface water from Virginia (VA), USA, which had an average DOC of 3.2 mg/L. Two hour uptake experiments using MIEX, PFA444, and F400 and SJR and VA waters were used to calculate the sorbent dose necessary for 99% removal of the adsorbable fraction of DOC in a two-stage countercurrent process. Finally, bench-scale tests were conducted using MIEX, PFA444, and F400 and SJR and VA waters to simulate the two-stage countercurrent process using the doses calculated from the 2 h uptake experiments. The average two-stage removal of the adsorbable fraction of DOC in SJR water and VA water for F400, PFA444, and MIEX were 109% and 84%, 90% and 88%, and 85% and 94%, respectively. The results showed that the 2 h uptakes experiments and calculations were satisfactory in predicting the doses and corresponding DOC removal in the two-stage countercurrent process.