Magnetic ion exchange using MIEX® resin treatment process (Orica, Watkins, CO) is an effective technology for treating waters containing natural organic matter (NOM) (Mergen, 2008). MIEX® has been applied in both water and wastewater treatment to enhance the removal of dissolved organic carbon. The anionic magnetic exchange property of MIEX® resin beads allow them to increase the removal of dissolved organics, attract to other resin beads, and settle quickly.
MIEX® is made from macroporous, polyacrylic material with a nominal diameter of 150 to 180 micrometers. The porous nature of the resin beads increases the surface area of active sites and allows for the rapid exchange kinetics of MIEX® (Mergen, 2008). The ammonia functional groups on the surface of the resin are the source of anion exchange properties. Charged organic compounds are attracted to the active sites of the MIEX® resin. One limitation is that large organic molecules (>5000 Da) and small neutral organics, such as methane (molecular weight <1000 g/mol), are not effectively removed by MIEX®. According to research conducted to determine differences in single- use and multiple-use resin applications, waters with specific ultraviolet absorbance (SUVA) values, defined in Section 4.1.3, below 4 L/(m-mg) have higher DOC removal with multiple uses of resin.
Based on the wastewater quality of the Westford-Acton membrane effluent, it was hypothesized that MIEX® would effectively remove DOC (Mergen, 2008).
MIEX® can be regenerated and reused with little effect on the resin efficiency. A study conducted on the fluidized bed application of MIEX® in Sydney, Australia observed the effect of MIEX® regeneration on removal efficiency. This study found that for a 100 mL MIEX® bed with a fluid velocity of 8.6 m/h over the course of eight hours, the removal efficiency was not effected by more than 5% after five regenerations (Zhang, 2008). In a fluidized bed application, 5 to 10% of the resin is replaced by fresh resin after a specific number of laboratory-determined bed volume equivalents are treated. Bed volume equivalents are determined by the volume of wastewater which can be treated by a specified settled MIEX® volume divided by the settled MIEX® volume. Settling time for MIEX® is dependent on the size of the testing or operational unit. For one-liter jar tests, resin should be settled for one to ten minutes before decanting the treated water (Mergen, 2008). Regeneration is accomplished by thoroughly rinsing the used resin in a saturated salt solution. Resin can be stored in a cold, dark place, in a 5% brine solution for up to two years. To produce fresh resin for reuse, the regenerated resin is rinsed thoroughly with laboratory-grade water to remove the chloride ions from the active sites (Zhang, 2006). After the regeneration process, fresh resin can be stored in a cold, dark place in reagent grade water for up to one month before it is reused. The regeneration process of MIEX® is inexpensive and simple which is ideal for operational use. On-sight regeneration is affordable and requires the plant to purchase and dispose of less resin (Mergen, 2008). Figure 7 shows the regeneration process.
MIEX® has been applied in MBR plants as a pretreatment process to minimize fouling of the membrane. A study was conducted at the University of Technology in Sydney, Australia to determine if MIEX® resin is effective at significantly reducing DOC levels when used as a pre- treatment for a submerged membrane reactor (Zhang, 2006). This was determined by comparing different concentrations of MIEX® resin in the treatment. This research also compared the effectiveness of MIEX® and MIEX® with powdered activated carbon (PAC). The study found that the removal of organics increased with increased MIEX® concentration and that in less than an hour, the removal of TOC began to plateau. From this, the researchers concluded that a contact time of 20 minutes and concentration of 10 mL/L of MIEX® would optimize removal while considering cost and processing time. The study found that the MIEX® process alone is up to 60% efficient at DOC removal from wastewater and pairing MIEX® and PAC is up to 80% efficient (Zhang, 2006). Finally, the use of MIEX® as pre-treatment to a membrane system demonstrated reduced fouling of the membrane due to improved TOC and DOC removal. By studying the transmembrane pressure (TMP) over time, the researchers observed an approximately 10 kPa increase over eight hours when using MIEX® pre-treatment to a membrane system as opposed to a 45 kPa increase over eight hours with only PAC pre-treatment to a membrane system (Zhang, 2006).
Another study conducted at the University of Technology in Sydney, Australia used a fluidized bed of MIEX® to enhance dissolved organic removal with a semi-continuous process. The fluidized bed was tested with a bed volume of 20, 50, 100, and 150 mL of MIEX® to treat 100 bed volume equivalents of wastewater. The resin was regenerated with 2N sodium chloride solution after filtering 100 bed volume equivalents. Higher contact time is achieved through the larger MIEX® bed volumes. A removal of up to 75% of DOC with 100 mL of MIEX® per 100 bed volume equivalents of wastewater was achieved. This study also showed through multiple loading jar tests that a fluidized bed of MIEX® resin is capable of efficiently enhancing DOC removal as a pretreatment to a MBR by decreasing the DOC of the wastewater from 10 mg/L to approximately 4 mg/L (Zhang, 2007). In laboratory studies, a fluidized bed of MIEX® is simulated by multiple-loading jar tests. Resin is reused for 1250 to 2500 bed volume equivalents, and all treated water is combined to mimic the treated water from a fluidized bed of resin (Mergen, 2008). After treating a specified number of bed volumes, 5 to 10% of the resin would be regenerated in the full-scale application and replaced by fresh resin. Multiple loading jar tests are used to determine the optimum number of equivalent bed
volumes to treat before regeneration. The fluidized bed also allows for a continuous flow unit operation, which is capable of treating wastewater without disruption of the facility process.