The effect of preloading on rapid small-scale column test predictions of atrazine removal by GAC adsorbers

Abstract

Rapid small-scale column tests (RSSCTs) were evaluated for their ability to predict atrazine removal in pilot-scale granular activated carbon (GAC) adsorbers. The performance of both virgin and preloaded GACs was tested. Atrazine removal by virgin GAC was studied in post-filter adsorbers at Toulouse, France, and Choisy-le-Roi, France, using empty-bed contact times (EBCTs) of 10.3 and 14 min, respectively. For virgin GAC, RSSCTs successfully simulated atrazine removal over large-scale operating times of about 3.5–7 months. However, RSSCTs significantly overestimated atrazine removal at longer operating times. Atrazine removal by preloaded GAC was studied in pilot-scale post-filter adsorbers at Choisy-le-Roi, France, after preloading times of 5 months and 20 months. EBCTs were approximately 8.5 min. To describe the performance of pilot-scale adsorbers containing preloaded GAC, RSSCTs were initiated with virgin activated carbon, and preloading was simulated prior to the spiking of atrazine. For a pilot-scale adsorber containing GAC that had been preloaded for 5 months, the RSSCT data effectively described atrazine removal. However, the RSSCT was not successful in predicting atrazine removal by GAC after a preloading time of 20 months. Discrepancies between RSSCT and pilot data for long service times or after extended preloading periods may have been due to enhanced adsorption of background organic matter in the presence of oxygen. Overall, RSSCTs were judged to be most useful for predicting the initial performance of adsorbers containing virgin GAC.