Response in performance of the GAC-fluidized bed reactor process for BTX removal to perturbation in oxygen and nutrient supply

Abstract

Abstract The removal of benzene, toluene and xylenes (BTX) from contaminated groundwater is one of the largest and most pressing environmental problems of our time. There is an immediate need for new, cost-effective treatment techniques. One process option, the coupling of the high-rate biological fluidized bed process (FBR) with granular activated carbon (GAC) adsorption by using the GAC as the biological support surface (GAC-FBR system), is a promising technology just starting to see full-scale application. There are a number of questions concerning the GAC-FBR system's response to adverse environmental conditions that need to be addressed before this technology is to be fully embraced and unconditionally advocated. This research addresses the response of the GAC-FBR system to periods of interruption in oxygen and nutrient (nitrogen and phosphorus) supply. Data obtained using a laboratory-scale GAC-FBR, operated at various steady-state organic (and hydraulic) loading conditions and during perturbations such as interruptions in oxygen and nutrient supply, are summarized. Greater than 99% BTX removal was achieved at an organic loading rate of 6.7 kg COD/m3-day and an empty bed hydraulic retention time of 3 min. Interruption of nutrient supply for 24 h did not significantly impact system performance. A nutrient pulse feeding mode of 30 min on/30 min off was successfully used without affecting system performance. Bioregeneration of BTX adsorbed onto the GAC carrier during periods of interruption in oxygen supply was observed after oxygen was resupplied to the system. Compared with adsorption, GAC bioregeneration was a somewhat slower process. To remove the same amount of BTX adsorbed on the GAC during a period of oxygen deprivation via bioregeneration required a regeneration period approximately three times longer.