Is In-Service Granular Activated Carbon Biologically Active? An Evaluation of Alternative Experimental Methods to Distinguish Adsorption and Biodegradation in GAC

Abstract

In-service granular activated carbon (GAC) may transform into biological activated carbon (BAC) and remove contaminants through both adsorption and biodegradation, but it is difficult to determine its biodegradative capacity. One approach to understand the GAC biodegradative capacity is to compare the performance between unsterilized and sterilized GAC, but the sterilization methods may not ensure effective microbial inhibition and may affect adsorption. This study identified the 14C-glucose respiration rate as the best metric to evaluate the effectiveness of three sterilization methods: sodium azide addition, autoclaving, and γ irradiation. The sterilization protocols were refined, including continuously feeding 300 mg/L of sodium azide, three cycles of autoclaving, and 10–12 kGy of γ irradiation. Parallel minicolumn tests were conducted to identify sodium azide addition as the most broadly effective sterilization method with an insignificant effect on adsorption in most cases, except for the adsorption of anionic compounds under certain conditions. Nevertheless, this problem was solved by decreasing the azide dosage as long as it is still sufficient to provide effective microbial inhibition. This study helps to develop an approach that differentiates adsorption and biodegradation in GAC, which could be used by future studies to advance our understanding of BAC filtration.

New Perspectives on the Interactions between Adsorption and Degradation of Organic Micropollutants in Granular Activated Carbon Filters

“…To this end, the individual contributions of biodegradation and adsorption have primarily been estimated indirectly through the observed difference between a biologically active GAC filter and a sterilized GAC filter. − In wastewater, the use of this approach has indicated a positive contribution of GAC biofilms to the removal of several biodegradable micropollutants, such as diclofenac and sulfamethoxazole. ,, However, comparing biologically active and sterilized filters has inherent limitations. The sterilization methods that are applied might be unable to inhibit biological activitycompletely or selectivelywithout affecting adsorption conditions .…”