Effect of sludge retention time on bioregeneration of powdered activated carbon loaded with paracetamol

Abstract

Bioregeneration of activated carbon (AC) is used to describe the renewal of the adsorptive capacity of AC by microorganisms for further adsorption. Recently, bioregeneration of AC has attracted more attention due to its potential to overcome some challenging of costly ex-situ regeneration methods. This study aims to investigate the bioregeneration of powdered activated carbon (PAC) loaded with paracetamol (PAR) and the effect of sludge retention time (SRT) on bioregeneration. A modified method was used to determine the bioregeneration, and also the adsorption and desorption kinetics of PAR onto PAC and the degradation of PAR in abiotic/biotic conditions were assessed to reveal the bioregeneration mechanism. The adsorption efficiency of PAR onto PAC at equilibrium conditions was as high as 99.8%. The isotherm and kinetic model studies showed that chemisorption was dominant in the adsorption of PAR onto PAC. The desorption efficiency of PAR from PAC was 26.3% in the abiotic conditions although PAR is a hydrophilic pharmaceutical active compound (PhAC). The bioregeneration efficiencies of PAC at the SRTs of 10, 30 and 60 days were determined as 17.3, 26.8 and 20.1%, respectively. The concentration gradient contributed 11.4% to the bioregeneration efficiency at all SRTs and the difference between the bioregeneration amount and the concentration gradient was attributed to the extracellular enzymatic activity. The bioregeneration efficiency at the SRT of 30 days was the highest among all SRTs and the more dominant mechanism in bioregeneration was found as the extracellular enzymatic activity at this SRT. The low desorption capacity limited the bioregeneration efficiency in all SRTs due to the low adsorption reversibility caused by chemisorption although the biodegradability of PAR was high at all SRTs tested in this study. [GRAPHICS] .