Abstract
The wide occurrence of pharmaceuticals in aquatic environments urges the development of cost-effective solutions for their removal from water. In a circular economy context, primary paper mill sludge (PS) was used to produce activated carbon (AC) aiming the adsorptive removal of these contaminants. The use of low-cost precursors for the preparation of ACs capable of competing with commercial ACs continues to be a challenge. A full factorial design of four factors (pyrolysis temperature, residence time, precursor/activating agent ratio, and type of activating agent) at two levels was applied to the production of AC using PS as precursor. The responses analysed were the yield of production, percentage of adsorption for three pharmaceuticals (sulfamethoxazole, carbamazepine, and paroxetine), specific surface area (SBET), and total organic carbon (TOC). Statistical analysis was performed to evaluate influencing factors in the responses and to determine the most favourable production conditions. Four ACs presented very good responses, namely on the adsorption of the pharmaceuticals under study (average adsorption percentage around 78%, which is above that of commercial AC), and SBET between 1389 and 1627 m2 g-1. A desirability analysis pointed out 800 °C for 60 min and a precursor/KOH ratio of 1:1 (w/w) as the optimal production conditions.
Highlights
Pharmaceuticals are currently recognized as an important group of environmental contaminants that can affect the ecosystems, even at very low concentrations [1,2,3]
The results indicate that the highest temperature (X1) and the highest impregnation ratio (X3) were the most favourable conditions
These activated carbon (AC) have in common being produced with the maximum pyrolysis temperature here considered (800 oC), showing that this temperature positively influences the development of porosity
Summary
Pharmaceuticals are currently recognized as an important group of environmental contaminants that can affect the ecosystems, even at very low concentrations (ng L-1 to μg L-1 level) [1,2,3]. Pulp and paper industry generates a huge amount of residues [20, 21] and this application represents an unconventional and innovative way of waste management [20], contributing to minimize the high costs associated to the application of ACs in WWTPs. The production of AC can be performed via physical or chemical activation together with thermal decomposition under limited supply of oxygen (pyrolysis). KOH and K2CO3 are believed to act as intercalating agents with potassium ions functioning as template for the formation of porosity [24] These two activating agents present themselves as more environmentally friendly when compared with the use of acids or even ZnCl2. The AC used as reference was PBFG4, kindly provided by Chemviron
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