Abstract
This work aimed to assess the fixed-bed adsorptive performance of a primary paper mill sludge-based granular activated carbon (PSA-PA) for the removal of pharmaceuticals, namely carbamazepine (CBZ), sulfamethoxazole (SMX) and paroxetine (PAR), from water. The breakthrough curves corresponding to the adsorption of CBZ at different flow rates and in two different matrices (distilled and municipal wastewater) were firstly determined, which allowed to select the most favorable flow rate for the subsequent experiments. The fixed-bed adsorption of CBZ, SMX and PAR from single and ternary solutions in wastewater showed that the performance of PSA-PA was different for each pharmaceutical. According to the obtained breakthrough curves, the poorest bed adsorption capacity, either from single or ternary solution, was observed for SMX, which may be related with electrostatic repulsion at the pH of the wastewater used (pH ~ 7.3–7.7). Also, the bed adsorption capacity of PSA-PA for SMX, in the ternary solution, was notoriously lower compared to the single solution, while it slightly decreased for CBZ and even increased for PAR. The regeneration studies showed that the CBZ adsorption capacity of the PSA-PA bed decreased about 38 and 71% after the first and the second thermal regeneration stages, respectively. This decline was comparatively larger than the corresponding reduction of the PSA-PA specific surface area (SBET), which decreased only 5 and 25% for the first and second regeneration stages, respectively, and pointed to the lack of viability of more than one regeneration stage.
Highlights
The development of sustainable advanced processes is required for wastewater treatment to achieve environmental quality standards (EQS) and to protect water systems from potentially harmful pollutants
This Directive, which settled the necessity to develop a strategic approach to water contamination by pharmaceutical substances, established that future prioritization should be supported on the basis of results from Union-wide monitoring of emerging contaminants included in watch-lists that should be revised every two years
As it may be seen, in both matrices, the largest the flow rate, the steeper the breakthrough curve. This may be due to the fact that the increase in the flow rate implies a lessening of the contact time between the adsorbent (PSA-PA) and the adsorbate (CBZ), which leads to a reduction in the bed adsorption capacity and service time
Summary
The development of sustainable advanced processes is required for wastewater treatment to achieve environmental quality standards (EQS) and to protect water systems from potentially harmful pollutants In this sense, the European Union (EU) has been making efforts towards the implementation of EQS for priority substances, which were first set by Directive 2013/39/EU. GAC is frequently applied in the removal of organic compounds from water and wastewater (de Franco et al, 2017) and it can be used both in stirred-tank and column (fixed-bed) reactors; yet, fixed-bed columns are the most common for treating wastewater with GAC (Metcalf & Eddy, 2003) This type of reactor presents several advantages, namely, simple operation mode, effectiveness and easiness of scaling-up for industrial applications (de Franco et al, 2017). After fixed-bed saturation, GAC can be subjected to regeneration (so minimizing the demand of virgin adsorbents), which may be advantageous in terms of economic viability, environmental and energetic sustainability (Radhika et al, 2018)
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