Conversion of waste plastics into carbonaceous adsorbents and their application for wastewater treatment

ABSTRACT

Potentially poisonous elements (PPEs) water pollution has become one of the key issues in the field of water treatment. In recent years, it has threatened ecosystems as well as human health. This study aims to remove PPEs such as chromium (Cr⁶⁺), copper (Cu²⁺), lead (Pb²⁺), and Zinc (Zn²⁺) from both vehicle wash wastewater and aqueous solutions through batch experiments utilising carbonaceous adsorbents. Carbonaceous adsorbents were prepared from waste polyethylene terephthalate (wPET) and waste polystyrene (wPS) by carbonisation under a N₂ atmosphere followed by chemical activation with 1 M KOH and 1 M HCl. The carbonaceous adsorbents were characterised by Fourier transform infrared spectroscopy, surface area analysis, as well as scanning electron microscopy. The results show that, except for Cr⁶⁺, the adsorption of PPEs from aqueous solutions is highly dependent on pH, and the highest removal rate was recorded at pH 6.0. However, the largest Cr⁶⁺ adsorption was noted at pH 3.0. Using 0.2 g of adsorbent, the adsorption reached equilibrium after 90 min. Results demonstrated that highest removal of Pb²⁺, Cu²⁺, Cr⁶⁺, and Zn²⁺ from aqueous solution achieved over wPET-AC adsorbent was 98.40%, 97.60%, 96.80% and 99.90%, respectively, whereas that of wPS-AC adsorbent was 96.30%, 95.64%, 94.22% and 97.60%, respectively. Root mean square error (RMSE) was also calculated for the validation of data. Isotherms as well as kinetics models are used to evaluate the adsorption capacity of carbonaceous adsorbents for PPEs. The experimental results have shown that the pseudo-second-order as well as Langmuir models are the most suitable for the data. Thermodynamic studies have shown that the adsorption of PPEs is spontaneous as well as endothermic in nature. This study shows that the novel carbonaceous adsorbent wPET-AC and wPS-AC has great potential to remove PPEs from vehicle wash wastewater.

KEYWORDS:

• Carbonaceous adsorbent
• potentially poisonous elements
• vehicle-wash wastewater
• aqueous solution
• adsorptive removal

Disclosure statement

No potential conflict of interest was reported by the author(s).

Ethical approval

The conducted research is not related to either human or animal use.

Additional information

Funding

The authors acknowledge the funding offered by University of Peshawar, Khyber Pakhtunkhwa, Pakistan.