Antibiotic removal from wastewater

Researchers report the adsorption of a strong polycation, poly(3-methacryloylamino propyl-trimethylammonium chloride) (PMAPTAC) on nanosilica (nano-SiO₂) extracted from rice husk. PMAPTAC was successfully synthesised and characterised by ¹H-nuclear magnetic resonance (¹H NMR) and gel-permeation chromatography (GPC) methods. PMAPTAC characteristics were found to be M_n = 1.61 × 10⁵, M_w = 2.16 × 10⁶, M_w/M_n = 13.4. Beta-lactam cefixime (CEF) removal was dramatically enhanced after polymer coating by pre-adsorption of PMAPTAC on nano-SiO₂.

The new adsorbent was dubbed PMAPTAC coated nano-SiO₂ (PCNS). Required time for adsorption, PCNS dosage, pH, and KCl concentration were thoroughly optimised for CEF removal and achieved at 120 min, 10 mg/mL, 4, and 1 mM, respectively. A two-step model can be used to fit the PMAPTAC on nano-SiO₂ and CEF on PCNS isotherms at different ionic strengths. Adsorption kinetics of CEF on PCNS appears to be pseudo-second-order. CEF removal using PCNS reached 89%, saturating at 10.9 mg/g. The driving force for CEF adsorption on PCNS was primarily Coulombic interaction of negative CEF species and positive surface charge of PCNS.

Real hospital wastewater sample

After three reuses, CEF elimination was still greater than 85%. The influence of some organics on CEF treatment using PCNS was insignificant while CEF removal from a real hospital wastewater sample was greater than 70%. The study indicates that a hybrid and new adsorbent based on nano-SiO₂ rice husk with pre-adsorption with PMAPTAC is useful for antibiotic removal from wastewater.

The study has been published in Progress in Organic Coatings, Volume 158, September 2021.