Green chemistry: advancing planetary phosphorus sustainability through the synergy of graphene oxide modified with magnetic nanoparticles (M@GO) for extracting tertiary effluent phosphorus in sewage treatment plants

Abstract

Securing the enduring sustainability of global phosphorus (P) utilization has become a key societal priority. The application of green chemistry and green engineering presents an opportunity to mitigate these challenges and contribute to the sustainable closure of the global phosphorus cycle by addressing the extraction of phosphorus from waste and subsequent reuse. In this manuscript the feasibility of a novel magnetic graphene oxide for wastewater phosphorus recovery/removal is described. The primary technical benefit of this solid adsorbent lies in its easy separation from treated water through magnetic field application. The key factors affecting the sorption efficiency (contact time, pH, and adsorbent dosage) are studied. During the first 30 min, at pH 8 and with a dosage of 0.8 g L⁻¹, 25% of the initial concentration is reduced. Among the 3 thermodynamic models proposed, the Langmuir isotherm provides the best fit to the experimental results, with a maximum adsorption capacity of 2.69 mg g⁻¹. Four kinetic models are evaluated to describe the adsorption of phosphorus on this magnetic graphene oxide for different initial adsorbate concentrations and adsorbent dosages. Among them, Langmuir kinetics provide the best fit to the experimental data. The adsorption rate constant is 0.72 L mg⁻¹ h⁻¹, and the desorption rate is 0.58 h⁻¹, in accordance with the identified Langmuir isotherm. Parameter values calculated from a mass transfer kinetic model indicate that the mass transfer of phosphorus between the bulk liquid and the solid surface is not the rate-limiting step of the adsorption process. Following the separation of this magnetic solid from the treated wastewater, an ammonia aqueous solution can recover the phosphorus from the solid adsorbent. Preliminary results show absorbed phosphorus recovery yields above 99% with a solid–liquid ratio up to 5 times higher than that used in the adsorption process.