Application of Box-Behnken design to optimize the phosphorus removal from industrial wastewaters using magnetic nanoparticles

Abstract

Phosphorus is essential for all living organisms and limits aquatic plant growth. Pulp mill effluents, particularly from Eucalyptus bleached kraft pulp mills, contain phosphorus concentrations that vary with operational conditions. This variability poses challenges for effective treatment and phosphorus removal. However, uncontrolled release of phosphorus-rich wastewaters causes eutrophication. This study focuses on optimizing phosphorus removal from such effluents using cobalt ferrite nanoparticles, with an emphasis on process optimization to address this variability. Minimizing phosphorus concentrations is crucial in wastewater engineering and surface water management. By employing design of experiments and response surface methodology, we aim to fine-tune the phosphorous removal process and pinpoint the key factors with the most significant impact. Optimal conditions for achieving over 90% removal from an effluent with 5 mg P/L were identified as a sorbent dose greater than 1.3 g/L and a pH range between 5 and 7, all within a contact time of only 15 min. For a contact time of 1 and 24 h, the conditions adjust to a sorbent dose greater than 0.97 and 0.83 g/L, respectively, with the pH range remaining the same. Our results highlight the effectiveness of cobalt ferrite nanoparticles as sorbents in the removal of phosphorus for water treatment purposes. This approach presents a sustainable and proficient strategy for phosphorus recovery from pulp mill effluents, thereby lessening environmental repercussions and offering a valuable resource for future use. This contributes to the maintenance of water quality and ecosystem preservation.

Keywords: Adsorption; Box-Behnken design; Cobalt ferrite nanoparticles; Design of experiments; Eutrophication; Phosphate; Response surface methodology.

Fig. 1

Pareto chart with the effects of the factors in the response studied (removal (%)) at (a) 15 min, (b) 1 h, and (c) 24 h of exposure. In the figure: A represents the initial P concentration (mg/L), B is the sorbent dose (g/L), and C is the pH. Factors with values below the dashed line are not significant

Fig. 2

Interaction plots between the main effects affecting P removal after (a) 15 min, (b) 1 h, and (c) 24 h of contact time

Fig. 3

3D response surfaces obtained for the P removal with the reduced models after (a) 15 min, (b) 1 h, and (c) 24 h of exposure to CoFe₂O₄ NPs, as a function of the dose of sorbent and pH (on the left), pH and initial P concentration (in the middle), and initial P concentration and dose of sorbent (on the right). The variable not present in the plot is fixed at the central point (14 mg P/L, pH 7, and sorbent dose of 1.35 g/L)