Phosphorus adsorption of a residue from the pulp and paper industry (grits): contributions to tertiary wastewater treatment

Phosphorus is related to the control of eutrophication and wastewater and is an important source of Phosphorus to aquatic environments. Brazil is the second largest producer of cellulose worldwide (12 million tons in first half of 2023). Thus, residues from this industry represent a challenge in waste management. The present study aimed to evaluate the Phosphorus adsorption capacity (q_max) of a residue from the pulp and paper industry, “grits”, which are rich in Calcium. The residues were characterized using diverse techniques, and kinetic and isothermal essays were performed with dried (105 °C) and calcined (650 °C) grits. Characterization indicated that the calcined grits maintained the same compounds present in the dried grits. Furthermore, calcination increased the specific surface area of the grits (from 1 m to 6.3 m² g^‒1). The pH_pzc for dried grits was 7.25, and for calcined grits 7.97. The kinetic tests revealed an equilibrium time of 12 h for dried grits, and 1 min for calcined grits. The isothermal tests reached maximum adsorption capacities (q_max) of 10.3 and 111.6 mgP g^‒1 for dried and calcined grits, respectively. The calcined grits were shown to be a better adsorption material, leading to faster removal of dissolved P. The use of grits provides a low-cost technological solution for tertiary wastewater treatment and might contribute to the circular economy, considering the possibility of reuse in agriculture (compound rich in Calcium and Phosphorus).