Preparation and Characterization of Pulp and Paper Mill Sludge-Activated Biochars Using Alkaline Activation: A Box-Behnken Design Approach

This study utilized pulp and paper mill sludge as a carbon source to produce activated biochar adsorbents. The response surface methodology (RSM) application for predicting and optimizing the activated biochar preparation conditions was investigated. Biochars were prepared based on a Box-Behnken design (BBD) approach with three independent factors (i.e., pyrolysis temperature, holding time, and KOH:biomass ratio), and the responses evaluated were specific surface area (SSA), micropore area (S-micro), and mesopore area (S-meso). According to the RSM and BBD analysis, a pyrolysis temperature of 800 degrees C for 3 h of holding and an impregnation ratio of 1:1 (biomass:KOH) are the optimum conditions for obtaining the highest SSA (885 m(2) g(-1)). Maximized Smicro was reached at 800 degrees C, 1 h and the ratio of 1:1, and for maximizing S-meso (569.16 m(2) g(-1)), 800 degrees C, 2 h and ratio 1:1.5 (445-473 m(2) g(-1)) were employed. The biochars presented different micro- and mesoporosity characteristics depending on pyrolysis conditions. Elemental analysis showed that biochars exhibited high carbon and oxygen content. Raman analysis indicated that all biochars had disordered carbon structures with structural defects, which can boost their properties, e.g., by improving their adsorption performances. The hydrophobicity-hydrophilicity experiments showed very hydrophobic biochar surfaces. The biochars were used as adsorbents for diclofenac and amoxicillin. They presented very high adsorption performances, which could be explained by the pore filling, hydrophobic surface, and pi-pi electron-donor-acceptor interactions between aromatic rings of both adsorbent and adsorbate. The biochar with the highest surface area (and highest uptake performance) was subjected to regeneration tests, showing that it can be reused multiple times.

Automated summary

This study utilized pulp and paper mill sludge to produce activated biochar adsorbents and optimized the preparation conditions using response surface methodology. The results showed that the biochars prepared under specific conditions exhibited high surface area and excellent adsorption performance, making them effective adsorbents for pollutant removal.