Utilization of waste sludge: Activation/modification methods and adsorption applications of sludge-based activated carbon

Over recent years, numerous studies have been concerned with recovering value-added products from sludge. Various methods have been used to prepare it as an adsorbent. Herein, a comprehensive and critical analysis of sources, pretreatments, activations, applications and environmental leaching risks of sludge-based activated carbon (SBAC) has been carried out. The characteristics and carbon-forming properties of sludges from different sources have been discussed, indicating that organic matter and minerals are the parts that favor carbon-forming. Comparing the BET surface area, pore volume and pore size distribution of SBACs obtained by different acti-vation strategies, it is found that chemical activation can significantly increase the porosity compared to physical activation. By critically reviewing the co-carbonization of waste sludge and other wastes, it has been concluded that factors such as temperature, raw material and doping ratio will determine the synergistic or antagonistic effect. The application of SBAC to absorb organic pollutants and heavy metals in water has been investigated. It has been found that the relationship between the particle size of pollutants and the pore size distribution of SBAC, and the interaction between pollutants and surface functional groups directly influence the adsorption effect of SBAC on environmental pollutants. Based on the summary of the recent research on SBAC, it is suggested that the research on SBAC should focus on improving chemical activation efficiency and the mechanism of the activation process. Moreover, it is proposed that the strategy of stabilizing heavy metals (such as adding metal oxides) should be actively studied in the future.