Development of sludge-based adsorbents: Preparation, characterization, utilization and its feasibility assessment

The increasing generation of sludge and its subsequent treatment are very sensitive environmental problems. For a more stable and sustainable treatment of sludge, there have been many studies, including the conversion of sludge into sludge-based adsorbents (SBAs) for pollutants removal. In this review, current SBAs preparation conditions and use as adsorbent for contaminant removal in water treatment are summarized and discussed. Carbonization, physical activation and chemical activation are three common preparation methods. The controlling key parameters include pyrolysis temperature, dwell time, heating rate, activator and feedstock type. The efficacy of SBAs in contaminant adsorption depends on their surface area, pore size distribution, surface functional groups and ion-exchange capacity. It has been demonstrated that SBAs can attain high uptakes of dyes and metal ions due to their high cation exchange capacity; whereas the strong antibiotics adsorption performance of SBAs derives from high degree of mesoporosity. In addition, thermal treatment significantly stabilizes heavy metals contained in sludge. The paper also discusses the economic feasibility and environmental safety of preparation and application of SBAs. Further research will include investigations on the migration and transformation of element in sludge by thermal treatment, more economical and efficient chemical activation reagents, obtaining SBAs for designated application, combination of coagulation and SBAs adsorption, regeneration of SBAs and full-scale tests.