Enhanced phosphate adsorption studies on several metal-modified aluminum sludge: preparation optimization, adsorption behavior, and mechanistic insight

Transforming Drinking Water Treatment Residuals into Efficient Adsorbents: A Review of Activation and Modification Methods

The management of drinking water treatment residuals (DWTRs) poses significant environmental and economic challenges for water treatment facilities; however, these residues have considerable potential as effective adsorbents for pollutant removal. The objectives of this review are to evaluate research conducted from 2015 to 2024 on treatment and modification techniques aimed at enhancing DWTRs' efficacy as adsorbents, analyze the influence of preparation methods on DWTRs performance, evaluate DWTRs adsorbents for different pollutants, and discuss the limitations and challenges in DWTRs applications. The review addresses the knowledge gap by detailed analysis of these advanced modification methods, which have not been extensively reviewed before, and their direct impact on the physicochemical properties and adsorption performance of DWTRs. The review explores various methods including thermal treatment, chemical activation, granulation, pelletization, and the development of composite materials. Key findings indicate that thermal treatment significantly increases surface area and porosity, while chemical activation introduces functional groups that enhance adsorption capacity. Composite DWTRs, incorporating metals, organic compounds, or magnetic properties, demonstrate superior performance in adsorbing diverse contaminants such as dyes and heavy metals. Despite these advancements, challenges remain, particularly in reporting the life cycles and costs of the treated and modified DWTRs and the regeneration of spent adsorbents. The review highlights the importance of optimizing preparation techniques to enhance the physicochemical properties and adsorption performance of DWTRs. By synthesizing existing knowledge and identifying key areas for future research, this review aims to advance sustainable practices in water treatment and resource recovery, aligning with global sustainability goals.

Sludge-derived alginate-like extracellular polymers (ALE) for preparation of Fe-ALE and FeCaMg-ALE: Application to the adsorption of phosphate

Excess phosphorus (P) in wastewater has potential risk of causing harmful algal bloom and eutrophication in receiving wastewater. In this study, alginate-like extracellular polymers (ALE) derived from conventional activated sludge were modified with ionic cross-linking agents (Fe3+, Ca2+, and Mg2+) to develop Fe-ALE and FeCaMg-ALE for the adsorption of phosphate from wastewater. The adsorption process of phosphate by Fe-ALE and FeCaMg-ALE can be well described by pseudo-second-order kinetics and Freundlich isotherm model with a high level of accuracy, indicating that the adsorption processes were chemical, multi-layer adsorption process. The maximum adsorption capacity of dry Fe-ALE and FeCaMg-ALE concerning phosphate were 15.06 and 20.10 mg/g, respectively at 298 K. The adsorption capacity remained relatively consistent across a pH range of 2.0-11.0. FT-IR, XRD, SEM coupled with XPS analysis demonstrated the ALE had been successfully compounded with Fe3+ or Fe3+/Ca2+/Mg2+. Based on the experimental results and characteristic analysis, the main mechanism of phosphate by Fe-ALE and FeCaMg-ALE are physical filling, electrostatic attraction, ligand exchange and precipitation reaction. This work provides a new perspective for preparing ALE-based adsorbent using conventional activated sludge as raw material, realizing the treatment of waste with waste and effectively recovering phosphate from wastewater.

Construction of 3D network aluminum sludge-based hydrogel beads: combination of macroization, amino functionalization, and resource utilization

An aluminum sludge-based composite material was constructed against the problems of phosphorus pollution and the waste of aluminum sludge resources. Utilizing metal Ce doping and hydrogel microbeads with pore preparation, the adsorption performance of the original sludge was improved. Meanwhile, the macroscopic body was constructed, and on this basis, polyethyleneimine (PEI) was introduced to complete the amino functionalization further to enhance the adsorption of phosphorus by the adsorbent, and NH-CeAIS-10 microbeads were successfully prepared. In adsorption, microbeads with larger specific surface area and richer functional groups are better choice compared to original sludge. The results of SEM, BET, FT-IR, and XPS analyses indicate that the adsorption of phosphorus by the microbeads is mainly achieved through electrostatic interactions, ligand exchange, and the formation of inner-sphere complexes. According to the Langmuir model, the maximum phosphorus adsorption capacity of NH-CeAIS-10 was 29.56 mg g-1, which was four times higher compared to native aluminum sludge. This also confirms the significant enhancement of phosphorus adsorption through the modification of aluminum sludge. Besides, in dynamic adsorption column experiments, the material exhibited up to 99% removal in simulated wastewater for up to 30 days, demonstrating the great adsorption potential of NH-CeAIS-10 in engineering applications.