Resource utilization of drinking water treatment aluminum sludge in green cementing materials: Hydration characteristics and hydration kinetics.

As a byproduct of water treatment, drinking water treatment aluminum sludge (DWTAS) has challenges related to imperfect treatment and disposal, which has caused potential harm to human health and the environment. In this paper, heat treatment DWTAS as a supplement cementitious material was used to prepare a green cementing material. The results show that the 800°C is considered as the optimum heat treatment temperature for DWTAS. DWTAS-800°C is fully activated after thermal decomposition to form incompletely crystallized highly active γ-Al2O3 and active SiO2. The addition of DWTAS promoted the formation of ettringite and C-(A)-S-H gel, which could make up for the low early compressive strength of cementing materials to a certain extent. When cured for 90 days, the compressive strength of the mortar with 30% DWTAS-800°C reached 44.86 MPa. The dynamic process was well simulated by Krstulovic-Dabic hydration kinetics model. This study provided a methodology for the fabrication of environmentally friendly and cost-effective compound cementitious materials and proposed a "waste-to-resource" strategy for the sustainable management of typical solid wastes.

Effects of freeze-thaw cycles on nutrient removal from bioretention cells.

There have been numerous summaries of the runoff purification characteristics of bioretention cells in warm climates. However, little has been done on the effects of freeze-thaw cycles (FTCs) that frequently occur in cold regions on bioretention cell performance. Three experimental columns were constructed to simulate the operation of the bioretention cell under the FTCs. The effects of FTCs on the nutrient removal efficiency of different filling bioretention cells were analyzed. The results showed that the ammonia nitrogen (NH4+-N) concentration in the effluent of the wood chip bioretention cell under the T3 conditions (WBCF) (2.35 mg/L) was significantly higher than that of the wood chip bioretention cell operating at room temperature (WBCR) (0.62 mg/L). The effluent NH4+-N concentration of aluminum sludge bioretention cell (ABCF) (0.096 mg/L) under the FTCs was lower than that of WBCF (0.91 mg/L). Under the T3 condition, the effluent nitrate nitrogen (NO3--N) and total nitrogen (TN) concentrations of WBCF (5.33 mg/L and 8.86 mg/L) were higher than those of WBCR (5 mg/L and 6.11 mg/L) at room temperature. Under FTCs conditions, both WBCF and ABCF had high NO3--N removal efficiency (up to 85.87% and 24.75%) at the initial stage of thawing of the filler, and the efficiency gradually decreased with the thawing of the filler. With the increase of FTCs, the NO3--N removal efficiency of WBCF gradually decreased (always higher than 13.6%), while the removal efficiency of ABCF fluctuated wildly (the removal efficiency was primarily negative). The total phosphorus (TP) concentration in the effluent of WBCF (0.11 mg/L) under the T3 conditions was lower than that of WBCR (0.02 mg/L) at room temperature, and the TP concentration of ABCF (0.021 mg/L) in the effluent under the FTCs was slightly lower than that of WBCF (0.031 mg/L). The FTCs have a more significant impact on removing nitrogen pollutants in runoff, but have little effect on phosphorus. Compared with aluminum sludge, wood chips are more suitable for efficient removal of nitrogen pollutants in runoff under the FTCs. The experimental conclusions can provide a reference for the construction of bioretention cells in cold regions.

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.

Management of selected waste generated during cable production.

The subject of the research was the recovery of raw materials from waste generated in the production of cable insulation and the management of aluminum sludge. It was found that 49% (w/w) acetophenone, 6.8% (w/w) α-methylstyrene, and 17.2% (w/w) cumyl alcohol can be recovered from waste with a loss on ignition of 95% and used in various industries. A gas chromatograph equipped with a mass spectrometry detector was used to identify the recovered compounds. A waste distillation process was proposed to remove the water layer and obtain a concentrated acetophenone fraction. A method of neutralizing the water fraction and distillation residues is presented. The proposed waste management method is an alternative method to the currently used thermal transformation method. In turn, aluminum sludge was used to produce aluminum sulfate, which was used in the plant's sewage treatment plant as a coagulant. The effect of this action was a reduction of 67% in the content of total iron, 60% of trivalent iron, and 32% of chemical oxygen demand. The above-mentioned examples of waste management are part of a closed-loop waste management strategy.

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

To solve the problems such as water eutrophication caused by excess phosphorus, the potential residual value of aluminum sludge was fully exploited and its phosphate adsorption capacity was further improved. In this study, twelve metal-modified aluminum sludge materials were prepared by co-precipitation method. Among them, Ce-WTR, La-WTR, Y-WTR, Zr-WTR, and Zn-WTR showed excellent adsorption capacity for phosphate. The adsorption performance of Ce-WTR on phosphate was twice that of the native sludge. The enhanced adsorption mechanism of metal modification on phosphate was investigated. The characterization results showed that the increase in specific surface area after metal modification was 9.64, 7.5, 7.29, 3, and 1.5 times, respectively. The adsorption of phosphate by WTR and Zn-WTR was in the accordance with Langmuir model, while the others were more following the Freundlich model (R2 > 0.991). The effects of dosage, pH, and anion on phosphate adsorption were investigated. The surface hydroxyl groups and metal (hydrogen) oxides played an important role in the adsorption process. The adsorption mechanism involves physical adsorption, electrostatic attraction, ligand exchange, and hydrogen bonding. This study provides new ideas for the resource utilization of aluminum sludge and theoretical support for preparing novel adsorbents for efficient phosphate removal.

Achieving win-win outcomes with cerium-loaded porous aluminum sludge hydrogel microspheres for enhanced phosphate removal.

Breaking the technical bottleneck of traditional powdered adsorbent in phosphate adsorption application treatment, a macroscopic high adsorption performance aluminum sludge-based composite hydrogel material was constructed to synergistically solve the problems of water eutrophication and aluminum sludge resourcization. In this study, porous Ce-modified aluminum sludge hydrogel microspheres (Ce-AlS-SA) were prepared to improve the surface chemical structure and microscopic morphology of the macroscopic adsorbent material to enhance the adsorption capacity and achieve effective solid-liquid separation. The best adsorption performance of the material (Ce-AlS12-SA1) was obtained when the Ce-AlS: SA: Na2CO3 was 12:1:1, and obtained the optimal adsorption conditions by Response Surface Method (RSM) with 1.5 mg/L of the dosage, 4 of pH and 50 mg/L of Cphosphate. The maximum adsorption of 20.36 mg P/g was obtained by the Langmuir model at 303 K, which was 2.92 times more than raw sludge. According to the Freundlich and pseudo-second-order kinetic model, the adsorption process is chemisorption; the multi-stage adsorption process is reflected in the intraparticle diffusion and film diffusion models. The main mechanisms combined with the characterization analysis are electrostatic gravity, ligand exchange, and inner-sphere complexation. Meanwhile, Ce-AlS12-SA1 shows good resistance to interference in the coexistence of multiple ions. Therefore, this material can be recognized as a new material with in-depth, diversified and practical needs for resourceful utilization, which is expected to achieve extensive engineering applications in the future.

Structured sludge derived multifunctional layer for simultaneous separation of oil/water emulsions and anions contaminants.

The effective treatment of complex oily wastewater is of great significance but still a considerable challenge, since single-function, expensive reagents, and complicated process have emerged as shackles for practical applications. Herein, with the objective to waste-control-waste, we proposed a facile and sustainable strategy to fabricate a low-cost multifunctional layer from hazardous waste aluminum sludge (WAS) for complex oily wastewater management. The as-designed layered double oxides/WAS (LDOs/WAS) layer with three-dimensional (3D) hierarchical rough surface exhibited excellent underwater superoleophobicity even under corrosive conditions and low adhesion to oil without any chemical modification reagent treatment. Significantly, the layer can be applied to gravity-directed simultaneous efficient oil-in-water emulsions and anions (taking phosphate as an example) separation with a separation efficiency for emulsion and phosphate up to 99.4% and 99.1%, respectively, and a high separation flux of above 2585 L m-2 h-1. Notably, the flux can be controlled simply and flexibly by adjusting the thickness of the layer. Furthermore, the layer also displayed excellent thermal stability, chemical stability, durability and recyclability. Therefore, this work not only presents a promising approach to design sludge-based multifunctional materials for complex oily wastewater remediation, but also shows great potential and value in environmental pollutions reduction and industrial applications.

The performance and mechanism of iron-modified aluminum sludge substrate tidal flow constructed wetlands for simultaneous nitrogen and phosphorus removal in the effluent of wastewater treatment plants.

Aiming at the poor N and P removal performance in the effluent of wastewater treatment plants by constructed wetlands (CWs), aluminum sludge (AS) from water supply plants was used to prepare iron-modified aluminum sludge (IAS), and tidal flow constructed wetlands (TFCWs) using IAS as substrates were constructed. By means of high-throughput sequencing, X-ray diffractometer (XRD), etc., the removal mechanism of N and P in the system and fate analysis of key elements were also interpreted. Results showed that an interlayer structure beneficial to adsorbing pollutants was formed in the IAS, due to the iron scraps entering into the molecular layers of AS. The removal rates of TP and TN by IAS-TFCWs reached 95 % and 47 %, respectively, when the flooding/resting time (F/R) and C/N were 6 h/2 h and 6. During the three-year operation of the IAS-TFCWs, the effluent concentrations of CODCr, NH4+-N, and TP could comply with Class IV Standard of "Environmental Quality Standards for Surface Water" (GB3838-2002). The mechanism analysis showed that the N removal was effectuated through Fe2+ as the electron donor of Fe(II)-driven the autotrophic denitrifying bacteria to reduce nitrate, while the P removal mainly depended on the adsorption reaction between FeOOH in IAS and phosphate. In conclusion, the stable Fe-N cycle in the IAS-TFCWs achieved simultaneous and efficient N and P removal.

Preparation of aluminum sludge composite gel spheres and adsorption of U(IV) from aqueous solution.

A novel three-dimensional aluminum sludge/polyvinyl alcohol/sodium alginate(AS/PA/SA) gel spheres were designed and prepared for uranium(VI) adsorption, and it overcomes the shortcomings of poor recycling of powdery aluminum sludge adsorbent and poor stability of sodium alginate. Experiments show that the P-S-AS has a good pH range for removal of uranium (4-5). Fitting experimental data with pseudo-first-order kinetic model and pseudo-second-order kinetic model shows that the adsorption of U(VI) by P-S-AS is a chemical action. The fit of the Langmuir isotherm model and Freundlich isotherm model to the experimental data found that the P-S-AS adsorbed U(VI) to a single layer. Thermodynamic analysis shows that the adsorption occurs spontaneously, and an increase in temperature is favorable for the adsorption of uranium by the P-S-AS. Fourier transform infrared (FTIR) and X-ray photoelectron spectroscopy (XPS) analysis of the P-S-AS before and after adsorption showed that the main adsorption mechanism was the complexation reaction between functional groups and U(VI), the bonding reaction between metal oxides and U(VI).