Study on the preparation of granular alum sludge adsorbent for phosphorus removal

Application of modified water treatment residuals in water and wastewater treatment: A review

Large quantities of sludge known as water treatment residuals (WTRs) are generated from water treatment facilities across the world. Various attempts have been made to reuse these residuals. Among the different applications of WTRs, their reuse in water and wastewater treatment has received more attention. However, direct application of raw WTRs is associated with some limitations. In the last decade, in order to improve their characteristics, numerous investigators have modified WTRs by different methods. This paper reviews the different methods applied to WTRs to enhance their characteristics. The effects of these modifications on their characteristics are explained. The applications of modified WTRs as a filtration/adsorption medium for treating textile/dye wastewater, groundwater containing different anionic and cationic pollutants, storm water runoff, and as a substrate in constructed wetlands are presented in detail. Future research needs are highlighted. The review clearly indicates the potential of different modification methods to improve the removal of a variety of pollutants by WTRs from water and wastewater.

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 C_phosphate. 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.

Ceramsite made from drinking water treatment residue for water treatment: A critical review in association with typical ceramsite making

The use of ceramsite to construct filtration systems (e.g., biofilters) is a common method for water treatment. To promote such applications, the development of low-cost, high-performance, and environmentally friendly ceramsites has received increasing attention from scientists, and a critical step in the development is the preparation of raw materials. As an inevitable and non-hazardous by-product during potable water production, drinking water treatment residue (DWTR) is typically recycled to make water treatment ceramsite to promote recycling in filtration systems. This study aims to bridge the knowledge gap regarding DWTR in making ceramsites for water treatment. The results suggest that the fabrication methods for DWTR-based ceramsite can be generally classified into sintering and non-sintering procedures. For the sintering method, owing to the heterogeneous properties (especially aluminum, iron, and calcium), DWTR has been applied as various sub-ingredients for raw materials preparations. In contrast, for the non-sintering method, DWTR is commonly applied as the main ingredient, and natural curing, physical crosslinking, and thermal treatment methods have been typically adopted to make ceramsite. However, DWTR-based ceramsites tend to have a high adsorption capability and favorable microbial effects to control different kinds of pollution (e.g., phosphorus, nitrogen, and organic matter). Future work is typically recommended to thoroughly evaluate the performance of DWTR-based ceramsite-constructed filtration systems to control water pollution concerning the making procedures, the potential to control pollution, the stability, and the safety of raw DWTR-based ceramsite, providing systematic information to design more proper planning for beneficial recycling.

Ecologically Engineered Systems for Treating Agriculture Runoff by Integrating “Wastes” into Constructed Wetlands

Runoff from agricultural irrigation is contaminated and loaded with pesticides. Frequent toxic levels of pesticide detection in the ecosystem motivate scientists and engineers to diminish agro-chemicals flowing into the environment. Constructed wetland, CWs, treatments are a sustainable methodology of special interest since it possess a symbiosis value. Flytek (FT) pesticide use has increased at an unprecedented rate for crop production as well as an increase in runoff loaded with Flytek. This study introduces the use of constructed wetlands based on an alum- sludge substrate for the purpose of Flytek (FT) removal performance. The system is based on an adsorption column and a sludge cake coupled with gravel acting as a carrier in order to be an adsorption bed and filtration system for Flytek removal. The structure, morphology and characteristics of the adsorption bed material “alum sludge” were characterized using X-ray diffraction spectroscopy and Scanning Electron Microscope (SEM). Additionally, Fourier-Transform infrared spectroscopy (FTIR) was explored. The experimental results revealed that a vertical flow constructed wetland is significant in eliminating the Flytek pesticide. However, the amount and height of sludge in a wetlands column affects its removal efficiency with the optimal removal (96%) being linked to the presence of sludge in 80%. Moreover, temperature, pH and the FT load showed a significant effect in removals, with the optimal operating conditions being recorded at 7.2 pH, 26 °C and 100 ppm of FT. The kinetic modeling is also investigated to validate the practical life applications and designs, and the results verified the reaction follows the pseudo 2nd-order reaction kinetic model according to the correlation coefficient factor. Furthermore, according to the isotherm model results the scheme follows the Freundlich isotherm model. Such preliminarily data of a gravel-alum-sludge-adsorption-column scheme is a good indicator in developing a constructed wetland facility being a good candidate for controlling agriculture effluent streams.

Immobilization of Magnetic Nanoparticles on Cellulosic Wooden Sawdust for Competitive Nudrin Elimination from Environmental Waters as a Green Strategy: Box-Behnken Design Optimization

The role of engineering in our society is not to just to continue creating chemicals, but sharing the responsibility for environmentally sound appropriate design of substances for a circular economy. Concerning this contemporary strategy, waste wooden sawdust (WSD) as a biobased by-product is augmented with magnetite (Mag) nanoparticles to meet the concept of cyclic application of resources in environmentally relevant photocatalytic reactions. The physical properties of the prepared WSD:Mag material were characterized to emphasis their structure and morphology by using X-ray diffraction (XRD) and transmission electron microscopy (TEM), then the prepared catalyst was applied in augmentation with hydrogen peroxide as a type of photocatalyst in the form of Fenton's reaction system to oxidize Nudrin pesticide in queues media. Twinned WSD:Mag has been verified to exhibit higher performance than pristine single-phase catalysts. System parameters, i.e., pH, hydrogen peroxide, catalyst dozing, and temperature, were studied to check their effect on the reaction activity. In the present study, further promotion of photocatalytic activity of twinned WSD:Mag was obtained by optimizing the process parameters at the optimal reaction time of 30 min. The optimal results investigated via Box-Behnken design regression model based on response surface mythology (RSM) showed that the photocatalytic activity of the twinned catalyst could reach 94% at pH 2.5 and 386 and 38 m/L of H₂O₂ and WSD:Mag, respectively. The regression coefficient and probability obtained from analysis of variance (ANOVA) were used to check the adequacy of the applied model, and were 92% and 0.02, respectively. Additional confirmatory tests were carried out under optimum conditions for verification and agreed with the predicted values. Experimental data analysis revealed that the reaction is well fitted with the second-order reaction model. Thermodynamic parameters highlighted the oxidation reaction is non-spontaneous at high temperature and exothermic in nature and proceeds at a low activation energy barrier (31.46 kJ/mol). Catalyst recyclability was also checked, which confirmed catalyst sustainability and high removal rates (78%) after six cycles of use. This work introduces a new concept to design a promising environmentally benign photocatalyst with high potential for applicability to environmental remediation of agricultural effluents with a view to a circular economy.

Enhanced removal of heavy metals and phosphate in stormwater filtration systems amended with drinking water treatment residual-based granules

To address the clogging issues in stormwater filtration systems, a drinking water treatment residual (DWTR)-based granule (DBG) substrate was developed herein by pyrolyzing and granulating the DWTR with bentonite and corncob. Toxicity characteristic leaching procedure studies indicated that fabricating into DBG stabilized the Al and heavy metals in DWTR and restrained the leaching risk. Then the removal performance of phosphate (PO₄-P) and heavy metal ions by the DWTR and DBG was evaluated in batch and laboratory-scale column experiments. Results from batch tests showed that the amount of Pb(Ⅱ) adsorbed by DBG (18.47 ± 0.56 mg g⁻¹) was approximately 2.3 times of that adsorbed by DWTR (8.05 ± 0.19 mg g⁻¹), whereas the PO₄-P adsorption capacity of DBG (8.63 ± 0.24 mg g⁻¹) was much lower than that of DWTR (25.33 ± 0.81 mg g⁻¹). This could be ascribed to the addition of corncob and bentonite (at a mass ratio of 20% and 40% in DBG, respectively), which provided extremely high cation exchange capacity for the Pb(Ⅱ) adsorption, while no effective PO₄-P adsorption component was involved. Moreover, the pyrolysis process could improve the Pb(Ⅱ) and PO₄-P adsorption capacity of the raw-mixture by 42% and 7%, whereas granulation process decreased those of the pyrolysis-mixture by 15% and 20%, respectively, owing to the reduction of accessible surface area in the DBG. Under various stormwater runoff conditions, the involvement of DBG in stormwater filtration systems exerted consistently fancy performance of Cu(Ⅱ), Pb(Ⅱ), Cd(Ⅱ) and PO₄-P removal, with average removal rates of over 86.20% and desorption rates of less than 3.50%, indicating irreversible and strong complexion between the contaminants and DBG. The DBG column manifested good permeability and stable hydraulic conductivity (2.74-2.52 m d⁻¹) over a 54-day rainfall period, which was beneficial to address the clogging issue of DWTR. Overall, this study provides an alternative pathway to enhance the hydraulic condition and treatment performance of the stormwater filtration systems for urban runoff management.

Granulation of Drinking Water Treatment Residues: Recent Advances and Prospects

Beneficial reuse of drinking water treatment plant residues (WTRs) has been intensively studied worldwide in the last decades, but few engineering applications can be found. The majority of WTRs were directly reused in cake form (after dewatering), e.g., alum sludge cake as main substrate used in constructed wetlands (CWs), or oven dried and ground powdery form, e.g., sorbent for pollutant removal. However, WTRs reuse in such forms has several drawbacks, i.e., difficulty of recovering and easy clogging (in CWs), which result in limited WTRs engineering applications. Granulation or pelleting could widen and be a wiser WTRs reuse route and also seems to be a promising strategy to overcome the “application bottleneck” issues. In the literature, a number of trials of WTRs granulation have been reported since 2008, including sintering ceramsite, gel entrapment and newly emerged techniques. Hence, there is a need to overlook these studies and promote WTRs granulation for further development. To this end, this review firstly provides a piece of updated comprehensive information and critical analysis regarding WTRs granulation/pelleting technology. It aims to enhance WTRs granulation studies in the developing stage and thus enlarge WTRs engineering applications.