Sustainable utilization of water treatment residue as a porous geopolymer for iron and manganese removals from groundwater

Improving the adsorption properties of low surface area hardwood biochar for the removal of Fe+ and PO₄3- from aqueous solution

Biochar produced from wood residues may provide a new method and material for managing the environment, particularly in terms of carbon sequestration and contaminant remediation. Additionally, biochar produced from wood residues is free of chemical fertilizers, likewise in rice straw, wheat straw, corn straw, etc. This study investigated the removal of iron from aqueous solutions by a novel low-cost and eco-friendly biochar made from hardwood trees and modified by adding MgCl2 for effective phosphate removal. Optimal adsorption conditions were determined through studies of adsorption time, pH, and adsorbent dosage. Batch equilibrium isotherm and kinetic experiments and pre/post-adsorption characterizations using FESEM-EDS, XRD, and FTIR suggested that the presence of carboxyl group elements and colloidal and nano-sized MgO (periclase) particles on the biochar surface were the main adsorption sites for aqueous iron and phosphate respectively. In this study, the HW and MgO-HW biochar showed excellent Dubinin-Radushkevich isotherm (D-R) maximum adsorption capacities of 289.45 and 828.82 mg/g for iron and phosphate. The kinetic study for iron and phosphate adsorption was described well by pseudo second-order model and pseudo second-order model respectively. The HW biochar and the prepared MgO-HW biochar exhibited commendable iron adsorption (98.25%) performance at 10 pH units and phosphate (96.22%) at pH 6 respectively. Thus, this research reveals a waste-to-wealth strategy by converting hardwood waste into mineral-biomass biochar with excellent Fe and P adsorption capabilities and environmental adaptability.

Making waves: Breaking the bottleneck of recycling drinking water treatment residue for practical engineering applications in water pollution control

Drinking water treatment residue (DWTR), an inevitable byproduct of water treatment plants, is typically recycled to control water pollution. DWTR poses a low environmental risk and has the potential to function as a functional material for various applications. However, the practical engineering applications of DWTR are limited. These limitations arise from a disconnect between fundamental research and the practical needs of engineering applications, creating a bottleneck for the effective recycling of DWTR. Previous studies have primarily focused on exploring potential DWTR recycling methods that reuse Al, Fe, Mn, Ca, Si, and organic C. However, the varying properties of DWTR obtained from different water treatment plants tend to differ with respect to potential recycling methods, confusing managers and engineers in using relevant knowledge to guide practical engineering applications. To address this challenge, the author advocates for a shift in research toward establishing guidelines that provide direct guidance for practical engineering applications of DWTR. The key components of these guidelines should include risk assessment, capability evaluation, and environmental application procedures with sustainability assessment to break the bottleneck associated with the recycling of DWTR.

Induced crystallization for the simultaneous removal of hardness-iron-manganese in groundwater: An experimental study

Hardness, iron, and manganese are common groundwater pollutants, that frequently surpass the established discharge standard concentrations. They can be effectively removed, however, through induced crystallization. This study has investigated the effectiveness of the simultaneous removal of hardness-iron-manganese and the crystallization kinetics of calcium carbonate during co-crystallization using an automatic potentiometric titrator. The impacts pH, dissolved oxygen (DO), and ion concentration on the removal efficiency of iron and manganese and their influence on calcium carbonate induced crystallization were assessed. The results suggest that pH exerts the most significant influence during the removal of hardness, iron, and manganese, followed by DO, and then the concentration of iron and manganese ions. The rate of calcium carbonate crystallization increased with pH, stabilizing at a maximum of 10-10 m/s. Iron and manganese can be reduced from an initial level of 4 mg/L to <0.3 mg/L and 0.1 mg/L, respectively. The removal rate of iron, however, was notably higher than that of manganese. The DO concentration correlates positively with the removal of iron and manganese but has minimal impact on the calcium carbonate crystallization process. During the removal of iron and manganese, competitive interactions occur with the substrate, as increases in the concentration of one ion will inhibit the removal rate of the other. Characterization of post-reaction particles and mechanistic analysis reveals that calcium is removed through the crystallization of CaCO3, while most iron is removed through precipitation as Fe2O3 and FeOOH. Manganese is removed via two mechanisms, crystallization of manganese oxide (MnO2/Mn2O3) and precipitation. Overall, this research studies the removal efficiency of coexisting ions, the crystallization rate of calcium carbonate, and the mechanism of simultaneous removal, and provides valuable data to aid in the development of new removal techniques for coexisting ions.

High efficiency of drinking water treatment residual-based sintered ceramsite in biofilter for domestic wastewater treatment

Aluminum (Al)-based drinking water treatment residue (DWTR) has often been attempted to be recycled as dominant ingredient to produce sintered ceramsite for water treatment. This study aimed to determine the long-term performance of DWTR-based ceramsite in treating domestic wastewater based on a 385-d biofilter test and by using physicochemical, metagenomic, and metatranscriptomic analyses. The results showed that the ceramsite-packed biofilter exhibited high and stable capability in removing phosphorus (P) and chemical oxygen demand (COD), with removal efficiencies of 92.6 ± 3.97% and 81.1 ± 14.0% for total P and COD, respectively; moreover, 88-100% of ammonium-nitrogen (N) was normally converted, and the total N removal efficiency reached 80-86% under proper aeration. Further analysis suggested that the forms of the removed P in the ceramsite were mainly NH4F- and NaOH-extractable. Microbial communities in the ceramsite biofilter exhibited relatively high activity. Typically, various organic matter degradation-related genes (e.g., hemicellulose and starch degradations) were enriched, and a complete N-cycling pathway was established, which is beneficial for enriching microbes involved in ammonium-N conversion, especially Candidatus Brocadia, Candidatus Jettenia, Nitrosomonas, and Nitrospira. In addition, the structures of the ceramsite had high stability (e.g., compressive strength and major compositions). The ceramsites showed limited metal and metalloid pollution risks and even accumulated copper from the wastewater. These results demonstrate the high feasibility of applying ceramsite prepared from Al-based DWTR for water treatment.

Geopolymers: Advanced Materials in Medicine, Energy, Anticorrosion and Environmental Protection

The initial predictions of the importance of geopolymers primarily assumed use mainly in the construction sector. However, as research progresses, it is becoming clear that these versatile materials demonstrate the ability to greatly exceed their original applications, as characterized in detail in this review article. To the best of our knowledge, there is no literature review concerning geopolymer materials that compiles the diverse applications of these versatile materials. This paper focuses on geopolymer applications beyond the construction industry. The surprising application potential of geopolymers in medicine has become a topic of particular interest. Therefore, considerable attention in this paper is devoted to characterizing the utility of these materials in tissue engineering, dentistry and drug delivery systems. Geopolymers not only have exceptional heat resistance and compressive strength, making them durable and resistant to manipulation (over five times less drug released from the geopolymer carrier compared to the commercial formulation), but also provide a robust solution for extended-release drug delivery systems, especially in opioid formulations. Their chemical stability, porous structure and ability to maintain structure after repeated regeneration processes speak to their potential in water treatment. Geopolymers, which excel in the energy industry as refractory materials due to their resistance to high temperatures and refractory properties, also present potential in thermal insulation and energy storage. It was demonstrated that geopolymer-based systems may even be 35% cheaper than conventional ones and show 70% lower thermal conductivity. In terms of protection against microorganisms, the possibility of modifying geopolymers with antimicrobial additives shows their adaptability, maintaining their effectiveness even under high-temperature conditions. Research into their use as anticorrosion materials is targeting corrosion-resistant coatings, with geopolymers containing graphene oxide showing particularly promising results. The multitude of potential applications for geopolymers in a variety of fields reflects their enormous potential. As research progresses, the scope of their possibilities continues to expand, offering innovative solutions to pressing global challenges.

Enhancing the Mn-Removal Efficiency of Acid-Mine Bacterial Consortium: Performance Optimization and Mechanism Study

In this study, an acclimated manganese-oxidizing bacteria (MnOB) consortium, QBS-1, was enriched in an acid mine area; then, it was used to eliminate Mn(Ⅱ) in different types of wastewater. QBS-1 presented excellent Mn removal performance between pH 4.0 and 8.0, and the best Mn-removal efficiency was up to 99.86% after response surface methodology optimization. Unlike other MnOB consortia, the core bacteria of QBS-1 were Stenotrophomonas and Achromobacter, which might play vital roles in Mn removal. Besides that, adsorption, co-precipitation and electrostatic binding by biological manganese oxides could further promote Mn elimination. Finally, the performance of the Mn biofilter demonstrated that QBS-1 was an excellent inoculant, which indicates good potential for removing Mn contamination steadily and efficiently.

Stabilization/solidification of Mn-contaminated clay slurry by using CaO-GGBS: Effects of anions

Clay sediment is removed by dredging, resulting in the disposal of enormous waste sediment clay slurries that consumes land space, as well as risks the human health and the environment. Manganese (Mn) is often identified in clay slurries. Quicklime (CaO)-activated ground granulated blast-furnace slag (GGBS) can be used to stabilize/solidify (S/S) contaminated soils; nevertheless, few studies have been published on the S/S of Mn-contaminated clay slurries using CaO-GGBS. Moreover, the anions contained in clay slurries may affect the S/S efficiency of CaO-GGBS in treating Mn-contaminated clay slurries, but this effect has hardly been investigated. Therefore, this study investigated the S/S efficiency of CaO-GGBS in treating MnSO₄-bearing and Mn(NO₃)₂-bearing clay slurries. The effect of anions (i.e. SO₄^2- and NO₃^-) on the strength, leachability, mineralogy, and microstructure of Mn-contaminated clay slurries treated with CaO-GGBS was explored. Results showed that CaO-GGBS could improve the strength of both Mn-contaminated slurries to meet the strength requirement for landfill waste outlined by United States Environmental Protection Agency (USEPA). The Mn leachabilities of both Mn-contaminated slurries were decreased to be less than the Euro limit for drinking water after cured for 56 days. The MnSO₄-bearing slurry generally produced higher UCS while lower Mn leachability than Mn(NO₃)₂-bearing slurry at the same CaO-GGBS addition. CSH and Mn(OH)₂ were formed, thereby enhancing strength and reducing leachability of Mn. Ettringite in CaO-GGBS-treated MnSO₄-bearing slurry, which was formed by the supply of SO₄^2- from MnSO₄, further contributed to the strength enhancement and the decrease of Mn leachability. Ettringite was the factor leading to the difference in strength and leaching properties between MnSO₄-bearing and Mn(NO₃)₂-bearing clay slurries. Hence, anions contained in Mn-contaminated slurries significantly affected the strength and the Mn leachability, and need to be identified before CaO-GGBS was used to treat such slurries.

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.

Revealing the role of calcium alginate-biochar composite for simultaneous removing SO42- and Fe3+ in AMD: Adsorption mechanisms and application effects

The remediation of acid mine drainage (AMD) is particularly challenging because it contains a large amount of Fe³⁺ and a high concentration of SO₄^2-. To reduce the pollution caused by SO₄^2- and Fe³⁺ in AMD and realize the recycling of solid waste, this study used distillers grains as raw materials to prepare biochar at different pyrolysis temperatures. Calcium alginate-biochar composite (CA-MB) was further synthesized via the entrapment method and used to simultaneously remove SO₄^2- and Fe³⁺ from AMD. The effects of different influencing factors on the sorption process of SO₄^2- and Fe³⁺ were studied through batch adsorption experiments. The adsorption behaviors and mechanisms of SO₄^2- and Fe³⁺ were investigated with different adsorption models and characterizations. The results showed that the adsorption process of CA-MDB600 on SO₄^2- and Fe³⁺ could be well described by Elovich and Langmuir-Freundlich models. It was further proved by the site energy analysis that the adsorption mechanisms of SO₄^2- onto CA-MDB600 were mainly surface precipitation and electrostatic attraction, while that of Fe³⁺ removal was attributed to ion exchange, precipitation, and complexation. The applications of CA-MDB600 in actual AMD proved its good application potential. This study indicates that CA-MDB600 could be applied as a promising eco-friendly adsorbent for the remediation of AMD.

Eco-friendly bioremediation of pollutants from contaminated sewage wastewater using special reference bacterial strain of Bacillus cereus SDN1 and their genotoxicological assessment in Allium cepa

The present study aimed to assess the Bacillus cereus SDN1 native bacterium's ability to clean up contaminated or polluted water. The isolated bacterium was identified by its morphological and biochemical characteristics, which were then confirmed at the genus level. Furthermore, the isolated B. cereus (NCBI accession No: MW828583) was identified genomically by PCR amplifying 16 s rDNA using a universal primer. The phylogenetic analysis of the rDNA sequence was analyzed to determine the taxonomic and evolutionary profile of the isolate of the previously identified Bacillus sp. Besides, B. cereus and the bacterial consortium were treated using sewage wastewater. After 15 days of treatment, the following pollutants or chemicals were reduced: total hardness particles removal varied from 63.33 % to 67.55 %, calcium removal varied from 90 % to 93.33 %, and total nitrate decreased range from 37.77 % to 22.22 %, respectively. Electrical conductivity ranged from 1809 mS/cm to 2500 mS/cm, and pH values ranged from 6.5 to 8.95. The outcome of in-situ remediation results suggested that B. cereus has a noticeable remediation efficiency to the suspended particles. A root tip test was also used to investigate the genotoxicity of treated and untreated sewage-contaminated waters on onion (Allium cepa) root cells. The highest chromosomal aberrations and mitotic inhibition were found in roots exposed to contaminated sewage water, and their results displayed chromosome abnormalities, including disorganized, sticky chain, disturbed metaphase, chromosomal displacement in anaphase, abnormal telophase, spindle disturbances, and binucleate cells observed in A. cepa exposed to untreated contaminated water. The study can thus be applied as a biomarker to detect the genotoxic impacts of sewage water pollution on biota. Furthermore, based on an identified bacterial consortium, this work offers a low-cost and eco-favorable method for treating household effluents.

Mechanism of Changes in Goaf Water Hydrogeochemistry: A Case Study of the Menkeqing Coal Mine

Goaf water in mining areas is widely found in China's coal mines. To clarify the hydrogeochemical characteristics of goaf water and the influence mechanism of water-rock interaction and further reveal microbial action on the formation of goaf water quality, the goaf water in the Menkeqing coal mine was taken as the object, and physical modeling was used to simulate the process of the real goaf changing from an oxygen-sufficient environment to an anoxic environment with the rise of groundwater level in this work. The experimental results showed that the water-rock interaction in the goaf was mainly the dissolution-precipitation of minerals in the rocks of the caving zone and fracture zone, cation exchange, and oxidation of pyrite in the coal layer. The primary sources of Na⁺ and K⁺ in the goaf water were the dissolution and reverse ion exchange of silicate minerals such as albite and potassium feldspar, while Ca²⁺ and Mg²⁺ mainly from the dissolution of minerals such as calcium feldspar, calcite, and chlorite. The oxidation of pyrite in coal was the main reason for the increase in SO₄^2- concentration, the enhancement of reduction, and the decrease in pH and DO (dissolved oxygen) in the goaf water. Relative abundance of sulfate-reducing bacteria (SRB) in goaf (e.g., Desulfosporosinus, Desulfobacterium, etc.) increased gradually, inhibiting the increase in SO₄^2- concentration in goaf water through the devulcanization of SRB. The inverse hydrogeochemical modeling was performed using PHREEQC for two stages of the simulation experiment: 0-30 days and 30-300 days. The simulation results show that the water-rock action in the formation of goaf water mainly occurred in the simulation experiment's early stage (0-30 days), and the mineral dissolution is dominant throughout the experimental stage. The results of the study provide a theoretical reference for the prediction of highly mineralized water pollution in goaf and its prevention and control.

Correlation of Phosphorus Adsorption with Chemical Properties of Aluminum-Based Drinking Water Treatment Residuals Collected from Various Parts of the United States

Over the past several decades, the value of drinking water treatment residuals (WTRs), a byproduct of the coagulation process during water purification, has been recognized in various environmental applications, including sustainable remediation of phosphorus (P)-enriched soils. Aluminum-based WTRs (Al-WTRs) are suitable adsorbent materials for P, which can be obtained and processed inexpensively. However, given their heterogeneous nature, it is essential to identify an easily analyzable chemical property that can predict the capability of Al-WTRs to bind P before soil amendment. To address this issue, thirteen Al-WTRs were collected from various geographical locations around the United States. The non-hazardous nature of the Al-WTRs was ascertained first. Then, their P adsorption capacities were determined, and the chemical properties likely to influence their adsorption capacities were examined. Statistical models were built to identify a single property to best predict the P adsorption capacity of the Al-WTRs. Results show that all investigated Al-WTRs are safe for environmental applications, and oxalate-extractable aluminum is a significant indicator of the P adsorption capacity of Al-WTRs (p-value = 0.0002, R2 = 0.7). This study is the first to report a simple chemical test that can be easily applied to predict the efficacy of Al-WTRs in binding P before their broadscale land application.