Contaminant Removal Mechanisms Research Articles

Stamping cleaning conception on cross-contamination free multi-ceramic bioglass-tricalcium phosphate core-shell structure fabrication

Multi-ceramic additive manufacturing has always been a topic of discussion, considering that implementing multiple materials in one structure can bring innovative functionalities to it. However, the realization of the fabrication system is still plagued by cross-contamination when alternating materials. Therefore, we developed a new machine and suggested a stamping cross-contamination prevention system to address this issue. The contaminant removal mechanism was understood, efficiency was improved, and the stamping process parameters were optimized. To demonstrate, a bone hierarchical structure naturally modeled with advanced functionality to withstand mechanical loads and assist metabolic reactions was replicated. The material combination chosen included chemically identical calcium phosphates and bioglass. First, specific properties such as compressive strength were measured, and in-vitro bioactivity was evaluated to assign appropriate roles. Subsequently, the functionality of the hierarchical structure was controlled and fabricated using the previously optimized parameters. Finally, cross-contamination and multi-functionality of the generated structure were confirmed again for conclusion.

Challenges in using Electrocoagulation Process in Removal of Nickel Metal in Wastewater: a Literature Review

In recent years, the surge in nickel production, driven by the growing demand for electric vehicle batteries, has raised concerns regarding environmental consequences. The nickel mining and processing industries contribute to increased nickel levels in wastewater, presenting a serious threat to aquatic ecosystems and human health. This article emphasizes the urgency of developing effective technologies for treating nickel-contaminated wastewater. Electrocoagulation emerges as a promising method, providing high efficiency, minimal sludge production, and cost-effectiveness. The article critically and systematically reviews the potential of the electrocoagulation process in nickel removal from wastewater. In the review, we identify and analyze nearly 32 studies published from 2013 to 2023. We discuss contaminant removal mechanisms and analyze trends in the use of operational parameters. This article identifies the most commonly applied conditions: aluminum electrodes, inter-electrode spacing ≥ 1 cm, current density ≤ 10 mA/cm², initial pH 6 ≤ pH < 11, electrolysis time < 60 min, batch operation, and initial nickel concentration > 50 mg/L. This comprehensive review serves as a foundational resource for advancing electrocoagulation technology in the removal of heavy metals from nickel wastewater.

Self-enhanced oxidation of resistant monocyclic aromatic compounds during ozone treatment: Applicability in groundwater remediation

The Peroxone process—which utilizes a combination of ozone and hydrogen peroxide to generate hydroxyl radicals—is frequently used in groundwater remediation to effectively remove ozone-resistant contaminants. However, some monocyclic aromatic compounds with low ozone reactivity have been found to be removed by ozone solely (without the need for hydrogen peroxide) through a self-enhanced mechanism. This self-enhanced removal occurs when the interaction of ozone with hydroxide ion generates sufficient amount of hydroxyl radicals, initiating a radical reaction that subsequently propagates through the degradation intermediates. This study leverages the self-enhanced degradation mechanism for the treatment of ozone-resistant compounds during groundwater remediation. Key environmental conditions, including water alkalinity and contaminant concentration, were investigated for their effect on the self-enhanced degradation of para-chloro benzoic acid (pCBA), which served as a model for ozone-resistant compounds. High pCBA removal was observed during ozonation in the concentration range of 0.5–5 μM, where the decay kinetics of pCBA and ozone significantly dependent on the initial pCBA concentration. Furthermore, decreased pCBA removal was noted in water matrices with increased alkalinity, largely due to the scavenging of OH radicals by carbonate species. Finally, pCBA removal was investigated in natural groundwater, where co-existing substances acted as ozone/radical scavengers, leading to reduced pCBA removal. Overall, this study highlights the importance of the self-enhanced removal mechanism of monocyclic aromatic contaminants when treating water with high contamination levels and low-to-moderate alkalinities.

Revisiting the role of H2O2 in periodate electro-activation system: The non-dependence in Bisphenol A (BPA) removal

The existence of hydrogen peroxide (H2O2) within the electro-activation of periodate (PI) system is conventionally considered as conducive to the removal of pollutants. However, this study discovered an unusual phenomenon: the contaminants removal efficiency and the yield of strong oxidizing species such as hydroxyl radical (OH) and iodate radical (IO3) were improved when H2O2 in the solution was quenched. The study deeply explored the role of H2O2 in graphite felt-based electro-activated PI system (GF-PI), particularly in the mechanism of active species generation and contaminants removal. Bisphenol A (BPA), as the model contaminant, achieves a degradation efficiency of 82.1% and 83.9% within 40 min in w/wo H2O2 system, respectively. Meanwhile, multiple probing techniques clearly identify the variety of active species and generation pathway such as Electron paramagnetic resonance (EPR), LC-QTOF-MS, and quenching experiment. There exist two distinct pathways for PI activation, including direct cathodic electroreduction and indirect in-situ generated H2O2 catalysis. The GF-PI system incorporated both of two pathways, while the GF-PI-catalase system only had the direct activation pathway. Electrogenerated H2O2 serves as a precursor for the generation of superoxide radical anions (O2−) and singlet oxygen (1O2), yet it diminishes the efficiency of direct cathode activation due to the consumption of PI. Furthermore, the system demonstrated excellent stability, applicability, and cleanliness, effectively removing contaminations without the accumulation of iodine byproducts. The degradation intermediates products of BPA are monitored and the toxicities are evaluated. The study provides novel insights into the regulation of active species for contaminant elimination, holding significant implications for specialized sewage treatment.

Reactive contaminant infiltration under dynamic preferential flow

Biodegradation is an important mechanism of contaminant removal from soils. We use numerical simulations to study the contaminant transport in heterogeneous soils subject to transient flow conditions and anaerobic multicomponent biodegradation. These processes and their interactions affect contaminant travel times, the extent of reactant mixing, solute and microbial biomass distributions in the soil, and biodegradation outcomes. Especially when flux variations are large, the combination of soil heterogeneity and transient flow gives rise to dynamic preferential flow zones, which affects reactant mixing and biodegradation outcomes. Results show that soil heterogeneity may reduce contaminant leaching due to enhanced reactant mixing, especially when biodegradation is more limited by reactant mixing. Furthermore, unlike under steady-state flow, under transient flow soil heterogeneity does not substantially reduce contaminant residence times. As preferential flow zones change dynamically, the spatio-temporally averaged transport, mixing, and biodegradation experienced by various parts of contaminant plumes become homogenized. Therefore, knowing the initial biodegradation rate of a contaminant upon infiltration, and its mean residence time in the soil, enables a relative sensitivity analysis. This allows biodegradation outcomes of various scenarios to be approximately ranked, even under soil heterogeneity and transient flow, using information that is straightforward to measure or estimate in the field.

Biomass gasification in rotary kiln integrated with a producer gas thermal cleaning unit: An experimental investigation

In this work, gasification of hazelnut shells grains is carried out in a bench-scale rotary kiln by using air as gasifying agent at 800 °C. The producer gas is directly treated in a thermal cleaning unit operating at 800–1100 °C with the aim to reduce the load of contaminants. The producer gas cleaning by thermal methods is usually studied by using model compounds, whilst herewith the behavior of a real producer gas is investigated. Results indicate that at high temperature CO2 reacts with tar and particulate to generate CO, thereby improving the quality of producer gas in terms of heating value, producer gas yield and contaminants content. Benzene is the most abundant organic contaminant of the producer gas, the concentration of which is significantly reduced upon thermal treatment. For the first time, a bench-scale rotary kiln gasifier with lignocellulosic biomass as feedstock is integrated with a thermal cleaning unit, providing experimental evidences about the suitability of rotary kiln for air gasification of lignocellulosic biomass and its integration with a thermal unit. The proposed approach could find application also when other types of gasifier are adopted, although a parametric study should be carried out in order to fully understand the reaction mechanism of contaminant removal and to find optimal operation conditions, also as a function of biomass feedstock features.

Revealing the generation of reactive oxygen species in hydrochar and pyrochar: Insight into rational regulation of free radicals and catalytic mechanism

The removal of organic pollutants by biochar has been extensively studied. However, the differences in the removal mechanisms of contaminants by biochar obtained from different preparation techniques have not been thoroughly elucidated. In this study, the catalytic performances of hydrochar (HC) and pyrochar (PC) were compared in the dark and light. Owing to more persistent free radicals (PFRs), greater defects and stronger charge transfer ability on the surface, PC could produce a certain concentration of superoxide radicals (•O2−) even in the dark, making its degradation efficiency for benzoic acid (BA) 11% higher than that of HC. On the contrary, when the light was turned on, HC rather than PC can generate a higher amount of hydroxyl radical (•OH), resulting in an 11% higher degradation efficiency of BA compared to PC. The improvement of catalytic performance in HC originated from its oxygen-containing functional groups (OFGs), which was beneficial for its effective production of singlet oxygen (1O2) and ·OH under light exposure. For PC, its photocatalytic activity depended mainly on the formation of 1O2 induced by the triplet of DOM (dissolved organic matter), but the lack of oxidative ·OH in its system leads to a lower degradation efficiency than that of HC. To prove the universal applicability of this rule for biochar materials, HC and PC materials obtained from soybean residue were also prepared for degrading BA. This work is devoted to an in-depth exploration of the catalytic activation mechanism of biochar obtained by different technological methods, and can create conditions for the generation of more dominant reactive oxygen species (ROS) on biochar, thus providing the guidance for environmental remediation.

Synthesis of mesoporous MIL-100(Fe) from acid mine drainage sludge for norfloxacin removal: Industrial sludge high value utilization, adsorbent performance and contaminant removal mechanisms

Recovery of heavy metals from acid mine drainage sludge (AMDs) and their conversion into high value-added materials such as metal-organic frameworks (MOFs) is of great significance for sustainable development. MOFs have broad application prospects in liquid phase pollutant removal, owing to super high specific surface area and adjustable structure. In this study, MIL-100(Fe) with mesoporous structures was successfully prepared from AMDs by acid leaching-hydrothermal method. And the obtained MIL-100(Fe) was employed as an adsorbent for adsorptive norfloxacin (NOR) removal from wastewater. The adsorption results showed that the maximum adsorption capacity can reach 280.84 mg/g under the condition of 298 K, the initial pH value of solution is 10 and the dosage of catalyst is 0.1 g/L. According to the N2 sorption–desorption isotherms, X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared (FTIR) characterization, the adsorption mechanism of NOR on MIL-100(Fe) is mainly attributed to electrostatic interaction, π-π stacking, pore filling and coordination. Furthermore, the adsorbent maintained 75.05% of its initial adsorption capacity after 5 cycles, indicating that MIL-100(Fe) has excellent stability. This study provides a new idea for the resource utilization of industrial sludge.

Pre-treatment of landfill leachate via coagulation-flocculation: Optimization of process parameters using response surface methodology (RSM)

Wastewater treatment is achieved mainly through the regeneration of resources and energy from wastewater, especially using pre-treatment technologies. In this study, coagulation pre-treatment of landfill leachate was performed using polymeric iron sulfate (PFS) as coagulation. Moreover, the whole experimental process was divided into two parts. In the first phase, the effects of PFS dosing, initial pH and PAM dosing on the removal of chemical oxygen demand (COD), total phosphorus (TP) and UV254 from the leachate were assessed using one factor one experiment (OFAT); In the second phase, the individual and interactive effects of parameters on COD%, TP%, and UV254% were evaluated using response surface methodology (RSM). Numerical multiple response optimization was conducted using RSM to maximize COD%. The COD%, TP%, and UV254% at optimum condition (PFS dose of 12.18 g/L, initial pH of 8.12, and PAM dosage of 11.29 mg/L) reached 62.30 %, 95.79 %, and 83.45 %, respectively. The 3D-EEM showed the effluent from the leachate after mixing. The chemical properties significantly changed, and the concentration of hard-to-degrade substances, such as humic acid, decreased. FTIR and ESM-EDX were used to delineate the intrinsic mechanism of contaminant removal, demonstrating that hydroxyl bonds are crucial in the extraction of leachate and the aggregation of folcs.

Design and analysis of heat melt refuse compactor for solid waste with E-control mechanism

As a technology, a Heat Melt Refuse Compactor (HMRC) has been developed to process municipal solid waste by converting into tiles and on-site valuable products. The HMRC compacts, heats the solid waste to 200°C and recovers the water from the MSW. The heating causes volatile contaminants to be released into the air. The model has evaluated the design and testing parametrs for MSW processing and analysis. HMRC testing has demonstrated water recovery upto 99%, waste volume reduction upto 80%, tile stabilization for long-term, passive separation of liquid/gas phase, and operations with low maintenance cost.Heat melt refuse compactor has designed to compress by compaction process, encapsulate the waste bi-product, residual gas/water at atmoshpheric pressure, waste volume reduction and microbial stabilization. The model design shows the benefit of a heat melt refuse compactor on-site use by converting the solid waste into valuable products with thermal and compression technique. HMRC model has processed ∼1300 kg of solid waste; which produced ∼700 kg of tile, recovered ∼400 kg of water, and ∼200 kg of gaseous and residual waste. The compression ratio (Cc) of solid waste has been estimated with a compression cell with a diameter between 65 to 100 mm, mesoscale data for a diameter of 195 mm to 265 mm and high-scale data for a diameter of 300 to 400 mm. Cc is a more sensitive variable in formation of bi-products from MSW. Ground base HMRC has designed for Cc stress ranges from 20 to 300 kPa to function within the physical and environmental constraints.E-control contaminant removal mechanism keeps the environment clean and safe.

Understanding the process of phosphate removal in Fe0/H2O systems using the methylene blue method

The removal mechanisms of contaminants in Fe0/H2O are still poorly understood, and characterized by contradictory findings. Therefore, the present study aims to improve the understanding of the processes involved in phosphate removal in Fe0/H2O system. Herein, the methylene blue method (MB method) is used to trace the dynamics within the investigated systems. The MB method utilizes the differential adsorptive affinity of MB onto sand and sand coated with iron corrosion products to evaluate the degree of Fe0 corrosion in Fe0/H2O systems. The extent of MB discoloration and phosphate removal in various Fe0-based systems was characterized in parallel quiescent batch experiments for two weeks and two months. Parallel experiments with Orange II (O-II) as a model contaminant allowed an improved discussion of the results. The investigated systems were: (i) Fe0 alone, (ii) MnO2 alone, (iii) sand alone, (iv) Fe0 + sand, (v) Fe0 + MnO2, and (vi) Fe0 + sand + MnO2. Additional experiments were conducted to test the influence of Fe0 type, Fe0 and sand mass loadings on dye discoloration and phosphate removal in Fe0/sand system. Each system was characterized by: (i) pH value, (ii) Fe concentration, (iii) dye discoloration (MB, O-II), and (iv) phosphate concentration. Results showed that the MB method was capable of tracing the extent of iron corrosion in the various investigated systems and clarified the role of in-situ generated iron corrosion products (FeCPs) in the removal of phosphate. The suitability of mixing sand aggregates with Fe0 for efficient phosphate removal is demonstrated through the MB method. Overall, the appropriateness of the MB method to characterize the dynamics of Fe0/H2O systems is validated.

Recent Advances in Thallium Removal from Water Environment by Metal Oxide Material.

Thallium is widely used in industrial and agricultural development. However, there is still a lack of systematic understanding of its environmental hazards and related treatment methods or technologies. Here, we critically assess the environmental behavior of thallium in aqueous systems. In addition, we first discuss the benefits and limitations of the synthetic methods of metal oxide materials that may affect the practicality and scalability of TI removal from water. We then assess the feasibility of different metal oxide materials for TI removal from water by estimating the material properties and contaminant removal mechanisms of four metal oxides (Mn, Fe, Al, and Ti). Next, we discuss the environmental factors that may inhibit the practicality and scalability of Tl removal from water. We conclude by highlighting the materials and processes that could serve as more sustainable alternatives to TI removal with further research and development.

Reaction analysis and the removal mechanism of organic contaminants in plasma cleaning: a molecular dynamics simulation

DBP clusters were removed by nitrogen and oxygen plasma. The effects of the incidence duration, particle energies, and particle types on the decomposition were investigated. Decomposition pathways were further confirmed by bond dissociation energies.

Coupling of submersible microbial fuel cell into aerobic granular sludge bioreactor for ciprofloxacin stress alleviation: Performance and mechanism

Ciprofloxacin (CIP) is widely existed in wastewater treatment systems, which can cause significant toxicity effect and sludge damage under long-term stress due to its remarkable chemical stability. Herein, a novel submersible microbial fuel cell (MFC) coupling of aerobic granular sludge (AGS) bioreactor was designed to simultaneously mitigate the CIP toxicity and improve system treating performance. At stable phase, the average NH4+-N, COD and CIP removal efficiencies in AGS-MFC were improved to 99.1%, 92.1% and 83.2%, whereas the AGS-Control were only 97.4%, 65.9% and 46.1%, respectively. The long-term exposure of CIP affected the morphology of AGS in the control group, resulting in a lower particle size than that in the AGS-MFC group. Moreover, less EPS was secreted in the AGS-MFC group than that of AGS-Control group due to the MFC alleviated the CIP toxicity. From functional microorganisms and metabolism pathways, Corynebacterium and Rhodococcus with drug-resistant electricity generation were enriched in the anodic biofilm. The predesign of submersible MFC significantly reduced the transmission of resistance genes (qnrS) in AGS. Additionally, Cytochrome P450-mediated microbial metabolism may be a potential way to achieve CIP removal in submersible MFC-AGS. The results of this study could provide an effective strategy for treating toxic wastewater by using MFC and AGS, and are of great significance for further understanding the collaborative mechanism of contaminant removal.

Various Types of Constructed Wetland for Wastewater Treatment-A Review

As per the World Health Organization 80% of wastewater is released to the environment without satisfactory treatment. Constructed Wetlands (CWs) are one of the natural wastewater (WW) treatment methods. CWs have been recommended as a low technology, low maintenance, low operation cost, and green technology wastewater treatment system. Many types of CWs are currently in use. This paper studies these different types based on the climate, area, base materials, temperature, contaminant removal efficiency, removal mechanism and physicochemical analysis of various wastewater parameters. It is found that wetlands are successful in removing organic matter–Biochemical Oxygen Demand (BOD5), Chemical Oxygen Demand (COD) and suspended solids and nutrients–total Nitrogen (TN) and total Phosphorus (TP). CWs need to be studied as a promising solution not only for effective treatment of wastewater but also as an economical method to improve the fertility of soil. Further, the paper discusses the scope of future research in CW to further improve the wastewater treatment technology.

Recent insights into greywater treatment: a comprehensive review on characteristics, treatment technologies, and pollutant removal mechanisms.

With the rapid socio-economic and industrial development, the problem of water shortage is becoming increasingly serious. Seeking alternative water sources to reduce the need for freshwater resources is an increasing concern. Household greywater production is high and accounts for about 50-80% of domestic wastewater. In recent years, the in situ treatment and reuse of greywater have received widespread attention. Treated greywater can be used for non-potable purposes such as toilet flushing and irrigation, which can greatly reduce the pressure of freshwater resource shortage. This paper reviews the sources and characteristics of greywater and analyzes its quantity and quality. In addition, this paper outlines and summarizes various greywater treatment technologies commonly used, including physical, biological, and chemical treatment technologies, as well as combination technologies. Understanding the mechanisms of contaminant removal is essential for effective greywater treatment. While discussing different treatment technologies, we focus on the removal mechanisms of pollutants from greywater, including organics, nutrients, surfactants, and emerging contaminants. Finally, future perspectives on greywater management and reuse are presented. Through a comprehensive review, we expect that this review will help the reader to better understand the characteristics of greywater and to more rationally select the appropriate treatment technology based on the removal mechanism of pollutants.

Metallic Iron for Water Remediation: Plenty of Room for Collaboration and Convergence to Advance the Science

Scientific collaboration among various geographically scattered research groups on the broad topic of “metallic iron (Fe0) for water remediation” has evolved greatly over the past three decades. This collaboration has involved different kinds of research partners, including researchers from the same organization and domestic researchers from non-academic organizations as well as international partners. The present analysis of recent publications by some leading scientists shows that after a decade of frank collaboration in search of ways to improve the efficiency of Fe0/H2O systems, the research community has divided itself into two schools of thought since about 2007. Since then, progress in knowledge has stagnated. The first school maintains that Fe0 is a reducing agent for some relevant contaminants. The second school argues that Fe0 in-situ generates flocculants (iron hydroxides) for contaminant scavenging and reducing species (e.g., FeII, H2, and Fe3O4), but reductive transformation is not a relevant contaminant removal mechanism. The problem encountered in assessing the validity of the views of both schools arises from the quantitative dominance of the supporters of the first school, who mostly ignore the second school in their presentations. The net result is that the various derivations of the original Fe0 remediation technology may be collectively flawed by the same mistake. While recognizing that the whole research community strives for the success of a very promising but unestablished technology, annual review articles are suggested as an ingredient for successful collaboration.

Porous metal–organic framework-based filters: Synthesis methods and applications for environmental remediation

• MOFilter synthesis methods and environmental applications are summarized. • A comparison of various MOFilter architecture and substrates is provided. • Potential technologies for customizing MOFilter pore morphology are evaluated. • Mechanisms controlling effectiveness and structures of MOFilters are discussed. • Our perspectives on future developments of MOFilters are presented. Hazardous contaminants emitted from anthropogenic activities are widespread and threaten human health and ecological sustainability. Porous metal–organic framework-based filters (MOFilters) are emerging hybrid materials for high-performance environmental treatment technologies. They are widely used for the treatment of environmental problems, including the removal of particulate matter (PM), volatile organic compounds (VOCs), hazardous gases, volatile radioactive species, metal ions, dyes, chemical warfare agents (CWA) and oils. Through customizing their architectures and functionalities, MOFilters can enhance the performance of current environmental treatment technologies. This review summarizes the design concepts and synthesis strategies of MOFilters, and the latest progress and challenges for air purification and water treatment. The underlying mechanisms of contaminant removal via filtration, adsorption and degradation are also summarized to aid the design and optimization of the structural properties of MOFilters for specific applications. This review will guide the design of MOFilters for environmental remediation.

Free radicals accelerate in situ ageing of microplastics during sludge composting

Composting is the last “barrier” for microplastics (MPs) in the entry of organic solid wastes into the environment. The transformation of MPs is thought to be mainly driven by microorganisms during composting, whereas the contribution of abiotic processes that involve free radicals is often overlooked. Herein, we provide initial evidence for the generation of free radicals during sludge composting, including environmental persistent free radicals and reactive oxygen species, which accelerate the oxidative degradation of MPs. The ·OH yield of composting fluctuated greatly from 23.03 to 277.18 μmol/kg during composting, which was closely related to the dynamic changes in Fe(II) (R2 = 0.926). Analyses of the composted MPs physicochemical properties indicated that MPs were aged gradually with molecular weights decrease from 18% to 27% and carbonyl index value increase from 0.23 to 0.52. Further investigation suggested that the microbially-mediated redox transformation of iron oxides could occur on the MPs surface accompanied by the production of abundant free radicals, thereby leading to the damage of MPs during composting. These results reveal the critical role of free radicals in MPs ageing under oxic/anoxic alternation conditions of composting and provide new insights into the bio-chemical mechanism of contaminant removal or transformation during sludge composting.

Tracking macrolides, sulfonamides, fluoroquinolones, and tetracyclines in sludge treatment wetlands during loading and resting periods

• Ofloxacin was the most abundant antibiotics in sludge. • Planted STW with aeration tubes had the highest removal rates in antibiotics. • The removal rates of antibiotics in STWs in summer were higher than that in winter. • Microbial degradation and substrate adsorption were main ways to remove antibiotic. This study investigated the removal efficiency and mechanism of antibiotic contaminants in sludge treatment wetlands (STWs) using liquid chromatography–mass spectrometry. We examined one aeration control and two STWs: unit1 was a treatment unit with aeration tubes only; unit2 was an STW with reeds and aeration tubes, and unit3 was an STW with reeds only. The results showed that the STWs effectively removed antibiotics, with removal rates of 41.8 % (norfloxacin) and 90.4 % (sulfamethoxazole). Comparing the STWs, the mass of each antibiotic accumulated in the residual sludge of unit1 (4.0 – 199 mg) was higher than that of unit2 (2.4–101 mg) and unit3 (2.8–121 mg). This showed that unit2 with plants and aeration tubes had the highest removal effect on antibiotics. The mass balance analysis of antibiotics revealed that microbial degradation (11.8–58.0 %), substrate adsorption (20.0–34.8 %), and plant uptake (0.35–3.1 %) were important methods for antibiotic removal from wetlands, and microbial degradation was the main method for removing antibiotics.