Pollutant Removal Capacity Research Articles

Synergistic enhancement in hydrodynamic cavitation combined with peroxymonosulfate fenton-like process for bpa degradation: New insights into the role of cavitation bubbles in regulation reaction pathway

The combination of hydrodynamic cavitation (HC) and Fenton-like oxidation technology can dramatically enhance the pollutant removal capacity, however, the synergistic effect of cavitation and catalysts on reactive oxygen species (ROS) generation remained enigmatic. In this study, we established a combined system based on HC and Ce-MnFe2O4 activated peroxymonosulfate (PMS) for BPA removal, and attentions were paid on the role of cavitation bubbles. The results show that the combination of HC in Ce-MnFe2O4 activated PMS could mediate the degradation of BPA from the non-radical pathway dominated by 1O2 to •O2− dominated radical pathway. Both controlled experiments and theoretical calculations revealed that the cavitation bubbles with different sizes play the dominant role in ROS generation. The microjets produced by the collapse of cavitation bubbles could create a large number of oxygen vacancy defects on Ce-MnFe2O4 surface, which modify the activation barrier of PMS and facilitate the generation of •O2− thermodynamically. The stable existing cavitation bubbles with the size of 100∼400 nm could create considerable gas-liquid interface. The molecular dynamics simulations show that the nano bubbles can concentrate the BPA and increase the probability of contacts between BPA and Ce-MnFe2O4, hence effectively solve the issues of short lifetime of •O2− radicals and limited mass transfer distance to strengthen the reaction. In addition, the PMS/Ce-MnFe2O4/HC system not only achieves the satisfied COD (95 %) and TOC (65 %) removal efficiency but also enabled the BPA-contaminated water with a low energy cost of 0.065 kWh·m−3 and oxidant cost, highlighting the application potential of the HC technology for contaminated water.

Fabrication of Ti3CN quasi-MXene based poly glycidyl methacrylate and poly (3,4-ethylene dioxythiophene): Poly (styrene sulfonate) conducting polymer coated materials for photocatalytic eradicator of organic pollutants

MXene, a two-dimensional (2D) transition metal carbide or nitride, has gained significant attention due to its exceptional properties and wide-ranging applications. MXenes exhibit distinctive physical and chemical characteristics, making them suitable for electrocatalysis, supercapacitors, semiconductors, batteries, sensors, biomedicine, water splitting, and photocatalysis. In environmental photocatalysis, efforts have been made to improve conductivity, structural stability, and morphology. This study synthesized a photocatalyst by coating or doping a conducting polymer onto a quasi-MXene (Ti3CN) substrate. Initially, Ti3AlCN was exfoliated using HF to form 2D Ti3CN quasi-MXene, which was then doped with GMA and PEDOT: PSS conducting polymers for photocatalytic dye degradation. The broad heterogeneous interfaces in this network significantly enhance photocatalytic performance and pollutant removal capacity. The Ti3CN@GMA/PEDOT: PSS photocatalyst was characterized through SEM, FTIR, XPS, XRD, BET, and EDX techniques and tested for the degradation of various pollutants in wastewater under visible light. The degradation rates achieved were 94.1 % for Rose Bengal, 91.6 % for Rhodamine B, and 90.6 % for Methylene Blue, with corresponding rate constants of 0.0366 min−1, 0.0400 min−1, and 0.0388 min−1 over 60 min. The photocatalyst demonstrated excellent performance, highlighting several advantages, including low energy consumption, cost-effectiveness, non-toxic properties, and environmental compatibility, making it a promising solution for wastewater treatment applications.

Reuse of plastic waste as bio-carriers for domestic wastewater treatment – An approach towards circular economy

With the rapid growth of economic development, the circular economy has been raised in many internationalenvironmental and socio-economic conferences and forums nowadays. The recycling of plastic waste was oneof those aspects. This paper studied the potential of directly reusing plastic bottle caps as bio-carriers in movingbed bioreactors without further waste processing. As the caps had lower surface areas than the commercial carriers, total bacteria communities on the commercial carriers (K3) were 3-4 times higher than those on the bottle caps at different counting magnitudes. Nevertheless, the bottle caps could accommodate similar nitrogen-based bacteria (ammonia-oxidizing bacteria - AOB and nitrite-oxidizing bacteria - NOB density), which promotes well for the nitrification and denitrification processes. The COD and N-NH4 removal efficiencies were 92% and 86% on average, respectively. The high pollutant removal capacity reveals the very promising potential of bottle caps as bio-carriers for domestic wastewater treatment, promoting waste reduction and treatment expenses and presenting an excellent example of economic circular.

Exploring granular filter media in sustainable drainage systems (SuDS) for stormwater pollutant adsorption: A pilot study

Granular filter media are integral to sustainable drainage systems (SuDS) for their efficiency in removing pollutants from urban runoff. This study focuses on understanding the filtration processes within these media by combining a pilot experimental study with a modeling approach. The experimental study involved characterizing the physical and hydraulic properties of various granular filter media materials, including sand, pea-gravel, gravel, and geotextile membranes. Three laboratory-scale stormwater filtration rigs were tested to evaluate the filter media's pollutant removal capacity and hydraulic performance. This work presents a phenomenological model that predicts the spatial variation in the concentrations of stormwater and urban runoff substances, specifically nitrate ions (NO3-), phosphate ions (PO43-), chemical oxygen demand (COD), and suspended solids, by studying their concentration profiles. The stormwater quality model was used to predict the concentration profiles for stormwater with an average inflow consisting of 2.9 mg/L nitrates, 3.4 mg/L phosphate ions, 225 mg/L COD, and 3.3 mg/L of suspended solids. The predicted outlet concentrations matched well with measured experimental data. The results showed that adding geotextile membranes to a granular filter significantly improves its ability to adsorb dissolved species for stormwater applications. This research highlights the importance of understanding the physical and hydraulic properties of granular filter media and their impact on stormwater pollutant removal efficiency. The developed model can assist in the design and optimization of stormwater treatment systems by predicting the performance of different filter media materials, allowing for informed decision-making and improved system functionality.

A recyclable and durable magnetic cobalt nanoparticle-embedded mesoporous graphene nanohybrid for removal of pollutants from aqueous media

Cobalt nanoparticles (Co NPs) embedded in mesoporous graphene (MG) were prepared via a hydrothermal reaction followed by carbothermal reduction in an argon atmosphere. This cobalt nanoparticle-embedded mesoporous graphene (CoMG) was systematically investigated for structural, morphological, and magnetic properties before and after 10 successive cycles of adsorption and regeneration, using methylene blue (MB) dye as a model pollutant. The CoMG nanohybrid has a superior specific surface area of 807 m2 g−1, with a significant mesopore volume of 1.63 cm3 g−1 that allows fast and high pollutant removal efficiency of ∼84 % within 30 min as well as the maximum adsorption capacity of 178.6 mg g−1 with MB solution of 100 mg L−1, which is well described with pseudo-second-order adsorption kinetics. The consecutive adsorption−regeneration experiments revealed that the CoMG nanohybrid retained more than half of the initial dye removal efficiency even after being reused 10 times. After the tenth cycle, the regenerated CoMG maintained a high specific area of 688 m2 g−1 and a large mesopore volume of 1.51 cm3 g−1, indicating the long-lasting porous structure of the CoMG nanohybrid. The metallic cobalt phase and ferromagnetic nature of the Co NPs in the nanohybrid are retained because of the host MG, which prevents nanoparticle aggregation and serves as a protective environment for the embedded Co NPs in aqueous media during the adsorption−regeneration cycle tests of the adsorbent. The experimental results demonstrate that the CoMG nanohybrid has superior pollutant removal capacity and maintains more than half of the initial efficiency even after 10 cycles of use, making it a cost-efficient and energy-saving material for the removal of organic pollutants from aqueous media and in other environmental applications.

Bifunctional nanocomposites formed from magnetic lignin-derived carbon and molybdenum disulfide for efficient pollutant removal

The development of inexpensive and robust bifunctional nanocomposites toward efficient pollutant removal is crucial for wastewater remediation. Herein, we report a novel strategy for fabrication of magnetic nanocomposites loaded with molybdenum disulfide (Fe3O4/PLC-MoS2) using lignin biomacromolecules for efficient pollutant removal. The Fe3O4/PLC-MoS2 exhibit excellent pollutant removal capacity: The adsorption capacity of Pb(II) achieve 236.1 mg/g and the methylene blue (MB) degradation rate is up to 90.0 % within 20 min. The adsorption mechanism reveal that the enhanced removal properties is due to that the S atoms on the loaded MoS2 could convert into soluble sulfide and react with Pb(II) to form white precipitate β-Pb3O2SO4. Moreover, the experiments results demonstrate that the Fe3O4/PLC-MoS2 has a low bandgap, which can activate PMS to produce reactive oxygen species and degrade MB molecules efficiently. Notably, the Fe3O4/PLC-MoS2 demonstrate continued outstanding wastewater remediation capabilities even in scenarios where Pb(II) and MB coexisted. Overall, this study offers a viable and eco-friendly design of dual function removal material by using lignin waste toward promising implications for wastewater treatment.

A Laboratory Investigation of the Adsorption Performance and Mechanism of Organics in Industrial Wastewater on mp-Zr(OH)4

We reported on the development of mesoporous zirconium hydroxide (mp-Zr(OH)4) sorbents with high capacity for adsorptive removal of organic pollutants from industrial wastewater. The sorbent was prepared by a one-step chemical precipitation method at room temperature. The adsorption capacity and removal efficiency for the chemical oxygen demand (COD) of the industrial wastewater were studied using an automatic adsorption measurement apparatus. The effects of different parameters (adsorbent dosage, adsorption time, regeneration times, adsorbate's molecular weight and adsorbate solubility), isotherm, thermodynamics, and kinetics were evaluated. By analyzing scanning electron microscopy (SEM) images and powder X-ray diffractograms (XRD) no obvious differences were observed for the sorbents before and after the adsorption of the organics, which indicated a structural stability of the sorbent. The specific surface area was reduced from 450 m2/g to 189 m2/g on adsorption, and after desorption of the organics the specific surface area was 350 m2/g. The adsorption of COD was analyzed in a Langmuir model that described the data better than the empirical Freundlich model. This finding points towards that the adsorption occurred as a monolayer on the mp-Zr(OH)4. The free energy of adsorption (ΔG) is in the range of −20 kJ/mol < ΔG < 0. Entropy changes are ΔS > 0. The kinetics of the adsorption of COD is better described with a Quasi-second-order dynamic model than with a Quasi-first-order dynamic model, which elucidates its primary reliance on porous adsorption surfaces and incorporation of chemical adsorption.

Comprehensive comparison of integrated fixed-film activated sludge (IFAS) and AAO activated sludge methods: Influence of different operational parameters

Due to limited land availability in municipal wastewater treatment plants, integrated fixed-film activated sludge (IFAS) technology offers significant advantages in improving nitrogen removal performance and treatment capacity. In this study, two systems, IFAS and Anaerobic-Anoxic-Oxic Activated sludge process (AAO), were compared by adjusting parameters such as hydraulic retention time (HRT), nitrifying solution recycle ratio, sludge recycle ratio, and dissolved oxygen (DO). The objective was to investigate pollutant removal capacity and differences in microbial community composition between the two systems. The study showed that, at an HRT of 12 h, the IFAS system exhibited an average increase of 5.76%, 8.85%, and 12.79% in COD, NH4+-N, and TN removal efficiency respectively, compared to the AAO system at an HRT of 16 h. The TP concentration in the IFAS system reached 0.82 mg/L without the use of additives. The IFAS system demonstrated superior effluent results under lower operating conditions of HRT, nitrification solution recycle ratio, and DO. The 16S rDNA analysis revealed higher abundance of denitrification-related associated flora, including Proteobacteria, Bacteroidetes, and Planctomycetota, in the IFAS system compared to the AAO system. Similarities were observed between microorganisms attached to the media and activated sludge in the anaerobic, anoxic, and oxic tanks. q-PCR analysis indicated that the incorporation of filler material in the IFAS system resulted in similar abundance of nitrifying bacteria genes on the biofilm as in the oxic tank. Additionally, denitrifying genes showed higher levels due to aeration scouring and the presence of alternating aerobic-anaerobic environments on the biofilm surface, enhancing nitrogen removal efficiency.

Characterization and microbial mechanism of pollutant removal from stormwater runoff in the composite filler bioretention system

Abstract Bioretention systems are a low-impact development (LID) measure to effectively control stormwater runoff and reduce pollutant concentrations. In this paper, three groups of bioretention cells with different filling materials (1# bioretention soil media (BSM), 2# BSM + 5% biochar, and 3# BSM +5% biochar +biological filler) were constructed to analyze the pollutant removal characteristics and microbial action under different simulated rainfall conditions. Results showed that the overall pollutant removal capacity of systems 2# and 3# was higher than that of system 1#, with system 3# having the lowest effluent concentrations of 2.71 mg/L for total nitrogen (TN) and 64.3 mg/L for chemical oxygen demand (COD). The load reduction effect for heavy metals of the three systems was ranked as 2# &amp;gt; 1# &amp;gt; 3#, and average load reduction rates were 80.3, 75.1, and 84.8% for Cu, Pb, and Zn in 2#. Microbial community analysis indicated that Proteobacteria and Firmicutes were the absolute dominant bacteria of the three bioretention systems, and the dominant genera included Bacillus, Hyphomicrobium, Micrococcaceae, and Nitrospira. In addition, the total number of denitrifying functional bacteria genera in systems 2# and 3# was increased by 1.39 and 52.1% compared to system 1#.

Mechanism of Iris sibirica and aeration combination on promoting the water purification performance of constructed wetland under low temperature.

Temperature is an important factor affecting the water purification performance of constructed wetland (CW). In the previous study, the combined measures of Iris sibirica and aeration at the bottom of the first quarter filtration chamber could improve the pollutant removal capacity of CW at low temperature. However, the mechanism between the combined measures of Iris sibirica and aeration on enhancing the performance of domestic sewage treatment is unclear. Our study aims to provide scientific validation for the combined measure through monitoring the concentrations of dissolved oxygen (DO), chemical oxygen demand (CODCr), ammonia nitrogen (NH4+-N), and total nitrogen (TN) along the water flow pathway of the CW and measuring the superoxide dismutase (SOD) activities of the plants and the abundance of nitrogen cycle-related microbial functional genes in the substrates of CW to explore the mechanism of combined measures promoting the removal efficiency of the CW under low-temperature stress. Results showed that aerating at the bottom of the first quarter filtration chamber increased DO concentration in the front part of the CW, which benefited the aerobic removal of pollutants and the activities of microorganisms, and the removal CODCr and NH4+-N occurred mainly in the front part of the CW. SOD activities showed that I. sibirica had better resistance to low temperature than Canna indica did. The combined measures of I. sibirica and aeration activated the activities of microorganisms, increased the abundance of the denitrification process genes along the water flow pathway and formed a clear nitrification-denitrification zone in the CW, thus promoted the nitrogen removal efficiency at low temperature. Therefore, this study confirmed the feasibility of the combined measures from a mechanistic perspective.

A Review on Various Bio-Resources as a Tool to Reduce Water Pollution Via Eco-Friendly Adsorption Technology

Pollution of water bodies is a raising concern in today’s world. Water pollution occurs when harmful compounds enter water bodies and lowers the water quality. It is necessary to treat wastewater before its final disposal into aquatic bodies and environment. Among all the conventional water treatment techniques, adsorption technology attracted much attention owing to its simplicity and eco-friendly nature. Several studies were reported with the application of different kinds of adsorbents in the treatment of both organic and inorganic pollutants in wastewater. However, demand for the development of more suitable adsorbent with selective pollutant removal capacity and good economic feasibility is still rising. Therefore, this review aims to provide a detailed review about the adsorption technology and its mechanisms in pollutant removal process. The adsorption ability of certain important adsorbents were discussed along with future perspectives. Effective, economical, and environmentally friendly wastewater management should be the ultimate objective of any wastewater treatment process. Keeping that in view, this review article highlighted the importance of wastewater management and treatment via adsorption technology.

Transformation of waste into valuable materials: Utilizing waste printer powder to remove hazardous organic dye and pharmaceutical pollutants from wastewater

A global concern of considerable significance revolves around electronic waste and the contamination of water due to antibiotics and persistent organic dyes, leading to the emergence of antibiotic resistance and an alarming increase in environmental pollution. The substantial accumulation of waste printer powder generated by printers is undeniably an unwanted and valueless byproduct, as both its substantial production and recycling would result in significant financial burdens and environmental pollution challenges. Polypyrrole-grafted waste printer powder, (Ppy@wp), constitutes a viable solution due to its established reputation as a capable adsorbent. To maximize the reutilization of this waste powder, we have investigated a straightforward and practical approach for repurposing waste printer powder (wp) to craft a super magnetic Ppy@wp nanocomposite. This composite is put forth as a highly effective material for the elimination of methylene blue (MB) dye and tetracycline (TC) from solutions. The wp was mixed with pyrrole, followed by polymerization and carbonization to synthesize the final composite. The pollutant removal capacity of the as-prepared Ppy@wp nanocomposite has been evaluated by removing MB and TC. The Ppy@wp nanomaterial was found to be highly effective in removing 50 ppm of MB and TC with a removal rate of around 95.36% and 90.23%, respectively, within just 50 min. The Ppy@wp nanomaterial was evaluated for regeneration and desorption and it was shown to be effective for up to six cycles, with removal efficiency of TC being 79.23% and MB being 86.56%. This is a cost-effective, innovative, and highly efficient adsorbent process with a great perspective on environmental pollution clean-up. The result demonstrated that the synthesized material was magnetically separated from the solution within 2 min after adsorption. Therefore, this research has provided value-added significance for developing inexpensive composites from waste material to remove toxic chemicals from the waste stream.

Growth, Biomass Production, Pollutant Removal Capacity of Chlorella Vulgaris Cultivated in Water Polluted with Phosphates, Nitrates, Cadmium and Lead Ions; A Possible Strategy for Bioremediation, Carbon Dioxide Utilization and Simultaneous Biodiesel Productivity

The main objective of the work reported herein was to study the possibility of simultaneous use of microalgae for bioremediation and biodiesel production. Determination of optimum nitrate and phosphate concentrations for the maximum algal growth in the presence of heavy metal ions in the growth media was the other objective. In this regard, Chlorellavulgaris, a microalga, was cultivated separately for 30 days at ~28 °C in the presence and absence of known cadmium, lead, phosphate ion concentrations in growth media containing an optimum nitrate ion concentration. The concentrations of these ions in the growth media, dry algal biomass and extractable algal-oil percentage after 30 days of their growth were determined. According to the study, the optimum total nitrate and total phosphate concentrations required for the maximum algal growth were 200 mg L-1 and 10 mg L-1, respectively. The maximum tolerable Pb2+ and Cd2+ concentrations were 8 mg L-1 and 2.5 mg L-1, respectively. The results revealed that Chlorellavulgaris has a high capacity for both removing these ions (&gt; 70%) from the growth medium, and generating algal biomass, simultaneously. Moreover, the algal biomass generated under these harsh conditions yields algal-oil (~41% in terms of dry algal biomass) that is free from these ions.

Resilience of stormwater biofilters following the deposition of wildfire residues: Implication on downstream water quality management in wildfire-prone regions

Stormwater treatment systems such as biofilters could intercept and remove pollutants from contaminated runoff in wildfire-affected areas, ensuring the protection of water quality downstream. However, the deposition of wildfire residues such as ash and black carbon onto biofilters could potentially impair their stormwater treatment functions. Yet, whether and how wildfire residue deposition could affect biofilter functions is unknown. This study examines the impact of wildfire residue deposition on biofilter infiltration and pollutant removal capacities. Exposure to wildfire residues decreased the infiltration capacity based on the amount of wildfire deposited. Wildfire residues accumulated at the top layer of the biofilter, forming a cake layer, but scraping this layer restored the infiltration capacity. While the deposition of wildfire residues slightly changed the pore water geochemistry, it did not significantly alter the removal of metals and E. coli. Although wildfire residues leached some metals into pore water within the simulated root zone, the leached metals were effectively removed by the compost present in the filter media. Collectively, these results indicate that biofilters downstream of wildfire-prone areas could remain resilient or functional and protect downstream water quality if deposited ash is periodically scraped to restore any loss of infiltration capacity following wildfire residue deposition.

Impacts of wind flow across street-side building gaps on traffic pollutant dispersion at pedestrian level with different block heights

Urban neighborhoods, which contains numerous buildings and gaps between the buildings, are usually simplified as a single air-impermeable block in numerical simulations of urban air environments. Such a simplification reduces the computational costs but underestimates the pollutant removal capacity of the street, because the high-speed wind flow through the building gaps causes a flushing effect on pollutant distribution in the street. However, the influences of the gap flow on traffic pollutant dispersion remain unclear. Therefore, a four-way street network surrounded by four neighborhoods is assumed as a representative urban area, and the characteristics of the gap flow and its correlation with building height (H/W = 0.5–2, W = 30 m) are investigated numerically. The results show that the flow pattern within the street depends on the relative intensity of the flow across the gaps and the parallel bulk flow along the street. For lower (H/W = 0.5) or higher (H/W = 2) building heights, the gap flow is strong enough to break through the barrier of the bulk flow, and then enters the street to dilute the pollutants, causing the concentrations in the leeward region of the street to be lower than those in the windward region. Opposite results are found for medium building heights (H/W = 0.75–1.5), where the flow in the street is dominated by the parallel flow itself. The results also indicate that there exists a critical height, H/W = 1.5, below which the air environment is good in both the streets and neighborhoods.

Controlled Synthesis and Visible-Light-Driven Photocatalytic Activity of BiOBr Particles for Ultrafast Degradation of Pollutants.

For the purpose of regulating the visible-light-driven photocatalytic properties of photocatalysts, we selected BiOBr as the research target and various routes were used. Herein, via the use of a hydrothermal method with various solvents, BiOBr particles with controllable morphology and photocatalytic activities are obtained. In particular, through changing the volume ratio of ethylene glycol (EG) to ethanol (EtOH), BiOBr compounds possess microspheres, in which samples synthesized by using EG:EtOH = 1:2 have the highest photocatalytic activity, and can completely decompose RhB under visible light irradiation within 14 min. Furthermore, we also used different volume ratios of EG and H2O reaction solvents to prepare BiOBr particles so as to further improve its pollutant removal ability. When the volume ratio of EG to H2O is 1:1, the synthesized BiOBr particles have the best photocatalytic activity, and RhB can be degraded in only 10 min upon visible light irradiation. Aside from the reaction solvent, the impact of sintering temperature on the photocatalytic properties of BiOBr particles is also explored, where its pollutant removal capacities are restrained due to the reduced specific surface area. Additionally, the visible-light-triggered photocatalytic mechanism of BiOBr particles is determined by h+, ·OH and ·O2- active species.

3D Monolayer Silanation of Porous Structure Facilitating Multi-Phase Pollutants Removal.

Activated carbon (AC) is widely used to removing hazardous pollutantsfrom air and water, owing to its exceptional adsorption properties. However, the high affinity of water molecules with the surface oxygen-containing functional groups can adversely affect the adsorption performance of AC. In this study, a facile and efficient method is presented for fabrication of hydrophobicAC through surface monolayer silanation. Compared to initialAC, the hydrophobicAC improves thewater contact angle from 29.7°to 123.5°while maintaining high specific surface area and enhances the removal capacity of multi-phase pollutants (emulsified oiland toluene).Additionally, the hydrophobicAC exhibits excellent adsorption capabilityto harmful algal bloom species (Chlorella) (97.56%) and algal organic matter(AOM)(96.23%) owing to electrostatic interactionsand surface hydrophobicity.Thestudy demonstrates that this method of surface monolayer silanation can effectively weaken the effect of water molecules on AC adsorption capacity, which has significant potential for practical use in air and water purification, as well as in the control of harmful algal blooms.

Effects of increasing the degree of building height asymmetry on ventilation and pollutant dispersion within street canyons

Rational urban design helps to build sustainable cities with high ventilation capacity and pollutant removal capacity, but the effect of building height on ventilation and pollutant dispersion inside asymmetric canyons has not been fully studied. In this paper, we studied the effect of increasing the degree of building height asymmetry (DBHA) on canyon ventilation and pollutant diffusion in shallow and deep asymmetric street canyons by considering six different building height ratios (BHR = 3/4, 1/2, 1/3, 4/3, 2/1 and 3/1). The results show that increasing the DBHA in asymmetric canyons can improve the ventilation and pollutant removal capacity. For step-up canyons, increasing the downwind building height is very useful to improve ventilation and pollutant removal. For shallow/deep step-up canyons with BHR = 1/3, the air exchange rate (ACH) increased to 211.2% and 380.1% of the flat canyons, respectively. The spatially-average pollutant concentration in the pedestrian zones (leeward Kavg* ang windward Kavg*) decreases significantly with the increase of DBHA, especially for the deep step-up canyon with BHR = 1/3, the leeward Kavg* and windward Kavg* decrease to 15.3% and 3%, respectively. Also, increasing the upwind building height can also improve the ventilation capacity in the step-down canyons. For the deep step-down canyon with BHR = 3/1, the leeward Kavg* and windward Kavg* decreased to 40.6% and 24.1% of the deep flat canyon, respectively. Notably, the ventilation capacity is very low for step-down canyons with BHR = 4/3, and for step-down canyons with BHR ≥ 2/1, the ventilation capacity and pollutant removal capacity increase significantly with the increase of DBHA. Therefore, in urban planning, step-down canyons with BHR = 4/3 should be avoided and designed to satisfy the condition of BHR ≥ 2/1. These findings will be a valuable reference for urban designers to build sustainable cities with high ventilation capacity.

A clay-coal fly ash based dual hydraulic-reactive liner for controlling acid mine drainage.

Hydraulic liners are used to restrict hazardous leachates such as acid mine drainage (AMD) from entering the hydrogeological system. In this study, we hypothesized that: (1) a compacted mix ratio of natural clay and coal fly ash with a hydraulic conductivity of at most 1 × 10- 8 ms- 1 can be achieved, and (2) mixing clay and coal fly ash in the right proportion can result in increased contaminant removal efficiency of a liner system. The effects of adding coal fly ash to clay on the mechanical behavior, contaminant removal efficiency, and saturated hydraulic conductivity of the liner were investigated. All clay:coal fly ash specimen liners with less than 30% coal fly ash had significantly (p < 0.05) lower cohesion stress values, and were discarded without further tests. Saturated hydraulic conductivity values showed no significant effect (p > 0.05) on the results of clay:coal fly ash (7:3) specimen liners and compacted clay liner. The clay:coal fly ash mix ratios of 8:2 and 7:3 significantly (p < 0.05) reduced the leachate concentration of Cu, Ni, and Mn. The pH of AMD increased from an average of 2.14 to 6.80 after permeating through a compacted specimen of mix ratio 7:3. Overall, the 7:3 clay to coal fly ash liner showed superior pollutant removal capacity and its mechanical and hydraulic properties were comparable to compacted clay liners. This laboratory scale investigation emphasizes potential limitations with column scale evaluation of liners and provides new information on the application of dual hydraulic reactive liners for engineered hazardous waste disposal systems.

Evaluación de polisacáridos en floculación mediada por complejo polielectrolítico

Water is an increasingly valuable resource because its availability, primarily it is limited to precipitation and water storage; for that reason, increasing population density and climate change can interfere with water accessibility. Urban and industrial activities can produce wastewater and pollute waterbodies that could represent a significant water source; however, it needs to be treated prior to its use. Flocculation is an important pollutants removal method to reduce a variety of organic and inorganic molecules from wastewater, using the flocculant’s intrinsic charges to stabilize/precipitate them, by different methods, one of them being via polyelectrolyte complex. Flocculant versatility depends on its capacity to remove pollutants and there are commercial flocculants with remarkable efficiencies. However, their toxicity can limit their use in waterbodies or for former human use. Research shows that polysaccharides are great option as flocculants because of their easily charged conformation and high molecular weight to neutralize pollutants and precipitate flocs, they are biocompatible, biodegradable, and easy to modify to modulate the flocculant interaction due to the functional group’s high density. This review explores the latest research on polysaccharide polyelectrolyte flocculation and derivatives and their pollutant removal capacity, the polysaccharides evaluated were the most commonly researched such as chitosan, cellulose, chitin, alginate, gums, dextran, among others. Recent research tendencies on these polysaccharides flocculation capacity, showed promising results (up to 99% removal efficiencies) with a wide variety of contaminants, making them excellent candidates for their application in green flocculation.