Journal of Environmental Engineering

Abstract

As an effort to observe the impact of pollution on the aquatic environment, water quality monitoring calls for the development of early detection technologies that are fast, efficient, and inexpensive. Currently, electrochemical sensors are an alternative technology to sensitively analyze pollutants in the aquatic environment. Engineering working electrodes to sense polluting compounds is the target of technology development. This work studies material compositions consisting of graphite carbon with ${\mathrm{TiO}}_2$ nanoparticles as a photoelectrode to analyze chemical oxygen demand (COD) in methylene blue (MB) organic dye wastewater. The materials were prepared by physically mixing the two components and one-pot chemical synthesis, characterizing their microstructure and crystallinity. Then, their analytical performance was assessed by measuring MB dye as a sample against the mass variation of 1:1 (w/w) and 1:2 (w/w) photoelectrodes. The results showed similar 1:1 (w/w) performance with the relevant and theoretical COD. The straightforward synthesis and eco-friendly materials are key factors in the fabrication of COD sensor.

Practical Applications

This study proposes a technical process for the fabrication and application of photoelectrodes in detecting the chemical oxygen demand (COD) of methylene blue dye. It solves the problems of COD detection in identifying water quality in wastewater, and the problems of long and the problems of dangerous materials used against COD determination. It provides a new understanding of rapid COD detection to measure water quality in wastewater. In practical applications, the fabricated photoelectrode was placed into dye solution and connected to a potentiostat instrument, which was irradiated by ultraviolet (UV) light to initiate the photoelectrocatalytic reaction. The accumulation of organic dye in water will generate the electrical properties (photocurrent) of the photoelectrode, which can the be measured by a multipulse amperometry system. It performs two performance functions at once, namely photoelectrodegradation and COD sensing. In COD sensor performance, the photocurrent response is plotted against the time duration where the photocurrent generated is proportional to the oxidation performance against the organic dye concentration and calculated by the Faraday equation. This research offers several advantages, such as fast response time and real-time detection for COD determination. It also provides more sensitive and accurate measurement of organic pollutants in water. The COD photoelectrocatalysis method can be a practical application for rapid detection of methylene blue organic dye.

Abstract

In wastewater treatment design, it is common practice to test aeration equipment in clean water first, and then extrapolate the result to wastewater via a correction factor. The most commonly adopted procedure for testing in clean water is the ASCE/EWRI Standard 2-22 that measures the oxygen transfer rate (OTR) as a mass of oxygen per unit time dissolved in a volume of water by an oxygen transfer system operating under a given gas rate and power conditions, based on a simplified mass transfer model. The procedure is applicable to ordinary test conditions, such as overhead pressure (atmospheric pressure), water temperature (between 10°C and 30°C), water depth (between 3 and 6 m), mixing conditions (as produced by ordinary gas flow), and so forth. It may not be suitable for outside these boundary conditions. A weakness of this standard is temperature correction, where it was recommended to use a correction factor named theta ($Ɵ$) to adjust the test result to a common temperature of 20°C. A recent discovery of the validity of the mass transfer model opens the door to a more precise method of estimating correction factors, the findings of which have been published in various journals. This article proposes a Rational Method in dealing with the problem of temperature correction that has led to overestimations or underestimations of the mass transfer coefficient (MTC) at standard conditions.

Practical Applications

Inaccurate determination of the mass transfer coefficient at standard conditions poses many serious problems down the line, from equipment bidding to projection of usage in the field. An overestimation in particular may lead to specifying equipment that can underperform in the field. By eliminating the effects of extensive properties (scale-dependent properties), such as tank height (water depth), the environmental conditions (temperature and pressure), gas flow rate, agitation, mixing, and so forth, we find that a constant coefficient may be obtained from the standard mass transfer model. To do this for an aeration system, the baseline from a single clean water test (or a series of tests) must be determined. The baseline mass transfer coefficient is denoted by the symbol $K_L{a}_0$. Then, one can translate any test result to 20°C using a temperature correction model only suitable for the baseline to give ($K_L{a}_0$)₂₀, from which a scale-up model for depth correction will produce a reasonable $(K_{L}a{)}_{20}$. In verification of the Rational Method, based on various experiments cited in the literature, they do all seem to give the same $(K_L{a}_0{)}_{20}$. Therefore, the results seem promising for evaluating $(K_{L}a{)}_{20}$ for any test. These are best explained by way of various examples given in the paper based on extracted data from cited literature.

Pollution caused by the heavy metal cadmium (Cd) in smelting site soil has become an environmental problem that cannot be ignored. The process of Cd ion adsorption, migration, and diffusion in soil is influenced by various factors, including soil solid–phase composition and soil environment conditions. In order to investigate the adsorption behavior of Cd in smelting site soil, this study collected uncontaminated soil samples from the vicinity of a smelter, with kaolinite, mica, and goethite identified as abundant components of the soil solid phase. We conducted batch adsorption experiments, zeta-potential analysis, scanning electron microscopy (SEM), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS) to investigate the mechanism of adsorption of Cd ions by kaolinite, mica, and goethite. Our results showed that the pH of the solution significantly influenced the adsorption of Cd ions by these minerals, with increased adsorption observed as the pH increased. Furthermore, the adsorption of Cd ions on kaolinite, mica, and goethite exhibited the best fit with the Freundlich model. SEM and XRD analyses indicated that the crystal structures of the minerals remained unchanged after Cd ion adsorption, suggesting that the Cd ions were primarily bound to the mineral surfaces. XPS measurements of the binding energy changes in the O1s and Cd3d orbitals before and after adsorption were compared with standard binding energy spectra. This comparison confirmed that heavy metal Cd primarily existed on mineral surfaces in the form of outer-sphere and inner-sphere complexes. This study examined the impact of pH on the adsorption of Cd by three types of mineral; fit the data using the isotherm adsorption model equation; and analyzed the mechanisms of binding Cd on different mineral surfaces through characterization techniques. The study’s findings should contribute to a better understanding of Cd adsorption mechanisms and provide valuable insights into the behavior of cadmium in soil at smelting sites.

The present study investigated the copper tolerance and bioremediation potential of endophytic bacteria because endophytic bacteria are the most common bacterial strains associated with heavy metal bioremediation. The acute toxic effects of copper on living organisms were determined using two endophytic bacterial species, Bacillus sp. and Streptomyces griseus (S. griseus). After 4 days of acute toxicity test, changes in metal and bacteria concentrations in water, inhibition (%), bioaccumulation rate, and bioconcentration factors were evaluated. According to the evaluations, cell weights decreased, and inhibition rate (%) increased with increasing metal concentration after a certain level ($10\mathrm{mg}/\mathrm{L}\mathrm{Cu}$). With increasing metal concentrations from 5 to $25\mathrm{mg}/\mathrm{L}$, biosorption efficiency decreased from 35.94% to 20.73% for S. griseus and from 56.36% to 34.47% for Bacillus sp. The bioaccumulation quantities increased with increasing metal concentrations for both species. Based on the present findings, it is concluded that Bacillus sp. and S. griseus are suitable candidates for the bioremediation of copper ions from contaminated environments. These endophytic bacteria use hyperaccumulating plants for more effective bioremediation of heavy metals.

Abstract

Recently, lightweight expanded-clay aggregates (LECAs) have emerged as a promising material for various geoenvironmental applications. This study aimed to explore the potential of LECAs as an adsorbent in a laboratory-scale constructed wetland to mitigate the impact of antibiotics, specifically erythromycin (ery) and doxycycline (doxy). The physical characteristics of LECA were determined, including hydraulic conductivity of $1.12\times {10}^{-3}\mathrm{m}/\mathrm{s}$, a specific surface area of $\mathrm{2,890}{\mathrm{m}}^2/\mathrm{kg}$, and a pH value of 7.6. In the laboratory-scale batch study, Langmuir ($K_L=3.2565\mathrm{L}/\mathrm{mg}$) and Freundlich [$K_f=0.2376$ ($\mathrm{mg}/\mathrm{g}$) ($\mathrm{L}/\mathrm{mg}$)] isotherm models provided the best fit for doxy and ery, respectively. Additionally, the pseudo-second-order kinetic model exhibited the best fit for both antibiotics. The adsorption of doxy was primarily attributed to $\pi –\pi$ interactions and hydrogen bonding, explaining why it followed the Langmuir isotherm with most sorbents. On the other hand, ery exhibited electrostatic sorption and cation exchange as the dominant mechanisms, potentially demonstrating its multilayer sorption behavior. A shift from an acidic to an alkaline pH significantly enhanced the adsorption of both doxy (16% to 94%) and ery (45% to 89%). Similarly, raising the temperature from 5°C to 45°C increased the sorption capacity to 83% for doxy and 88% for ery. In the one-dimensional vertical-column study using LECA as the adsorbent, the exhaustion time for ery and doxy was determined to be 70 and 84 h, respectively. These results aligned well with the findings obtained from the HYDRUS model. Constructed wetlands employing LECA beds demonstrated remarkable removal efficiencies, with doxy removal from 93% to 96% and ery removal from 92% to 97%. A long-term study on LECA after pouring studied antibiotics solution in cycles revealed an appreciable drop in removal efficiencies at the end of an extensive period. Based on these observations, it can be concluded that LECA possesses a significant adsorption capacity against doxy and ery due to high in situ pH, specific surface area, and hydraulic conductivity. Under acidic conditions, ery exhibited higher sorption capacity in comparison to doxy because of the preponderance of ${\mathrm{H}}^{+}$ ions. However, in an alkaline state, the abundance of ${\mathrm{OH}}^{-}$ ions hindered the release of ${\mathrm{H}}^{+}$ ions, resulting in minimal changes in the adsorption capacity of ery, unlike doxy, which displayed a steady increase. Furthermore, elevated temperatures enhanced the adsorption capacity by accelerating intraparticle diffusion.

Practical Applications

The use of LECA in constructed wetlands has emerged as a cost-effective, sustainable, and highly efficient strategy for mitigating the release of antibiotic-laden wastewater into the environment, particularly water bodies. Extensive research has already established LECA as an exceptional sorbent, and this study further reinforces its remarkable efficacy in adsorbing antibiotics from aqueous solutions. These findings position LECA as a leading candidate for implementation as bed material in scaled-up constructed wetland systems in actual field conditions. The long-term advantages of utilizing LECA are manifold. First, it offers easy production, ensuring a readily available supply. Additionally, LECA exhibits a long life span, durability, and the ability to withstand changes in pH and temperature without degradation or decomposition. These characteristics make it a reliable and robust material for sustained use in constructed wetlands. Moreover, the simplicity of the approach, requiring minimal expertise for setup and maintenance, makes LECA an attractive option for government organizations, pharmaceutical industries, and rural communities alike. The broad applicability of LECA extends beyond antibiotic removal, because it effectively eliminates contaminants from wastewater, thereby safeguarding surface and groundwater bodies from pollution. Thus, LECA is an ideal solution for removing antibiotics and other pollutants from wastewater in constructed wetland systems. Its low-cost production, longevity, resilience, and user-friendly nature make it an appropriate choice for large-scale implementation. By adopting LECA, the impact of antibiotic contamination on the environment can be significantly reduced and can help preserve the integrity of precious water resources.

Conventional vacuum electroosmosis consolidation theory tends to assume that the electric permeability coefficient remains unchanged or attenuates linearly. In contrast, the sediment from environmental dredging projects contains copper contaminants, whose electrochemical reactions during electroosmosis may influence the soil properties. Consequently, electroosmosis experiments were conducted for copper-contaminated sediments. It was found that the electric permeability coefficient attenuated rapidly due to the generation of copper hydroxide flocculant deposits under electrochemical reactions. The attenuation was 67.89% after 48 h, and its attenuation trend had obvious nonlinear characteristics. On this basis, an expression for the attenuation of the electric permeability coefficient with time was obtained by fitting an exponential function. A two-dimensional vacuum electroosmosis consolidation model considering the nonlinear attenuation rule of the electric permeability coefficient was established, and the analytical solution of the pore water pressure was deduced. Vacuum electroosmosis experiments on contaminated sediment were carried out, and the measurement results of pore water pressure at the anode verified the rationality of the analytical solution. It was also compared with conventional vacuum electroosmosis consolidation theory, which showed that the analytical solution in this study is better able to predict the dissipation of pore water pressure during long-term vacuum electroosmosis.

In this work, a class of transition metal-modified MCM-41 mesoporous silica supported ionic liquids nanocatalysts were constructed and efficiently used as catalysts for the effective carboxylation of terminal alkynes through ${\mathrm{CO}}_2$ utilization. The main factors affecting the catalytic performance of carboxylation and its possible reaction mechanism were sufficiently discussed. The results showed that when the dosage was 0.2 g, the temperature was 40°C and the ${\mathrm{CO}}_2$ pressure was 0.3 MPa, the supported catalyst MCM-41@IL-Sm showed the optimal catalytic efficiency. The novel catalyst proved to be highly efficient for the sustainable synthesis of alkynyl carboxylic acids attributing good to excellent yields of 82%–95% within 7–12 h. Moreover, MCM-41@IL-Sm could be recycled and reused six times without noticeable decrease in catalytic activity from two-phase system under external heterogeneous field. The application of supported ionic liquids in the field of carbon dioxide carboxylation has injected a new power source for the efficient and effective production of value-added chemicals from waste ${\mathrm{CO}}_2$.

The effects of planting ryegrass combined with sludge addition and arbuscular mycorrhizal fungi (AMF) inoculation on organic carbon accumulation in reclaimed mine substrates (RMS) were investigated. A 6-year field experiment was carried out; in the 0–15-cm edaphic layer, a mixed matrix was constructed according to the ratio of fly ash to coal gangue to $\mathrm{sludge}=1:6:3$, with $0.5\mathrm{kg}/{\mathrm{m}}^2$ of AMF inoculated and ryegrass sowed annually. The particle size, carbon fraction, enzyme activity, AMF-related protein and ryegrass rhizosphere effect of RMS aggregates were monitored regularly. The cumulative contribution of the above factors to organic carbon in RMS was quantitatively explored by path analysis. After reclamation, the texture of reclamation matrix in mining area was improved, the stability of aggregates augmented significantly with the proportion of large aggregates increased gradually. Organic carbon in RMS increased by 1.96 times to $38.12\mathrm{g}/\mathrm{kg}$; the contents of total N and available P increased significantly year by year, mainly concentrated in aggregates. Path analysis showed that the underground biomass of ryegrass and 0.5–2-mm aggregates were the two factors with the strongest direct positive effect on organic carbon accumulation in RMS. In addition, available phosphatase and easily extractable glomalin affected the process through complex interaction with each other. A combination of ryegrass-AMF-sludge on a reclamation mining field could improve the quality of RMS through aggregates by promoting the process of soil formation, and ryegrass root growth conducive to organic carbon accumulation.

Stormwater is considered a pathway of microplastics to surface water systems, but the magnitude of microplastic pollution in stormwater and the efficacy of existing stormwater treatment methods are unknown. One potential solution for minimizing microplastics in surface waters is leveraging green infrastructure, such as green roofs, bioswales, and bioretention cells, which can be optimized for the removal of conventional and emerging contaminants. The goals of this study were to (1) establish baseline types and quantities of anthropogenic microparticles, including microplastics, found in stormwater, and (2) evaluate bioretention as a possible solution for reducing microplastics in stormwater. To understand baseline conditions, samples were taken from five different catch basins in north Portland, Oregon, during four storm events and analyzed to quantify and characterize microparticles between 106 μm and 5 mm. A baseline concentration of $4.5\pm 2.2$ (range 1.1–9.7) particles/L was found, with no observed differences in concentrations between sampling locations or storm events. Most identified microparticles were fibers (66%), and approximately 47% of the particles were cotton, followed by polyester/blend (33%) and nylon (9%). Microparticle concentrations were correlated with the concentration of total suspended solids and the number of pieces of litter collected during a litter survey. To determine the efficiency of bioretention systems for microplastic removal, laboratory bioretention columns were constructed and filled with three different geomedia (a City of Portland, Oregon, standard mix, a proprietary mix, and layered sand and compost). A total of nine columns (three replicates of each geomedia) were tested with stormwater collected from a catch basin in Portland that was spiked with synthetic microplastics (106–5,000 μm). A removal efficiency of 99.8% was observed across all bioretention columns, regardless of the media type. Results indicate green stormwater infrastructure, such as bioretention, may be an effective tool for reducing observed microplastic transport from urban runoff to receiving water bodies.

The two-parameter Elovich isotherm is increasingly being used to describe the adsorption of water contaminants on solid materials. This isotherm is derived from a modified version of Langmuir’s kinetic theory for saturable adsorption. However, despite incorporating a saturation capacity parameter, the Elovich isotherm fails to predict an adsorption maximum at high concentrations. As a result, there are disparities between the estimated and observed saturation capacities. In this study, we have identified a conceptual flaw within the Elovich isotherm responsible for this anomaly. By introducing modifications to the theoretical derivation of the Elovich isotherm, we have rectified the conceptual defect. The modified isotherm retains the two parameters of the Elovich isotherm but possesses a different mathematical structure. In contrast to the Elovich isotherm, the new isotherm provides estimated saturation capacities that align closely with the observed values. A comparative analysis demonstrates the superiority of the new isotherm over the Elovich isotherm in fitting data featuring a plateau. However, the new isotherm is loading-implicit, posing challenges in data fitting. To overcome this limitation, we have developed a novel method to convert the loading-implicit isotherm into an explicit form. This conversion enables convenient data fitting and facilitates the evaluation of the site energy distribution of heterogeneous adsorbents.

A novel method is developed and demonstrated for identifying the dominant component of rainfall-driven infiltration and inflow (I&I) in sanitary sewers. The method uses synoptic measurements of rainfall, sewer flow rates, and water-table elevations to extract the ratio of infiltration to total I&I as a function of rainfall amount. The method is based on three quantifiable relations: the incremental flow rates resulting from rainfall events of different magnitudes, the responses of the water-table elevations to rainfall events of various magnitudes, and the responses of dry-weather flow rates to changes in water-table elevations. Application of the method is demonstrated at 10 locations in South Florida. The results show that infiltration is the dominant mechanism for small rainfall events at five of the 10 locations, and inflow is the dominant mechanism for large rainfall events at nine of the 10 locations.