Journal of Environmental Engineering

Forum papers are thought-provoking opinion pieces or essays founded in fact, sometimes containing speculation, on a civil engineering topic of general interest and relevance to the readership of the journal. The views expressed in this Forum article do not necessarily reflect the views of ASCE or the Editorial Board of the journal.

Perfluoroalkyl substances (PFAS) have been observed around the world in air, water, and soil. Recent research and monitoring studies have alluded to the widespread presence of PFAS, but most observed the impact of PFAS as a snapshot in time and space. In an effort to better understand PFAS fate and transport in the environment, computational models have been developed. Here, we synthesized the model applications of PFAS fate and transport via water medium through surface water, vadose zone, groundwater, and streamflow as well as their uptake and accumulation in plants and aquatic organisms. Meanwhile, the water medium is permeable to incoming (sources) and outgoing (sinks) PFAS compounds. Ultimately, knowledge gaps in modeling PFAS for each environmental area were identified. The knowledge gaps highlight the simplicity of the models to date, with most simulating small and isolated systems. Future work opportunities are apparent for both sampling efforts and model development given the knowledge gaps identified.

Hydroxyl radicals generated from advanced oxidation processes (AOPs) are broadly applied to mitigation of refractory organics in landfill leachate. However, following treatment by AOPs, the wastewater still contains highly oxidized organics that are recalcitrant to further chemical oxidation, thereby providing a challenge to established wastewater-treatment technologies. This study aimed to validate whether advanced reduction processes (ARPs), an emerging chemical degradation process driven by highly reductive hydrated electrons (${\mathrm{e}}_{\mathrm{aq}}^{-}$), can effectively decompose persistent and complex organics in a Fenton pretreated landfill leachate. Results showed that ARPs poorly cleave C-C bonds in the Fenton pretreated leachate organic matter (LOM) due to low reactivity of the mixed organics toward ${\mathrm{e}}_{\mathrm{aq}}^{-}$. However, ${\mathrm{e}}_{\mathrm{aq}}^{-}$ and ultraviolet (UV) irradiation during the ARP treatment could attack certain chromophores to reduce ${\mathrm{UV}}_{254}$ absorbance by 53%. The transformation particularly occurred to the low-molecular-weight ($<10\mathrm{kDa}$) and hydrophobic LOM fractions. Meanwhile, the carboxylic content declined after the ARP treatment, whereas the phenolic concentration remained constant, suggesting that ${\mathrm{e}}_{\mathrm{aq}}^{-}$ principally reacted with electron withdrawing groups rather than electron donating moieties on the Fenton pretreated LOM. This study highlights that ARPs can serve as a promising post-treatment after AOPs for treatment of refractory organic wastes in landfill leachate.

Degradable plastics, the substitute for conventional plastics, are becoming the new pollutant in the ocean. However, studies investigating the impact of freshwater and seawater on the basic aging process of microplastics and involving degradable plastics are still lacking. To accurately compare the potential hazards of degradable microplastics aging in seawater and freshwater, the role of salinity in the ultra-violet ray (UV) aging process of degradable microplastics (MPs) was explored in this study. Polylactic acid (PLA) aged under UV and 0‰, 10‰, and 40‰ salinities was taken as the subject. The results showed that salinity combined with UV accelerated the aging process, and PLA had more holes and cracks on the surface, larger specific area ($S_{\mathrm{BET}}$), and significantly more oxygen-containing functional groups and negative charges. The $S_{\mathrm{BET}}$ of PLA aged under UV and 40‰ salinity was $2.97\pm 0.11$, 33% more than that aged by UV only. Additionally, salinity increased the adsorption capacity of PLA. The adsorption quantity of oxytetracycline (OTC) and ${\mathrm{Cu}}^{2+}$ by 40‰ salinity-aged PLA were 4.822 and $9.606\mathrm{mg}/\mathrm{g}$, 30% and 32% more than that aged by UV only. There was a drop in the desorption rate of OTC but a rise in that of ${\mathrm{Cu}}^{2+}$ by PLA aged in salinities. Moreover, the desorption quantity and rate of pollutants on PLA in simulated intestinal fluid were greater than those in water, and PLA might have a higher carrier effect on pollutants after aging under salinity conditions. These results showed that the potential hazard of PLA existing in seawater may be more serious than that in freshwater. This study also revealed the effect of salinity, enabling the environmental risk assessment of degradable MPs to be more scientific and more comprehensive.

Three different ${\mathrm{MnO}}_2$ polymorphs, $\alpha {\text{-}\mathrm{MnO}}_2$, $\beta {\text{-}\mathrm{MnO}}_2$, and $\delta {\text{-}\mathrm{MnO}}_2$, with ${\mathrm{K}}^{+}$-tuned tunnel structures were loaded on sludge-based biochar (BC). Then ${\mathrm{MnO}}_2$-loaded BCs served as the catalyst for ciprofloxacin (CIP) removal. Results showed that as-prepared materials exhibited better catalytic activity than raw BC, among which $\mathrm{BC}\text{-}\alpha {\text{-}\mathrm{MnO}}_2$ achieved superior CIP removal than $\mathrm{BC}\text{-}\beta {\text{-}\mathrm{MnO}}_2$ and $\mathrm{BC}\text{-}\delta {\text{-}\mathrm{MnO}}_2$. CIP removal increased when pH increased from 3 to 5, then slightly decreased with further increase of pH. Desorption experiments confirmed that both adsorption and degradation contributed to the CIP removal by ${\mathrm{MnO}}_2$-loaded BCs. Compared with the raw BC, the contribution of degradation increased 27.87%, 19.87%, and 14.19%, respectively, for $\mathrm{BC}\text{-}\alpha {\text{-}\mathrm{MnO}}_2$, $\mathrm{BC}\text{-}\beta {\text{-}\mathrm{MnO}}_2$, and $\mathrm{BC}\text{-}\delta {\text{-}\mathrm{MnO}}_2$. The radical quenching experiments and electron paramagnetic resonance tests demonstrated the existence of reactive oxidation species (ROS) including ${\mathrm{O}}_2^{-}•$, •OH, and ${}^1{\mathrm{O}}_2$. The ${\mathrm{O}}_2^{-}•$ and •OH were the main ROS during CIP degradation by BC, while ${}^1{\mathrm{O}}_2$ was the main ROS for ${\mathrm{MnO}}_2$-loaded BCs. $\mathrm{BC}\text{-}\alpha {\text{-}\mathrm{MnO}}_2$ featured the most abundant ROS, followed by $\mathrm{BC}\text{-}\beta {\text{-}\mathrm{MnO}}_2$ and $\mathrm{BC}\text{-}\delta {\text{-}\mathrm{MnO}}_2$. The persistent free radicals and Mn in ${\mathrm{MnO}}_2$-loaded BCs may serve as the active site for electron transfer during the degradation process, thus leading to the generation of ${\mathrm{O}}_2^{-}•$, •OH, and ${}^1{\mathrm{O}}_2$.

In the urban water cycle, adsorption facilitated by engineered granular media increasingly is deployed for solute separation in potable water, stormwater, and wastewater systems. Of these systems, stormwater treatment is inordinately complex. Stormwater systems are passive, decentralized, and subject to highly unsteady and uncontrolled fluxes with multiphase interactions. This study proposes a multiphase and multiphysics computational fluid dynamics (CFD) model, interAdsFoam, to simulate turbulence mixing and adsorption with dynamic water–air interface and reaction zones. An original CFD model is proposed, benchmarked, and validated with data sets across a range of scales: (1) bench-scale columns for model parameter estimation, (2) physical modeling of a radial flow adsorption reactor (RFR) subject to controlled fluxes, and (3) field monitoring of a commercial volumetric radial flow adsorption reactor (VRFR) system subject to uncontrolled event-based fluxes. The results illustrate (1) the nonuniqueness of numerical solutions for parameter estimation in adsorption modeling; (2) that regulating the parameter estimation process with isotherms improves model generalizability; (3)  inverse modeling of the RFR hydraulic resistance with the quadratic Thiem model can provide a more accurate representation than the Ergun model; and (4) that turbulence transport and chemical adsorption are dynamically coupled with the air–water momentum balance. The proposed CFD model predicts total dissolved phosphorus (TDP) transport and fate based on field monitoring of the VRFR. System dynamics and treatment functionality are elucidated, and implications for practical reactor design are discussed. The proposed open-source CFD model provides a novel framework for higher-fidelity urban water adsorption reactor simulation, design, and optimization than current methods for adsorption.

This work developed three computational fluid dynamics (CFD) models of a full-scale oxidation ditch, one three-dimensional (3D) model and two one-dimensional (1D) models, to compare their predicted wastewater treatment performance. The models incorporated biokinetics through the Activated Sludge Model 1 (ASM-1) to predict the treatment performance of the ditch based on concentrations of pollutants: readily biodegradable substrate ($S_S$), soluble ammonium ammonia nitrogen ($S_{NH}$), and soluble nitrate nitrite nitrogen ($S_{\mathrm{NO}}$). When comparing the time series of the concentration of ASM-1 pollutants averaged over the ditch for 40 days, all three models displayed similar trends with slight differences in steady-state values, except for $S_{NO}$. The steady-state value of $S_{NO}$ was greater by more than 150% for the 1D model than the 3D model. This difference is attributed to spatial heterogeneities in dissolved oxygen concentration predicted by the 3D model that were not captured by the 1D model, leading the latter to underpredict the denitrification process. Specifically, the spiraling flow around the aerators that plays an important role in determining the spatial distribution of dissolved oxygen cannot be represented in the 1D model.

As the main solid waste of wastewater treatment plants (WWTPs), sewage sludge has the characteristics of large output and high contents of organic matter and inorganic metals. In this study, sewage sludge was used as raw material to prepare a unique sludge-based biochar. In order to obtain the best modification method for ammonium and phosphorus adsorption removal in wastewater, the sludge-based biochar was modified by loading four kinds of metal, respectively, including Mg, Al, Fe, and Mn, to improve the adsorption capacity of the biochar. A large number of adsorption experiments showed that Mg-modified sludge–based biochar (BC-Mg) had the best adsorption effect. At 25°C, the maximum adsorption capacity of ${\mathrm{NH}}_4^{+}$ and ${\mathrm{PO}}_4^{3-}$ reached 30.58 and $400.00\mathrm{mg}·{\mathrm{g}}^{-1}$, respectively. In the double-solute coadsorption experiment, Mg-BC also had the best adsorption effect. In addition, kinetics, isotherms, and various characterization analyses [Fourier transform infrared spectrometer (FTIR), X-ray diffraction (XRD), Brunauer, Emmett and Teller (BET), scanning electron microscope (SEM), X-ray photoelectron spectroscopy (XPS), and zeta potential, among others] were used to study the physicochemical properties of the modified sludge–based biochar and the adsorption mechanism of ${\mathrm{NH}}_4^{+}$ and ${\mathrm{PO}}_4^{3-}$. It mainly includes ligand exchange, ionic bond, deposition reaction, and electrostatic attraction to pollutants. This study not only provides a feasible strategy for efficient utilization of sewage sludge resources, but also provides a practical method for ammonium and phosphorus removal in water.

A three-dimensional (3D) bench-scale, low-porosity fractured-sandstone network experiment was used to evaluate the behavior and effectiveness of in situ chemical oxidation (ISCO) using potassium permanganate (${\mathrm{KMnO}}_4$) to deplete tetrachloroethylene (PCE) dense nonaqueous phase liquid (DNAPL). The purpose of the 3D fracture experiment was to compare mass removal during steady state DNAPL dissolution conditions to ISCO, and to determine how the presence of fracture intersections affected the formation of reaction byproducts in the experimental 3D fracture network. DNAPL dissolution in the fracture network was evaluated and described using an effective parameter: the bulk mass transfer coefficient ($K_L$). Residual DNAPL saturation and subsequent steady state DNAPL dissolution conditions were established during ambient groundwater flow through the experimental network, and then ISCO was applied. PCE mass removal rates during steady state DNAPL dissolution conditions were compared to mass removal rates achieved during ISCO experiments. The effective DNAPL-water interfacial area (${\mathrm{a}}_{\mathrm{i}}$) was characterized and evaluated using conservative and interfacial area tracer tests. The ${\mathrm{a}}_{\mathrm{i}}$ was used to compare availability of DNAPL-water contact during dissolution studies as well as pre- and post-ISCO applications. The results of this research indicate that, in the experimental 3D fracture network, mass removal rates during steady state DNAPL dissolution conditions were generally greater than mass removal rates during ISCO experiments over the same timeframe. Research data indicate that, similar to what has been observed in fracture plane studies, the formation of reaction products [manganese dioxide (${\mathrm{MnO}}_2$) and carbon dioxide (${\mathrm{CO}}_2$)] limited contact of the oxidant with the network DNAPL, and thus limited mass removal during ISCO. The reduction in DNAPL-water contact due to reaction byproduct formation was supported by the lack of quantifiable ${\mathrm{a}}_{\mathrm{i}}$ following ISCO. The reaction byproducts are believed to have altered the flow paths during ISCO, which limited the DNAPL-oxidant contact and reduced the PCE mass removal rates. Experimental results suggest that stopping the application of ISCO when PCE mass removal is no longer effective (i.e., when the generated chloride concentration is within 10% of the background chloride concentration), the ISCO will successfully remove more PCE than dissolution alone. Subsequent experiments that evaluate DNAPL entrapment due to reaction byproduct formation, not simply flow path alteration, are needed to better understand if this as a viable option to address DNAPL in fracture network settings.

The objective of this study was to investigate the content characteristics of heavy metals, metalloids, and nutrients in farmland soil in the entire Hunan Province, China. In addition, the spatial distribution features, pollution risk, and probability health risk were further analyzed using a geographic information system, integrated pollution risk index, and Monte Carlo simulation. The results showed a significant Cd accumulation in the soils of Hunan Province. Total nitrogen and soil organic matter were at a higher nutrient level, whereas total phosphorus was relatively low. Areas with high Hg, Cd, As, and Pb levels mainly appeared in Chenzhou, Hengyang, and southern Zhuzhou, where nonferrous metal mining and smelting activities were frequent. High-nutrient areas were mainly located in Xiangtan, Lou Di, and the surrounding areas of Dongting Lake. The pollution risk assessment showed that Cd in soils was at a moderately pollution level, Hg was at a moderate to slight pollution level, and As, Cr, and Pb had the lowest pollution risk. The carcinogenic risk caused by accidental ingestion of Cr and As in soil was high, and farmers had a 75% probability of facing potential health threats. This study provides baseline and scientific data for formulating and implementing corresponding preventive measures and public policies.

This study explored the remediation of coal tar–contaminated sand with smoldering combustion using vegetable oil as supplemental fuel. In this work, bench-scale column experiments were conducted one factor at a time to identify the minimum concentration limit of coal tar and the feasibility of vegetable oil as supplemental fuel. A range of key parameters including various concentrations of vegetable oil ($\mathrm{10,000}–\mathrm{50,000}\mathrm{mg}/\mathrm{kg}$), types of vegetable oil (sunflower, soybean, and corn oils), and oil to coal tar mass ratios that affect smoldering combustion were examined in detail. Results demonstrated that exceeding 80,000 mg coal tar in 1 kg sand caused smoldering exceeding 630°C. The posttreatment coal tar concentration in treated sand was $648\mathrm{mg}/\mathrm{kg}$, indicating more than 99% initial coal tar was destroyed. Further, corn oil was a relative suitable supplemental fuel, which possessed higher average peak temperature and removal efficiency. To be specific, the sum of the concentration of corn oil and coal tar reaching $\mathrm{50,000}\mathrm{mg}/\mathrm{kg}$ was found to be a necessary requirement to determine whether smoldering combustion occurred or not; in addition, the content of coal tar was not less than $\mathrm{20,000}\mathrm{mg}/\mathrm{kg}$. Overall, this study indicated that smoldering with injection of vegetable oil has potential to be effective in situ remediation application for low-concentration coal tar–impacted sand ($<\mathrm{80,000}\mathrm{mg}/\mathrm{kg}$).

This study investigates the pollutant removal performance and cleaning characteristics of six sand-based bioretention systems. The sand-based bioretention systems used fine sand and peat soil as the primary substrates mixed with volcanic rock, green zeolite, coal slag, vermiculite, and perlite as additives, and a system without additives was used as the control. The influence of the influent concentration and rainfall intensity on the pollutant removal performance was investigated, and the cleaning characteristics of the six systems were explored using the total suspended solids (TSS), total phosphorus (TP), ammonium nitrogen (${\mathrm{NH}}_4^{+}\text{-}\mathrm{N}$), total nitrogen (TN), and the chemical oxygen demand (COD) as pollutant indicators. The results showed that (1) the influent concentration had a more obvious influence on the TP, ${\mathrm{NH}}_4^{+}\text{-}\mathrm{N}$, and COD, which were primarily removed by the adsorption of fillers, (2) high intensity rainfall was more detrimental for the removal of ${\mathrm{NH}}_4^{+}\text{-}\mathrm{N}$ and TN than for the other pollutants, but the addition of media with a good nitrogen removal performance, such as green zeolite and vermiculite, mitigated this detrimental influence, and (3) dissolved pollutants such as TP, ${\mathrm{NH}}_4^{+}\text{-}\mathrm{N}$, TN, and COD retained in the sand-based bioretention systems all had the potential to be flushed out during next rainfall event, and the ease of being flushed out varied among the different fillers.

Sulfamethoxazole (SMX) is frequently detected in water, which can cause bacterial resistance and spread resistance genes. Activated carbon, graphite rods, and carbon fiber were used as electrodes to construct biofilm electrode systems for the removal of SMX in water. According to the SMX removal efficiency during three experimental batches, the carbon brush electrodes (CB) had the best removal efficiency; the removal rate of SMX reached 98.23% within 192 h at Cycle 3. However, the removal efficiencies of activated carbon (AC) electrodes and graphite rod (GR) electrodes were only 88.31% and 16.80%. The properties of different electrodes, including specific surface area, contact angle, and resistivity, were the crucial factors affecting the electrode’s biocompatibility and electron-transfer properties. The 16S ribosomal ribonucleic acid (rRNA) gene sequencing results revealed that the richness and diversity of the microbial community on CB electrodes were higher than those of the other electrodes. The linear discriminant analysis effect size (LEfSe), analysis showed that the dominant functional bacteria were enriched on the CB electrodes. The phylogenetic investigation of communities by reconstruction of unobserved states (PICRUSt) analysis results further demonstrated that the CB electrodes could utilize their unique properties to enhance the relative abundance of cellular process functions, thus promoting the degradation of SMX in the biofilm electrode systems. This study explained the mechanism of different electrode materials in affecting the SMX removal efficiency in the biofilm electrode systems. It provides a reference and theoretical basis for selecting electrode materials in bioelectrochemical systems.

Abstract

A three-dimensional ordered macroporous cerium dioxide ($3{\mathrm{DOM}\mathrm{CeO}}_2$) was synthesized using a template method combining the sol-gel method, and ${\mathrm{LaFeO}}_3$ was synthesized and immobilized on $3{\mathrm{DOM}\mathrm{CeO}}_2$ via the sol-gel method combining the impregnation method. The thermogravimetric (TG), scanning electron microscope (SEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), Brunauer-Emmett-Teller (BET), X-ray photoelectron spectroscopy (XPS), and inductively coupled plasma optical emission spectrometry (ICP-OES) were used to characterize the samples. The catalytic performance and reaction mechanism of the catalyst were studied with methylene blue (MB) as the model pollutant. The MB catalytic behavior showed that the addition of $3{\mathrm{DOM}\mathrm{CeO}}_2$ increased the specific surface area of the pristine perovskite. At the same time, there was a synergistic effect between ceria support and perovskite, which significantly improved the activity and stability of the pristine perovskite catalyst. ${\mathrm{LaFeO}}_3/3{\mathrm{DOM}\mathrm{CeO}}_2$ had a wider pH range and higher ${\mathrm{H}}_2{\mathrm{O}}_2$ utilization rate than homogeneous Fenton catalyst. At the same time, in the test range, the leaching concentration of Fe in ${\mathrm{LaFeO}}_3/3{\mathrm{DOM}\mathrm{CeO}}_2$ was less than $0.2\mathrm{mg}·{\mathrm{L}}^{-1}$, which is conducive to reducing the production of iron sludge and greatly controlling the secondary pollution. Furthermore, the ${\mathrm{LaFeO}}_3/3{\mathrm{DOM}\mathrm{CeO}}_2$ catalyst also possessed superior stability of activity and structure in 10 cycles. The results of quenching tests and electron spin resonance (ESR) analyses showed that the catalytic degradation of MB was mainly completed under the action of high-activity $•\mathrm{OH}$. The redox cycle between ${\mathrm{Ce}}^{4+}$ and ${\mathrm{Ce}}^{3+}$ is conducive to improving the efficiency of electron transfer, thereby increasing the production efficiency of $•\mathrm{OH}$ in the heterogeneous Fenton process. Catalytic degradation of MB approximately conformed to first-order kinetics. The aforementioned results indicate that the novel ${\mathrm{LaFeO}}_3/3{\mathrm{DOM}\mathrm{CeO}}_2$ has great application potential in the field of heterogeneous Fenton treatment of organic pollutants.

Practical Applications

A novel ceria-perovskite composite ${\mathrm{LaFeO}}_3/3{\mathrm{DOM}\mathrm{CeO}}_2$ was successfully prepared in this experiment, and the catalytic performance and reaction mechanism of the catalyst were studied with methylene blue (MB) as the model pollutant. The ${\mathrm{LaFeO}}_3/3{\mathrm{DOM}\mathrm{CeO}}_2$ has higher catalytic activity and stability than ${\mathrm{LaFeO}}_3$ prepared by the sol-gel method, and it has higher pH adaptation range and hydrogen peroxide utilization than ${\mathrm{FeSO}}_4·7{\mathrm{H}}_2\mathrm{O}$. At the same time, in the test range, the Fe leaching concentration in ${\mathrm{LaFeO}}_3/3{\mathrm{DOM}\mathrm{CeO}}_2$ is lower than $0.2\mathrm{mg}·{\mathrm{L}}^{-1}$, which significantly reduces the generation of metal sludge and greatly controls the secondary pollution. Furthermore, the ${\mathrm{LaFeO}}_3/3{\mathrm{DOM}\mathrm{CeO}}_2$ catalyst also possessed superior stability of activity and structure in 10 cycles. During the reaction, there were ${\mathrm{Fe}}^{3+}\leftrightharpoons {\mathrm{Fe}}^{2+}$ and ${\mathrm{Ce}}^{4+}\leftrightharpoons {\mathrm{Ce}}^{3+}$ cycles on the surface of ${\mathrm{LaFeO}}_3/3{\mathrm{DOM}\mathrm{CeO}}_2$ during the reaction process. The two cyclic reactions synergistically initiated the efficient Fenton reaction, resulting in a large number of highly active $•\mathrm{OH}$, thereby realizing the efficient degradation of MB. In summary, ${\mathrm{LaFeO}}_3/3{\mathrm{DOM}\mathrm{CeO}}_2$ can be used as an excellent heterogeneous Fenton catalyst for the treatment of organic pollutants.

The number of poly- and perfluoroalkyl substances (PFAS) and their sources, fates, and avenues of transport is vast. With every new discovery, a new question arises regarding the impact they are having on the environment. Therefore, this study aims to assess the capabilities and shortcomings of widely used models to study large-scale PFAS fate and transport. A surface water model [Soil and Water Assessment Tool (SWAT)], a groundwater model [Modular Finite-Difference Model (MODFLOW)], and a streamflow model [Water Quality Analysis Simulation Program (WASP)] were set up and integrated to simulate PFAS fate and transport in a large watershed. The study area was the Huron River watershed, a highly PFAS impacted watershed in southeastern Michigan. All of the aforementioned models were calibrated and validated for streamflow and base flow on a daily basis with Nash-Sutcliffe model efficiency coefficient (NSE) above 0.6, the ratio of the root-mean square error to the standard deviation of measured data (RSR) less than 0.6, and percent bias (PBIAS) less than $\pm 5\%$. The results showed that the integrated model adequately captured the overall trends for perfluorooctane sulfonate (PFOS) but underestimated the magnitude of perfluorooctanoic acid (PFOA) concentration due to a lack of information from diffusive sources and historical loads. Therefore, it is important to organize monitoring studies and consider further model enhancements to improve our understanding of PFAS fate and transport in large watersheds.