Journal of Environmental Engineering

Per- and polyfluoroalkyl substances (PFAS) are a particularly challenging issue as the widespread contamination of PFAS in the environment and its subsequent effects on both the environment and public health have gained increasing attention in recent years. Commendable research has been conducted to better understand the role of PFAS and the extent of its environmental and public health effects. However, most of these studies have focused on PFAS contamination in surface water and groundwater sources. This paper provides an overview of PFAS contamination in various environmental media with an in-depth analysis of atmospheric contamination and the modeling of fate and transport of PFAS in air. The mechanism and modeling of atmospheric PFAS are presented as well as their suitability, limitations, and areas necessitating additional research. The fate and transport models reviewed in this paper are incorporated for dry deposition, wet deposition, or combined dry and wet deposition. Each study concluded that deposition is a substantial removal mechanism of atmospheric PFAS, and further research must be conducted to assess the particle size distributions of PFAS as well as to account for the degradation of PFAS in the atmosphere prior to deposition.

To improve the understating of viral pathogens’ resuspension from bed sediment and their attachment to suspended sediment, a series of flume experiments using a coliphage surrogate, PhiX174, were conducted with two sediments: sand and sandy loam. Using this data, a conceptual model was developed that quantifies the resuspension rate using a dynamic virus-sediment attachment ratio. The resuspension flux was calculated as the product of virus concentrations in bed sediment and the resuspension velocity. Two resuspension models were derived for the sediments with and without cohesive material. The resulting models correlated nondimensional bed shear stress with the virus concentration in the water. Predictions of the models satisfactorily matched the observed virus concentration. The results shed light on the underlying physics of the attachment of virus to sediment. The attachment ratio increases with bed shear stress until reaching the critical shear stress, and then decreases with a further increase of bed shear stress. Moreover, the virus reverses its attachment to sediment particles after reaching the critical condition for sediment incipient motion. The conceptual model as well as the experimental data shed light on the key processes governing the fate and transport of viral pathogens in sediment laden flow.

This research applies a previously validated bioenergetics model to determine whether the formation of elemental sulfur (${\mathrm{S}}^0$) from hydrogen sulfide is thermodynamically possible during the anaerobic digestion (AD) process. The investigation was sparked by recent studies that reported that the presence of electronically conductive materials (e.g., magnetite) in the AD process could potentially facilitate elemental sulfur formation from hydrogen sulfide rather than the formation of ferrous sulfide (FeS), which is typically formed during the addition of iron salts (e.g., ferric chloride) into the AD environment for hydrogen sulfide control. The net Gibbs free energy change for the overall reaction resulting from the oxidation of hydrogen sulfide to elemental sulfur (${\mathrm{S}}^0$) during the microbial conversion of organic matter to methane (${\mathrm{CH}}_4$) was estimated to be -9.90 kilojoules per mole of electrons transferred ($\mathrm{kJ}/\mathrm{mol}{\mathrm{e}}^{-}$). The exothermic characteristics of the overall bioenergetics reaction suggest that there may be a competitive growth advantage for anaerobic microorganisms that can establish themselves within the vicinity or region of electronically conductive materials. Based on the overall energy transfer estimated during ${\mathrm{S}}^0$ and ${\mathrm{CH}}_4$ formation, a theoretical biomass yield ($Y$) of 0.097-g of volatile suspended solids formed per gram of chemical oxygen demand removed (VSS/gram COD) was obtained. Given that the estimated theoretical $Y$ is well within the range anticipated for facultative bacteria grown under anaerobic conditions, the bioenergetics model appears to be well suited for predicting microbial reaction products from simple thermodynamic considerations. These present modeling results indicate that ${\mathrm{S}}^0$ formation is theoretically possible during methane formation. However, reported experimental evidence suggests that the presence of an electron transfer shuttle is required to facilitate this reaction.

In a mixed anaerobic biotreatment process, sulfate is converted into sulfide by sulfate-reducing bacteria (SRB). Sulfidogens and methanogens in a mixed anaerobic culture can compete for electrons. Diverting a larger fraction of electrons into the sulfate-reduction process can inhibit methanogens and increase overall anaerobic digestion process efficiency. The purpose of this study was to examine the efficiency of SRB in the sulfate-reduction process in presence of two 18 carbon long-chain fatty acids (LCFAs), namely oleic acid (OA), and stearic acid (SA), under mesophilic conditions. Sulfate reduction was examined using glucose in a mixed mesophilic anaerobic culture at 37°C and neutral pH in the presence OA and SA. The control experiments with LCFAs plus sulfate and sulfate alone showed no improvement in sulfate reduction due to the addition of LCFAs (OA and SA), with sulfate reductions of 10% and 9% over 7 days, respectively. In control experiments with glucose and sulfate, sulfate reduction was around 32% over the same period. In experiments with glucose and sulfate, increasing OA concentrations resulted in an increase in electron flux to sulfidogenesis, while negatively impacting glucose degradation rates. Maximum sulfate reduction of 73% over 7 days was observed at the highest OA concentration of $\mathrm{1,000}\mathrm{mg}/\mathrm{L}$, which is about a threefold improvement over the control. Despite methanogenic inhibition and diversion of electron flow toward sulfate reduction in the presence of OA, no ${\mathrm{H}}_2$ was detected. In contrast to OA, no significant increase in sulfate reduction was observed with increasing concentration of SA, up to the maximum tested concentration of $\mathrm{1,000}\mathrm{mg}/\mathrm{L}$. In general, the findings indicate that OA can be effective in redirecting more electrons and thus improving sulfate reduction during the anaerobic treatment process.

Heavy metals including Cd, Pb, and Zn are prevalent stormwater and groundwater contaminants derived from natural and human activities, and there is a lack of cost-effective treatment for their removal. Recently, biochar has been increasingly recognized as a promising low-cost sorbent that can be used to remediate heavy metal contaminated water. This study evaluates the immobilization/release performance of dairy manure-derived biochar (DM-BC) as a sustainable material for competitive removal of coexisting heavy metal ions from water and explains the underlying mechanism for regeneration/reusability of biochar. Results showed that the metal ions exhibited competitive removal in the order of ${\mathrm{Pb}}^{2+}\gg {\mathrm{Zn}}^{2+}>{\mathrm{Cd}}^{2+}$. The pH played a decisive role in influencing metal ion speciation affecting the electrostatic attraction/repulsion and surface complexation. Higher pH led to greater removal for ${\mathrm{Pb}}^{2+}$ and ${\mathrm{Cd}}^{2+}$, whereas ${\mathrm{Zn}}^{2+}$ showed maximum removal at $\mathrm{pH}\approx 7.5$. Diffuse reflectance infrared spectroscopy, scanning electron microscopy, and X-ray diffraction confirmed the interactions and precipitation reactions of oxygen-containing functional groups (e.g., ─ OH, ${\mathrm{CO}}_3^{2-}$, and Si─ O) as key participants in metal immobilization. Langmuir, Freundlich, and Redlich–Peterson isotherm modeling data showed varied and unique results depending on the metal ion and concentration. The removal kinetics and model fitting showed that the three steps of intraparticle diffusion might be more representative for describing the immobilization processes of metal ions on the external surface and internal pores. In the flow-through columns, DM-BC effectively retained the mixed metal ions of ${\mathrm{Cd}}^{2+}$, ${\mathrm{Pb}}^{2+}$, and ${\mathrm{Zn}}^{2+}$ showing 100% removal for the duration of the column run over three cycles of regeneration and reuse.

Microbial fuel cells (MFCs) are potential bioelectrochemical devices that are now being researched for various emerging applications, such as treating wastewater with antibiotics removal. Ciprofloxacin (CIP) is a synthetic antibiotic that is commonly used to treat infections such as pneumonia and influenza. This work investigated the performance of dual-chambered MFCs with two different types of anodes to remove CIP and chemical oxygen demand (COD) and power production. The findings of the experiments revealed that the multiwall carbon nanotubes-coated graphite felt (MWCNT-GF) had a higher power density ($\mathrm{1,512.9}\mathrm{m}{\mathrm{W}\mathrm{/}\mathrm{m}}^{\mathrm{2}}$) and COD removal (95.4%) than the control graphite-felt anode ($816.3\mathrm{m}{\mathrm{W}\mathrm{/}\mathrm{m}}^{\mathrm{2}}$, COD removal 93.2%) under the same circumstances. Further, MFCs were also tested for four different concentrations with average CIP removal rate with MWCNT-coated GF anode to 58.575% and GF anode of 54.25%. Higher CIP removal rate and power performance of MWCNT-GF anodes are due to its macroporous structure, which promotes microbial interaction on the electrode surface. Also, it shows an additional effect of increasing extracellular electron transport. The findings suggest that a dual-chambered MFC operating with a MWCNT-GF anode is a highly effective means of achieving high power performance and CIP removal, with a broad range of application possibilities in bioelectrochemical systems.

To find an economically feasible and directly usable natural permeable reactive barrier (PRB) filler, sponge iron was selected from seven natural materials with excellent removal efficiencies of Cr(VI). The synergism of sponge iron and maifanite increased by 20.90% and showed the best removal effect of 40.187%. In the dynamic column experiment, sponge iron played a major role in the removal of Cr(VI), so increasing its proportion could improve the removal efficiencies, but the permeability of the reaction system would decline. Maifanite can effectively promote the fixation of Cr(III) and inhibit the reduction of permeability. Reducing Cr(VI) concentration and prolonging the hydraulic retention time were favorable for chromium removal. Thomas, Yoon-Nelson, and Adams-Bohart models can all well simulate the penetration curve under the high proportion of sponge iron. After adsorption, chromium in the reaction medium mainly existed as residue and oxidation rather than a water-soluble state, indicating that Cr(VI) in water was reduced to Cr(III) and fixed permanently. Comprehensively considering the saturated adsorption capacity and hydraulic properties, a ratio of sponge iron to maifanite of $5:1$ is reasonable to apply in restoration Cr(VI) contaminated groundwater.

The anaerobic/aerobic sequencing batch reactor (SBR) (A/O-SBR) system has been a major focus of recent research because of its high nitrogen (N) and phosphorus (P) removal efficiencies in wastewater treatment plants. The feasibility of using the A/O-SBR system in plateau regions (altitude 3,000 m) remains unclear. In this study, two A/O-SBR systems were established, and the effect of atmospheric pressure on nutrient removal performance was studied. High N and P removal efficiencies of $90.19\%\pm 3.96\%$ and $98.83\%\pm 1.90\%$, respectively, were achieved in the A/O-SBR system under low atmospheric pressure (72 kPa, called R2). The A/O-SBR system under low atmospheric pressure had higher P-uptake activity ($24\mathrm{mg}/\mathrm{L}$), indicating that P removal was higher in R2 than in the A/O-SBR system under normal atmospheric pressure (97 kPa, called R1). The 16S rDNA sequencing analysis showed that the abundance of denitrifying glycogen accumulating organisms was higher in R2 than in R1, which was opposite to the pattern of P-accumulating organisms (PAOs), denitrifying PAOs, and ammonia-oxidizing bacteria. Batch tests were consistent with the microbial community analysis. Therefore, efficient N and P removal performance was achieved under low atmospheric pressure, and the functional microbial abundance and microbial activities related to N and P removal were significantly affected. The results of this study have implications for removing pollutants during wastewater treatment in plateau regions.

Metronidazole (MNZ) is a typical nitroimidazole antibiotic that often enters the environment via wastewater, and the demand for its degradation in wastewater is increasing in view of the potential environmental risks. Bioelectrochemical systems can effectively improve the degradation of refractory pollutants and are environmentally acceptable. In this study, the MNZ degradation performance of a bioelectrochemical system was investigated. The majority of MNZ in aqueous solutions could be degraded rapidly (within 180 min) at a current of 1 mA in the bioelectrochemical system, and its removal followed the pseudo–first-order kinetic model. The MNZ degradation rate constant in the bioelectrochemical system was nearly eight and two times higher than those in open circuit and nonbiological cathode systems, respectively. Increasing the electric current within a certain range could accelerate the degradation of MNZ, and increasing the initial MNZ concentration led to a slight reduction of the degradation efficiency. Furthermore, the activity of the electrode biofilm was examined, and the microbes were found to be in an active state. High-throughput sequencing analysis revealed that the microbial community structure varied greatly among the tested systems. Finally, the possible degradation mechanism of MNZ in bioelectrochemical systems with the stimulation of electric current was proposed. The synergetic biodegradation of the biofilm and electrochemistry may be responsible for MNZ degradation. These results indicate that bioelectrochemical systems have significant potential for the efficient treatment of wastewater contaminated with antibiotics, which would facilitate a more comprehensive understanding of the contaminant removal process.

The potential for stacking ensemble modeling to enhance the performance and generalizability of machine learning (ML) models for the estimation of total suspended solids (TSS) concentration was assessed by comparing the results with ensemble boosting, bagging, and single ML models. Seven stacking ensemble models (M1 to M7) were created using combinations of basic learners, including single, bagging, and boosting models. Adaptive Boosting (AdB) was used as an aggregation method in M1 to M6. The six models showed coefficient of determination (${\mathrm{R}}^2$) values ranging from 0.87 to 0.95, root mean square error (RMSE) values ranging from 50 to $90\mathrm{mg}/\mathrm{L}$, and mean absolute error (MAE) values ranging from 11 to $86\mathrm{mg}/\mathrm{L}$ where the best ${\mathrm{R}}^2$, RMSE, and MAE values were 0.95, $50\mathrm{mg}/\mathrm{L}$, and $12\mathrm{mg}/\mathrm{L}$, respectively. To further improve the predictions, we tested aggregation methods, including AdB, Random Forest (RF), Variable Weighting kNN (VW-kNN), Regression Tree (RT), and Support Vector Regression (SVR) using the structure of the highest-performing M6 model. This led to a new best fit model (M7) with RF as an aggregation method with ${\mathrm{R}}^2$, RMSE, and MAE values of 0.98, $32\mathrm{mg}/\mathrm{L}$, and $11\mathrm{mg}/\mathrm{L}$, respectively.

Often it is implied that hydraulic particle separators that incorporate vortex technology provide enhanced particle settling. In this study, a generic vortex particle separator was closely examined using physical modeling to help understand typical flow hydraulic conditions. The study was conducted using particle capture analyses under different internal structure configurations, inflow rates, and inlet pipe configurations to examine how resulting changes to flow conditions influenced the settling of particles. The purpose of this study was not to evaluate performance or obtain absolute particle removal rates of a particular particle separator design; instead, the focus was on understanding how modifications to the flow conditions in the examined separator could affect the particle-settling efficiency. The comparison results show that the inflow-generated large internal vortex does not effectively improve particle settling; possible explanations are given based on hydraulics and physics principles. The study method and results can be extended to examine and improve other hydraulic particle separators.

Nonthermal plasma (NTP) is a promising technology for the removal of persistent organic contaminants in wastewater thanks to its ability to generate powerful oxidizing species. In this work, a gliding arc discharge NTP was used for an experimental study to investigate the influence of relative humidity (RH) on reactive species generation depending on a plasma atmosphere (air and oxygen). In addition, an organic dye, Eriochrome Black T (EBT), was treated to investigate the removal potential of this plasma. Dimethyl sulfoxide was used as chemical probe for the detection of ${}^{•}\mathrm{OH}$ and as a radical scavenger to explore the role of ${}^{•}\mathrm{OH}$ in EBT removal. Hydrogen peroxide, nitrite, and nitrate quantification was also assessed. Results indicated that for air plasma, a RH of 30% contributed to the highest oxygen species generation, while dry conditions gave the best results under ${\mathrm{O}}_2$ plasma. The treatment of EBT revealed that humid air plasma ($\mathrm{RH}=30\%$) is more effective regarding decolorization. However, mineralization experiments showed that ${\mathrm{O}}_2$ plasma is more capable of mineralizing an EBT solution. The use of a radical scavenger showcased the potential of plasma gliding arc in humid air for the removal of organic contaminants when radicals’ reactivity is inhibited. Therefore, this study may provide an effective and feasible method of applying NTP in wastewater treatment.

Among the subdisciplines of engineering, environmental engineering is distinctive in three aspects. First, descriptions of the profession of environmental engineering emphasize that environmental engineers solve problems to prevent harm, which typically is an important motivation for taking a job in care work. Second, the percentage of degrees awarded to women is highest for environmental among all subdisciplines of engineering (i.e., 53.3% of bachelor’s degrees, 46.3% of master’s degrees, and 43.6% of doctoral degrees in environmental engineering conferred in 2020 were awarded to women). Third, median salaries for environmental engineers–controlling for other variables–are lowest among engineering subdisciplines (i.e., $82,036 per year in 2019), despite high levels of educational attainment and training. Our analysis of environmental engineers working in the United States strongly suggests that the profession of environmental engineering is highly susceptible to what is known as the care penalty. The care penalty is a function of market dynamics, which tend to undervalue work that generates substantial unpriced benefits for others. The care penalty often is observed in jobs characterized by high levels of intrinsic motivation, such as concern for human welfare. Additional data would be useful to further evaluate the care penalty in environmental engineering in other countries. To address the care penalty, we do not suggest that environmental engineers should become less caring. Rather environmental engineers should be aware of this potential economic risk and seek to mitigate the care penalty in two specific ways. First environmental engineers should encourage life-cycle principles and environmental full-cost accounting in order to increase fungibility among different measures of the components of the triple bottom line of people (i.e., human welfare), planet (i.e., planetary health), and prosperity (i.e., financial gain). Second, environmental engineers should clearly demonstrate the unique contributions that technically skilled commitments to human welfare can generate. We suggest that a greater awareness of these issues could build on and strengthen growing public concerns regarding environmental sustainability. Finally, we suggest that distinctive attributes of environmental engineering may prove critical to unlocking growth in the engineering workforce as care for human welfare and planetary health.

This study sought to coalesce sector knowledge on the use of systems approaches for sustainable water, sanitation, and hygiene (WASH) service delivery in low-income countries. To accomplish this objective, we remotely convened a panel of WASH sector experts within a multiround survey to identify, characterize, and prioritize the necessary attributes of WASH systems approaches. The first survey round asked experts to comment on the conceptual differences between traditional approaches and systems approaches to WASH. Emerging within responses from the first survey round were attributes of WASH systems (i.e., factors, actors) and attributes of WASH systems approaches (i.e., flexible, scalable). A three-round Delphi survey was then administered to reach consensus on these emerging attributes. By the final round of the Delphi, consensus was reached on every attribute of WASH systems, indicating alignment between the experts on the fundamental characteristics and implications of WASH systems. Consensus was also reached on the majority of attributes of WASH systems approaches, including the inherent interconnected and complex nature of WASH systems. However, consensus was not achieved on attributes related to mapping WASH system interconnections, convening stakeholders in collective action, and the appropriateness and feasibility of applying systems approaches at scale. This indicates a need for future research that explores practical and scalable tools and techniques to map and evaluate WASH system interactions, and ways to engage relevant actors in these approaches to collectively apply systems knowledge.