Journal of Environmental Engineering

A $\mathrm{ZnO}/\mathrm{g}\text{-}{\mathrm{C}}_3{\mathrm{N}}_4$ photocatalyst was successfully synthesized via an impregnation method. The high-resolution transmission electron microscope (HRTEM) result shows that $\mathrm{g}\text{-}{\mathrm{C}}_3{\mathrm{N}}_4$ had coated the surface of ZnO, indicating a sufficient blending between ZnO and $\mathrm{g}\text{-}{\mathrm{C}}_3{\mathrm{N}}_4$ during synthesis. Reduced photoluminescence (PL) intensity of the $\mathrm{ZnO}/\mathrm{g}\text{-}{\mathrm{C}}_3{\mathrm{N}}_4$ reveals the synergic effect of the hybrid nanoparticles on the recombination of photoinduced electron–hole pairs. The resultant $\mathrm{ZnO}/\mathrm{g}\text{-}{\mathrm{C}}_3{\mathrm{N}}_4$ photocatalysts show higher degradation efficiency of phenol than that of pure ZnO under simulated sunlight irradiation. Especially, the $\mathrm{ZnO}/(5\mathrm{wt}\%)$ $\mathrm{g}\text{-}{\mathrm{C}}_3{\mathrm{N}}_4$ demonstrate the highest photodegradation efficiency of phenol because of the high amount of •OH radicals generated in the photocatalytic reaction. Process parameters such as photocatalyst amount, initial phenol concentration, and solution pH show a remarkable effect on the photocatalytic activity of $\mathrm{ZnO}/\mathrm{g}\text{-}{\mathrm{C}}_3{\mathrm{N}}_4$. The degradation mechanism of phenol is also detailed through identification of product intermediates and detection of reactive species. Moreover, the $\mathrm{ZnO}/\mathrm{g}\text{-}{\mathrm{C}}_3{\mathrm{N}}_4$ photocatalyst could be reused several times without appreciable loss of activity, showing great potential to be an excellent candidate for environmental remediation.

The reaeration-rate coefficient (${\mathit{K}}_2$) is an essential parameter in water quality simulation because it aids predicting the water’s ability to assimilate organic pollutants. Several methods have been used to determine ${\mathit{K}}_2$, but some of them are too expensive and others are not always accurate. A new method is presented in this paper, in which ${\mathit{K}}_2$ can be estimated using the convective heat transfer coefficient (h), which is obtained from a solid metal during cooling in a jet-agitated tank. The results show a very good correlation ($r>0.98$) between ${\mathit{K}}_2$ and h. This method is promising because of its simplicity and low cost. This new method took a short period of time to achieve its results and used simple materials. Other methods for determining reaeration-rate coefficients usually take more time and require more sophisticated materials than the proposed method.

Several studies have reported that wastewater treatment plants may facilitate the occurrence of resistant bacteria in effluents, creating a growing concern about their impact on animal and human health. For this study, 254 Enterobacteriaceae were isolated from influent wastewater, effluent wastewater, and sludge in a municipal wastewater treatment plant and from river water receiving their effluent, with a predominance of Klebsiella pneumoniae. Susceptibility tests showed that amikacine and ciprofloxacine were the most active antibiotics. High resistance rates ($>80\%$) were observed with penicillins and cephalosporins. A set of 143 strains (56.30%) were defined as extended-spectrum beta- lactamase producers. The findings revealed a decrease in the rate of extended-spectrum beta-lactamase (ESBL)–producing Enterobacteriaceae in the effluent wastewater compared to influent wastewater. In addition, nonnegligible levels of these bacteria were found in the river water (17.50%) and sludge (29.41%). This study demonstrated that the municipal sewage may be a reservoir of the dissemination of extended-spectrum beta-lactamase–producing Enterobacteriaceae into the environment, thereby contaminating natural water resources. This survey highlighted the serious negative impact of discharging urban sewage into the environment on public health and suggests that the topic requires further evaluation and appropriate control techniques.

Adsorbent dosage and initial adsorbate concentration are usually used as two factors for a batch sorption experiment to investigate the sorption characteristics of heavy metals on soils. In the present study, another factor was defined as the ratio between initial adsorbate concentration and adsorbent dosage, and its relation with the sorption characteristics of heavy metals on soils was analyzed by performing a series of batch sorption experiments and literature review. The results indicated that the sorption capacity increased with the increase in the initial adsorbate concentration to adsorbent dosage ratio, and the effects of adsorbent dosage and initial adsorbate concentration could be uniformly illustrated by the effect of the ratio. Based on the experimental results and literature analysis, an empirical equation was developed to describe the relationship between sorption capacity and initial adsorbate concentration to adsorbent dosage ratio at equilibrium. The sorption characteristics of heavy metals on soil could be directly predicted with the developed empirical equation.

In the past, forward osmosis (FO) models were developed to evaluate the effects of concentration polarization (CP), including external CP (ECP) and internal CP (ICP), on FO performance. However, these models are not clear about the reverse salt flux of FO membranes because they often assume the osmosis reflection coefficient $\sigma$ to be 1. In addition, these models need some empirical parameters that are difficult to obtain via experiments. In this study, a new set of FO models was developed, for the first time, on the basis of mass transmission coefficient (${\eta }_{\mathrm{MT}}$) and $\sigma$. These models were used to evaluate the impact of ECP and ICP on FO performance under the influence of different parameters and conditions. Data from previous studies were used to verify the models based on experimental and model-calculated ${\eta }_{\mathrm{MT}}$. Sensitivity analysis was conducted for these models to find the most sensitive parameters to ECP, ICP, ${\eta }_{\mathrm{MT}}$, and FO water flux ${\mathit{J}}_{\mathit{v}}$. Results indicate that $\sigma$ is the most relatively influential parameter to concentrative ECP or concentrative ICP, revealing the FO membrane’s reverse salt flux. The models developed can be used to analyze how ECP, ICP, and ${\eta }_{\mathrm{MT}}$ change under different FO systems and experimental conditions, including FO reactor configuration, mixing intensity, water velocity, FO membranes, and draw-solution concentration.

Applications of biosurfactant in enhanced aquifer remediation processes have been widely studied. In order to clarify the significant parameters and analyze their interactions, and thus be able to describe the processes in an efficient and robust approach, as well as evaluate the performance of biosurfactant, this research performed a parameterization study for modeling biosurfactant-enhanced aquifer remediation (BSEAR) processes based on flow cell experiments. Lab synthetized surfactant solution was deployed together with soil flushing using water to remove the diesel contaminants from the soil sample. By using the developed hybrid stochastic and design of experiment (DOE)–aided parameterization method, it was revealed that the interactions between the distribution coefficient and Henry’s constant were significant in general for modeling the removal of benzene, toluene, ethylbenzene, and xylene (BTEX). In particular, the interaction between the distribution coefficient and the first 12-h loading ratio is significant in modeling the removal of ethylbenzene. It was also found that enhanced mobility and solubility increase of contaminants were achieved after applying the surfactant solution. After parameterization, $R^2$ values showed good consistency, which indicated the effectiveness in modeling BSEAR processes.

Catchment geomorphology is one of the most important factors governing runoff and erosion. However, its complexity is difficult to describe accurately; thus, for simplicity, many studies assume hillslopes with a uniform sloping profile. The influence of this simplification on estimating the rainfall-runoff and sediment loss processes is not well understood. In an effort to improve our understanding, this study relies on laboratory experiments using a movable rainfall simulator and a 6-m-long, 3-segment soil flume to simulate the effect of static and moving storms on differently shaped hillslopes: uniform, convex, concave, convex-concave, and concave-convex profiles. Therefore, variables, such as rainfall intensity, soil and water characteristics, and storm speed, were kept constant throughout the experiments. The work confirms empirically that storm movement and hillslope shape are central factors in the soil loss and overland flow processes. The results led to the following conclusions: (1) hillslope shape affected erosion for both nonmoving and moving rainstorms; (2) downslope moving storms led to higher runoff and sediment loss peaks than upslope moving storms; and (3) convex surfaces were the most hazardous in terms of the generation of runoff and erosion.

This paper presents an investigation into the remediation of an anthracene-contaminated clay soil through experimental tests. Samples were prepared of uncontaminated and contaminated soil-cement with 20 and 30% cement. Unconfined compression tests (UCT) were conducted on the natural soil and on soil contaminated with anthracene. Similar tests were carried out on uncontaminated and contaminated soil-cement at various curing times. Leaching tests were also conducted on contaminated soil and contaminated soil-cement with 20 and 30% cement at various curing times by using high performance liquid chromatography (HPLC) apparatus. The results showed that adding cement to the contaminated soil increased the strength of the soil and that the amount of increase in strength was a function of the percentage of the cement and the curing time. The results of the leaching tests on the contaminated soil showed a major reduction in the concentration of anthracene. The results also indicated that adding cement to the anthracene-contaminated soil caused a reduction in the concentration of anthracene after the leaching tests and that the amount of the reduction increased with the increase in the curing time for a given cement content (20 or 30%). Increasing the percentage of cement is an important factor in the reduction of the concentration of anthracene.

Optimization of total nitrogen (TN) removal via the nitrite path was studied at a sequential batch reactor (SBR) from anaerobic reject water (ARW) with a content of slowly degrading organic matter of lipid structure. The study was conducted as a pilot-scale side-line treatment in a large-scale municipal and industrial wastewater treatment plant (WWTP). Operational mode was modified based on feeding pattern, sequence order, phase duration, and number to maximize TN removal and minimize lipid-related interferences. Ammonium loading rate (ALR) proceeded at $0.2–0.7\mathrm{kg}\mathrm{N}/{\mathrm{m}}^3·\mathrm{day}$ and the optimum range was determined for maximum TN removal. An insufficient ${\mathrm{HCO}}_3^{-}/\mathrm{N}$ ratio was further lowered by volatile fatty acids (VFA) production via beta-oxidation of long-chain fatty acids (LCFA) during nitritation. The organic content of ARW and VFA showed a low degradability by denitrifying bacteria and limited TN removal. Modifications in the operational mode increased ammonium and nitrite removal and reduced toxic-free VFA and nitrous acid (FNA) with increased anoxic and aerobic denitritation. Ammonium nitrogen at $180–478\mathrm{mg}\mathrm{N}/\mathrm{L}$ was reduced to approximately $20\mathrm{mg}\mathrm{N}/\mathrm{L}$ in all effluents and TN removal was achieved at 84–86%. Temperature sensitivity was higher for denitritation than nitritation.

The calcined $\mathrm{Ca}\text{-}\mathrm{Al}\text{-}({\mathrm{NO}}_3)$ layered double hydroxide (LDH) was synthesized by a coprecipitation method and was applied for the adsorptive removal of fluoride from the aqueous solution. The isotherm experiments were conducted in the various initial fluoride concentration ranges. The estimation of isotherm parameters from the various isotherm models as well as the adequacy of these models exhibited the significant variation in the different concentration ranges. A generalized isotherm model was employed based on the Langmuir and Freundlich isotherms. The proposed model segregates the adsorption from the other influencing factors. The model was applied in different concentration ranges and provides maximum adsorption capacity as 351.066, 364.868, and $365.425\mathrm{mg}/\mathrm{g}$ in the concentration ranges of 0–10, 0–100, and $0–\mathrm{1,000}\mathrm{mg}/\mathrm{L}$. However, the same was found as 8.964, $1.175\times {10}^5$, and $477\mathrm{mg}/\mathrm{g}$ from the Langmuir isotherm. The significant variation of the isotherm parameters in the different concentration ranges clearly indicates an ambiguity in this field. The proposed model overcomes the drawback associated with the estimation of the isotherm parameters and can be applied as a generalized model to demonstrate the adsorption equilibrium.

Anaerobic digestion is a generally used microbial process in wastewater treatment plants, and anaerobic digestion sludge often possesses unacceptable characteristics including high resistance to solid-liquid separation and high concentration of nutrients, such as phosphorus and nitrogen. Gamma-ray irradiation was used to improve the dewaterability of anaerobic digestion sludge, and the struvite (magnesium ammonium phosphate) precipitation method was utilized to recover increased orthophosphate (${\mathrm{PO}}_4^{3-}\text{-}\mathrm{P}$) and ammonium nitrogen (${\mathrm{NH}}_4^{+}\text{-}\mathrm{N}$) from the postirradiation liquor. An absorbed dose of 5–15 kGy would be potentially successful for dewaterability improvement, and the optimal dewaterability occurred at 10 kGy, which could reduce the water content of sludge cake from 80.08 to 73.46%. The mechanism for the enhanced dewaterability was also analyzed, and the lysis of extracelluar polymeric substances and reduction of particle surface charges were found to be the major reasons. Furthermore, the recovery rate of ${\mathrm{PO}}_4^{3-}\text{-}\mathrm{P}$ and ${\mathrm{NH}}_4^{+}\text{-}\mathrm{N}$ were 86.07 and 15.08%, respectively, under the condition of Mg/P of 1.8 (molar ratio), pH 9.6, and reaction time of 30 min.

This research assesses the performance and methane production of a novel combined system for treatment of high-strength organic wastewater. The proposed system is composed of a rotating biological contactor (RBC) process under anaerobic conditions, in conjunction with a moving-bed biofilm reactor (MBBR) as the combining aerobic process. Various operational parameters were tested to maximize the chemical oxygen demand (COD) removal performance and methane gas production from treating high-strength synthetic wastewater. The identified optimal parameters include hydraulic retention time, organic loading rate, and disk rotational speed, equal to 5 days, 7 rotations per minute (rpm), and $2\mathrm{kg}\mathrm{COD}/{\mathrm{m}}^3/\mathrm{day}$, respectively. Under these conditions, the combined system achieved high removal efficiency (98% from influent COD of $\mathrm{10,000}\mathrm{mg}/\mathrm{L}$) with the additional benefit of methane production [$116.60\mathrm{L}/\mathrm{day}$ from a 46-L anaerobic rotating biological contactor (AnRBC) reactor]. Also, analysis of kinetic models of experimental results from the AnRBC stage indicated the suitability of the Stover-Kincannon model with a prediction accuracy of 93%. The results confirmed the effectiveness of integrated AnRBC systems in achieving both high removal efficiency and methane production. Thus, this system is recommended for treating high-strength organic wastewater.

Activated sludge model calibration based on dynamic data of the biological process is a frequently used methodology. However, because dynamic measurement campaigns are expensive and time-consuming, adequate planning is needed. A poor adjustment of model parameters will be achieved if variables less sensitive to parameter perturbations are included in the calibration procedure. Therefore, a procedure based on sensitivity analysis of the Biological Nutrient Removal Model Number 1 (BNRM1), which takes into account physical, chemical, and biological processes that occur in a wastewater-treatment plant (WWTP), has been carried out in this work to select the model variables that are greatly affected by parameter perturbations. These variables should be sampled to perform the dynamic calibration of the BNRM1 model. In addition, a comprehensive study of the most influential parameters has been carried out to understand the linked effects that occur in the BNRM1 model.

The application of single-wall carbon nanotubes (SWCNTs) in aqueous solutions is limited due to their release and inability for restraint. Therefore, change in the chemical and physical properties of carbon nanotubes through modification to prevent their release seems essential. This study was an attempt to cover single-wall carbon nanotubes by magnetic nanoparticles to better the adsorption capacity and strengthen the separation of single-wall carbon nanotubes from an aqueous solution. In this research, the experimental design was applied to optimize the parameters of toluene removal by single-wall carbon nanotubes-magnetic nanoparticles (SWCNT-MN).The maximum removal of toluene (99.6%) occurs in initial concentration $100\mathrm{mg}/\mathrm{L}$, adsorbent, retention time 20 min, dose $2\mathrm{g}/\mathrm{L}$, and pH 8, which can be considered as the optimal condition for toluene removal by SWCNT-MN nanoreactors. The results, obtained in both batch and continuous column modes, indicate that the removal efficiency in column mode is less than batch mode. This worksuggested that the SWCNT-MN has a great potential for toluene removal from aqueous solutions with controlled releasing.

For many of its intended civil engineering applications, tire-derived aggregate (TDA) comes into contact with water and may leach organic and inorganic compounds. The primary objective of this study is to investigate the rate that potential water quality contaminants leach from TDA as a function of time. A laboratory and field experiment were conducted to provide insight into both controlled and field settings. The laboratory experiment suggested that benzene, methyl isobutyl ketone (MIBK), cadmium, zinc, iron, manganese, total phosphate, and total suspended solids leach from TDA and dissolved oxygen is altered by TDA. A dramatic decrease in release rate over time was observed for all constituents under all water exposure conditions. The field experiment suggested that a TDA-soil system provides removal of many constituents from urban stormwater runoff, including acetone, cadmium, chemically oxidizable organic compounds, iron, lead, manganese, MIBK, oil and grease, phosphate, and zinc. The results suggest that TDA can be used as a water-saturated fill material without risking immediate or long-term degradation of water quality for receiving water bodies.

Methane transport was evaluated using column tests for simulated interim cover profiles composed of soil only or soil over a geomembrane (GM). Tests were conducted with a co-extruded GM of ethylene-vinyl alcohol (EVOH), a linear low-density polyethylene (LLDPE) GM, a polyvinyl chloride (PVC) GM, or a polyethylene (PE) geofilm used in conjunction with one of three soils (clay, silt, or sand). Methane breakthrough from the simulated covers with LLDPE and PVC GMs (6–8 days) was approximately three times more rapid relative to the cover with the EVOH GM (22 days). Breakthrough from the simulated cover with a geofilm (2 days) was ten times more rapid relative to the cover with the EVOH GM. Methane diffusion coefficients for the co-extruded EVOH GM obtained by inversion of the column data were 190–290 times lower than diffusion coefficients for the conventional GMs and the 0.1-mm PE geofilm. Soil type had minimal influence on methane transport through the interim covers relative to GM type. Predictions made with a numerical model parameterized using diffusion coefficients obtained from the column tests indicate that methane fluxes from interim landfill covers with an EVOH GM are approximately two orders of magnitude lower than methane fluxes from an interim cover with a conventional GM and six orders magnitude of lower than with soil alone.

In a novel development on previous computational fluid dynamics studies, the work reported here used an Eulerian two-fluid model with the shear stress transport $k$–$\omega$ turbulence closure model and bubble interaction models to simulate aeration tank performance at full scale and to identify process performance issues resulting from design parameters and operating conditions. The current operating scenario was found to produce a fully developed spiral flow. Reduction of the airflow rates to the average and minimum design values led to a deterioration of the mixing conditions and formation of extended unaerated fluid regions. The influence of bubble-induced mixing on the reactor performance was further assessed via simulations of the residence time distribution of the fluid. Internal flow recirculation ensured long contact times between the phases; however, hindered axial mixing and the presence of dead zones were also identified. Finally, two optimization schemes based on modified design and operating scenarios were evaluated. The adjustment of the airflow distribution between the control zones led to improved mixing and a 20% improvement to the mass transfer coefficient. Upgrading the diffuser grid was found to be an expensive and ineffective solution, leading to worsening of the mixing conditions and yielding the lowest mass transfer coefficient compared with the other optimization schemes studied.

Two independent methods were used to assess if atmospheric deposition was a major source of nitrate nitrogen ($\mathrm{N}{\mathrm{O}}_3\text{-}\mathrm{N}$) to stormwater in two small urban watersheds located in Lincoln, NE. First, event mean concentrations (EMCs) of $\mathrm{N}{\mathrm{O}}_3\text{-}\mathrm{N}$ in stormwater during approximately 13 storms were compared with corresponding $\mathrm{N}{\mathrm{O}}_3\text{-}\mathrm{N}$ concentration in regional wet deposition. Second, $\mathrm{N}{\mathrm{O}}_3\text{-}\mathrm{N}$ contributions to stormwater were estimated using Bayesian inference based on isotopic composition (${\delta }^{15}\mathrm{N}$ and ${\delta }^{18}\mathrm{O}$ in $\mathrm{N}{\mathrm{O}}_3^{-}$). EMC values indicated that roughly half of the total N in storm runoff was from $\mathrm{N}{\mathrm{O}}_3\text{-}\mathrm{N}$. Average mass flux per hectare between the watersheds was significantly different for organic nitrogen (N) but not for inorganic N (nitrate and ammonia N), suggesting inorganic N originates from similar sources. Both methods showed that atmospheric deposition was a major source of $\mathrm{N}{\mathrm{O}}_3\text{-}\mathrm{N}$ in stormwater for smaller storms ($<32\mathrm{mm}$ in this study), when most runoff is likely to be derived from impervious cover. In larger storms, the relative contribution from atmospheric deposition was smaller, with nitrified soil and fertilizer being the largest proportional contributors.

Manufactured treatment devices (MTDs) are increasingly installed to treat pollutants from stormwater in urban areas, but few peer-reviewed studies have assessed their field-scale performance. The Filterra biofiltration unit is a box filter combining high-flow engineered media with potential for biological treatment from a planted tree. A Filterra device was monitored for its impact on hydrology and water quality of runoff from a 0.10-ha impervious watershed in Fayetteville, North Carolina, for 22 months. Undersizing of the system and clogging of the media bed likely caused 22% of runoff to bypass the system. Although peak flows were significantly reduced ($p<0.0001$) by a median 57% (likely owing to parking lot detention), postdevelopment peak flows were not consistently reduced to predevelopment flows. The Filterra provided stormwater treatment by significantly reducing event mean concentrations (EMCs) and total pollutant loadings for sediment (total suspended solids and suspended sediment concentration), nutrients (total phosphorus, total nitrogen, total ammoniacal nitrogen, and total Kjeldahl nitrogen), and zinc. Median EMC removal efficiency ranged from 35 to 97% and median loading efficiency was 39–80% for these pollutants. The device did not reduce nitrate/nitrite, total dissolved phosphorus, or copper. Nutrient concentrations of stormwater discharged from the Filterra generally met “good” water-quality thresholds established for the state of North Carolina and EMC targets established by the state of Washington for emergent MTDs. Clogging susceptibility and frequent maintenance of the Filterra unit were notable. Overall, results suggest the Filterra is an effective MTD for treating stormwater from small impervious watersheds.