Journal of Environmental Engineering

Use of microorganisms in contaminated water remediation is one of the most studied processes of recent years. The recovery of metal contaminants by converting them into high-value nanomaterials represents a scarcely explored topic with high potential economic impact. In this work, the authors determine the capacity to remove As and Cd from aqueous solutions by Antarctic bacteria previously reported as capable of biosynthesizing CdS fluorescent nanoparticles (NPs) at low temperatures. Bacterial characteristics favoring metal bioremediation, such as As and Cd resistance as well as high biofilm formation and metal removal (kinetic/sorption tests), were determined in Antarctic strains. In addition, the effect of As on the biosynthesis of CdS fluorescent NPs [quantum dots (QDs)] was evaluated. The presence of As inhibits the biosynthesis of CdS QDs by Antarctic bacteria. Arsenic inhibition does not involve the disruption of the Cd nanostructure or a decrease in ${\mathrm{H}}_2\mathrm{S}$ levels produced by cells, suggesting that As inhibits CdS biosynthesis by avoiding the interaction of ${\mathrm{Cd}}^{2+}$ with ${\mathrm{S}}^{2-}$ required to produce the nanocrystal. Obtained results have significant consequences for the development of metal bioremediation strategies aimed at removing environmental heavy metals through the generation of NPs.

A major function of clarifiers (basins or tanks) for urban drainage (stormwater or wastewater) is separation of particulate matter (PM) and PM-associated constituents. Clarifier response is often indexed to geometric parameters of surface area (SA) or length to width (L/W) ratio. Yet in urban areas, clarifier geometry is constrained by infrastructure and alternative opportunity land uses. As a result, retrofitting clarifiers with baffles is considered to improve hydraulic and PM separation response. While most studies evaluate such response based on steady flow, stormwater unit operations (UO) are subject to highly unsteady flows. This study examines baffle configuration [direction and flow tortuosity (${\mathit{L}}_e/\mathit{L}$) as an analog for L/W], flow rate, and hydrograph unsteadiness ($\mathrm{\lambda }$) on hydraulic response through the Morrill index (MI), volumetric efficiency (VE), and N-tanks-in-series (N) metrics. Results are generated from physical and computational fluid dynamics (CFD) models for clarifier designs with and without baffles. For clarifiers without baffles, but of differing cross-sectional geometries, VE and N increased while MI decreased with increasing flow rate. Clarifiers with baffles produced an asymptotic relationship between N and the Péclet number (P). The MI and N trends were a function of $\mathrm{\lambda }$ and ${\mathit{L}}_e/\mathit{L}$. For a fixed SA, a higher baffle number (higher ${\mathit{L}}_e/\mathit{L}$) generated greater PM separation. Although there is not a singular hydraulic response for clarifiers as a function of $\mathrm{\lambda }$; increasing ${\mathit{L}}_e/\mathit{L}$ does confer a more consistent, reproducible response.

Accurate predictions of time of travel and concentration of the plume are critical for decision makers to respond to a spill. A quick response to an incident requires availability of data in a timely manner and a methodology for analysis. Data available during a spill event consist of flow and concentration of contaminants. Flow is an important component in spill response modeling because velocity, depth, width, and dispersion are calculated from this parameter. Parameters required for flow analysis may not be readily available along the downstream path of the plume. Contamination data are collected as the event unfolds; therefore, the number of samples at each monitoring location varies. Lack or unavailability of flow parameters or a small number of contaminant samples available from the spill site do not give confidence to the incident responders or decision makers about the usefulness of the results. This paper demonstrates an alternate approach, which addresses the availability, usefulness, and efficiency of data from national and transboundary databases for use in a spill model for simulating downstream transport.

Sulfamethoxazole is an emergent contaminant in waters. It is an antibiotic for humans and animals that is difficult to biodegrade in drinking water and sewage treatment plants. As the most frequent sulfonamide, its treatment and removal is difficult. In its anionic form, it can be retained by ion exchange, although competition with other ions, especially salts present in natural and treated water, needs to be taken into consideration because of competition between the anions for the active sites of the resin. This work investigated the removal of sulfamethoxazole (SMX) from low saline waters. An anionic ion exchange resin, Lewatit MP500, was used to remove SMX in synthetic solutions in the presence of chloride, sulfate, and nitrate salts. Multicomponent system solutions containing a fixed concentration of salts and different concentrations of SMX were tested in batch experiments. The presence of ${\mathrm{Cl}}^{-}$, ${\mathrm{SO}}_4^{2-}$, and ${\mathrm{NO}}_3^{-}$ suppressed the adsorption of SMX, especially the presence of ${\mathrm{SO}}_4^{2-}$, which showed the highest adsorption capacity onto the resin. Adsorption equilibrium constants were determined using the Langmuir isotherm and the extended Langmuir isotherm for multicomponent systems. The maximum adsorption capacity for the SMX and salts system was $105\mathrm{mg}/\mathrm{mL}$ wet resin and the equilibrium constants $1.4\mathrm{L}/\mathrm{g}$ SMX, $6\mathrm{L}/\mathrm{g}{\mathrm{NO}}_3^{-}$, $9\mathrm{L}/\mathrm{g}{\mathrm{SO}}_4^{2-}$. Kinetics was analyzed using the pore diffusion model, getting a diffusivity value of $1.3\times 10{\mathrm{cm}}^2/\mathrm{s}$ for SMX. Finally, two operational load and elution cycles were carried out in a fixed-bed column using mixture synthetic solutions of SMX and salts to obtain the corresponding breakthrough curves. Results show that the resin is able to retain SMX despite the high competition of the other anions and can be regenerated completely after each cycle.

Because of the relation between water quality and sediment quantity, the quantification of sediments in rivers and open channels is of utmost importance. This paper applies the theory of entropy to determine sediment concentration. A major limitation in applying the theory of entropy is the large number of parameters used in the model. To solve the equations, several parameters must be modeled. To reduce empiricism, it is important to know the behavior of the model parameters regarding the factors that could influence sediment concentration. Therefore this paper finds the existing relation of the parameter Ƨ with the granulometry and flow depth. Functions are presented according to the particle diameter. The results are satisfactory for different particle sizes and concentrations. This paper obtains smaller errors than other works. This technique is promising because it allows sample reduction to determine sediment concentration and can be performed in different flow conditions.

Most recent researches have focused on acrylamide (AM) biodegradation with the pure culture of various microorganisms including Enterobacter aerogenes. In this study, the acrylamide biodegradations from synthetic wastewater containing different acrylamide concentrations by mixed-culture bacteria, E. aerogenes, and a mixture of both bacteria in a sequencing batch reactor (SBR) wastewater-treatment systems controlled at the solid retention time (SRT) of 10 days were comparatively evaluated under aerobic conditions. The results revealed that both bacteria could immediately remove acrylamide in the SBR systems, but E. aerogenes did not biodegrade acrylamide as efficiently as reported in culture media. The growth rate of E. aerogenes was limited at 10 days SRT, resulting in low biomass production and intracellular polyphosphate accumulation, thereby reducing heterotrophic nitrification. However, it was found that E. aerogenes removed acrylamide at higher rate than mixed-culture bacteria in the SBR system. In this study, it is reported that free ammonia nitrogen (FAN), as one product from acrylamide biodegradation, inhibited amidase activities, resulting in lower acrylamide removal efficiencies in the SBR systems after a long-term operation. FAN also inhibited autotrophic nitrification in the SBR system containing mixed-culture bacteria, resulting in FAN accumulation. A mixture of both bacteria enhanced acrylamide biodegradation because simultaneous autotrophic nitrification and heterotrophic nitrification minimized the FAN accumulation.

Efficient removal of nanoparticles (NPs) is particularly important in view of the increasing long-term persistence and evidence of considerable ecotoxicity of some nanoparticles. The aim of this study was to understand the effects of flowrate (0.5, 1, and $1.5\mathrm{mL}/\min$), concentration (1, 10, and $100\mathrm{mg}/\mathrm{L}$), and the type of nanoparticles (ZnO, CuO, and $\mathrm{ZnO}+\mathrm{CuO}$) on the removal of the nanoparticles in an activated carbon column. Flowrate, concentration of NPs, and type of NPs were found to influence the removal at room temperature. Complete removals of both ZnONPs and CuONPs in both single and binary suspensions from water were achieved. Breakthrough was achieved after treating 3 L of water for nearly 50 h for concentrations of 1 and $10\mathrm{mg}/\mathrm{L}$ of ZnONPs and CuONPs. The breakthrough was reached faster for Cu (49.5 h) than Zn (53 h). More work is required to understand the effect of water quality on the removal, to develop methods for quantifying the concentration of nanoparticles after any kind of nanoparticle-water interaction, and to understand the fate and removal mechanism of NPs in the column.

The present study reports the effect of magnetic multiwalled carbon nanotubes (MMWCNTs) as an adsorbent for removing total dissolved solids (TDS) from water. MMWCNTs and multiwalled carbon nanotubes (MWCNTs) were characterized by X-ray diffraction (XRD), Fourier transform infrared (FTIR), X-ray photoelectron spectroscopy (XPS), vibrating sample magnetometer (VSM), and transmission electron microscopy (TEM). The results indicate that $\mathrm{MWCNTs}/{\mathrm{Fe}}_3{\mathrm{O}}_4$ nanocomposites were well synthesized. The MMWCNTs can be easily blended in water and separated by a magnetic field. For the purpose of the study, experimental design in conjunction with central composite design was used to examine the impact of adsorbent dosage per initial concentration of total dissolved solids (D/TDS) [$(\mathrm{mg}{)}_{\mathrm{adsorbent}})/(\mathrm{mg}/\mathrm{L}{)}_{\mathrm{initial}}$] and initial pH on percentage of TDS removal. The following optimum results for the maximum elimination TDS from an aqueous solution were obtained: $\mathrm{D}/\mathrm{TDS}=20\mathrm{mg}/(\mathrm{mg}/\mathrm{L})$ and initial $\mathrm{pH}=3.00$. Under optimal amount of process parameters, maximum removal (96%) was achieved. The Langmuir, Freundlich, Temkin, Sips, and Dubinin–Radushkevich (D-R) adsorption models were used to analyze the experimental data, and the Sips isotherm model was found to be better than other isotherm models for a high concentration of TDS {$625–\mathrm{1,000}\mathrm{mg}/\mathrm{L}$ [parts per million (ppm)]}. The findings suggest that the MMWCNT can undoubtedly be considered an successful adsorbent and new solution to reduce TDS in watery solutions.

Arsenic(V) removal using activated alumina (AA) was carried out in batch mode and was modeled using response surface method. The Doehlert design of experiment (DOE) was used to model the experimental data, and the Doehlert design matrix was used to have uniformly distributed experimental points. The effect of contact time, adsorbent dose, pH level, and initial arsenic(V) concentration was studied. The statistical model developed for arsenic(V) removal suggested that maximum removal took place at a pH value of 6.26. There was strong interaction between pH and arsenic(V) removal. Within the range of the factors studied (pH level 2–12; dose of AA 1–5 g; contact time 1–6 h; and arsenate conc. $0.1–0.5\mathrm{mg}/\mathrm{L}$), the optimum condition for arsenic(V) removal obtained using the model was at $\mathrm{pH}=6.26$, dose of $\mathrm{AA}=3.29\mathrm{g}$, shaking $\mathrm{time}=3.16\mathrm{h}$, and arsenic(V) $\mathrm{conc.}=0.213\mathrm{mg}/\mathrm{L}$. The maximum removal obtained at optimum condition was found to be 93.06%. The model predicts arsenic(V) removal condition with reasonably low error and high coefficient of determination ($R^2=0.9835$). The model validation result suggested very low error (2.20%) in predicting targeted removal. The model developed can effectively predict adsorption and can be used for designing contact system for arsenic(V) removal from contaminated water.

Biotreatment of heavy metals in acid mine drainage (AMD) with sulfate-reducing bacteria (SRB) is considered the most promising technique in the ecological restoration of mines. In the present work, the authors evaluated the ability of bioprocessing acidic water ($\mathrm{pH}=6.0$) containing different concentrations of ${\mathrm{Mn}}^{2+}$ (ranging from 1.0 to $\sim 102.28\mathrm{mg}/\mathrm{L}$) and ${\mathrm{Pb}}^{2+}$ (ranging from 1.0 to $\sim 11.6\mathrm{mg}/\mathrm{L}$) and coexisting with sulfate ($0.8–1.1\mathrm{g}/\mathrm{L}$) with a native SRB Desulfuromonas alkenivorans S-7 obtained from a coal gangue dump. Furthermore, the organic functional groups and sulfur components involved in the bioprocess mediated with SRB were investigated with Fourier transform infrared spectroscopy (FT-IR) and detailed in a Peakfit analysis. The results showed that the S-7 strain could remove 93.1% ${\mathrm{Mn}}^{2+}$ and 90.0% ${\mathrm{Pb}}^{2+}$ from acid mine drainage after 7 days’ culture, respectively. Three clear stages of biotreatment of ${\mathrm{Mn}}^{2+}$ and ${\mathrm{Pb}}^{2+}$ were identified as initial rapid precipitation, subsequent absorption, and a final equilibrium state. The removal of heavy metals included chemical precipitation and biosorption. FT-IR spectroscopy results showed that the OH, ${\mathrm{NH}}_2$, $\mathrm{C}═\mathrm{O}$, and amide group might play an important role in the absorption of ${\mathrm{Mn}}^{2+}$ and ${\mathrm{Pb}}^{2+}$ by extracellular polymeric substances. Furthermore, the intermediate sulfite products of the sulfate-reducing process were also identified in the cell samples. The present study proves that biotreatment of heavy metals with a native SRB S-7 is possible, and thus provides potential information for its future application in the ecological restoration of coal gangue dumps.

In this work, the complexation of the hazardous $\beta$-lactamic antibiotic amoxicillin (AMX) with ${\mathrm{Fe}}^{3+}$ ions during coagulation was investigated. New bands in the ultraviolet-visible (UV-vis) spectra suggested that AMX molecules bind to ${\mathrm{Fe}}_{\mathrm{aq}}^{3+}$ and also displace ligands from a stable Fe thiocyanate complex. Electrospray ionization mass spectrometry (ESI-MS) showed strong signals at $m/z=784$ and 816, corresponding to the ${[\mathrm{Fe}+(2\mathrm{AMX}-2\mathrm{H})]}^{+}$ and ${[\mathrm{Fe}+(2\mathrm{AMX}-2\mathrm{H})+{\mathrm{CH}}_3\mathrm{OH}]}^{+}$ species, respectively, also indicating the complexation of ${\mathrm{Fe}}^{3+}$ with AMX molecules. Density functional theory (DFT) calculations showed that among the different coordination modes of AMX to ${\mathrm{Fe}}^{3+}$, complexation via the carboxylate group is more stable and less sterically hindered. These results suggest that during coagulation, the ${\mathrm{Fe}}^{3+}$-AMX complexation-form stable intermediates are probably bound/trapped in the iron hydroxide precipitate. As a result of this process, significant amounts of AMX (approximately 69%) can be removed from aqueous solution. Experiments with heavily contaminated pharmaceutical industrial wastewaters showed very promising results with a strong decrease in AMX, TOC, and acute toxicity.

An experimental study was performed by using the world standard treated drinking water of the city of Ankara. Chlorine is known to be consumed in the bulk liquid phase and at the pipe wall. In the present study the bulk decay pattern was investigated in the absence of pipe wall decay. The test results presented describe how chlorine bulk decay might change with the travel time (residence time) of water in a pipe and the temperature of water in the network. Other than the single constant bulk decay coefficient of chlorine for the first-order exponential decay equation frequently used in many previous studies and models, a parameter coupling residence time of water might be more representative for the water of a city supply network. The test data also showed that chlorine decay of stagnant water in bottles does not differ in magnitude from that of flowing water in a pipe. Additionally, the test results reveal no correlation between initial chlorine concentration level and the bulk decay pattern.

The applicability of microwave-assisted ball milling for the treatment of p-nitrophenol (PNP) was investigated in this study. The degradation process of PNP was studied by using UV-vis (ultraviolet-visible) spectra, total organic carbon (TOC), fluorescence intensities, electroconductivity, and X-ray diffraction (XRD). PNP was degraded 99.1% after microwave-assisted ball milling for only 15 min at pH 3 when the initial concentration of PNP was $300\mathrm{mg}/\mathrm{L}$. When the pH value of solution was 3, PNP can be mineralized completely in 12 min by microwave-assisted ball milling and adding hydrogen peroxide. The new high-activity nanoscale zero-valent iron (NZVI) was produced constantly in the process of stirring, collision, and spalling, preventing nanoparticles from reuniting. Further, the hydroxyl radical generated in the coupling effect of microwave and mechanical force also improved the reaction rate.

In this paper, a $\mathrm{nano}\text{-}{\mathrm{Fe}}^0/\text{polyethyleneimine}$ (PEI) composite was synthesized via $\mathrm{nano}\text{-}{\mathrm{Fe}}^0$ and PEI cross-linked by glutaraldehyde. The removal rate of Cr(VI) by $\mathrm{nano}\text{-}{\mathrm{Fe}}^0/\mathrm{PEI}$ composite was investigated and compared with that of Pb(II) and Ni(II). The effects of reacting time, dosage, initial concentration, pH value, and coexisting heavy metal on removal rates of Cr(VI), Pb(II), and Ni(II) are discussed. The characteristics of $\mathrm{nano}\text{-}{\mathrm{Fe}}^0/\mathrm{PEI}$ composite and its removal mechanism for Cr(VI) were analyzed by scanning electron microscope (SEM), Fourier transform infrared (FTIR) spectroscopy, and X-ray diffraction (XRD). The results show that the removal rate of Cr(VI) (92.6%) by $\mathrm{nano}\text{-}{\mathrm{Fe}}^0/\mathrm{PEI}$ composite is obviously higher than that of Pb(II) (60.2%) and Ni(II) (23.8%). $\mathrm{nano}\text{-}{\mathrm{Fe}}^0/\mathrm{PEI}$ composite is effective for Cr(VI) removal. The heavy-metal ions coexisting in the mixture solution have a remarkable effect on the removal of Cr(VI). The paper concludes that Cr(VI) was reduced into Cr(III) by $\mathrm{nano}\text{-}{\mathrm{Fe}}^0$ before chelating with PEI.

This study investigates the effect of multiwalled carbon nanotubes (MWCNTs) on the performance of polyethersulfone membranes in cerium ion removal from aqueous solution. Neat polyethersulfone (PES) membrane and mixed-matrix membranes (MMMs) containing MWCNTs are fabricated by the wet phase inversion technique. The MWCNTs are functionalized by (3-aminopropyl)-trimethoxysilane (APTMS) to improve their adhesion to the polymeric matrix. The MWCNTs (before and after functionalization) are analyzed using Fourier-transform infrared spectroscopy (FTIR), Raman spectroscopy, and thermogravimetric analysis (TGA). Morphological properties of the fabricated membranes are evaluated by scanning electron microscopy (SEM) and field emission scanning electron microscopy (FESEM) methods. Fabricated membranes are subjected to further experiments in order to evaluate cerium ion removal efficiency. Permeation test results show that permeate flux and cerium (Ce) ion rejection increase as MWCNT content increases in the polymer matrix. The results also show that permeate flux and cerium ion rejection increase as operating pressure and feed flow rate increase while inversely decreased by increasing the cerium ion concentration in the feed solution. Application of ethylenediaminetetraacetic acid disodium (EDTA) drastically increases cerium ion rejection.

An analytical model for degradable organic contaminant transport in a triple liner consisting of a geomembrane (GMB), a geosynthetic clay liner (GCL), and an attenuation layer (AL) was developed. Both advective transport through the defects of the GMB and diffusive transport in intact GMB are considered. The dimensionless analytical solution for semi-infinite bottom boundary condition was obtained by using the Laplace transformation. The method of separation of variables was used for the case with the fixed concentration bottom boundary condition. For the semi-infinite bottom boundary condition, with Damkohler number $Q=1$, the dimensionless concentration $C_N$ and the dimensionless flux $F_N$ increase by factors of 3.4 and 4.4, respectively, as the Peclet number of AL $P_1$ increases from 0 to 1. It is indicated that advection through the defects of the GMB is more important than diffusion in the intact part of the GMB in the cases with $P_1\ge 0.26$ when $Q=1$. Biodegradation plays a major role in organic contaminant transport in the triple liner with $P_1\le 1$ and $Q\ge 1$. As the length of the wrinkle $L_w$ decreases from 1,000 to 100 m, the base flux decreases by factors of 49.6 and 11.1 for semi-infinite and fixed concentration bottom boundary conditions, respectively. The base flux decreases by a factor of 8.6 for the fixed concentration bottom boundary condition as the half-life of toluene decreases from 100 to 1 year. The hydraulic conductivity of GCL and the leachate head have a more important effect on the performance of the triple liner than the interface transmissivity and the permeability of AL based on the statistical analysis. The 20-year base flux for the scenario with length of $\text{wrinkle}=100\mathrm{m}$ is the lowest. It is approximately 2.3 times less than the scenario with hydraulic conductivity of $\mathrm{GCL}=5\times {10}^{-12}\mathrm{m}/\mathrm{s}$ for the case with fixed concentration bottom boundary, indicating the length of wrinkle has a more important influence on performance of the triple liner than the other involved parameters. The proposed analytical models can be used for evaluating experimental data, verifying complicated numerical models, and preliminary design of triple liners.

The development of nanotechnology has provided a range of diverse nanoscale carriers that can be potentially applied for enzyme immobilization. Among the different types of support, magnetic nanoparticles (mNPs) have received increasing attention because they can be easily recovered from the reaction medium by applying an external magnetic field. In the present study, silica-coated magnetic nanoparticles (${\mathrm{Fe}}_3{\mathrm{O}}_4@\mathrm{Si}{\mathrm{O}}_2$) were prepared, characterized, and used for covalent immobilization of laccase from Trametes versicolor. Different concentrations of the functionalization agent (3-aminopropyltriethoxysilane), cross-linker (glutaraldehyde), and laccase allowed a maximum enzyme loading of $2.68\pm 0.08\mathrm{U}{\mathrm{mg}}^{-1}$ mNP. Several factors, including pH, T, presence of inactivating compounds, enzyme stability, and reusability of the support, were evaluated. The oxidative action of the enzyme toward xenobiotics was proven in the formation of the chromogenic radical of 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) and the biotransformation of the endocrine-disrupting compound Bisphenol A (BPA). The enhancement of catalytic activity and stability of the nanobiocatalyst was evidenced by the increase of ABTS oxidation. Moreover, the superparamagnetic characteristic of the support allowed simple and fast recovery of the nanobiocatalyst. With the development of nanobiocatalyst-driven applications in mind, the development of magnetic nanoparticle synthesis at large scale as well as the design of bioreactors that assure the retention and recovery of the nanobiocatalyst need to addressed.

Modeling air movement in sewer systems is important because of its importance in addressing sewer odor issues and pipe corrosion. In this study, a steady-state model was developed for simulating the air pressure and movement in a prototype sewer pipe network with dropshafts and a pump station. It was found that the model was able to simulate the air pressure distribution along the trunk line with reasonable assumptions and simplifications. The lateral leakage model presented in this study suggested that the air leakage at lateral connections is a function of lateral pipe properties and the number of pipes. Increasing the pipe number has limited influence on the leakage air flow. The air pressure force, wastewater drag, and the friction force by pipe wall are dominant factors affecting the air flow in sewer pipes. The operation of the pump station affects the air pressure in the system significantly as a result of the alternate partially full and full-pipe flow condition near the pump station. The dropshafts were regarded as the key contribution for downstream pressurization of the sewer headspace.

This study involves high-rate thermophilic anaerobic digestion of sewage sludge at 10 days hydraulic retention time by using thermal pretreatment (170°C and 1 h) of the waste-activated sludge portion in influent sludge and trace metal supplementation (0.49 mg Ni and 0.54 mg Co per liter of influent). The thermal pretreatment not only increased destruction of volatile solids (VS) and volatile suspended solids (VSS) by 6 and 9%, respectively, but also much improved dewaterability of the digested sludge. The trace metal supplementation showed limited effect on the overall performance, except for reduced volatile fatty acid concentrations in the digested sludge. The diffusive gradients in thin-films (DGT) technique was applied to estimate bioavailability of the trace metals in digested sludge filtrates. The DGT analysis suggests that 70–88% ($96–113\mathrm{\mu g}/\mathrm{L}$) of soluble Ni and only 5–10% ($0.9–2.1\mathrm{\mu g}/\mathrm{L}$) of soluble Co were present in a bioavailable form.

This study analyzed the intra-annual patterns of nutrient and sediment exports from eight watersheds in the Lake Erie and Ohio River basins over long-term monitoring durations (8–32 years). These primarily agricultural watersheds are the major source of pollutants delivered to Lake Erie, and through the Mississippi River system to the Gulf of Mexico. Suspended sediment (SS), total phosphorus (TP), and total oxidized nitrogen (TON) (${\mathrm{NO}}_3-\mathrm{N}+{\mathrm{NO}}_2-\mathrm{N}$) levels were analyzed using weighted circular statistics in two phases based on (1) the entire observed daily data sets; and (2) the largest events. The data analysis evaluated the timing of river flows, pollutant concentrations, and corresponding loads in 1 year for each watershed. The results showed that pollutant concentrations could occur in any season, and their corresponding loads were concentrated during high-flow periods in winter and early spring, even though the largest rain events occurred in late spring and early summer. Circular statistical analyses of data and large-event examinations indicated that SS loads were more evenly distributed over the year compared with the TP and TON loads. The results indicated that a temporal difference exists between the peak riverine pollutant export and the poorest water quality conditions in the receiving water bodies. This difference underscores the need for better management through coordinated monitoring and regulatory efforts during periods of high load export. The weighted circular analysis method provided a clearer visualization and analysis tool through finer time scales than the traditional monthly analysis of nutrient and sediment data.

Understanding hydrogen sulfide (${\mathrm{H}}_2\mathrm{S}$) emission into sewer air space and the rate of ventilation to the atmosphere is important in preventing/mitigating odor and corrosion problems in sewer systems. This study presents the results of a field monitoring program on the air pressure and ${\mathrm{H}}_2\mathrm{S}$ levels in a 3-km-long sanitary sewer system in Edmonton, Alberta, Canada, which has drop structures in the upstream section and a pump station in the downstream section. Nineteen manholes were monitored, including six drop structures. A positive correlation was found between the sewage flow rate and the observed diurnal patterns of air pressure and ${\mathrm{H}}_2\mathrm{S}$ concentration. Drop structures were found to have caused significant pressurization in the downstream sewer air space. More than 1 km of the trunk sewer upstream of the pump station was submerged due to the pump station operation. This reduces flow velocity, increases sewage retention time, and potentially enhances the generation of ${\mathrm{H}}_2\mathrm{S}$. A unique pressure pattern was found at several locations upstream of the pump station, which was closely related to the sewage level variation in the wet-well as a result of pump operations. The results reveal the ventilation condition in the study sewer system and will be useful for developing sewer odor mitigation measures.

A large-scale comprehensive survey of indicator bacteria, pathogen viruses, coliphages, microbial source tracking (MST) indicators, and antibiotic resistance genes was carried out in the Shafdan soil aquifer treatment (SAT) of the Tel Aviv, Israel area. The study reveals complete elimination of pathogen viruses—enterovirus, adenovirus, norovirus, parechovirus, and coliphage—and of the bacterial indicators total and fecal coliforms, fecal streptococcus, and microbial source tracking (MST) Bacteroides already in the vadose zone below the percolation basins. Trace levels of antibiotic resistance genes (ARGs) were detected in the recovery wells, but these were also detected in wells not impacted by effluent, suggesting that these genes are associated with native aquifer bacterial communities. This is the first comprehensive survey describing four types of microbial indicators—bacteria, pathogenic viruses, coliphages, and MST—for SAT research, and the first to address the occurrence of antibiotic resistance genes in SAT systems. The results should provide guidance to regulatory agencies regarding the attainable efficiency of optimally designed and operated SAT systems and the monitoring point locations. Most of the pathogen removal occurs in the vadose zone underneath the basins, which can be monitored more rapidly than the water quality in the recovery wells.

This investigation evaluated five hypothetical scenarios relating nitrate sources in the recharge of the Volusia Blue Spring to eutrophication in the St. Johns River. In the Volusia Blue recharge area of Florida, decades of nitrate loadings have impacted the quality of springwater discharged from the confined Floridan aquifer. Simulators and field observations were used to develop and define a procedure for the first time by which local and Florida state agencies can better manage nitrate pollution. The simulations were based on population growth projections and nitrogen loads from treated wastewater discharges, septic tanks, and fertilized areas. A one-tailed t-test comparing observed with simulated nitrate values in spring discharge indicates that there is insufficient evidence of discrepancies between observed and simulated results. Results from the simulation of five nitrate management scenarios were used to estimate probable construction costs that were compared with $\mathrm{mg}{\mathrm{L}}^{-1}$ of nitrate removed. Constructed wetlands and targeted septic tank removal were the two most cost-effective nitrate management approaches. However, septic tank removal resulted in the greatest benefit with a 36% nitrate decrease in a 39-year projection of springwater quality.

Most pulp and paper mills use aerobic biological treatment for their effluents. Aeration is the single most energy intensive process of a treatment plant. Surfactants, commonly occurring in pulping wastewaters, have been shown to decrease the oxygen transfer rate. The aim of this study was to decrease the surface activity of surfactants and thereby increase the oxygen transfer rate in pulp mill effluents by the use of chemical pretreatment in very low doses. Trials using $5\mathrm{g}/{\mathrm{m}}^3$ ferric iron showed statistically significant improvement on both $k_L{a}_{@20}$ and surface tension. No sludge was precipitated owing to the very low ferric iron dosage. The novel use of chemical pretreatment, in very low doses, aiming specifically at improving oxygen transfer rate, is a promising concept for reducing the need for aeration in wastewater treatment and thus lower the electricity requirement of the wastewater treatment plant.