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Soil colloids play critical roles during the fate and transport of micropollutants (e.g., pesticides and hormones) due to their high sorption affinity and mobility. In this study, the authors developed a centrifugation and mass balance-based methodology for studying sorption of testosterone to soil colloids of different size fractions (DSFs). The method should allow one to conduct the sorption tests with the whole soil first and then separate soil colloids of DSFs to evaluate their contributions to sorption. Results indicate the colloids diameter ranges (i.e., 900-600, 600-400, and 400-200 nm) can be controlled by a group of series centrifuge conditions (i.e., speed and time). The sorption affinity of soil colloids for testosterone is three times higher than that of the bulk soil and increases significantly with decreasing diameter size because of the difference of specific surface area and organic carbon content. The authors propose that the centrifuge condition of 2,844 relative centrifugal force ðRCFÞ þ 30 min is required to separate the dissolved (dnano < 200 nm) and particle-associate phases to ensure the error of sorption results less than 2%. One may use the methodology to develop a framework to study the sorption of micropollutants on soil colloids of DSFs with whole soils or sediments as testing material media. [ABSTRACT FROM AUTHOR]

Nitrate reduction by Fe(II) species was previously known to occur only in Cu2+-catalyzed and alkaline conditions or at high temperatures. In this study, a reactant system consisting of nitrate, iron oxide particles, and Fe(II) (in different forms) was used to study possible reactions between nitrate and Fe(II). At near-neutral pH, nitrate could not be reduced by aqueous Fe(II) species or by FedOHT2 gel. In the presence of magnetite (Fe3O4) particles, however, a significant amount of Fe2+ could be adsorbed onto an Fe3O4 surface at pH = 7.3 and became surface-bound Fe2+(S:B: Fe2+), which could react with nitrate via the reaction: 12 S:B: Fe2+ + NO.3- 13H2O ×4 Fe3O4 +NH4+ t 22H+. The reaction stopped when pH decreased to <6.8. Introducing trace amount of O2 or Fe3tdaqT into the nitrate- Fe2t reactant system was as effective as seeding magnetite particles in triggering the nitrate-Fe(II) reaction, suggesting that lepidocrocite (ƒÁ-FeOOH) is a precursor for initiating the nitrate-Fe(II) reaction. Hematite and Kaolinite particles could also serve as the reactive sites for the nitrate-Fe(II) reaction upon surface transformation by S:B: Fe2t. The observed abiotic nitrate reduction by Fe(II) could be an important link between the nitrogen cycling and the Fe(II)/Fe(III) redox couple in the biosphere or geosphere. [ABSTRACT FROM AUTHOR]

In this study, batch sorption and desorption experiments were conducted for testosterone using four agricultural soils and five clay minerals. Significant differences in sorption behavior were observed between abiotic and biotic systems. The Freundlich sorption coefficient Kf (μg)/(#956;g/mL)n ranged from 8.53 to 74.46 for soils and from 35.28 to 1,243 for clays. The maximum sorption capacity (μg/g) of soils ranged from 25.25 to 440.61 for soils and from 168.46 to 499.84 for clays. Correlation of the sorption model parameters with the soil properties indicated that both clay content and soil organic matter are important variables in predicting testosterone sorption behavior. Observed testosterone desorption from agricultural soils ranged from approximately 14 to 100% after three desorption cycles, and the desorption percentage decreased as the initial testosterone concentration decreased. It was determined that the temperature, ionic strength, water/soil ratio, and soil depth influenced the sorption and desorption of testosterone. Desorption significantly increased with the soil depth (p < 0.05) and with the increase in the water/soil ratio. Temperature had an inverse effect on the sorption capacity of the soils tested. Thermodynamic calculations showed that the enthalpy change (ΔH0) of the soils tested ranged from 12.9 to 20.7 kJ/mol, indicating a weak interaction between the testosterone and soil. The authors' results suggest that additional studies on how soil particles with different size fractions affect hormones' fate and transport are needed to determine the potential risk of testosterone leaching or runoff. [ABSTRACT FROM AUTHOR]

This paper reports a new approach to understanding membrane fouling in membrane bioreactors (MBR). The foulants were categorized into those inside the membrane (internal fouling) and those on the membrane forming the so-called external fouling layer (external fouling). The volumes of the internal and external foulants were determined with the aid of a confocal laser scanning microscope (CLSM) after staining the foulants. Thus, the porosities of both the membrane and the external fouling layer were calculated, which explained the contributions of internal and external fouling to transmembrane pressure (TMP) from the standpoint of fundamental filtration theory. The categorical method indicates that external fouling may dominate the long-term operation of MBR with the formation of the external fouling layer, whereas internal fouling, in the form of pore constriction, may cause both initial and final TMP jumps under the operating conditions in the current study. In addition, a mathematical model was developed to dynamically link TMP with the basic filtration parameters (e.g., porosities of the membrane and external fouling layer, thickness of the external fouling layer, pore size inside the membrane, and size of the particles forming the external fouling layer). The model quantitatively describes the contributions of both internal and external fouling and further supports the experimental results. [ABSTRACT FROM AUTHOR]

Biofilm density, porosity, and thickness are biofilm architecture properties that are important but often difficult to measure. In this study, wet and dry biofilm densities and biofilm porosity in shredded tire biofilters were measured using a volumetric displacement method and a new porosity equation. Methods for determining the surface area and mean thickness of biofilms attached to shredded tires were developed on the basis of the box- and ellipsoid-shape models with the data of (1) the volume calculated from the measured weight of the filter medium () or (2) the three longest lines of the filter medium measured with a digital caliper. As a benchmark, the surface area of the shredded tire particles were calculated from X-ray computed tomography (CT) scanning and compared to, and linearly correlated with, the results from the models. The ellipsoid-shape model with the modified length-width-depth data and was determined to be the best model to compute the surface area and biofilm thickness. The method of biofilm thickness measurement may be applicable in attached growth systems packed with other irregular-shaped media. [ABSTRACT FROM AUTHOR]

Sulfur–limestone autotrophic denitrification (SLAD) processes are very efficient for treatment of ground or surface water contaminated with nitrate. However, detailed information is not available on the interaction among some major variables on the design and performance of the SLAD process. In this study, the response surface method was used by designing a rotatable central composite test scheme with 12 SLAD column tests. A polynomial linear regression model was set up to quantitatively describe the relationship of the effluent and influent nitrate–nitrogen concentration and hydraulic retention time (HRT) in the SLAD column reactors. This model may be used for estimating the effluent nitrate–nitrogen concentration when the influent nitrate–nitrogen concentration ranges between 20 and 110 mg/L and the HRT ranges between 2 and 9 h. Based on our model and the requirement for nitrite control, we recommend that the HRT of the SLAD column reactor be kept >=6 h and the nitrate loading rate less than 200 g NO3-–N/day m3 media to achieve high nitrate removal efficiency (>99%) and prevent nitrite accumulation from being >1 mg/L NO2-–N. [ABSTRACT FROM AUTHOR]

Nitrate reduction in an iron/nitrate/water system with or without an organic buffer was investigated using multiple batch reactors under strict anoxic conditions. Nitrate reduction was very limited (<10%) at near-neutral pH in the absence of the organic buffer. However, nitrate reduction was greatly enhanced if the system: (1) had a low initial pH (∼2–3); (2) was primed with adequate aqueous Fe2+; or (3) was in the presence of the organic buffer. In Cases (1) and (3), nitrate reduction usually was involved in three stages. The first stage was quick, and H+ ions directly participated in the corrosion of iron grains. The second stage was very slow due to the formation of amorphous oxides on the surface of iron grains, while the third stage was characterized by a rapid nitrate reduction concurrent with the disappearance of aqueous Fe2+. Results indicate that reduction of nitrate by Fe0 will form magnetite; Fe2+ (aq.) can accelerate reduction of nitrate and will be substoichiometrically consumed. Once nitrate is exhausted in the system, no more Fe2+ will be consumed. In the presence of nitrate, Fe2+ (aq) will be adsorbed onto the surface of iron grains or iron oxides; the surface-complexed Fe(II) (extracted by acetate with pH=4.1) might be oxidized and become structural Fe(III), resulting in a steadily increasing ratio of Fe(III)/Fe(II) in the oxides formed. The transformation of nonstoichiometric amorphous iron oxides into crystalline magnetite, a nonpassive oxide, triggers the rapid nitrate removal thereafter. [ABSTRACT FROM AUTHOR]

A conventional tracer study using Li+ and Cl- was conducted on four Fe0-packed column reactors for nitrate removal. Both Li+ and Cl- showed strong adsorption onto iron media and thus were not ideal tracers for the study. Tests using an impulse loading of nitrate were then innovated to investigate the transport and reduction of nitrate in the reactors. The impulse loading was superposed on a continuous constant feeding of nitrate which generated a steady effluent baseline. A multivariable model incorporating hydraulic dispersion, adsorption/desorption, and reduction of nitrate was developed and numerically solved. Both Langmuir adsorption and linear adsorption isotherms were separately applied to describe nitrate adsorption on the reactive surface. The parameters of the model were estimated by fitting the model with the response curves from the impulse loading tests. These estimated parameters were consistent with previous studies. Specifically, the modeling results suggest a significant adsorption of nitrate by the iron media, causing an evident retardation effect. The research may lead to new methods for studying the fate of contaminants in porous reactive environments. [ABSTRACT FROM AUTHOR]

Tests were conducted in Fe0-packed columns to investigate the effects of adding selected cations on nitrate removal by Fe0. Due to a rapid passivation of Fe0, only negligible nitrate was reduced in the columns without adding the selected cation. However, adding certain selected cations (Fe2+, Fe3+, or Al3+) in feed solution can significantly enhance nitrate reduction. Extending hydraulic retention time (HRT) increased nitrate removal by the columns, but the increase was not linearly proportional to HRT. Decreases in columns’ hydraulic conductivity (K) were monitored in an 8 month operating period. A modest decrease in K was recorded in the upper and the middle section of the media bed, whereas a significant decrease in K occurred in the inlet section. X-ray diffraction analyses indicate that magnetite (Fe3O4) was the dominant species of the iron corrosion products in the entire height of the column media under anoxic and other test conditions. In the inlet section, however, lepidocrocite and goethite were also identified. Cementation was found to occur only in the inlet section, suggesting that lepidocrocite and goethite, rather than magnetite, might be responsible for the cementation and thereby cause the hydraulic clogging. The magnetite coating would not necessarily cause clogging of the media. [ABSTRACT FROM AUTHOR]

The effects of three selected Good’s pH buffers on the performance of an Fe0/nitrate/H2O system were evaluated. The Good’s pH buffer itself did not reduce nitrate directly. Nitrate reduction by iron powder at near-neutral pH was negligible in an unbuffered system, but it was greatly enhanced with the presence of the buffer. A significant amount of aqueous Fe2+ (or Fe3+) was released after adding the Good’s pH buffer into the Fe0/H2O system with or without nitrate. In general, the pH of the buffered solution increased from the initial pH (=∼4.6–5.3, depending on buffer’s pKa) to near-neutral pH. After the initial pH hiking, the pH in the system was more or less stable for a period of time (∼5–10 h, usually concurrent with a fairly stable aqueous Fe2+). The pH then drifted to ∼7.1 to 8.6, depending on the buffer’s initial concentration, the buffer’s pKa, and the consumption of Fe2+ concurrent with nitrate reduction. While a common assumption made by researchers is that Good’s pH buffers do not directly participate in reaction processes involved in contaminant remediation, this study shows that as side effects, the Good’s pH buffer may react with iron powder. [ABSTRACT FROM AUTHOR]

Although considerable research has been conducted on nitrate reduction by zerovalent iron (ZVI), the process kinetics at near neutral pH has not been studied thoroughly. In this study, a kinetic model with a double-Langmuir-adsorption formulation was developed to represent site saturation effects of aqueous Fe[sup 2+] and NO[sub 3][sup -] on nitrate reduction in a ZVI system at near neutral pH. Both an analytical solution and a numerical solution of the proposed model were developed. The kinetic parameters were evaluated based on batch experiments with two types of ZVI. Sensitivity analysis indicates that it is rather difficult and unreliable to estimate the parameters of the proposed multivariable nonlinear kinetic model from a single test curve. A better strategy is to obtain reliable parameters by designing specific experiments to target one parameter each time. The results indicate that, although the values of the kinetic parameters might change with different types of iron powder, the kinetic model can fit the experimental data very well, and therefore is consistent with the proposed mechanism. [ABSTRACT FROM AUTHOR]

Presents a study which investigated the feasibility of using sulfur:limestone autotrophic denitrification pond reactors to treat nitrate-contaminated water or wastewater. Method of the study; Results and discussion; Conclusion.

Focuses on a study which evaluated nitrate removal using sulfur and limestone autotrophic denitrification (SLAD) processes. Optimum design criteria of the fixed-bed SLAD columns; Effects of biofouling on the SLAD column preformance.

With the increase in the chemical oxygen demand (COD) of the influent and the organic/hydraulic loading rate (OLR/HLR), the treatment efficiency of the vermifiltration (VF) process decreases. Also, the treatment performance of the VF process varies with the type of wastewater, even if all the other operating conditions remain the same. To date, the inhibitory effects of wastewater, e.g., its composition, concentration, and OLR/HLR, on earthworms (EWs) and VF's treatment efficacy have been completely overlooked. Herein, such inhibitory effects on the survival, growth, and reproduction of the EWs have been investigated using real brewery, dairy, domestic, and diluted brewery wastewater. The acute and chronic tests were performed in vertical subsurface flow reactors in accordance with the guidelines with some modifications. Results showed that 50% mortality of EWs occurred within 11–21, 16–33, 21–41, and 24–48 days for brewery, diluted brewery, dairy, and domestic wastewater, respectively, at the HLR of 8–4 m3 m−2day−1. For each wastewater, the maximum growth of EWs was observed at the lowest tested HLR (4 m3 m−2day−1). Domestic sewage ensured the highest number of juvenile (20–38 nos. EW−1) and cocoon production (10–15 nos. EW−1), followed by dairy (juveniles: 7–21; cocoons: 5–10), diluted brewery (juveniles: 4–15; cocoons: 2–9), and brewery wastewater (juveniles: 2–12; cocoons: 2–7), with the HLR and OLR having a negative impact on the same. Therefore, brewery wastewater had the highest biological inhibition on survival and biological activities of the EWs, whereas domestic sewage had the least. The dilution given to brewery wastewater reduced the extent of the inhibitory effects imposed on the survival, growth, and reproduction of EWs. Results of this study indicated that the VF technology is more suitable for treating domestic sewage, can treat dairy wastewater substantially, and can treat brewery wastewater, but appropriate pretreatment (such as bioaugmentation or dilution) may be necessary. [ABSTRACT FROM AUTHOR]

The article reflects on the importance of an engineering decision to the engineering education. Engineers are faced with issues that require a good decision to produce a positive objective and outcome for future ventures of companies including design challenges, production risks and construction alternatives. Hence, engineering students should be provided with an engineering curricula that instructs necessary knowledge on methodology and framework useful in decision-making to avoid marketing disasters.

The presence of emerging contaminants (ECs) in the environment, especially in the water and wastewater matrices, has become a major headache for the competent authorities, because even with the mildest of exposure aquatic organisms, as well as humans, can exhibit chronic/acute toxicity. In the last few years constructed wetlands (CWs) have become a popular method to eradicate ECs from water and wastewater, because they are an environmentally benevolent, economically feasible, and aquatic plant-based natural technology. However, information is not readily available on how to configure a CW (or combination of CWs, for hybrid CWs) to ensure the substantial removal of ECs. Thus, the present review analyzes how the various physicochemical properties of ECs govern their major removal pathways in different CWs and how the design configuration of a CW can lead to better EC removal. Finally, some recommendations regarding the possible configuration or combination of CWs on the basis of the ECs' known physicochemical properties are made. This review article will help in selecting the proper combinations of CWs to eliminate the ECs of concern (known or unknown) from the aquatic matrices. [ABSTRACT FROM AUTHOR]

In this study, effects of aeration and wastewater composition were evaluated on the clogging process in four laboratory-scale wavy subsurface-flow and vertical-flow constructed wetlands (WSVFCWs) used for secondary and tertiary treatment. The relationship between the accumulated solid material and infiltration rate, the content and particle size distribution as well as the ratio of organic and inorganic matter of the accumulated material in the filter media were determined, and the mechanisms of clogging were elucidated. The clogging mainly occurred in the upper 0-40 cm layer, and the accumulated material decreased with filter depth (along the flow direction). The main particle size contributing to clogging was ~40 μm in the WSVFCWs for secondary treatment and >110 μm in those for tertiary treatment. The accumulated material had 30-40% of organic matter. The clogging mechanisms varied as the composition of influent and aeration conditions are different in WSVFCWs. Aeration promoted the growth of biofilm and mineralization of the accumulated material as well as provided shear force in the WSVFCWs. Aeration has a good effect in extending operational time in the tertiary WSVFCW but has a mild effect in the secondary WSVFCWs because of high organic loading rate there. Both the organic and suspended solids (SS) loading rate are important factors and should be controlled to mitigate the clogging problem in WSVFCWs. [ABSTRACT FROM AUTHOR]

To investigate the effects of different types and concentrations of organic matter on anaerobic ammonium oxidation (anammox), the effects of short-term stresses induced by organic matter on anammox-based nitrogen removal and the associated microbial community were evaluated by adding different organic matter (e.g., glucose, acetic acid, sodium acetate, methanol, and phenol) and concentrations (e.g., 20–250 mg COD/L) into anammox batch reactors (serum bottles) with 46 h. Results indicated that the addition of glucose, acetic acid, and sodium acetate (i.e., at concentrations ranging from 20 to 250 mg COD/L) promoted nitrite removal. Methanol was the most potent inhibitor on ammonium removal, while phenol inhibited ammonium removal even at a low concentration (e.g., 20 mg COD/L). The microbial community structure and composition under organic matter addition was illustrated by high-throughput Miseq sequencing analyses. The phylum Firmicutes was predominant in all samples, followed by Planctomycetes, Proteobacteria, and Chloroflexi, respectively. Planctomycetes, which was related to anammox bacteria, including Candidatus Jettenia and Candidatus Brocadia, dramatically decreased under sodium acetate and methanol stress, respectively. [ABSTRACT FROM AUTHOR]

While forward osmosis (FO) has great potential to be the next generation water treatment technology, it is constrained by the development of ideal draw agents and membranes. Herein, a series of copolymerized hydrogels based on strong ionic monomer sodium 2-acrylamido-2-methylpropane sulfonate (AMPS-Na) and thermosensitive monomer -isopropylacrylamide (NIPAM) have been synthesized and used for the first time as draw agents in the FO process. The effects of the composition of poly(NIPAM- co-AMPS-Na) [P(NIPAM- co-AMPS)] hydrogels and operational conditions including draw agent concentrations, temperature, membrane orientation, salinity of feed solution, velocity of feed solution, and running times on the FO performance have been evaluated systematically. The results demonstrate that the water flux increases with increases of the content of AMPS-Na incorporated into the hydrogel and hydrogel concentration in the draw solution, e.g., from 0.40 LMH rising up to 2.85 LMH. Besides, the water flux increases by 18% as the temperature increases from 5 to 27°C. In addition, these hydrogels remained active even after five times regeneration and reuse with a total water flux decrease of less than 5%. Furthermore, these hydrogels have negligible reverse diffusion through the FO membrane as compared with the corresponding monomer mixture and NaCl, which may avoid possible contamination on the feed solution and lower the renewable cost. All these results indicate that these synthesized P(NIPAM- co-AMPS) hydrogels are promising draw agents for the FO process. [ABSTRACT FROM AUTHOR]