Journal of Environmental Engineering

The baffled flask test (BFT) has been proposed by United States Environmental Protection Agency to be adopted as the official standard protocol for testing dispersant effectiveness. The mixing energy in the baffled flask is investigated in this paper. Particle image velocimetry (PIV) was used to measure the water velocity in the flask placed at an orbital shaker that was rotated at seven rotation speeds: 100, 125, 150, 160, 170, 200, and 250 rpm. Two dimensional velocity fields in large and small vertical cross sections of the flask for each rotation speed were obtained. The one-dimensional (1D) energy spectra indicates the existence of inertial subrange. The estimated average energy dissipation rates were in the range $7.65\times {10}^{-3}$ to $4\mathrm{W}/\mathrm{kg}$ for rotation speeds of $\mathrm{\Omega }=100–250\mathrm{rpm}$, of which it is larger than the one estimated by prior studies using single-point velocity measurement techniques for $\mathrm{\Omega }=100$ and 200 rpm. Factors such as instruments used, velocity components measured, and different analysis methods could contribute to the discrepancies in the results. The Kolmogorov scale estimated in this study for all seven rotation speeds approached the size of oil droplets observed at sea, which is 50–400 μm. The average energy dissipation rate,$\epsilon$ and Kolmogorov microscale, $\eta$, in the flasks were correlated to the rotation speed, and it was found that $\overline{\epsilon }=9.0\times {10}^{-5}\mathrm{Exp}(0.043\mathrm{\Omega })$ with $R^2=0.97$ and $\overline{\eta }=\mathrm{1,463}\mathrm{Exp}(-0.015\mathrm{\Omega })$ with $R^2=0.98$.

Sorption and desorption have been found to be critical in the fate and transport of hormones in soils. Previous study indicated that the sorption and desorption properties of soil particles of different size fractions associated with hormones were very different. However, the interaction mechanisms of hormones with these soil particles are still unclear. This study investigated the influence of aquatic conditions [e.g., temperature, hydrogen ion concentration (pH), ionic strength, soil/water ratio, organic matter] on the sorption and desorption of soil particles of three size fractions [i.e., sand (0.425–0.075 mm), silt (0.045–0.002 mm), and clay ($0.6–2\mu \mathrm{m}$)] associated with testosterone at environmentally relevant concentrations (i.e., $20–150\mathrm{ng}/\mathrm{L}$) in batch reactors. The results indicate that lower temperature will facilitate sorption but hinder desorption of testosterone onto/from all of the soil particles. Lower pH and higher organic matter content will favor the sorption of testosterone onto all of the soil particles, especially for clay, but will impede desorption. A higher soil/water ratio would impede desorption of testosterone from all of the soil particles. The main sorption mechanism of trace-level testosterone onto sand is electrostatic attraction, whereas that onto clay is mainly hydrogen bonding and functional groups, and that onto silt is in the middle of sand and clay. The study provides insights on controlling/predicting the behavior/fate of hormones in the soil environment.

The objective of this study was to predict As(V) removal by an iron-oxide impregnated carbon (L-Act, 9% Fe(III) amorphous iron-oxide) over a range of environmental conditions using the surface complexation modeling (SCM) approach. The L-Act surface sites and electric double layer were modeled using the two monoprotic site-diffuse layer model (2MDLM). As(V) and ${\mathrm{PO}}_4$ surface complexes were modeled as bidentate complexes at low hydrogen ion concentration (pH) and monodentate complexes at high pH. $\mathrm{L}\text{-}\text{Act}\text{-}\mathrm{As}/{\mathrm{PO}}_4$ surface complexation constants were determined from a single pH-adsorbent edge, and these were used to effectively predict pH-dependent removal of As(V) and ${\mathrm{PO}}_4$ across a range of adsorbent/adsorbate ratios in single and binary adsorbate systems and from a National Sanitation Foundation challenge water. The 2MDLM also successfully predicted As(V) removal by three literature-based iron-based adsorbents: two iron-impregnated ion exchange resins (PWX5, 16% Fe; PWX3, 10% Fe) and a hydrous ferric oxide that was incorporated into a porous diatomite.

The nano zero-valent iron supported granular activated carbon (${\mathrm{nFe}}^0/\mathrm{GAC}$ or $2.5\%\text{-}{\mathrm{nFe}}^0/\mathrm{GAC}$) was synthesized by the liquid chemical reduction method and further used for the oxidative degradation of quinoline. The $2.5\%\text{-}{\mathrm{nFe}}^0/\mathrm{GAC}$ was characterized by various techniques such as Brunauer-Emmett-Teller (BET) surface area, Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), and field emission scanning electron microscopy (FE-SEM). It was ascertained that iron is of zero state and well dispersed on GAC. The $2.5\%\text{-}{\mathrm{nFe}}^0/\mathrm{GAC}$ exhibited an H4 type hysteresis loop with a surface area of $\sim 240{\mathrm{m}}^2/\mathrm{g}$. The kinetic study reveals that quinoline degradation follows the pseudo–first order. At optimum conditions of $\mathrm{pH}=4$, $\mathrm{m}=7.5\mathrm{g}/\mathrm{L}$, ${\mathrm{C}}_o=100\mathrm{mg}/\mathrm{L}$, and $\mathrm{T}=303\mathrm{K}$, it was observed that (1) $\sim 93\%$ of quinoline and $\sim 63\%$ of total organic carbon (TOC) removal is obtained, (2) iron leaching is within the permissible limit, and (3) it requires $\sim 63\pm 5\min$ for completion of the half-life of quinoline. The activation energy is $\sim 22.4\mathrm{kJ}/\mathrm{mole}$, which indicates that quinoline removal is controlled by a chemical surface reaction. The degradation by-products of quinoline were analyzed. The mass fragments (of $\mathrm{m}/\mathrm{z}=146$ and 178) due to hydroxylation were obtained, which were further reduced into low $\mathrm{m}/\mathrm{z}$ fragments, which may lead to mineralization of quinoline.

The degradation of reactive brilliant red X-3B (X3B) in a simulated ${\mathrm{sunlight}/\mathrm{S}}_2{\mathrm{O}}_8^{2-}/\mathrm{steel}$ slag system at near neutral pH has been studied. The influence of initial pH value, persulfate concentration, quantity of steel slag, and temperature on the degradation of X3B in aqueous solution were investigated. Up to 79.2% of X3B was removed in the simulated ${\mathrm{sunlight}/\mathrm{S}}_2{\mathrm{O}}_8^{2-}/\mathrm{steel}$ slag system within 5 min at a pH of 6.0. Simulated sunlight played a catalytic role in the ${\mathrm{S}}_2{\mathrm{O}}_8^{2-}/\mathrm{steel}$ slag system and resulted in an enhancement of X3B degradation of approximately 11%. The degradation of X3B decreased with an increasing pH in the solution, whereas high temperature facilitated the activation of persulfate. The cycling of ${\mathrm{Fe}}^{2+}{/\mathrm{Fe}}^{3+}$ facilitated the reuse of steel slag under simulated sunlight irradiation. The steel slag was passivated after coming into contact with the oxidant within 1 min. The sequential addition of steel slag promoted X3B degradation, yielding a removal efficiency of 91%.

This paper shows the extent to which the application of real-time control techniques can help in reducing the flows discharged from quality oriented combined sewer overflow (CSO) devices in sewer systems. To this end, a quality oriented CSO device, namely the high-crested side-weir (HCSW) with downstream gate, was taken into account for the analysis. A numerical model able to simulate routing of flows in proximity to CSO devices was specifically used to evaluate the benefits of the HCSW with downstream gate, in comparison with the more traditional low-crested side-weir (LCSW), and the coupled use of HCSWs and in-sewer mobile gates controlled in real time. The model was applied by considering four different modeling scenarios to the case study of a sewer catchment in Italy, in which real storm-water events had been recorded during previous experimental investigations. Results of the simulations prove the HCSW with downstream gate always considerably reduces CSO volumes in comparison with LCSW overflow devices. Significant additional benefits are obtained by the implementation of underflow gates controlled by real-time control (RTC), even if the presence of such mobile devices may sporadically lead to a local increase in the overflow discharge.

Elevated levels of bromide have been shown to contribute to increased formation of disinfection byproducts (DBPs). Both produced water from unconventional oil and gas wells, which are hydraulically fractured using high volumes of fluids, and produced water from conventional oil and gas wells, which are also typically hydraulically fractured but with lower volumes of fluids, can contain high levels of bromide. If these produced waters are treated in conventional commercial wastewater treatment plants, bromide may not be removed from the effluent and is discharged to receiving water bodies. Elevated bromide levels at drinking water plant intakes is a concern for public health reasons if elevated bromide levels cause elevated levels of DBPs. This study used data from commercial wastewater treatment plants and river flow data in western Pennsylvania to construct generic discharge scenarios that illustrate the potential impacts from disposal of five classes of water that were developed from flowback and produced water bromide concentrations. Months with the historical high and low flows in the Allegheny River (Pennsylvania) and Blacklick Creek (Pennsylvania) were chosen for simulation, and treatment plant discharge rates were set at 100, 50, 33, and 25% of the permitted value for the purpose of varying the mass loading. Steady-state simulation results showed the highest probably of impact, defined as concentrations above target levels of 0.02 and $0.10\mathrm{mg}/\mathrm{L}$, for produced water in the creek at both high and low flows (100%), and produced water in the river at low flows ($>75\%$). High probability of impact ($>50\%$) occurred in the river at low flows and all flows in the creek with treated mixed/flowback water discharge. Modeled reduction in the effluent discharge rate reduced downstream impacts proportionally. Transient simulation showed that transient peak concentrations may exceed time-averaged concentration by up to a factor of four when mixing conditions are met.

The study of sediment transport in water natural bodies is a challenging task. There have been several attempts to describe sediment mathematically using hydraulic characteristics of water bodies. Most researchers who developed empirical formulas to describe sediment transport performed laboratory experiments with assumptions that did not take into account variations of hydraulic parameters and the fine sediment sizes that are part of this phenomenon. Recently, new approaches for studying sediment transport have been developed involving the use of machine-learning algorithms that have proven accuracy and efficiency in predicting sediment transport. A novel machine-learning method, the Multivariate Relevance Vector Machine (MVRVM), has yet to be tested to model sediment transport and water quality in estuaries and lakes. The selection of the MVRVM is suggested by the limited field observations that present challenges for alternative statistical learning machines, and by the promise of using the MVRVM approach to inform future data-collection efforts. This paper tests the success of calibrating the MVRVM model to predict suspended fine-sediment transport and other environmental measures in Mud Lake, southeastern Idaho, United States. In addition, the authors introduce and explain the technique that can be used to arrange the data which will allow the model to work. Training and validation results for turbidity, total suspended solids (TSS), pH, dissolved oxygen (DO), and water temperature are presented. These results emphasize that modeling the water-quality constituents and sediment transport with few observations is possible using the MVRVM.

Storm rainfall on and runoff from a 3.35-ha low-impact development (LID) residential subdivision in the Piedmont region of North Carolina were monitored for 6+ years, which included predevelopment, during-development, and postdevelopment phases. Runoff was monitored and sampled at two stations using automated samplers. Along with residences, the drainage area to one of the stations (PC1) included an undisturbed wooded riparian buffer with level spreaders to distribute runoff, while the area to the other station (PC2) included four bioretention areas, permeable pavement, a roof runoff collection system, a detention pond, and other LID measures. Monitoring results documented that the postdevelopment, runoff to rainfall ratio, and pollutant export at both stations were significantly greater than those of the predevelopment phase, during which time the land use on the site was mature woods. The total nitrogen (TN), total phosphorus (TP), and total suspended solids (TSS) export at both LID monitoring stations was 23 to 92% less than those from a nearby conventionally-developed subdivision monitored previously. These data indicated that LID subdivisions constructed on moderately to slowly permeable soils may not be able to maintain the runoff to rainfall ratio and TN, TP, and TSS export if the predevelopment land use was mature woods; however, if the predevelopment land use was cropland mixed with woods, then it may be possible to maintain predevelopment runoff to rainfall ratio and TN, TP, and TSS export. Further, the extensive use of LID techniques/measures in this residential subdivision resulted in less TN, TP, and TSS export compared to a similar conventional subdivision.

The hyporheic zone (HZ) has the potential to mitigate nonpoint source pollution that threatens urban streams, but limited flows and inefficient interchange typically constrain its water quality improvements. This paper presents coordinated streambed hydraulic conductivity (K) modifications, termed Biohydrochemical Enhancement Structures for Streamwater Treatment (BEST), to efficiently drive interchange, attenuating nutrients, metals, and pathogens. Numerical models consisted of sandy HZ with high and low K streambed media components, and variable slope and in situ sediment K. BEST contaminant mitigation was estimated using hyporheic flow and residence time (RT) simulations and contaminant removal rate constants from literature for specific porous media. Hyporheic flows improved, whereas mean RT decreased approximately linearly with increasing slope and in situ K. Despite vast differences in flow and RT, contaminant removal potential was relatively consistent among BEST in which reaction time scales were similar to or shorter than RTs. However, BEST with excessive RTs were less efficient. Most contaminants could be attenuated within a series of BEST 50 m in length, suggesting that BEST could be an effective stormwater best management practice for small streams.

The soil-contaminant interaction is significantly influenced by various attributes of soil and contaminant, and it can be quantified by employing a term known as distribution coefficient ($k_d$). However, because of the involvement of many parameters related to soil and contaminant, determination of $k_d$ becomes a tedious and time-consuming exercise that requires extensive experimental investigations. In this context, application of the Taguchi method for minimizing the number of experiments and establishing the most critical parameters which influence $k_d$ (obtained from the linear isotherm) has been shown to be quite useful by the researchers in the recent past. Keeping this point in view, application of L25 orthogonal array (OA) used in the Taguchi method has been employed to design experiments which would facilitate establishment of the influence of various parameters concomitantly on $k_d$ and its prediction as well. The $k_d$ has been predicted by employing two methods viz, the Taguchi method and the statistical regression model (SRM). With this in view, four parameters (viz, cation exchange capacity of the soil, ionic species, temperature, and interaction time of the soil-contaminant system) were selected for developing the L25OA, and it has been clearly demonstrated that these methodologies help in easily (1) identifying the most significant parameter on which $k_d$ is dependent and (2) predicting the precise $k_d$ by inputting the four parameters. Moreover, based on this study, the sorption mechanism that yields a maximum $k_d$ for a given soil-contaminant system (SCS) by employing the most optimized parameters has also been proposed.

The full-scale start-up of a novel BIO4GAS digester system, a highly economic, small-scale biogas plant was monitored for 6 months. The digester was loaded with cattle manure, and a new slow temperature increase strategy (12–37°C at $0.25°\mathrm{C}{\mathrm{d}}^{-1}$) was tested, rendering a daily methane yield of $289\pm 148\mathrm{mL}{\mathrm{g}}^{-1}$ volatile solids. Stable biogas production, pH, and high reduction of volatile fatty acids (from 5.2 to $0.6{\mathrm{g}\mathrm{L}}^{-1}$) indicated a well working process. The prokaryotic community was monitored by cloning and quantitative real-time PCR of the 16S rRNA gene. Archaeal diversity decreased at the taxonomic class level, whereas the bacterial community was affected only up to the family level. A shift from hydrogenotrophic methanogens toward a consortium dominated by metabolically versatile methanogens occurred with Methanosarcina outcompeting Methanobrevibacter under the changing conditions of volatile fatty acid concentrations. Main bacterial phyla (Firmicutes, Bacteroidetes, and Proteobacteria) did not change during the start-up; however, minor populations of cellulose-degraders (Ruminococcaceae), syntrophic fatty acid oxidizers (Syntrophomonas), and acetogens (Sedimentibacter) established. The results provide experimental evidence of a dynamic archaeal community and a relatively stable bacterial community during dramatic environmental changes of a successful reactor start-up.

Siloxanes, impurities in the biogas produced from anaerobic digestion of wastewater sludges, are transformed to silica dioxide sand during combustion of the biogas, which damages the heat exchanger and engine. Decamethylcyclopenta-siloxane (D5) and octamethylcyclotetra-siloxane (D4) were added to return activated sludge (RAS) and treated using a pulsed-electric field method [focused pulsed (FP)] that makes the sludge solids more readily converted to methane. With an FP treatment intensity ($TI$) of $36{\mathrm{kWh}/\mathrm{m}}^3\text{-}\mathrm{RAS}$, the D4, and D5 removal efficiencies were $32\pm 4.0$ and $11\pm 0.2\%$, respectively. Removals of D4 and D5 increased proportionally with $TI$ whether $TI$ was affected by sludge conductivity or FP pulse frequency. FP treatment of activated sludge before methanogenic batch tests lowered the amount of both siloxanes in the produced biogas, and evidence suggests that the siloxanes were biotransformed during the batch tests.

Vegetable oil–based cutting fluids are a relatively recent development in large-scale metal machining. A metal machining factory in Wales that switched from mineral oil-based to vegetable oil-based cutting fluids has experienced the occurrence of a problematic floating sludge within the settling and holding tanks at the on-site effluent treatment plant. Physicochemical analyses have found that the sludge is composed of on average 33% water, 20% oleic acid, and 18% palmitic acid, originating from the vegetable oil–based cutting fluids used at the factory. A solvent separation step was devised and used successfully to separate water inherent within the sludge so as to study the division of the inorganic elements within the water and organic phases of the sludge. It was found that only a minor constituent of the sludge can be accounted for by Ca-bonded fatty acids. Formation of the sludge is suspected to be due to the biologically induced hydrolysis and oxidation of the oils from esters to the free fatty acids and subsequent creaming, forming a layer of stable floating sludge on the surface of the effluent storage tanks.

This paper presents a laboratory study on electrokinetic dewatering (EKD) of sewage sludge with fixed and moving electrodes. The experiments with fixed electrodes were conducted in two purposely designed Perspex cylinders to investigate the mechanism of attenuation in electroosmotic flow and dewatering efficiency. The experiments with moving electrodes were performed in an innovatively designed apparatus, in which the anode made of an array of stainless rods can be moved toward the fixed cathode plate. The fixed-electrode experiments showed that the electrical resistance of the dewatered section near the anode increased with the treating time, and hence the voltage gradient left for the undewatered section decreased. The increased electrical resistance resulted in an increase in the invalid energy consumption, and the reduced voltage gradient at the undewatered section resulted in an attenuation in electroosmotic flow and dewatering effect. Comparison tests conducted with the moving-anode apparatus further demonstrated the attenuation mechanism. Only a slight attenuation in the electroosmotic flow was observed in the moving-anode experiments, in which the anode array was moved to pass by the dewatered section and keep the voltage gradient on the undewatered section unchanged. As compared with the fixed-electrode experiments, the dewatering effect for the moving-anode experiments was much better, and the energy consumption in terms of removed water volume was significantly lower. When the moving-anode method was applied with a voltage gradient of $8\mathrm{V}/\mathrm{cm}$ and an initial electrode spacing of 1 cm, the sludge with a water content of 82.1% can be dewatered to 62.2%, and the estimated energy consumption is as low as $18\mathrm{kWh}·{\mathrm{m}}^{-3}$. The research findings shine a light on the use of the moving-electrode method for improving the treatment efficiency of EKD.