Journal of Environmental Engineering

Transfer of oxygen across the capillary fringe and water table is a critical oxygen source for aerobic biodegradation of hydrocarbon light nonaqueous phase liquids (LNAPLs) at or near the water table. However, significant resistance to oxygen mass transfer may be associated with the capillary fringe. This work evaluates the hypothesis that a decrease in the water-saturated thickness of the capillary fringe due to the presence of a hydrocarbon LNAPL, and the reduced resistance to oxygen mass transfer in the hydrocarbon phase, will enhance oxygen transfer relative to natural reaeration. Oxygen flux in the absence and presence of an LNAPL pool is conceptually evaluated using the two-film model. Abiotic experiments in a bench-scale sand-tank reactor demonstrated that oxygen transport through the water table interface was enhanced when an LNAPL (dodecane) pool was present at the water table compared to natural reaeration. Biotic experiments demonstrated that the increased oxygen transport in the presence of the LNAPL pool also increased biodegradation of a solute (glucose) plume passing beneath the LNAPL pool. Biodegradation also apparently further bioenhanced the oxygen transfer.

Modeling particulate matter (PM) separation has been a significant topic since unit operations (UOs) has been introduced for clarification of combined sewer overflows (CSOs). In contrast with surface overflow rate (SOR) model, long debated for the limits of its applicability, computational fluid dynamics (CFD) has been an emerging tool for accurately predicting hydrodynamics and PM transport in UOs. In this study an Eulerian-Lagrangian CFD model and a SOR model coupled with particle size distribution (PSD) are used to predict PM separation from three Type I settling UOs with same surface area (SA) but different inlet locations. UOs are loaded with hydraulic conditions and PM gradation measured from samples collected in the combined sewer system of the city of Cosenza, Italy. Specifically, the samples characterize the influent flow entering into a detention tank located downstream of the combined sewer system. The detention tank is used for treating the combined sewer by gravitational settling. The two models predict the overall PM separation efficiency and the separated PM percentage as a function of flow rate and particle size for three different UO configurations. The difference between results from the two models increases as a function of flow rate (differences ranging from about 5 up to 23%) for all three UO configurations. This is probably because of the fact the SOR does not account for the mixing phenomena because of turbulence generated by high hydraulic loadings. Under those conditions, CFD model, properly validated with field measurements, may represent a more accurate predictive tool for design of stormwater settling tanks (STs) than a SOR model.

Nanoscale iron particles (NIP) can be used for in situ remediation of a variety of organic contaminants in the subsurface. NIP can effectively degrade contaminants due to their large reactive surface area. NIP transport in subsurface soils is hindered due to their agglomeration and sedimentation, and surface-modified NIP are suggested to enhance the transport. This study investigated the transport and reactivity of bare NIP and lactate-modified NIP (LMNIP) in field sand spiked with 2,4-dinitrotoluene (DNT at $740\mathrm{mg}/\mathrm{kg}$), a representative nitroaromatic organic compound found at munitions waste sites. Column tests were conducted using NIP and LMNIP at two different concentrations (1 and $4\mathrm{g}/\mathrm{L}$) and two different flow velocities (0.75 and $1.2\mathrm{cm}/\min$). During the testing, changes in the magnetic susceptibility (MS) values across the soil column were measured and effluent was collected and its volume was measured at different time periods. After the end of the testing period, the soil was extruded and sectioned, and concentrations of iron (Fe) and DNT were measured in each soil section and effluent. Measured Fe concentrations in the soil and corresponding magnetic susceptibility were found to have a linear correlation. Therefore, the MS measurements made during the testing were used to assess the extent of transport of NIP and LMNIP at different times during the testing. The results showed that $4\mathrm{g}/\mathrm{L}$ LMNIP was transported more successfully than the $4\mathrm{g}/\mathrm{L}$ bare NIP, but there was no significant difference in the transport of NIP and LMNIP at the low concentration of $1\mathrm{g}/\mathrm{L}$. As a result of the enhanced transport, $4\mathrm{g}/\mathrm{L}$ LMNIP caused greater degradation of the DNT. The higher flow rate increased the transport of NIP and LMNIP, thus increasing the DNT degradation.

Urban storm water runoff can carry a wide range of contaminants, many of which exceed federal maximum contaminant levels, into surface water resources (e.g., rivers and lakes). The use of filtration systems has received greater attention for its potential to remove particulate matter and other contaminants. Biochar is expected to have excellent potential as an adsorbent or filter given its large surface area and microporous structure. This study evaluated the potential use of biochar as a filter media through a series of column experiments. A column with an inner diameter of 7 cm (2.75 in.) and a length of 61 cm (24 in.) using biochar as filter media was constructed to examine its effectiveness for the removal of mixed contaminants [total suspended solids (TSS), nutrients, heavy metals, polycyclic aromatic hydrocarbons (PAHs), and E. coli] from synthetic storm water. The results demonstrated that this filter reduced the TSS in the storm water effluent by an average of 86% and the concentrations of nitrate and phosphate by 86 and 47%, respectively. After filtration, the concentration of Cd, Cr, Cu, Pb, Ni, and Zn (heavy metals) decreased by 18, 19, 65, 75, 17, and 24%, respectively. The variation can be explained in terms of the chemical behavior of the different heavy metals as well as the properties of the biochar. Among the three PAHs tested, biochar successfully removed phenanthrene (almost 100% removal efficiency) and achieved 76% removal efficiency for naphthalene but resulted in no removal of benzo(a)pyrene; the average removal for the three PAHs was 68%. Biochar was not efficient in removing E. coli from storm water, and the concentration of almost $\mathrm{7,400}\mathrm{MPN}/100\mathrm{mL}$ in the inflow was reduced to approximately $\mathrm{5,000}\mathrm{MPN}/100\mathrm{mL}$ in the outflow, representing a mean removal efficiency of 27%. Overall, the biochar used in this study showed promise to be an effective filter media for the removal of selected contaminants from urban storm water runoff. However, additional research should be conducted using different types of biochars, produced from different feedstock and production conditions, to determine the most effective biochar that can simultaneously remove multiple contaminants from urban storm water.

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 $N$-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.

Vegetation or grass-planted covering has been demonstrated to be a cheap and effective method to prevent fugitive particular matter, which is a typical air pollution source emitted from exposed areas like farmlands or construction sites. A series of systematic experiments were carried out to continuously measure the dynamic variability of particulate matter sized less than 10 μm (${\mathrm{PM}}_{10}$), and thus the reduction efficiencies of ${\mathrm{PM}}_{10}$ calculated using the experimental data. The reduction efficiency was found significantly affected by the grass covering height, and maximum reduction efficiency was concluded to be not more than 45%. Correlated with grass height, a useful correlation is proposed to estimate the reduction efficiencies that would be valid under the appropriate conditions suggested by this work. Using this correlation, the reduction efficiencies of ${\mathrm{PM}}_{10}$ can be predicted and provide a practical guideline for environmental management or engineering applications. It must be emphasized that the reduction efficiency approaches zero as the grass height is less than about 2 cm. This implies that ${\mathrm{PM}}_{10}$ reduction is inefficient if the grass is not high enough over the exposed area. Another point of interest is that total elimination of ${\mathrm{PM}}_{10}$ emission is not possible even when the grass is high enough with full coverage over the exposed area. Some constraints to applying the results obtained from this work are also discussed.

Experimental studies with granular bed filters composed of sized metallic granules have demonstrated their use in aerosol filtration. However, the effectiveness of metallic membrane filters against bioaerosols has not been established. In this work, the filtration efficiency and filter quality of these filters against airborne B. subtilis endospore and MS2 virus were determined as a function of face velocity and loading time. In experiments, a physical removal efficiency greater than 99.9% and a viable removal efficiency greater than 99.999% were observed for both bacterial spore and viral aerosols. A lower face velocity produced both higher collection efficiency and filter quality for virus but was not a statistically significant factor for spore filtration. Although the filter had high filtration efficiency of the test bioaerosols, its high pressure drop resulted in a low filter quality ($0.25–0.75{\mathrm{kPa}}^{-1}$). Overall, filters with micrometer-sized collectors capture bioaerosols effectively but their applications in aerosol filtration may be limited by their high pressure drop.