Journal of Environmental Engineering

Concerted efforts to remediate subsurface systems contaminated with dense nonaqueous-phase liquids (DNAPLs) have met with limited success when measured by comparing solute concentrations to drinking water quality standards. One-dimensional and three-dimensional laboratory experiments and a field-scale experiment are used to investigate the effectiveness of source-zone remediation and to assess factors that contribute to the observed results. The three-dimensional laboratory experiment and the field-scale experiment used a surfactant flush followed by vapor extraction to reduce the DNAPL saturation, while vertical DNAPL mobilization was controlled using a brine barrier. DNAPL mobilization and recovery in the field-scale experiment was relatively ineffective due in part to the low saturation levels of the DNAPL. The results show essentially that complete removal of a DNAPL is required to reach typical cleanup standards and that details of the morphology and topology of a DNAPL distribution, in addition to the saturation, play an important role in determining the rate of mass transfer. The results are interpreted in terms of guidance for remediation approaches, realistic expectations for source-zone remediation, and elements needed for improved models of such systems.

Modeling the behavior of contaminants in a subsurface flow is important in predicting the fate of the pollutants, in risk assessment, and as a preliminary step of the mitigation process. A two-dimensional transport model with advection and dispersion is used as the deterministic model of a conservative contaminant transport in the subsurface. With the system model alone, it is very difficult to predict the true dynamic state of the pollutant. Therefore, observation data are needed to guide the deterministic system model to assimilate the true state of the contaminant. Extended Kalman Filter (EKF), which is essentially a first order approximation to an infinite dimensional problem, is used in this study to predict the contaminant plume transport. A traditional root mean square error (RMSE) of pollutant concentrations is used to examine the effectiveness of the EKF in contaminant transport modeling. The result shows that EKF can reduce 74 to 91% of prediction errors compared to the numerical method while working with the full set of observation data and using the analytical solution as the true solution. It can reduce 24 to 90% of prediction errors while working with only 2.25% observation-site data and a simulated random true field.

Clogging in porous media is a problem in environmental engineering, hydrogeology, soil science, and petrology. However, a comparison of the literature reveals qualitatively different clogging behavior in different porous media: in granular media filters, increasing clogging is associated with slower flow, more flocculated conditions, and smaller fractal dimensions. In soils and dead-end membranes, increasing clogging is associated with faster flow, more dispersed conditions, and larger fractal dimensions. This paper documents these differences, discusses them in light of two key intermediate variables, colloid accumulation and deposit morphology, then presents a new conceptual model that explains the reported clogging phenomena as a function of specific deposit, fractal dimension, and a new variable, deposit location. Testing this model is possible using recently introduced experimental techniques.

Substrate-dependent evolution of a bacterial community capable of transforming nitrate was examined in sulfur-based autotrophic denitrification columns. The 16S rRNA genes and denaturing gradient gel electrophoresis (DGGE) analysis revealed that the initial bacterial consortium was well adapted to column operation time and distribution of nitrate concentration. In the lower part of a 200-day operated column where nitrate was introduced, a bacterial strain designated OTU DE-1 was abundant, occupying 92% of the community. The species was identified as Thiobacillus denitrificans with a similarity of 97% by BLAST search. A heterotroph designated as OTU DE-2 showing a similarity of 94% to Cenibacterium arsenoxidans was then enriched in the middle part of the column occupying 82% of the community, indicating the presence of organic electron donors. Interestingly, OTU DE-5 with a similarity of 98% to Chlorobium limicola, which is commonly present in hydrogen sulfide-rich environments, was found in the upper part of the column where sulfate level was high with little nitrate. The microbial community was consistent with observed concentrations of nitrate, nitrite, and sulfate with column height and operation time.

A new kinetic model has been proposed that describes the kinetics of the biosorptive processes. The proposed model is based on the concept of “available active sites.” The developed model has been investigated at different sorbent dose and temperature. Uptake of a cationic dye, Basic Violet 16 by a biosorbent prepared from the dead macrofungus, Fomitopsis carnea, has been considered to validate the model. This model has been used to determine the mass transfer coefficients under various sorption conditions. Sorbent concentration-time profiles generated by the model have been compared with the experimental data to validate the model. The model generated concentration profiles match the batch kinetic data closely.

Many biological water treatment plants for removal of iron and manganese from groundwater are in place for quite a long time, and thus their filters are aged—naturally coated with metal oxides and associated biomass. The particular reactivity and high adsorption capacity of these biogenic surface coatings make them potentially applicable for cost effective removal of arsenic and other heavy metals from contaminated water. However, the nature of interaction between various toxic elements and the composite materials in biological filters is not well understood. This study combines macroadsorption experiments with electron probe analysis to evaluate the adsorption properties of the biogenic surface coatings of an aged biofilter medium (BFM) for cationic lead and cadmium as well as arsenate anion. Results of batch adsorption showed that BFM has higher adsorption capacity for lead and cadmium as compared to arsenate anion. At pH 5.5, the maximum adsorption capacities of the medium for As(V), Pb(II), and Cd(II) were 17.03-, 80.77-, and 179.05-mg/g surface coatings, respectively. However, the column performance of BFM for Cd(II) was rather low. In particular, the breakthrough adsorption capacities $\left(q_b\right)$ of the BFM for As(V), Pb(II), and Cd(II) were 0.247-, 31.168-, and 4.084-mg/g surface coatings, respectively. These values represent about 1.5, 38.6, and 2.3% of the respective theoretical maximum adsorption capacities $\left(q_{\text{max}}\right)$ of BFM for these metals. Data from the X-ray electron probe analysis corroborated well with that of the macroadsorption experiments. Results of this study strongly suggest that the Mn/Fe ratio and the presence of preadsorbed competing ions were two of the principal characteristics of the BFM, governing its affinity and adsorption capacity for different toxic metals.

To optimize the design parameters of rectangular primary settling tanks, we used two-dimensional laser Doppler velocimetry (2D LDV) to conduct flow field measurements in five cases and used a previous model to simulate the flow field. The relative baffle submergence height and the ratio of tank length to height were optimized in a low suspended solid (LSS) concentration $\left(\text{LSS}<150–200\text{mg}/\text{L}\right)$ . The experimental and simulation results show that a large recirculation zone exists behind the reaction baffle and the flow magnitude is small in the recirculation region; the length of recirculation increases with an increasing flow rate; the length of recirculation increases as the depth of the submerged reaction baffle increases; and the variation of the reaction baffle height can affect the flow field more significantly than does the variation of the flow rate. We also determined that to reach a higher removal rate and to optimize the area dimensions of a sedimentation tank, a length-to-height design ratio between 8 and 12 is optimal.

An integrated fuzzy ranking analysis (IFRA) method was developed to help evaluate the quality of waste composts under a variety of system complexities and uncertainties. It combined the latent component analysis and ameliorated $G$ -index fuzzy relationship analysis into a general framework. The IFRA could handle different types of uncertainties, investigate the complex interrelationships among multiple indicators, and determine the best-quality product among a variety of alternatives. The IFRA was then applied to assess eight types of composts. An example standard was established in relation to potting grade and soil amendment. Two main policy scenarios were investigated. The obtained results could help decision makers distinguish the compost products by different usages, and distribute the products to appropriate markets. Moreover, the IFRA method could help promote new policies that would ultimately improve the marketing and development strategies for the composting industry.

Increases in stream temperatures by heated storm-water runoff from impervious surfaces are a serious environmental problem. An underground detention with slow-release facility is a versatile storm-water best management practice (BMP) for buffering high flows. Temperature reductions in underground storm-water storage BMPs, however, have not been quantified. A field study on an underground detention BMP located in Maryland was undertaken to characterize its effect on storm-water runoff temperatures. In colder months, when the runoff temperature ranged from 5 to $15°\text{C}$ , small or no temperature change was observed. Runoff produced during summer storm events, however, with event mean temperatures over $20°\text{C}$ , exhibited mean temperature reductions of $1.6°\text{C}$ through the BMP. While statistically significant, the reductions were not sufficient to cool the summer runoff discharges below the Maryland Class III temperature standard $\left(20°\text{C}\right)$ 100% of the time. The results indicate that underground facilities can moderate high runoff temperatures, but that more efficient designs are needed for heat transfer.

Treatment of storm-water runoff may be necessary before discharge to surface waters. In urban areas, space constraints limit selection of conventional treatment systems, and alternative systems are needed. This research program involves design and laboratory testing of a small footprint nonproprietary detention basin which consists of pipes and box culvert sections with a specialized inlet and outlet system. This system can be placed below grade near the roadway section as part of the conventional drainage system and does not require additional right-of-way. A mathematical model, based entirely on hydraulic principles, is developed to estimate particle removal efficiency of the rectangular detention basin for the treatment of storm-water runoff by extending ideal horizontal tank theory under the condition in which water level is varied. A physical model was built in 1/5 scale to measure particle removal performance and validates the conceptual model. Experiments were performed for steady inflow conditions with different inflow rates, durations, and suspended sediment concentrations. Measured time series outflow suspended sediment concentrations and particle removal efficiency compare well with calculated results from the conceptual model. The outflow particle-size distribution can also be estimated using the conceptual model.

Storm-water experts agree that the currently used best management practice (BMP) percent removal methodology metric has many flaws, and some have suggested using a BMP effluent concentration metric. This case study examines establishing an effluent target concentration for BMPs that relates to the health of macroinvertebrates in the receiving water. In North Carolina, 193 ambient water quality monitoring stations were paired with benthic macroinvertebrate health ratings collected in very close proximity. Water quality for the sites ranged from excellent to poor and was divided into three distinct ecoregions: Mountain, Piedmont, and Coastal. Statistically significant relationships were found in one or more ecoregions for dissolved oxygen, fecal coliform, ${\text{NH}}_3$ , ${\text{NO}}_{2-3}-\text{N}$ , total Kjeldahl nitrogen, total nitrogen (TN), and total phosphorus (TP). BMPs can then be selected and designed to meet these target effluent concentrations. Based upon this research, a development, and therefore set of BMPs, in Piedmont North Carolina could be required to release TN and TP effluent concentrations of 0.99 mg/L and 0.11 mg/L, respectively. These concentrations are both associated with “good” benthos health. The new method was most effective in the Piedmont ecoregion, however with more data collection, the Mountain and Coastal ecoregions may also benefit.

The Edward C Little Water Recycling Facility (ECLWRF) is the largest high-purity water recycling facility in the United States. Here, microfiltration (MF) membranes play a critical role in treating the secondary effluent and serving as pretreatment to the downstream reverse osmosis systems. New chemical clean-in-place (CIP) formulations were evaluated through pilot-scale tests for their ability to improve the performance restoration for the Phase III continuous MF (CMF) membranes at the ECLWRF. Membrane autopsies found that the primary fouling mechanisms for the CMF membranes were biological and organic in origin. It was also determined that the current CIP protocol provided an incomplete removal of the biological and organic foulants. The cleaning test results found that the current CIP regime for the Phase III system performed better than the four commercially available cleaning solutions evaluated here. However, improved results were obtained when hydrogen peroxide was added to the current CIP regime consisting of caustic soda and the commercially available Memclean C cleaning solution. The effects of the addition of hydrogen peroxide to the standard cleaning procedure shows some promise; however, further research is needed to understand the cleaning mechanisms and long-term effects of using hydrogen peroxide as a cleaning additive.

A variety of air pollution control strategies have been investigated to reduce mercury emissions from coal-fired sources. The most developed and deployed technologies are based on adsorption of mercury onto powdered activated carbon followed by carbon collection. Mercury oxidation over selective catalytic reduction catalysts followed by wet scrubbing is another potential technique, and tests suggest that emissions reductions of $20–\mathrm{80\%}$ are possible, but test results are variable and ultrahigh removal $\left(\mathrm{95\%}+\right)$ is unusual. The objective of this study was to investigate the effectiveness of electron beam irradiation to oxidize mercury vapor, to improve mercury removal with wet scrubbers or wet electrostatic precipitators (ESPs). Metallic mercury vapor samples in air and other atmospheres were prepared at concentrations of approximately $16\mu {\text{g/m}}^3$ . Samples were electron irradiated at energy levels of 2.5–10 kGy, equivalent to $3.1–12.4\text{kJ}/{\text{m}}^3$ stack gas. Results show that mercury oxidation rate was dependent on both the gaseous atmosphere composition and the irradiation energy level. At medium energy levels, approximately 98% of gaseous mercury vapor was readily oxidized. Electron beam irradiation demonstrated high levels of mercury oxidation at the bench scale, and the technology might help improve mercury removal in wet scrubbers or wet ESPs when employed as a primary or secondary mercury oxidation technique.