Journal of Environmental Engineering

The solute transport in a tropical, coastal aquifer of southern India is numerically simulated considering the possible cases of aquifer recharge, freshwater draft, and seawater intrusion using numerical modeling software. The aquifer considered for the study is a shallow, unconfined aquifer with lateritic formations having good monsoon rains up to about 3,000 mm during June to September and the rest of the months almost dry. The model is calibrated for a two-year period and validated against the available dataset, which gave satisfactory results. The groundwater flow pattern during the calibration period shows that for the month of May a depleted water table and during the monsoon month of August a saturated water table was predicted. The sensitivity analysis of model parameters reveals that the hydraulic conductivity and recharge rate are the most sensitive parameters. Based on seasonal investigation, the seawater intrusion is found to be more sensitive to pumping and recharge rates compared to the aquifer properties. The water balance study confirms that river seepage and rainfall recharge are the major input to the aquifer. The model is used to forecast the landward movement of seawater intrusion because of the anticipated increase in freshwater draft scenarios in combination with the decreased recharge rate over a longer period. The results of the predictive simulations indicate that seawater intrusion may still confine up to a distance of approximately 450–940 m landward for the scenarios considered and thus are sustainable.

Water quality is an important aspect of health assessment of rivers, lakes, and estuaries, which requires systematic data collection from various components of the aquatic environment. The analysis of this data is used to judge the health state of these environments. It is well known that long-term surveillance of surface waters is costly. Thus, sound strategies are necessary to select the best locations of monitoring stations to collect the most reliable data efficiently to improve the performance of a monitoring system. This can be accomplished by optimizing the location of monitoring stations with respect to the hydrodynamic and transport characteristics of the surface water system. It is expected that such an approach may improve the effectiveness and also reduce the overall cost of the monitoring system. Since the hydrodynamics and the contaminant migration pathways in surface waters are complex, the optimal solution of this problem is also complex. To analyze this problem, a two-dimensional hydrodynamic simulation model is developed using the finite-element method. The best monitoring locations are selected that minimize the detection time of the potential contaminant presence in the surface water body and maximizes the reliability of the system performance. Due to the nonlinear nature of the hydrodynamics, a genetic algorithm (GA) is used for the solution of the optimization problem. Examples are provided for wind-driven hydraulic circulation for a circular lake, and tidal and wind-driven circulation in a natural tidal estuary.

Coastal freshwater aquifers are highly vulnerable to climate change and other anthropogenic environmental impacts. Therefore, managing coastal freshwater for future use requires critical planning. This is especially true for small barrier islands where, in most cases, groundwater could be the only freshwater resource. In this study, the combined effects of climate change, land-use changes, and increased groundwater pumping on freshwater resources of a barrier island were studied. A case study was completed using the field data available for Dauphin Island, a small barrier island located in Alabama, U.S., and by using the simulation data generated from multiple water-resource-management models. Soil and Water Assessment Tool (SWAT) simulations provided recharge estimates under various future land use/land cover and climate-change scenarios. Downscaled global circulation model provided precipitation and temperature patterns for the period 2011–2030. The recharge estimates from SWAT were then used as input in a numerical groundwater model to evaluate saltwater-intrusion effects and forecast the changes in freshwater storage within the island aquifer system. Various groundwater-management scenarios were simulated using the MODFLOW-family computer code SEAWAT to assess the sensitivity of the groundwater system to increased pumping rates and decreased recharge due to climate change and/or future developments. SEAWAT was used to predict the lateral saltwater-intrusion effects and its impacts on groundwater quality and freshwater volume. The simulation results show that the saltwater wedge would advance laterally under all future climate-change scenarios. These results indicate that the shallow unconfined aquifer might not be able to sustain any significant future population growth, especially under adverse climate-change conditions. Analysis of changes in the volume of freshwater lens provided a broader understanding of the coupled effects of climatic and anthropogenic changes on freshwater storage and this information can be used to better manage Dauphin Island’s unconfined groundwater system.

Disinfection of hot water systems is critical in reducing the incidence of disease outbreaks caused by pathogenic bacteria. Electrochemical disinfection (ED) has been identified as an economical, low-maintenance, and chemical-free alternative in the fight against waterborne pathogenic microorganisms. It also provides the residual disinfection needed to inactivate the planktonic bacteria released by the biofilm. The work presented here includes fundamental small-scale laboratory optimization experiments in a flask where platinum-coated electrodes were immersed in 3.5 L of tap water contaminated with Escherichia coli (NCT10418) with an initial population density between $3\times {10}^5$ and $1.6\times {10}^5$ colony forming $\mathrm{units}/\mathrm{mL}$ ($\mathrm{CFU}/\mathrm{mL}$) or Legionella pneumophila serogroup 1 (NCTC12821) ranging from 180 to $244\mathrm{CFU}/\mathrm{mL}$. Voltage, electrode area, interelectrode distance, spiking time, volume of contaminated water, and mixer speed were varied to determine the optimal geometrical and operational requirements needed to kill bacteria. Experimental results indicate ED to be an effective control method, with a $>4$-log inactivation of E. coli and a $>5$-log inactivation of Legionella in 10 and 45 min, respectively, at a current density of $\approx 4\mathrm{mA}/{\mathrm{cm}}^2$. The findings of the flask experiments were translated into real-world conditions by evaluating the long-term performance of an optimized ED prototype device installed in the hot water recirculation system of a small-size healthcare center building. The results showed that ED is effective at minimizing pathogen contamination of the hot water distribution system from initial values, with total bacteria levels and Pseudomonas species being reduced in all of the samples over a 15-month period following activation of the ED device.

The overall goal of this research was to understand and quantify the impact of dissolved organic matter (DOM) quantity and character on the granular (GAC) adsorption of the carcinogenic volatile organic compound (cVOC) 1,2 dichloroethane (1,2 DCA). Three different groundwaters and one surface water were spiked with low concentrations of cVOCs ($0.1–50\mathrm{\mu g}/\mathrm{L}$) and treated with GAC using bench-scale flow-through adsorbers with empty bed contact times (EBCTs) of 7.5 and 15 min. Little difference—less than 10%—was found in breakthrough behavior as a function of EBCT. Relative to results in clean water, DOM reduced GAC capacity for 1,2 DCA by almost 50%. Unlike other efforts with low- and $\mathrm{sub}\text{-}\mathrm{\mu g}/\mathrm{L}$ influent target compound concentrations, this effort did not find normalized target compound breakthrough to be independent of influent concentration. The lack of an EBCT effect and dependence on influent 1,2 DCA concentration were attributed to the DOM’s weak adsorbing character and its low concentrations. Regressions to predict column breakthrough were created that combined a fluorescent indicator, a total organic carbon (TOC) mass term, and a target compound mass term from 19 column runs with $R^2$ values greater than 0.83.

Chemical oxidation is a promising approach for in situ or ex situ treatment of heavy, long-chain (${\mathrm{C}}_{12}{-\mathrm{C}}_{40}$) petroleum-hydrocarbon impacted soils. Aqueous chemical oxidation treatments (sodium percarbonate, hydrogen peroxide, sodium persulfate, chlorine dioxide, sodium permanganate, and ozone) using two oxidant concentrations were tested in batch tests on soils containing ${\mathrm{C}}_{12}{–\mathrm{C}}_{40}$ total petroleum hydrocarbon (TPH) concentrations of 1.6 and 2.0% weight/weight (w/w) resulting in TPH reductions from 20 to 90%. Gas chromatography with flame ionization detector (GC-FID) chromatograms for hydrocarbons were obtained and presented as chain-length fractions. Sodium percarbonate and hydrogen peroxide achieved the highest TPH reduction. There was little difference between 1 and 10% weight/volume (w/v) for all oxidant doses on TPH removal. Soluble organics in the liquid supernatants after oxidation of the TPH-containing soils were characterized by TPH analysis and excitation-emission matrix fluorescence spectroscopy. Benchmark Soil 1 (BM1) containing 1.6% w/w TPH was more susceptible to solubilization than Benchmark Soil 2 (BM2, containing 2.0% w/w TPH) according to TPH removal data and posttreatment supernatant quality. Some of the oxidants achieving the greater reduction in soil TPH resulted in higher aqueous phase organic content, based upon TPH measurements and fluorescence spectroscopy. Persulfate achieved intermediate TPH reduction in soil, but the separated aqueous phase had lower carbon content. This work showed chemical oxidation can transform and mobilize heavy hydrocarbons in soil and can produce more water-soluble organics. Chemical oxidation alone may achieve regulated TPH soil concentration, or it could also be used in conjunction with other technologies such as bioremediation or surfactant washing to further reduce TPH in soil.

Rain gardens are one of the technologies often recommended for residential stormwater management. It is not difficult to find rain garden design recommendations, but more difficult to find quantitative assessments of how effective these gardens are at reducing runoff. Analysis is presented to illustrate how well a common rain garden design would work when subjected to the hydrological and meteorological extremes experienced across the contiguous United States. Results of 3-year hourly continuous simulations indicate that, because of variations in the amount and pattern of precipitation, the effectiveness of comparable rain gardens would vary from about 51.3 to 99.8% across the contiguous United States. Identical gardens would be least effective in Atlantic and Gulf Coast states and most effective in northern Midwest and Mountain states. Results also indicate garden evapotranspiration and evaporation have a negligible impact ($<1\%$) on runoff reductions. This is true even for the warm, sunny climates of southwestern states. Results also indicate that, if common design recommendations on minimum infiltration rates are followed, it would be unlikely for standing water to persist in gardens long enough for mosquitoes to breed.

Based on experimental data, this study determined the water footprint of biodiesel production from freshwater microalgae cultivated in photobioreactors. The findings highlighted the necessity of recycling harvest water and applying undiluted wastewater to grow microalgae in efforts to save freshwater resources. Without water recycling, approximately 3,494 kg freshwater was required to produce 1 kg microalgal biodiesel. By contrast, recycling harvest water at the degree of 50 and 100% to regrow microalgae could reduce the water utilization by 39.4 and 93.0%, respectively. The results also showed that using undiluted wastewater to grow microalgae could decrease the usage of freshwater by 93.7%, reaching as low as $219\mathrm{kg}\mathrm{water}/\mathrm{kilogram}$ microalgal biodiesel produced. Factors that affect the water footprint of microalgal biodiesel production were also discussed in this study.

Nanozero-valent iron/activated carbon (nZVI/AC) composite is investigated as a possible stabilization agent for heavy metals in river sediment. Effects of stabilization were tested by leaching tests such as synthetic precipitation leaching procedure (SPLP), atoxicity characteristic leaching procedure (TCLP), and a horizontal method that simulates various environmental conditions. In addition, changes in heavy metal forms before and after the addition of nZVI/AC were studied via sequential extraction method. Heavy metals such as Cu, Cd, and Pb were effectively stabilized by nZVI/AC. The stabilization could be attributed to the changes in bonding of heavy metal with sediment. The nZVI/AC in sediment increased the fraction of strongly bound heavy metals. Investigations on the impacts of nZVI/AC dosage, particle size, and time on stabilization and metal speciation showed that they all had significant effects. Generally, leaching dropped as dosage increased and a high dosage led to more metals in strong bindings with sediment. Particles of size 0.075–0.12 mm manifested the highest stabilization. Tests on the long-term stabilization effect revealed that nZVI/AC stabilization was stable over long period of time and no increase in leaching was observed for up to 150 days.

Magnesium hydroxide $[\mathrm{Mg}(\mathrm{OH}{)}_2]$ is a commonly used chemical for controlling corrosion and odor problems in sewers by reducing the transfer of hydrogen sulfide from the liquid to the gas phase through pH elevation. The effectiveness of many current dosing practices is unsatisfactory due to negligence of the dynamics of sewage flow and characteristics, and their effects on sewage pH. This paper reports the design and validation of the first online control algorithm for $\mathrm{Mg}(\mathrm{OH}{)}_2$ dosing to sewers. The control algorithm consists of a combination of feedforward and feedback loops. A feedback controller is used to calculate the $\mathrm{Mg}(\mathrm{OH}{)}_2$ dosing rate to raise the sewage pH at the pumping station to the set-point. A feedforward controller is then used to calculate the additional $\mathrm{Mg}(\mathrm{OH}{)}_2$ dose based on the prediction of acid production in the downstream sewer pipe due to in-sewer processes. A further feedback controller is used to adjust the $\mathrm{Mg}(\mathrm{OH}{)}_2$ dosing rate to correct the error between the sewage pH at the end of the pipe and the pH set-point. Following comprehensive assessment using modeling and simulation, the control was successfully validated and its effectiveness demonstrated in a 2-month field study. The online control algorithm reduced the variation of pH at the discharge point, i.e., from $8.73\pm 0.21$ to $8.59\pm 0.10$. In addition to improved sulfide control, the controller also resulted in 15% saving in chemical consumption, leading to significant financial benefits and lower environmental footprint. It was also found that the sewage flow rate should be predicted online for sewers influenced by rainwater infiltration as the variation of flow rate and sewage dilution are important disturbances for the controller.

Sewerage management in pilgrimage cities has been a challenging task because the sudden influx of pilgrims exerts tremendous pressure on the sewer system. It is a much more challenging problem in the city of Karbala, Iraq, where the number of pilgrims during peak pilgrimage days is gradually increasing because of the rapid growth of the Muslim population due to their improving economic status and mobility. The objective of the present study is to investigate the impact of population on sewer flow in Karbala. A multiple linear regression based on a statistical analysis approach is used to quantify the impacts of population variation in sewer flow in Karbala. The results show that sewer flow in the city typically increases around $0.0115{\mathrm{m}}^3/\mathrm{s}$ for every increase by 1,000 in population. This will be a helpful calculation in understanding, predicting, and abating sewer overflow problems in Karbala.

A study of the existing state and the challenges encountered in Medina Al-Munawarah sewage treatment plant has triggered the need for a better sludge management system. The climatic data revealed on site, with a yearly average solar radiation of $6.05\mathrm{kWh}/{\mathrm{m}}^2/\mathrm{day}$, and air temperature and relative humidity of 299.2 K and 28%, respectively, in addition to the capital and operating financial factors, had favored the use of solar drying application as an appropriate mean to treat $100\times {10}^6\mathrm{kg}$ (20% dry solids) of mechanically dewatered sludge yearly. By applying the principles of exchanging heat and energy in a $\mathrm{25,000}{\mathrm{m}}^2$ of covered solar drying cells, a minimum total water evaporation rate of $\mathrm{3,000}\mathrm{kg}/{\mathrm{m}}^2/\mathrm{year}$ can be reached. In this process, the sludge will be dried until an 80% solid content is achieved. The stabilized product, brought to a reduced mass and pathogen content, is now an asset to be used in various uses, allowing Medina Al-Munawarah to sustain its future green plans.

Bioretention has been found to treat many pollutants, but nitrogen is difficult to control. A modified bioretention system with an internal water storage zone to encourage denitrification was installed in a silage storage area at the University of Connecticut in Storrs, CT. Flow volumes were measured and flow-weighted samples were analyzed for total nitrogen (TN). The median TN concentration at the inlet was $12.3\mathrm{mg}{\mathrm{L}}^{-1}$ (mean 12.3), whereas median outlet TN concentration was $4.0\mathrm{mg}{\mathrm{L}}^{-1}$ (mean 5.1). Outlet concentrations were significantly ($p<0.001$) lower than inlet concentrations, with a 67.3% reduction in the median TN concentration. TN mass was reduced by 61.6%. Results indicate that this modified bioretention could be used in urban or agricultural areas to reduce N loading to receiving waters.

Two 4-L anaerobic moving bed–biofilm reactors (AMBBR) with different quantities of cubic media (25 and 35% by volume) were examined. Reactors were fed synthetic protein-based feed and both were shown to be capable of treating up to $20\mathrm{kg}/{\mathrm{m}}^3\mathrm{day}$ of chemical oxygen demand (COD), achieving 80% COD removal. Beyond that load the performance began to decrease. The maximum biogas production observed was $9.25{\mathrm{m}}^3{\mathrm{CH}}_4/{\mathrm{m}}^3\mathrm{day}$ at an organic loading rate (OLR) of $20\mathrm{kg}\mathrm{COD}/{\mathrm{m}}^3\mathrm{day}$. The methane composition varied between 60 and 70%. Averaged methane yields of $0.36\pm 0.07{\mathrm{m}}^3{\mathrm{CH}}_4/\mathrm{kg}\mathrm{COD}$ removed and specific removal rates from 0.4 to $20\mathrm{kg}\mathrm{COD}/{\mathrm{m}}^3\mathrm{day}$ were achieved. At the maximum OLR above $20\mathrm{kg}\mathrm{COD}/{\mathrm{m}}^3\mathrm{day}$, the specific surface area activity was calculated as 98 and $75\mathrm{g}\mathrm{COD}/{\mathrm{m}}^2\mathrm{day}$ in the 25 and 35% reactors, respectively. Kinetic tests performed at the maximum OLR revealed that free-floating suspended biomass contributed to no more than 2.5% of the total removal. The reactors were also capable of treating brewery wastewater, reliably attaining 80% COD removal with methane yields of $0.36\pm 0.06$ and $0.39\pm 0.03{\mathrm{m}}^3{\mathrm{CH}}_4/\mathrm{kg}\mathrm{COD}$ from the 35 and 25% reactors, respectively.