Journal of Environmental Engineering

A box-type transport model can be a useful tool for screening-level, long-term predictions of contamination and the relevant environmental assessment, especially when data are scarce and quick decisions are needed. In most box-type transport models, only advective flux is simulated to account for the interaction between boxes. In reality, however, significant mass transfer may also occur through the boundary between two boxes as a result of dispersion. For volatile contaminants (e.g., pesticides), the mass transfer through the boundary may involve both dissolved and vapor phases. In this study, an improved box-type analytical pesticide transport model with dispersive flux through the boundary layer (APTM-DF) was developed for simulating fate and transport of three-phase pesticides in the vadose zone, which was further divided into the surface zone, plant root zone, and deep vadose zone. The model also simulated pesticide leaching, degradation, volatilization, sorption, partition between dissolved and vapor phases, plant root uptake, runoff, and erosion. Analytical solutions were derived for both instantaneous and continuous pesticide applications. The performance of APTM-DF was evaluated in an application by comparing it with a regular APTM (no dispersive flux) and an integrated pesticide transport model (IPTM-CS) that provided detailed spatial and temporal distributions of pesticides. The modeling results indicated that, without accounting for dispersive flux through the boundary layer, pesticide exposure levels in deeper soil were significantly underestimated.

Accurate information about contaminant plume migration in the subsurface plays an important role in risk assessment and emergency response during site remediation. Rapid emergency response during severe soil contamination can help to reduce the extent of damage and the risk of groundwater contamination. The use of subsurface contaminant transport models, coupled with stochastic data assimilation schemes, can provide accurate prediction of contaminant transport to enhance the reliability of risk assessment in the area of environmental remediation. In this study, a two-dimensional deterministic model is used to simulate the advective and diffusive transport of benzene in the subsurface. A robust adaptive Kalman filter (AKF) is constructed as a stochastic data assimilation scheme to improve the prediction of the benzene contaminant plume. The AKF has been proposed to overcome the limitations of the conventional Kalman filter (KF) by reducing the uncertainties associated with the process and observation noise statistics. The impact of the adaptive filter on the KF performance is examined by comparing model predictions with a simulated true field, which is created by introducing random noise into an observation model. The results show that the KF data assimilation scheme can give a more accurate prediction of the benzene plume than the conventional numerical approach although its prediction accuracy is minimal in comparison to the AKF scheme. The KF scheme reduces the root-mean-square error (RMSE) of the plume estimate from $5.0$ to $1.1\mathrm{mg}/\mathrm{L}$ at the end of the 10-day simulation. Furthermore, by constructing the AKF data assimilation scheme, the prediction error of KF reduces from $1.1$ to $0.9\mathrm{mg}/\mathrm{L}$, indicating 18% improvement in prediction accuracy. Also, the results of the sensitivity test suggest that filter stability and accuracy greatly depends on the window size, which must be specified to start the adaptive process.

The concept of using lumping analysis to reduce the complexity associated with the sorption of 12 neutral organic compounds (NOCs) comprising complex mixtures to simulated aquifer sorbents was evaluated. The sorbates covered a wide range of octanol–water partitioning coefficients, $K_{ow}$ (i.e., $-0.24\le \log K_{ow}\le 4.23$), and the sorbents included different types of mineral surfaces and humic acid–mineral complexes with different fractions of organic carbon, $f_{oc}$ (i.e., $0.006\%\le f_{oc}\le 0.221\%$). Both a priori lumping criteria (i.e., the aqueous activity coefficient at saturation ${\gamma }_w^{\mathrm{sat}}$, and the organic carbon partitioning coefficient, $K_{oc}$) and experimentally derived lumping criteria (i.e., Freundlich sorption parameters) were evaluated as potential lumping criteria. The results indicated that the sorption behavior of the 12 NOCs contained in mixtures could be approximated reasonably well by lumping them into a fewer number of pseudocompounds (four to six) with similar sorption behaviors based on Freundlich sorption parameters, and that both ${\gamma }_w^{\mathrm{sat}}$ and $K_{oc}$ could be used as viable a priori lumping criteria. However, the number and compositions of the pseudocompounds were a complex function of the hydrophobicity (i.e., ${\gamma }_w^{\mathrm{sat}}$ and $K_{oc}$) of the NOCs and varied as a function of the type of mineral surface (e.g., uncoated, $\alpha$-FeOOH-coated, and ${\mathrm{Al}}_2{\mathrm{O}}_3$-coated sands) and the $f_{oc}$ of the sorbent.

This study investigates the role of turbulence and temperature on changes in chemistry (dissolved ${\mathrm{Ca}}^{2+}$ and pH) of leachate within transmission pipes in bioreactor landfills, using synthetic and real leachate from the Brady Road Landfill in Winnipeg, Manitoba. Sealed reactors with rotating propellers were used to mimic leachate flow through the transmission pipes. The reactors were operated under turbulent conditions at 32, 83, and 180 rpm for 6 h on and 18 h off to represent the daily leachate injection operation of a general landfill. A control reactor was operated parallel to the reactors at 0 rpm. During the Off phase, the reactors were either sealed or open to the atmosphere. Under sealed conditions and pH values lower than 7.2, no significant changes in chemistry were observed for the synthetic or real leachate. However, for the mixers and control reactors containing real leachate at pH values higher than 7.4, pH dropped approximately by 0.3–0.4 units. This is explained by ${\mathrm{Ca}}^{2+}$ removal as ${\mathrm{CaCO}}_3$ decreasing the carbonate buffering capacity of the leachate, outcompeting the re-equilibration of ${\mathrm{CO}}_2$ evolved to the headspace of the reactors and its pH effect. The geochemical modeling software MINEQL+ was used to verify this interpretation, showing the same pH trend. Under open conditions, ${\mathrm{CO}}_2$ evolution, as it equilibrated with the atmospheric concentration, was responsible for increasing the pH by one unit for the synthetic leachate and between 0.35 to 0.45 units for the real leachate. The control reactor also exhibited an increased of pH under open conditions for the synthetic and real leachate. This shows that temperature had a significant impact on ${\mathrm{CO}}_2$ evolution and leachate pH, and may also affect the concentration of dissolved ${\mathrm{Ca}}^{2+}$ within the leachate, accumulating as inorganic solids similar to those clogging the leachate transmission pipes.

To predict climate-induced change in aquatic environments, it is necessary to understand the thermal constraints of various fish species and to understand the timing of current and projected coastal temperatures. This paper presents a newly developed model of the relationship between air and water temperature that was constructed on the basis of harmonic analysis. The model is novel because it requires only a single variable (air temperature) to predict water temperature and captures the hysteresis patterns of the rising and falling limbs and their historic memories. The model was calibrated and validated with data collected from monitoring buoys in Mikawa Bay, Japan between 2005 and 2009. The model validation showed a good performance with a root mean squared error (RMSE) in the range of 0.8–1.0°C. It is especially encouraging that the suggested model can predict water temperature with a reasonable level of accuracy once an acceptable relationship between air temperature and water temperature has been constructed from previously measured data.

Because a baffle is a device used for altering the flow pattern in a tank, the use of a baffle wall was considered to modify an existing potable water service reservoir operating as a storage tank to achieve better water quality. Therefore, it is of great interest to study the effects of baffle configurations on the performance of the service reservoir. With the advancement of computational science and resources, a Computational Fluid Dynamics (CFD) method has become a reliable alternative to flow and tracer tests. Adopting dynamic meshes, this study investigates the effects of baffles, located at various locations, on the flow pattern and chlorine concentration distribution of a potable water service reservoir in Singapore during the refilling phase. The results of this study show a dual effect of the baffles located at the flow recirculation region. On one hand, it can break up the vortex to shorten the flow path. On the other hand, the velocity magnitude of the fluid is reduced after flowing past the baffle, because of the impact and viscous forces induced by the baffle. These two effects are contradictory to one another in enhancing the performance of the service reservoir acting as a storage tank, because short flow path and high velocity magnitude is preferred to achieve better water quality. The overall effect of baffling is found to be counter-productive in this feasibility study. The results also demonstrate the importance of studying the effects of baffle configurations under dynamic flow condition.

To maintain the effectiveness of a storm-water detention/retention pond, the sediments accumulating at the bottom the pond must be periodically removed and treated for ultimate disposal. The required pond clean-outs may be executed during the winter months to minimize the impact on the pond’s operation and the recreational use of surrounding areas. However, the difference in trace element concentrations of storm-water sediments between the winter and summer months has not been fully investigated because most earlier studies focused on the summer season and sediment samples were seldom collected during the winter months. In this study, sediment samples were deliberately collected during both the winter and summer seasons at the same location. Neutron activation analysis (NAA) and prompt gamma ray techniques were used to determine the trace element concentration in the sediment samples, while a laser diffraction particle size analyzer and an optical microscope were used to analyze the sizes and shapes of sediment particles. The results show that the concentrations of Al, Na, and Cl in the winter samples are higher than those in the summer samples, while the concentrations of Ca and Mg in the summer sediment samples are higher than those in the winter sediment samples. The five regulated elements in both the summer and winter samples are higher than the Lowest Effect Level defined for sediment quality by the Government of Ontario, Canada. In the winter sample, the concentration of Cr is even higher than the Severe Effect Level. The concentrations of other detected elements are same level of concentration between the winter and summer sampled sludges.

Because of their consistently high effluent quality, small footprint, and robustness to variations in influent quality, membrane bioreactors (MBRs) have become the technology of choice for small-scale reuse applications, such as in office buildings, hotels, and on cruise ships. The emergence of these systems arises from a number of drivers: lack of sewerage infrastructure, requirement for planning permission, subsidies, new guidelines for green buildings, and the public profile of recycling generally. This paper details the design and operation of a small-scale MBR providing $25{\mathrm{m}}^3·{\mathrm{d}}^{-1}$ of reclaimed water for toilet flushing and irrigation. Operational experience and outcomes from a 2-year evaluation period are included. An economic analysis of operational expenditures (OPEX) is also presented, revealing that for a plant of this scale, staffing costs account for the largest component (53%) of the OPEX followed by energy consumption (28%). The optimum design of these systems should therefore be focused on reducing operational complexity to minimize manual intervention.

Before the Gulf War, the population of Iraq enjoyed a relatively high level of water supply and sanitation services. The sector operated efficiently, utilizing then-current technologies. Since, the water supply and sanitation sector has experienced a steady but devastating decline. Aging infrastructure, poorly maintained equipment, leaking water and sewer networks, and low technical capacity and morale are some of the key problems of the sector. The lack of funding led to insufficient imports, lack of maintenance, and curtailment of needed expansion. These services were surpassed by other national priorities, which resulted in a serious degradation of the quality and extent of services delivered. Diseases associated with poor sanitation, unsafe water, and unhygienic practices had increased to alarming rates. For the purpose of this study, samples were collected from eight stations along the Tigris River. The major sources of data are the Ministry of Environment, Ministry of Health, and Ministry of Water Resources. Various statistical techniques, for example, student’s t-test, Kendall’s test, trend test, ANOVA test, are used to determine the water quality of the Tigris River. The cities lying in the outskirts of Baghdad are found in poor condition in terms of water supply and sewerage. In central Baghdad, the water treatment plants are satisfying the standard conditions but the water supply network is in a poor condition.

Hydrogen peroxide (${\mathrm{H}}_2{\mathrm{O}}_2$) is suggested to be an environmentally benign chemical that may be used for wastewater purification. A recent study on the application of ${\mathrm{H}}_2{\mathrm{O}}_2$ in a wastewater stabilization pond (WSP) showed that ${\mathrm{H}}_2{\mathrm{O}}_2$ is a promising method to decrease high amounts of potentially toxic cyanobacteria. However, WSPs are complex biological systems that require healthy bacterial, phytoplankton, and zooplankton communities for optimal performance. Therefore, if ${\mathrm{H}}_2{\mathrm{O}}_2$ is to be regularly used in WSPs, its effect on all components of a healthy WSP food web, including zooplankton, must be assessed. This study quantifies the acute toxicity of ${\mathrm{H}}_2{\mathrm{O}}_2$ to Moina and Daphnia, two zooplankton genera that are common in WSPs in Western Australia’s Mediterranean climate. The results indicate that Daphnia carinata is less susceptible to ${\mathrm{H}}_2{\mathrm{O}}_2$ than Moina sp., as mean survival time was significantly higher at concentrations $\ge 2\mathrm{mg}{\mathrm{H}}_2{\mathrm{O}}_2/\mathrm{L}$. Additionally, the $\mathrm{L}{\mathrm{C}}_{50}$ was $5.6\mathrm{mg}{\mathrm{H}}_2{\mathrm{O}}_2/\mathrm{L}$ in Daphnia and $2\mathrm{mg}{\mathrm{H}}_2{\mathrm{O}}_2/\mathrm{L}$ in Moina, whereas the no observed adverse effect concentration (NOAEC) was 3 and $1.5\mathrm{mg}{\mathrm{H}}_2{\mathrm{O}}_2/\mathrm{L}$ for Daphnia and Moina, respectively. These values are below ${\mathrm{H}}_2{\mathrm{O}}_2$ doses that effectively removed toxic cyanobacteria from WSPs, and therefore indicate the urgent need to critically assess the effect of ${\mathrm{H}}_2{\mathrm{O}}_2$ on biological communities during field trials to ensure continuous performance of WSPs.