Journal of Environmental Engineering

A dual-staged nanofiltration process is being evaluated as an alternative to reverse osmosis for seawater desalination. The primary goal of this system is to reduce energy consumption while producing potable water at an acceptable recovery rate. Investigation of this system at the bench-scale level focused on membrane surface characterization, ion rejection (including boron, bromide, and iodide rejection), and flux decline. Results from this study showed that two commercially available nanofiltration membranes can effectively desalinate seawater. Although fouling was apparent—and resulted in approximately 20% flux decline over 3 days—a critical flux was not identifiable. Operation of the system at different cross-flow velocities revealed the significance of hydrodynamic conditions on the polarization modulus, and hence on membrane performance.

This modeling study evaluated the aquatic environment affected by the Chernobyl nuclear accident and the effectiveness of remediation efforts. The study results indicate that radionuclide concentrations in the Pripyat and Dnieper rivers were well above the drinking water limits immediately after the Chernobyl accident but have decreased significantly in subsequent years due to flushing, burying, and decaying. Because high concentrations of ${}^{90}\mathrm{Sr}$ and ${}^{137}\mathrm{Cs}$ , the major radionuclides affecting human health through the aquatic pathways, are associated with flooding, two earthen dikes were constructed along the Pripyat River. The left-bank dike alone was successful in reducing the ${}^{90}\mathrm{Sr}$ concentration in the river by half. The $100\text{-}\mathrm{m}$ -high, movable New Safe Confinement (NSC), which will cover the current Chernobyl Shelter, will reduce radionuclide contamination further in these rivers and nearby groundwater. If the Chernobyl Shelter should collapse before the NSC is built, the resulting peak radionuclide concentrations in the Dnieper River are expected to still remain below the drinking water limits. The radionuclide influx to groundwater through the NSC should not have any effect on concentrations in the Pripyat River.

The probabilistic flow within capillary barrier models is evaluated by coupling a first-order reliability (probabilistic) model to a variably saturated flow model. The objective is to determine the most significant uncertain variable to probabilistic flow and the effect of different textural combinations. The model inputs include the mean and standard deviation of each uncertain variable. The van Genuchten curve-fitting model for unsaturated flow is used. The uncertain flow variables are saturated water content, residual water content, saturated hydraulic conductivity, and model parameters alpha $\left(\alpha \right)$ and $\mathbf{n}$ . A clay loam soil sample overlying a loamy sand sample, a clay loam sample overlying a sand sample, and a loamy sand sample overlying a sand sample are used to represent finer soils overlying coarser soil. Evaluations near the textural interface show that model parameters alpha $\left(\alpha \right)$ and $\mathbf{n}$ =most significant uncertain variables. These are related to the water entry pressure and the width of pore size distribution of the soils. Generally, soils that have the least uniform pore size distribution are the most effective capillary barriers. In this study, the clay loam overlying loamy sand satisfied this condition and performed better than the other soil combinations.

The solute transport equation is commonly used to describe the migration and fate of solutes in a groundwater flow system. Depending on the problem nature, the source of the solute may be represented as a point source term in the equation or specified as the first-type or third-type boundary condition. The solutions derived under the condition that the solute introduced into the flow system is from the boundary is herein considered as the boundary-source solutions. The solution obtained when solving the transport equation with a point-source term is considered as the point-source solution. The Laplace transform technique is employed to derive the formulas for those solutions expressed in terms of the normalized mass release rate. The underlying nature of different source release modes and the differences among those boundary-source solutions and the constant point-source solution can be easily and clearly differentiated based on the derived formulas for one-dimensional transport. The methodology could, however, be easily extended to two- and three-dimensional problems.

As landfills mature, biodegradable matter in leachate is consumed and remaining compounds are increasingly recalcitrant. In this work, ferrate was compared to Fenton’s reagent for the purpose of removing nonbiodegradable organic compounds from mature leachate. Oxidation conditions (time, pH, and dose) were optimized to yield maximum organic removal using two leachate samples from 20- and 12-year-old solid waste cells. Results from this study demonstrated that Ferrate and Fenton’s reagent had similar optimum pH ranges (3–5), but different organic removal capacities, ranging from 54 to 79% of initial leachate organic contents. An advantage of ferrate was that it was effective over a wide pH range. Advantages associated with Fenton’s reagent include that it had higher organic removal capacity, produced more oxidized organic compounds (measured as chemical oxygen demand/dissolved organic carbon), and produced more biodegradable byproducts (measured as chemical oxygen demand/5-day biochemical oxygen demand). Finally, both treatments were found to attack larger molecules $(>\mathrm{1,000}\mathrm{Dalton})$ , as indicated by an increase in smaller molecule contribution to organic carbon.

In ice-covered rivers, dissolved oxygen (DO) might fall below critical levels for aquatic biota in the absence of surface aeration, combined with low winter flow conditions and reduced photosynthesis rates. Open-water zones, however, can be created downstream of a diffuser by warm effluent discharges, resulting in an increase in surface aeration. In this study, we modeled the behavior of the effluent plume and the resulting open-water lead development in the Athabasca River, Alberta, Canada downstream of a pulp mill diffuser. The DO was found to increase by $0.26\mathrm{mg}∕\mathrm{L}$ due to surface aeration of an open-water lead of $6.07\mathrm{km}$ . We also evaluated oxygen injection into the effluent pipeline to increase the DO in the river. At an injection rate of 3,500 and $\mathrm{5,000}\mathrm{lb}∕\mathrm{day}$ of liquid oxygen, the DO was increased by 0.16 and $0.21\mathrm{mg}∕\mathrm{L}$ , which corresponded to an absorption efficiency of about 50%. The artificial aeration technique evaluated here appears to be an effective alternative to increase DO levels in ice-covered rivers. The results of this study are important in developing accurate DO models for ice-covered rivers and in evaluating oxygen injection systems.

The marshland upwelling system (MUS) is an alternative onsite wastewater treatment system developed for coastal communities. The phosphorus treatment efficiency of the MUS operated under high background salinity conditions $(\sim 32\mathrm{ppt})$ was examined over the course of a one-year field study. Five individual studies were investigated by intermittently injecting wastewater at a depth of $3.8\mathrm{m}$ using flow rates/injection frequency regimes of $1.9\mathrm{L}∕\min$ $(30\min ∕3\mathrm{h})$ , $5.5\mathrm{L}∕\min$ $(30\min ∕3\mathrm{h})$ , $2.8\mathrm{L}∕\min$ $(30\min ∕3\mathrm{h})$ , and $2.8\mathrm{L}∕\min$ $(15\min ∕\mathrm{h})$ . There were two studies conducted within the $2.8\mathrm{L}∕\min$ $(30\min ∕3\mathrm{h})$ flow regime: (1) with normal influent and (2) with high strength synthetic wastewater. Over the course of the study, no signs of phosphorus saturation were observed. The overall system efficiency for the entire study was estimated to be $>98\%$ . Removal rate coefficients ranged from 0.73– $1.25{\mathrm{m}}^{-1}$ and 0.66– $1.08{\mathrm{m}}^{-1}$ for total phosphorus and orthophosphate, respectively. Upon completion of the final $2.8\mathrm{L}∕\min$ $(15\min ∕\mathrm{h})$ study, it was determined that a travel distance of only $9.4\mathrm{m}$ would be needed to reduce influent concentrations below $0.1\mathrm{mg}\mathrm{P}∕\mathrm{L}$ .