Journal of Environmental Engineering

Denitrification drainage bioreactors are emerging as an innovative practice to address water quality concerns stemming from nitrate leaching from drained agricultural lands. Although installation of these systems has begun in farms in the midwestern United States, the understanding of their design and in-field performance remains deficient. This study utilized a set of pilot-scale drainage bioreactors to evaluate the impact of bioreactor geometry on reactor hydraulic properties and to determine nitrate removal under steady-state conditions and during a simulated storm event. Bioreactors with different cross-sectional geometries but similar depths and total volumes were evaluated. The percent reduction of the influent nitrate mass was linearly correlated to the theoretical hydraulic retention time (HRT) with 30 to 70% ${\mathrm{NO}}_{3^{-}}\mathrm{\text{-}}\mathrm{N}$ removals observed within the 4 to 8 h of retention time suggested for field installations. Tracer tests revealed that in situ HRTs were at least 1.5 times larger than theoretical HRTs.

Contamination of groundwater by radioactive contaminants can be harmful to the environment. Various prediction models have been adopted to simulate the state of contaminants in the subsurface. Conventional numerical models are simplified by approximation and the model parameters are assumed to be constant, thereby introducing error to the prediction results. Particle and Kalman filters are used in this research to simulate the radioactive contaminant cobalt-57 transport in a subsurface environment by using a two-dimensional advection-dispersion model. A radioactive contaminant concentration was predicted spatially and temporally within boundary conditions. The errors in the prediction results were assessed by using the root-mean-square-error (RMSE) equation. The results show that the Kalman filter performs better than the particle filter when the prediction model is linear. Furthermore, the results from filters are closer to the true value in comparison with the numerical solution, and the filters are capable of reducing the RMSE of the numerical solution by approximately 80%.

Near-field mixing downstream of a multiport diffuser in a wide shallow river was studied with a field dye test. Dye concentrations at different depths and lateral locations were measured. The near-field mixing was analyzed in four zones: the free jet zone, the jet surface-impingement zone, the merging zone, and the vertical mixing zone. Analytical models were proposed to derive the three-dimensional concentration field after the jets impinged the water surface. After the impingement, the dye concentration can be predicted well by treating the multiple jets as a simple mathematical summation of individual jets. The vertical mixing zone was dominated by the riverbed friction-induced turbulence, with little effect from the effluent momentum and buoyancy. The results of the field data were also used to validate the applicability of some existing models for multiport diffusers.

The generation of reactive species in activated persulfate systems under different conditions of basicity was investigated using three probe compounds. Anisole was used to detect both sulfate radical and hydroxyl radical. Nitrobenzene was used to detect hydroxyl radical, and hexachloroethane was used as a reductant probe. Minimal probe compound degradation occurred in persulfate reactions conducted at $\mathrm{pH}\le 10$, demonstrating that a low flux of reactants is generated at acidic, neutral, and slightly basic pH regimes. In persulfate reactions at pH 12, sulfate and hydroxyl radical were generated but minimal reductants were produced. Scavenging studies showed that the dominant reactive species at basic pH was hydroxyl radical. The generation of reductants increased at high molar ratios of base to persulfate; however, hydroxyl radical generation rates increased only when molar ratios of base to persulfate were $>3:1$. The results of this research demonstrate that the hydroxyl radical is the dominant reactive oxygen species in base-activated persulfate formulations and that overall reactivity increases with increasing base:persulfate ratios.

Laboratory and full-scale experiments were conducted to investigate the development and effect of heterogeneity caused by filter media nonuniformity, biofilm, particles, precipitates, and gas bubbles in rapid sand filters used for drinking-water treatment. Salt tracer experiments were conducted in laboratory columns and in a waterworks, where a new tracer method for rapid sand filters was developed. Pore-water velocities and dispersivities were estimated by fitting an analytical solution to the measured breakthrough curves. Results of the column experiments showed an increase in average longitudinal dispersivity of more than 33% in the 116 h after the start of filtration with a constant pore-water velocity and a zero-order nitrification rate of $9\mathrm{mg}\mathrm{N}/\mathrm{L}/\mathrm{h}$. The full-scale experiments showed that the rapid sand filter was heterogeneous with pore-water velocities ranging from 2.2 to $3.3\mathrm{m}/\mathrm{h}$ for the same inlet flow. A first-order nitrification reaction with spatially variable pore-water velocity could be interpreted as a zero-order reaction with a constant pore-water velocity. A model demonstrated that filter heterogeneity could result in higher filter outlet ammonium concentrations.

This study demonstrates yet another innovation in the application of multivariate analysis to the understanding of regional hydrochemical processes in a tropical setting. Sequential Q-mode hierarchical cluster analysis (HCA) and factor analysis were used jointly with geographic information systems (GIS) and conventional graphical methods to determine spatial groundwater types in Ghana, and the spatial variation of the major sources of hydrochemical change in groundwater in Ghana. This study finds that two major groundwater types exist in the country: the Na-Cl groundwater types, which dominate the coastal aquifers where groundwater salinity is high, and Na-K-$\mathrm{HC}{\mathrm{O}}_3$ groundwater types, which dominate aquifers farther inland. The major source of variation in hydrochemistry of groundwater in Ghana is mineral weathering and saline water intrusion. Silicate mineral weathering has strong effects in the more inland aquifers whereas saline water intrusion has the greatest effects along the coast. Chemical fertilizers, organic manure, and domestic sewage represent the second-most important source influencing groundwater hydrochemistry in Ghana. Effects of these are highest in areas where aquifers are relatively shallow and chemicals are heavily used, such as the Keta Basin. The third-most important source is the oxidation of organic carbon by nitrate. Maps showing the variation of these three sources across the country have been generated using ordinary kriging and are discussed here.

This study presents the first water quality indexes developed to evaluate surface water in Vietnam. The basic water quality index (${\mathrm{WQI}}_B$) can be effectively used to evaluate the spatial and temporal variations of surface water quality as well as to identify water pollutants. The overall water quality index (${\mathrm{WQI}}_O$) can provide additional information, particularly on toxic substances contributing to water pollution. The water quality indexes developed for this paper were applied to the national surface-water quality monitoring data taken from 1999 to 2007. Water pollutants were classified into three subcategories: organic and nutrients, particulates, and bacteria. Surface water in northern and central Vietnam was poor in quality and contained organic matter, nutrients, and bacteria. Water in the southern part was mainly polluted by bacteria. Trend analysis results reveal a deterioration in water quality in those provinces under pressure from rapid population growth, urbanization, and industrialization. Vietnam has established an official policy to ensure comprehensive nationwide water quality monitoring by 2020. The implementation of water quality indexes may provide the guiding data for sustainable water-resources management in Vietnam.

This paper presents a novel design concept for using rock filters as in-line natural media in waste stabilization ponds. A pilot-scale algae-rock-filter pond (ARP) system was investigated in parallel with algae-based ponds (ABPs) over a period of 6 months to evaluate the treatment efficacy of both systems. Each system entailed four equally sized ponds in a series and was continuously fed with domestic wastewater from Birzeit University. The removal rates of organic matter, nutrients, and fecal coliforms were monitored within each treatment system. The results obtained revealed that the ARP system was more efficient in the removal of organic matter [total suspended solids (TSS) and chemical oxygen demand (COD), 86% and 84%, respectively] and fecal coliforms ($4\log$) than the ABP system (81%, 81%, $3\log$, respectively). The ARPs showed higher removal rates for ammonium and phosphorus (68.8% and 50.0%, respectively) compared with the ABPs (57.9% and 41.5%, respectively). The biogenic-aerated ARP option is a cost-effective and land-saving alternative with effluent quality suitable for restricted agricultural irrigation. The ARPs utilizing a new algae-biofilm design concept should be investigated at a large scale to enhance the information available to relevant decision makers, who are seeking sustainable on-site wastewater treatment alternatives.

Polymeric films and fibers are used extensively in industrial and personal products. Many of these products are intended to be disposable and, after initial use, are disposed in landfills that are increasingly expensive and limited. Proprietary additives are being promoted to enhance the biodegradation of polypropylene (PP) and related materials. A test was run on samples of diapers containing PP in simulated landfills and in convection ovens over a period of 52 weeks. Samples in the oven treatment lost all strength properties in less than 27 weeks. Back sheet and cuff samples in the landfill lost insignificant ($P<0.05$) strength under landfill conditions over 52 weeks. Statistics show significant differences ($P<0.05$) in strength and sample percent elongation during testing for time, temperature, and time-temperature interactions for both the oven and landfill tests. The study led to the conclusion that the polypropylene additive was efficacious for programmable destruction in an oxidative environment but not efficacious in an anaerobic environment.

Flocculation is universally modeled on the basis of the seminal work of M. von Smoluchowski. The key equation is a particle number balance that expresses the net rate of formation of particles of a given type as the difference between the rate at which such particles are formed by collisions of smaller particles and the rate at which they are destroyed by collisions with other particles to form larger ones. The equation is commonly presented in a concise form in which the rates of formation and destruction of particles of a given size are each represented by a single summation containing the term ${\beta }_{ij}{n}_i{n}_j$, in which ${\beta }_{ij}$ = collision frequency function, and $n_i$ and $n_j$ = number concentrations of type-$i$ and type-$j$ particles, respectively. Although the product ${\beta }_{ij}{n}_i{n}_j$ has been interpreted as the rate of collisions between $i$ and $j$ particles in several important publications, that interpretation is correct only for collisions between unlike particles; the collision rate between like particles is ${\beta }_{ij}{n}_i{n}_j/2$ (i.e., ${\beta }_{ii}{n}_i^2/2$). This fact alters the interpretation of both the formation and loss terms in the Smoluchowski equation for collisions between like particles. This technical note clarifies the basis for those terms.

Evapotranspiration (ET) covers have gained considerable interest as an alternative to conventional covers for the final closure of municipal solid waste (MSW) landfills, but often produce higher rates of percolation in regions that receive more than $32\mathrm{cm}{\mathrm{year}}^{-1}$ of precipitation. The goal of this project is to design ET covers for MSW landfills in northwestern Ohio (long-term annual rate of precipitation of $83\mathrm{cm}{\mathrm{year}}^{-1}$) that produce rates of percolation $<32\mathrm{cm}{\mathrm{year}}^{-1}$, the rate considered acceptable by the Ohio Environmental Protection Agency (OEPA), and promote habitat restoration. To attain this goal, an adequate soil water-storage capacity was provided using dredged sediment amended with organic material. Two plant mixtures were tested to evaluate the performance of ET covers immediately following construction (immature plants seeded onto the soil) and in the future (mature plants transplanted from a restored tall-grass prairie that is more than 10 years old). ET covers were constructed in drainage lysimeters (1.52-m diameter, 1.52-m depth) and watered at a rate of 91.12 to $95.72\mathrm{cm}{\mathrm{year}}^{-1}$, which included simulated 100-year rain events (11.7 cm over 24 h) in July and October. During the 1-year monitoring period, the ET covers using the mature plant mixture produced considerably less percolation (0.12 to $11.44\mathrm{cm}{\mathrm{year}}^{-1}$) than the covers with the immature plant mixture (6.71 to $24.16\mathrm{cm}{\mathrm{year}}^{-1}$). Thus far, all ET covers have produced rates of percolation less than the maximum standard by the OEPA, and they will continue to be monitored.