Journal of Environmental Engineering

The technological performance and social acceptance of ceramic water filters impregnated with silver nanoparticles for point-of-use water treatment were investigated in the laboratory and in the field in the Guatemalan highland community of San Mateo Ixtatán. In the laboratory, filters were constructed with clay and sawdust collected from the Guatemalan community and were tested to determine the effects of percent sawdust and silver nanoparticle treatment on the transport and removal of E. coli. For ceramic filters without silver treatment, size-exclusion and/or sorption is the mechanism of removal and a lower mass-percent sawdust corresponds to greater bacteria removal. The addition of silver nanoparticles to the ceramic filters improved the performance for all mass percentages of sawdust relative to filter media without nanoparticle treatment. Filters with higher porosity achieved higher bacteria removal than those with lower porosity, suggesting an increase in burnable material percentage is advantageous, assuming structural integrity is not compromised. Subsequent to laboratory testing, ceramic filters were manufactured with local materials and labor in San Mateo Ixtatán, Guatemala, and distributed to 62 households in this peri-urban community. The study participants were randomly divided into two groups, and filters were tested periodically over 23 months or 12 months. Filtered effluent samples were tested for turbidity reduction, bacteria removal, and silver leaching. Over the course of the study, the average percent reduction in total coliforms and E. coli was 87% and 92%, respectively. The average effluent turbidity was 0.18 nephelometric turbidity units (NTUs) and average effluent concentration of ionic silver was $0.02\mathrm{mg}/\mathrm{L}$ (below the U.S. EPA standard of $0.1\mathrm{mg}/\mathrm{L}$). Filters distributed to the second study group consistently performed better than the first study group as manufacturing techniques improved and contact with researchers increased. Overall, users were satisfied with the filters, citing them as easy to use and maintain while improving water quality. The findings of this study suggest that locally manufactured ceramic filters can significantly improve the microbiological quality of water when used as a point-of-use water-treatment technology.

In many environmental jurisdictions worldwide, surface soil contamination is regulated using guidance values that specify the maximum amount of pollutant that can be present without prompting a regulatory response. Three of the four chlorinated methanes are among the seven most frequently regulated synthetic surface soil contaminants. There are at least 80 U.S. regulatory jurisdictions and at least 30 international jurisdictions with guidance values for at least one of the chlorinated methanes, yielding as many as 106 values (for dichloromethane) for the same regulatory consideration. This analysis explores the variability of these values. Results indicate that the values span at least 5 orders of magnitude and are distributed in patterns similar to a lognormal random variable, but fit distributions that are statistically distinct. The distributions also contain value clusters that may imply emerging consensus about appropriate regulatory levels or demonstrate the impact of regulatory leadership to suppress variability. Simulation based on the current U.S. Environmental Protection Agency risk analysis model are used to estimate the degree to which value ranges may be attributed to uncertainty in exposure models. Approximately 50% of guidance values fall within the 95% confidence interval uncertainty bounds of risk model results.

Acidic groundwater generated from pyrite oxidation in acid sulfate (AS) soil is a major geoenvironmental problem in Australia. This study aims to evaluate recycled concrete as a reactive material in permeable reactive barriers (PRBs) for the remediation of acidic groundwater in low-lying AS soil floodplains. Laboratory experiments were systematically conducted to investigate the acid neutralization behavior of recycled concrete and its potential to remove dissolved Al and Fe. The results confirmed that recycled concrete could effectively treat acidic groundwater from an AS soil terrain, resulting in near neutral effluent over a long period with complete removal of Al and Fe. The major mechanisms involved in neutralizing acidic groundwater are thought to be the precipitation of Al and Fe as oxides, oxyhydroxides, and hydroxides. However, the accumulation of secondary minerals could decrease the reactivity of the recycled concrete. For example, chemical armoring could decrease the neutralizing capacity of recycled concrete by up to 50% compared with the theoretical acid neutralization capacity of this material. The results reported here also show that the neutralization capacity and reactive efficiency of recycled concrete are dependent on the initial pH value and also the concentration of Al and Fe in acidic groundwater.

U.S. Environmental Protection Agency (USEPA) regulations require the capture of spills from liquid tanks containing hazardous chemicals by using a secondary containment system. Compacted clay or geomembrane liners are commonly used in secondary containment systems, but they are cumbersome when used in conjunction with existing liquid tanks because of pipeline networks surrounding the tanks. This study evaluates the formation of hydraulic barriers for secondary containment through the permeation of colloidal silica grout. A simplified infiltration model is presented to predict the downward movement of the colloidal silica grout into a soil layer, considering the time-dependent increase in dynamic viscosity of the colloidal silica for different concentrations of an electrolyte accelerator. Because the simplified infiltration model cannot predict the soil-grout interaction or the permeation of the colloidal silica by fingering, its results were calibrated by using the observations from a large-scale column test involving the permeation of colloidal silica into sand. The predicted position of the wetting front was found to match that of the experiment when the parameter governing the change in viscosity of the colloidal silica was increased by a factor of 30. The infiltration model calibrated with observations from column infiltration experiments provides a simple approach to the design of the secondary containment systems using permeation of colloidal silica.

The study explores the potential of iron-activated persulfate oxidation of an azo dye in model wastewater. The influence of the type of iron activator on process efficiency was investigated by using ferrous and zero valent iron. The Box-Behnken experimental design and response surface methodology were applied for the modeling of the ${\mathrm{Fe}}^{2+}/{\mathrm{S}}_2{\mathrm{O}}_8^{2-}$ and ${\mathrm{Fe}}^0/{\mathrm{S}}_2{\mathrm{O}}_8^{2-}$ processes. The combined effect of three important process parameters was investigated and presented by the means of the quadratic polynomial model. The statistical analysis of model performance was evaluated by ANOVA. The optimal process conditions giving the maximal mineralization for both processes were determined: pH 4.81, $[{\mathrm{Fe}}^{2+}]=1.64\mathrm{mM}$, and $[{\mathrm{S}}_2{\mathrm{O}}_8^{2-}]=84.87\mathrm{mM}$ predicting 35.14% mineralization and pH 5.52; $[{\mathrm{Fe}}^0]=4.27\mathrm{mM}$ and $[{\mathrm{S}}_2{\mathrm{O}}_8^{2-}]=138.43\mathrm{mM}$ predicting 54.38% mineralization by the ${\mathrm{Fe}}^{2+}/{\mathrm{S}}_2{\mathrm{O}}_8^{2-}$ and ${\mathrm{Fe}}^0/{\mathrm{S}}_2{\mathrm{O}}_8^{2-}$ processes, respectively. The predicted values of dye mineralization obtained by model equations were in good agreement with the experimental values. The type of iron activator was demonstrated to significantly influence both process efficiency and optimal conditions.

The treatment of effluent of pilot- and full-scale upflow anaerobic sludge blanket (UASB) reactors operating at steady state was studied in an aeration-settling system. The fine pore submerged diffusers were used to aerate the effluent of UASB reactors under different operating conditions. Forty to 55% of the biochemical oxygen demand (BOD) and the chemical oxygen demand (COD) removal efficiencies were achieved by the direct aeration of the UASB effluent in the laboratory. The maximum removal efficiencies were achieved at 30 min hydraulic retention time (HRT) and a dissolved oxygen (DO) of $5–6\mathrm{mg}/\mathrm{L}$ or high $K_{L}a$ (vigorous aeration). Batch experiments on nitrogen purging and the aeration of sulfides, volatile organic compounds (VOCs), and nonpurgeable organic carbons (NPOCs) were performed to ascertain the mechanism of BOD/COD removal. During aeration, BOD and COD were reduced by the stripping of ${\mathrm{H}}_2\mathrm{S}$ and VOCs and by the chemical oxidation of total sulfides and organic carbon. The stripping and chemical oxidation depended on the HRT and DO. The performance of a full-scale surface aeration system was compared to the performance of a pilot-scale diffused aeration system. Final sedimentation was effective only in removing the solids from the effluent of the aeration system. The results were confirmed by organic mass balance.

The degradation and mineralization of amoxicillin in an aqueous solution was accomplished by using a photo-Fenton treatment. An ultraviolet light source with a 254-nm wavelength was used with hydrogen peroxide (${\mathrm{H}}_2{\mathrm{O}}_2$) and iron(II). The effects of reagent concentrations on amoxicillin degradation and mineralization were investigated systematically by using the Box-Behnken statistical experiment design. Amoxicillin ($10–200{\mathrm{mgL}}^{-1}$), ${\mathrm{H}}_2{\mathrm{O}}_2$ ($10–500{\mathrm{mgL}}^{-1}$), and iron(II) ($0–50{\mathrm{mgL}}^{-1}$) concentrations were considered independent variables; the percent amoxicillin degradation and the total organic carbon (TOC) removal (mineralization) were the objective functions to be maximized. Both ${\mathrm{H}}_2{\mathrm{O}}_2$ and iron(II) concentrations affected the extent of the amoxicillin degradation and mineralization. The amoxicillin degradation was completed within 2.5 min, and 53% mineralization took place within 60 min. The optimum ${\mathrm{H}}_2{\mathrm{O}}_2:\mathrm{Fe}:\mathrm{\text{amoxicillin}}$ ratio that resulted in complete amoxicillin degradation and 53% mineralization was $100:40:105{\mathrm{mgL}}^{-1}$.

The effect of potassium permanganate (${\mathrm{KMnO}}_4$) preoxidation on the treatment of low-turbidity reservoir water was investigated through two years of operational data in a large-scale drinking water treatment plant (DWTP). ${\mathrm{KMnO}}_4$ facilitated the removal of pollutants [e.g., turbidity and chemical oxygen demand (${\mathrm{COD}}_{\mathrm{Mn}}$)] by different units such as clarification, sand filtration, and granular activated carbon (GAC) adsorption. Although the addition of ${\mathrm{KMnO}}_4$ increased the color and total Mn concentrations, the results of removal by clarification and filtration are promising. The average run length of anthracite filters decreased from 48 to 40.8 hours after the introduction of ${\mathrm{KMnO}}_4$ and exhibited a negative correlation with ${\mathrm{KMnO}}_4$ dosages ($r^2=0.6912$). The hydrous manganese dioxide in situ formed ($\delta {\mathrm{MnO}}_2$) dominated in aiding coagulation and improving filtration to enhance pollutant removal in the ${\mathrm{KMnO}}_4$ preoxidation process, and these effects were achieved at the expense of more frequent backwashing of anthracite filters.

Bacterial levels in Buffalo Bayou in Houston commonly exceed contact recreation standards. Potential sources of bacteria include wastewater treatment plants, sanitary sewer overflows, septic systems, wet and dry nonpoint-source discharges via direct runoff and pipes, direct deposition, and sediment. A water-quality model in the Hydrologic Simulation Program—FORTRAN (HSPF) was calibrated and validated for hydrology, sediment, and Escherichia coli and subsequently used to evaluate the impacts of the bacterial sources in the watershed. In addition, simple estimates of bacterial loads were calculated along with source evaluations from load duration curves. Load reductions based upon the simple estimates indicated that water-quality standards were met by reducing dry-weather indicator bacterial loads by 69% and wet-weather loads by 98%. When these load reductions were implemented in the HSPF model, however, standards were not met under dry-weather conditions. Residual nonpoint-source loading was found to cause the discrepancy between simple load estimate calculations and the developed water-quality model. This paper demonstrates that runoff can play a significant role in maintaining high levels of bacteria under all flow conditions and that understanding the temporal variations in bacterial source loading is critical to ensure that load reductions will achieve water-quality standards.

The surface structural properties of biofouled membranes from a laboratory-scale submerged anaerobic membrane bioreactor (SAnMBR) treating kraft pulping evaporator condensate after cleaning were studied. A flat sheet polyvinylidene fluoride (PVDF) membrane was used for the study. Three different cleaning methods, physical cleaning (PC), maintenance chemical cleaning (MCC), and recovery cleaning (RC) were applied to the fouled membrane surface, and the treated membranes were subject to flux recovery and surface structural analysis by using spectroscopic methods, zeta potential measurement, attenuated total reflectance-Fourier transform infra red spectroscopy (ATR-FTIR), and advanced correlative microscopic methods, including confocal laser scanning microscopy (CLSM), atomic force microscopy (AFM), and scanning electron microscopy (SEM). Neither PC, MCC, nor RC methods restored the membrane permeability to initial conditions. Adhesion of a thin extracellular polymeric substance (EPS) layer, consisting of proteins and polysaccharides with a thicknesses of 4.0 µm, 5.3 µm, and 7.1 µm and roughness of 190 nm, 236 nm, and 273 nm was observed on RC, MCC, and PC treated membrane surfaces, respectively. Partial flux recovery was achieved with the MCC and RC methods. This was correlated to the reduction of the protein associated with the foulant. Polysaccharides were found to be the most stable and predominant EPS constituent in relation to protein on the biofouled layer of RC and MCC membrane surfaces.

The purpose of this technical note is to present two analytic solutions for modeling one-dimensional gas flow in municipal solid waste landfills with horizontal gas collection systems. In previous work, vertical flow was considered. In the present communication, situations in which cylindrical or spherical symmetry apply are considered. These models, although not perfect descriptions of typical landfill geometries, should be useful during the “roughing-out” stage of gas collection systems and may be used to estimate maximum pressures with a minimal effort. Because all the requisite background is developed in the cited reference; the reader is directed to consult it for that purpose.

Protecting slow sand filters (SSFs) from high-turbidity waters by pretreatment using pebble matrix filtration (PMF) has previously been studied in the laboratory at University College London, followed by pilot field trials in Papua New Guinea and Serbia. The first full-scale PMF plant was completed at a water-treatment plant in Sri Lanka in 2008, and during its construction, problems were encountered in sourcing the required size of pebbles and sand as filter media. Because sourcing of uniform-sized pebbles may be problematic in many countries, the performance of alternative media has been investigated for the sustainability of the PMF system. Hand-formed clay balls made at a 100-year-old brick factory in the United Kingdom appear to have satisfied the role of pebbles, and a laboratory filter column was operated by using these clay balls together with recycled crushed glass as an alternative to sand media in the PMF. Results showed that in countries where uniform-sized pebbles are difficult to obtain, clay balls are an effective and feasible alternative to natural pebbles. Also, recycled crushed glass performed as well as or better than silica sand as an alternative fine media in the clarification process, although cleaning by drainage was more effective with sand media. In the tested filtration velocity range of $(0.72–1.33)\mathrm{m}/\mathrm{h}$ and inlet turbidity range of (78–589) NTU, both sand and glass produced above 95% removal efficiencies. The head loss development during clogging was about 30% higher in sand than in glass media.