Journal of Environmental Engineering

Surface soil contamination is often regulated using guidance values that specify the maximum amount of pollutant that can be present without prompting a regulatory response. In the United States, there are at least 89 value sets (and worldwide there are another 29) that provide guidance for at least one of the nine chlorinated ethanes. The most commonly regulated chlorinated ethane is 1,2-dichloroethane (108 values), and it is the third most commonly regulated synthetic organic surface soil contaminant. Pentachloroethane (17 values) is the least regulated chlorinated ethane. Overall, there are at least 690 guidance values for chlorinated ethanes. This analysis explores the origin, magnitude, and form of the variability of these values. Results indicate that the values span from 3.7 to 7.6 orders of magnitude and are distributed in patterns similar to log-normal random variables. Less than 20% of these values are similar to those of national regulatory agencies such as the U.S. EPA or the Canadian Council of Ministers of the Environment, but more than 60% of the values fall within the 95% confidence interval bounds of the uncertainty in U.S. EPA risk model calculations.

Soil vapor extraction (SVE) is a common remediation practice typically implemented without a rigorous design process because of insufficient or unspecific design data. Field observations have shown that the mass of contaminant removed by SVE often tails off over time. Significant time has been spent modeling SVE to gain a better understanding of the governing processes and the cause of tailing. Studies have shown that improper mass transfer coefficients affect modeling accuracy. As a result, considerable effort has been spent studying the mass transfer coefficients directly related to the non-aqueous-phase liquid (NAPL), with less emphasis on aqueous air and sorbed-aqueous mass transfer coefficients, despite affecting the observed tailing behavior. Accordingly, a laboratory and modeling study was undertaken with toluene to determine the appropriate aqueous air and sorbed-aqueous mass transfer coefficients. SVE column data generated in laboratory experiments were used to back-calculate the mass transfer coefficients by using FRACMAT, a numerical model. The developed experimental protocol allowed the placement of toluene contamination in the unsaturated soil environment without the development of a NAPL phase. The data generated by the SVE column with soils with organic matter and without organic matter, showed that the aqueous-air mass transfer coefficient was exponential, with the aqueous concentration the independent variable. For the zero to moderate organic matter content soils tested, the aqueous-air mass transfer coefficient varied from $1{\mathrm{s}}^{-1}$ to $0.001{\mathrm{s}}^{-1}$. Some sorbed contamination was also observed, requiring a sorbed-aqueous mass transfer coefficient. Numerical modeling with FRACMAT showed that the best sorbed-aqueous mass transfer coefficient was a constant value of $0.01{\mathrm{s}}^{-1}$. The aqueous-air mass transfer coefficient was observed to be the controlling rate limitation in SVE when no NAPL was present in the soil with the zero to moderate organic matter content soil. Studies with silty loam soil showed that additional mass transfer resistances occurred, which could be attributed to the increase in organic matter content and decrease in particle size.

Zero-valent iron particles are an effective remediation technology for ground water contaminated with halogenated organic compounds. In particular, nanoscale zero-valent iron is a promising material for remediation because of its high specific surface area, which results in faster rate constants and more effective use of the iron. An aspect of iron nanoparticle reactivity that has not been explored is the impact of anions present during iron metal nanoparticle synthesis. Solutions containing chloride, phosphate, sulfate, and nitrate anions and ferric ions were used to generate iron oxide nanoparticles. The resulting materials were dialyzed to remove dissolved by-products and then dried and reduced by hydrogen gas at high temperature. The reactivity of the resulting zero-valent iron nanoparticles was quantified by monitoring the kinetics as well as products of carbon tetrachloride reduction, and significant differences in reactivity and chloroform yield were observed. The reactivity of nanoparticles prepared in the presence of sulfate and phosphate demonstrated the highest reactivity and chloroform yield. Furthermore, substantial variations in the solid-state products of oxidation (magnetite, iron sulfide, goethite, etc.) were also observed.

Catalytic decomposition of dichlorodifluoromethane (CFC-12) in the presence of water vapor and oxygen was studied over a series of solid superacids, ${\mathrm{Mo}}_2{\mathrm{O}}_3/{\mathrm{ZrO}}_2$, that had different ${\mathrm{ZrO}}_2$ content by using a fixed-bed reactor. ${\mathrm{CO}}_2$ and ${\mathrm{CClF}}_3$ were the main products and no CO was detected as by-product. The decomposition activity of solid superacid largely depended on the content of ${\mathrm{ZrO}}_2$ and the calcination temperatures of ${\mathrm{Mo}}_2{\mathrm{O}}_3/{\mathrm{ZrO}}_2$. The optimal calcination temperature and content of ${\mathrm{ZrO}}_2$ for preparing ${\mathrm{Mo}}_2{\mathrm{O}}_3/{\mathrm{ZrO}}_2$ with the highest activity for catalytic decomposition of CFC-12 were 450°C and 20–40% by weight, respectively. Adopting a low concentration of oxygen and CFC-12 together with a high concentration of water vapor was preferable for having the high conversion efficiency of CFC-12 and the selectivity for ${\mathrm{CO}}_2$. The catalytic activity of ${\mathrm{Mo}}_2{\mathrm{O}}_3/{\mathrm{ZrO}}_2$ remained steady for 100 h in continuous operation.

This research developed a differential kinetic model to predict the partial degradation of natural organic matter (NOM) during ultraviolet plus hydrogen peroxide ($\mathrm{UV}/{\mathrm{H}}_2{\mathrm{O}}_2$) advanced oxidation treatment. The absorbance of 254 nm UV, representing chromophoric NOM (CNOM) was used as a surrogate to track the degradation of NOM. To obtain reaction rate constants not available in the literature, i.e., reactions between the hydroxyl radical (${}^{•}\mathrm{O}\mathrm{H}$) and NOM, experiments were conducted with “synthetic” water, using isolated Suwannee River NOM, and parameter estimation was applied to obtain the unknown model parameters. The reaction rate constant for the reaction between ${}^{•}\mathrm{O}\mathrm{H}$ and total organic carbon (TOC), $k_{{}^{•}\mathrm{O}\mathrm{H},\mathrm{TOC}}$, was estimated at $1.14(\pm 0.10)\times {10}^4\mathrm{L}{\mathrm{mg}}^{-1}{\mathrm{s}}^{-1}$, and the reaction rate constant between ${}^{•}\mathrm{O}\mathrm{H}$ and CNOM, $k_{{}^{•}\mathrm{O}\mathrm{H},\mathrm{CNOM}}$, was estimated at $3.04(\pm 0.33)\times {10}^4\mathrm{L}{\mathrm{mol}}^{-1}{\mathrm{s}}^{-1}$. The model was evaluated on two natural waters to predict the degradation of CNOM and ${\mathrm{H}}_2{\mathrm{O}}_2$ during $\mathrm{UV}/{\mathrm{H}}_2{\mathrm{O}}_2$ treatment. Model predictions of CNOM degradation agreed well with the experimental results for $\mathrm{UV}/{\mathrm{H}}_2{\mathrm{O}}_2$ treatment of the natural waters, with errors up to 6%. For the natural water with additional alkalinity, the model also predicted well the slower degradation of CNOM during $\mathrm{UV}/{\mathrm{H}}_2{\mathrm{O}}_2$ treatment, owing to scavenging of ${}^{•}\mathrm{O}\mathrm{H}$ by carbonate species. The model, however, underpredicted the degradation of ${\mathrm{H}}_2{\mathrm{O}}_2$, suggesting that, when NOM is present, mechanisms besides the photolysis of ${\mathrm{H}}_2{\mathrm{O}}_2$ contribute appreciably to ${\mathrm{H}}_2{\mathrm{O}}_2$ degradation.

Nutrient limitation was examined for two contrasting tropical reservoirs in Singapore: the semiurban, freshwater Kranji Reservoir and the highly urbanized, estuarine Marina Reservoir. Nutrient enrichment experiments in the laboratory showed that the Kranji Reservoir was phosphorus limited, whereas the Marina Reservoir was nitrogen limited. This was supported by field measurements of nitrogen (N) to phosphorus (P) ratios that showed average values of 16 and 8.3 for the Kranji Reservoir and Marina Reservoir, respectively. In addition to nutrient concentrations, total suspended solids measurements (TSS) showed high levels of turbidity in the Marina Reservoir (average $\mathrm{TSS}=74.2\mathrm{mg}/\mathrm{L}$) compared to the Kranji Reservoir (average $\mathrm{TSS}=3.9\mathrm{mg}/\mathrm{L}$). Thus, light could also be a significant limiting factor for algal growth in the Marina Reservoir. To estimate whether the estuarine system was a source or sink for nutrients, budget models were used to determine fluxes of nitrogen, phosphorus, and carbon. The calculations showed that there was a net loss of nitrogen from the estuarine Marina Reservoir through denitrification and a net loss of carbon. Phosphorus, in contrast, was estimated to be released from the sediments. These results support the earlier findings that the Marina Reservoir is currently nitrogen-limited. The next logical step is to trace the main sources of nutrients into the reservoirs and to deal with nutrient load reduction, bearing in mind that one reservoir is phosphorus limited and the other is nitrogen limited. The implication is that different remediation methods may need to be employed to tackle the eutrophication problems in the two contrasting reservoirs.

The Land Use Input Canal Output Model (LUICOM) was created for the purpose of predicting canal-mediated, total suspended solids (TSS) loading in receiving estuaries. Tidal flushing (related to the tidal prism) within a subject estuary (i.e., Yellow Bluff Creek) was also evaluated. Estimates of flushing times were based on those estimated for Georgia and South Carolina creeks that have better coverage of hypsometric data. Two rain events were sampled for this effort, and TSS concentrations predicted by LUICOM compared favorably with observed values. With subsidence of each rain event, TSS concentrations gradually decreased to baseline concentration in the receiving estuary. Moreover, LUICOM provided a reasonable estimate of the time of peak TSS. The results of this study suggest that TSS measured in the subject canal and creek increase as the result of significant rain events ($>1.0$ in. in 3 h). The correlation between model-derived and measured TSS values suggest LUICOM could be used to evaluate changes in a basin’s land use as it relates to predicting subsequent increases in TSS discharges. The simplicity of the model makes it an ideal tool for resource managers concerned with changes in land use within coastal areas.

Porous landscape detention basins (PLDBs) capture and filter storm water while taking advantage of the intrinsic quality of plants to act as water treatment systems. A two-layered subbase filtering medium is recommended for building PLDBs. The current design method creates the opportunity for incorporating waste symbiosis. In this study, the beneficial reuse of mixing urban waste stream materials into the subbase filtering media is identified. Based on the waste screening tests conducted in this study, three mixes were selected and examined for their leaching and clogging potentials over the years of service. They are (1) peat-sand mix, (2) compost-paper-sand mix, and (3) compost-paper-sand-tire mix. Laboratory tests showed no significant differences among these three mixes in infiltration capacity and leaching contents of nutrients, pathogens, and total metals. Subbase clogging tests were also conducted for these three mixes using sample storm water. The decay of clogged infiltration rate was measured as the sediment load was accumulated on and through the filtering layer using the selected mix. Three empirical formulas were derived to predict the clogging effect for these three waste-incorporated mixes. Using the recommended threshold infiltration rate of $2.5\mathrm{cm}/\mathrm{h}$, the life spans of these three mixes were assessed for an example PLDB built in the field. Based on a bench-scale test of dynamic infiltration rates, the waste-incorporated mix is predicted to reduce the clogging potential of PLDB by approximately 20% compared with the currently recommended mix using peat and sand. However, shredded tires were also found to float in water and can be washed out of the basin during overflow events. Based on environmental benefits, construction cost, material availability, and life-span potential, the subbase mix using compost, paper, and sand is recommended for PLDB designs.

Small island developing states (SIDS) have limited access to imported goods, and their associated patterns of consumption and waste generation are affected by space limitations. They are also impacted by the global presence of marine litter that reaches their shores from the ocean. A material flow analysis (MFA) was applied to household solid waste and marine litter collected from Kayangel Island in the Republic of Palau to provide a comprehensive characterization and spatial accounting of the inflow of nonputrescible materials that become solid waste. Approximately 15,100 kg of nonputrescible solid waste are generated annually on Kayangel Island (0.42 kg per capita per day), with 57% being marine litter derived from the ocean and 43% derived from household activities. Household generation of nonputrescible solid waste (that ignores inputs of marine litter) ranged from $0.14–0.18\mathrm{kg}/\mathrm{capita}\mathrm{\text{-}}\mathrm{day}$ for the school in session and nonschool periods, respectively. The most significant waste categories (by mass) include mixed material and nonrecyclable plastic wastes from both household sources and ocean-derived marine litter. Once nonputrescible solid waste is introduced, 0.39 kg per capita per day accumulates, 0.02 kg per capita per day is removed from the island via shipping, and 0.01 kg per capita per day is processed by open pit burning. Applying an MFA to solid waste on a SIDS links local and global solid waste generation with material fates, and may assist solid waste management practices.

The adsorption of perfluorooctane sulfonate (PFOS) and perfluorooctanoate (PFOA) onto powdered activated carbon (PAC) was investigated in the presence and absence of effluent organic matter (EfOM) at an environmentally relevant concentration range ($0.1–500\mu \mathrm{g}/\mathrm{L}$). Adsorption of PFOS and PFOA to PAC fitted the Freundlich model well ($r^2>0.98$), and adsorption capacity of PFOS ($K_F=17.48$) and PFOA ($K_F=10.03$) in the absence of EfOM was more than one order of magnitude higher than that in the presence of EfOM ($K_F=0.66$ for PFOS, $K_F=0.20$ for PFOA), indicating that EfOM greatly reduces the adsorption capacity of PAC. Moreover, EfOM was characterized by ultrafiltration, and fractions of nominal molecular weights were obtained to investigate their effect on the PFOS and PFOA adsorption. The fraction of $<1\mathrm{kDa}$ had greater effect on adsorption than the fraction of $>30\mathrm{kDa}$, indicating that the similar molecular size of target compounds was the major contributor to adsorption competition. Additionally, biosorption of PFOS and PFOA to activated sludge fitted the linear isotherm ($r^2>0.9$) within a concentration range of $50–400\mu \mathrm{g}/\mathrm{L}$. On the basis of our data, the estimated partition coefficient, $K_d$, was $729\mathrm{L}/\mathrm{kg}$ for PFOS and $154\mathrm{L}/\mathrm{kg}$ for PFOA, respectively, suggesting that PFOS and especially PFOA have a low tendency to partition onto sludge.

Toxin-producing cyanobacteria constitute a serious threat to human and environmental health. It is thus essential that an effective treatment guarantees the removal of cyanobacteria from wastewater before its inclusion in water recycling or environmental flow. Hydrogen peroxide (${\mathrm{H}}_2{\mathrm{O}}_2$) has been shown to induce cyanobacterial decay in laboratory cultures. However, its application for the removal of cyanobacteria from wastewater treatment ponds under environmental conditions has not been investigated. To examine the effects of environmental factors, field trials were performed at both the mesocosm and full-scale levels. The mesocosm trial was completed under field conditions of incident radiation, with various ${\mathrm{H}}_2{\mathrm{O}}_2$ concentrations. A concentration of $1.1\times {10}^{-4}\mathrm{g}{\mathrm{H}}_2{\mathrm{O}}_2/\mu \mathrm{g}$ chl-$a$ resulted in a 32% decrease in cyanobacterial concentration after 24 h, and this approximate concentration was then applied to a wastewater treatment pond in the full-scale trial. In the full-scale experiment, intense spatial and temporal monitoring of phytoplankton concentrations and temperature throughout the pond was performed. Cyanobacterial biomass was reduced by 57% and total phytoplankton biomass by 70% within 48 h of ${\mathrm{H}}_2{\mathrm{O}}_2$ addition. Mixing and radiation were shown to control the depth reached by ${\mathrm{H}}_2{\mathrm{O}}_2$ following addition to the ponds. The synergistic effect of ${\mathrm{H}}_2{\mathrm{O}}_2$ addition with environmental factors increased the effectiveness of cyanobacterial removal compared with laboratory experiments. The concentration of ${\mathrm{H}}_2{\mathrm{O}}_2$ required for the removal of cyanobacteria under field conditions may be decreased from laboratory studies by an order of magnitude.

The majority of variable estimation studies in water resources investigate the temporal variation of the variable. In this study, we examined the depth-dependent estimation of a lake’s dissolved oxygen (DO) using two artificial neural network (ANN) methods: (1) the radial basis functions (RBFs) and the feed forward back-propagation (FFBP), and (2) the multilinear regression (MLR). We tested two different input layer configurations. In the first case, we employed all other available lake parameters—total dissolved solids (TDS), pH, conductivity, lake depth, and lake temperature—to estimate DO. In the second case, we considered only depth and temperature to estimate DO. The performance evaluation criteria of these two cases were close. ANN estimation performances were noticeably superior to those of MLR, as reflected in the performance evaluation criteria and DO lake depth plots. We saw that the spatial variation of the lake’s DO can be captured by ANNs satisfactorily, even if available measurements are quite limited.

Storm water ocean outfalls discharging into recreational waters pose a human health threat because of increased potential exposure to bacteria and other pathogens. The dune infiltration system (DIS) was designed and implemented at two ocean outfall sites in response to concerns by the North Carolina Department of Transportation and the town of Kure Beach, North Carolina The systems were designed to divert storm water runoff from 1.9 ha (4.7 acre) and 3.2 ha (8.0 acre) watersheds into the beach dunes. Following construction, data were collected from 25 storms during March through October 2006. The systems captured a combined total of nearly $1,800{\mathrm{m}}^3$ ($63,500{\mathrm{ft}}^3$), or 95% of the influent storm water runoff—a significant reduction of runoff volume and peak flow discharging directly onto the beach ($p<0.0001$). Fecal coliform and enterococci concentrations were measured in the inflowing storm water runoff and groundwater downslope of the systems. Both groundwater bacteria concentrations near the systems were significantly lower than the bacteria concentrations in the inflowing storm water ($p<0.001$). Furthermore, groundwater fecal coliform concentrations after implementing the DISs were statistically similar to preconstruction levels ($p<0.05$). The initial results are promising, and the system should be considered for more widespread use. However, further comprehensive research is recommended to more thoroughly understand the viability of the DIS as a storm water best management practice and the fate and transport of the bacteria within the dunes.