Journal of Environmental Engineering

This study investigates the effects of uncertainties associated with pollutant wash-off dynamics in the context of stormwater management practices modeling. A formal Bayesian approach is adopted for the calibration and the uncertainty analysis of a commonly used wash-off model under (1) the unverified assumption of homoscedastic, independent, and normally distributed residuals; and (2) using a more correct heteroscedastic and autoregressive error model. The results obtained for each of these approaches are compared, and the uncertainty associated with water quality modeling is later propagated through a conceptual best management practices (BMP) model for various stormwater management scenarios so as to assess the effect of this uncertainty for BMP modeling and clarify the benefits of a robust description of error structure. This study indicates that the violation of the statistical assumptions about the residuals may result in unreliable estimation of model parameters and total predictive uncertainty. However, the effect of the uncertainty in the intraevent variability of concentrations in runoff is found to have only a limited effect on the outputs of the BMP model, regardless of the error model adopted for calibration.

Fluoride is a geogenic pollutant found in groundwater in several parts of the world. A possible treatment strategy for removing fluoride from groundwater to meet drinking water standards is the use of electrocoagulation (EC). EC has to be combined with filtration to meet drinking water standards for fluoride and turbidity. The objective of this study was to evaluate the use of iron (Fe) electrodes (mild steel) for defluoridation of groundwater using EC and filtration in continuous-flow mode. Different operating conditions were examined and included the use of baffles, varying flow rates, voltages, and different reactor configurations. The use of baffles was observed to increase removal efficiency. EC and filtration in continuous flow mode with Fe electrodes and no baffles gave a maximum removal efficiency of 36.2%. Addition of baffles improved efficiency to 42% with two baffles and 46.7% with one baffle; the difference between one versus two baffles was within analytical variability. The pH increased in all experiments indicating the need for neutralization after EC and filtration. The average energy consumed per unit volume was $4.73\mathrm{Wh}/\mathrm{L}$ (or ${\mathrm{kWh}/\mathrm{m}}^3$) in continuous-flow experiments.

Single-layered graphene oxide (SLGO) nanosheets are distinguished from other colloids by their extreme anisotropy, which likely exerts a strong control on their transport behavior. Hence, this study investigates the influence of both environmentally relevant pH and ionic strength on the transport of SLGO nanosheets through saturated quartz or iron oxide–coated sands. Both the nanosheets and quartz sands are negatively charged throughout the experimental conditions, resulting in very little nanosheet deposition onto the quartz sands. However, increasing ionic strength and decreasing pH did cause measurable increases in nanosheet deposition, likely due to decreases in the magnitude of negative charges near the respective surfaces. Conversely, nanosheets and iron oxide–coated sands are oppositely charged throughout the experimental conditions, resulting in significant nanosheet deposition onto the iron oxide–coated sands. These trends suggest that nanosheet deposition is largely controlled by electrostatic forces, although the deposition rate of the high ionic strength iron oxide–coated sand treatment could not be explained by electrostatic interactions alone and instead may be influenced by nanosheet aggregation. Collectively, these measurements enable prediction of SLGO transport throughout a range of realistic environmental and geologic conditions.

A 2-year monitoring study was conducted at a sewer pumping station to investigate volatile sulfur compound (VSC) and volatile organic compound (VOC) emission dynamics over a range of timescales to gain an understanding of how they impact the design and execution of sewer odorant monitoring. It is demonstrated that the sewer system was highly dynamic and influenced by a range of processes at different time scales. Based upon odor activity values, hydrogen sulfide and methyl mercaptan had strong potential to be odorous, while dimethyl sulfide and dimethyl disulfide were potentially odorous at source concentrations. In general, VOCs were not likely to be odorous at source concentrations, although some episodic elevations in aromatic hydrocarbon and terpene concentrations to potentially odorous levels were observed and as a result VSCs are the primary targets for sewer odor abatement. A strong diurnal emission cycle was observed, with dynamic ranges (ratio of peak to average concentration) between 2.34 and 4.55 for specific VSCs and 1.82 to 10.6 for specific VOCs. Interday variability over a 1-week period was relatively low for many VSCs, with coefficients of variance generally ranging from 11 to 30%, while VOC emissions had greater variability, with coefficients of variance ranging from 29 to 220%.

Floc blankets are concentrated, fluidized beds of particles utilized in some water treatment plants. Floc blankets occur in vertical-upflow sedimentation tank configurations and are reported to enhance removal of suspended solids. In this research, floc blankets were formed in the laboratory at an upflow velocity of $1.2\mathrm{mm}/\mathrm{s}$ and at varying alum coagulant dosages with influent turbidities of 10 nephelometric turbidity units (NTU), 100 NTU, and 500 NTU. Image analysis was utilized to quantify floc blanket suspended solids concentration and floc-water interface height over time. Blankets formed with higher influent turbidities required a lower ratio of coagulant dose to influent turbidity, formed more quickly, had higher steady-state suspended solids concentrations, and achieved better suspended solids removal efficiency. Increasing alum coagulant dose decreased steady-state floc blanket suspended solids concentration and resulted in lower effluent turbidities. At an influent turbidity of 100 NTU, effluent turbidity was strongly correlated with coagulant dose at coagulant doses of 1 to $7.5\mathrm{mg}/\mathrm{L}$ alum. Diminishing improvement in turbidity removal was observed for coagulant doses above $15\mathrm{mg}/\mathrm{L}$ alum for both 100 and 500 NTU. A higher ratio of coagulant dose to influent turbidity could be used by water treatment plant operators to allow floc blankets to form quickly, and after formation of the floc blanket, the coagulant dose could be reduced without significant impact on the removal of suspended particles.

Ammonium is a nitrogen species that can directly enter a stormwater control measure (SCM) or be produced from degradation of organic nitrogen available in stormwater runoff. Clinoptilolite zeolite (ZT) and a hydrous aluminosilicate (CA) were investigated for ammonium removal use in filtration-based SCMs. Sorption capacity, kinetics, and strength of attachment were completed in batch settings. For the four different background electrolytes tested at neutral pH, ZT showed the highest uptake, particularly at 0.03 M NaCl, followed by 0.01 M ${\mathrm{CaCl}}_2$. The lowest uptake was found to occur for ${\mathrm{K}}^{+}$ electrolytes. Kinetics of ammonium uptake was also found to be more rapid for ZT (i.e., 30 min for ZT and 240 min for CA), and increase in concentrations of ${\mathrm{Ca}}^{2+}$ and ${\mathrm{K}}^{+}$ slowed the sorption process from 30 to 240 min. Extraction studies indicated high extractability of ammonium in ZT, while CA showed slightly smaller extractable ammonium; the results suggest that ammonium removed by CA is less exchangeable and possibly less bioavailable. Based on these observations, the use of clinoptilolite in stormwater filtration systems is recommended.

In this study, a novel material, chemically activated cow bone (CAB), was further evaluated for fluoride removal via laboratory batch and field column studies using fluoride-impacted groundwaters in the Rift Valley of Ethiopia. Regeneration of the exhausted CAB was evaluated using 0.05 M NaOH and 0.01 M $\mathrm{Ca}(\mathrm{OH}{)}_2$ solutions. Water-quality parameters were analyzed to ensure that the CAB-treated water is safe for human consumption. The study indicated that the CAB produced in the laboratory and field showed fourfold improvement in fluoride removal capacity as compared to thermally activated cow bone (commonly known as bone char). The study also showed that more than 92% adsorption capacity of the exhausted CAB media can be regained using 0.05 M NaOH and 0.01 M $\mathrm{Ca}(\mathrm{OH}{)}_2$ solutions. The water-quality analysis conducted on the highly fluoride-impacted drinking waters treated using CAB media were found to be safe for public consumption. Therefore, these results further reinforce that CAB media can be used to provide access to safe drinking water for communities living in highly fluoride-impacted areas in developing countries and beyond.

Bioretention plant selection for nutrient removal (and even basic plant survival) is an understudied and not-well-understood component of this stormwater control measure. Twelve bioretention cells were constructed to evaluate 16 plants growing in three different media for their ability to remove nutrient pollution from urban stormwater runoff with high nutrient loads. Plants evaluated were pairs of natives and cultivars and included trees (Magnolia and Betula), shrubs (Viburnum and Itea), herbaceous perennial flowers (Helianthus and Eupatorium), a rush (Juncus), and an ornamental grass (Panicum). Eleven of the 16 species (B. nigra; B. Dura-Heat; M. virginiana; M. Sweet Thing; I. virginica; I. Henry’s Garnet; J. effusus; P. Shenandoah; H. angustifolius; H. First Light; and E. Gateway) performed well (grew and were aesthetically acceptable) in the bioretention cells and can be recommended as bioretention plants. Species and cultivar impacted the levels of remediation of the high N and P loads applied. The woody B. nigra and its cultivar stored the most N and P per specimen and per cost per unit canopy area. The herbaceous species P. virgatum and H. angustifolius sequestered the most N and P per unit area. However, if both low cost per nutrient uptake and high nutrient uptake per area are desired, then three species appear to be the optimal choices: P. virgatum; P. Shenandoah; and E. Gateway. The maximum nutrient mass any plant (B. Dura-Heat) accumulated in its dry biomass was nearly 11% of the inflow load.