Journal of Environmental Engineering

Laboratory experiments were performed in discretely-fractured sandstone blocks to evaluate the use of chemical oxidants to treat residual dense nonaqueous phase liquid (DNAPL) tetrachloroethene (PCE). Persulfate (chelated ferrous iron and alkaline activated) and permanganate oxidants were evaluated. Results showed that the maximum DNAPL mass removal rates ranged from $4,700\mathrm{mg}/\mathrm{L}/\mathrm{day}$ by using permanganate, to 2,600 mg/L/day by using chelated iron activated persulfate, to $480\mathrm{mg}/\mathrm{L}/\mathrm{day}$ by using alkaline activated persulfate. The rate of DNAPL mass removal rapidly declined over the 10 to 60 day application period, limiting DNAPL mass removal rates to only 2 to 20% of the residual DNAPL present on the fractures. The permanganate experiment was terminated after 10 days owing to plugging of the fracture. In the persulfate-treated fractures, substantial rebound in dissolved PCE concentrations were observed after persulfate addition ceased. Use of interfacial tracers in the persulfate experiments showed that the decrease in DNAPL removal accompanied a decrease in the effective DNAPL-water interfacial area, likely owing to obstruction of these interfaces resulting from oxidation by-products. Fracture aperture distribution, oxidant type, and oxidant activation all affected overall treatment effectiveness, and DNAPL dissolution mass transfer controlled the overall treatment process.

In this study, precipitation of $\mathrm{Al}(\mathrm{OH}{)}_{3(\mathrm{am})}$ was used to modify a sand filter medium by fluidized-bed pretreatment. A mixture of alum, sodium hydroxide, and tap water was applied to the filter bed in the last stage of the backwash cycle. The placement of $\mathrm{Al}(\mathrm{OH}{)}_{3(\mathrm{am})}$ in the filter pores was evaluated for both alum-treated raw water (contact filtration) and untreated raw water. The filter pretreated with $\mathrm{Al}(\mathrm{OH}{)}_{3(\mathrm{am})}$ achieved better than 99.98% removal of an untreated clay suspension, with a filter effluent turbidity below the detection limit of 0.01 NTU. $\mathrm{Al}(\mathrm{OH}{)}_{3(\mathrm{am})}$ -pretreated filters that were challenged with clay and humic acid achieved $\ge 99.8\%$ turbidity removal efficiency for 14 h of operation in the contact filtration mode. Pretreatment with $\mathrm{Al}(\mathrm{OH}{)}_{3(\mathrm{am})}$ also enhanced turbidity removal efficiency (up to 99.8%) when the filter was challenged with clay and humic acid, even when the raw water was not coagulated. The aluminum concentration in the filter effluent of an $\mathrm{Al}(\mathrm{OH}{)}_{3(\mathrm{am})}$ -pretreated filter was below the EPA secondary drinking water maximum contaminant level ( $200\mu \mathrm{g}/\mathrm{L}$ for aluminum) when the raw water pH was between 6 and 7; the pretreated filter had the best performance at pH 6.

This study proposes a state-updating scheme and a mechanism-updating scheme for a subsurface contaminant model so as to compose a dual state-mechanism adjustment adaptive filter (DAAF) to improve the plume transport prediction. An ensemble Kalman filter (EnKF) is constructed as a state-updating scheme to incorporate the knowledge of uncertainties from both the model and the sparely scattered measurements. As an implementation of the proposed DAAF concept, a simulation with data assimilation and calibration (SDAC) system, which can adjust both the state and the mechanism, is then built to show the enhanced strength of a combined EnKF and forward data assimilation backward genetic algorithm (FDA-BGA) system. With several test cases examined, the results support the conclusion that DAAF is able to reduce both the systematic and random errors efficiently and that it provides predictions closer to the true field with lower root-mean-square errors.

Methods for effective delivery of remediation amendments for in situ remediation of contaminated clay till sites are sought. The capabilities of direct-push delivery are promising but not yet scientifically documented. Therefore, a field study of direct-push delivery was carried out at an uncontaminated, naturally fractured, basal clay till site ( $K\sim {10}^{-7}-{10}^{-10}\mathrm{m}/\mathrm{s}$ ) in 2008–2009. A mixture of tracers (brilliant blue, fluorescein, and Rhodamine WT), the characteristics of which are comparable to several current remediation amendments, was delivered in aqueous solution at pressures of $\sim 5-10$ bar at several locations and depth intervals [2.5–9.5 m below surface (b.s.)], representing both the vadose and saturated zones. Extensive coring to 12 m b.s. and excavation to 5 m b.s. were carried out to identify the lateral and vertical extent of tracer distribution. A tracer distribution radius of minimum 1 m was achieved at all depths. Close vertical spacing of delivery points (10–25 cm) provided good vertical distribution without significant merging of individual delivery propagation paths. The results are promising with regard to achieving adequate distribution of remediation amendments in clay till.

High loads of inorganic particles received following runoff events from terrigenous sources can cause elevated turbidity ( $T_n$ ) levels in water supply lakes and reservoirs. The development, successful testing, and application of a mechanistic $T_n$ model is documented for Kensico Reservoir, New York, the terminal reservoir of New York City’s multireservoir unfiltered water supply, where a standard of $T_n<5$ nephelometric turbidity units (NTU) must be met in the withdrawals. The model includes three submodels: (1) hydrothermal/transport; (2) turbidity; and (3) alum floc deposition. The alum floc deposition submodel supports simulation of the extent of local deposits formed from alum additions made to reduce high $T_n$ delivered from extreme runoff events. The modeling is supported by long-term monitoring of the inflows, reservoir, and withdrawals, characterization of the turbidity-causing particles (mostly clay minerals, $1–10\mu \mathrm{m}$ in diameter), resolution of specific conductance (tracer) patterns with rapid profiling instrumentation, and characterizations of the alum floc deposits. The two-dimensional hydrothermal/transport and $T_n$ submodels are demonstrated to perform well in both long- and short-term simulations. Predictions of extent and magnitude of the alum floc deposits are shown to be consistent with the available information. Application of the tested model establishes violations of the $T_n$ standard that would have occurred for extended intervals without the alum additions. The volume of the in-reservoir floc deposit formed from this practice is estimated.

Small public water supplies that use surface water as a source for drinking water are frequently faced with elevated levels of color and natural organic matter (NOM) that are precursors for chlorinated disinfection byproduct (DBP) formation. Nanofiltration (NF) systems can prevent DBP formation by removing color and NOM before chlorination. Research studies were conducted on Fall Lake water in Minnesota and dechlorinated potable water spiked with NOM in Ohio by using nanofiltration (Fyne process). Several types of tubular membranes with various molecular weight cutoffs were studied. The effectiveness of the Fyne process in producing safe drinking water was gauged by measuring the removal efficiency of total organic carbon, color, 2–3 micron particles, Bacillus subtilis as a surrogate for bacteria removal and MS2 bacteriophage as a surrogate for virus removal. Results of tests conducted under controlled laboratory conditions and field conditions indicated that Fyne process NF membranes could be used by small system drinking water treatment systems for DBP precursor and pathogen removal.

This study aimed to determine the effect of different water chemistry conditions on the bactericidal properties of silver nanoparticles (AgNPs). Reduced disinfection performance of AgNPs was obtained in divalent cationic solutions in comparison with monovalent solutions with the same concentration. Average particle size of AgNPs increased with increasing electrolyte concentration as divalent cations ( ${\mathrm{Ca}}^{2+}$ and ${\mathrm{Mg}}^{2+}$ ) produced larger AgNPs aggregates than those formed with monovalent solutions. $\xi$ -potential measurements showed that AgNPs in divalent cationic solutions had low absolute $\xi$ -potential values ( $-9.8$ to $-23.2\mathrm{mV}$ ), whereas the values obtained in monovalent solutions were considerably more. The measurements of the concentration of ionic silver released indicated that the fraction of dissolved ${\mathrm{Ag}}^{+}$ ( $5.9–18.8\mu \mathrm{g}/\mathrm{L}$ ) was around 0.1% of the total mass of ${\mathrm{Ag}}^0$ added. The contribution of ${\mathrm{Ag}}^{+}$ to the overall disinfection performance was negligible at the conditions tested. In this study, different physicochemical properties of silver nanoparticles and the survival rate of Escherichia coli (E. coli) in different AgNPs solutions were analyzed. The data collected lead to a correlation between survival rate of E. coli and average size of AgNPs. The results show a strong correlation between these two parameters that can be fitted to a saturation type curve, reaching a survival plateau around 20% survival at an average particle size of 200 nm for all the water chemistry conditions tested.

Biomass settleability, filament content, density, and factors known to affect density were monitored at a full-scale enhanced biological phosphorus (EBPR) plant to characterize system performance during start-up and several subsequent short-term process disruptions. Settleability fluctuated for two months after initial start-up, which corresponded to changes in both filamentous bacteria content and biomass density. Following start-up, a rain event was associated with greatly increased density (possibly because of washing of inorganic particulates to the system), and decreased filament content, and both of these factors may have contributed to improved settleability. Five months after start-up, a 36-hour repair-related process disruption resulted in decreased biomass density and stored polyphosphate simultaneously with degraded settleability, whereas filament content remained at low levels, and actually decreased after the disruption. During recovery, biomass density increased (simultaneously with increased storage of high-density polyphosphate) and settleability improved. A second, shorter aeration disruption also was linked to decreased density and degraded settleability, but not to changes in filament content. Although the observed changes in settleability were not severe, these results suggested that short-term process upsets can affect biomass density, and this in turn can affect the performance of biomass sedimentation. This research confirmed that well-performing EBPR can improve settleability by increasing biomass density, and it provided insights to how process disruptions can affect settleability. This may aid in the development of strategies for system recovery after disruptions; for example, avoiding planned disruptions during periods of lower density (e.g., winter months) may be useful to minimize negative effects on settleability, and prioritizing recovery of EBPR after a disruption may also help recover settleability.

Little attention has been paid to the fast-growing biohazardous wastewater (BHW) in recent years, even though it may pose severe biohazards and toxicity to the general public and environment. Two processes including Fenton oxidation (FO) and a sequential combination of coagulation/flocculation (CF) and FO were evaluated for treatment of actual BHW from biological and pathological laboratories in China. The $[{\mathrm{H}}_2{\mathrm{O}}_2]/[{\mathrm{Fe}}^{2+}]$ molar ratio was controlled at 20 throughout all FO experiments. The FO performed noticeably well in reducing biohazards and toxicity with $6\mathrm{g}/\mathrm{l}$ ${\mathrm{H}}_2{\mathrm{O}}_2$ at initial pH 3 for 24 h, but was unable to remove the organic contaminants efficiently. To reduce the organic load, CF was introduced as a pretreatment. When the CF and FO were operated in sequence, the dosage of ${\mathrm{H}}_2{\mathrm{O}}_2$ and its reaction time were significantly reduced to $3\mathrm{g}/\mathrm{l}$ and 4 h at an initial pH of 3.5. Under these conditions, the total plate count (TPC), adenosine triphosphate (ATP), chemical oxygen demand (COD) and linear alkylbenzene sulfonates (LAS) decreased by 100, 100, 96, and 98%, respectively, indicating the biohazards and organic pollutants were significantly reduced. The toxicity indicated by the inhibition ratio of luminescence (IR) was also greatly eliminated (99% removal). This work demonstrates that a sequential combination of CF and FO offered a feasible alternative for treating real BHW by eliminating biohazards, toxicity and organic pollutants simultaneously and effectively.

This study examined the functionality of a porous pavement storm-water management system in coastal New Hampshire where 6 months of subfreezing temperatures typically occur. The usage of porous pavements for storm-water management in northern climates has many challenges, most of which relate to the extreme cold and significant frost penetration into the porous media. The porous pavement system was monitored for hydraulic and water-quality performance from 2004 to 2008. The use of porous pavements for parking lots for new and redevelopment projects are one watershed-based strategy that can both mitigate impacts for new development and reverse impacts in areas with redevelopment. Surface infiltration capacity and frost penetration were measured monthly to assess winter performance. Because of the well-drained nature of the porous pavement and reservoir base, issues related to frozen media were minimized. Significant frost penetration was observed up to depths of 71 cm without declines in hydrologic performance or observable frost heave. No consistent statistical difference was observed for seasonal hydrologic performance with mean infiltration capacity ranging from 1,490 to $2,690\mathrm{cm}/\mathrm{h}$ . Adverse freeze-thaw effects, such as heaving, were not observed, and for that reason, the life span is expected to exceed that of typical pavement applications in northern climates. Observed hydrologic response resembled shallow depth groundwater drainage, as is the goal for low-impact development designs. Peak flows were reduced by 90% to $0.58{\mathrm{m}}^3/\mathrm{s}/{\mathrm{km}}^2\pm 0.74$ in comparison with $\mathrm{\text{standard impervious cover}}=5.5{\mathrm{m}}^3/\mathrm{s}/{\mathrm{km}}^2\pm 7.7$ . There was exceptional water-quality treatment performance for petroleum hydrocarbons, zinc, and total suspended solids with nearly every value below detection limits. Only moderate removal was observed for phosphorous, and treatment for nitrate (NO3) was negative.

Given the spatial complexity of urban drainage systems, the numerous system appurtenances and unit operations are a maintenance challenge. Maintenance can be the Achilles heel for best management practices (BMPs), and washout is of crucial importance for hydrodynamic separators (HS) that commonly function as preliminary unit operations to separate coarse particulate matter (PM) in urban systems. This study combines physical and computational fluid dynamics (CFD) models to quantify washout from two common HS types; screened (SHS) and baffled (BHS). Washout of particle size distributions (PSDs) for a range of flows is examined. Trajectory analysis of PM illustrates entrainment and washout as a function of PSDs and PM deposit depth. Velocity distributions identify washout-critical PM sizes and areas. Bed profiles are modeled by integrating velocity distributions across washout areas. A Shields washout criterion contradicts physical and CFD results, illustrating the portability challenges of open-channel approaches to nonuniform complex flows in BMPs. The driving parameter for washout is flow intensity at the PM deposit interface. The physically validated CFD model reproduces washout as a function of PSD and flow rate. A baffled HS provides volumetric isolation of deposited PM and generates low washout as tested with a fine hetero-disperse PSD. In comparison to the low washout of the baffled HS for a finer and hydraulically isolated PM deposit, a screened HS generates higher washout for a coarse monodisperse PM deposit, and over 50% of the volumetric domain has an upward velocity vector.

The thousands of kilometers of highways in North Carolina have the potential to generate large amounts of storm-water runoff. Thus, investigation of storm-water control measures (SCMs) for these somewhat unique linear catchments, where space is limited for SCM implementation, was needed. This study examined the quantity and quality of highway runoff at four sites over a 48-km stretch of Interstate 40 in the coastal plain of North Carolina. The highway had a 4-cm overlay of permeable asphalt, known as permeable friction course (PFC), which influenced the export of sediment-bound pollutants and produced median effluent concentrations of total suspended solids (TSS) of $8\mathrm{mg}/\mathrm{L}$ , $8\mathrm{mg}/\mathrm{L}$ , $9\mathrm{mg}/\mathrm{L}$ , and $17\mathrm{mg}/\mathrm{L}$ at the four sites, well below concentrations observed from standard asphalt highway runoff. Two vegetative filter strips (VFSs), two traditional dry swales, and two wetland swales were also tested for pollutant removal efficacy at the four highway research sites. The filter strips generally produced higher pollutant concentrations than the edge of pavement due to a lack of vegetative cover, substantial soil compaction, and high slopes. Total nitrogen (TN) median effluent concentrations were significantly lower for wetland swales ( $1.02\mathrm{mg}/\mathrm{L}$ and $1.03\mathrm{mg}/\mathrm{L}$ ) than for dry swales ( $1.50\mathrm{mg}/\mathrm{L}$ and $1.63\mathrm{mg}/\mathrm{L}$ ). TN load export appeared lower from wetland swales when compared with dry swales, potentially due to the greater number of nutrient removal mechanisms that are present in wetland swales. Maintenance of highway SCMs was shown to be extremely important, as one of the dry swales produced an effluent TSS concentration of $70\mathrm{mg}/\mathrm{L}$ due to a head cut in the thalweg of the channel. As noted in other scientific literature, vegetative SCMs did not further reduce pollutant concentrations released by the PFC because TSS and sediment-bound pollutant concentrations seemingly were at or near irreducible concentrations. This study showed that incorporating wetland elements in the design of swales and the use of PFC should be considered by roadway designers.

Increasing stream chloride ( ${\mathrm{Cl}}^{-}$ ) concentrations have been observed over the last several decades in regions that receive regular road salt. In many cases, these increases occur even when road salt application has remained nearly constant, indicating the presence of multiyear attenuation within watersheds. This paper presents a simple mixing model to interpret the relationship between ${\mathrm{Cl}}^{-}$ inputs and ${\mathrm{Cl}}^{-}$ in stream discharge. The model was applied to data collected between 1972 and 2003 from Fall Creek in central New York, and the results indicate that stream salt concentrations may continue to increase for several decades. The estimated average residence time of road salt in the watershed was approximately 50 years, although the uncertainty in road salt application history suggests residence times of 40–70 years are reasonable. Hydrologists may be able interpret historical road salt applications and stream salt responses as essentially a regional tracer experiment to gain insights into macroscale watershed characteristics that could dominate average water residence time.

The adsorption efficiency for both arsenite [As(III)] and arsenate [As(V)] by iron [Fe(III)], doped and loaded onto and into RH-MCM-41, was tested in a batch reactor. Fe-RH-MCM-41 at the $\mathrm{Si}/\mathrm{Fe}$ mole ratio of 10, prepared by the direct hydrothermal technique (DHT), gave the higher adsorption values with both arsenic species, compared with Fe/RH-MCM-41 prepared by the wetness impregnation technique (WIT). The equilibrium times for As(III) and As(V) were 16 and 4 h, respectively. The adsorption values for Fe-RH-MCM-41 (DHT-10) were affected by initial arsenic concentration and by initial solution pH. For As(V), adsorption was highest at pH 3; for As(III), it was highest at pH 9 (but the factor did not prove significant). The adsorption isotherm fit well with the Langmuir model for both arsenic species. The pseudo-second-order kinetic model could explain As(III) and As(V) adsorption results. The adsorbent system tested here could be upscaled to a packed bed column to treat water for arsenic, especially in remote communities.

High-molecular-weight polymer flocculants are used for accelerated dewatering of mature fine tailings (MFTs) to reclaim the land occupied by containment ponds. Two anionic polymers were used to flocculate an MFT sample containing 98% by weight of fines smaller than 44 μm in diameter, with 85% of this fraction being clay minerals. The polymer solutions and polymer-treated MFT followed the Herschel-Bulkley and Bingham equations of state, respectively. The coupling of shear thinning and structural breakdown of the flocculated MFT gave rise to cavern formation during mixing. The mixing energy input for a series of MFT flocculation tests, in which other conditions were held constant, was proportional to the mixing time. The mixing tools used for the flocculation process were a Rushton turbine (RT), a pitched-blade turbine (PBT), a vane, and hydrofoil impellers. The flocculation outcome was evaluated on the basis of the amount of water released and the capillary suction test time (CST). The CST of the treated MFT was inversely proportional to its water release volume in settling columns. There was a clear peak in the rate of water release and a minimum in the CST as a function of mixing time, clearly showing that there is an optimal mixing energy that corresponds to the most rapid dewatering of flocculated MFT.