Journal of Environmental Engineering

The goal of this research was to compare the pollutant removal effectiveness of biofiltration systems containing different media and plant species. A laboratory column study was conducted by using three media and two plant species, each with and without a submerged zone intended to promote denitrification. Twenty experiments were run by using synthetic storm water over the course of nine months, and ten of them were analyzed. The three media used were concrete sand, masonry sand, and a medium that meets the City of Austin’s biofiltration specifications. The plant species were Buffalograss 609 and Big Muhly, both commonly found in Texas. The results of this study showed a significant improvement in nutrient removal with the presence of these plants in the filter. The columns without plants were found to export substantial amounts of nitrate/nitrite, whereas the columns with the plants demonstrated a substantial removal of nutrients (59–79% of the total nitrogen and 77–94% of the total phosphorus). Solids removal remained high through the entire set of experiments for all columns (88–97%). Hydraulic conductivity experienced an initial rapid decrease in all columns but then stabilized.

The design of a green roof plays a significant role in performance. In a ground-level field study, 28 built-in-place green roof models, four modular units, and four roof decks with standard black membrane were arranged in a completely randomized design. Storm-water runoff quantity and quality were monitored from September 2005 through June 2008. Results indicate that green roof systems significantly reduced storm-water runoff and that system design, growth media depth, and presence of plants impacted storm-water retention. In a second study on a building roof, two modular systems were used to evaluate water loss through evapotranspiration. Water loss of both systems was significant and influenced by system design, growth media type, and presence of plants. Finally, runoff quality analyses from the ground-level field study and from a laboratory pot experiment indicate that nitrate, total suspended solids, and turbidity are generally low in runoff after a first-flush event. Runoff water quality was also influenced by system design, growth media type, and presence of plants.

On-site sequestration and accumulation of heavy metals in bioretention cells introduces the potential for short- and long-term management concerns regarding the metals’ environmental availability, human health impacts, and implications for maintenance practices. Media samples from a 4-year-old bioretention cell were collected across the cell surface and to a depth of 90 cm to assess the spatial distribution of accumulated lead, copper, and zinc in the media. Analyses consisted of total metal, a five-step sequential extraction, bioavailable lead, and media pH and organic matter content. Metal concentrations in the media have increased substantially over the original levels but are well below regulatory cleanup thresholds. Metals are strongly bound to bioretention media and are largely immobile. Lead bioavailability is comparable to generic soil estimates. Most metal accumulation is near the inflow point in the top 3–12 cm of media. Based on trends observed after 4 years of operation, many years of capacity are estimated to remain in the cell with respect to metals. Regulatory cleanup thresholds are likely to be first reached at a localized hotspot near the inflow point, although routine maintenance actions may be able to delay attainment of such thresholds indefinitely.

A phytoremediation study was undertaken at a disused fire training runoff lagoon at an ecologically sensitive area in England. The sediments in the semisaline lagoon were highly contaminated with over $145,000\mathrm{mg}/\mathrm{kg}$ dry weight diesel range organics (DRO). Initial microcosm studies indicated that Phragmites australis and Typha latifolia were able to grow in this sediment, and P. australis was subsequently used for test planting in the lagoon. In situ DRO and microbial populations were investigated over a 15-month period. Results were difficult to interpret due to highly variable DRO concentrations in the sediment and varying water levels. Overall DRO concentrations fell but with no significant differences between planted and unplanted sites. DRO and bacterial numbers were related to moisture content. Hot weather, combined with low water levels, gave the lowest DRO levels. Destructive testing of the microcosms after 3 years also showed no difference in DRO between planted and control; however, elevated microbial numbers were observed in P. australis planted systems. Therefore, longer-term studies are recommended to evaluate the potential of phytoremediation in such environments.

Remediation of sediments contaminated with persistent organic compounds such as polycyclic aromatic hydrocarbons has been problematic due to the lack of oxygen in saturated sediments. Certain wetland plants have the potential to create aerobic conditions in the anoxic sediments through radial oxygen loss into the rhizosphere. The objective of the current study was to utilize several methods of measuring radial oxygen loss to identify wetland species with relatively high rates of oxygen loss into the rhizosphere. The results show clearly that there are significant differences between plant species in terms of radial oxygen loss. Rates in the current study ranged from $0{\mathrm{cm}}^2$ (Lobelia cardinalis) oxygenated to $56{\mathrm{cm}}^2$ (Sagittaria latifolia). In addition, the three methods of measuring radial oxygen loss showed consistency in the high radial oxygen loss species, but we found that the methylene blue agar method was more sensitive in detecting differences between species and also enabled visualization of where the radial oxygen loss was taking place across the root system.

The contribution of green roofs to urban water quality is a subject of increasing interest. This study examined heavy metals in runoff from simulated green roof systems after 22–32 months in the field to assess source or sink behavior. The green roof systems were not sources of metals, except for one instance of elevated Cu in runoff. On some dates, runoff metal concentrations were significantly lower than that from an ethylene propylene diene terpolymer (EPDM) membrane roof simulation, suggesting intermittent sink behavior. This sink behavior did not in most cases decrease runoff metals below the U.S. EPA water quality criteria for chronic Cd or Pb toxicity. If there were metals in the rainwater input from wet deposition, the green roof systems did not seem to sequester those metals, as runoff metal concentrations were not reduced relative to the EPDM roof simulation. The lack of consistency in source or sink behavior indicates that pollutant concentrations in runoff are influenced by a complex interaction of factors. The contribution to urban water quality provided by these specific substrates if used in green roofs systems, or from modular green roofs, could be equally inconsistent.

Constructed storm-water wetlands with different types of vegetation are capable of removing organics and nutrients from water while providing other important environmental and ecological services. The objectives of this study were to compare the efficiencies of organic and nutrient removal from a simulated storm-water runoff between the duckweed ponds (DWPs) and the algae ponds (APs) and to establish a potential link between the population of ammonia-oxidizing organisms and effluent water quality. Two replicate ponds were operated under identical conditions in which duckweeds initially thrived off the water, but they were taken over by filamentous algae after the complete removal of duckweeds. The ponds were able to remove $74\pm 4\%$ chemical oxygen demand (COD); $90\pm 3\%$ ${\mathrm{NH}}_4^{+}-\mathrm{N}$; $94\pm 2\%$ ${\mathrm{NO}}_3^{-}-\mathrm{N}$; and $47\pm 7\%$ orthophosphate in the DWPs in contrast to only $64\pm 6\%$ COD; $77\pm 6\%$ ${\mathrm{NH}}_4^{+}-\mathrm{N}$; $85\pm 4\%$ ${\mathrm{NO}}_3^{-}-\mathrm{N}$; and $21\pm 6\%$ orthophosphate in the APs. The dissolved oxygen (DO) levels were significantly different between the ponds. In the DWPs, the diurnal DO pattern (from 0.9 to $3.9\mathrm{mg}/\mathrm{L}$) associated with anoxic-aerobic sequencing conditions was related to the higher phosphorus (P) removal than in the APs. Archaeal and bacterial amoA abundance in the DWPs ranged from $(1.1\pm 0.2)\times {10}^6$ to $(2.1\pm 0.2)\times {10}^9\mathrm{copies}/\mathrm{g}$ dry soil and from $(1.6\pm 0.3)\times {10}^7$ to $(1.1\pm 0.4)\times {10}^{10}\mathrm{copies}/\mathrm{g}$ dry soil, respectively. The hydric soil in the DWPs harbored more ammonia-oxidizing bacteria (AOB) and oligotrophic ammonia-oxidizing archaea (AOA) than any other samples in the ponds by approximately three orders of magnitude. For comparison, the high DO concentrations (an average of $5.5\mathrm{mg}/\mathrm{L}$) in the APs were linked to the absence of AOA, whereas the abundance of amoA from AOB ranged from $(1.3\pm 0.3)\times {10}^7$ to $(1.6\pm 0.2)\times {10}^9\mathrm{copies}/\mathrm{g}$ dry soil. These results suggest that the duckweeds play an important role by creating different microbial niches and cyclic anoxic-aerobic conditions and thus lead to improved organic and nutrient removal.

Runoff has important meaning in the context of the performance of post-construction best management practices (BMP) and compliance with National Pollutant Discharge Elimination System (NPDES) storm water permits. To illustrate, this work uses continuous simulation modeling to estimate water balance components from bioretention and compares the results to those of a representative natural condition for the St. Louis, Missouri, area. Three different bioretention scenarios were modeled, each with different capture volumes and design features. The water balance of the representative natural condition is based on a prairie landscape in clayey silt soil over limestone bedrock. If runoff is defined as all discharge originating from the BMP, then none of the scenarios achieved the target natural condition. This is because evapotranspiration (ET) is the dominant process removing runoff in a natural condition, deep infiltration (deep recharge) in the St. Louis area is limited by geology, and ET is a small part of runoff removal in bioretention. If runoff is defined as the sum of overflow and underdrain flow, then any of the three bioretention scenarios could be adequate. However, there is a significant difference in BMP size, and by correlation, construction and land costs. This work demonstrates why an assessment of the capability of BMP performance in the context of local conditions is needed before setting BMP performance standards into NPDES permits. The BMP water balance indicates that in geology typical of St. Louis, Missouri, mimicking or restoring the pre-development runoff volume is not achievable with BMPs that primarily rely on infiltration to reduce volume. Bioretention is predicted to increase stream base flow, but the overall volume of water discharged to sewers, creeks, and rivers would be greater than the natural condition.

Dechlorination of chlorinated water and wastewater is most often achieved by chemical reduction through the addition of sulfur-IV compounds before discharge into the aquatic receiving environment or upon entry in the distribution system. However, reasonable doubts subsist about the efficiency of sulfur-IV compounds as dechlorination mediators for the reduction of chlorine and organic chloramines. As a consequence, alternative treatments have been investigated over the past few years but little information remains available on the kinetics of dechlorination at different dosages. In this study, the kinetics of dechlorination promoted by five selected dechlorination agents were observed at different stoichiometric ratios ($1x$, $3x$, and $10x$), and ANOVA was applied to the results in order to assess their statistical significance. Hydrogen peroxide (HP) was shown to promote faster than expected dechlorination; ascorbic acid and calcium thiosulfate also presented viable alternatives to treatment by sulfur-IV compounds represented by sodium sulfite and bisulfite in this study. This study challenges the common perception that HP dechlorination is slow and provides a comparative analysis for dechlorination kinetics using regression analysis, half-life values, and rate constants.

When designing wastewater aeration systems, fine-pore diffusers are typically selected for their potential energy efficiency. Because aeration is one of the most energy-intensive unit operations during treatment, the accurate quantification of aeration performance parameters is crucial to minimize the process energy footprint. Oxygen transfer efficiency in process water is the key design parameter; however, performance indicators that account for fouling and increased pressure drop with time must be considered. Both fouling and pressure drop increase cause an increase in blower power requirements. This paper presents a new approach to improve this design procedure, without altering the technical structure of the classical approach. Although the administrative and bidding milestones are underway (i.e., in the first few months of the project), an independent aeration team can test candidate diffusers suitable for design in an in situ aeration column. Subsequently, an extended fouling test in the plant’s wastewater can be carried out within the design timing, providing the designers with site-specific aeration performance data. This methodology improves the accuracy of the design process and increases overall energy savings.

Research was conducted to investigate the impact of particle size on ${\mathrm{H}}_2\mathrm{S}$ gas emissions and estimate a decay rate constant for ${\mathrm{H}}_2\mathrm{S}$ gas generation from the anaerobic decomposition of drywall. Three different particle sizes of regular drywall and one particle size of paperless drywall were evaluated. The experiment was conducted in a carbon-limited environment. The paperless drywall generated significantly less ${\mathrm{H}}_2\mathrm{S}$ gas than regular drywall at the same particle size. No significant differences were found between the rates of ${\mathrm{H}}_2\mathrm{S}$ gas generated from the different particle sizes of regular drywall investigated ($p=0.44$), which most likely was the result of the carbon limitation. The volume of ${\mathrm{H}}_2\mathrm{S}$ gas emitted from drywall was modeled as a first-order decay with correction factors that take into account the impacts of pH, temperature, and liquid-gas partitioning. The first-order decay model resulted in an average decay constant value of $0.14\pm 0.01$ and $0.031{\mathrm{year}}^{-1}$ for regular and paperless drywall, respectively, using a theoretical gas generation potential of $124{\mathrm{m}}^3{\mathrm{mg}}^{-1}$. Although the proposed model is unique in terms of taking into account the impact of gas-liquid phase partitioning, and the pH on the volume of ${\mathrm{H}}_2\mathrm{S}$ gas emissions, ${\mathrm{H}}_2\mathrm{S}$ generation and emission from construction and demolition (CD) landfills are influenced by many other factors for which the writers do not account. Thus, more research is needed to accurately predict ${\mathrm{H}}_2\mathrm{S}$ emissions from CD landfills. Nonetheless, the presented model offers a tool to landfill owners and engineers to estimate a baseline volume of ${\mathrm{H}}_2\mathrm{S}$ gas that may be emitted from landfilled drywall.

Waste-activated sludge (WAS) samples that were generated over a range of solids residence times (SRTs) under controlled operating conditions were employed in bench-scale sonication tests to characterize the impact of physical pretreatment processes on WAS anaerobic digestion and to assess the applicability of indicators for characterizing WAS digestibility. Physical, chemical, and biochemical analyses were conducted on raw and pretreated WAS samples and the results were compared to those obtained in biochemical methane potential (BMP) and biochemical acid potential (BAP) tests. The solublization responses indicated that the materials that were solublized were affected by the WAS SRT and sonication level. Despite differences in solublization responses, BMP tests revealed that sonication only marginally increased the ultimate biodegradability of the sludges. ${\mathrm{NH}}_4$ responses from the BMP tests and volatile fatty acids (VFAs) responses from the BAP tests were found to be indicative of the impact of sonication on the rate of hydrolysis and acidification/ammonification. Both responses suggested an increase in the rate of hydrolysis, which is typically the rate-limiting process in WAS digestion.

This study evaluated the system performance in terms of sorbent usage rate (SUR) of single column, two-column parallel, and lead-lag configurations, both with and without bypass blending, based on two normalized parameters describing the breakthrough profile (mass transfer zone length to lag ratio, or MTZ:Lag) and treatment objective ($C/C_o$). The pore surface diffusion model was used to simulate a range of single compound scenarios to develop a framework for comparing configurations. From this analysis, regions on a MTZ:Lag versus $C/C_o$ plot could be identified in which particular configurations yielded the lowest system SUR. At low MTZ:Lag ratios, bypass blending (single column or lead-lag operation) offered significant improvements because of the ability to bypass untreated flow and reduce sorbent bed mass. However, at low target $C/C_o$ values, bypass offered little improvement. Lead-lag without bypass performed best at high MTZ:Lag ratios by passing the mass transfer zone through two columns in series. At high MTZ:Lag ratios and high target $C/C_o$ values, two-column parallel configurations yielded significant benefits by blending high and low concentration effluents and improving sorbent utilization.

This paper describes the development and validation of a one-dimensional, large-strain consolidation-coupled contaminant transport model. The RCM-XPORT2 model uses the CS2 large-strain consolidation approach coupled with reactive advective/dispersive solute transport through a deforming saturated porous media, capped with a reactive sequestering geomaterial known as a reactive core mat (RCM). Validation of the model is presented by simulating consolidation-coupled contaminant transport experiments performed on naphthalene-spiked sediment from the Neponset River in Milton, Massachusetts. Finally, the paper presents a hypothetical case study of pre- and post-RCM application polychlorinated biphenyl (PCB) fate and transport in the Lower Neponset River using RCM-XPORT2 and U.S. EPA Water Quality Analysis Simulation Program surface water quality model. The Neponset River case study evaluates the long-term effect of sediment RCM capping on reducing the water column PCB concentration.

The development of appropriate disposal options for copper-based treated wood waste has been encouraged owing to stringent regulations regarding solid-waste landfilling or burning. Previous studies identified an efficient chemical process for removing metals from wood treated with chromated copper arsenate (CCA), alkaline copper quaternary (ACQ), copper azole (CA), and micronized copper quaternary (MCQ). The objective of this research was to identify optimal leaching parameters for removing copper from ACQ-, CA-, and MCQ-treated wood in terms of efficiency and operating costs. A $2^4$ Box-Behnken design was used for determining influential parameters (sulfuric acid concentration, temperature, retention time, and number of leaching steps) on the copper removal and for identifying optimal leaching conditions. The results obtained showed that sulfuric acid concentration and number of leaching steps were the main influential parameters on copper solubilization from alternatively treated wood. The values of $R^2>0.91$ for the mathematical models indicate a high correlation between observed and predicted values. The leaching conditions were optimized using response surface methodology, in which copper removal from ACQ-, CA-, and MCQ-treated wood wastes were to be maximized and operational costs were to be minimized. The optimum copper solubilization conditions were satisfied after three leaching steps of 2 h and 40 min each at room temperature and with an acid concentration fixed at 0.13 N followed by three rinsing steps. These optimal conditions led to 90, 90, and 93% of copper recovery from ACQ-, CA-, and MCQ-treated wood for a total cost of about US$180 per ton of treated wood. According to these results, chemical remediation from copper-treated wood appears to be an interesting solution to wood waste disposal problems.

Persistent organic pollutants (POPs) are organic substances that have characteristics of persistence in the environment; transboundary movement, or the ability to travel long distances through air and water; toxicity; and bioaccumulation in living things. Perfluorooctane sulfonate (PFOS), a toxic chemical that never breaks down, was added to the Stockholm Convention on POPs and was listed in the Annex B restrictions with many exemptions to continue using PFOS. This study focused on the occurrence of PFOS in the water system of Bangkok, Thailand, including the Chao Phraya and Bang Pakong Rivers, tap water in industrial zones and residential areas, drinking water, and industrial wastewater. Seasonal effect of PFOS between dry season and wet season was also observed for more than 3 years. Solid phase extraction (SPE) coupled with HPLC-ESI-MS/MS was used for the analysis of these compounds. PFOS was detected in most water samples. The average concentration of PFOS in the Chao Phraya River (urban area) was $1.70\mathrm{ng}/\mathrm{L}$, whereas lower concentrations were detected in the Bang Pakong River (suburban area), residential tap water, and bottled drinking water, with averages of 0.7, 0.4, and $0.5\mathrm{ng}/\mathrm{L}$, respectively. Higher concentrations (an average of $25.1\mathrm{ng}/\mathrm{L}$) were found in industrial tap water, whose sources were from surface water near the industrial zones. Much higher concentrations were detected in industrial wastewater, with the maximum of $6,100.8\mathrm{ng}/\mathrm{L}$. These results indicated that industrial wastewater was one of the major sources of PFOS contamination in the water system of the city of Bangkok. This study provided data on the spatial occurrence, its seasonal effect, and distribution of PFOS in the water environment of Bangkok and surrounding areas, which need continuous attention to this emerging contaminant.

The addition of iron salts to sewers for sulfide control has a significant impact on downstream wastewater-treatment performance, in which iron ions can be resolubilized from iron sulfide precipitates in aeration tanks to precipitate phosphate, thus enhancing phosphorus removal from the wastewater. In this study, the impact of iron salt dosage to sewers on the performance of anaerobic sludge digesters was investigated at bench scale. Anaerobic digesters were fed with mixed primary sludge, activated sludge, and sludge that contained ferric phosphate precipitates, formed by aerating iron sulfide- and phosphate-containing wastewater with activated sludge. In anaerobic conditions, ferric ions were released from ferric phosphate precipitates and utilized for a third time to precipitate sulfide that formed during sludge digestion, which ultimately resulted in complete control of ${\mathrm{H}}_2\mathrm{S}$ emissions from digesters. The results indicate that iron salt addition to sewers at typical dosing rates (e.g., $5–20\mathrm{mg}\mathrm{Fe}{\mathrm{L}}^{-1}$) would provide an excessive quantity of iron salts for sulfide control in sludge digesters. Methane production and other digestion processes were not negatively impacted by iron addition to the wastewater.