Journal of Environmental Engineering

Bioretention, or variations such as bioinfiltration and rain gardens, has become one of the most frequently used storm-water management tools in urbanized watersheds. Incorporating both filtration and infiltration, initial research into bioretention has shown that these facilities substantially reduce runoff volumes and peak flows. Low impact development, which has a goal of modifying postdevelopment hydrology to more closely mimic that of predevelopment, is a driver for the use of bioretention in many parts of the country. Research over the past decade has shown that bioretention effluent loads are low for suspended solids, nutrients, hydrocarbons, and heavy metals. Pollutant removal mechanisms include filtration, adsorption, and possibly biological treatment. Limited research suggests that bioretention can effectively manage other pollutants, such as pathogenic bacteria and thermal pollution, as well. Reductions in pollutant load result from the combination of concentration reduction and runoff volume attenuation, linking water quality and hydrologic performance. Nonetheless, many design questions persist for this practice, such as maximum pooling bowl depth, minimum fill media depth, fill media composition and configuration, underdrain configuration, pretreatment options, and vegetation selection. Moreover, the exact nature and impact of bioretention maintenance is still evolving, which will dictate long-term performance and life-cycle costs. Bioretention usage will grow as design guidance matures as a result of continued research and application.

Storm-water monitoring generally uses flow-weighted automatic composite samplers to collect a representative sample of an entire storm event. Automatic samplers are convenient but unfortunately they can be expensive, especially for temporary sampling needs or for short-term research projects. An alternative method is to use a series of grab samples. This paper examines the accuracy of event mean concentrations (EMCs) and mass first flush ratios calculated from a finite number of grab samples, and compares them to results from flow-weighted automatic samples. Both sampling techniques were evaluated using data collected from a three-year investigation of three highway sites. A large number of grab samples is needed to approach the accuracy and precision of flow weighted composite samples, and 30 grab samples per storm event generally estimated the EMCs within 20% average error. To detect a first flush, it is necessary to take even more grab samples or to adjust the timing of the sample collection toward the beginning of the storm. The superiority of automatic sampling for estimating EMCs for constituents compatible with automatic sampling is demonstrated.

Lack of widespread adoption of low-impact development (LID) designs in northern climates is in large part due to concerns about poor winter performance relating to (1) frozen filter media; and (2) dormant biological functions. An examination of six varied LID designs, in contrast with conventional best-management practices (BMPs) and manufactured systems illustrated that seasonal functionality was evident for many systems; however, the LID designs were consistently top storm water management performers. The designs were tested and monitored for cold climate performance from 2004–2006 to assess: filter media frost penetration, hydraulic efficiency, and seasonal variations of contaminant removal efficiency. LID systems evaluated included: two types of bioretention systems, a surface sand filter, a subsurface gravel wetland, a street tree, and porous asphalt. The LID performance data were contrasted with conventional structural BMPs (swales, retention pond) and some select manufactured storm-water systems (hydrodynamic separators); (3) a filtration system, and a subsurface infiltration system. Seasonal performance evaluations indicate that LID filtration designs differ minimally from summer to winter, while smaller systems dependent largely on particle settling time demonstrated a marked winter performance decline.

Gas collection systems of various designs have been used to control landfill gas emissions, which can be problematic, particularly before installation of final landfill covers. In this work, an innovative gas collection system that includes a permeable layer near the top surface of landfills was evaluated for enhancing capture of landfill gas and reducing fugitive methane emissions. A computational model that accounts for advective and diffusive fluxes of multiple gas components was used to evaluate the efficiency of this new design for intermediate landfill covers. The utility of the high-permeability gas-conductive layer was illustrated for several conditions of interest including varying refuse permeability, varying degrees of permeability anisotropy, and temporal atmospheric pressure changes. Simulations showed that the permeable layer decreased methane emissions by 43% when the horizontal to vertical permeability ratio for refuse was $k_h∕k_v=3$ and the domain average $k_h=3\times {10}^{-12}{\mathrm{m}}^2$ , while reductions in methane emissions decreased to 17% for the same anisotropy but with $k_h={10}^{-11}{\mathrm{m}}^2$ . With this design, barometric pressure changes did not significantly affect oxygen intrusion or methane emission rates.

Modern water treatment must maintain an acceptable balance between the microbial safety of potable water supply, the costs of treatment, and the formation of potentially harmful disinfection by-products (DBPs). In order to achieve the optimum balance, it is essential to understand and predict both the formation of DBP and the decay of chlorine, in relation to source water, treatment processes, storage, and supply. Reported herein are new data which demonstrate the lack of durability, precision, and accuracy associated with earlier empirical chlorine decay rate equations. This work develops an improved methodology for the prediction of variation in chlorine decay rates in distribution systems enabling practical, cost-effective prediction of the effects of both seasonal variations and management interventions on chlorine levels at treatment works and in distribution systems.

Aerobic granular sludge technology was applied to the simultaneous nitrogen and phosphorus removal from livestock wastewater that contains high concentrations of nitrogen and phosphorus (TN: $650\mathrm{mg}∕\mathrm{L}$ ; TP: $125\mathrm{mg}∕\mathrm{L}$ ). A lab-scale sequencing batch reactor was operated in an alternating anaerobic/oxic/anoxic denitrification mode. Granular sludge was first formed using synthetic wastewater. When livestock wastewater was diluted with tap water, the shape and settleability of aerobic granular sludge were maintained even though livestock wastewater contained suspended solids. Simultaneous nitrification, denitrification, and phosphate uptake were observed under an aerobic condition. However, when nondiluted livestock wastewater was used, the diameter of granular sludge and the denitrification efficiency under an oxic condition decreased. When the concentrations of nitrogen and phosphorus in wastewater increased, hydraulic retention time (HRT) increased resulting in a decrease in selection pressure for granular sludge. Therefore, the sustainment of granular sludge was difficult in livestock wastewater treatment. However, by applying a new excess sludge discharge method based on Stokes’ law, the shape of granular sludge was maintained in spite of the long HRT $\left(7.5\text{days}\right)$ . To select large granular sludge particles, excess sludge was discharged from the upper part of settled sludge because small particles localized there after settling. Finally, excellent nitrogen and phosphorus removal was accomplished in practical livestock wastewater treatment. The effluent concentrations of $\mathrm{N}{\mathrm{H}}_4–\mathrm{N}$ , $\mathrm{N}{\mathrm{O}}_x–\mathrm{N}$ , and $\mathrm{P}{\mathrm{O}}_4–\mathrm{P}$ were $<0.1$ , 1.4, and $1.2\mathrm{mg}∕\mathrm{L}$ , respectively.

Aluminum industry wastes are solid residues contaminated with polycyclic aromatic hydrocarbons (PAHs) and fluorides. The aluminum industry waste used in this study contained $1,129\mathrm{mg}{\mathrm{kg}}^{-1}$ of benzo(b,j,k)fluoranthene. On application of toxicity characteristic leaching procedure (TCLP), a leachate containing $448\mathrm{mg}{\mathrm{L}}^{-1}$ of fluoride ions was obtained. The decontamination of aluminum industry wastes was carried out in cycles and included a stage of flotation, followed by stabilization and neutralization. The flotation treatment in the cell containing wastes contaminated with a concentration of 15% $\left(\mathrm{w}{\mathrm{v}}^{-1}\right)$ in the presence of surfactant cocamydopropyl hydroxysultaine (0.25% $\mathrm{w}{\mathrm{w}}^{-1}$ ) allowed 47 to 83% removal of benzo(b,j,k) fluoranthene. The subsequent step of lime stabilization (8% $\mathrm{w}{\mathrm{v}}^{-1}$ ) allowed production of nonhazardous wastes. The concentration of fluoride ions resulting from the TCLP test $\left(67\mathrm{mg}{\mathrm{L}}^{-1}\right)$ remained lower than the permissible level $\left(150\mathrm{mg}{\mathrm{L}}^{-1}\right)$ .

This paper presents three steady-state mathematical models for the design of ${\mathrm{H}}_2∕\mathrm{C}{\mathrm{O}}_2$ fed gas-lift reactors aimed at biological sulfate reduction to remove sulfate from wastewater. Models 1A and 1B are based on heterotrophic sulfate reducing bacteria (HSRB), while Model 2 is based on autotrophic sulfate reducing bacteria (ASRB) as the dominant group of sulfate reducers in the gas-lift reactor. Once the influent wastewater characteristics are known and the desired sulfate removal efficiency is fixed, all models give explicit mathematical relationships to determine the bioreactor volume and the effluent concentrations of substrates and products. The derived explicit relationships make application of the models very easy, fast, and no iterative procedures are required. Model simulations show that the size of the ${\mathrm{H}}_2∕\mathrm{C}{\mathrm{O}}_2$ fed gas-lift reactors aimed at biological sulfate removal from wastewater highly depends on the number and type of trophic groups growing in the bioreactor. In particular, if the biological sulfate reduction is performed in a bioreactor where ASRB prevail, the required bioreactor volume is much smaller than that needed with HSRB. This is because ASRB can out-compete methanogenic archaea (MA) for ${\mathrm{H}}_2$ (assuming sulfate concentrations are not limiting), whereas HSRB do not necessarily out-compete MA due to their dependence on homoacetogenic bacteria (HB) for organic carbon. The reactor sizes to reach the same sulfate removal efficiency by HSRB and ASRB are only comparable when methanogenesis is inhibited. Moreover, model results indicate that acetate supply to the reactor influent does not affect the HSRB biomass required in the reactor, but favors the dominance of MA on HB as a consequence of a lower HB requirement for acetate supply.

Hydraulic structures, such as stepped cascades and weirs, involve air entrainment (aeration) and oxygen transfer. Therefore, they can increase dissolved oxygen levels. Weir aeration occurs in rivers, fish hatcheries, and wastewater treatment plants. A stepped cascade aerator is another type of aeration structure. A stepped cascade consists of a series of steps or drops, built into the face of the chute. Often, the hydraulic head is naturally available and incurs no operating cost. For the preaeration process, weir and stepped cascade structures can be previously designed for clarifiers where weirs can be used as an aid to aeration process of treatment plants. Therefore, this paper aims to review the design considerations of circular clarifiers with combined weir and stepped cascade structures as a new approach and alternative preaeration system without energy requirement before aeration tank units. The detailed example for preaeration in circular clarifiers with combined weir and stepped cascade structures is presented. Thus, the circular clarifiers with weir and stepped cascade structures as effluent and preaeration strucures can be effectively redesigned with given new design considerations.

A global ban on the use of tributyltin has resulted in the need to screen new antifouling agents to control algal growth in aquatic environments. Standard methods for the quantification of algal biomass are disruptive in nature; therefore, they are not applicable for the screening studies requiring successive observations at specified time intervals. The objective of this study was to develop a nondisruptive method to quantify algal growth on a variety of surfaces. Image analyses and chlorophyll extraction methods were used to quantify an algal biomass on a concrete surface containing different additives. For concrete samples containing single additives, the coefficient of determination between both techniques ranged from 0.74 to 0.84. However, for concrete samples containing multiple additives, the coefficient of determination of both methods ranged from 0.72 to 0.75. Results suggest that an image analyses technique can be used to accurately quantify various types of algae growing on a variety of solid surfaces.