Journal of Environmental Engineering

Distribution patterns of particulate matter 2.5 (${\mathrm{PM}}_{2.5}$) inside urban street canyons varies according to the street canyon enclosure ratio (SCER) and traffic flow states, and therefore they affect people in different positions of street canyons to different extents. This paper studied ${\mathrm{PM}}_{2.5}$ distribution patterns in both symmetric and asymmetric street canyons by using the computational fluid dynamics technique. Simulation experiments were conducted in a series of isolated street canyons in Beijing with five SCERs and three types of traffic flow states. The results of the simulation experiments were verified with on-site data. The results are threefold: (1) ${\mathrm{PM}}_{2.5}$ emitted by the vehicles gathers around the corners of leeward buildings of street canyons, and this phenomenon tends to be aggravated by heavy traffic flow states in most scenarios; (2) of five SCERs, it was the most difficult for ${\mathrm{PM}}_{2.5}$ to spread out of the canyons with SCER = 2:1:2, whereas it was the easiest for ${\mathrm{PM}}_{2.5}$ to spread out of the canyons with SCER = 2:2:1; and (3) pedestrians and residents on the leeward side of asymmetric street canyons are exposed to the highest ${\mathrm{PM}}_{2.5}$ concentration. The findings of this research will assist in designing street canyons, controlling the traffic flow, and developing measures to reduce the harm of ${\mathrm{PM}}_{2.5}$ to the public.

Stormwater basins, which are subject to highly unsteady flows and loads, function as clarifiers for particulate matter (PM) and PM-bound constituents. Quasi-steady flow hydrodynamics in water and wastewater treatment plant units, from grit to contact chambers, are known to impact treatment. In contrast, there is sparse basin design guidance for unsteady hydrodynamics and clarification interactions. Basins can become impaired with needed retrofits. Lumped models, such as surface overflow rate (SOR), are less suitable for complex geometries, hydrodynamics, and loadings. A computational fluid dynamics (CFD) and evolutionary optimization framework as higher-fidelity tools is proposed for relatively shallow basins with permeable baffle retrofits. This study extends previous research and optimizes baffle configuration by further considering routing effects and unsteady loading on clarification. For an influent heterodisperse particle size distribution (PSD), baffles improve PM clarification by 58.8% based on baffle number. Strategically altering the baffle position, length, and angle yields an optimal configuration with improved clarification of 32% in comparison to conventional baffle configurations. Baffle optimization leads to construction costs that are one-third to one-fifth those of conventional baffle configurations.

This study examined primary data on the energy use (electricity and natural gas) of nine surface water treatment plants in and around Salt Lake City, Utah, and how their energy use relates to their sizes, processes, and climates. The energy intensities per unit of treated water, averaged over a 3-year period, ranged from 0.059 to $0.565\mathrm{kW}·\mathrm{h}/{\mathrm{m}}^3$ [$220–\mathrm{2,140}\mathrm{kW}·\mathrm{h}/\mathrm{million}\mathrm{gal.}$ (MG)] with a weighted average of $0.162\mathrm{kW}·\mathrm{h}/{\mathrm{m}}^3$ ($610\mathrm{kW}·\mathrm{h}/\mathrm{MG}$), concurring with the literature. The data confirmed economies of scale: larger plants and higher production had lower energy intensities. The analysis found energy differences for certain disinfection processes; ozone and ultraviolet disinfection required more energy than did chlorination. Significant energy baseloads (presumably for ventilation, lighting, and other building systems) were observed, even when little or no water was being treated. All sites had significant natural gas use, which was attributed mostly to space heating—33% to 67% of total energy—which should not be overlooked in energy management programs. Additional recommendations for sustainable planning, design, and operation of water treatment plants were discussed.

Eulerian–Lagrangian methods are common for computational fluid dynamics (CFD) modeling of particle fate. Near-wall turbulence flow profiles are frequently modeled with wall function (WF) for computational efficiency and stability. However, WF does not provide the viscous and buffer sublayers solution for Lagrangian particle tracking (LPT). This study examines Reynolds-averaged Navier-Stokes (RANS)-LPT model combinations with near-wall models (two-layer, low-Reynolds number, WF), common LPT boundary conditions (trap, reflect), near-wall grids resolution ($\mathrm{\Delta }{y}^{+}$), and LPT solver configurations. Near-wall LPT in an open channel clarifier illuminates embedded numerical errors/artifacts generated by widely-used RANS-WF-LPT model combinations as benchmarked to direct numerical simulations (DNS). Near-wall LPT can be subject to grid resolution irrespective of particle-boundary interactions and LPT boundary conditions applied. Clarifier simulations illustrate LPT solver configurations influence particulate matter (PM) separation. RANS-LPT solutions are a function of particle diameter, maximum particle integration steps, and to a lesser degree on tracked particle number. Low-Reynolds number and two-layer models improve per particle size separation predictions compared to the WF model by up to 50% for 25–100 μm particles based on physical model benchmarking.

Inline chlorination technologies can provide a flexible option for water treatment in a variety of scenarios in low-resource settings. However, limited efficacy data on chlorine dosing and the resulting free chlorine residual (FCR) levels under controlled conditions increases the barrier to use for both field practitioners and end users. In this paper, we report FCR data on the Aquatabs Flo device, a passive inline chlorinator, for common operating conditions including flow rates between 2 and $18\mathrm{L}/\min$ (0.5 and $4.8\mathrm{gal}\mathrm{.}/\min$), pressure levels between 137.9 and 551.6 kPa (20 and 80 psi), and device positions (horizontal, tilted left or right, leaning forward or backward). In addition, we demonstrate a modification to the device to enable point-of-collection applications. Results suggest that variations in pressure do not influence FCR values, whereas device positions (i.e., misalignments) do. Finally, device modifications can reduce the FCR values for point-of-collection applications. The data reported here can be used to build decision support tools for field practitioners.