Journal of Environmental Engineering

Enhanced biological phosphorus removal (EBPR) is an effective nutrient removal process that has been engineered and successfully applied in wastewater treatment for decades. Although the prevalent microorganism performing EBPR in full-scale activated sludge plants was identified nearly a decade ago as Candidatus Accumulibacter phosphatis, it still remains an unculturable organism. In this paper, the authors describe research that has been aimed at identifying and isolating microorganisms responsible for EBPR, along with the fundamental metabolic, genetic, and ecological advances that have been recently made in the characterization of Cand. A. phosphatis. Furthermore, evidence is presented that Cand. A. phosphatis can perform the EBPR cycle under nitrogen-limiting conditions, a characteristic that could be potentially incorporated into strategies to obtain pure cultures of this organism. Finally, possible research directions that could be enabled when a pure culture of this organism is obtained were discussed.

Floc blankets are fluidized beds of aggregated suspended particles utilized in some upflow sedimentation tanks for drinking water treatment. Floc blankets can significantly enhance particle removal and may reduce operation and maintenance costs. An experimental apparatus was built with the goal of developing an understanding of floc blanket physics and to establish a mechanistic basis for optimizing floc blanket performance. Visual insights into floc blanket mechanics are obtained by analyzing transmitted light intensity through a 1.3-cm-thick section of a floc blanket. Floc blankets were formed under simulated raw water conditions of 100 nephelometric turbidity units (NTU), an alum coagulant dose of $45\mathrm{mg}/\mathrm{L}$ ($4.1\mathrm{mg}/\mathrm{L}$ as Al), and at sedimentation tank upflow velocities ranging from 0.4 to $1.8\mathrm{mm}/\mathrm{s}$. This study presents nondestructive methods for measuring floc blanket concentration and position of the floc-water interface, steady-state performance data from the experimental apparatus, and the effect of upflow velocity on solids concentration in a floc blanket.

One of the great challenges of gravity settling is the difficulty of effectively removing suspended solids from the water column and retaining the settled particles in the settling basin under high inflow rates and short resident times. To address these issues, a new concept of using a bottom grid structure (BGS) for enhancing suspended solids removal by introducing a downward vertical vortex force and reducing disturbances of the bottom settled sediment was proposed and tested in the laboratory. A series of comparative laboratory experiments, without and with BGS, were carried out in a $2.47(\mathrm{L})\times 1.46(\mathrm{W})\times 0.39\text{-}\mathrm{m}$ (D) tank. The experimental results revealed that for the tested flow rates ranging from 4 to $8\mathrm{L}/\mathrm{s}$, the removals of test particles with the BGS in the tank were about 10 to 30% higher than those obtained for the same conditions, but with a smooth tank bottom. Thus, the newly proposed BGS acts as a structure trapping and storing solids. In general, the improvement of particle removal rates was proportional to the inflow rate (or flow speed along the BGS top surface), before reaching a maximum value. This indicated that particles settled in the BGS cell on the tank bottom were effectively protected from disturbances by the fast bottom flows or external forces. To further examine the retention of deposited sediment by the proposed BGS, comparative experiments were conducted by placing particles on the tank bottom before activating inflow, with and without the BGS present. The results showed that for an inflow rate of $6\mathrm{L}/\mathrm{s}$, 67% of the placed particles were retained in the settling tank with the BGS; without it, the corresponding percentage was just 26%. Thus, the BGS retained 41% more of the particles settled in the bottom. A computational fluid dynamics (CFD) model was also used to describe the hydraulic conditions in the settling tank under various inflow rates and such results were helpful for establishing the relationships between the improved removal of suspended solids and the bottom flow speed and flow patterns in general. BGS offers a great promise of improving the performance of engineering facilities (e.g., stormwater detention ponds) serving to remove suspended solids from environmental flows.

This paper addresses the design and experimentation aspects of scaled contact tanks, a key type of treatment units in water works worldwide. The paper covers the effects of scale and discharge variation on the dynamic similitude and hydraulic efficiency of such tanks. The flow patterns tending to complete mixing (CM) and plug flow (PF) were studied, each assessed in a prototype and three further geometrically similar models of L-shaped and serpentine geometries. Tracer experiments were conducted under five discharge values. The sensitivity of each flow pattern to the changing conditions was assessed based on the residence time distribution curves and hydraulic efficiency index values, contrasted for prototypes and their scaled models. Although the CM flow pattern was insensitive to the variation of scale and discharge, within the ranges tested in this study, the PF pattern was affected by both variations when the flow regime was not turbulent in a model tank. A dependency of the dispersion number on the Reynolds number was observed, leading to the proposal of a new model to support the design and upscaling of results in contact tank studies.

Batch experiments were performed to evaluate sorption of zwitterionic and anionic cephapirin (CHP° and ${\mathrm{CHP}}^{–}$, respectively), a cephalosporin antibiotic, in two quartz-rich sands spiked with iron (0.5–5% by weight). Sand A was approximately 65% quartz and 29% feldspar, with a grain diameter of 0.11 mm. Sand B was approximately 97% quartz and approximately 2% feldspar with a grain diameter of 0.39 mm. Bulk CHP sorption was evaluated relative to four added iron phases, namely, Fe° [zero-valent iron (ZVI)], ${\mathrm{Fe}}_3{\mathrm{O}}_4$ (magnetite), and two forms of ${\mathrm{Fe}}_2{\mathrm{O}}_3$ (dull and specular hematite). Iron-particle sizes matched the respective sands to which they were added. Experiments were performed at two temperatures (21 and 39°C) and the results were compared with CHP sorption in unspiked sands. Maximum sorption occurred in Sand B and was approximately $225\mathrm{mg}/\mathrm{kg}$ of spiked sand for initial aqueous CHP concentrations of 5–50 ppm, at 39°C and pH 5. Addition of ZVI caused the largest increase in CHP sorption with distribution coefficients ($K_d^{\prime }s$) nearly 12 times those of ZVI-free sands. The study results imply the potential use of microscale ZVI, and to a lesser extent iron oxides, in the remediation of cephalosporin-contaminated groundwater and soil.

Effects of solids retention time (SRT) on both steps of the nitrification process (e.g., ammonia oxidation and nitrite oxidation) and the nitrifier community in a complete-mix activated sludge process were studied. At a SRT less than or equal to 20 days, the effluent ammonia concentration was lower than the effluent nitrite concentration. At the 40-day SRT, however, the effluent nitrite concentration became equal to or less than the effluent ammonia concentration. Quantitative Polymerase Chain Reaction (QPCR) assays indicated that increasing SRT significantly increased nitrite-oxidizing bacteria/ammonia-oxidizing bacteria (NOB/AOB) ratio. Further investigation indicated that Nitrosomonas europaea/eutropha were the dominant AOB for ammonia oxidation under all SRTs. However, for nitrite oxidation, Nitrobacter-like NOB played the key role at low SRTs, while Nitrospira-like NOB played the key role at high SRTs. Modeling results indicated that, for AOB and NOB, the values of maximum specific growth rate ($\mu$) were 0.24 and $0.18/\mathrm{day}$, respectively, while the values of decay coefficient ($K_d$) were 0.066 and $0.045/\mathrm{day}$, respectively. The half-velocity constants ($K_S$) for both AOB and NOB were approximately $0.02\mathrm{mg}/\mathrm{L}$, and the maximum specific substrate utilization rate ($k$) for AOB and NOB were 1.3 and $3.0\mathrm{g}\text{-}\mathrm{N}/\mathrm{g}$-VSS-day, respectively. These values suggest that AOB had an advantage over NOB at a lower SRT, mainly because AOB grew faster than NOB did. On the contrary, the increased NOB/AOB ratio at a longer SRT was likely due to NOB having a smaller $k_d$. The very low $K_S$ values for both AOB and NOB imply that a plug-flow reactor may not have much kinetic advantage over a complete-mixed reactor for a complete nitrification process. The mass concentrations of AOB and NOB in the activated sludge can also be calculated based on the measured nitrification capacity and their $k$ value.

Geomembrane–bentonite composite barrier is known as one of the most reliable and effective technologies for containing underground contamination. Analytical solution for one-dimensional diffusion of an organic solute in the three-layered composite barrier is presented for the case in which the barrier is keyed in aquitard. Parametric analyses were conducted to investigate the effects of partition coefficient and installation location of high-density polyethylene (HDPE) geomembrane, retardation factor, and thickness of bentonite slurry wall on the barrier performance using this analytical solution. The analysis results demonstrate that the containment performance of the composite barrier depends much on the partition coefficient of HDPE geomembrane over the target pollutant. The HDPE geomembrane exhibits an excellent resistance to the hydrophilic organics, which have a low partition coefficient. However, the hydrophobic organics, which have a high partition coefficient, can diffuse readily through the HDPE geomembrane. It is found that there is a special value of partition coefficient (i.e., $S_{gf}=40$) at which a peak value was calculated for the mass flux through the composite barrier and a minimum value for the breakthrough time. The containment performance of the composite barrier can be enhanced by 10–20% by choosing an optimal installation location of HDPE geomembrane. An increase in the retardation factor $R_d$ of the bentonite results in a delay in the occurrence of the stable mass flux, but does not change its magnitude. An increase in the wall thickness not only delays the occurrence of the stable mass flux, but also significantly reduces its magnitude.

This paper develops a template-based fuzzy inference system (TFIS) capable of simulating the dissolved oxygen (DO) concentration of an example stream by using daily data (2009–2012). Stepwise regression (SR) analysis and Mallows’ Cp statistic were employed to select the best set of independent parameters for the input vector of the TFIS and the regressive models. The most effective inputs were determined for temperature and specific conductivity ($P\text{-}\mathrm{value}=0.000$), whereas flow rate ($P\text{-}\mathrm{value}=0.002$) and pH ($P\text{-}\mathrm{value}=0.004$) were found to be less effective parameters. The TFIS and SR models undersimulated the magnitude of high DO concentrations ($>12.5\mathrm{mg}/\mathrm{L}$), whereas the low and medium DO concentrations were oversimulated. However, they were closer to the observed data. A comparison of the prediction accuracy of the TFIS and SR methods indicated that the TFIS approach was more accurate in simulating DO concentrations, except for low concentrations of DO ($<10\mathrm{mg}/\mathrm{L}$). The TFIS method was found to be superior to the conventional SR model.

Acetaminophen (ACT), an over-the-counter analgesic and antipyretic, remains one of the most frequently used household medications. This drug persists in domestic effluents in significant concentrations even after conventional treatment. This study demonstrates the effectiveness of fluidized-bed Fenton process to decompose acetaminophen in synthetic wastewater. Parametric studies were conducted to evaluate the effects of initial pH, initial ACT concentration, ${\mathrm{Fe}}^{2+}$ and ${\mathrm{H}}_2{\mathrm{O}}_2$ dosages on ACT oxidation. At optimum operating parameters, up to 97.83% ACT degradation was attained after 2 h of reaction. For interference studies of organic acids (oxalic, fumaric, maleic, acetic, succinic, malonic, and formic acids), oxalic acid was found to limit ACT degradation to only 9.26%.

The search for sustainable and effective water reclamation technologies has been stimulated by increasingly urgent water scarcity. Graywater (GW) is an excellent potential resource for relieving the water scarcity problem because it has a relatively low pollution level and because it is abundant and accessible. GW makes up approximately 70% of domestic wastewater. A new technology, shredded tire biofilter (STB), combined with a membrane bioreactor (MBR), was demonstrated to be an efficient method for treating GW to a level that satisfies the USEPA’s water reuse guidelines. In the proposed technology, the MBR ensured adequate effluent water quality, and the STB pretreated the GW. The technology may significantly reduce the energy required to treat GW by MBRs alone. It was further observed that increasing hydraulic retention time and decreasing shredded tire particle size enhanced the removal of ${\mathrm{BOD}}_5$ in the STBs. Analysis of biofilms on shredded tire chips showed that microorganisms could attach and grow on tire shreds. Moreover, this combination would be economically feasible and environmentally sustainable for an average household (i.e., three to four people), making it a potentially promising technology for decentralized wastewater treatment.

This paper reports on the results of dispersion modeling of mobile source air toxics (MSATs) near seven intersections and seven freeway segments in the state of Florida. Different modeling approaches were used, all with the focus on a hot-spot analysis to obtain the worst-case (highest) 1-h concentration. To accomplish the worst-case modeling, the CAL3QHC model was modified to handle inputs of several individual MSATs and to predict the concentrations of these MSATs around roadways. Real-world data (traffic volumes and site geometry) were gathered, meteorological input data were selected, and mobile source emission factors (EFs) were obtained from the U.S. EPA’s mobile-source emissions model, MOVES2010a. Based on a literature search of short-term effects, maximum acceptable concentrations (MACs) for a 1-h averaging time were proposed for comparison with the modeled results. Results from this study indicate that for all of the intersections and freeway segments, the worst-case 1-h modeled concentrations of the MSATs were several orders of magnitude below the proposed short-term MACs. It is recognized that long-term exposures and chronic health effects are a major concern associated with MSATs. With this in mind, additional modeling (using CAL3QHCR and AERMOD) was conducted to show how the prediction of long-term concentrations could potentially be addressed.