Journal of Environmental Engineering

This paper aims to develop a general reaeration model for water bodies subject to small surface perturbation, such as ripples that may be induced by wind, waves, and surface current. A test rig was specially designed and fabricated to study the influence of waves on the reaeration process. The wave frequency varied from 0.125 Hz to 0.425 Hz for various wave heights, $H$, ranging from 0.15 cm to 1.5 cm. Based on the findings of the experimental study, the authors developed a modified film model and introduced a diffusive film-layer thickness ${\delta }_D$ as the characteristic length scale for the reaeration process. The thickness of the diffusive film layer may be determined readily in one of two ways: (1) as the ratio between the molecular diffusivity of dissolved oxygen and the measured oxygen transfer coefficient; and (2) estimated using its established functions with other concentration boundary layers proposed by various researchers. The modified film model was found to unify the present experimental data and published data.

The objective of this research was to characterize the performance of a pilot scale downflow bubble contact (DBCA) hypolimnetic aerator, the Speece Cone. The effect of two key design factors, inlet water velocity and the ratio of gas flow rate to water flow rate on four standard units of oxygen transfer, was examined: (a) the oxygen transfer coefficient, $K_{L}a$, corrected to 20°C, $K_L{a}_{20}({\mathrm{h}}^{-1})$; (b) the standard oxygen transfer rate, SOTR ($\mathrm{g}{\mathrm{O}}_2·{\mathrm{h}}^{-1}$); (c) the standard aeration efficiency, SAE ($\mathrm{g}{\mathrm{O}}_2·\mathrm{kW}{\mathrm{h}}^{-1}$); and (d) the standard oxygen transfer efficiency, SOTE (%). Two sources of oxygen, pressure swing adsorption (PSA) oxygen (87% purity oxygen) and air ($\sim 21\%$ oxyzen) were compared. $K_L{a}_{20}$, SOTR, and SAE increased with an increase in the ratio of gas flow rate to water flow rate for both air and oxygen, over a range of 0.5% to 5.0%; while SOTE deceased. An increase in inlet water velocity resulted in a decrease in $K_{L}a$, corrected to 20°C, SOTR, and SAE, but an increase in the SOTE. Experimental treatments with air showed similar, but much less dramatic effect of the gas flow rate to water flow rate ratio and water inlet velocity on $K_L{a}_{20}$, SOTE, SAE, and SOTE, when compared to treatments with PSA oxygen. The best oxygen transfer performance was achieved with an inlet water velocity of $6.9–7.6\mathrm{m}·{\mathrm{s}}^{-1}$ and oxygen flow rate to water flow rate ratio of about 2.5%. At this combination, the SOTE was about 66–72%. Further experimentation with inlet water velocity is required to increase oxygen transfer performance to the $>95\%$ range which has been reported in the literature for Speece Cone oxygenation systems.

The research reported in this paper compares the soil characteristics in terms of their microbial structures and activities under several pervious pavements. Due to differences in texture, construction, and permeable characteristics among these pavements, diverse microbes flourish in the underlying soil. The writers hypothesized that the soil structure under the JW pavement, a high-load-bearing water-permeable pavement, allows colonization of abundant and diverse microbes, thus supporting active and versatile microbial metabolism. The writers collected two soil layers, (1) aggregate and (2) soil bases, under the JW and three other pervious pavements, (1) asphalt, (2) concrete brick, and (3) concrete-glass block, installed side-by-side on a university campus in Taiwan. The writers analyzed the granulometry, water content, soil pH, total organic carbon, total nitrogen content, enzymatic activities, community-level physiological profiles, and phylogenetic bacterial diversity, and performed a microbiological assay. Results revealed that the activation and versatility of microbial activities, and the abundance and diversity of bacterial communities, were mainly related to the total organic carbon content among the pavements. The microbial compositions and their activities under the JW pavement were both superior to those under the other pervious pavements, except for the abundances of fungi and actinobacteria. Bacterial communities under the JW pavement were more abundant and diverse. The soil under the JW pavement also reflected more-activated and more-versatile microbial metabolism in all substrates and for specific types of functional guilds. These results were due to the characteristics of a looser structure, higher moisture, and a higher total organic carbon content.

The overall performance of 18 commonly used reaeration rate coefficient prediction equations was evaluated using statistical metrics of prediction accuracy and bias by comparing predicted reaeration coefficients to a database of values measured using gas tracer techniques. Adapting a commonly applied concept, predictive equations were evaluated in discrete regions of the velocity-depth space. Results indicate that rarely is there a single best prediction equation in a given velocity-depth region, rather there usually is a group of statistically indistinguishable top-performing equations. Also, no single reaeration equation performed well over all hydraulic conditions. Prediction equations, which include slope as a variable are more accurate and have lower bias than those that do not. However, even the top-performing equations exhibited large prediction errors of at least 40–50% and exceeded 100% in some regions. This level of error in predicting reaeration rate coefficients will continue to have a major impact on the uncertainty of dissolved oxygen forecasts from receiving water quality models.

The effects of aging should be considered for reliable long-term assessments of the environmental risks of the use of refuse-derived-fuel (RDF) fly ash as landfill top cover liner material. Mineral transformations that occur in RDF fly ash, and the effects of selected factors on these transformations, were studied on compacted fly ash specimens in an accelerated aging experiment using a reduced factorial design. Carbon dioxide concentration, temperature, relative air humidity, time, and the quality of added water were varied in six factor combinations. Acid neutralization capacity and leaching behavior were analyzed after four different periods of time. The results were evaluated with multivariate data analysis. A significant change in the acid neutralization capacity, a decrease in leaching of Ba, Ca, ${\mathrm{Cl}}^{-}$, Cr, Cu, Pb, K, and Na, and an increase in solubility of Mg, Si, Zn, and ${\mathrm{SO}}_4^{2-}$ could be attributed to different aging conditions.

A Bayesian chemical mass balance (CMB) model was used to identify the sources of heavy metals in a highly urbanized area at the vicinity of the Anacostia River in Washington, DC. This method uses the elemental profiles of potential sources and the storm water runoff samples at two outfalls into the Anacostia River to infer the contribution of each source by providing the joint probability densities of the contribution of each source and the credible intervals of the inference. For this purpose, the potential sources of heavy metals in the urban catchment were identified and multiple samples of each were collected and analyzed by using an inductively coupled plasma mass spectrometry technique to determine their elemental profiles. Next, a Bayesian CMB method was employed to infer the contribution of various sources to the storm water runoff. The results of the analysis revealed that paved surfaces that accommodate traffic (i.e., street, bridge, and parking lot) are the major contributors to both dissolved and particulate metals in storm water. It was also found that for both dissolved fraction and total pollutants, the wet deposition source has a small contribution to all elements and that the runoff originating from roofs can be responsible for up to 50% of the Pb in the storm water.

Natural organic matter (NOM) present in surface water sources undergoes significant structural and chemical changes during the application of vacuum ultraviolet (VUV)–based advanced oxidation process (AOP), which leads to the formation of undesired by-products such as aldehydes. Partial NOM mineralization can occur depending on the fluence received. In this paper, the VUV-induced degradation of NOM and the subsequent formation of by-products were experimentally studied. Two natural waters (Trepanier Creek and Capilano Reservoir, in British Columbia, Canada) and two synthetic waters (Suwannee River, Southern Georgia and Northern Florida; Nordic Reservoir, Vallsjøen, Skarnes, Norway) were used. While the process started with partial oxidation of NOM, extensive irradiation (i.e., high $\mathrm{UV}+\mathrm{VUV}$ fluence) led to complete mineralization of NOM. The rates of mineralization were greatly dependent on the nature of NOM and on the presence of inorganic compounds in the water matrix, such as carbonates and bicarbonates. A faster mineralization rate was obtained with waters containing NOM with a lower average molecular weight. Size exclusion chromatography analysis showed that high-molecular-weight (HMW) molecules were readily degraded, even from the beginning of the treatment. The fraction of low-molecular-weight (LMW) compounds also reduced, but at a slower rate, largely because LMW compounds were both formed through partial degradation of HMW compounds and degraded by hydroxyl radicals. The concentration of aldehydes and trihalomethane formation potentials increased up to 120–700 ppb, respectively, after receiving a $\mathrm{UV}+\mathrm{VUV}$ fluences in the range of $1–3\mathrm{J}{\mathrm{cm}}^{-2}$), but decreased with relatively higher $\mathrm{UV}+\mathrm{VUV}$ fluencies ($>4\mathrm{J}{\mathrm{cm}}^{-2}$).

The ASTM method for measuring the infiltration rate of in-place pervious concrete provides limited guidance on how to select test locations and how results should be interpreted to assess surface condition and maintenance needs. The ASTM method is written specifically for pervious concrete, so additional research is needed to determine the applicability of this method to other permeable pavement types. In 2009, the U.S. Environmental Protection Agency constructed a 0.4-ha parking lot surfaced with permeable interlocking concrete pavers (PICP), pervious concrete (PC), and porous asphalt (PA). Surface infiltration testing was conducted for almost three years, and two methods were used to select test locations: monthly testing at randomly selected locations and quarterly testing at fixed locations. Infiltration rates were significantly different for each pavement type. With almost three years of use, maintenance has yet to be required, although infiltration has decreased in areas immediately downgradient of impermeable asphalt driving lanes and to a greater extent where disturbed soil was present. The longevity was attributed to the clogging mechanism. Runoff transports solids to the upgradient edge of the permeable pavement surface where the solids are filtered and accumulate as runoff infiltrates. As surface clogging progresses from the upgradient edge, the method of selecting a random location across the entire area typically resulted in most locations being on an unaffected area. This did not produce a meaningful change in infiltration rate to suggest maintenance was needed for the entire surface. The results of this study indicate that the ASTM C1701 method may be applicable to PICP; however, for PA, further evaluation is needed. It is recommended that future infiltration testing should strategically select fixed test locations based on expected clogging patterns. Furthermore, less water can be used, enabling more tests to be conducted at strategic locations over the pavement surface area to better determine locations of clogging.

Mechanistically based scalable algorithms for design and operation of hydraulic flocculators were developed in this research based on observations of residual turbidity for a range of influent turbidities (5–500 NTU) and coagulant doses (0.01–0.15 mM Al), for two hydraulic residence times (800 s and 1,200 s) and for two coagulant types (polyaluminum chloride and aluminum sulfate). Kaolin clay was used as a model colloid to create synthetic raw water turbidities. Data were obtained over a range of sedimentation capture velocities using a bench-scale laminar-flow tube flocculator and quiescent settling column. Tap water with a pH of approximately 7.6 was used for all experiments. Seemingly disparate results were unified through creation of a composite dimensionless parameter that considers collision potential in the flocculator and coagulant surface coverage of colloids. One adjustable model parameter was used to fit data ($R^2\approx 0.9$) from over 136 experiments to create a model for each of the two coagulants. The model was found to be applicable over a range of sedimentation tank capture velocities and accurately reflected the effects of coagulant dose, raw water turbidity, flocculator residence time, and coagulant type. The model was validated by successfully predicting results from independent data sets. The predictive model is expected to be a useful tool for evaluating design trade-offs between coagulant cost to increase surface coverage relative to capital cost to increase residence time and energy cost used to increase the velocity gradient.

Problems with fat, oil, and grease (FOG) in sewer systems have received relatively little attention, although in the longer term this might imply (inter alia) blockages and sanitary overflows. Therefore, the experiences of Swedish and Norwegian executive water engineers concerning FOG-related issues were assessed using a comprehensive questionnaire that was distributed to all Swedish and Norwegian municipalities (with a response rate of 35% and 25% in Sweden and Norway, respectively). Blockages caused by FOG in sewers and pumping stations were the most prevalent reported problem, followed by increased demand for line flushing. The water engineers singled out city centers as the areas whose sewers had the most severe problems with FOG buildups. Most municipalities mandated the use of grease interceptors (GIs) by businesses, but the maintenance and functional status of these devices were reported to be inadequate. Commonly, water engineers had faith in the functioning of the GI despite the lack of stringent inspections. Where FOG collection systems had been implemented, they generally targeted businesses and other enterprises rather than private households. Because problems caused by FOG buildups are likely to become more common in the future, it is important that prevention strategies characterize management to a higher degree than ones based on removal.

A new kind of ${\mathrm{Fe}}^{3+}/\mathrm{polyvinylidene}$ fluoride membrane (PVDF)-polymethyl methacrylate (PMMA) asymmetric catalytic membrane was prepared by the phase inversion method and used as a heterogeneous Fenton-like catalyst to degrade Orange IV in the presence of ${\mathrm{H}}_2{\mathrm{O}}_2$. The effect of pH, initial concentration of ${\mathrm{H}}_2{\mathrm{O}}_2$ and Orange IV, reaction temperature and catalyst dosage, and the stability of catalyst on the degradation of Orange IV were investigated. The results show that the ${\mathrm{Fe}}^{3+}/\mathrm{PVDF}\text{-}\mathrm{PMMA}$ catalytic membrane can effectively decolorize Orange IV in the pH range of 3.1–5.2. The ${\mathrm{Fe}}^{3+}/\mathrm{PVDF}\text{-}\mathrm{PMMA}$ catalytic membrane’s retention rate decreased with the increase of concentration of Orange IV. The reaction rate constant is proportional to the initial concentrations of Orange IV. The ${\mathrm{Fe}}^{3+}/\mathrm{PVDF}\text{-}\mathrm{PMMA}$ catalytic membrane exhibits low iron leaching and good structural stability after five recycle times. The integrated process of membrane separation and heterogeneous Fenton-like catalytic oxidation was confirmed to be an effective process for degradation of Orange IV in wastewater.