Journal of Environmental Engineering

Hypolimnetic oxygenation can improve water quality by decreasing hypolimnetic accumulation of reduced compounds that complicate potable water treatment. Historically, aeration systems have been undersized because designers have not accounted for increases in sediment oxygen demand (SOD) resulting from the operation of aeration systems. A comprehensive study was performed to estimate the hypolimnetic oxygen demand (HOD) in San Vicente Reservoir, a eutrophic raw water reservoir in San Diego. Chamber experiments confirmed that turbulence and oxygen concentration at the sediment-water interface dramatically affected SOD. Values ranged from under $0.2\mathrm{g}∕{\mathrm{m}}^2∕\mathrm{day}$ under quiescent low-oxygen conditions to over $1.0\mathrm{g}∕{\mathrm{m}}^2∕\mathrm{day}$ under turbulent high-oxygen conditions. Based on a statistical evaluation of historical oxygen concentrations in the reservoir and anticipated increases in SOD resulting from operation of an oxygenation system, a design HOD of $\mathrm{16,400}\mathrm{kg}∕\mathrm{day}$ was estimated. This is approximately four times the HOD observed in the spring after the onset of thermal stratification. Laboratory chamber experiments confirmed that maintenance of a well-oxygenated sediment-water interface inhibited the release of phosphate, ammonia, iron, and manganese from sediments. In addition, hydrodynamic modeling using DYRESM-WQ showed that operation of a linear diffuser oxygenation system would not significantly affect thermal stratification.

The development and testing of a “turbidity” model is documented for a water supply reservoir, Schoharie Reservoir, NY, where inorganic terrigenous particles received during runoff events in turbid density currents from the primary tributary cause distinct periodic degradation. The model state variables are fractions (two or three) of the beam attenuation coefficient at $660\mathrm{nm}$ $\left({\mathbf{c}}_{660}\right)$ , a surrogate optical metric of turbidity. The fractions of ${\mathbf{c}}_{660}$ correspond to slow and rapidly settling components; the latter implicitly accommodates particle aggregation. The transport framework is a two-dimensional (laterally averaged), independently tested, hydrodynamic model. Model testing is supported by detailed measurements of the dynamics of tributary and meteorological drivers and ${\mathbf{c}}_{660}$ within the reservoir, during and following twelve runoff events. The model is demonstrated to meet the demanding temporal and spatial predictive needs of water supply lakes and reservoirs, by performing well in simulating the timing and magnitude of ${\mathbf{c}}_{660}$ peaks, the vertical and longitudinal patterns of ${\mathbf{c}}_{660}$ , diminishment following runoff events, and the dependence of impact on magnitude of a runoff event. Further advancements in turbidity modeling, including multiple particle size classes as state variables and explicit representation of particle aggregation and resuspension inputs, are considered.

Precipitative softening is an option to remove silicon and boron from natural waters. Silicon was removed from hard waters by precipitative softening when the molar ratio of Mg:Si was less than 6:1 by the formation of an amorphous magnesium silicate. This solid had an apparent solubility product constant of ${10}^{-25.66}$ and was stoichiometrically similar to the mineral forsterite, ${\mathrm{Mg}}_2\mathrm{Si}{\mathrm{O}}_4$ . Boron removal was consistent with sorption to this amorphous magnesium silicate and could be roughly described by a Freundlich isotherm: ${\mathrm{B}}_{\mathrm{sorb}}∕{\mathrm{Mg}}_2\mathrm{Si}{\mathrm{O}}_{4\left(\mathrm{s}\right)}=21\times {\mathrm{B}}_{\mathrm{sol}}^{0.51}$ .

Whereas ion exchange is an attractive technology for treating perchlorate and nitrate in drinking water, a major disadvantage is that the resin must be regenerated using a brine, producing wastes with high concentrations of nitrate, perchlorate, and salt. This study investigates the potential for simultaneous nitrate and perchlorate reductions in high-salt conditions using the ${\mathrm{H}}_2$ -based membrane biofilm reactor (MBfR). The autotrophic biological reductions produce harmless ${\mathrm{N}}_2$ and ${\mathrm{Cl}}^{-}$ , making the brine safe for reuse or disposal. A very high-strength brine ( $\sim 15\%$ salt) from a commercial ion-exchange membrane, Purolite, supported biofilm accumulation and allowed slow reduction rates for nitrate and perchlorate. Reduction rates increased significantly when the Purolite brine was diluted by 50% or more. A synthetic high-strength salt medium containing nitrate, perchlorate, or both supported more rapid reduction rates for as high as $20\mathrm{g}∕\mathrm{L}$ $(\sim 2\%)$ $\mathrm{NaCl}$ , while $40\mathrm{g}∕\mathrm{L}$ $\mathrm{NaCl}$ slowed reduction by 40% or more, confirming that the microorganisms in the MBfR were inhibited by high salt content. An increase of ${\mathrm{H}}_2$ pressure gave higher fluxes for $20\mathrm{g}∕\mathrm{L}$ $\mathrm{NaCl}$ , demonstrating that ${\mathrm{H}}_2$ availability controlled the reduction kinetics when the system was not salt-inhibited.

Dewatering and drying of residuals are extremely energy intensive processes, which are necessary to reduce the quantity of wet residuals produced from the water and wastewater treatment operations. Meteorological conditions are a major factor in the drying of residuals, which can greatly affect the drying period. A mathematical model is developed for the process of drying of water treatment residuals. A steady-state heat-balance equation is applied for a control volume of residuals that takes into account the heat transfer by radiation, convection, and evaporation. The mathematical model was validated using drying experiments conducted in a wind tunnel as well as other experiments conducted in an open environment equipped with a weather monitoring station. Good agreement was obtained between model predictions and experimental observations. The model can be used to predict the drying time of a given application of water treatment residuals with the knowledge of meteorological conditions.

An original model by Mutoti in 2003 was developed mathematically, and empirically, to predict the increase in total iron concentration in distribution systems. This model, referred to as a flux model, relates the increase in iron concentration in a reach of unlined or galvanized iron pipe to the surface area of the pipe in contact with the water. A flux term, defined with a dimension of mass per area per time was used. The effects of water chemistry, pipe material and hydraulic conditions were incorporated into the flux term. This paper describes the verification of the flux model using independent pilot data obtained with variable water quality under worst case, laminar flow conditions. The original model accurately predicted iron release for this independent verification data, with an overall $R^2$ of 0.80. For laminar flow conditions, the increase in iron concentration is proportional to the flux and the hydraulic residence time, and is inversely proportional to the pipe diameter.

The objective of this paper was to assess the effects of secondary disinfectants on internal corrosion and water quality in copper piping under stagnant conditions. In particular, this study evaluated the effects of free chlorine, monochloramine, chlorine dioxide, and no disinfectant (as a control) on copper release under a range of corrosion inhibition conditions. Corrosion inhibition factors that were considered include pH and alkalinity. Each of the corrosion factors and each chemical disinfectant was varied at two levels (e.g., high and low concentration) to create a $2^3$ factorial design for each chemical disinfectant. The water in the copper pipes was sampled and replaced after a $72\mathrm{h}$ stagnation period. Results show a decrease in copper release for all disinfectants used as compared to the control. In particular, the highest copper concentration measured was $2.55\mathrm{mg}∕\mathrm{L}$ , which corresponded to a pH of 7.2 and alkalinity of $100\mathrm{mg}∕\mathrm{L}$ and no chemical disinfectants. The lowest total copper concentration was $0.29\mathrm{mg}∕\mathrm{L}$ , which corresponded to the high pH and low alkalinity for the high dose of chlorine.

In this work, the effect of the pulsing flow on the start-up efficiency and hydraulics of upflow anaerobic filters (UAF) has been assessed. With this aim, a reactor operated in pulsing form (P) was compared with a conventional nonpulsed UAF reactor (NP). Although the operation of the two reactors was similar, the pulsed UAF attained a higher efficiency (92 versus 85%) at a higher organic loading rate (15 versus $11\mathrm{kg}$ chemical oxygen $\mathrm{demand}∕{\mathrm{m}}^3\mathrm{day}$ ), after a start-up period of 140 days. The hydraulic behavior, determined from residence time distribution curves, of the two reactors showed that the useful liquid volume in the pulsed reactor was 10% higher than in the NP reactor. Further, the useful volume of the pulsed UAF was higher (76%) than in reactor NP (58%), which indicates the efficiency of the pulsing device for degasification.

The use of a single-unit, single-zone submerged attached growth bioreactor (SAGB) for the combined removal of carbonaceous organics and nitrogen from a municipal wastewater was demonstrated. A nitrification efficiency of 97% was achieved at a total organic loading of $3.47\mathrm{kg}\mathrm{bCOD}∕{\mathrm{m}}^3\text{day}$ . The total nitrogen loading varied from $0.2\text{to}0.3\mathrm{kg}\mathrm{N}∕{\mathrm{m}}^3\text{day}$ and resulted in effluent total nitrogen concentrations ranging from $4.2\text{to}8.5\mathrm{mg}∕\mathrm{L}$ . Concurrent denitrification was achieved at rates ranging from $0.077\text{to}0.29\mathrm{kg}\mathrm{N}∕{\mathrm{m}}^3\text{day}$ . This single-unit SAGB, by providing dual treatment capacities, represents a cost-effective option that is particularly attractive for facilities with limited space and budget for system upgrade.

Liquid-liquid extraction system (LLES), including extraction section and reverse extraction section, had been applied successfully in the treatment of phenolic wastewater. In this paper, a novel pilot scale system, the extraction-evaporation system (EES) without reverse extraction section was introduced. The treatment capacity of both LLES and EES reached $4.0{\mathrm{m}}^3∕\mathrm{h}$ . According to experimental results and economical analysis, EES had higher removal efficiency and lower treatment cost than those of LLES in the treatment of the phenolic wastewater containing $\mathrm{3,200}–\mathrm{6,300}\mathrm{mg}∕\mathrm{L}$ phenol, the concentrations of most resin and dye industrial effluents. The highest extractive efficiency of EES could reach 99.0% within the concentration range of $\mathrm{4,000}–\mathrm{5,000}\mathrm{mg}∕\mathrm{L}$ phenol, and remnant phenol in wastewater varied from 43.6 to $51.2\mathrm{mg}∕\mathrm{L}$ . The highest extracted efficiency in LLES arrived at 98.2% and the remaining phenol concentration reached $95.0\mathrm{mg}∕\mathrm{L}$ . The average removal efficiency of EES increased 1%, and the treatment cost of EES decreased 4.6%. The pretreated wastewater by EES was able to meet the demands of biological or adsorptive process. Despite that the total investment cost of EES was higher than that of LLES, treatment cost of wastewater per ton by EES was lower than that of LLES.

In many watersheds located in southern California, efforts are being focused on urban runoff because of its adverse impact on receiving water quality. The Sweetwater River watershed is a good example, where the drainage area is rapidly urbanizing and deteriorating reservoir water quality. Contaminated storm water is captured and diverted but as urbanization increases, additional runoff will be generated which will overload the existing infrastructure. To better manage the diversion systems and minimize future construction, storm-water volumes and pollutant loadings need to be estimated. Due to the lack of real-time storm-water runoff monitoring data, pollutant loadings must be estimated from land use information. We used satellite imagery to estimate selected storm-water pollutant loads and compared the results to predictions using land use information from public records. Satellite imagery was useful in estimating storm-water pollutant loads and identifying high loading areas. Satellite imagery with appropriate classification is a promising tool for watershed management and for prioritizing best management practices.

This paper investigates how straining mechanisms of angular media (crushed limestone) provide improved filtration performance compared to rounded media (river stone). Columns of granular media were set in resin, sectioned, photographed, and digitized to produce a three-dimensional model of pore space geometry. This process was repeated for four filter media, each representing different grain shapes or packing densities. From measured pore throat distributions, a stepwise particle movement model was used to estimate the maximum volume of particles that could be stored in the bulk of the filter media. The results showed that the more angular the media, the wider the range of particle sizes that could be strained in the bulk of the filter. The stepwise model was applied only to individual particles; trapping of colloidal particles was not considered. However, when individual particles are too small to be strained, the same pore throat trapping contributes to the physical capture of avalanches and flocculates. Thus the findings of this work are relevant to deep bed filtration applications where headloss results from straining, such as storm-water best management practices or soil filters.

Alternative methods to describe water quality using an aggregate index consisting of subindices for individual water quality variables are examined. Most aggregation methods suffer from three shortcomings: Ambiguity, eclipsing, and rigidity. Ambiguity problems exist when all the subindices indicate acceptable water quality for a given use, but the aggregated index does not. Eclipsing problems exist when the aggregated index fails to reflect poor water quality of one or more water quality variables. Rigidity problems exist when additional variables are included in the index to address specific water quality concerns, but the faulty aggregation function might artificially reduce the value of the water quality index such that it does not accurately reflect the true water quality. As the number of water quality variables increases, the magnitude of the aggregated index decreases raising the issue of ambiguity again. The writers developed a mathematical formulation for aggregate indices that avoids the problems of ambiguity, eclipsing, and rigidity with respect to the number of water quality variables required to be aggregated in a given index.

The interaction between fluid dynamics and microbiological organisms is an integral aspect of aquatic ecosystems that has received only sporadic attention over the years. The effects of fluid motion on bacterial growth kinetics and on the traditional biochemical oxygen demand (BOD) test were investigated. Laboratory experiments were performed to study the physiology of E. coli in a well-defined flow system with an emphasis on BOD measurements. Several methods were applied to quantify bacterial abundance and viability including viable plate counts; membrane integrity Live/Dead BacLight; respiratory 5-cyano-2,3-ditolyl tetrazolium chloride; and direct bacterial count $4^{\prime }6$ -diamidino-2-phenylindole staining methods. A turbulent fluid flow was generated using an oscillating grid reactor. Microscale fluid flow in the experimental setup was analyzed using a laser-Doppler velocimeter. Our results demonstrate that bacterial physiology and the corresponding BOD measurements depend on hydrodynamic mixing conditions. Microbial growth and BOD were facilitated by small-scale fluid motion. BOD was minimal in a stagnant fluid that is the condition that replicates the traditional BOD test.

The purpose of this research is to consider a novel concept for measuring and monitoring (M&M) the presence and levels of contaminants in soil. Current M&M techniques include direct sensing for the target contaminant and the surrogate indicators of respired ${\mathrm{O}}_2$ and $\mathrm{C}{\mathrm{O}}_2$ . The method suggested here is based on nitric oxide (NO). It is an alternative M&M method that could become quicker, easier, more reliable, and less expensive than the other M&M methods being used currently. NO emission from toluene contaminated soil and soil microbial activity were investigated to understand the NO-toluene-soil microbial relationships using fluorescent in situ hybridization molecular technique combined by enzymatic method. The relationships have been analyzed by the comparison of experimental measurements coming from analysis of variance statistical analysis, referring to toluene concentrations. Relationships between NO emissions and the microbial activity were significantly correlated $(P<0.01)$ with the level of toluene concentration and duration of toluene contamination. Thus, NO emissions are suggested as a useful indicator of microbial activity in toluene contaminated soils.

Complex industrial and consumer products, such as automobiles, contain significant amounts of potentially recyclable materials, but these materials are not necessarily recovered after their useful life. The current recovery process for automotive hulks manages to capture nearly all of the metal content, but few of the plastics. Except for selected high value plastic parts, most remain with the vehicle and are shredded. Extensive hand dismantling, which is effective, is currently not cost-efficient. However, if materials or components can be designed to separate by their characteristic sizes after comminution, then the material recovery from product waste can be enhanced. Such efforts would support industry design-for-environment and design-for-recycling initiatives. In this study, samples made from acrylonitrile butadiene styrene and polyvinyl chloride were assembled with a variety of thicknesses, configurations, and fastening methods, and were comminuted in two passes through a plastics granulator to determine if they resulted in size-based separation characteristics that could be exploited in the recovery process. A detailed evaluation found that particle size distributions fit a modified Gaudin size distribution relationship well. Of all the sample variations studied, only the granulator exit screen size had a significant impact on the average and distribution of comminuted particle sizes. The pi breakage theory, generally advocated for its use in waste processing, did not hold well in this situation of more complex material configurations. The selection function values were found to decrease with the decreasing size of feed particles.