Journal of Environmental Engineering

Plunging water jets are used for oxygenation purposes due to their inherent advantages such as simplicity, energy efficiency, and low operational cost. Specifically, these provide an efficient gas-liquid interfacial area for dissolving oxygen in water. Oxygen transfer by plunging jets into stagnant water has received considerable attention; however, the oxygenation capacity of plunging water jets discharging into turbulent cross-flow has received limited attention. The flow characteristics such as volumetric oxygen transfer coefficient and standard oxygen transfer efficiency are evaluated considering water jet to cross-flow velocity ratio, jet fall height, cross-flow depth, and jet impact angle. Two equations are proposed for estimating the oxygen transfer rate for a single plunging jet in a turbulent cross-flow. Moreover, the dynamic behavior of the resulting two-phase air-water flow is investigated with the aid of flow visualization.

In Central and Eastern Europe huge wastewater treatment (WWT) developments have been carried out in the last 25 years. These include the building and upgrading of wastewater treatment plants (WWTPs), especially extending their lifetimes through nutrient removal and digester gas production. In Hungary, for example, in 1990, 42% of households were connected to a WWT, and this number had increased to 75% by 2015, an increase of 33%. Currently, medium-sized WWTPs with a capacity of up to around 120,000 population equivalent (PE) are facing further development needs, especially in their technical and energy-efficiency aspects. This paper presents the results of a comprehensive investigation program that included 21 WWTPs with capacities ranging from 10,000 to 120,000 PE. The investigations included an evaluation of all important parameters, such as inflowing wastewater (WW) characteristics, mechanical and biological WWT, and effluent wastewater quality and removal efficiency. These were investigated with reference to their electrical energy consumption. The extension of these WWTPs with anaerobic sludge digestion has led to the possibility of producing electricity from digester gas. This prospect is currently of great interest for medium-sized WWTPs and so was also investigated. The results are also compared to international data, standards, and guidelines obtained for this research. As a basis for a development strategy, the main bottleneck areas of design and operation are considered, and further upgrading requirements are explored.

Batch studies on selenium reduction were conducted to assess the reduction rate of Se(VI) as well as Se(IV) using Escherichia coli Strain EWB32213 isolated in the laboratory. The rate of Se(VI) reduction to Se(IV) in the first stage was faster than that of Se(IV) reduction to Se(0) in the second stage. The Se(VI) reduction was complete within 1.5 days, with the Se(VI) concentration ranging from 10 to $400\mathrm{mg}/\mathrm{L}$, while a Se(IV) concentration higher than $100\mathrm{mg}/\mathrm{L}$ was only partially reduced to Se(0) after 10 days. The batch culture was capable of reducing Se(VI) and Se(IV) upon Se(VI) and Se(IV) respikes, albeit at decreasing rates. The data were successfully analyzed with a two-stage kinetic model using both the Simplex and Universal Global algorithms embedded in a computer program package. Eight biokinetic parameters of ${\mu }_1$ of $1.9875\mathrm{mgVSS}/\mathrm{mgSe}(\mathrm{VI})\text{-}{\mathrm{d}}^{-1}$, ${\mu }_2$ of $0.1206\mathrm{mgVSS}/\mathrm{mg}\mathrm{Se}(\mathrm{IV})\text{-}{\mathrm{d}}^{-1}$, $K_1$ of $206.8446\mathrm{mg}/\mathrm{L}$, $K_2$ of $50.0748\mathrm{mg}/\mathrm{L}$, $K_I$ of $792.0883\mathrm{mg}/\mathrm{L}$, $b$ of $0.3824{\mathrm{d}}^{-1}$, $Y_1$ of $0.6299\mathrm{mgVSS}/\mathrm{mg}$ Se(VI), and $Y_2$ of $0.7004\mathrm{mgVSS}/\mathrm{mg}$ Se(IV) were obtained. The good fit of the data to the model simulation indicated the robustness and rigorousness of the model.

Vegetable tanning effluents have very high and difficult-to-treat chemical oxygen demand (COD). The main environmental damage is due to the low biodegradability of tannins, that can create environmental problems. Tannins are recalcitrant molecules and resist microbial attack; they are toxic to a variety of microorganisms. In this work, electrocoagulation with aluminum electrodes in a batch reactor was applied to remove polyphenolic compounds of vegetable tannins from aqueous solutions. Two types of commercial tannin extracts were used: chestnut, as a representative of hydrolyzable tannins, and mimosa, as a typical condensed tannin. The effects of operating parameters on the efficiency of electrocoagulation—current density, pH, ionic strength, interelectrode distance (IEA), electrolysis time, concentration of tannin extracts, and the like—have been investigated. It has been shown that the removal efficiency of tannin polyphenols increased with the increasing applied current density and increasing ion strength. The optimum current density ($J$) was $47.6\mathrm{A}/{\mathrm{m}}^2$ for chestnut and $71.4\mathrm{A}/{\mathrm{m}}^2$ for mimosa at $\mathrm{1,000}\mathrm{mg}/\mathrm{L}$. Within these values, 97.4 and 98.8% of tannin polyphenols can be removed, respectively. On the other hand, the most effective removal capacity can be achieved at normal pH (without correction) of each tannin solution in the optimum range. However, the removal efficiency of vegetable tannins from water decreases at more acidic and alkaline pH. The addition of NaCl to the solution helps increase removal efficiency and could save power consumption significantly. The optimal electrode distance is determined to be 2 cm for the electrolysis cell employed. The optimal time for achieving maximum removal of polyphenols increases with increasing tannin concentration. Nevertheless, it can be reduced by increasing the applied current.

This study aimed to explore the potential impact of algal blooms on the survival of viruses in aquatic environments by using Microcystis and somatic coliphage phiX174 as a model algae and model virus, respectively. The phiX174 concentration was determined by double-agar-layer plaque assay (DAL), and the Microcystis density was determined by optical density (OD) measurement at 678 nm. Individual samples were measured before and after filtration through a membrane with pore size of 0.22 μm to account for the differences between unassociated viruses suspended in the water column and the total viable viruses in the sample. The results showed that no significant inactivation or adsorption of phiX174 was caused by Microcystis either in dark condition or under light. However, algae could act as a source of natural organic matter (NOM) and affect phiX174 inactivation. The presence of algae could also reduce phiX174 inactivation because of light attenuation. Therefore, the presence of algae could potentially prolong the survival of virus in aquatic environment.

This paper presents a new solution for a soil venting problem, in which a vertical, partially penetrating well is operated at a fixed pressure under covered, uncovered, or leaking ground surface conditions. The method of domain decomposition is applied to solve the problem of a mixed-type boundary condition imposed along a well screen, which in previous solutions was usually handled by discretization of the screen. The new solution is also capable of predicting the flow field beneath the well bottom, which is commonly neglected by other solutions. The authors found that the present solution may predict different pressure distributions from those given by a solution employing a constant flux rate at a well screen. The radius of influence for soil vapor extraction (SVE) operations is strongly affected by the radial permeability, the vertical permeability, and the ratio between the two. Vacuum pressure values were predicted with the proposed solution and compared against measurements at different observation wells and depths under venting tests at a former SVE-operated site. The measured vacuum pressure and gas flow velocity values around the wells were found to be substantially lower than the predicted values. Thus, the wellbore soils of the site were suspected to be positive skin zones.

Thermophoresis has been used to develop various thermal precipitators; however, their collection performance for ambient particulate matter (PM) with an aerodynamic diameter less than 10 μm (${\mathrm{PM}}_{10}$) has been rarely reported, and the effect of the temperature gradient adopted in the precipitator on the evaporation loss of the organic fraction of collected particles has not been discussed to the authors’ knowledge. In this study, a cylindrical thermal precipitator consisting of two coaxially aligned cylinders with an annular space of 0.51 mm and a two-inlet impactor was designed for collecting ${\mathrm{PM}}_{10}$. The effects of the sampling flow rate and temperature gradient on the collection efficiency were examined. The precipitator was also tested for its collection efficiency for particle-bound polycyclic aromatic hydrocarbons (PAHs). At a temperature gradient of $72.6°\mathrm{C}/\mathrm{mm}$ and a flow rate of $7.74\mathrm{L}/\min$, the collection efficiency could reach 100% for PM with an electrical mobility diameter $(D_p)<0.5\mathrm{\mu m}$ and decreased gradually to 70% as $D_p$ increased from 0.5 to 1.0 μm. For PM with $D_p>1.0\mathrm{\mu m}$, the collection efficiency increased due to impaction at the inlet. The collection efficiency increased with an increase in the temperature gradient or a decrease in the inlet flow rate. The semiempirical model could reasonably fit the collection efficiency curve of the precipitator. No significant evaporation loss of PAHs was found when the temperature of the cold cylinder surface was approximately 0°C. It was concluded that the thermal precipitator could be used to collect ambient fine PM with a size less than 0.5 μm, and the inlet impactor design could improve the collection efficiency for coarse particles.

Microbially induced corrosion (MIC) is a process that can take place in concrete sewers, septic tanks, and transfer stations and can result in concrete deterioration. MIC is attributable to the microbial oxidation of hydrogen sulfide (${\mathrm{H}}_2\mathrm{S}$) to sulfuric acid (${\mathrm{H}}_2{\mathrm{SO}}_4$) by a biofilm community that is established on a concrete surface. The rate and extent of this process will be influenced by the environment in which it takes place (e.g., temperature, ${\mathrm{H}}_2\mathrm{S}$ concentration), as well as the composition of the concrete itself. Laboratory experiments were conducted to examine the effect of concrete composition and admixtures on MIC. The experiments were conducted in an isolated chamber where the climate was controlled, including the ${\mathrm{H}}_2\mathrm{S}$ concentration. Concrete specimens representing 13 mixtures were inoculated with an aqueous suspension containing a mixture of four Acidothiobacillus spp. that have been associated with MIC in sewer systems. Results indicated that calcium aluminate cement (CAC) mortar, blended cement, and incorporation of a silane quaternary amine (SQA) antimicrobial agent can improve resistance to MIC under moderate exposure conditions (i.e., surface $\mathrm{pH}>2.0$). The rapid deterioration of specimens exposed to more aggressive conditions in the chamber indicated that degradation of concrete under the most severe MIC conditions (i.e., concrete surface $\mathrm{pH}<2.0$) was not prevented by simply manipulating concrete mixture proportions. A second set of experiments was conducted to quantify the effectiveness of SQA for the inactivation of pure cultures of planktonic bacteria. Results indicated that the antimicrobial agent performed well for the inactivation of pure cultures of Acidothiobacillus spp., except A. thiooxidans, which represent bacteria that are likely to be active under the most severe conditions (i.e., surface $\mathrm{pH}<2$).

During the past 50 years, wet stormwater ponds have been constructed to reduce negative environmental impacts of urban stormwater discharges on receiving aquatic environments. However, in many jurisdictions there is little information on the current operational status of such ponds and their functioning. This paucity of information prompted a field survey of 25 Swedish municipal stormwater ponds, aged between 3 and 26 years. The pond survey focused on estimating the pond hydraulic loading and efficiency, the state of littoral vegetation, characteristics of bottom sediment in the inlet and outlet zones (sizes and the chemistry), and the overall operational pond status, including the access for maintenance. The hydraulic efficiencies of ponds were estimated for pond footprint shapes and relative locations of the inlets and outlets using literature data. The estimated hydraulic efficiencies correlated well with the pond length-to-width ratios and the ratio of the pond surface area to the impervious area of the runoff contributing catchment (i.e., the hydraulic loading). Littoral vegetation was inspected visually and found to be overgrown at some facilities, which impeded the maintenance access. Benthic sediments in ponds contained silt and clay ($<63\mathrm{\mu m}$), sand and gravel fractions, and when compared with the literature data, such sediments appeared relatively coarse. Chemical characteristics of sediments reflected anthropogenic (traffic) activities, but without excessive contamination warranting special disposal requirements. Of the 25 ponds surveyed, four were fenced off and inaccessible to machinery. In fact, the design of these four ponds was such that it made inspection and maintenance very difficult, which may pose potential risks to ponds operation. Fifty-four percent of the investigated ponds were in need of minor maintenance, primarily because of sediment and litter accumulation in their inflow and outflow sections. The fact that the inspection survey revealed relatively few minor issues that could be corrected easily demonstrates the importance of relatively simple regular inspections serving to detect minor problems at an early stage before they would seriously impact pond functioning. The above survey methodology should be helpful for developing similar low-cost surveys in other jurisdictions.

On Cape Cod, eco-toilets could help mitigate an existing pollution problem, but observed adoption rates have been extremely low. A household survey was used to examine primarily nonmonetary factors affecting homeowners’ willingness to adopt eco-toilets. This study is the first of its kind, surveying potential buyers and users of in-home eco-toilets in the United States who must manage an urgent sewage-driven pollution problem. Although the respondents were highly educated, the pollution problem and possible solutions were not well understood by all participants. At the same time, willingness to use eco-toilets in various settings (46% “completely willing” to stay at a hotel with eco-toilets) and even install them in the home (34% neutral, 22% “completely willing”) was considerably higher than expected based on the low adoption rate to date. Perceptions of positive and negative consequences of installing eco-toilets were of particular importance. The results suggest that education efforts would improve the public’s understanding of eco-toilets, and along with monetary and nonmonetary incentives, would likely increase adoption rates.

The data and the analysis applied to it in a 1996 paper on the statistical distribution of Cryptosporidium in a reservoir are re-examined with the objective of clarifying general understanding of the way in which Cryptosporidium oocysts and Giardia cysts are distributed in water. General objectives of monitoring for these protozoan parasites are summarized along with essential assumptions used in statistical analysis. The 1996 analysis is reviewed and an alternative analysis is proposed. The key distinction is that the Poisson model assumption of a homogeneous population was not appropriate as applied to the data set consisting of 52 consecutive weekly samples, leading to likely misinterpretation of the data. The critical issue is interpretation of negative (zero) results, whether as absence and hence intermittent presence or as continuous presence but below the limit of detection. The alternate analysis shows that the typically skewed annual data set can be effectively described as lognormal. The lognormal distribution of the 1996 data is compared to previously published data on Cryptosporidium and Giardia from reservoirs elsewhere with apparent similarity. The application of the Poisson model to understanding the relation between ambient concentrations of Cryptosporidium and Giardia, sample volumes, and recovery efficiency is described with its importance to effective planning of monitoring and data analysis.