Journal of Environmental Engineering

Water utilities can experience problems from bubble formation during conventional treatment, including impaired particle settling, filter air binding, and measurement as false turbidity in filter effluent. Coagulation processes can cause supersaturation and bubble formation by converting bicarbonate alkalinity to carbon dioxide by acidification. A model was developed to predict potential bubble formation during coagulation, and its accuracy was confirmed using an apparatus designed to physically measure the actual volume of bubbles formed. Alum acted similar to hydrochloric acid for initializing bubble formation, and higher initial alkalinity, lower final solution pH, and increased mixing rate tended to increase bubble formation.

Several years after beginning to study submerged biological aerated filters, the Environmental Technology and Environmental Microbiology Research Group (University of Granada, Spain) optimized the performance of this system, using a ceramic-based material bed. This material is generated by ceramic materials factories, as a waste product which is then grinded. Therefore, the use of this bed material maximizes the use of discarded material. A comparative study of height for the ceramic-based material bed, with regard to the TBOD₅ and suspended solids parameters, is presented. For every bed material height, relations among volumetric loads applied and effluent concentrations are presented, as well as relations among hydraulic loads applied and effluent concentrations. Aiming for a maximum consumption value of 1.2 kg O₂/kg TBOD_5,eliminated, the air volume supplied was fixed. The real values obtained for this parameter are presented in relation to the TBOD₅ volumetric load applied. The tests were performed at a pilot plant with full-scale height and a pilot scale cross-sectional area. The influent that was the primary effluent of a conventional treatment plant, was injected in the top of the filter, to create countercurrent flow.

This study evaluated the ability of a slip feed system to maintain the pollutant-degrading activity of biomass in a vapor phase bioreactor during periods of little or no contaminant feed. Three slip feed fractions (1, 5, and 9% by mass) were investigated in a bioreactor treating toluene-contaminated air. Results indicate that the slip feed system improved the contaminant degradation capacity in the carbon-deprived bioreactor zones by approximately 30% regardless of the slip feed fraction supplied. This yielded a 10–20% improvement in toluene removal efficiency when the entire bioreactor column was subjected to a sudden threefold spike in toluene loading. When a 12% slip feed was supplied to the bioreactor during a short-term (3 days) or longer-term (1 week) shutdown period, it reduced the reacclimation time required following restart by as much as 70%. These results indicate that as long as the biomass receives at least a trace of the pollutant by means of a slip feed system, it can maintain sufficient pollutant degrading capacity to respond quickly to pollutant loadings upon restart.

This work summarizes the results of a feasibility study in support of a soil venting-thermal desorption (SVTD) process for remediating lampblack-impacted soil. Lampblack is the solid residue resulting from the gasification of crude oil. The SVTD process couples soil vapor extraction with in situ heating. The objective of this study is to determine the required temperature for desorbing polycyclic aromatic hydrocarbons (PAHs), the compounds of regulatory concern, from lampblack. Bench-scale results are reported for the treatment of a soil-lampblack matrix containing 11 PAHs totaling about 4100 ppm (mg/kg) total PAH (TPAH). Solids characterization analyses suggested that these PAHs constitute about 60% of the organic residue on a solid matrix dominated by fine-grained sand and carbon-based lampblack particles. Thin section imagery supports the conceptual model of hydrocarbons associated with the surface of sand grains. SVTD testing for the sand-lampblack solids indicates that temperatures in excess of about 250°C are sufficient to mobilize most of the PAHs. Specifically, at temperatures between 250°C and 300°C, the TPAH level in the soil-lampblack matrix was reduced to less than 100 ppm in 10 days. The dynamics of PAH removal were captured reasonably well by a mass balance accounting for the temperature dependent volatilization of an ideal PAH mixture. Both simulated and experimental results support the finding that the vast majority of the PAH removal from this sand-lampblack matrix was controlled by thermodynamic considerations (as opposed to mass transfer resistances). A small residual PAH fraction (roughly 40 ppm TPAH) was observed to persist in the solids even at temperatures in excess of 650°C. Although the specific state of these persistent PAHs is unknown, they may reside within an extremely nonvolatile residue or be otherwise strongly sequestered in the solid matrix.

A pure 4A/X (60/40) zeolite product was synthesized from silica extracts of the Meirama fly ash in northwestern Spain. A high cation-exchange capacity (4.7 meq/g) was obtained for the zeolitic material. The potential application of this coal fly ash conversion product for decontamination of high heavy metal waters was evaluated using three high heavy metal waters from acid mine drainage around the pyrite Huelva belt. The results were compared with those obtained with an equivalent pure commercial synthetic zeolite. A considerable reduction in the heavy metal content was attained (Zn from 174 to <0.1 mg/L, Cu from 36 to 0.1 mg/L, Fe from 444 to 0.8 mg/L, Mn from 74 to <0.1 mg/L, Pb from 1.5 to <0.1 mg/L, and Cd from 0.4 to <0.1 mg/L), even in high Ca and Fe waters using zeolite doses from 5 to 30 mg/L. Both precipitation and cation-exchange processes accounted for the reduction in the pollutant concentration in the treated waters. Leachable hazardous elements from coal fly ash, such as Mo, B, As, V, and Cr, were not fixed in the synthesis of pure zeolites from the silica extracts. Consequently, they did not restrict the potential applications of this material as an ion exchanger, unlike the zeolitic material obtained from fly ash by direct alkaline conversion.

High-gradient (>1%), low-order streams, characterized by hydraulically nonuniform and heterogeneous channels, represent a problem for the most widely employed habitat-based in-stream flow methods (IFIM-PHABSIM). In a nonuniform high gradient and turbulent channel, as low-order streams usually are, the classical 1D hydraulic modeling, ordinarily employed by in-stream flow models to simulate the changes in fish habitat with the flow, could be questionable, if not completely inapplicable. Channel morphology in fact plays a major role in association with hydraulics in determining the abiotic environments (biotopes) in which aquatic communities live. Particularly, in low-order river systems, different channel form features shape the biological community that can be hosted in a certain biotope. For this reason, the link between morphology and discharge is important when evaluating possible impacts of flow reduction on aquatic organisms. To represent the relationship between hydraulics and channel morphology quantitatively, a hydraulic diversity concept has been adopted. Studies from the literature have revealed that, in a regulated river, a decrease of the environmental variability including hydraulic diversity quite often resulted in a downstream decrease of the macro-invertebrate diversity, which can consequently affect fish biomass. These considerations create the ground for a hydraulic diversity-discharge–based in-stream flow method with the aim to promote high community diversity in a low-order regulated stream. A statistic ordination technique (correspondence analysis) applied to 370 hydraulic sections helped to identify four main morphological units (pools, deep pools, and slow and fast riffles) in terms of hydraulic diversity. In each morphological unit, the hydraulic diversity-discharge relationship was investigated and modeled by means of best-fit regression curves. Combining the hydraulic diversity-discharge curves from different morphological units (pools and riffles), a simplified model of the stream [pool quality index (PQI)] was obtained. This model has been applied to make recommendations for the minimum flow requirements in six low-order river sites. PQI recommendations were consistent with hydrology and other hydrology-based in-stream flow methodologies. Finally, a multiple regression model indicated that in 12 low-order stream sites a good deal of the variability of macro-invertebrate diversity is explained by the availability of hydraulic environments modeled by means of PQI curves. In conclusion, given the encouraging cues about the ecological meaning of PQI and the possibility to overcome difficulties typically encountered by other methods in the low-order river modeling, PQI can be considered a valid alternative for assessing the in-stream flow needs of low-order streams.

Highway runoff disposal without concern for its specific characteristics may be associated with high material and environmental costs. An understanding of storm water management has enlightened the importance of the impacts that nonpoint pollution may cause to both surface waters and groundwater. Several systems for highway runoff treatment exist, often based on detention and infiltration processes. This paper suggests a method for design and evaluation of the design of infiltration ponds for use in semiarid climates. The design principle is based on capture and infiltration of the most polluted runoff. It takes into account the rainfall and soil hydraulic characteristics for the determination of the design volume. Seasonal variations in rainfall and evaporation were considered. The soil characteristics—hydraulic conductivity, texture, pH, and cation exchange capacity—the volume of runoff which is infiltrated, and the infiltration area are used to calculate the movement of the most mobile heavy metal, Zn, in the soil. The method presented was based and applied to highway runoff but can be used for treatment of stormwater runoff from other sources.

A laser in situ scattering and transmissometry (Lisst-100) probe has been used for estimating the particle-size distribution of phytopankton, purple photosynthetic sulphur bacteria (Chromatiaceae), and suspended inorganic sediments in different lakes. Results from Lisst-100 have been compared to laboratory measurements, such as those obtained by using a Galai laser size analyzer (GL), an optical microscope (OM), and a flow cytometer (FC). Although all of these instruments were shown to provide reliable values of the particle number concentration for the given populations, the Lisst-100 was the fastest and most reliable instrument because it did not require manipulation of the samples—which is not the case of GL, OM and FC instruments—and avoided the tedious procedure of microscopic counts. The total particle volume concentration results obtained with Lisst-100 differed from those obtained with GL for populations with large and porous aggregates, such as phytoplankton cells. The difference was attributed to the breakage of fragile algal aggregates resulting from the measuring procedure used by GL. Although for suspended sediment particles both instruments gave the same results for the total particle volume concentration, the particle-size distribution obtained with GL was found always shifted to smaller diameters than with Lisst-100, probably because inorganic sediment particles present compact aggregates. When these aggregates break, they split into a high number of small particles that contribute the same to the total volume concentration as the previous aggregates. Finally, results of the total particle volume concentration with Lisst-100 were in accordance with those obtained with GL for the Chromatiaceae population, because cells remained in a dispersed phase. A good correlation was found between the total particle volume concentration of Chromatiaceae measured with Lisst-100 and the concentration of bacteriochlorophyll a (BChl a), which is the parameter habitually used to estimate the concentration of Chromatiaceae. Therefore, Lisst-100 was found to be a reliable instrument to estimate the Chromatiaceae concentration in aquatic ecosystems.

This paper presents a derived probability model that can be used to estimate vehicle and labor requirements for municipal solid waste collection systems. The model consists of closed-form solutions for important performance parameters such as the mean and variance of the total collection time for a route of given size. The results of the model agree well with the results of Monte Carlo–simulation models of curbside collection, but the derived probability model has several advantages over simulation techniques. The analytical nature of the model allows it to be easily and directly implemented on a spreadsheet. The proposed model will allow solid waste managers to examine a wide range of collection alternatives without the time and expense of simulation modeling.

Three applications are used to demonstrate the utility of a derived probability model of curbside solid waste collection. First, the model is used to estimate the time required to collect waste from a route when the vehicle is constrained by time only. Second, the performance of a collection vehicle subjected to a capacity constraint is modeled. Finally, the model is used to compare the cost of using vehicles of different capacities. The results of the derived probability model compare well with the results of Monte Carlo simulations and with results reported in the literature. However, results can be obtained more directly with the derived probability model than from other methods.

Many uncertain factors affect the operation of wastewater treatment plants. These include the physical and chemical properties of wastewater streams as well as the degradation mechanisms exhibited by biological processes. Because of the rising concerns about environmental and economic impacts, improved process control algorithms, using artificial intelligence technologies, have received wide attention. Recent advances in control engineering suggest that hybrid control strategies, integrating some ideas and paradigms existing in different soft computing techniques, such as fuzzy logic, genetic algorithms, and neural networks, may provide improved control of effluent quality. The methodology proposed in this study employs a three-stage analysis that integrates three soft computing approaches for generating a representative state function, searching a set of multiobjective control strategies, and autotuning the fuzzy control rule base used for controlling a treatment plant. The case study, using an industrial wastewater treatment plant in Taiwan as an example, demonstrates the applicability of the approach. The findings from this research suggest that a genetic-algorithm–based hybrid fuzzy-neural controller can produce better plant performance than does a simple fuzzy logic controller, in terms of both environmental and economic objectives. This methodology can be extended to control many other types of wastewater treatment processes, as well, by making only minor modifications.