The primary purpose of water aeration is to increase the oxygen saturation of the water. This can be achieved by using hydraulic structures because of substantial air bubble entrainment at these structures. This paper reviewed the literature on hydraulic structures used in water aeration processes. The hydraulic structures were divided into two groups as the high-head flow systems and the free-surface flow systems. The high-head flow systems were circular and venturi nozzles, pipe with venturi tube, and high-head conduit, and the free-surface flow systems were weir, stepped cascade, and free-surface conduit. Air/water flow ratio and aeration efficiency in circular nozzles with air holes and venturi nozzles were significantly high. Pipes with venturi tubes showed high aeration efficiency although they had low air/water flow ratio. In high-head and free-surface conduits, almost full oxygen transfer, up to the saturation value, occurred. Forty-five degrees triangular sharp-crested weir had significantly better air/water flow ratio and aeration efficiency than other sharp-crested weir shapes. Stepped cascades, in particular nappe flow regime, were very efficient means of aeration.

The impact of autochthonous anaerobic bacteria on the release of metals in river sediment was studied. The sediments were characterized and bacterial activity was monitored in a batch reactor, where the sediments were incubated with a synthetic substrate solution containing glucose as carbon source. The results showed that metal release was correlated to the bacterial growth (carbon mineralization). In particular, a relationship between iron reduction and metal release was observed indicating that iron-reducing bacteria had a strong influence. By reductive dissolution of iron oxides, bacteria also released their associated toxic elements into the liquid phase. While organic analysis showed acetate and butyrate production leading to a decrease in pH and indicating a Clostridium fermentative bacteria activity, the results did not indicate any direct role of organic acids in the dissolution of iron and their associated metals.

Exudation of low molecular weight organic acids by fungi was studied in a project focusing on bioremediation of metal-contaminated soils. The production of acids (mainly oxalic and citric acid) as a response to nutrient variations and presence of metals has recently been reported (Arwidsson et al. 2009). A significant release of metals was observed and was related not only to the production of organic acids but also to the resulting pH decrease in the systems. The processes governing the release and redistribution of metals in the soil–water fungus system were the focus of the present continuation of the project, based on observations of Aspergillus niger, Penicillium bilaiae, and a Penicillium sp. The release of lead was 12% from the soil with the second highest initial load (1,600 mg kg−1), while the release of copper was 90% from the same soil (140 mg kg−1). The dominating mechanism behind the release and subsequent redistribution was the change in pH, going from near neutral to values in the range 2.1–5.9, reflecting the production of organic acids. For some of the systems, the formation of soluble complexes is indicated (copper, at intermediate pH) which favors the metal release. Iron is assumed to play a key role since the amount of secondary iron in the soils is higher than the total load of secondary heavy metals. It can be assumed that most of the heavy metals are initially associated with iron-rich phases through adsorption or coprecipitation. These phases can be dissolved, or associated metals can be desorbed, by a decrease in pH. It would be feasible to further develop a process in technical scale for remediation of metal-contaminated soil, based on microbial metabolite production leading to formation of soluble metal complexes, notably with copper.

Assessing air quality in street canyons is a crucial concern, as the highest pollution levels and threshold exceedances are usually experienced within this kind of urban streets. A brief overview based on experimental studies and modelling techniques undertaken in literature is presented, including characteristic features affecting wind flow and pollutant dispersion within street canyons. In this work, a numerical street canyon model intercomparison has been performed in a typical urban canyon in Florence, Italy. In particular, STREET, Canyon Plume Box Model (CPBM) and Operational Street Pollution Model (OSPM) have been applied to compute the street-level 1-h carbon monoxide (CO) concentrations. In addition, the CALINE4 model has been applied to test the site morphology. Input data cover a 1-year time period and include meteorological observations as well as measured traffic volumes and driving speeds. Hourly road emissions have been calculated using the COPERT methodology taking into account vehicle fleet, traffic flows and driving speed, as well as ambient temperature to account for cold overemissions. A preliminary experimental data analysis has been carried out in order to investigate the dependence of observed CO concentrations on meteorological and traffic parameters. Hourly CO concentrations observed over the full year have been used to compare the STREET, CPB and OSP models, resulting in a detailed statistical analysis carried out by wind sector as well as on a seasonal basis.

The city of La Plata and its surroundings are a very populated area, which has an important Industrial Pole and intense traffic activity but environmental studies have been rare so far. This article presents and discusses the importance of wind frequencies and velocities for the transport of air pollutants. The study emphasizes the importance of knowing wind patterns on an hourly basis that can be helpful for designing a monitoring network as well as for preventing exposure to pollutants. Correlation between monthly SO₂ concentrations and wind frequencies and velocities are discussed for a particular set of directions NNW-NE that carry pollutants from industrial sources toward populated areas. As a result, averaged wind frequencies have been found to be very important for determining patterns influencing pollutants transport; the influence of averaged velocities has shown low variability (hourly and monthly). Hierarchical cluster analysis applied to wind roses provided a useful approach for analyzing and describing the general daily occurrence of winds.

Phosphorus (P) loss from agricultural soils to water is a major contributor to eutrophication. In an incubation experiment with five contrasting soils, lime and gypsum showed potential as source measures to decrease P loss risk, as assessed by water extractions. Soils were incubated with lime to achieve a target pH of 6.5 and with gypsum at equivalent Ca rates for 108 days. P was added (17 kg P ha⁻¹) as KH₂PO₄ in solution. Gypsum appears to have greater potential as a source measure, decreasing molybdate-reactive P (RP) solubility by 14-56% and organic P (OP) by 10-53% across all soils. RP and Ca may have precipitated or co-sorbed, and OP may have been stabilised in organic matter complexes due to the bridging effect of Ca and the flocculating effect of increased ionic strength. Greater effectiveness of gypsum may be due to its higher solubility and the fact that it increases Ca concentrations without increasing pH. Lime decreased RP solubility in two soils (by 4% and 20%) but increased solubility in two and had no effect in a third. The overall effect of lime may depend on several competing effects of raised pH and Ca concentration that may vary in importance depending on soil characteristics such as base cation and P status. For the highest P status soil, both lime and gypsum were effective, decreasing RP solubility by 4% and 15%, respectively. Targeted treatment of high P soils may be an effective and economical strategy to minimise P losses.

Bioaerosols are conglomerates of biological particles such as bacterial and fungal propagules and are produced in sewers and sewage treatment plants through evaporation and turbulence. In order to evaluate the hazard to employees in wastewater treatment plants, airborne microorganisms were measured at two different sites in the sewage systems and in the grit chamber of a treatment plant. Two additional samples were taken during high-pressure cleaning in the relief sewer. Outdoor air samples served as background values. Airborne microorganisms were collected using the impaction method with the MAS-100® and the impingement method with the SKC Biosampler®. The concentrations of coliform bacteria as well as the fungal species Aspergillus fumigatus were determined in addition to mesophilic bacteria counts (cfu/m³). The highest concentrations of mesophilic bacteria were found in the encased grit chamber. Coliform bacteria were found infrequently only in the aerosol of the sewage systems; A. fumigatus was detected at all sampling sites both indoors as well as outdoors. During high-pressure cleaning, total bacteria concentrations reached up to 4.0 × 104 cfu/m3, coliforms up to 3.0 × 103 cfu/m3. These results show that personnel protective measures should be recommended to decrease the exposure risk to biological particles.

The goal of this work was to investigate the occurrence of emerging contaminants in drinking water of the city of Campinas, Brazil. Tap water samples were analyzed using SPE-GC-MS for 11 contaminants of recent environmental concern. Six emerging contaminants (stigmasterol, cholesterol, bisphenol A, caffeine, estrone, and 17β-estradiol) were found in the samples. The latter two were detected only during the dry season, with concentrations below quantification limits. Stigmasterol showed the highest average concentration (0.34 ± 0.13 µg L⁻¹), followed by cholesterol (0.27 ± 0.07 µg L⁻¹), caffeine (0.22 ± 0.06 µg L⁻¹), and bisphenol A (0.16 ± 0.03 µg L⁻¹). In Campinas, where surface drinking water supplies receive large amounts of raw sewage inputs, the emerging contaminants levels in drinking waters were higher than median values compiled for drinking and finished water samples around the world.

The objectives of this study were algal control and health assessments in a temperate eutrophic reservoir. Laboratory and mesocosm-scale in situ top-down biomanipulation experiments using planktivorous fishes and filter-feeding macroinvertebrates were conducted along with identification of the limiting nutrient using nutrient enrichment bioassays (NEBs), and ecosystem health evaluation based on the modified index of biological integrity model (Reservoir Ecosystem Health Assessment; REHA). Nutrients and N/P ratio analyses during 5 years revealed that the reservoir was in a eutrophic-hypertrophic state and that the key limiting nutrients, based on the NEBs, varied among seasons. Reservoir trophic guilds indicated declines in sensitive and endemic fish species and dominance of tolerant omnivores. Model values from multimetric REHAs averaged 25.8, indicating that the ecological health was in “fair to poor” condition. Overall microcosm biomanipulation tests suggested that macroinvertebrates, specifically Palaemon paucidens and Caridina denticulata, were effective candidates for phytoplankton control, compared to fishes. In situ mesocosm experiments revealed the highest removal rates with bluegreen algae and a phytoplankton size fraction of 2-19 μm (R e > 90%, Mann-Whitney U = 64.5-74.0, p < 0.01), the dominant fractions in the reservoir. Our biomanipulation technique may provide a key tool for efficient management and restoration of eutrophied reservoirs.

Cultures of the flagellate Isochrysis galbana were used to carry out the ecotoxicological evaluation of four PAHs [(naphthalene, phenanthrene, pyrene (Pyr) and fluoranthene (Flu)] by monitoring growth rate and the fluorescence variables F ₀, F m, F v and F v/F m, determined with a fast repetition rate fluorometer. The results presented in this investigation showed that F v was a suitable endpoint in acute ecotoxicological tests with marine phytoplankton. The derived effective concentrations followed the known narcotic mechanism of toxicity and showed sensitivity levels comparable to marine invertebrate embryo-larval bioassays. Pyr and Flu showed the lowest EC₁₀, which ranged between 168-279 and 189-697 nM, respectively.