The fate of chlorine in recirculating cooling towers Field results

Chlorine and chloramines are volatile compounds which are stripped (“flashed off”) from recirculating cooling water systems by the large volumes of air which flow through the water in the cooling tower. The fraction of a volatile gas, such as hypochlorous acid (HOCl), which is removed by stripping is determined by Henry's constant H for that gas: H = X_G/X_L, where X_G is the mole fraction of the gas in the air and X_L is the mole fraction of the gas in the water. We have measured H for HOCl, OCl⁻, NH₃, NH₂Cl, NHCl₂ and NCl₃ at 20 and 40°C. We found H = 0.076 for HOCl, compared to 0.71 for NH₃, at 20°C. At 40°C, H was about 2.5-fold larger for HOCl. This means that 10–15% of the HOCl is stripped from cooling water on each passage through a typical cooling tower. The measured flashoff of free available chlorine (HOCl + OCl⁻) was markedly pH-sensitive with a pK of 7.5, exactly as expected if HOCl is volatile but OCl⁻ is not. The data permit a quantitative understanding of the fate of chlorine in cooling systems. The values of H at 40°C for NH₂Cl, NHCl₂ and NCl₃ were 1.28, 3.76 and 1067. This means that all of the chloramines are quickly stripped in a cooling tower.     

Plant crown traits and carbon sequestration capability by Platanus hybrida Brot. in Rome

Measurements of carbon dioxide (CO₂) concentration carried out in the city of Rome in the period January–December 2005 showed a mean yearly CO₂ concentration of 414 ± 45 ppm; polluted sites (P sites) had 21% higher CO₂ concentration than control sites (C sites). The significant (p < 0.01) correlation analysis between CO₂ concentration and traffic density measured during the study period at P sites showed that traffic density explained 51% of the CO₂ variation. The CO₂ trend during the traffic limitation days (provision imposed by ordinance of the City Council) did not show significant differences as regards regular traffic days, suggesting the ineffectiveness of this provision. Leaf area index (LAI) of Platanus hybrida Brot. was on an average 11% lower at P sites than at C ones associated with a lower total photosynthetic leaf surface area (SPT, 34% lower at P sites than at C ones). P. hybrida had a total carbon sequestration of 117 ± 13 kg year⁻¹ (mean value of P and C sites) playing an important role in sequestering CO₂. Thus, the choice of plant species for urban areas may be set out taking into account their own air amelioration capability. Plant traits of each species may be used for urban tree planting programs to ameliorate urban air pollution.     

Hydrogen sulfide (H2S) and sour gas effects on the eye. A historical perspective

The toxicology of hydrogen sulfide (H₂S) and sour gas on the eye has a long history beginning at least with Ramazzini's observations [Ramazzini B. Diseases of Workers—De Morbis Artificum Diatriba—1713. Wright WC (trans). New York, C. Hafner Publishing Co Inc.; 1964. 98-99 pp.]. In contrast, a recent review by Alberta Health and Wellness (AHW Report) concluded that there is little evidence of eye irritation following short-term exposures to H₂S at concentrations up to 100 ppm and that the H₂S literature on the eye is a series of unsubstantiated claims reproduced in review articles dating back to the 1930s [Alberta Health and Wellness (AHW report). Health effects associated with short-term exposure to low levels of hydrogen sulfide: a technical review, Alberta Health and Wellness, October 2002, 81pp.]. In this paper, we evaluated this claim through a historical review of the toxicology of the eye. Ramazzini noted the effects of sewer gas on the eye [Ramazzini B. Diseases of Workers—De Morbis Artificum Diatriba—1713. Wright WC (trans). New York, C. Hafner Publishing Co Inc. 1964. 98-99 pp.]. Lehmann experimentally showed eye effects in men at 70-90 ppm H₂S and also in animals [Lehmann K. Experimentalle Studien uber den Einfluss technisch und hygienisch wichtiger Gase und Dampfe auf den Organismus. Arch Hyg 1892;14:135-189]. In 1923, Sayers, Mitchell and Yant reported eye effects in animals and men at 50 ppm H₂S. Barthelemy showed eye effects in animals and men at 20 ppm H₂S [Barthelemy HL. Ten years' experience with industrial hygiene in connection with the manufacture of viscose rayon. J Ind Hyg Toxicol 1939;21:141-51]. Masure experimentally showed that H₂S is the causative agent of eye impacts in animals and men [Masure R. La Keratoconjunctivite des filatures de viscose; etude clinique and experiementale. Rev Belge Pathol 1950;20:297-341]. Michal upon microscopic examination of the rat's cornea, found nuclear pyknosis, edema and separation of cells in the eye following exposures for 3 h at 36 ppm H₂S [Michal FV. Eye lesions caused by hydrogen sulfide. Cesk Ophthalmol 1950;6;5-8]. In 1975, in Alberta, irreversible eye damage and photophobia were experimentally produced in calves exposed to 20 ppm H₂S for 1 week [Nordstrom GA. A study of calf response of ammonia and hydrogen sulfide gases. Thesis, University of Alberta, Department of Agricultural Engineering, Edmonton Alberta; 1975, 218 pp.]. Alberta Environmental Centre documented clinical irritation of the eye at 40 ppm H₂S in 6 hours in rats [Alberta Environmental Centre. Morphological observations in rats exposed for six hours to an atmosphere of 0, 56, or 420 mg/m³ hydrogen sulfide. AECV86-A1. Alberta Environmental Centre, Vegreville, Alberta; 1986b. 28 pp.]. In two sour gas blow-outs in Alberta, in the early 1980s, eye injury was documented in humans and animals at 0.5 ppm H₂S. Community studies in the United States, Europe and New Zealand suggest that acute exposure to 25 ppb H₂S is the lowest concentration to irritate the eyes; with chronic exposure, serious eye effects are suggested. In contrast to the conclusion, all of the studies, except one, cited in the AHW Report indicate toxic effects on the eye below 100 ppm H₂S [Alberta Health and Wellness (AHW report). Health effects associated with short-term exposure to low levels of hydrogen sulfide (H₂S): a technical review, Alberta Health and Wellness, October 2002, 81pp.]. In addition, the AHW Report (2002) mis-presented two studies as ‘clinical studies’, claiming they reported no evidence of eye effects in humans from 2 and 30 ppm H₂S for 30-40 minutes [Alberta Health and Wellness (AHW report). Health effects associated with short-term exposure to low levels of hydrogen sulfide (H₂S): a technical review, Alberta Health and Wellness, October 2002, 81pp.].     

Preserving Shipboard AFFF Fire Protection System Performance While Preventing Hydrogen Sulfide Formation

There is a very serious problem aboard US Navy ships from generation of toxic hydrogen sulfide (H₂S) in Aqueous Film-Forming Foam (AFFF) solutions used for shipboard fire protection. This is the result of the action of sulfate reducing bacteria (SRB) in mixtures of seawater and AFFF, which remain stagnant for significant time periods in shipboard fire protection system piping. Similar to microbial generation of H₂S in sewage, over time microbes present in seawater consume organic materials in the AFFF mixture and can deplete the dissolved oxygen. If the reduction-oxidation potential falls low enough, anaerobic action of the SRB on the sulfate present in seawater can then result in H₂S generation, reaching dangerous levels. The recommended ceiling for exposure to H₂S is only 10 ppm. If the microbes causing oxygen depletion and/or the SRB can be eliminated (or sufficiently minimized), the dangerous generation of H₂S would not occur. The Navy Technology Center for Safety and Survivability is participating in a research project for the Naval Sea Systems Command (NAVSEA) to evaluate several treatment modalities for their ability to inhibit H₂S formation in AFFF/seawater mixtures and for possible deleterious effects on AFFF performance. Various approaches have been considered employing laboratory evaluations (dynamic surface tension and Ross-Miles foamability), and 28 ft² (2.6 m²) pool fire extinguishment and burnback protection field tests (Military Standard MIL-F-24385F). The protocol selected for NAVSEA shipboard H₂S generation mitigation testing is a combination of a commercial broad-spectrum biocide with a molybdenum compound which is a specific inhibitor of SRB.     

Efficiency and energy requirements for the transformation of organic micropollutants by ozone, O3/H2O2 and UV/H2O2

The energy consumptions of conventional ozonation and the AOPs O₃/H₂O₂ and UV/H₂O₂ for transformation of organic micropollutants, namely atrazine (ATR), sulfamethoxazole (SMX) and N-nitrosodimethylamine (NDMA) were compared. Three lake waters and a wastewater were assessed. With p-chlorobenzoic acid (pCBA) as a hydroxyl radical (^•OH) probe compound, we experimentally determined the rate constants of organic matter of the selected waters for their reaction with ^•OH (k_OH,DOM), which varied from 2.0 × 10⁴ to 3.5 × 10⁴ L mgC⁻¹ s⁻¹. Based on these data we calculated ^•OH scavenging rates of the various water matrices, which were in the range 6.1-20 × 10⁴ s⁻¹. The varying scavenging rates influenced the required oxidant dose for the same degree of micropollutant transformation. In ozonation, for 90% pCBA transformation in the water with the lowest scavenging rate (lake Zürich water) the required O₃ dose was roughly 2.3 mg/L, and in the water with the highest scavenging rate (Dübendorf wastewater) it was 13.2 mg/L, corresponding to an energy consumption of 0.035 and 0.2 kWh/m³, respectively. The use of O₃/H₂O₂ increased the rate of micropollutant transformation and reduced bromate formation by 70%, but the H₂O₂ production increased the energy requirements by 20-25%. UV/H₂O₂ efficiently oxidized all examined micropollutants but energy requirements were substantially higher (For 90% pCBA conversion in lake Zürich water, 0.17-0.75 kWh/m³ were required, depending on the optical path length). Energy requirements between ozonation and UV/H₂O₂ were similar only in the case of NDMA, a compound that reacts slowly with ozone and ^•OH but is transformed efficiently by direct photolysis.     

Use of photosynthetic bacteria for hydrogen sulfide removal from anaerobic waste treatment effluent

The feasibility of using photosynthetic bacteria to remove H₂S from anaerobic waste treatment effluent was investigated by growing fixed films of photosynthetic bacteria in a packed column or in a submerged tube system (“phototube”). Growth and enrichment for these organisms depended on constant illumination, anaerobic conditions and a substratum for attachment of the bacteria. Both systems were operated as flow-through processes using effluent from anaerobic (upflow) filters.Results showed that photosynthetic bacteria in fixed films can be effectively used for H₂S removal. Removal efficiencies of 81–95% were obtained on a 24-h retention time. Residual H₂S remained in the process effluent. The submerged “phototube”, showed dramatic improvement over the column, yielding a final effluent completely devoid of H₂S, at significantly shorter retention times and higher loading rates than the column. Performance appeared dependent on cell-H₂S contact and adequate illumination. The green photosynthetic sulfide-oxidizing bacterium, Chlorobium, was identified as a common organism in this phototube.This biological sulfide removal process offers the following advantages over currently used physical-chemical techniques: simplicity, no need for aeration or chemical additives and odor-free. Much research in process design is necessary before pilot or full scale application of the technique is possible.     

Greywater treatment by UVC/H2O2

Greywater treatment by UVC/H₂O₂ was investigated with regard to the removal of chemical oxygen demand (COD). A COD reduction from 225 to 30 mg l⁻¹ (overall removal of 87%) was achieved after settling overnight and subsequent irradiation for 3 h with 10 mM H₂O₂. Most of the contaminants were removed by oxidation since only 13% COD was removed by settlement.The removal of COD in the greywater followed a second-order kinetic equation, r = 0.0637[COD][H₂O₂], up to 10 mM H₂O₂. A slightly enhanced COD removal was observed at the initial pH of 10 compared with pH 3 and 7. This was attributed to the dissociation of H₂O₂ to O₂H⁻. The treatment was not affected by total concentration of carbonate (c_T) of at least 3 mM, above which operation between pH 3 and 5 was essential. The initial biodegradability of the settled greywater (as BOD₅:COD) was 0.22. After 2 h UVC/H₂O₂ treatment, a higher proportion of the residual contaminants was biodegradable (BOD₅:COD = 0.41) which indicated its potential as a pre-treatment for a biological process.     

Molecular hydrogen (H2) emissions from gasoline and diesel vehicles

This study assesses individual-vehicle molecular hydrogen (H₂) emissions in exhaust gas from current gasoline and diesel vehicles measured on a chassis dynamometer. Absolute H₂ emissions were found to be highest for motorcycles and scooters (141 ± 38.6 mg km^− 1), approximately 5 times higher than for gasoline-powered automobiles (26.5 ± 12.1 mg km^− 1). All diesel-powered vehicles emitted marginal amounts of H₂ (∼ 0.1 mg km^− 1). For automobiles, the highest emission factors were observed for sub-cycles subject to a cold-start (mean of 53.1 ± 17.0 mg km^− 1). High speeds also caused elevated H₂ emission factors for sub-cycles reaching at least 150 km h^− 1 (mean of 40.4 ± 7.1 mg km^− 1). We show that H₂/CO ratios (mol mol^− 1) from gasoline-powered vehicles are variable (sub-cycle means of 0.44-5.69) and are typically higher (mean for automobiles 1.02, for 2-wheelers 0.59) than previous atmospheric ratios characteristic of traffic-influenced measurements. The lowest mean individual sub-cycle ratios, which correspond to high absolute emissions of both H₂ and CO, were observed during cold starts (for automobiles 0.48, for 2-wheelers 0.44) and at high vehicle speeds (for automobiles 0.73, for 2-wheelers 0.45). This finding illustrates the importance of these conditions to observed H₂/CO ratios in ambient air. Overall, 2-wheelers displayed lower H₂/CO ratios (0.48-0.69) than those from gasoline-powered automobiles (0.75-3.18). This observation, along with the lower H₂/CO ratios observed through studies without catalytic converters, suggests that less developed (e.g. 2-wheelers) and older vehicle technologies are largely responsible for the atmospheric H₂/CO ratios reported in past literature.     

Detoxification of seawater used for gas scrubbing in the steel industry

Cyanide ion present in seawater after scrubbing blast furnace and coke ovens gases can be removed by sedimentation of hexacyanoferrate complexes followed by oxidation of residual cyanide with Caro's acid. Zinc ion is removed at the same time by adsorption on the hexacyanoferrate/hydrous ferric oxide precipitate.Sulphide is precipitated as ferrous sulphide, then oxidised by atmospheric oxygen. At 25°C and using an Fe/CN ratio of 1·00, initial concentrations of 50 mg l⁻¹ of CN⁻ and 10 mg l⁻¹ of Zn²⁺ in seawater are reduced to 5–7 mg l⁻¹ and 0·1 mg l⁻¹. Subsequent treatment with H₂SO₅/CN = 1·2 reduces the [CN⁻] to 0·1 mg l⁻¹.Treatment of a combined blast furnace/coke ovens effluent ([CN⁻] = 24 mgl⁻¹, [Zn²⁺] = 4·0 mgl⁻¹) with Fe/CN = 1·5 reduced [CN⁻] to 0·2 mg l⁻¹ and [Zn²⁺] to <0·1 mgl⁻¹. Subsequent treatment with H₂SO₅/CN = 2·0 reduced [CN⁻] to 0·2 mg l⁻¹. The process operates best in the pH range 7–9 and so is not affected by the buffer characteristics of seawater.     

Comparative effect of simulated solar light,UV, UV/H2O2 and photo-Fenton treatment (UV–Vis/H2O2/Fe) in the Escherichia coli inactivation in artificial seawater

Innovative disinfection technologies are being studied for seawater, seeking a viable alternative to chlorination. This study proposes the use of H₂O₂/UV₂₅₄ and photo-Fenton as disinfection treatment in seawater. The irradiations were carried out using a sunlight simulator (Suntest) and a cylindrical UV reactor. The efficiency of the treatment was compared for Milli-Q water, Leman Lake water and artificial seawater. The presence of bicarbonates and organic matter was investigated in order to evaluate possible effects on the photo-Fenton disinfection treatment. The photo-Fenton treatment, employing 1 mg L⁻¹ Fe²⁺ and 10 mg L⁻¹ of H₂O₂, led to the fastest bacterial inactivation kinetics. Using H₂O₂/UV₂₅₄ high disinfection rates were obtained similar to those obtained with photo-Fenton under UV₂₅₄ light. In Milli-Q water, the rate of inactivation for Escherichia coli was higher than in Leman Lake water and seawater due to the lack of inorganic ions affecting negatively bacteria inactivation. The presence of bicarbonate showed scavenging of the OH^• radicals generated in the treatment of photo-Fenton and H₂O₂/UV₂₅₄. Despite the negative effect of inorganic ions, especially HCO₃^-, the disinfection treatments with AOPs in lake water and seawater improved significantly the disinfection compared to light alone (simulated sunlight and UV₂₅₄). In the treatment of photo-Fenton with simulated sunlight, dissolved organic matter had a beneficial effect by increasing the rate of inactivation. This is associated with the formation of Fe³⁺-organo photosensitive complexes leading to the formation of ROS able to inactivate bacteria. This effect was not observed in the photo-Fenton with UV₂₅₄. Growth of E. coli surviving in seawater was observed 24 and 48 h after treatment with UV light. However, growth of surviving bacteria was not detected after photo-Fenton with UV₂₅₄ and H₂O₂/UV₂₅₄ treatments.     

Anatoxin-a degradation by Advanced Oxidation Processes: Vacuum-UV at 172 nm, photolysis using medium pressure UV and UV/H2O2

Two Advanced Oxidation Processes, namely vacuum-ultraviolet (VUV) photolysis at 172 nm and ultraviolet/hydrogen peroxide (UV/H₂O₂) were investigated for the degradation of anatoxin-a in aqueous solutions. Solutions of anatoxin-a-fumarate were treated with VUV light at 172 nm with a UV dose of 200 mJ/cm², where fumaric acid served as a reference compound for a competition kinetics analysis. The second-order rate constant for the reaction between anatoxin-a and the hydroxyl radical was found to be (5.2 ± 0.3) × 10⁹ M⁻¹ s⁻¹ and was independent of pH, temperature, and initial concentration of anatoxin-a. The direct photolysis of anatoxin-a using a medium pressure (MP) UV lamp was also investigated, in which case a UV dose of 1285 mJ/cm² was required to degrade anatoxin-a by 88% and 50% at concentrations of 0.6 mg/L and 1.8 mg/L of toxin, respectively. Treatment of anatoxin-a with a low pressure (LP) UV lamp in the presence of 30 mg/L of H₂O₂ was examined, where it was found that more than 70% of toxin could be degraded at a UV dose of 200 mJ/cm². The degradation arises from the oxidation of the toxin by hydroxyl radicals. The addition of H₂O₂ clearly enhanced the degradation of anatoxin-a, up to a concentration of 40 mg/L, after which addition of more H₂O₂ had little effect on the degradation kinetics of anatoxin-a. The effect of background constituents in the water on the degradation of anatoxin-a was also investigated using natural and synthetically produced model waters.     

Degradation of bromoxynil and trifluralin in natural water by direct photolysis and UV plus H2O2 advanced oxidation process

The degradation of two pesticides, bromoxynil and trifluralin, was investigated in ultrapure and natural water solutions under ultraviolet (UV) light and a combination of UV and hydrogen peroxide (H₂O₂). The effect of pH on the photooxidation of the pesticides was also studied. The results indicated that under direct photolysis with monochromatic light at 253.7 nm and different conditions, the photochemical rates followed first-order kinetics, with fluence-based rate constants ranging from 9.15 × 10⁻⁴ to 6.37 × 10⁻³ cm² mJ⁻¹ and 7.63 × 10⁻³ to 1.47 × 10⁻² cm² mJ⁻¹ for bromoxynil and trifluralin, respectively. Quantum yields, in the range of 0.08-0.25 for bromoxynil and 0.12-0.72 for trifluralin, were observed in experiments using ultrapure water. The study also found that the UV/H₂O₂ process enhanced the oxidation rate in comparison to direct photolysis. A 90% degradation with UV dose of 333 and 188 mJ cm⁻² was achieved for bromoxynil and trifluralin, respectively, in natural water, in presence of 8.8 × 10⁻⁴ M H₂O₂. To assess the aquatic toxicity, the Microtox^® 81.9% screening test protocol was used before and after treatment. The test results indicated a decrease in the acute toxicity of the samples after treatment for both pesticides.     

The influence of substrate, pH, diet and temperature upon cadmium accumulation in the asiatic clam (Corbicula fluminea) in laboratory artificial streams

The influence of substrate, pH, diet and temperature upon the accumulation of cadmium (0.05 mg l⁻¹ dose < 0.001 mg l⁻¹ control) in the visceral mass of the Asiatic clam Corbicula fluminea was studied in laboratory artificial stream systems at intervals of 0, 3, 5, 7, 10 and 14-day exposures. Four substrate conditions, sand; sand, silt and clay (SSC); sand, clay and organic matter (SCO); and no substrate (NoS), were considered. The greatest tissue accumulation of cadmium in C. fluminea occurred at 0.05 mg l⁻¹ Cd in NoS and the lowest in clams occupying SCO. Complexation of available metals, lower clam filtering rates and physical protection by the substrate were attributed to the depressed cadmium accumulation of clams exposed in the SCO substrate. Lower pH exposures (5.0 vs 7.8) significantly (P 0.05 level) reduced cadmium uptake at 21°C but had little effect at 9°C. Uptake was higher in clams fed with cadmium-exposed Chlamydomonas reinhardt at 21°C but not at 9°C. In temperature exposures alone at 0.05 mg l⁻¹ Cd, accumulation was significantly higher in C. fluminea exposed at 21°C than at 9°C. The results are discussed relative to the importance of standardized laboratory protocol and the use of C. fluminea as a bioindicator of heavy metal stress.     

Robust control of plate vibration via active constrained layer damping

In this paper, the theoretical modeling of a plate partially treated with active constrained layer damping (ACLD) treatments and its vibration control in an H_∞ approach is discussed. Vibration of the flat plate is controlled with patches of ACLD treatments, each consisting of a viscoelastic damping layer which is sandwiched between the piezo-electric constrained layer and the host plate. The piezo-electric constrained layer acts as an actuator to actively control the shear deformation of the viscoelastic damping layer according to the vibration response of the plate excited by external disturbances. In the first part of this paper, the Mindlin–Reissner plate theory is adopted to express the shear deformation characteristics of the viscoelastic damping layer, meanwhile GHM (Golla–Hughes–McTavish) model of viscoelastic damping material and FEM (finite element model) are incorporated to describe the dynamics of the plate partially treated with ACLD treatment. In the second part, particular emphasis is placed on the vibration control of the first four modes of the treated plate using H_∞ robust control method. For this purpose, an H_∞ robust controller is designed to accommodate uncertainties of the ACLD parameters, particularly those of the viscoelastic damping core which arise from the variation of the operation temperature and frequency. Disturbances and measurement noise are rejected in the closed loop by H_∞ robust controller. In the experimental validation, external disturbances of different types are employed to excite the treated plate. The results of the experimental clearly demonstrate that the proposed modeling method is correct and the ACLD treatments are very effective in fast damping out the structural vibration as compared to the conventional passive constrained layer damping (PCLD).     

Growth kinetics of the filamentous microorganism Sphaerotilus natans in a model system of a food industry wastewater

Bulking by Sphaerotilus natans has been attributed to several factors such as low dissolved oxygen in the aeration basin, wastes with high C:N ratios and phosphorus limitation; however, the occurrence of bulking has been reported in fruit, vegetable, meat and poultry wastewaters in which the ratio C:N is variable.Growth of S. natans was analyzed in a model system of a food industry wastewater (potato processing waste) that was characterized by HPLC determining that citric acid was the most important identified component. The effect of several carbon sources on S. natans growth was also studied; different C:N ratios were tested in a continuous culture system (chemostat). This strain grew in a mineral medium with citric acid as a sole carbon source, in spite of the contradictory results found in literature. Chemostat studies showed that the medium was carbon-limited when C:N ratios <19 mgCOD (mgN-NH₃)⁻¹. Monod kinetic growth coefficients, determined for this strain in chemostat were: maximum specific growth rate, μ_max=0.301 h⁻¹; Monod constant, K_S=4.6 mgCOD l⁻¹; true biomass growth yield, Y^T_X/S=0.490 mgVSS (mgCOD)⁻¹; endogenous decay rate, k_d=0.011 h⁻¹ and maintenance coefficient, m_S=0.022 mgCOD (mgVSS)⁻¹ h⁻¹. The obtained parameters were compared with literature data and the effect of glucose and citric acid as carbon sources was discussed; these parameters are useful in modeling the growth of S. natans in potato processing wastewaters (or in other effluents under carbon-limiting conditions) especially when citrate is the main component and can be used to control filamentous bulking by metabolic or kinetic selection.     

Impact of salinity and pH on the UVC/H2O2 treatment of reverse osmosis concentrate produced from municipal wastewater reclamation

While reverse osmosis (RO) technology is playing an increasingly important role in the reclamation of municipal wastewater, safe disposal of the resulting RO concentrate (ROC), which can have high levels of effluent organic pollutants, remains a challenge to the water industry. The potential of UVC/H₂O₂ treatment for degrading the organic pollutants and increasing their biodegradability has been demonstrated in several studies, and in this work the impact of the water quality variables pH, salinity and initial organic concentration on the UVC/H₂O₂ (3 mM) treatment of a municipal ROC was investigated. The reduction in chemical oxygen demand and dissolved organic carbon was markedly faster and greater under acidic conditions, and the treatment performance was apparently not affected by salinity as increasing the ROC salinity 4-fold had only minimal impact on organics reduction. The biodegradability of the ROC (as indicated by biodegradable dissolved organic carbon (BDOC) level) was at least doubled after 2 h UVC/H₂O₂ treatment under various reaction conditions. However, the production of biodegradable intermediates was limited after 30 min treatment, which was associated with the depletion of the conjugated compounds. Overall, more than 80% of the DOC was removed after 2 h UVC/3 mM H₂O₂ treatment followed by biological treatment (BDOC test) for the ROC at pH 4-8.5 and electrical conductivity up to 11.16 mS/cm. However, shorter UV irradiation time gave markedly higher energy efficiency (e.g., EE/O 50 kWh/m³ at 30 min (63% DOC removal) cf. 112 kWh/m³ at 2 h). No toxicity was detected for the treated ROC using Microtox^® tests. Although the trihalomethane formation potential increased after the UVC/H₂O₂ treatment, it was reduced to below that of the raw ROC after the biological treatment.     

Photooxidation of the antidepressant drug Fluoxetine (Prozac®) in aqueous media by hybrid catalytic/ozonation processes

This article examines the oxidative disposal of Prozac^® (also known as Fluoxetine, FXT) through several oxidative processes with and without UV irradiation: for example, TiO₂ alone, O₃ alone, and the hybrid methods comprised of O₃ + H₂O₂ (PEROXONE process), TiO₂ + O₃ and TiO₂ + O₃ + H₂O₂ at the laboratory scale. Results show a strong pH dependence of the adsorption of FXT on TiO₂ and the crucial role of adsorption in the whole degradation process. Photolysis of FXT is remarkable only under alkaline pH. The heterogeneous photoassisted process removes 0.11 mM FXT (initial concentration) within ca. 60 min with a concomitant 50% mineralization at pH 11 (TiO₂ loading, 0.050 g L⁻¹). The presence of H₂O₂ enhances the mineralization further to >70%. UV/ozonation leads to the elimination of FXT to a greater extent than does UV/TiO₂: i.e., 100% elimination of FXT is achieved by UV/O₃ in the first 10 min of reaction and almost 97% mineralization is attained under UV irradiation in the presence of H₂O₂. The hybrid configuration UV + TiO₂ + O₃ + H₂O₂ enhances removal of dissolved organic carbon (DOC) in ca. 30 min leaving, however, an important inorganic carbon (IC) content. In all cases, the presence of H₂O₂ improves the elimination of DOC, but not without a detrimental effect on the biodegradability of FXT owing to the low organic carbon content in the final treated effluent, together with significant levels of inorganic byproducts remaining. The photoassisted TiO₂/O₃ hybrid method may prove to be an efficient combination to enhance wastewater treatment of recalcitrant drug pollutants in aquatic environments.     

Semicontinuous Fenton oxidation of phenol in aqueous solution. A kinetic study

This work investigates the Fenton oxidation of phenol in a semicontinuous reactor where the overall amount of H₂O₂ is distributed as a continuous feed upon the reaction time. The experiments were carried out at 25 °C and atmospheric pressure, with 100 mg/L initial phenol concentration and iron dosages from 1 to 100 mg/L. H₂O₂ aqueous solution was continuously fed during 4 h reaction time up to an overall dose varying within the range of 500-5000 mg/L. The results in terms of evolution of phenol, H₂O₂ and intermediates, as well as TOC abatement were compared with those obtained in conventional batch operation. It was found that the oxidation rates for phenol and intermediates were lower when adding the H₂O₂ continuously. However, a higher abatement of TOC was reached at the end of the 4-h reaction time, in spite of a similar overall H₂O₂ consumption. This is the result of a more efficient OH generation throughout the semicontinuous process, favouring the reaction with the organic species and reducing the occurrence of competitive scavenging reactions involving Fe²⁺, H₂O₂ and OH. Two kinetic models were proposed, one for describing the evolution of phenol, aromatics and H₂O₂ and the other for TOC. The influence of the operating conditions on the kinetic constants was also studied, looking for the optimal conditions in terms of both, environmental and economic points of view.     

The use of Bacillus thuringiensis var. israelensis to control the nuisance fly Sylvicola fenestralis (Anisopodidae) in sewage filter beds

The effectiveness of using the microbial insecticide Bacillus thuringiensis var. israelensis (Bti) to control the nuisance fly Sylvicola fenestralis at Rossendale Sewage Works, Lancashire, was investigated. Following a provisional trial in 1987, the whole Works (28 filter beds) was treated with a two-stage application of Bti in 1988; the first application in late April was separated from the second in late May by about half the length of the Sylvicola life-cycle. The Bti treatment was timed to reduce fly nuisance in June, the month when most complaints (71%) had been received. For each application, 0.161. of the Bti preparation, containing nearly 10¹⁰ spores·cm⁻³, was applied per square metre of bed surface. An 80 and 98% kill of Sylvicola larvae was recorded following the first and second applications respectively. The lower kill achieved by the first application was believed to be due to insufficient mixing of the Bti with the settled sewage prior to dosing. Nuisance caused by the flies was considerably reduced; there were no complaints from the public during June, although a few were received in late July, early August. Sewage purification efficiency was not affected by Bti treatment. The maximum concentration of Bti spores in the Works' effluent was 7 × 10⁴ spores·cm⁻³. This concentration did not appear to affect the already impoverished macro-invertebrate fauna of the receiving river.     

Bioconcentration and metabolism of phenyltin chlorides in carp

Bioconcentration factors (BCF) in carp (Cyprinus carpio L.) and partition coefficients between n-octanol and water (P_ow) were measured for triphenyltin chloride (Ph₃SnCl), diphenyltin dichtende (Ph₂SnCl₂) and monophenyltin trichloride (PhSnCl₃). Log P_ow was 2.11 for Ph₃SnCl, 1.43 for Ph₂SnCl₂ and 1.73 for PhSnCl₃. The order of log BCF was kidney > liver > muscle gallbladder for Ph₃SnCl, liver > kidney > gallbladder > muscle for Ph₂SnCl₂ and kidney liver > gallbladder > muscle for PhSnCl₃. Further, metabolism in carp was studied on Ph₃SnCl. Ph₂Sn²⁺ and PhSn³⁺, the metabolites of Ph₃SnCl were detected in muscle and viscera. The ratio of Ph₃SnCl, Ph₂Sn²⁺ (Ph₂SnCl₂) and PhSn³⁺ (PhSnCl₃) concentrations by metabolism in each part of carp corresponded to that of BCF by carp for the same phenyltin chlorides.