Mass transfer and reaction kinetics in the ozone/tap water system

The mass transfer and the reaction kinetics of ozone in tap water were examined. The contacting system was a well-mixed reactor with perpendicular jets. The ozone residual range was the lowest detectable range. A simple mathematical model was proposed to describe the mechanism of the ozone in the reactor and was checked over the range of water flow rates from 2.170 to 3.080 l min⁻¹, gas flow rates from 0.667 to 1.333 l min⁻¹ and different temperature conditions. The proposed model describes quite accurately the mass-transfer behavior in the reactor and determines the operational parameters which control the reactor operation. There is a linear relationship between the ozone feed rate and ozone residual. Zero order kinetics best describe the autodecomposition of ozone in plain tap water. The mass transfer coefficient is about 1.14 min⁻¹. Without use of agitation, there is a large decrease in the value of the mass transfer coefficient, to about 0.250 min⁻¹. The magnitude of the reactor rate constant is between 0.05 and 0.13 mg min⁻¹ l.     

Toxicity vs mutagenicity of some crude oils,distillates and their water soluble fractions

Ames tests conducted on a range of oils and oil products (Kuwait crude, Saran Gach crude, Diesel 25, Bunker C, used motor oil) confirmed the mutagenicity of used (crankcase) motor oil. The other oils, when tested whole, were either toxic or showed no significant mutagenicity. Water-soluble fractions (WSF) of all products, including WSF of used crankcase oil, also gave no significant indication of mutagenicity. However, in several tests (including both whole oils and WSF-preparations) MR values (ratio of induced revertants to spontaneous revertants) between 1.3 and 1.8 were obtained which, while not significantly indicative of mutagenicity, exceeded non-mutagenic background levels.In contrast to the non-mutagenicity of the whole Kuwait crude oil, parallel assays of chromatographically obtained fractions showed significant mutagenicity in the F4 (acetone or methanol) fraction (presumed to be a strongly polar, DMSO-soluble large molecular weight component of Kuwait crude). This mutagenicity was not enhanced by metabolic activation. None of the other fractions showed evidence of mutagenicity. However, marked toxicity was associated with the F1 (hexane) fraction of the oil.The data suggest that low mutagenicity scores of crude oils and oil products could result from the masking of mutagenic activity of some components by the toxicity of other components of these products.     

Water dechlorination by activated carbon, ultraviolet radiation and sodium sulphite: A comparison of treatment systems suitable for fish culture

The characteristics of water dechlorination by activated carbon filtration, u.v. irradiation and sodium sulphite injection were examined. A pilot plant water treatment system composed of sand and diatomaceous earth filtration, ozonation and activated carbon filtration was evaluated. Activated carbon did not completely eliminate chlorine under any conditions tested but the post-carbon chlorine concentrations were relatively insensitive to large variations in incoming chlorine levels and water flow rates. Carbon filtration also reduced total dissolved organic carbon concentrations by 65% and reduced various halogenated methane derivatives by 97–100%. Ultraviolet irradiation eliminated up to 99% of the total chlorine in municipal water but u.v.-dechlorination was sensitive to flow rate with a rate constant of 2.02 min⁻¹ between 10 and 27 l min⁻¹. Water temperatures ranging from 7.5 to 20.6°C did not affect the efficiency of dechlorination by activated carbon or u.v. irradiation. Sodium sulphite at a 3:1 molar ratio to chlorine completely eliminated chlorine from municipal water while a sulphite:chlorine ratio of 6:1 was required to completely dechlorinate water which had been partially dechlorinated by activated carbon. The results are discussed in relation to the design of a multi-stage system suitable for providing dilution water for aquatic toxicity studies and fish culture.     

Flow behaviours comparison of crude oil–polymer emulsions

The flow characteristics of crude oil–polymer (COPE) emulsions were investigated in terms of viscosity and shear stress. Two commonly used polymers in the enhanced oil recovery were employed. These two different polymers are Alcoflood and Xanthan gum. Rheostress RS100 was used in this study for measuring and analysing the experimental measurements. A cone and plate sensor of RS100 rheometer was utilised for this investigation. The experimental measurements of viscosity and shear stress of different COPE were examined over the shear rate range of 0.1–1000?s^?1. The polymer concentration range of 500–10^4?ppm was examined and two crude oil concentrations of 25% and 75% by volume were tested. A detailed investigation of the flow behaviour of COPE in the presence of two different polymers was completed. The flow behaviour of all COPE exhibit non-Newtonian shear thinning behaviour that can be presented by the power-law model for crude oil-AF1235, however the other types of COPE can be predicted by the Casson model. For a low polymer concentration of 500?ppm, this investigation showed that the flow behaviour of Xanthan emulsions is slightly higher than the Alcoflood emulsions till a shear rate of 100?s^?1. For the higher polymer concentrations, both polymer emulsions exhibited more or less similar flow behaviours till the beginning of the shear thickening for the AF1285 emulsions.     

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.     

Deleterious effects of water-soluble fraction of petroleum, diesel and gasoline on marine pejerrey Odontesthes argentinensis larvae

Accidental discharges and oil spills are frequent around the world. Petroleum-derived hydrocarbons are considered one of the main pollutants of aquatic ecosystem. The importance of petroleum and refined fuels is notorious because today's society depends on them. Researches related to the toxic water-soluble fraction (WSF) of petroleum and derivatives to aquatic biota are scarce. For this reason, deleterious effects of WSF of Brazilian petroleum, automotive diesel and unleaded gasoline to marine pejerrey Odontesthes argentinensis larvae were studied employing toxicity tests and histopathological examination. Each WSF was generated in a laboratory by mixing four parts of seawater with one part of pollutant by approximately 22 h. Larvae were exposed during 96 h to different concentrations of WSF of petroleum, diesel, and gasoline, plus a control. After 96 h of exposure to the different WSFs, three larvae were sampled for histopathological studies. The median lethal concentration after 96 h (LC50) of exposure for WSF of petroleum was equal to 70.68%, it was significantly higher (P < 0.05) than the values for WSF of diesel and gasoline, which were 13.46% and 5.48%, respectively. The histological examination of pejerrey larvae exposed to WSF of petroleum, diesel and gasoline after 96 h revealed a variety of lesions in the larvae. The gills, pseudobranchs and esophagus presented epithelial hyperplasia, and the liver presented dilatation of hepatic sinusoids, hepatocitomegaly, bi-nucleated and nuclear degeneration of hepatocytes, such as pyknotic nuclei. The acute toxicity of diesel and gasoline is at least fivefold higher than Brazilian petroleum. However, all toxicants induced histopathological abnormalities in pejerrey larvae. The results are of importance since much attention has been paid to large visible surfaces of petroleum spills instead of potential toxic effects of dissolved aromatic hydrocarbons, which are more available to marine biota.     

Comparative effectiveness of antifouling treatment regimes using chlorine or a slow-releasing bromine biocide

Five chlorine (Cl₂) and three slow-releasing bromine biocide [1-bromo-3-chloro-5,5-dimethylhydantoin (BCDMH)] treatment regimes were compared under laboratory conditions to determine their effectiveness in controlling the fouling of 304L stainless steel heat exchanger tubing. The most effective Cl₂ treatments were low level (0.1 ppm or less) continuous applications. Three intermittent Cl₂ treatments (1 h day⁻¹ at 1.0 ppm, 1 h day⁻¹ at 0.5 ppm, and 3 × 20 min day⁻¹ at 0.5 ppm) were about equally effective. However, all three intermittent regimes were significantly less effective than the low level continuous treatments. The effectiveness of BCDMH treatment was similar to Cl₂ when used intermittently at similar residual concentrations as Cl₂ for 1 h day⁻¹ and continuously at low levels. These experiments indicated that low level continuous treatment was more effective than intermittent treatment for controlling biofouling.     

Restoration of heavily polluted branches of the Shatt Al-Arab river, Iraq

In view of the desire to improve the water quality of the heavily polluted branches of the Shatt al-Arab River at the City of Basrah, it was proposed to maintain effective flushing as well as contracting sewerage system. The present study was conducted in order to examine the water quality of these branches in an attempt to evaluate the effectiveness of the proposed flushing system. It has been found that their waters contained very low levels of dissolved oxygen and relatively high amounts of both COD and BOD₅. The annual average water quality parameters for Basrah Branches were: dissolved oxygen 3.4 ppm; pH 7.67; hydrogen sulphide 1.4 ppm; ammonia 97 μg-at. N l⁻¹; COD 15.9 mg l⁻¹; BOD₅ 12.7 mg l⁻¹; dissolved silicates 202 μg-at. Si l⁻¹; dissolved reactive phosphate 13.4 μg-at. P-PO₄³⁻ l⁻¹; nitrate 10.4 μg-at. N-NO₃⁻ l⁻¹; nitrite 2.1 μg-at. N-NO₂⁻ l⁻¹ and chlorophyll-α 14.3 mg m⁻³. Based on our calculations, it has been concluded that the proposed system is effective, thus within a flushing cycle all of the above mentioned parameters will become within the acceptable values of the Shatt al-Arab water quality. Moreover, this system has no appreciable effect upon the water quality characteristics of the Shatt al-Arab River due to the fact that it discharges a high volume of water annually. However, It has been recommended to dredge the deposited sludge to a minimum depth of 50 cm.     

Acute toxicity of crude and dispersed oil to Octopus pallidus (Hoyle, 1885) hatchlings

There is an increasing risk of a major oil spill in Australian waters over the next 20 years but there have been few studies on the impact of oil spills, and subsequent remedial action, on native Australian fauna. Octopus pallidus is a native Australian octopus species found in south-eastern Australia. The aim of the experiment was to investigate the effects of acute exposure to crude and dispersed crude oil and 4-chlorophenol (a reference toxicant) on recently hatched O. pallidus by calculating the 48-h LC50. Water-accommodated fraction (WAF) of Bass Strait crude oil was prepared using a ratio of one part crude oil to nine parts filtered seawater and mixing for 23 h. Dispersed-WAF was prepared using a ratio of one part Corexit 9527 to 50 parts crude oil and an oil to water ratio of one to nine and mixing for 23 h. Mean (SE) 48 h LC50 values were 0.39 (0.04), 1.83 (0.64) and 0.89 (0.08) ppm for WAF, dispersed-WAF and 4 chlorophenol, respectively. These results demonstrate that addition of the chemical dispersant Corexit 9527 to WAF does not increase the toxicity of WAF to O. pallidus hatchlings.     

Construction and utilization of rock caverns in Singapore Part D: Two proposed cavern schemes

This paper considers cavern schemes for crude oil storage and warehouse-shelter facilities. The crude oil storage scheme, which consists of five caverns, provides a net storage capacity for crude oil of 800,000 m³; the total cost for the facility, including civil construction, mechanical and electrical instrumentation, is in the order of S$80–100 million. The warehouse-shelter scheme consists of five storage caverns with combined storage capacity of 210,000 m³, and a defence shelter with capacity of 2000 persons. The cost for the warehouse-shelter scheme is S$66 million, including all mechanical and electrical utilities, systems for ventilation, fire prevention and smoke extraction, and pump installations for discharging leakage water.     

Determination of nitrate ion in waste and treated waters by laser raman spectrometry

The determination of NO₃⁻ ion in pure and natural waters by laser Raman spectrometry has been examined. It is shown that in the case of pure water samples, the detection limit of NO₃⁻ is about 2 ppm, and that the analytical curve in 6–100 ppm can be fitted well enough to a straight line. In the case of waste and treated waters, the detection limit becomes about an order of magnitude higher than that in the case of pure water because of the strong luminescence of water samples. In this study, the reduction of this background has been pursued by various methods, and it is demonstrated that the addition of potassium iodide as a quencher makes the background markedly smaller. By this procedure, the sensitivity becomes comparable to that in the case of pure water samples. It is proved that under such circumstances, laser Raman spectrometry can be applied satisfactorily enough to the analysis of NO₃⁻ in actual waste and treated waters.     

Estimation of inorganic and organic pollutants in Kuwait groundwaters used in irrigation: a study after the gulf war

Kuwait was invaded on August 2, 1990. Around 700 oil wells were destroyed during the Iraqi aggression. Many septic tanks and drainage systems were destroyed. One of the major concerns following the Iraqi invasion is the possibility of ground water contamination. A study of underground water in Kuwait during the period June to December 1993 with regard to irrigation is presented. Water from four different aquifers were analysed for organics and inorganics. A hydrochemical study of these waters indicated that water from (Su‐123), (E‐15) and (PW‐1OL) are suitable for irrigation. The boron concentration in these plants is less than 1 ppm, making it suitable for sensitive and semisensitive crops. Nickel and vanadium are the major inorganics found in crude oil. No appreciable rise in the concentration of these elements was observed. The concentration of polyaromatic hydrocarbons (PAH) and total organic carbon (TOC) is found to vary from 0.01 to 0.07 ppm and 0.21 to 0.9 ppm. PAH is found to vary with location while TOC is found to vary with time.     

An in situ method to compare the potential for periphyton productivity of lotic habitats

A simple field method for measuring relative net productivity in flowing waters is described. To assess its sensitivity and practicality, the eutrophication potential of a tertiary sewage treatment plant effluent was assayed on the Fort River of Amherst, Massachusetts. Two sets of three 10 m lexan tubes (1.25 cm i.d.) were anchored to the river bed 100 m upstream and downstream from the sewage plant outfall. Data collection began following a 2 week colonization period for the periphyton community. Substrate primary productivity (mg O₂ min⁻¹) was determined by subtracting inflow dissolved oxygen concentrations from these levels at the discharge ends of each tube and multiplying the difference by the flow rate. The downstream tubes demonstrated an enhanced response at a 0.01 level of significance to an increment of 0.005 and 0.1 ppm of phosphorous and nitrogen respectively. Data analysis revealed a highly significant regression of the net productivity on stream flow which was adjusted for by an analysis of covariance. The productivity of the downstream station was distinctly higher (0.4522 mg O₂ min⁻¹) then the value of the upstream station (0.2584 mg O₂ min⁻¹). The protocol thus affords a biological summation of the sewage effluent through comparison with the control station replicates.     

The fate of chlorine and chloramines in cooling towers Henry's law constants for flashoff

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.     

The fate of oil and oil—dispersant mixtures in freshwater ponds

The fate, distribution and composition of oil and oil—dispersant mixtures were studied in a series of five, lined, inground ponds containing sandy gravel sediment and mesotrophic water. Norman Wells crude oil and Corexit 9527 were added at nominal concentrations of 100 and 20 ppm, respectively, to two of the ponds, and the crude oil alone was added at 100 ppm to a third pond. The water surface, water column, the sediment, pond liner and attached biota were systematically sampled for a year. While only about 2% of the oil remained in the water column of the pond with no dispersant addition, in the pond with the dispersant, about 10% of the oil persisted in the water for several weeks. Most of the oil initially dispersed in the water returned to the water surface, then eventually sank to the sediment. Thinner surface films showed a higher dispersant content than the thicker slicks, and the thinner films had higher infrared carbonyl absorption. Final distribution calculations revealed that about 45% of the oil had degraded in the oil—dispersant-treated ponds during the one year study, while only 23% could not be accounted for in the oil pond. Changes in the oil composition during the experiment were similar in all ponds, with no evidence to suggest that the dispersant affected oil composition in any special manner.     

Control of activated sludge filamentous bulking—III. Effect of sludge loading

Previous experiments have indicated a possibility of controlling the filamentous bulking of activated sludge by cultivating a mixed culture in a system with the plug flow pattern or in a system with a selector. These experiments, however, were conducted at approximately constant sludge load [0·3–0·4 kg BOD₅(kg MLVSS day)⁻¹] and sludge age (4·5–5·0 days) so that the results obtained had only a limited validity. Further experiments were, therefore, carried out in order to find if the previous findings hold also for activated sludge systems with high sludge loads and low sludge ages.The experiments were conducted on four activated sludge systems with different flow patterns: two of them as complete-mixing reactors and the other two as reactors with the plug flow pattern, having dispersion numbers of 0·08 and 0·07. A mixture of starch and peptone was used as the substrate. All systems were operated at sludge ages 2 and 3 days and at sludge loads from 0·5 to 2·3 kg BOD₅(kg MLVSS day)⁻¹.It was found that at sludge loads above 0·5 kg kg⁻¹ day⁻¹ mixed cultures developed in the systems with the plug flow pattern possessed high values of the SVI and contained high portions of filamentous microorganisms. This was found in spite of sufficiently high concentration gradients of the substrate along these systems. It means that plug flow and, consequently, the concentration gradient of the substrate along the activated sludge system may not be the only factor in controlling the selection of microorganisms in a mixed culture. An additional factor must exert an influence on the population dynamics and selection of microorganisms in mixed cultures at high sludge loads and low sludge ages.The experiments have confirmed findings of others that values of the SVI depend on the sludge load. However, different trends of dependence were observed in the systems with different flow patterns. While in the complete-mixing systems the SVI decreased with increasing sludge loading in the systems with the plug flow pattern it increased.A greater phosphorus demand was observed in plug flow systems than in those with complete mixing.     

The quantitative and qualitative analysis of the water soluble fraction of jet fuels

This paper describes two methods of analyzing the water soluble fraction (WSF) of hydrocarbon fuels. This fraction is the most ubiquitous form of fuels spilled or leaked to the aquatic environment and bioassays have emphasized exposure of the WSF to test species. One method of analysis involves organic solvent extraction, and the other method utilizes purge-and-trap of volatile components. The suitability of these methods is evaluated for the quantitative and qualitative analysis of jet fuels used in commercial and military aircraft.     

Biodegradation of 3,4,4′-trichlorocarbanilide, TCC, in sewage and activated sludge

As part of the studies to elucidate the environmental consequences from bacteriostat usage the extent of biodegradation of 3,4,4′-trichlorocarbanilide, TCC^®, in sewage systems was examined. TCC samples uniformly labeled in either the p-chloroaniline ring (¹⁴C PCA TCC) or the dichloroaniline ring (¹⁴C DCA-TCC) were monitored in activated sludge systems by measurements of ¹⁴CO₂ evolution. As was expected, the p-chloroaniline (PCA) ring of TCC was more rapidly degraded than the dichloroaniline (DCA) ring. In a continuous flow activated sludge system (10 h retention time, 200 μg1⁻¹ TCC) acclimation to primary biodegradation was readily gained. ¹⁴CO₂ evolution from ¹⁴C PCA TCC was consistent with complete metabolism of the PCA ring while that from ¹⁴C-PCA-TCC indicated about 50% biodegradation of the DCA ring. Analysis of effluents from continuous flow activated sludge units established that TCC undergoes primary biodegradation to its chloroaniline components which are in turn biodegraded.     

Effects of oil dispersants and oil emulsions on marine animals

The toxicities to marine animals of nine oil dispersants, three oil emulsions with Corexit and of a dispersion of Oman crude oil, have been studied in continuous flow aquarium systems at 96-h exposures followed by a recovery period in clean sea-water. New types of dispersants were found to be less toxic than older types and oil emulsions more toxic than dispersants alone or crude oil alone. Fishes and bivalves were found most sensitive. Crustaceans were the most resistant to dispersants but very susceptible to oil emulsions. The tolerance of different species was found to be related to their mode of life, more active species being more susceptible. Delayed mortality of bivalves increased their susceptibility if the recovery period was included. Effects on locomotory behaviour of fishes and crustaceans, breathing rate of fish, valve-closure of bivalves and byssal thread formation of common mussels have been demonstrated for both dispersants and oil emulsions. The general sequence of such effects was: increased activity; successively impaired activity; immobilization; and death. Recovery is good for fish and crustaceans but poor for bivalves due to the delayed effects. Ecological consequences of dispersants and oil pollution in the marine environment are discussed.     

Identification and Adaptive Control for Open Channel Water Flow Systems

Abstract: Despite the continuous advances in the control design for water flow systems such as irrigation and sewer systems, the design and deployment of efficient water flow control systems requires a careful and efficient fine‐tuning of their parameters prior and during the actual system operation. In the majority of water flow control applications, the controller design is based on simplified models (e.g., linear models assuming a fixed time‐delay) for the water flow dynamics and as a result the initial controller design calls for a major fine‐tuning at the initial deployment of the control system; moreover, the frequent changes in water management commands/needs as well as the severe exogenous disturbances call for a continuous update of the controller parameters. Conventional controller tuning approaches cannot be used for the efficient tuning of the controller parameters in water flow control systems, mainly due to the highly nonlinear dependence of the time‐delay with respect to the water flow. In this article, we first introduce and analyze both by means of mathematical analysis and simulation experiments, a computationally simple and efficient methodology for the identification of water flow system dynamics as a State‐dependent Delay Difference Equation (sdDDE) model. The main advantage of this methodology is that it can explicitly identify the nonlinear relationship between the water flow system states and the system time‐delay. Then, we show that such an sdDDE identification scheme can be used for the efficient adaptive tuning of a general class of water flow control systems. More precisely, by exploiting the knowledge—obtained using the sdDDE identification scheme—regarding the nonlinear characteristics of the time‐delay, we come up with a convergent adaptive control scheme, which is able to quickly track rapid changes in setpoint commands and efficiently attenuate severe exogenous disturbances. Simulation results demonstrate that the proposed scheme out‐performs significantly existing well fine‐tuned linear and nonlinear control schemes.