Nitrification process in a packed bed reactor with a chemically active bed

A laboratory scale submerged filter filled with crushed marble was used for the nitrification process investigation. The results obtained showed that the alkaline reactor filling material react with the hydrogen ions released during the process course which enables reactor exploitation without any pH value or alkalinity control.     

A model study of ozone-sparged vessels for the removal of organics from water

Ozone-sparged vessels for the oxidation of a model organic compound, methanol, was studied. The parameters under study included superficial gas velocity, the gas phase ozone concentration, the rate of ozonation of methanol and its oxidative products, the residence time, etc. The scale-up method based on the mathematical model developed in this study accurately predicts the superficial gas velocity and the gas phase ozone concentration required for two larger geometrically similar vessels to achieve the same level of total organic carbon removal obtained in a small vessel.     

The effects of pH and suspended solids in the removal of organics from waters and wastewaters by the activated carbon adsorption process

The effects of pH, inorganic suspended solids and organic suspended solids on the adsorption of organics by activated carbon were investigated using sewage effluents and selected organic compounds of varying size, structure, molecular weight and properties in model solutions. It was found that suspended solids, and in particular organic suspended solids, could interfere with the adsorption process, both in terms of adsorption capacity and adsorption rate; the effect of the solids diminished as the size of the adsorbate increased. The effect of pH variation became more significant as the acidity or basicity of the adsorbate in solution increased. Adsorption of organics from biologically treated sewage effluents was somewhat more effective in the acid and alkaline pH regions than in the neutral pH region.     

The removal of chromium(VI) from dilute aqueous solution by activated carbon

The removal of chromium(VI) by activated carbon, filtrasorb 400, is brought by two major interfacial reactions: adsorption and reduction. Chemical factors such as pH and total Cr(VI) that affect the magnitude of Cr(VI) adsorption were investigated. The adsorption of Cr(VI) exhibits a peak value at pH 5–6. The particle size of carbon and the presence of cyanide species do not change the magnitude of chromium removal. The reduced Cr(VI), e.g. Cr(III) is less adsorbable than Cr(VI).The free energy of specific chemical interaction, ΔG^chem was computed by the Gouy-Chapman-Stern-Grahame model. The average values of ΔG^chem are −5.57 RT and −5.81RT, respectively, for Cr(VI) and CN. These values are significant enough to influence the overall magnitude of Cr(VI) and CN adsorption. Results also indicate that HCrO⁻₄ and Cr₂O²⁻₇ are the major Cr(VI) species involved in surface association.     

Method of selective dissolution for characterization of particulate forms of Radium and Barium in natural and waste waters

A new method is proposed for characterization of particulate forms of radium and barium in natural and waste waters. Particulate solids suspended in 1–3 l. of water are first concentrated by membrane filtration or by centrifugation to 20–50 ml of a concentrate which is then filtered through a small-size membrane filter. The solids retained by the filter are successively washed with three selective solvents releasing “loosely bound”, “acid soluble” and “barium sulfate” forms of radium and barium. Compositions and volumes of the selective solvents have been chosen using model experiments and partially checked by analysis of natural samples. Radium and barium “in crystalline detritus” remain on the filter and are determined after an acid digestion of the filter. The principal criteria and selectivity of the method are discussed.     

Total mercury and methyl mercury levels in British estuarine and marine sediments

Total mercury and methyl mercury levels in some British estuarine and marine sediments are presented. Results are compared for estuaries of the Rivers Clyde and Mersey. These, together with data from Irish Sea sediments, are discussed in comparison with other literature values. The use of the methyl mercury to total mercury ratio is examined.     

Environmental occurrence and mass spectral identification of ethylene glycol derivatives

Ethylene glycol derivatives are commonly used, commercial products. Surprisingly, there have been very few reported incidences of environmental contamination caused by these compounds even though their commercial production is quite high. Since few mass spectra of these chemicals are in reference collections, their proper identification could have been simply overlooked. Mass spectral characteristics of these compounds are outlined, along with methods for their exact structural determination.     

Air pollution, hygiene and health of Danish schoolchildren.

A comprehensive investigation forming part of a joint European study under the auspices of "WHO Long-Term Air Pollution Programme" uses 7-13 year old schoolchildren as the target group. The study has included social, housing, hygienic and epidemic factors as well as family smoking habits. The results indicate that, at exposure to low levels of air pollution, these factors dominate as causes for the impairment of health especially that of respiratory health.     

Measurements of alkyllead compounds in the gas and aerosol phase in urban and rural atmospheres

Alkyllead compounds in the gas and aerosol phase were determined simultaneously in urban and rural atmospheres using gas chromatography--atomic absorption spectroscopy and wet chemical (iodine monochloride) methods. The difference in results between the two methods suggests the presence of vapour-phase tri- (and/or di-)alkyllead in both urban and rural air. Concentrations of 0.06-1.6 and 16-205 ng Pb m-3 were found for vapour-phase organolead compounds other than tetraalkyllead in rural and kerbside urban air, respectively. Tetraalkyllead and trialkyllead compounds were identified in atmospheric aerosols at both sites, but these were found to be present at concentrations less than 1.2% of the total gas-phase alkyllead.     

The effect of pH and hardness metal ions on the competitive interaction between trace metal ions and inorganic and organic complexing agents found in natural waters

The effect of pH and hardness metal ions on the interactions between trace metals and both inorganic and organic complexing agents has been studied under conditions simulating natural aquatic conditions, by employing anodic stripping voltammetric titration techniques. The complexation of Bi(III), Cd(II), Cu(II), Pb(II), and Tl(I) with the hydroxo- and carbonato-ligands found in a carbonate medium has been observed to generally increase with increasing pH. Both labile and nonlabile interactions have been observed. Nonlabile interactions are predominant at low pH and labile interactions generally increase with increasing pH. Neither calcium nor magnesium affects these interactions. The complexation of humic acids with trace metals in a carbonate medium was found to be more intense than metal ion-inorganic complexation. Both labile and nonlabile complexation was found; however, no generalizations can be made concerning the type and extent of complexation because of the individual nature of the interactions of each trace metal. Calcium was found to be more effective than magnesium in inhibiting trace metal-organic complexation. The effect of calcium is to inhibit labile complexation and is most pronounced with the cadmium-humic acid system.     

Aeration as a tool to improve water quality and reduce the growth of hydrilla

Aeration of artificial, model lake systems was studied as a tool to improve water quality and to control the growth of a nuisance aquatic weed, Hydrilla verticillata (L.F.) Royle, which has been recognized as a plant pest since the mid-1960s. Aeration decreased the growth of Hydrilla by 20% fresh weight and 18% dry weight on average after 21 days. The effect was due to the oxygenation of the water and not the mechanical effect of the bubbles, as verified by studies using pure nitrogen. Aeration also affected water quality. Inorganic carbon decreased; nitrate-nitrite-nitrogen decreased, more slowly in test systems than in control systems; dissolved oxygen increased to saturation within 24 h and pH increased 0.5–1.5 unit over the period of study. Phosphate-phosphorus concentration was unaffected. The concentrations of zinc, calcium and iron decreased as well. The effect of aeration upon Hydrilla growth appears to be correlated with a decrease of iron. After 7 days, iron concentrations decreased to less than 20 ppb. Iron toxicity is proposed as the mechanism responsible for creating a limiting condition for Hydrilla growth.     

Estimation of nitrifying biomass and kinetics in wastewater

A technique is proposed for the in situ measurement of nitrifying bacterial kinetics in mixed culture. A direct addition of known quantities of pure nitrifiers to a mixed liquor sample, along with selective inhibition of Nitrosomonas activity allows the estimation of nitrifier populations and maximum specific substrate removal rates. The method demonstrates that nitrification is zero order for substrate and first order with respect to bacterial concentration. The constant rate responses of batch kinetic tests require only a simple analysis and can be adapted to situations where nitrifier concentrations are small. Application of the technique to a carbon removal-nitrification system subjected to a variety of total Kjeldahl nitrogen loadings indicates that for a fixed carbon loading, nitrifier populations are strongly dependent on the nitrogen concentration of the feed.     

Total mercury and methyl mercury levels in British estuarine sediments—II

Results from a large-scale study of Mersey Estuary, U.K. sediments are discussed. Correlations are drawn between total mercury, methyl mercury, silt and organic carbon contents of the sediments. These correlations are compared to earlier results, and coefficients range from 0.55 to 0.94.The influence of redox potential and the sulphide content of a sediment on both the ambient level of methyl mercury and the extent of a growth and decay effect in methyl mercury levels in sediments after sampling is discussed. The results show that in an esturary (Clyde, U.K.) where sulphide levels vary from 0 to 8.5 mg g⁻¹ there is a maximum level of methyl mercury found at approximately 5.8 mg g⁻¹ sulphide, suggesting that sulphide concentrations may control methyl mercury levels.     

Characterization of trace metal species and measurement of trace metal stability constants by electrochemical techniques

Differential pulse polarography and differential pulse anodic stripping voltammetry were used to determine copper, lead, cadmium and zinc complexes of relevance to environmental conditions. The dependency of peak current on pH and alkalinity was interpreted in terms of the variation in the metal species present. Stability constants of copper and lead complexes with carbonate were determined from the magnitude of the shift of peak potential using the method of Lingane. Inclusion of the transfer coefficient, calculated from the peak half-width for electrochemically irreversible systems, was used to determine the stability constant. By using both electroanalytical techniques, the investigator validates the correctness of his results without needing to rely on prior determinations of the stability constant for verification.     

Design and operational charts for complete mixing activated sludge systems

This paper provides charts enabling the derivation of design and operational procedures for an activated sludge waste water treatment system including the final settler. These charts are based on a mathematical model including Monod relationships describing the microbial growth and the substrate removal in the aerator, while sedimentation in the final settler is assumed to follow the limiting flux theory. Charts represent the minimum required settler area, insuring that given effluent standards will be met, as a function of either the hydraulic retention time or the recycle rate. Most design and operational characteristics of the activated sludge system can be read directly on the charts, while a simple equation is provided for the sludge wasting rate.Operational procedures under constant or variable inflow conditions are first derived from the charts. It is concluded that operational policies including a constant recycle sludge concentration are especially attractive in response to various types of influent variations. Such policies allow one to maintain either the effluent substrate concentration or the recycle flow rate at the same level in most situations. Furthermore, the required settler area remains reasonably small. Large aerators provide considerable operational flexibility and appear to be required when hydraulic overloads are expected.The charts allow one to design the activated sludge system in such a way that expected overload conditions can be overcome. Least-cost design is briefly studied through simplified cost functions. This allows derivation of the best compromise between sufficient operational flexibility and least-cost design, leading to the “optimal overdesign” of the system.Parameter variability has a significant influence on the charts. Hence, correct determination of the model parameters is required before calibrating and using the charts.     

Chronic and reproduction studies in rats exposed to gasifier ash leachates

Ash from the coal gasification process contains a broad spectrum of elements which through leaching (gasifier ash leachates) may enter into the environment. The health effect of such leachates i.e. complex mixtures of inorganic elements is insufficiently known. We investigated the effect of gasifier ash leachates in a chronic-(9-month) and in a three-generation reproduction study. The leachates were prepared weekly by water extraction of ash from a Lurgi coal gasification plant in Yugoslavia, and given to experimental animals instead of drinking water. In the chronic experiment exposed animals showed no changes in mortality rate, haematological findings, concentration of Fe, Zn, Mn in kidneys, liver, testicles and femur, as well as in femur composition and morphometry, gross pathology and organ histology. In the reproduction study the number of pregnancies, weight and number of newborns, and concentration of Fe, Zn, Mn in carcasses of sucklings were the same in control and experimental animals.     

Dynamic modelling and control simulation of a biological wastewater treatment process

A dynamic control model of a two-stage biological wastewater treatment reactor is developed. The sludge recycle rate is manipulated according to deviations in the exit substrate concentration (feedback control) or to changes in the entering substrate concentration and flow rate (feedforward control).Four kinetic organism growth models are investigated for their influence on the process control: a linear model and a Monod model, both with and without time delay functions.Computer simulations of the system response to sine variations in inlet flow and concentration for various control modes indicate that feedback on-off control is satisfactory for the linear growth model, whereas feedforward control is more effective for the non-linear Monod kinetics.     

An assessment of the contribution from paint flakes to the lead content of some street and household dusts

A method has been developed for estimating crudely the quantity of lead in dusts derived from paint flakes. This involves an assessment of the paint mass in the dust: gravimetrically in the coarse fractions, and by microscopic measurement in the fine fractions. Some street and house dust samples were examined. The street dusts contained up to 20% of lead from paint, and the house dusts up to 15%. However, it was the least lead-polluted dusts that contained the highest proportions of lead from paint. In the samples examined the paint flakes contained only low to moderate amounts of lead (0.07-4.21% w/w) and in the case of high lead paints the contribution from this source could be considerably greater.     

Algae as a chemical speciation monitor—I A comparison of algal growth and computer calculated speciation

An alga, Selenastrum capricornutum, was used to monitor the relationship between metal speciation and toxicity. The principal effect of copper on the algae was a decrease in growth rate constant as the total concentration of copper increased. A 24-h growth experiment was used to monitor the effect of metal on the algae. Chlorophyll measurements at 17 and 23 h were used to estimate the growth rate constant. A plot of growth rate constant versus the speciation variable (total copper, pCu, pCuL, etc.) was used to determine the toxic species and the algicidal concentrations. Solutions containing EDTA, TRIEN, NTA, HIMDA and bicine became algicidal at pCu of 8.0 whereas solutions containing ethylenediamine and citric acid became algicidal at pCu 8.65 and 9.5, respectively. A comparison of growth and calculated speciation suggests that Cu en⁺² and Cu CIT OH⁻² were toxic species.     

The distribution and origin of mutagens in airborne particulates, detected by the salmonella/microsome assay in relation to levels of lead, vanadium and PAH

At three stations in central Copenhagen, Denmark, samples of particulate matter were collected simultaneously with different contributions from automobile exhaust products. Samples were obtained at street level, 22 m above street level and within a hospital zone; 32 samples were analysed for levels of polycyclic aromatic hydrocarbons (PAH) and elements, as well as for mutagenicity towards S. typhimurium TA1538. Two classes of mutagens were quantified: a non-polar extract rich in PAH and, other promutagens, and a polar extract containing direct acting mutagens (not requiring microsomal activation). Covariances between lead and mutagenicity, and the varying distribution of the polar and non-polar mutagens at the stations, indicate that at all stations the mutagenicity of the non-polar extract is dominated by automobile exhaust products. The polar extract is relatively less influenced by primary traffic emissions; a considerable part of the activity of this extract is attributed to secondary emissions, transformed by atmospheric reactions, and primary emissions from stationary sources.