The removal of colour from effluent using various adsorbents—IV. Silica: Equilibria and column studies

The rate of adsorption of Astrazone Blue, a basic dye, on Sorbsil Silica has been studied. The parameters studied include particle size, initial dye concentration, agitation and dye solution temperature. The rate controlling step is mainly intraparticle diffusion, although a small boundary layer resistance is experienced. The activation energy for the adsorption of Astrazone Blue on silica is 13.2 ± 0.6 kJ kg⁻¹. The diffusion coefficients vary from 9 × 10⁻⁹ cm² s⁻¹ at 20°C to 10 × 10⁻⁸ cm² s⁻¹ at 82°C.     

Septage disposal in waste recycling ponds

Experiments were carried out to investigate the feasibility of septic tank sludge (septage) disposal into pilot-scale waste recycling ponds for the production of algae and fish. A septage loading of 100 kg COD ha⁻¹ day⁻¹ to four 4-m² single-stage ponds resulted in the production of algal biomass and dissolved oxygen in the pond water, suitable for Tilapia growth. Some microbiological investigations of this waste recycling scheme were undertaken using ten earth ponds (each with the dimensions of 20 × 10 × 1.3 m: length × width × depth). It was found that the densities of coliform bacteria and bacteriophages in the pond water and sediment tended to increase with increased septage loadings and loading periods. The ponds fed with septage at the loading of 100 kg COD ha⁻¹ day⁻¹ were found to contain higher densities of these microorganisms than those of the control pond without septage feeding. The possible public health impact resulting from this practice was assessed.     

Sorption and accumulation of cadmium in the sediment of the Tama River

Cadmium contents in the water and the sediment samples collected from the Tama River and several branches were measured. Cadmium (above 0.005mgl⁻¹) was detected in only four of the water samples, while the sediment samples showed cadmium content of 1.0–9.8 μg g⁻¹ dry sediment. Cadmium concentration in the sediments of the main stream was correlated against ignition loss of the samples and it was found that 1 g of ignition loss (organic matter) corresponded to 35 μg of cadmium.The batch adsorption experiment in the laboratory using an aqueous solution of cadmium for 14 sediment samples with a higher concentration of cadmium indicated that the amount adsorbed by the sediment is highly dependent on the ignition loss. The amount adsorbed on unit mass of ignition loss q_IL could be correlated by a Freundlich-type equilibrium relation as where C is the equilibrium concentration in the aqueous phase ranging between 7 × 10⁻³ and 10 mg l⁻¹, while k_IL and n are equilibrium constants.The adsorption rate measurement showed that the intraparticle diffusion coefficient of cadmium in the sediment was about 1.1 × 10⁻⁶ cm²s⁻¹, which is of a reasonable order of magnitude assuming the pore diffusion mechanism inside the particle.The results suggest that suspended solid particles of high organic content in flowing water contribute significantly to the transport of cadmium along the river.     

Heavy metals in animals of Lake Balaton

Hg, Cd, Cu, Pb, Zn, Fe and Mn concentrations were measured in Chironomidae larvae, Crustacea plankton, as well as in various organs of mussels and fishes collected from the open water area of Lake Balaton. The values were comparatively low. However, there were significant differences in the metal concentrations of species and tissue.Most Cd was found in the gill of Unio pictorum L., most Pb, Zn and Mn in the gill of Anodonta cygnea L., most Cu in Crustacea plankton and in the liver of Abramis brama L., and most Hg and Fe in Chironomidae larvae. Low concentrations occurred in fishes, the lowest in the flesh of Stizostedion lucioperca L.Accumulation of metals in organs as compared with their concentration in the lake water was in the range of 3.4 × 10²−2.6 × 10³ for Hg; 7.0 × 10²−6.8 × 10³ for Cd; 3.3 × 10²−9.7 × 10³ for Cu; 6.9 × 10²−8.1 × 10³ for Zn; 1.5 × 10³−2.4 × 10⁴ for Pb; 3.5 × 10²−3.1 × 10⁴ for Fe; and 5.0 × 10¹−3.5 × 10⁵ for Mn.     

Kinetics of attached microbial growth in a continuous stirred tank reactor

Kinetics of attached heterotrophic microbial growth was investigated experimentally using a continuous stirred tank reactor (121) for stream self-purification studies. Glucose was fed as the only source of carbon to the reactor in low concentration (4.5 27. mg-glucose l⁻¹).Substrate consumption rate was dependent not on substrate concentration but on substrate loading. Oxygen consumption rate had a linear relationship with substrate consumption rate. The respiration rate of attached microbial population was 9 mgO₂g⁻¹ cell per hour.At steady state, attached growth rate was independent of substrate consumption rate because the attached growth was presumably suppressed by the limitation on attached surface area. Growth yield for substrate decreased with increasing substrate loading.     

Field studies on coliphages and coliforms as indicators of airborne animal viral contamination from wastewater treatment facilities

The occurrence of animal viruses in the aerosol emissions of wastewater treatment facilities was evaluated by direct assay and by the use of coliforms and coliphages as indicator organisms. Coliforms and coliphages were compared and evaluated with regard to their suitability as indicators of airborne animal viral contamination from wastewater treatment facilities. Two plants, one with treatment by activated sludge and the other by trickling filtration, were studied. Field air sampling procedures used large-volume air samplers, with recirculation devices, and Andersen samplers. Airborne viruses were enumerated by a most probable number (MPN) procedure. Partially treated liquid sewage contained about 1.0 × 10² pfu l⁻¹ of animal viruses assayed on Buffalo Green Monkey (BGM) cells, 3.6 × 10⁵ and 5.0 × 10⁵ pfu l⁻¹ of coliphages, depending upon the E. coli host strain used for assay, and 2.0 × 10⁹ colonies l⁻¹ of coliform bacteria. No airborne animal viruses were recovered, airborne coliphage levels averaged 2.3 × 10⁻¹ and 3.0 × 10⁻¹ MPN m⁻³, coliforms from aerosol emissions were 2.1 × 10² colonies m⁻³. Ratios of coliphages to animal viruses indicate that wastewater treatment plants may be continuous sources of low level concentrations of animal virus aerosols. Evidence shows coliforms to be much less stable than coliphages in the airborne state. Coliphages may be a more acceptable indicator of airborne animal viral contamination than coliforms.     

Oxygenation par le peroxyde d'hydrogene des biomasses fixees utilisees en traitement biologique des eaux

Because of their advantages as compared to flocculated biomass processes, there is now a revival of interest in fixed biomass processes:no mishaps due to bad flocculation, particularly with filamentous organisms (bulking)compact equipment owing to the ability to obtain greater biomass concentrations (several g l⁻¹), which is impossible in flocculated biomass.In this paper, we will consider mainly bio-discs and submerged fixed bed filters. In bio-disc investigations, Hoehn and Ray's (1973), Kornegay and Andrew's (1968) now classical results showed that the bacterial film only acts on the surface, over a thickness which, at best, does not exceed 150 μm. At the same time, Bungay's (1969) very accurate measurements showed that the film active thickness coincides with the depth where the oxygen concentration in the film is higher than the critical oxygen concentration. In submerged filters, Elmaleh (1976) and Grasmick's (1978) theoretical studies permit one to define a Useful Column Height (UCH) which corresponds to the active part of the reactor and which is superposed on the height where oxygen concentration is higher than the critical oxygen concentration. In classical devices, the UCH is relatively low: approx. 0.50-1 m. In both cases, the system is provided with oxygen through an exchange between the air and the effluent to be treated, at a gas-liquid interface. This procedure limits the O₂ concentration to about 9 mg O₂ l⁻¹, at the ambient temperature. Therefore, to increase the UCH of a submerged reactor or the active thickness of a bio-disc film by increasing the oxygen penetrating depth, the oxygen partial pressure in the gas phase should be increased by either using pure oxygen or increasing total gas phase pressure.These two methods are somewhat difficult to use and we prefer to use another method: bringing dissolved oxygen directly into the liquid phase without the exchange at the gas-liquid interface. This is feasible by using an oxygen liberating labile chemical reagent i.e. hydrogen peroxide. We consider two types of fixed biomasses: the bio-discs and the submerged filters.Bio-discs. The apparatus used is shown in Fig. 1. The utilization of H₂O₂ resulted in a very sharp increase in the substrate removal efficiency. It is observed that the substrate removal efficiency (Figs 5 and 6) and the reduced pollution flux (Figs 4 and 7) show a maximum when these are plotted as a function of the ratio: equivalent quantity of O₂ given by H₂O₂/O₂ demanded by the effluent and as a function of dissolved oxygen in the liquid phase. Moreover, these curves suggest that oxygen acts as an inhibitor and different attempts at modeling, based on standard models of inhibiting effects, lead to the exponential model giving the lowest deviation (Fig. 8).Submerged packed reactors. The apparatus used is shown in Fig. 3. This unit is fed by urban effluents and the oxygenation in the reactor is carried out by using diluted H₂O₂ (0.5-1.5 N).     

Electrodeposition of six heavy metals on reticulated vitreous carbon electrode

Six heavy metals, copper, cadmium, chromium, lead, uranium and zinc were deposited on cathodes made of a newly developed form of carbon, Reticulated Vitreous Carbon, in a laboratory scale electrochemical reactor. Different metals varied in the extent of their removal with copper depositing 100% at a flow rate of 0.24 cm min⁻¹ in a single pass while it would require a maximum of 20 passes for 100% chromium deposition at a flow rate of 1.8 cm min⁻¹, initial concentrations for both metals being 50 μmol 1⁻¹.Experiments conducted using 0.5 × 10⁻³ M CuSO₄ in 0.5 M Na₂SO₄ supporting electrolyte resulted in a mass transfer coefficient of the order of 10⁻³ cm s⁻¹ and a current efficiency of 64% for the electrodeposition of copper at a cell voltage of 4.0V. Because of very high porosity, 97%, high specific surface area, up to 66 cm² cm⁻³ for RVC grade 100, and useful electrochemical characteristics, RVC can be advantageously used as electrode material for heavy metal removal from dilute industrial effluents.     

Effect of temperature and dissolved oxygen on biodegradation of nitrilotriacetate

The effect of temperature and dissolved oxygen on the rate of biodegradation of nitrilotriacetate (NTA) was examined in water samples collected from the Rur River. Biodegradation of NTA was first order with respect to NTA concentration over a concentration range of 50–1000 μg l⁻¹. First order rate constants showed a typical temperature dependency (temperature coefficient, Q₁₀ = 2) and biodegradation of NTA was observed over a temperature range of 2–24°C. The effect of temperature on the rate of NTA biodegradation was described by the Arrhenius equation, with calculated activation energies in the range reported for ordinary enzyme reactions. Biodegradation of NTA was also observed at low dissolved oxygen concentrations (0.3 mg l⁻¹), although at reduced rates compared to high oxygen concentrations (13 mg l⁻¹). Biodegradation of NTA was oxygen-dependent, suggesting an obligate oxygen requirement for the initial steps in NTA metabolism by natural microbial communities in surface waters. In general, our results indicate that NTA biodegradation will occur in natural waters under conditions of low temperature and low dissolved oxygen and also at low NTA concentrations.     

New light on mechanism of air-water oxygen exchange in quiescent systems

Experiments employing novel apparatus which permits measurement of the rate of oxygen transport across liquid strata indicate that the diffusivity of oxygen through water immediately adjacent to the free air-water interface of a quiescent system is the same as its molecular diffusivity in bulk water remote from an interface. A molecular diffusivity of 2.07 × 10⁻⁵cm²s⁻¹ is reported. Water strata of thickness ranging from 0.3 to 3.6 mm are shown to be effectively isotropic with respect to their resistance to oxygen transport. Thicker strata were found to exhibit a reduced but significant resistance consistent with the spontaneous development of a mechanically disturbed bulk zone between the boundary layers.     

The synthesis of the dissimilatory nitrate reductase under aerobic conditions in a number of denitrifying bacteria, isolated from activated sludge and drinking water

A number of denitrifying bacteria were isolated from activated sludge and drinking water. These bacteria were tested for the synthesis of the dissimilatory nitrate reductase under aerobic conditions (dissolved oxygen concentration above 4 mg · l⁻¹). The synthesis of this enzyme varied from total repression by oxygen in some bacteria, especially those isolated from drinking water, until a nearly non oxygen-repressed synthesis in other bacteria (strains 15 and N4). The effect of the dissolved oxygen concentration during growth of the bacteria on the synthesis of the dissimilatory nitrate reductase in cells of strain 15 was studied more extensively. A considerable repression of the enzyme synthesis was obtained when the dissolved oxygen concentration was relatively high (approx 15 mg·l⁻¹). Addition of chlorate to the growth medium of strain 15 (using NH⁺₄-N as nitrogen source) also resulted in a serious repression of the nitrate reductase synthesis during aerobic growth (dissolved oxygen above 4 mg·l⁻¹). The dissimilatory nitrate reductase of aerobically grown cells of strains 15 and N4 was found to be mainly localized in the membrane fraction.     

Bromide concentration in Swedish precipitation, surface and ground waters

The occurrence of bromide in precipitation, surface and ground waters in Sweden has been investigated (300 samples). The concentration of bromide in precipitation is 0.05–0.15 μM in the south and <0.05 μM in the north of Sweden. The concentrations of bromide and chloride are well correlated. For river water the same areal distribution pattern as for precipitation is found, but the concentrations are 2–4 times higher. The molar ratio Br/Cl is 1 × 10⁻³ which is lower than that for sea water (1.54 × 10⁻³) and, most likely, also lower than for precipitation. A detailed study of Lake Mälaren has been made. The north-eastern feeder streams, passing an area of post-glacial clay, showed unusually high bromide concentrations (0.3–3 μM) and Br/Cl quotients (2 × 10⁻³-8 × 10⁻³). No correlation between the concentrations of bromide and chloride was found. Rough calculations indicate that fertilizers and chemicals added to the fields could only contribute a minor fraction of the bromide found. Analysis of 18 ground water samples indicated increased bromide levels as compared to surface waters.     

Effect of copper on nitrification in activated sludge

The concentration of free copper in activated sludge with copper added is strongly influenced by pH. For example, at pH 6.5 with 9.13 × 10⁻⁵ mol Cu l⁻¹, the free copper concentration is 4.0 × 10⁻⁷ mol l⁻¹ (pCu = 6.4) and at pH 8.4 this concentration is 10⁻⁸ mol l⁻¹ (pCu = 8.0). In both cases the activated sludge concentration is 0.7 g MLSS l⁻¹. The free copper concentration is also affected by the concentration of mixed liquor suspended solids (MLSS).In batch experiments with constant pH, the effect of copper on the nitrification rate was not regulated by total copper concentration but by copper/sludge ratio or by free copper concentrations. Experiments at different pH showed a linear correlation between nitrification capacity and free copper concentration, suggesting that the pH effect on nitrification below 8.3 is in fact a copper effect.Activated sludge with copper did not become acclimatized to the copper in a period of three days. Addition of nitrilotriacetic acid (NTA) within one day did cancel the copper inhibition.The results were compared with the effect of copper on acetate removal by heterotrophic micro-organisms. The nitrifiers proved to be no more susceptible to copper than heterotrophic micro-organisms.     

Factors affecting the denitrification rate in two water-sediment systems

Effects of temperature, oxygen and nitrate concentrations of the overlying water, and the thickness of the sediment layer on the rate of denitrification in the sediment were investigated in two water-sediment systems, A and B. At 4°C, denitrification started after a prolonged lag period in contrast to nitrification which did not occur significantly. At 15°C, and particularly at 25°C, both processes proceeded readily. The disappearance of NO₂⁻ - N from the overlying water was more rapidly than that of NO₃⁻ - N.The denitrification rate was slightly reduced by increasing the dissolved oxygen concentration in the overlying water from 0 to approximately 2 mgl⁻¹. A further rise of the dissolved oxygen concentration had no further decreasing effect on the denitrification rate.The denitrification rate in sediment was dependent on the nitrate concentration in the overlying water approximating first order kinetics at lower concentrations, gradually becoming independent of the nitrate concentration at higher nitrate contents (zero order kinetics).When starting with a nitrate-nitrogen concentration of 25.2 mgl⁻¹, a sediment layer of 7 mm with A and 14 mm with B was roughly found to be involved in denitrification.Denitrification rates found in the present laboratory experiments were supposed to be considerably lower than those occurring under natural conditions as additional mechanisms for the transport of nitrate into sediments occurred in natural environments.     

Determination of ozone in water by the indigo method

The concentration of aqueous ozone can best be determined by the decolorization of indigo trisulfonate (600 nm, pH below 4) whenever the ozone cannot be measured directly by its u.v. absorption. The method is stoichiometric and extremely fast. The change of absorbance vs ozone added is −2.0 ± 0.1 × 10⁴ M⁻¹ cm⁻¹ and is independent of the concentration of aqueous ozone in the range 0.005–30 mg 1⁻¹. The precision of the analysis is 2% or 3 μg 1⁻¹ for low concentrations if a spectrophotometer or a good filter instrument is used. Visual methods can be used to measure 0.01 mgl⁻¹ ozone. Secondary oxidants produced by ozone in natural water, including hydrogen peroxide or chlorite, do not interfere; chlorine can be masked. The reagent solution is stable for 3 months. The method is recommended for kinetic measurements, for studies of ozonation processes and for visual field methods.     

Preliminary studies on the leaching of some trace metals from kitchen faucets

Preliminary studies were carried out on the leaching of copper, zinc, chromium, cadmium and lead from eight kitchen faucets by samples of raw, filtered and distributed Ottawa water, a sample of well water and deionized water containing 2 mg l⁻¹ aqueous fulvic acid. Leaching was effected by allowing the test solutions to stand in the inverted faucets for two successive 24-h periods. Concentrations of the metals found in the leachates were copper: first leaching, 0.12–28.0 mg l⁻¹, second leaching, 0.08-3.54 mg l⁻¹; zinc: first leaching, 0.13-10.25 mg l⁻¹, second leaching, 0.06-2.85 mg l⁻¹; chromium: first leaching, < 1.0 × 10⁻³ − 0.395 mg l⁻¹, second leaching, < 1.0 × 10⁻³−0.032 mg l⁻¹; cadmium: first leaching, < 0.05 × 10⁻³−0.01 mg l⁻¹, second leaching, < 0.05 × 10⁻³−4 × 10⁻³ mg l⁻¹; and lead: first leaching, < 0.2−110.0 mg l⁻¹, second leaching, < 0.2−82.0 mg l⁻¹. The faucets containing lead-soldered copper joints released high concentrations of lead, particularly in the case of leaching with the aqueous fulvic acid solution. Under the conditions of the present investigations it is indicated that in some cases the concentrations of metals leached could lead to intakes in excess of the maximum permissible limits for these metals. However, further investigations will be required to determine the possible contribution of these faucets to metal intake under normal usage.     

A study of the copper-complexing compounds released by some species of cyanobacteria

The production of copper-complexing extracellular material by cyanobacteria was studied by using ion specific electrodes. The species studied were Plectonema boryanum and Anabaena cylindrica. The values of the conditional stability constants for the copper complexes (K′), for the two species at pH 6.60 (±0.05) were, respectively 2.8 (±0.8) × 10⁶ and 5.9 (±2.0) × 10⁷. A strain of P. boryanum that was made tolerant to a concentration of 1 × 10⁻⁶M copper produced greater amounts of copper-complexing products than the normal strain although the K′ value for the copper complexes was the same. When stressed with copper, P. boryanum and A. cylindrica produced more complexing material than under the usual growth conditions.     

On computing normal reliabilities

No expression currently used for computing reliabilities given by the normal distribution is adequate over the entire range of interest in structural design. Although the expressions may involve small absolute errors, they introduce excessively large relative errors in the failure probabilities over some ranges. It is impractical to have two expressions depending on the reliability index β. Two equations are proposed here. The simpler one involves relative errors smaller than 1.7% when β 1. The other introduces relative errors smaller than 2 × 10⁻⁴ when B 0 and smaller than 4.5 × 10⁻⁵ when β 1.     

The effect of dissolved oxygen concentration on nitrification

The effect of dissolved oxygen concentration on the rate of nitrification has been investigated by a number of researchers using both pure and mixed cultures, and cultures found in wastewater treatment systems. The maximum growth rate of both nitrification reactions are reported to be affected by dissolved oxygen concentration over the range of 0.3 mg l⁻¹ to as much as 4.0 mg l⁻¹. In some instances, it has been reported that a dissolved oxygen concentration in excess of 4.0 mg l⁻¹ is required to achieve maximum nitrification rates, while other investigators have found that only 0.5 to 1.0 mg l⁻¹ is required.It has been proposed that several factors are responsible for the wide range of reported nitrification rates with varying dissolved oxygen concentrations. Among these factors are the effects of oxygen diffusion in flocs, variation between measured results due to steady-state and dynamic measuring techniques, and double-substrate limited kinetics. This paper reviews the nitrification literature with respect to the effects of dissolved oxygen concentration, and shows that double-substrate limiting kinetics could account for the variation in the reported results.     

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.