Chlorine disappearance in sea-water

A series of chlorination studies were carried out on natural and artificial sea-water. It was determined that both the forward and back titration procedures accurately described the two phases of chlorine losses in sea-water: a rapid initial loss followed by a continuous loss at a sharply reduced rate. The order of adding the iodide and buffer reagents was found to be crucial in affecting the rapid initial loss. The initial loss was found to reach a saturation level that varied widely between natural sea-water samples and appeared to be related to a true organic demand. In contrast, the second phase was difficult to explain. Losses continued over 10 day periods and were pronounced in both natural and artificial sea-water containing bromide. In the absence of bromide, long term losses in artificial sea-water were greatly reduced, indicating that the lost applied chlorine was associated with the bromine chemical system in sea-water. The fate of the lost chlorine was not determined and the untitratable halogen compounds must remain suspect as potential biocides.     

Field measurement of the air flow characteristics of big mechanically ventilated spaces

Air speeds induced by mechanical ventilation systems in the occupied zone are studied experimentally in seven railway stations in Hong Kong. Values of air speed at different positions are measured. From these values, air speed contours and turbulence intensities are calculated. Macroscopic numbers describing airflow in a space including the Reynolds number and the jet momentum number are estimated and their potential uses are discussed.     

Profiles of mean wind speeds and vertical turbulence intensities measured at seashore and two inland sites using Doppler sodars

The authors’ group has been conducting full-scale measurements of wind velocities with Doppler sodars. It is very important to accurately assess the profiles of mean wind speeds and turbulence intensities in relation to terrain roughness. In this study, the profiles were evaluated for all data measured over a long period at a seashore and two inland sites. It is confirmed that for strong winds the profiles can be approximated by a single power law at altitudes between 50 and 340 m. The power law exponents of the mean wind speed profiles are approximately 0.1 for wind from the sea and 0.2-0.3 for wind blown over land. Those of the turbulence intensity profiles are approximately 0 and −0.2 to 0.4, respectively.     

A steady-state model for the rotating biological disc reactor

A steady-state model for substrate removal in a rotating biological disc reactor is presented. The model considers the consumption of substrate by micro-organisms in the biofilm attached to the rotating disc, and mass transfer from the attached liquid film to the biofilm. A mass balance on substrate over the liquid in the trough provides an expression for effluent substrate in terms of the microbial kinetic constants, the geometry of the system and the operating conditions. In order to simplify the solution of the equations in the model, first order kinetics are assumed for the rate of microbial growth and substrate utilization. This simplified model can be solved, for example, by using a programmable calculator. The model predicts that the fractional removal of substrate per stage is strongly dependent on the hydraulic loading rate per unit disc area but independent of feed substrate concentration. It predicts constant removal independent of disc size provided the hydraulic loading per unit area is kept constant. The rotational speed has only a slight predicted effect on the rate of substrate removal. The predictions of the model are compared with published data from the literature for both domestic wastewater and some industrial wastes. Trends observed in the field are predicted qualitatively by the model.     

Essais d'aerateurs: Enseignements tires de 500 essais en eau claire effectues dans 200 stations d'epuration differentes—II ResultatsTests on aerators: Conclusions drawn from 500 clean water tests conducted in 200 different sewage treatment plants—II Data interpretation

The large number of aerator tests conducted in the field by the CEMAGREF teams has allowed developing a critical review of tests results by means of statistical analysis. Measurement quality is estimated from the variation of the transfer coefficient values from one sampling point to another. Individual transfer coefficient values $\text{(}\text{K}{}_{\mathrm{L}}\text{a)i}$ are compared with the average value of the test $\text{(}\text{K}{}_{\mathrm{L}}\text{a). (K}{}_{\mathrm{L}}\text{a)i/}\text{K}{}_{\mathrm{L}}\text{a}$ ratios correlating with one year's data are gathered in histogramms (Fig. 1).A χ² test is used for evaluating the fit of a Normal distribution on each histogram (Tables 1 and 2 results for two kinds of surface aerators). When the Normality is not rejected, the variances between distributions are compared by means of a Fisher test.$\text{(K}{}_{\mathrm{L}}\text{a)i/}\text{K}{}_{\mathrm{L}}\text{a}$ variations in a same run are independent of transfer coefficient when the K_La ranges 1–10 h^?1 and applied specific power ranges 15–70 W m^?3. Those variations allow evaluating the technique of measuring, the reliability of oxygen probes and the operator's experience (Table 3).In a well mixed tank and when the recommended procedure is correctly implemented the relative error in measuring the specific oxygen input (kg O₂ kWh^?1) is 5%. In less favorable cases it reaches 10%.Tables 4 and 5 show the reproductibility of repetitive run results in the same plant and of tests performed with the same aerator in different plants.The histograms of the performances of the main types of mechanical surface aerators (high speed vertical shaft turbine, slow speed vertical shaft turbine, horizontal shaft aerator) are presented (Figs 2, 4, 5). Relations between oxygenation capacity and specific power consumption are plotted in Figs 3 and 6. As to other aeration systems, fewer data are available. Table 6 summarizes the usual range of performances.In 1974, after a series of measurements performed on 72 different plants, CEMAGREF stated that the oxygenation capacities claimed by manufacturers were, on the average, 40% higher than actual results. Now, the performances predicted by manufacturers in France are generally very close to the measured values. A difference higher than 10% between predicted values and measured ones now occurs as an exception.     

Assessment of nitrification in groundwater filters for drinking water production by qPCR and activity measurement

In groundwater treatment for drinking water production, the causes of nitrification problems and the effectiveness of process optimization in rapid sand filters are often not clear. To assess both issues, the performance of a full-scale groundwater filter with nitrification problems and another filter with complete nitrification and pretreatment by subsurface aeration was monitored over nine months. Quantitative real-time polymerase chain reaction (qPCR) targeting the amoA gene of bacteria and archaea and activity measurements of ammonia oxidation were used to regularly evaluate water and filter sand samples. Results demonstrated that subsurface aeration stimulated the growth of ammonia-oxidizing prokaryotes (AOP) in the aquifer. Cell balances, using qPCR counts of AOP for each filter, showed that the inoculated AOP numbers from the aquifer were marginal compared with AOP numbers detected in the filter. Excessive washout of AOP was not observed and did not cause the nitrification problems. Ammonia-oxidizing archaea grew in both filters, but only in low numbers compared to bacteria. The cell-specific nitrification rate in the sand and backwash water samples was high for the subsurface aerated filter, but systematically much lower for the filter with nitrification problems. From this, we conclude that incomplete nitrification was caused by nutrient limitation.     

The effect of temperature on the removal of non-ionic surfactants during small-scale activated-sludge sewage treatment—I. Comparison of alcohol ethoxylates with a branched-chain alkyl phenol ethoxylate

The degree of biodegradability of three non-ionic surfactants has been assessed using small-scale activated-sludge sewage treatment plants. The effect of temperature on biodegradability was studied by operation at 15°, 11° and 8°C.The two alcohol ethoxylate surfactants tested were well degraded at all three operating temperatures. The alkyl phenol ethoxylate surfactant tested was well degraded at 15°C but at lower temperatures the biodegradability was dependent on concentration. At 5 mg 1⁻¹, greater than 90 per cent removal was achieved but at 20 mg 1⁻¹ the degree of removal fluctuated between 40 and 95 per cent at 11°C and between 20 and 80 per cent at 8°C.The present results have been compared with those obtained using the same surfactants in community trials at a small sewage works employing biological filtration. Although a similar temperature effect was observed with the alkyl phenol ethoxylate, the biodegradabilities obtained in the laboratory were consistently greater than those obtained at the sewage works, perhaps because of the constant conditions of the laboratory test.