Hazards associated with the use of chlorinated oxidation pond effluents for irrigation

Eight milligrams per litre chlorine applied to oxidation pond effluents caused no algal kill within the first 2 h of contact. The available chlorine attacks bacteria causing coliform count to drop from 10⁵ 100 ml⁻¹ to a few tens. Enterovirus counts dropped from about 80 100 ml⁻¹ before chlorination to 37 100 ml⁻¹ (after chlorination). Vibrio cholerae (El-Tor) were killed under these adverse conditions, and MPN dropped from 10³ 100 ml⁻¹ in the influent wastes to 2 100 ml⁻¹ in the effluents. A 5 mg l⁻¹ dose of chlorine at 1 h contact time killed these sensitive bacteria decreasing MPN to less than 2 100 ml⁻¹.Differences between the efficiency of chlorination experiments under laboratory and field conditions would necessitate the application of 15 mg l⁻¹ chlorine for 2 h of contact.     

Enhancement of Nitrobacter activity by heterotrophic bacteria

The present work shows that a supply which is not sterile and which contains organic matter does not interfere with the performance of a column filled with a support previously inoculated with Nitrobacter winogradskyi serotype agilis.Measurements of oxidation rates give results higher than those obtained under axenic conditions (maximum oxidation rate: 220 mg NO₂⁻ h⁻¹ l⁻¹ of reactor volume under non-sterile conditions: 160 mg NO₂⁻ h⁻¹ l⁻¹ of reactor volume under axenic conditions).This finding has concentrated our work on the effect of heterotrophic bacteria and of organic matter on the growth of Nitrobacter. We show that a fermentation filtrate of a heterotrophic bacterium (Pseudomonas sp.) added to a fermenter culture of Nitrobacter produces an increase of activity. Experimental results indicate an appreciable reduction in the latence period (15-0 h) and a considerable increase in the rate of growth of Nitrobacter. (Maximum growth rate with 10% of heterotrophic filtrate: 0.044 h⁻¹; without filtrate: 0.032 h⁻¹.)     

Denitrification en continu a l'aide de microorganismes immobilises sur des supports solides

In this paper, we describe a study of biological denitrification by immobilized cells. Nitrates are reduced in sterile solutions by Pseudomonas aeruginosa immobilized in a fixed bed reactor, and in synthetic waste water by mixed cultures immobilized into a fluidized bed reactor.The fixed bed reactor is a Plexiglas column filled with corn stovers (Table 1). It is 0.05 m in diameter and 0.55 in height, its volume being approx. 11. The fresh medium is injected at the base of the column and the liquid level is regulated by an overflow weir. Reactor and carrier are sterilized with ethylene-oxide. After sterilization 1 l. of a growing batch culture of Pseudomonas aeruginosa is introduced aseptically and the reactor is then fed continuously (45 ml h⁻¹) with fresh medium (N---NO₃ = 40 mg l⁻¹) until the first steady state is reached.Nitrates and nitrites are determinated by means of a colorimetric method.Reactor efficiency remains constant for over 40 days. Nitrates and nitrites concentrations are measured inside the reactor for flow varying from 2 to 16 ml min⁻¹ (Fig. 2). Reductions of nitrates and nitrites seem to be two first-order reactions (Fig. 3 and Table 2) and constant rate increases with flow rate (Fig. 4). Until nitrate concentration reaches 960 mg/l⁻¹ (N---NO₃) degradation is correct (Figs 5 and 6), beyond nitrites, which have been formed, seem to be inhibitor.Using this reactor, 50 mg N---NO₃ have been reduced per hour and per liter of empty reactor, but it may be possible to reduce 140 mg N---NO₃ l⁻¹ h⁻¹ if fresh medium contains 200 mg N---NO₃ l⁻¹.The fluidized bed reactor is a Plexiglas column filled with earthenware. It is 0.05 m in diameter and 3.15 m in height, its volume being approx. 6.201. Fresh medium is injected at the base of the column and the liquid level is regulated by an overflow weir. Figure 7 shows the retention time of the liquid in the reactor in relation to flow. The first steady state has been reached after 2 weeks, and it has not been possible to know half life time of the column.Four experiments were conducted (Table 3) and, for each nitrate, nitrite and methanol concentrations in the reactor were measured (Fig. 8). So, it appears that reduction of nitrates and nitrites are two first-order reactions (Table 4) and that constant rate values, which are higher than in fixed bed reactor, increase with flow.The reactor is more affected by a flow shift than by a nitrate concentration shift in fresh medium, and biomass linked onto carrier is about 76 mg of dry matter g⁻¹ of earthenware.So, our fluidized bed column is able to reduce 560 mg N---NO₃ h⁻¹ l⁻¹ of empty reactor, then retention time of liquid is less than 3 min.     

A mercury-free accelerated method for determining the chemical oxygen demand of large numbers of water samples by autoclaving them under pressure with acid-dichromate

In order to fulfill the objective of a water control program based on frequent sampling in several wastewater treatment plants, rivers and lakes a simplified method for measuring COD was developed. The procedure, in this article called the RR-method, includes: small sample and reagent volume; rapid addition of a mixture of all reagents to the sample; exclusion of mercury; autoclaving at 120°C for 1 h in flasks with fitted glass stoppers. To avoid dilution before analysis the method has been adapted for wastewater (I: 10–300 mg O₂ l⁻¹) and fresh water (II: 10–100 mg O₂ l⁻¹).Parallel analyses on different types of water samples according to Standard Methods showed that the yield by the RR-method was about 10% lower (Table 2). With water from the wastewater treatment plant at Uppsala (COD around 20 mg O₂ l⁻¹), the two methods gave an identical result. The somewhat lower yield was mostly due to decreased dichromate concentration and oxidation temperature. The lower oxidation potential made correction for chloride interference unnecessary below 1 g Cl⁻ l⁻¹ (Table 1).The RR-method also showed a good correlation to the values for KMnO₄-consumption. Parallel analyses of 318 samples from 14 wastewater receiving lakes gave the correlation coefficient r = +0.90 (Fig. 1).     

Enrichment of bacteria possessing catechol dioxygenase genes in the rhizosphere of Spirodela polyrrhiza: A mechanism of accelerated biodegradation of phenol

The bacterial community structure in bulk water and in rhizosphere fractions of giant duckweed, Spirodela polyrrhiza, was quantitatively and qualitatively investigated by PCR-based methods using 6 environmental water samples to elucidate the mechanisms underlying selective accumulation of aromatic compound-degrading bacteria in the rhizosphere of S. polyrrhiza. S. polyrrhiza selectively accumulated a diverse range of aromatic compound-degrading bacteria in its rhizosphere, regardless of the origin of water samples, despite no exposure to phenol. The relative abundances of the catechol 1,2-dioxygenase (C12O) gene (C12O DNA) and catechol 2,3-dioxygenase (C23O) gene (C23O DNA) were calculated as the ratios of the copy numbers of these genes to the copy number of 16S rDNA and are referred to as the rhizosphere effect (RE) value. The RE values for C12O DNA and C23O DNA were 1.0 × 10¹–9.3 × 10³ and 1.7 × 10²–1.5 × 10⁴ times as high, respectively, in rhizosphere fractions as in bulk water fractions, and these higher values were associated with a notably higher sequence diversity of C12O DNA and C23O DNA. The RE values during phenol degradation were 3.6 × 10⁰–4.3 × 10² and 2.2 × 10⁰–1.7 × 10², respectively, indicating the ability of S. polyrrhiza to selectively accumulate aromatic compound-degrading bacteria in its rhizosphere during phenol degradation. The bacterial communities in the rhizosphere fractions differed from those in the bulk water fractions, and those in the bulk water fractions were notably affected by the rhizosphere bacterial communities. S. polyrrhiza released more than 100 types of phenolic compound into its rhizosphere as root exudates at the considerably high specific release rate of 1520 mg TOC and 214 mg phenolic compounds/d/g root (wet weight). This ability of S. polyrrhiza might result in the selective recruitment and accumulation of a diverse range of bacteria harboring genes encoding C12O and C23O, and the subsequent accelerated degradation of phenol in the rhizosphere.     

Application de l'analyse des correspondances a des resultats d'essais de traitement d'eaux de surface

Many results show that if a conventional coagulation-flocculation-clarification treatment line is combined with pre-ozonation, removal efficiency as regards pariculate and dissolved organics is substantially enhanced. However, research on the optimum balance between pre-ozonation and coagulation treatment has turned out to be difficult because of the numerous parameters that are involved. In order to identify the most significant among clarification criteria it was in fact necessary to develop a more elaborate model than is required for conventional statistical analysis, capable of comparing all the intervening factors. This we finally achieved by a program based on stepwise regression analysis.Measuring samples and parametersSamples. Samples were taken from the pilot plant located at Choisy-le-Roi on premises belonging to the Paris Suburbs Water Authority, over a period of 3 months from 1 April to 24 June, i.e. exactly 43 days of research.The plant shown in Fig. 1 consists of 4 trains working in parallel arrangement. This layout allows practically two complete treatment runs daily so that 8 different ozone-coagulations could be tested each day on the same quality of raw water. 387 samples were thus taken with 344 treated waters and 43 raw waters. The campaign was designed over this rather long period to achieve two ends:

1. (1) to gather enough results to give real significance to the mathematical computation. During the 43 day experimental campaign, each ozone-WAC combination was repeated more than 10 times;

2. (2) to find a means of allowing for fluctuation in the river in relation to phenomena of great amplitude such as rises in temperature and changes in flow rate, so that acquired results could eventually be extrapolated for application to industrial treatment plant management.

Parameters. Twenty-two parameters were measured in respect of each sample of raw and treated water. The aim of the research being to define the main parameters on which to base the combination, it was essential to begin with a study of all the magnitudes normally representative of suface waters.These parameters can be divided into various types:

treatment parameters: WAC + O₃; the concentration tested are shown in mg l⁻¹ in Table 2 and Fig. 2;

parameters concerning suspended solids: total number of particles per ml (NT) and their equivalent diameter (D), turbidity (Tu) expressed in drops of mastics and zeta potential (Z_p);

parameters concerning organics: total organic carbon (COT) in mg l⁻¹ of C, KMnO₄ in mg l⁻¹ of O₂, dissolved O₂ in mg l⁻¹, u.v. absorption at 254 nm, NTK and ammonia (NH₄⁺), both in mg l⁻¹.

Besides pH and temperature which vary very little in Siene river water, total aluminium (ALT) in mg l⁻¹ and residual ozone (RO₃) were monitored.Analysis of data. The basic data represented in the following matrix (I × J), in which I is the sum of the sampling steps and J the sum of the concentrations of the different chemical elements, are too vast for conventional statistical analysis. By factor analysis, one can obtain as a final result a geometrical figure in a two-dimensional space but that simultaneously accounts for all the combinations of I and J. We thus obtain a factorial chart analysing the proximity between variables in terms of correlation and that between individual points in terms of similarity of behaviour toward these variables as a whole.Each component i of I and j of J is represented in profile form ƒ_jⁱ (or ƒ_I^j)=k(i,j)/k(i) as shown in the matrix below:

Full-size image (1K)

All of the profiles and I and J, each with a volume allocated pro rata the complete line (or column), make up a set of points with a corresponding volume in a multi-dimensional space. In the case under study, each components i (sampling steps) are in a space with 22 dimensions and each variable j (concentrations) in a 387-dimensional space. The purpose of the analysis is to obtain from the cloud as true a representation as possible brought down to a 2-dimensional space. This dimensional reduction consists in finding a sub-space in which the space between individual points i or j are as close as posible to the initial distances in IR₂₂ (or IR₃₈₇). The distance used in factor analysis is the distribution distance expressed as: . The plane thus located is defined by 2 perpendicular straight lines. They are the factorial or inertia axes. Inertia measures the total dispersal area of the cloud on one axis and shows the ratio between the points projected in space and the sum of the square-roots of the distances between the initial points. It measures the dispersion of data on the axis. The axes are called “factors”.Using this method, it becomes possible to described the accumulated data and quantify the phenomena that control both the variable parameters and their components (I or J) without any preconceived hypothesis as to the relative importance of the initial data. And, furthermore, we have a simultaneous geometric representation of samples and variables.Results. The first (horizontal) axis, F₁ represent the abatement of suspended particles and organics. The second (vertical) axis enables the different treatment trains to be interpreted in terms of ozone and residual ozone. Four distinct groups appear on plane F₁ × F₂:

Group 1: Group 1 represents water with no WAC or ozone treatment nor residual ozone. Characteristics include a very high suspended particles content and a certain amount of organics (i.e. variables N, D₁, D₂…D₁₀ and KMnO₄). This group is representative of raw waters in general.

The variable KMnO₄ factor quite realistically reflects the clarification treatment, a high KMnO₄ value indicating the presence of raw water, a low content the presence of treated water.

Group 2: This is an intermediate group between raw water and the water in trains A and B. It is characterized by poor abatement of both suspended solids and organics and corresponds to the majority of waters in train D with no pre-ozonation and train A with low-rate ozonation (0.3 mg l⁻¹).

Group 3: A high WAC rate and an average ozone rate are the predominant features of this group in which residual ozone is very low. A good level of suspended solids and organic removal was obtained, as is the case of treatments in general, and as practically demonstrated by trains A and B.

Group 4: This group corresponds to the treated water with a high ozone injection rate, hence a high residual ozone content. A good level of suspended solids and organics removal is obviously obtained, most of the water having been treated on train C. This maximum ozone residual for a similar abatement of organics concentration indicates that the extra ozone added was in excess of the amount required in order to oxidize the quantity of organics in the effluent. The optimum ozone dose must therefore be somewhere near that of the previous group, i.e. trains A and B.

In conclusion, analysis by stepwise regression identified the five main variables that define the complete clarification process: N_T, KMnO₄, TOC, WAC and ozone. As regards the last two mentioned, differentiation between groups 3 and 4 provides a means of determining the optimum dose rate for ozone in the treatment concerned, i.e. less than for train C (group 3) where the residual ozone rate is higher, hence approximately the same as for trains A and B—in the region 0.3–0.8 mg l⁻¹.     

The effects of phenol and some alkyl phenolics on batch anaerobic methanogenesis

Phenol and seven alkylphenols (o-, m- and p-cresol, 2.5-, 2.6-, 3.4- and 3,5-dimethylphenol) were added at various concentrations to aliquots of domestic anaerobic sludge in Hungate serum bottles and these were incubated at 37°C. The concentration of methane in the headspace gas was monitored to determine if the phenolics were fermented to methane or if they inhibited the anaerobic process. Only phenol and p-cresol were fermented to methane. At 500 mg l⁻¹ (but not at 300 mg l⁻¹) 2,5-, 3,4- and 3,5-dimethylphenol reduced the rate and the amount of methane produced. The cresols were inhibitory at 1000 mg l⁻¹ but not at 400 mg l⁻¹.In cultures supplemented with acetate and propionate (VOA), and in unsupplemented cultures, phenol at concentrations up to 500 mg l⁻¹ was fermented to methane. Between 800 and 1200 mg l⁻¹ phenol, methane production was neither enhanced nor inhibited relative to control cultures containing no phenol. Inhibition of methane production was evident when phenol was present at 2000 mg l⁻¹. Thus the methanogens are less susceptible to phenol inhibition than are the phenol-degrading acid formers. In similar experiments with p-cresol: enhanced methane production was observed at concentrations of 400 mg l⁻¹; no enhancement or inhibition was observed at 600 mg l⁻¹; and inhibition was noted when p-cresol was present at 1000 mg l⁻¹.     

Response of epiphytic bacteria to the treatment of two aquatic macrophytes with the herbicide paraquat

A mixed stand of aquatic macrophytes, including Elodea and Chara, was treated with 1.5 mg 1⁻¹ paraquat. Total numbers of epiphytic bacteria and viable numbers in different physiological groups were studied. The epiphytes of Elodea, which had died after 15 days, had all increased in number by ten days. Those on Chara, which survived, did not increase except for a short-lived initial rise. These results were explained by the presence of paraquat in the water and the release of nutrients by the treated plants.     

Whole lake responses to low level copper sulfate treatment

The impact of three low level copper sulfate applications to Cazenovia Lake, New York, was assessed through a high frequency monitoring program. Monitored parameters included: (1) filtered and total copper; (2) phytoplankton identification and enumeration; (3) chlorophyll-a, (4) in situ¹⁴C assimilation; (5) bacteria numbers; (6) zooplankton identification and enumeration, (7) macrophyte nutrient status and (8) filtered reactive and total phosphorus.The low level application caused only small increases (maximum of 5 μg/l) of short duration (2–5 days) in filtered copper. The treatments failed to induce effective algicidal action in the target phytoplankton populations of the lake, but they did induce short term stress and alterations in the natural seasonal succession processes within these populations. No definitive responses in the zooplankton, submerged macrophytes or water column phosphorus levels were noted. Dramatic reductions in the water column bacteria occurred immediately following each treatment, indicating direct negative impact. Phytoplankton and bacteria populations recovered within 1 week and several days, respectively.     

Influence de sediments argileux incorpores au milieu d'insemination sur le succes de la fecondation chez la truite arc-en-ciel (Salmo Gairdneri)

The aim of this paper is to determine whether clay sediments suspended in water can prevent trout eggs from being fertilized. Kaolinite-rich clays (granulometric fraction: <2μm) (Fig. 1) were suspended in an artificial insemination diluent in doses ranging between 0 and 20 g l⁻¹. The eggs were exposed for 1, 10 or 20 min (experiment A) or inseminated (experiment B) in the diluent-sediment mixture. In experiment (C), the eggs were exposed to this mixture at three different temperatures (10, 15, 20°C). After insemination, the eggs were incubated for 10 days at 10°C and the percentage of eyed-eggs was used as an approximation of the fertility rate. The presence of clay sediments in the medium in which artificial insemination was carried out did not affect fertilization rate after the ovules had been exposed during 1 min to clay suspensions, at any of the temperatures used (8°C: Fig. 3; 10–15 or 20°C: Fig. 5) or at any of the sperm dilution rates (10⁻², 10⁻³, 10⁻⁴) (Fig. 3). On the contrary, there was a significant decline (P < 0.01) in the fertilization rate after the eggs had been exposed for 10 min at 8°C to doses of sediment exceeding 1.2 g l⁻¹ (Fig. 2). The fertilization rate also decreased significantly (P < 0.05) when the dose of sediment in the medium increased after 20 min at 20°C and 40 min at 15°C (Fig. 4). The 15 and 20°C temperatures were unfavourable for the eggs anyway. It is probable that fertility decreased due to micropyle clogging when the eggs were exposed longer than 10 min to the sediments. It is concluded that presence of sediments in the medium in which the gametes meet does not prevent fertilization.     

Cultivation of a mixed bacterial population of sewage origin in the chemostat

Bacteria of distinctive colony morphology isolated from the biological stage of two typical sewage treatment works have been continuously cultured in a complex nutrient medium. Changes in the composition of the mixed population have been monitored by viable counts on casein, glycerol yeast extract agar and Christensen's agar. A selection of suitable species was attempted upon the basis of growth in pure and mixed batch culture. A reproducible mixed bacterial population has been cultured continuously for 170 h at a dilution rate of 0.166 h⁻¹. An increase in the dilution rate to 0.2 h⁻¹ did not prevent the maintenance of a mixed bacterial population, but caused changes in the population size, of individual species.     

Inactivation of heterotrophic bacterial populations in finished drinking water by chlorine and chloramines

The die-off of heterotrophic bacteria from a finished drinking water reservoir, located in southern California, was evaluated using chloramines and free chlorine. Understanding the inactivation of hetertrophic populations is valuable because it reflects the response to disinfection of naturally occurring organisms in their native state and environments. Disinfection studies with the heterotrophic bacterial group were performed during summer and winter months using different chloramine application techniques at pH 6 and 8. In addition, bacteria surviving exposure to chloramines and free chlorine was influenced predominantly by the presence of highly chlorine tolerant, red-pigmented bacteria, identified as Flavobacterium spp. Inactivation by chloramines, though, was chiefly dependent upon the method of application and pH. Viable bacteria recovered from the indigenous population after 60 min of exposure to chloramines (1.0 mg l⁻¹, pH 8) included members of Pseudomonas, Acinetobacter and Flavobacterium. In general, with contact times of 1 h or more, free chlorine and chloramine solutions (1.0–1.6 mg l⁻¹, pH 8) reduced total count levels below 50 colony forming units ml⁻¹.     

Structure et evolution d'un modele d'acide humique sous l'effet de l'ozonation

Humic acids are widely studied as complexing agents in surface waters, but little is known about the chemical structure of their potential sites of interaction with micropollutants. By means of powerful spectroscopic techniques such as u.v.-visible, infrared and electron spin resonance spectrometries run on a commercial model Fluka (AHF), we carried out the structural investigation of the concerned functional groups and studied their evolution under ozonation.Consecutively to the consumption of 1.24 mg ozone per mg of AHF, one can see (Table 1) that the decrease in phenol groups (21%) can be matched with that of aromaticity (16%). Moreover, an original study performed on ultrafiltration fractions: (1) M > 3.10⁵; (2) 3.10⁵ >M > 5.10⁴; (3) 5.10⁴ >M > 5.10³; (4) M < 5.10³ showed that half of the hydroxyl group disappears from fraction 1. Relatively high values of molar extinction coefficients (_254nm = 360,000 and _203nm = 458,000) suggest a polysubstitution state for aromatic cycles and this has been confirmed by infrared spectrometry. The relative position of benzenic substituents cannot be inferred from u.v. visible data (Table 2) but the well-resolved infrared spectra (Fig. 1 and Table 3) reveal the presence of phenolic, benzoate, phtalate and salicylate groups close to semiquinonic anion radicals, aromatic units being linked by some alcanoic chains, most of them formed by four methylene groups. The proposed structural scheme (Fig. 4) is in agreement with Murray and Linder's (1983).Investigation of the infrared characteristics of the four ultrafiltration fractions shows that these functional groups are not equally distributed over the molecular weight range. Polysubstituted aromatic cycles, phenolic and quinonic structures are mainly detected in fractions (1) and (2), whereas acid and ester groups are significantly observed in fractions (3) and (4).After ozonation, the 1720, 1700 and 1350 cm⁻¹ bands, assigned to stretching valence vibrations of aromatic esters are depressed. For fraction (I), ozonation of aromatic structures is substantial (Fig. 2 and Table 4), as it is expected for polysubstituted molecules (Decoret et al., 1984; Gilbert, 1978). Less substituted structures are divided on fractions (2) (3) and (4). Infrared spectra of fractions (3) and (4) are markedly disturbed. This reveals that quinonic and ethylenic groups increase as aromatic cycles do (780 cm⁻¹ band).Electron spin resonance investigation (Fig. 3 and Table 5) shows that AHF and its fractions (1) and (2) are endowed with electronic paramagnetism. As g values are close to 2.0040 and as this property disappears after ozonation, it must be due to semiquinonic anion radicals partly maintaining aggregative structures (Steelink et al., 1983; Wershaw et al., 1977), leading to quinonic structures by oxidation.     

The inactivation of faecal coliforms and Ascaris ova in faeces by lime

The inactivation effects of lime, when applied to faeces on faecal coliform bacteria and Ascaris lumbricoides ova, were investigated in the laboratory. A faecal coliform inactivation of about 5 orders of magnitude could be achieved at 19 g CaO l⁻¹ (or initial sample pH of 12) and contact times over a 3 h period, while negligible reduction of faecal coliform bacteria was obtained at 5.7 g CaO l⁻¹ (or initial sample pH of 9) with contact times from 3 to 48 h. However, only a 26.5% reduction of Ascaris ova was observed with 19 g CaO l⁻¹ and a contact time of 48 h. Microscopic examination of the treated samples suggested the ovicidal effects of lime upon the Ascaris ova was of a low efficiency.     

Some growth parameters of haliscomenobacter hydrossis (syn. streptothrix hyalina) a bacterium occurring in bulking activated sludge

A study has been made of the kinetics of two strains of the sheath-forming bacterium Halisco menobacter hydrossis (syn. Streptothrix hyalina) by growing the bacteria axenically in continuous culture, with glucose as the limiting substrate. The maximum specific growth rates were approx. 0.05 h⁻¹ for strain AN and 0.09h⁻¹ for strain AZ, corresponding to minimum doubling times of 14 and 9h, respectively. Depending on the history of the population, appreciably lower values were found in batch experiments. The maintenance coefficient was low, 20 and 21 mg glucose (g biomass)⁻¹ h⁻¹ for strain AN and strain AZ, respectively. The “true” yield coefficients were 0.59 and 0.42 g biomass (g glucose)⁻¹, for strain AN and strain AZ, respectively.     

Bioleaching of metals from sewage sludge: Microorganisms and growth kinetics

Microbial leaching is one of the advantageous methods of removing heavy metals from sewage sludge, however, the microbiological aspects of this technology have not been studied. This study presents the characterization of the naturally occurring microorganisms, responsible for the metal leaching activity, in 21 different sewage sludges. The results obtained indicate that the bioleaching of metals is carried out by successive growth of less-acidophilic and acidophilic thiobacilli. Several species of less-acidophilic thiobacilli participate in the sludge acidification, but Thiobacillus thioparus is the most important species. In contrast, Thiobacillus thiooxidans seems to be the only species involved in the acidophilic group of thiobacilli. The growth kinetics of the two groups of thiobaciili was followed in five different sewage sludges. After 5 days of incubation in shake flasks, the pH of the sludge was decreased to about 2.0 and this pH decrease solubilized the toxic metals (Cd: 83–90%; Cr: 19–41%; Cu: 69–92%; Mn: 88–99%; Ni: 77–88%; Pb: 10–54%; Zn: 88–97%). The maximum specific growth rate (μ_max) for the less-acidophilic thiobacilli varied between 0.079 and 0.104 h⁻¹ and that for the acidophilic thiobacilli varied between 0.067 and 0.079 h⁻¹.     

Etude descriptive fondamentale et modelisation de la croissance d'un film biologique—II. Nouveau concept de modelisation de la croissance d'un film biologique

In a recent publication [Belkhadir et al. (1988) Wat. Res.22, 59–69], the different characteristic phases of anaerobic biological film growth were described.To explain the evolution of the different parameters studied (substrate, biomass, fermentation products) with time (Figs 1 and 2), a new model was proposed based upon the definitions:

• — of an active bacterial growth intrinsic kinetic: r_Ma = μ₀ · M_a

• — an inactivity kinetic dependant upon cellular density (confinement effect) and the accumulation of inhibitors: r_Md = k_i · I · M_a.

One can thus define the accumulation rate of an active biomass on a given surface by the following expression: With (M_a)_max representing the maximal density in active microorganisms when the surface is entirely colonized (end of the dynamic phase). Moreover, this equation is compatible with the hypothesis of a limitation in growth imposed by the fraction of available surface (biological space concept): The study of the model was based on the knowledge of three parameters: μ₀, (M_a)₀ and (M_a)_max, that were evaluated experimentally (Figs 4 and 5) and by parametric estimation (Fig. 6).Model simulation permitted the characterization of the evolutions, with time, of the active (M_a), and inactive biomass (M_d) which then enabled us to determine the corresponding accumulation rates (Figs 7 and 8).The proposed model corresponded well with the experimental results obtained in the dynamic and linear growth phases.Biological processes thus seem to be controlled by physiological factors (inhibition, diffusional limitations in the vicinity of the bacteria …), which is contrary, to the view of most authors who attribute this phenomenon to a limitation of substrate diffusion in the biofilm. This concept, inspired by the notion of the heterogeneous catalysis in a porous medium, arbitrarily introduces the stratification structure of a biological film. A critical study of this approach will be presented in a future publication.     

Études des transformations des formes du carbone, azote, phosphore, soufre et des principaux éléments minéraux au cours de la mesure de la demande totale en oxygene—III transformation des formes du soufre

Previous experiments carried out with the laboratory TOD meter Ionics 225 of the DOW Chèmical made it possible (after a high temperature catalytic action) to characterize the stable forms of organic and inorganic carbon and nitrogen (NH₄⁺, NO₂⁻, NO₃⁻), and the principal cations (Na⁺, K⁺, Ca²⁺, Mg²⁺) in the course of the total oxygen demand (TOD) measurement.The object of this study is firstly to compare the oxidation capability of different techniques of organic pollution (particularly the COD and TOD) in relation to the constituent elements of the organic matter C, N, P, S, and to calculate the possible interferences of the inorganic compounds at the time of TOD test.These investigations warrant the application of this technique to measure the amount of organic pollution in relatively mineralized conditions (Industrial wastewater, sea-water…). The present publication is concerned more with the study of the transformation of the organic and inorganic sulphur forms (S²⁻, SO₃²⁻. SO₄²⁻) in the course of the TOD measurement.The study of the oxidizability of the organic sulphur compound type C_xH_yO_zS, made it possible to establish a specific relation with a ratio of 0–50 mg of organic sulphur l⁻¹, between the oxygen demand of this element [TOD (S)] and its concentration (TOD (S) = 0.97 [S]).These tests showed a partial oxidation of the sulphur to SO₂ and SO₃ as the literature claimed. On the other hand, the oxidation of the same compounds during the COD tests varies greatly and although it is not possible to establish a correlation between these two measurements, as applies in the case of organic nitrogen, nevertheless these experiments showed a greater reliability of the TOD compared with the COD in the oxidation of organic matter in general. We then carried out experiments on the different mineral forms of sulphur in order to distinguish the possible effects and to recommend simple improvements.A relative study on sulphate ions had been carried out with standard solutions which have the same TOD (the basic TOD is obtained using potassium phthalate acid) and the same increasing concentration of the salt M₂SO₄ type. The experiments showed that the basic TOD decreases when the concentration of sulphate ions is increased (Fig. 3). Therefore, the interference is negative and taking into consideration the specific oxygen demand of the cation, we can propose an evaluation of this interference (ΔTOD (SO₄²⁻) = 0.203 [SO₄²⁻]). The same experiments have been conducted with a salt of M₂SO₃ type and similar results obtained (Fig. 5).The specific interference of the sulphite ion is negative and can be estimated by the following equation (ΔTOD (SO₃²⁻) = 0.132 [SO₃²⁻]). In both cases, we have to note that the transformation of these inorganic anions occurs between those relative to the theoretical dissociation reaction corresponding to the appearance of the oxide SO₂ and SO₃. For sulphurous on the contrary, the interference is positive and therefore corresponds to an extra oxygen demand (Fig. 8).The experiments were conducted directly with the M₂S salts (M representing K or Na) in aqueous solution.The evaluation of this interference had been made in the consideration of two concentration ranges of the sulphurous ions (0–35 mg S²⁻ l⁻¹): TOD (S²⁻) = 0.4 [S²⁻] and (35–100 mg S²⁻ l⁻¹): TOD (S²⁻) = 1.2 [S²⁻] − 30.Therefore this study confirms a better oxidation of the organic matter by TOD test in comparison with COD test.But sulphate and sulfite have a negative interference in the TOD measurement, whereas sulphurous is positive.The evaluation model of these interferences allows a correction to be made of the TOD value or to verify TOD measurement of organic pollution obtained by this technique.     

Some effects of pulp and paper wastewater on microbiological water quality of a river

A study was conducted to detect the source of fecal indicator bacteria and measure the resulting impairment of water quality of the Sturgeon River at Sturgeon Falls, Ontario, Canada. The bacteriological water quality of the river above the dam at Sturgeon Falls was fairly good, while below the dam the water quality was degraded. The principal input of fecal indicator bacteria was traced to the paper mill at Sturgeon Falls. The impairment of water quality was detected all the way to recreational areas near the mouth of the river. The impaired stretch of the river had diminished aesthetic appeal. Other sources of indicator bacteria could be masked by the large numbers of similar bacteria discharged from the paper mill. The principal fecal coliform was Klebsiella pneumoniae. In pulp mill wastes the fecal origin of this bacterium can be disputed, and so its presence in large numbers interfered with the interpretation of fecal coliform results. K. pneumoniae is also an opportunistic pathogen which causes infections in humans. Thermotolerant oxidase positive bacteria which were isolated from the paper mill wastes, register as false positives in the fecal coliform test causing problems in interpretation. Pseudomonas aeruginosa was detected in the pulp mill wastewater, and at a level of 82 PA 100 ml⁻¹ in recreational areas of the river. This was considered to be of some hazard to users of the water. In addition, Escherichia coli was detected in the mill wastewater, at about 200 EC 100 ml⁻¹, and this probably indicated some measure of fecal pollution though likely of animal origin. Finally the nutrient rich wastewater led to an approx. 50-fold increase in density of aerobic heterotrophic bacteria in the river water, as well as the production of a slimy filamentous growth on surfaces, stones and wooden pilings, in the river. The principal organism in this slime was the fungus Leptomitus.