Oxygenation par le peroxyde d'hydrogene des biomasses fixees utilisees en traitement biologique des eauxOxygenation by hydrogen peroxide of the fixed biomass used in biological water treatment

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).     

Development of mathematical models for the treatment of an industrial wastewater by means of biological rotating disc reactors

In this study the extension of the mathematical model proposed by Grieves to experimental results obtained in the treatment of an industrial wastewater is examined. The laboratory-scale unit consists of three stages with seven discs per stage.The following conclusions are drawn: (1) the Grieves's model (originally derived for glucose solutions) is reliable also for an industrial wastewater; (2) within the range of organic loading of 8.7–27.7 g BOD₅ day⁻¹ m⁻², the diffusion of the organic substrate, through the liquid film adhering to the biological film, is the controlling step of the BOD₅ removal kinetics only when the disc rotational speed n is less than 0.6 rev min⁻¹; (3) for higher values of n, as those adopted for full-scale plants, bio-disc apparatus can be designed, with good approximation, by means of the Monod's equation, by considering the bio-disc unit as an idealized perfect mixing activated sludge reactor, whose volume and activated sludge concentration are equal to the volume of the active biological film and organism concentration in the same film.     

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.     

Denitrification en continu a l'aide de microorganismes immobilises sur des supports solidesContinuous denitrification by immobilized cells

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.     

Oxydation catalytique des phenols par le peroxyde d'hydrogene: Etude structurale des catalyseurs Fe/Al2O3 et Fe-Cu/Al2O3 par spectroscopie Mossbauer

This study recalls the results obtained on the oxidation by hydrogen peroxide of a number of hydroxyl aromatic compounds with alumina supported catalysts and more particularly the structural study of these catalysts. The catalysts were prepared under different conditions: without thermic treatment, by oxidation in air at 450°C and by thermic reduction at 500 and 700°C, under hydrogen flow. The structural study by Mössbauer spectroscopy of the catalysts Fe/Al₂O₃ and Fe-Cu/Al₂O₃ made it possible to specify in what form was found the iron, as a function of the conditions under which the catalysts were prepared. For the catalyst prepared by impregnation without thermic treatment the iron on the support was in hematite form (α-Fe₂O₃) well crystallized in small particles with 10–20% iron which could be ferric ions (Fe³⁺) chemically adsorbed on alumina or iron within the structure of the alumina (Figs 7 and 8). Thermic oxidation in air brought about the appearance of hematite in the form of large particles (Fig. 9) whereas the thermic reduction under hydrogen flow led to the formation of crystallized metallic iron (α-Fe) (Fig. 12). The reducibility of iron on the support increased with the increase in temperature of reduction and with the presence of copper (Figs 11 and 13). As for the activity of the different catalysts in oxidation reactions of phenols by hydrogen peroxide, we notice that whatever the form of the catalyst, the activity was more important for pyrocatechol than for phenol (Fig. 3). As far as stability of the metals on the support was concerned, during the oxidation reaction we noticed that it was greater with an oxidized catalyst than with a reduced one (Figs 4 and 5). The comparison between the results obtained in a batch and in a continuous reactor made it possible to show that the first phase of the reaction was probably due to the superposition of the phenomena of homogeneous (by the Fe ions passed into solution) and heterogeneous catalysts (Fig. 6). The comparative structural study reduced before and after use was quite in agreement with the solubilization of iron that we observed during oxidation (Figs 15 and 13). However on the oxidized catalyst hematite was not modified after use and the most significant change on the spectrum was a slight decrease of E_Q (0.1 mm s^?1) in the central doublet (Figs 14 and 9).     

Reacteur a cellules nitrifiantes immobilisees sur garnissage aere a co- ou contre-courant. Etude experimentale et modelisationNitrification by attached-cell reactors aerated at co- or counter-current. Experimental data and modelling

Attached-cell reactors using a bed of granular material for wastewater treatment develop a high biomass concentration which allows an important reduction of the required residence time (Jeris et al., 1977; Elmaleh, 1982). In nitrification of ammonia containing wastewater, oxygen is currently the limiting substrate; in theory, 4.18 g of oxygen are required per 1 g of nitrogen (Painter, 1970). Oxygen can be added with hydrogen peroxide (Grigoropolou, 1980; Seropian, 1980; Yahi et al., 1982) which is nevertheless expensive and it seems better to transfer oxygen from a gas phase, i.e. air, to the liquid phase through a fixed bed (Charpentier, 1976).Two attached-cell reactors (Fig. 1) were operated in parallel for nitrification of ammonia containing synthetic wastewater (Table 2). Air was upflowed through a granular packing (Table 1) maintained in fixed bed while the liquid influent was injected at co- or counter-current.

1. (1) Owing to the high oxygen transfer properties of the system and to the fact that the thickness of biofilm is always less than 100 μm, the whole process was not limited by oxygen concentration of which remained larger than 7 mg l⁻¹ (Fig. 2a) (Bungay et al., 1969). Oxidised nitrogen ammonia is completely converted into nitrate (Fig. 2b). Experimental conditions are given in Table 3.

2. (2) The plot of ammonia conversion against air superficial velocity shows a maximum (Fig. 3) after which conversion decreases rapidly by overloading of the packing (Prost, 1965). Experimental conditions are given in Table 4.

3. (3) Process efficiency decreases when superficial upflow velocity is increased (Fig. 4).

4. (4) Complete abatement of inlet pollution is reached when nitrogen concentration is less than 25 mg l⁻¹ (Fig. 5) which corresponds to a volumetric loading up to 0.6 kg N (NH₄⁺) m⁻³ day⁻¹.

Moreover, the experimental data were fitted to a model based on classical assumptions (Roques, 1980; Grady, 1982; Atkinson and Fowler, 1974; Grasmick et al., 1979; Grasmick, 1982; Harremoes, 1976, 1978; Jennings et al., 1976; Williamson and MacCarty, 1976); i.e. zero order intrinsic kinetics and diffusion transport (Table 5), and recently developed (Grasmick, 1982; Rodrigues et al., 1984). This model provides, particularly, a very easy method to check its own use—in reaction regime and in diffusion regime—when time spans or inlet concentration are changed; experimental results can indeed be plotted in such a way that straight lines are obtained (Table 6). Figures 6 and 7 show the data obtained with the counter-current nitrification reactor when respectively inlet concentration and time spans are varied. The plotted straight lines show that the overall reaction is zero order and that, therefore, the biofilm is fully penetrated. A critical time span θ_c and a critical inlet concentration C_c, for which complete conversion is achieved, are then calculated, θ_c is theoretically proportional to C₁ which is verified in Fig. 8. The straight line θ_c vs C₁ can then be used in reactor design.     

Microbial community distribution and activity dynamics of granular biomass in a CANON reactor

The application of microelectrodes to measure oxygen and nitrite concentrations inside granules operated at 20 °C in a CANON (Complete Autotrophic Nitrogen-removal Over Nitrite) reactor and the application of the FISH (Fluorescent In Situ Hybridization) technique to cryosectioned slices of these granules showed the presence of two differentiated zones inside of them: an external nitrification zone and an internal anammox zone. The FISH analysis of these layers allowed the identification of Nitrosomonas spp. and Candidatus Kuenenia Stutgartiensis as the main populations carrying out aerobic and anaerobic ammonia oxidation, respectively.Concentration microprofiles measured at different oxygen concentrations in the bulk liquid (from 1.5 to 35.2 mg O₂ L⁻¹) revealed that oxygen was consumed in a surface layer of 100-350 μm width. The obtained consumption rate of the most active layers was of 80 g O₂ (L_granule)⁻¹ d⁻¹. Anammox activity was registered between 400 and 1000 μm depth inside the granules. The nitrogen removal capacity of the studied sequencing batch reactor containing the granular biomass was of 0.5 g N L⁻¹ d⁻¹. This value is similar to the mean nitrogen removal rate obtained from calculations based on in- and outflow concentrations.Information obtained in the present work allowed the establishment of a simple control strategy based on the measurements of NH₄⁺ and NO₂⁻ in the bulk liquid and acting over the dissolved oxygen concentration in the bulk liquid and the hydraulic retention time of the reactor.     

Modeling the decay of ammonium oxidizing bacteria

A bench-scale sequencing batch reactor was used to study factors affecting the endogenous decay of the ammonium oxidizing biomass (AOB) in different operating conditions. AOB decay was very sensitive to oxygen concentration, and increased up to 0.4 d⁻¹ for oxygen concentration of 7 mg O₂ L⁻¹. The decay in anaerobic conditions was shown to be very low (0.03 d⁻¹) when compared to literature data.The effect of nitrite and nitrate on AOB decay was also studied. The correlation was quite weak suggesting that both nitrate and nitrite absence had little impact on decay which is contrary to what is typically assumed in some of the existing process models. A simple expression for the decay of AOB was proposed, calibrated and validated using the results of batch kinetic tests and of the continuous sequencing batch reactor monitoring.     

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.     

Operating characteristics of the aerated submerged fixed-film (ASFF) bioreactor

A multi-stage fixed-film reactor was developed in which a stationary submerged biofilm is attached to ceramic tiles under diffused aeration. Tracer studies revealed that the reactor's hydraulic regime is described by a CSTR-in-series model. Reactor performance at 20 °C was examined using sucrose wastewaters with organic strength up to 900 mg l⁻¹ COD, at hydraulic loadings up to 0.1 m³ m⁻²d⁻¹ and organic loadings up to 90 g CODm⁻² d⁻¹. The reactor demonstrated the capability of achieving 97% soluble COD removals at low loadings and exhibited efficient and stable performance at high hydraulic and organic loadings. Even at application rates near the rate-limiting mass loadings, there was only a 9% loss in efficiency. Reactor operation at high loadings appears to be advantageous since organic substrate removal rates and attached biomass per unit surface area increased with the increase in organic loading. This can be attributed to the good oxygen transfer and the considerable quantity and type of attached biomass attained. Staging of the reactor proved to be effective in eliminating short circuiting and damping excessive loadings, although the majority of COD removal occurs in the first stage which retains the greatest quantity of attached biomass. A good quality effluent was produced.     

Photocatalytic Destruction of Fulvic Acids by Various Oxidants in a Reactor with Immobilized TiO<Subscript>2</Subscript>

Comparison of the efficiency of photocatalytic oxidation of aqueous solution of fulvic acids (TOC₀—15.9–17.1 mg/dm³, pH0 6 ± 0.1) by oxygen of the air, hydrogen peroxide and ozone in a reactor containing a wide-porous ceramic block with immobilized TiO₂ with the variation of the concentration of H₂O₂, feed rate of O₃ and temperature showed advantages of photocatalytic ozonization and expediency of its use for deep destruction of natural organic substances in water. The maximum degree of destruction in photocatalytic systems O₂/TiO₂/UV, H₂O₂/TiO₂/UV and O₃/TiO₂/UV constituted respectively 41, 73 and 90% for TOC for 5, 4 and 3 h.     

Development of Biological Aerated Filters: A Review

Biological aerated filters are wastewater-treatment systems which contain support media for the development of a biofilm and provide oxygen at the base of the reactor for aerobic microbial processes. The origins of this type of filter date back to the early 1900s, and modern designs can provide a high level of treatment in small reactor 'footprints'.
This paper provides a review of the technology and development of biological aerated filters and submerged aerated filter systems.     

Impact of Hydrogen Peroxide on Photocatalytic Destruction of Anionic SAS in a Reactor with Immobilized TiO<Subscript>2</Subscript>

Using sodium dodecylbenzenesulfonate the article showed high efficiency of photocatalytic system H₂O₂/TiO₂/UV for deep destruction (~ 90% in terms of TOC) of anionic SAS in a aqueousmedium (C₀ = 50 mg/dm³, pH₀ 5.9) in a reactor containing wide–porous ceramic block with immobilized TiO₂ on its surface. The TiO₂ film for a long time preserved a stable photocatalytic activity     

Specific activity of nitrifying biofilm in water nitrification process

The effect of the accumulation of fixed biomass on the specific activity of nitrifying biofilm was studied in a continuous flow reactor. The specific activity of nitrifying biofilm was described by the specific removal rate of ammonium-N (q_obs). The observed relationship between q_obs and the film thickness was apparent to an inverse V-shaped curve. The maximum specific activity of biofilm was attained at a film thickness in the range 15–25 μm, at which a steady state was established in the liquid phase for different influent ammonium-N concentrations (S₀). Beyond such a range, the specific activity began to decline significantly with the additional accumulation of biofilm. It was demonstrated from both experimental and theoretical approaches that reduction in the specific activity of biofilm was closely related to the ratio of active biomass to the accumulation of inactive materials within the biofilm.     

Epuration hydrocarbonne en couche fluidisee triphasique etude experimentale et modelisationHydrocarbon removal in a three-phase fluidized experimental bed and modelling of the process

Biological treatment by immobilized cells on a submerged support allows important volume reduction of units owing to the high micro-organism concentration in the process. The efficiency of classical reactors, i.e. preoxygenated fixed bed, is, nevertheless, limited by oxygen supply to the reactive medium and the unit must be worked discontinuously because of the bed clogging.A 9.4 cm i.d. three-phase fluidized reactor has been tested in an attempt to solve these problems; the turbulence induced by air injection should remove the excess biomass. Step injections of synthetic sewage have been made for different values of the working parameters. Interesting efficiency results have been observed: elimination efficiency of 10 kg BOD₅ m⁻³ day⁻¹ without recycle, is independent of space-time over a wide range.Limitations of a three-phase fluidized reactor have also been found: insufficient oxygen transfer to the liquid phase due to rapid bubble coalescence is a consequence of fluidizing small particles and inefficient sloughing which allows the reactor to be segregated depending on biofilm thickness and, sometimes, clogged in the upper part of the column.A model based on previous work in fixed bed has been proposed. Interphase mass transfer and zero order reaction within the biofilm are taken into account and the liquid phase is assumed to be perfectly mixed. The two parameters of the model are a combination of the numbers of transfer units within the biofilm and through the boundary layer and of the number of reaction units in the biofilm. The limiting substrate may be oxygen, organic carbon or any other nutrient.Experimental efficiencies can be predicted by the model with 15% accuracy. Particles size distribution must be corrected with regard to segregation.Physicobiochemical assumptions can be used in the modelling of a reactor which would not be perfectly macromixed and could be basically used in a unified theory.     

Epuration hydrocarbonne en couche fluidisee triphasique etude experimentale et modelisation

Biological treatment by immobilized cells on a submerged support allows important volume reduction of units owing to the high micro-organism concentration in the process. The efficiency of classical reactors, i.e. preoxygenated fixed bed, is, nevertheless, limited by oxygen supply to the reactive medium and the unit must be worked discontinuously because of the bed clogging.A 9.4 cm i.d. three-phase fluidized reactor has been tested in an attempt to solve these problems; the turbulence induced by air injection should remove the excess biomass. Step injections of synthetic sewage have been made for different values of the working parameters. Interesting efficiency results have been observed: elimination efficiency of 10 kg BOD₅ m^?3 day^?1 without recycle, is independent of space-time over a wide range.Limitations of a three-phase fluidized reactor have also been found: insufficient oxygen transfer to the liquid phase due to rapid bubble coalescence is a consequence of fluidizing small particles and inefficient sloughing which allows the reactor to be segregated depending on biofilm thickness and, sometimes, clogged in the upper part of the column.A model based on previous work in fixed bed has been proposed. Interphase mass transfer and zero order reaction within the biofilm are taken into account and the liquid phase is assumed to be perfectly mixed. The two parameters of the model are a combination of the numbers of transfer units within the biofilm and through the boundary layer and of the number of reaction units in the biofilm. The limiting substrate may be oxygen, organic carbon or any other nutrient.Experimental efficiencies can be predicted by the model with 15% accuracy. Particles size distribution must be corrected with regard to segregation.Physicobiochemical assumptions can be used in the modelling of a reactor which would not be perfectly macromixed and could be basically used in a unified theory.     

Design parameters for sludge reduction in an aquatic worm reactor

Reduction and compaction of biological waste sludge from waste water treatment plants (WWTPs) can be achieved with the aquatic worm Lumbriculus variegatus. In our reactor concept for a worm reactor, the worms are immobilised in a carrier material. The size of a worm reactor will therefore mainly be determined by the sludge consumption rate per unit of surface area. This design parameter was determined in sequencing batch experiments using sludge from a municipal WWTP. Long-term experiments using carrier materials with 300 and 350 μm mesh sizes showed surface specific consumption rates of 45 and 58 g TSS/(m² d), respectively. Using a 350 μm mesh will therefore result in a 29% smaller reactor compared to using a 300 μm mesh. Large differences in consumption rates were found between different sludge types, although it was not clear what caused these differences. Worm biomass growth and decay rate were determined in sequencing batch experiments. The decay rate of 0.023 d⁻¹ for worms in a carrier material was considerably higher than the decay rate of 0.018 d⁻¹ for free worms. As a result, the net worm biomass growth rate for free worms of 0.026 d⁻¹ was much higher than the 0.009-0.011 d⁻¹ for immobilised worms. Finally, the specific oxygen uptake rate of the worms was determined at 4.9 mg O₂/(g ww d), which needs to be supplied to the worms by aeration of the water compartment in the worm reactor.     

Preliminary trial on degradation of waste activated sludge and simultaneous hydrogen production in a newly-developed solar photocatalytic reactor with AgX/TiO2-coated glass tubes

A solar fluidized tubular photocatalytic reactor (SFTPR) with simple and efficient light collector was developed to degrade waste activated sludge (WAS) and simultaneously produce hydrogen. The photocatalyst was a TiO₂ film doped by silver and silver compounds (AgX). The synthesized photocatalyst, AgX/TiO₂, exhibited higher photocatalytic activity than TiO₂ (99.5% and 30.6% of methyl orange removal, respectively). The installation of light collector could increase light intensity by 26%. For WAS treatment using the SFTPR, 69.1% of chemical oxygen demand (COD) removal and 7866.7 μmol H₂/l-sludge of hydrogen production were achieved after solar photocatalysis for 72 h. The SFTPR could be a promising photocatalysis reactor to effectively degrade WAS with simultaneous hydrogen production. The results can also provide a useful base and reference for the application of photocatalysis on WAS degradation in practice.     

A chemically enhanced biological process for lowering operative costs and solid residues of industrial recalcitrant wastewater treatment

An innovative process based on ozone-enhanced biological degradation, carried out in an aerobic granular biomass system (SBBGR - Sequencing Batch Biofilter Granular Reactor), was tested at pilot scale for tannery wastewater treatment chosen as representative of industrial recalcitrant wastewater. The results have shown that the process was able to meet the current discharge limits when the biologically treated wastewater was recirculated through an adjacent reactor where a specific ozone dose of 120 mg O₃/L_influent was used. The benefits produced by using ozone were appreciable even visually since the final effluent of the process looked like tap water. In comparison with the conventional treatment, the proposed process was able to reduce the sludge production by 25-30 times and to save 60% of operating costs.Molecular in situ detection methods were employed in combination with the traditional measurements (oxygen uptake rate, total protein content, extracellular polymeric substances and hydrophobicity) to evaluate microbial activity and composition, and the structure of the biomass. A stable presence of active bacterial populations was observed in the biomass with the simultaneous occurrence of distinctive functional microbial groups involved in carbon, nitrogen and sulphate removal under different reaction environments established within the large microbial aggregates. The structure and activity of the biomass were not affected by the use of ozone.