Automatisation et comparaison de différentes méthodes respirométriques d'estimation rapide de la DBO

II est bien connu que la DBO peut étre mesurée par des méthodes respiromédriques. Les manipulations sont ainsi rendues plus aisées mais la durée de la mesure reste inchangée. La demande biologique en oxygène à court terme (DBOACT) a été proposée pour évaluer rapidement la DBO. Habituellement, ces mesures étaient réalisées dans un respiromètre fermé avec une boue acclimatée et en état de respiration endogène. Récemment on a suggéré de travailler avec un respiromètre ouvert, aéré continuellement durant le test. Nous avons réalisé un tel appareil avec une acquisition et un traitement automatique des données, en utilisant un micro-ordinateur. De cette façon, il est facile de tester différentes méthodes (intégration de la courbe en sac, hauteur de pic, comparaison à des étalons, usage d'étalons internes) pour évaluer la DBO. Nous avons également examiné l'influence du type de substrat, de l'âge et des caractéristiques des boues. Notre conclusion est que aucune des méthodes testées ne fournit une détermination précise de la DBO5 pour des substrats complexes. La méthode reste utile pour contrôler la variabilité de l'influent dans une station d'épuration, lorsque la biomasse est acclimatée au substrat et qu'on ne désire pas une mesure très précise.The usual way of measuring BOD is the dilution method. The consumption of oxygen is measured in the dark at 20 °C during 5 days. Manometric methods were proposed already some decades ago. Their principle is that every molecule of oxygen consumed la transformed into CO2 which is absorbed in a solution of KOH, creating a pressure variation in the bottle. From this pressure variation the BOD can be calculated. By this way experiments were made easier but the duration of the measure remained unchanged. Other respirometric methods were also proposed, especially Short Term Biological Oxygen Demand (STBOD) to evaluate BOD rapidly. Usually such determinations were done in closed respirometers with acclimated sludge under endogeneous respiration condition. Recently, it was suggested to proceed in an open respirometer aerated continuously during the test. We set up this type of respirometer with acquisition and automatic processing of the data, using a microcomputer. In this way it was easy to test different procedures. Among these procedures we tested :- the method of integration of curve in sack-from,- the method of peak level,- the method of comparison to standards,- the method of internal standards.The principles of these methods are given in more detail in the text. We examined the influence of the type of substrate, of the type of biomass used and of the sludge retention time on the results. The substrates tested were :- glucose,- domestic waste water with and without detergent,- diluted eggs,- diluted beer,- effluents from the paper industry.Three different types of biomass and these sludge retention times (fresh, 5 days and 20 days) were used. Automatisation of the test and automatic processing of the data were carried out in basic language with an « Apple II » microcomputer.The test lasted between 37' and 3 hours 10', depending on the conditions (substrate, concentration, type of sludge,...)Analysis of the results were computerized by the Analysis of Variance (ANO-VA) method and results are lasted in 3 tables.From this study we can conclude that STOD methods have some advantages :- they are much faster than the classical method,- they can be easily automatized,- they are cheap,- oxygen is really consumed by biological processes.For simple substrates these methods can lead to good results but for complex substrates reproductibility and precision are rather poor. Among the methods tested the only acceptable one seems to be the integration of the curve in sack-form. Lack of reproductibility appears to be intrinsic to the method.Some possible improvements are presented, such as washing the activated sludge between two experiments, but are not very practical.Despite these limitations the method can be useful to control the variability of influent in a sewage treatment plant. In such a case, the biomass is acclimated to the substrate and variations of influent BOD can be measured

Traitement des eaux usées domestiques par un chenal algal à haut rendement (CAHR) agité par air lift sous climat semi-aride

De nombreux travaux de recherche ont montré l’efficacité des systèmes de traitement extensifs tels que le lagunage naturel et leur adaptabilité aux conditions climatiques et socio-économiques pour des pays comme le Maroc. Le lagunage à haut rendement est une variante de lagunage naturel qui a pu démontrer ses meilleurs performances épuratoires et son efficacité.Le but de la présente étude est : i) de déterminer les différents paramètres hydrauliques d’un chenal algal pilote fonctionnant avec un air lift; ii) d’étudier son fonctionnement et d’évaluer ses performances épuratoires (physicochimiques et bactériologiques), sous les conditions climatiques semi-arides de la ville de Marrakech. Il faut signaler que ce système d’agitation par air lift sera testé pour la première fois au Maroc.L’étude hydrodynamique a pu démontrer que les vitesses d’écoulement calculées pour le pilote fonctionnant avec un air lift rentrent dans la gamme des vitesses d’écoulement recommandées pour ce genre de système et avec d’autres systèmes d’agitation comme la roue à aubes qui est la plus souvent utilisée dans ce genre d’installation. Également, la capacité d’oxygénation du chenal est plus importante.L’étude physicochimique a porté sur le suivi des paramètres de charge organique (DCO et DBO5) et de nutriments (azote et phosphore), tout en utilisant des méthodes d’analyse standards. En matière de DBO5, la filière élimine environ 44 %, alors que les teneurs en DCO brute de l’effluent traité restent élevées. Dans ce genre de système (CAHR), on assiste à une transformation de la matière organique entrante sous forme de biomasse algale, ce qui explique les faibles performances du chenal en matière de DCO brute. Contrairement à la charge organique, le chenal a montré une efficacité remarquable dans l’élimination des nutriments (77 % pour PO4 et 90 % pour NH4).Arid and semi-arid climate areas such as Morocco are affected by water shortages, especially shortages in the water intended for irrigation. In this particular climatic context, the reuse of treated wastewater may partly contribute to solving this problem. Currently, a number of studies have shown the effectiveness of extensive treatment systems and their adaptability to Moroccan socio-economic conditions. The high rate algal pond (HRAP) is an efficient alternative to natural lagoons. The objective of this study was (i) to determine the various hydraulic parameters of a HRAP equipped with an air-lift agitation system, and (ii) to study its operation and to evaluate its performance (physico-chemical and bacteriological) under the semi-arid climatic conditions of Marrakech. The hydrodynamic study showed that the flow rates calculated for the pilot HRAP equipped with the air-lift met the flow range rates recommended for this installation and those of other agitation systems often used, such as the paddlewheel. The physico-chemical study related to the monitoring of organic load parameters (Chemical Oxygen Demand, COD; Biochemical Oxygen Demand, BOD5) and nutrients (nitrogen and phosphorus), was done in accordance to standard methods. For BOD5, the system eliminated approximately 44%, whereas total COD remained high. In the HRAP system, the transformation of the incoming organic matter into algal biomass was expected, and explains the weak performances of the HRAP with respect to total COD. In contrast to the results for the organic load, the pond system showed a remarkable efficiency for the elimination of nutrients (77% for PO4 and 90% for NH4)

MODELLING OF BACTERIAL SULPHATE REDUCTION IN ANAEROBIC PONDS : KINETIC INVESTIGATIONS

peer reviewedaudience: researcher, professional, student, popularization, otherThe aim of the study was first to develop a simple and practical model of anaerobic digestion including sulphate-reduction in anaerobic ponds. The basic microbiology of our model consists of three steps, namely, acidogenesis, methanogenesis, and sulphate reduction. This model includes multiple reaction stoichiometry and substrate utilization kinetics. The second aim was to determine some kinetic parameters associated with this model. The values of these parameters for sulfidogenic bacteria are used in the anaerobic pond model to describe the sulphate reduction processes and to evaluate the risk of odour generation

Green 4 Indoor - Wallonia Présentation AG SPHERES 18/12/2023

Présentation des résultats de recherche du projet G4i-W sur l'étude d'impacts en milieu intérieur des murs verts et sur la réutilisation des eaux grisesGreen 4 Indoor Walloni

Modeling of partial nitrification and denitrification in an SBR for leachate treatment without carbon addition

A process of partial nitrification and denitrification in a sequencing batch reactor (SBR) treating leachate was simulated by applying a modified version of activated sludge model no. 3 (ASM3), named ASM3_2step. This model modifies the ASM3 model by separating nitrification and denitrification into two steps with nitrite as an intermediate substrate. Three periods, including long term period, steady state and cycle evolution, were used for calibration. Three main processes were observed, including biomass production, nitrification (focusing on nitrite accumulation) and denitrification. The kinetic and stoichiometric parameters (μA\_NH, YA\_NH, YA_NO2, YH_O2, b A, KA\_NH), were determined from biokinetic and respirometry tests. Some of the default values of kinetic and stoichiometric parameters available in the ASM3 model and in the literature were kept constant, while some others were adjusted step by step until observed state variables fit with experimental data. The maximum specific growth rate of nitrite oxidizing bacteria (0.108 day−1) (simulated by the model) and that of ammonium oxidizing bacteria (0.61 day−1) (from biokinetic tests) are the parameters which have the highest influence on the nitrite accumulation, even more than oxygen supply intensity or Kla value. Other important parameters were KAO\_NH and KAO_NO2, calibrated at the values of 1.37 and 1.59 mg O2/L, respectively. The modified model and values of the kinetic and stoichiometric parameters obtained from the modeling process will be used for optimization of the partial nitrification in the next stud

Development of a SBR bench-scale to optimize the partial nitrification process in landfill laechate treatment and its possible application in Vietnam.

Landfill leachate treatment is a major issue in many developing countries including Vietnam. Leachates are characterised by very high nitrogen concentrations, especially ammonium, needing an appropriate treatment technology. Conventional treatment technology has some drawbacks: mostly its high costs and problems to meet discharged standards requirements. This study applies a more recent approach for nitrogen removal, which is known as partial nitrification, by using a sequencing batch reactor (Bernet et al., 2005) technique. For the first step, the experiments were done with Belgian leachates. Based on mathematical models derived from generally accepted ASM Model, specific growth rates of biomass (μ(T)) found is 0.48 (d-1), 0.39 (d-1), 1.56 (d-1) and 0.82 (d-1) for ammonium nitrifiers, nitrite nitrifiers, nitrite denitrifiers and nitrate denitrifiers respectively. Concentration of the active part of these four kinds of bacteria is estimated of 22.3 mg/L, 12.4 mg/L, 464 mg/L and 12.3 mg/L. Maintaining dissolved Oxygen concentrations in the range 0.8 to 2.1 mgO2/L, with typical value around 1.5 mg/L, the system yields nitrite accumulation (preliminary step of partial nitrification/denitrification). SBR cycle was changed from 4 hours/4 hours of aeration/mixing in turn to 5 hours/3 hours and then 6 hours/2 hours. The last cycle has shown the best partial nitrification capacity of the SBR (a nitrite accumulation of 89 %) but not yet yielding a 50/50 ratio of ammonium/nitrite at the end of nitrification process. However, a well managed SHARON process will be processed in the next step of the study to obtain higher nitrogen removal efficiency and the expected ammonium/nitrite ratio. It has also been shown that free ammoniac concentration affects the nitrite/(nitrite + nitrate) ratio at the end of aeration phase

A system for on-site performance evaluation of small wastewater treatment plants according to the European procedure

The new European standard project for performance evaluation of on-site systems (prEN 12566-3) provides a test procedure at user sites for individual on-site wastewater treatment. For each system, two plants of the same size have to be tested, one operating at 50% and the second one with a load greater than 75% of the nominal capacity. The test duration is one year and several stress tests are included in the program (holidays, bath water discharge and power breakdown). Flow based composite 24 h samples, on the influent and the effluent have to be used, with 30 day intervals for influent and 15 days for effluent. On each sample, the following measurements have to be done: BOD5 or COD, suspended solids, temperature, power consumption, daily flow. It appears that very few systems have been reported in the literature to follow up such facilities, especially describing how to sample at the inlet of on-site individual equipment. In order to obtain representative samples at the inlet and at the outlet of those on-site treatment systems, we have designed an original mobile sampler system. The whole system ensures the flow measurement and flow based sampling as well. In this paper, we present the different parts of the sampling system (pump, flowmeters, …), its validation and the results obtained at 5 user sites during the first 9 month period. Preliminary results are very interesting because they clearly demonstrate the need for an efficient on-site control of those user sites and for better legislation in this domain.</jats:p

Contribution of floating macrophytes (Lemna sp.) to pond modelization

The objective of the present study was to develop a methodology for the quantification of the growth rate of Lemnaceae biomass by digital image analysis. The effect of biomass surface coverage on the oxygen transfer coefficient (Kla) was also quantified. Contribution of Lemnaceae to oxygen balance was evaluated by closed respirometry. Monod-like equations could be derived from growth rate coefficients in various experimental conditions. This opens the way to a deterministic model of Lemnaceae ponds where uptake of nitrogen and phosphorus (even heavy metals) can be calculated.</jats:p

Nitrogen removal during leachate treatment: comparison of simple and sophisticated systems

Membrane bioreactors (MBR) have become common in treating municipal wastewaters. Applied to leachates treatment MBR were also successful with pilot scale experiments and full-scale facilities as well. We succeeded previously in designing an efficient nitrificationÐdenitrification process with an ethylene glycol byproduct as carbon source for denitrification. Moreover, an unexpectedly high inert COD removal efficiency was also observed in the full-scale MBR facility thereby making it possible to increase the operating time of the final GAC (Granulated Activated Carbon) adsorber. Since MBR are very sophisticated systems. Simpler and “lower” cost systems can also be considered. For example it is possible to nitrify leachates from sanitary landfill using a simple infiltrationÐpercolation technique with a low energy cost. To validate previously published laboratory experiments, a semi industrial-scale pilot installation was installed at the Montzen landfill site (Belgium). The process is based on infiltrationÐpercolation through a granular bed. This well known process was modified to increase the load, notably by changing the support medium, adding an electric fan that is run intermittently and maintaining temperatures greater than 15°C. The new material is a type of granular calcium carbonate with a large specific surface area. These technical improvements enabled the system to nitrify up to 0.4 kg NH4+-N/m3 of reactor bed per day at a hydraulic load of 0.35 m.d-1, with an ammonia removal rate in the range of 80 to 95%. Despite the high ammonia nitrogen inlet concentrations, this system exhibits remarkable nitrification efficiency. Moreover, these performances are achieved in a batch mode system without recirculation or dilution processes. If complete nitrification is needed, it can be obtained in a second in series of bioreactors. The system can be classified as a low cost process. An international patent is pending. Possible performances of those systems were compared with the usual methods for leachates treatment.</jats:p