Stimulation de la methanisation psychrophile par un bioactivateur pour fosse septique

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Título:
Stimulation de la methanisation psychrophile par un bioactivateur pour fosse septique
Autor: Maunoir, S ; Philip, H ; Rambaud, A
Assuntos: acetic acid ; activateurs biologiques ; acétate ; anaerobic digestion ; argile ; biological activator ; clays ; digestion anaérobie ; Eaux usées ; Eaux usées de toute autre origine ; fosse septique ; methane ; methanogenesis ; méthane ; méthanogénèse ; Pollution ; psychrophile ; psychrophilic ; Sciences appliquees ; Sciences exactes et technologie ; septic tank ; Traitement et pollution des eaux
É parte de: Water research (Oxford), 1990, Vol.24 (2), p.195-205
Descrição: L'étude met en évidence l'influence d'un activateur biologique pour fosse septique constitué de microparticule minérales argileuses sur la méthanisation á 20°C d'acide acétique (2 g/l). Les essais sont réalisés dans des flacons fermés type penicilline. L`inoculum provient d'une fosse septique. Il est introduit dans les flacons contenant un milieu de culture de base pour bactéries méthanogènes auquel est ajouté le substrat étudié et les microparticules minérales. Les descripteurs physico-chimiques utilisés pour suivre l'évolution des cultures au cours du temps sont: la DCO des matières solubles, la concentration en acétate, le pH et la production de gaz. Les différents essais ont permis de montrer que par rapport à un témoin les microparticules minérales utilisées à raison de 4 g/l ont accéléré la biodégradation de l'acide acétique et favorisé la production de méthane. Septic tanks ensure the pre-treatment of domestic wastewater by fulfilling two functions: settling of solid matter and liquefaction of the sludges by anaerobic digestion. Biological processes take place slowly because of the substrate composition (hardly biodegradable) and the operating conditions: low temperatures and no agitation. The system is thus similar to natural anoxic ecosystems. Various commercial products are known to improve anaerobic digestion of sludges. These biological activators are solid support which may be combined with freeze-dried bacteria, enzymes and/or nutritive substances. Philip et al. (1984) showed that an industrial product composed only of argillaceous microparticles (kaolinite) can effectively stimulate hydrolysis of sludge and reduce its volume. The work described here shows the effects of this product (4 g/l) on the methanation of acetic acid (2 g/l). Various tests were carried out using a batch method at 20°C with serum bottles (Miller and Wolin, 1974) containing a specific medium for the growth of anaerobic microorganisms (Touzel and Albagnac, 1983). Bottles with and without (control bottles, T1) microparticles were seeded under anaerobiosis using a 1% inoculum from a septic tank. Four physico-chemical variables were monitored as a function of time: COD of dissolved matter, volatile fatty acid concentration, biogas production and pH. With these techniques, bottles are opened at each date of analysis. The differences of evolution observed between the control (TI) and the system with mineral microparticles could thus not be attributed to random. However, as bottles could evolve differently, it is necessary to validate results with statistic tests. One bioassay allows the study of significant thresholds of observed differences (pair of means with the Wilcoxon test) and the study of results variability (hierarchized variance analysis—see Table 1—with Nested Anova software as described by Sokal and Rohlf, 1981). A surface pH of 6.9 and a redox potential of −500 mV in distilled water were found to be the most interesting results of the physico-chemical analysis of the mineral microparticles (Tables 2 and 3). The first preliminary assay of acetate methanation was run at 35°C. It shows the typical evolution of a batch volatile acids degradation (Roque, 1980): decrease of COD [Fig. 1(a)], increase of pH [Fig. 1(b)] and biogas production [Fig. 1(c)]. Also, the procedure is suitable for running a methanation on a small volume (50 ml) with a 1% inoculum. In addition, it shows the influence of the microparticles since in 11 days the maximum biodegradation rate is about 87% when it is about 26% in the control [Fig. 1(a)]. The second preliminary assay at 20°C shows that the endogenic digestion of the inoculum does not interfere with results and confirms the stimulating effect of the microparticles. Indeed, Fig. 2(a), (b), (c) and (d) shows the fluctuations of the inoculum characteristics: the maximum acetate concentration (80 mg/l) and the maximum methane production (50 ml/l) could be neglected. In this assay the COD decrease is up to 42% with the microparticles and up to 21% in control T1 [Fig. 3(a)]. Biodegradation of acetate was 54 and 17% for microparticles and T1 with a degradation rate 3 times higher for the series containing the microparticles (78 in comparison to 21 mg CH 3COOH/l/j) [Fig. 3(b)]. Methane production indicates that the maximum biodegradation rate (% of theoretical methane) is about 60 and 19% with and without microparticles [Fig. 3(c)]. Gas production shows also that the microparticles reduce the time of latency. pH fluctuates between 6.4 and 7.1 [Fig. 3(d)]. In a third test three bioassays (a, b and c) with three different inocula are realized simultaneously to evaluate the reproductibility of the methanogenesis and its stimulation in these experimental conditions [Fig. 4(a), (b), (c) and (d)]. Table 4 gives the anaerobic biodegradation parameters. We note that, according to the inoculum, acetate methanation takes place differently but that the stimulation remains patent. This stimulation itself is different according to the inoculum. In “a” we note mainly a reduced time of latency with the microparticles. In “b” this shorter time of latency is joined with a change of biodegradation rate. In “c” the methanation appears with microparticles only. A fourth test is realized in order to have a statistical validation of the stimulation. Three series of bottles with microparticles and three control series are monitored. Table 5 shows the results of methane production (mean ± SE) of triplicates) obtained after an incubation period of 44 and 60 days. The Wilcoxon test indicates that the differences between the test and the control bottles are significant ( P ≤ 2.5%). Table 6 shows the result (mean ± SE) of physico-chemical analysis of bottles with microparticles at the 44th day. These results are used to achieve a hierarchized variance analysis (Table 7). It is shown that the results variability is mainly due to sampling of septic tank sludges and that measurements are reliable. The conclusion of the study is that argillaceous microparticles stimulated batch biomethanation of acetic acid at 20°C. This effect was on the reduced time of latency and on the degradation rates.
Editor: Oxford: Elsevier Ltd
Idioma: Francês

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Stimulation de la methanisation psychrophile par un bioactivateur pour fosse septique

Maunoir, S ; Philip, H ; Rambaud, A

Oxford: Elsevier Ltd

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