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Degradazione di microinquinanti organici nel processo di digestione anaerobica di fanghi contaminati
No full textDecontamination and valorization of an actual contaminated activated sludge through anaerobic digestion
No full textOlive mill wastewaters anaerobid digestion in mesophilic and thermophilic batch packed-bed biofilm reactors for the accumulation of volatile fatty acids as monomers employed in the biological production of polyhydroxyalkanoates
No full textPolyhydroxyalkanoates (PHAs) are bioplastic whose properties and applicability are quite similar to these of polypropylene. In order to make PHA industrial production feasible, new low-cost processes have to be developed. In this research, an innovative process for PHA production is being studied. This process consists of three stages. In the first stage (anaerobic conditions), the acidogenic fermentation transforms an organic substrate into a mixture of volatile fatty acids (VFAs), the most suitable substrate for PHA production. In the second stage (aerobic conditions), the effluent of the first stage is fed to a Sequencing Batch Reactor (SBR), where the periodic feeding (“feast and famine” conditions) enriches the mixed microbial culture of the PHA-producing microorganisms. In order to optimize PHA productivity, this stage is operated at the highest organic load allowed from the need of maintain strong selective pressure on the sludge. In the third (batch) stage (aerobic conditions), the excess sludge from the second stage is fed with the effluent of acidogenic fermentation in order to increase its PHA content up to the maximum value. Then this PHA-rich sludge flows to the downstream processing of PHA.
Regarding the choice of the organic substrate to be used as feedstock for the process, olive mill wastewaters (OMWs) are particularly interesting. OMWs are the liquid effluent resulting from olive oil producing processes. Due to their high COD load, they are generally considered effluents of high environmental concern. The possibility of developing a biotechnological process fed with OMWs and addressed to the production of VFAs was explored in the present research. To this aim, Four packed-bed biofilm reactors (PBBRs) were employed in batch conditions in the anaerobic acidogenic digestion of an OMW. The effect on the process of the packing material and of the temperature were studied by filling two of the PBBRs with granular activated carbon (GAC) and the other two with ceramic cubes (VS), and by thermostating one GAC- and one VS-PBBR at 35°C and the other two at 55°C. The reactors were inoculated with an acclimated OMW-degrading consortium employed in a previous research (Bertin et al. 2004). Two one-month batch experiments were carried out by feeding the reactors with a diluted and amended OMW. For both experiments, the higher VFA production was observed in the PBBR filled with SV and operating at 35°C, where more then 3 g/l of VFA accumulated, this corresponding to a conversion of about the 60% of the initial COD. Acetic acid was the main component of the VFA mixtures collected from all the PBBRs. Significant concentrations of both propionic and butirric acid were also observed.
Bertin L.; Colao M.C.; Ruzzi M.; Fava F. "Technological features and molecular microbial characterisation of a granular activated carbon packed-bed biofilm reactor capable of an effective anaerobic digestion of olive mill wastewaters." FEMS MICROBIOLOGY ECOLOGY, 48:413-423 (2004
ANAEROBIC DIGESTION AS A PROCESS FOR THE DECONTAMINATION AND VALORIZATION OF ACTIVATED SLUDGES RESULTING FROM PLANTS TREATING WASTEWATERS CONTAMINATED BY XENOBIOTIC COMPOUNDS
No full textXenobiotic compounds accumulate in sewage sludges resulting from wastewater treatment plants serving both civil and industrial areas. The opportunity to use anaerobic digestion for the decontamination and beneficial disposal of the contaminated sludge from the Fusina’s wastewater treatment plant (Italy) was investigated in mesophilic and thermophilic microcosms monitored through an integrated chemical, microbiological and ecotoxicological procedure. The 10 months sludge incubation at 35°C resulted in an extensive production of a methane-rich biogas, a marked reduction of pathogenic cultivable bacteria and, importantly, a marked biodegradation of the sludge-carried organic pollutants, including some polychlorinated biphenyls and polycyclic aromatic hydrocarbons, to which corresponded a relevant sludge detoxification. The sludge decontamination seemed strictly correlated to the activity of methanogenic bacteria and was not affected by the presence of exogenous yeast extract or molasses. Lower sludge bioremediation and biomethanisation extents were observed under thermophilic conditions
Anaerobic digestion of sludges coming from biological wastewater treatment plants
No full textOrganic pollutants such as PAHs, PCBs and pesticides tend to accumulate in the primary and secondary sludges of biological plants treating domestic and industrial wastewaters. Thus, those sludges have to be submitted to a dedicated treatment, that generally consists in their thermal destruction. Anaerobic digestion could represent an alternative technology for the decontamination of such sludges. In fact, it can mediate the biodegradation of the occurring contaminants, the depletion of pathogenic microrganisms and the production of a biogas with a high content of methane. The effects of the anaerobic digestion (both under mesophilic and thermophilic conditions) on the final decontamination and disinfection of a sludge coming from a domestic water treatment plant and spiked with a mix of xenobiotics were investigated along with the possibility of enhancing the process by adding yeast extract. Methane production and xenobiotic removal were more efficient under mesophilic conditions while a complete disinfection of the sludge was achieved at 55°C. Yeast extract allowed to obtain better performances under mesophilic conditions both in terms of sludge decontamination and disinfection
Fate of xenobiotic pollutants occurring in a sewage sludge under aerobic and anaerobic conditions
No full textDecontamination and valorization of sludges deriving from biological wastewater treatment plants through anaerobic digestion
No full textOrganic pollutants such as PAHs, PCBs and pesticides tend to accumulate in the primary and secondary sludges of biological plants treating domestic and industrial wastewaters. Thus, those sludges have to be submitted to a dedicated treatment, that generally consists in their thermal destruction. Anaerobic digestion could represent an alternative technology for the disposal of such sludges, as it can mediate both their decontamination and their valorization, through the production of a biogas with a high content of methane.
In this study, two sludges coming from domestic water treatment plants were spiked with PCBs or with a mix of PAHs and chlorinated aromatic compounds and employed in the development of anaerobic microcosms. The effects of the anaerobic digestion on the sludges were evaluated in terms of methane production, biodegradation of the occurring contaminants and depletion of pathogenic microrganisms, both in mesophilic or thermophilic conditions. The contribute to the digestive process of the sole fermentative eubacteria or of the sole methanogenic and sulfate-reducing bacteria, along with the possibility of enhancing its performances by stimulating the indigenous anaerobic consortium with yeast extract, were also determined. Methane production and xenobiotic removal were more efficient under mesophilic conditions, while a complete disinfection of the sludge was achieved at 55°C. Yeast extract allowed to obtain better performances under mesophilic conditions both in terms of sludge decontamination and disinfection. All the selected microbial population seemed to be involved in the biodegradation of the contaminants
Production of polyhydroxyalkanoates through an integrated anaerobic-aerobic process fed with olive mill wastewaters as a renewable resource
No full textPolyhydroxyalkanoates (PHAs) are biopolimers whose properties and applicability are quite similar to these of polypropylene. However, their production on the large scale is actually too expansive. In this research, an innovative biotechnological low-cost PHA producing process, consisting of three stages, is being studied. The aim of the first anaerobic stage is to obtain an effluent rich in volatile fatty acids (VFAs), which represents the substrate for microbial PHA production, through the acidogenic fermentation of olive mill wastewaters (OMWs), which are the liquid wastes of olive oil producing processes and are generally considered effluents of high environmental concern. In the second aerobic stage, the anaerobic effluent is fed to a Sequencing Batch Reactor (SBR) where microbial populations able to transform VFAs in PHAs are selected. In the third aerobic stage, the excess sludge from the second stage is fed with the effluent of the acidogenic fermentation in order to increase its PHA content up to the maximum value. Packed-bed biofilm reactor technology was chosen to develop the anaerobic first stage. Packing material and temperature parameters were studied by developing 4 identically-configured PBBRs: two of them were filled with granular activated carbon (GAC), the other two with ceramic cubes (VS); one reactor for each material was thermostated at 35°C, the other two at 55°C. 2 one-month batch experiments were previously carried out by feeding the reactors with a diluted and amended OMW, so that the initial waste COD was 6.33 g/l. The higher VFA production was observed within the second experiment in the SVS-PBBR operating at 35°C, where a conversion of the initial COD in VFAs of about the 60% was observed. Acetic acid was the main component of the VFA mixtures collected from all the PBBRs. Significant concentrations of both propionic and butirric acid were also observed.. Then, the PBBRs were forced to operate in continuous conditions and fed with an organic load of about 8 g/l/d. GAC-PBBR operating at 35°C gave rise to the highest VFA production, even if the COD conversion in VFAs was lower than the one reported above for batch experiments, due to a significant methanogenic activity. Higher organic loads will be fed to the 4 PBBRs in order to optimize the OMW acidogenic fermentation stage. The second and third stages of the process were studied in aerobic sequencing batch reactors, fed with a synthetic mixture of acetic (85% on a COD basis) and propionic (15 %) acids. In particular the effect of the pH in the second stage was studied. Three runs were carried out at three different pH values: 7.5, 8.5 and 9.5. The highest substrate removal rates and polymer production rates were obtained at pH 8.5. Under these conditions, PHAs were produced at a rate of approximately 350 mgCOD/gCOD/h, with a storage yield of 45% (as COD). The produced polymer was a P(HB-HV) co-polymer, with 13% (mol/mol) HV content
REMOVAL OF ORGANIC XENOBIOTICS IN ACTIVATED SLUDGES UNDER AEROBIC CONDITIONS AND ANAEROBIC DIGESTION OF THE ADSORBED SPECIES
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