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Respirometry, chemical and microbial community analysis of solid waste aerobic biodegradation

Abstract : Understanding the metabolic process of organic matter aerobic biodegradation is of upmost importance as a first step to improve solid waste composting in terms of treatment duration, environmental impacts... In standardized conditions, the effectiveness of solid waste biodegradation depends principally on the organic matter content and composition of the initial waste as well as the activity of the microorganisms provided by the waste. In this study, we analysed the kinetics of aerobic biodegradation of two different solid wastes by a combination of respirometry, organic matter fractionation and analysis, and microbial community analysis. Methodology. The two studied wastes were slaughterhouse wastewater treatment sludge and a mechanically sorted household waste (exit from sieve 50 mm, MSW). For each waste, eleven biological aerobic reactors (10L) were monitored and stopped at different times (between 0h to 400h) to analyse the waste biodegradation kinetics. Each trial was run with constant aeration, temperature (40°C) and humidity of waste (50-55%). The oxygen consumption was measured online to analyse the microorganism's respiratory activity. The soluble and non-soluble organic matter content of the stopped reactors was analysed by global physico-chemical analysis (COD, NTK) and by HPLC-SEC coupled with UV and DEDL to determine the molecular weight of polymeric substances and carbohydrates. Microbial activity was monitored by dehydrogenase, urease and β-glucosidase enzymatic activities. Microbial growth was quantified by real time PCR targeting fungal and bacterial ribosomal RNA genes (rDNA). Results and discussion. As expected, both wastes underwent very different aerobic degradation kinetics as could be seen on their respirometric profiles. For sewage sludge, the oxygen consumption rate increased immediately from the beginning of the experiment to reach a maximum of 223 mmol O2.h-1. kg-1 of dry matter (DM) at 7.6 hours and then decreased exponentially until about 10 mmol O2. h-1.kg-1 of DM after 255 h. For the MSW however, a 10 h lag phase was first observed, followed by a short increase of the oxygen consumption rate up to 10 mmol O2.h-1.kg-1 of DM at 24 h. Oxygen consumption rate remained at this level for about 45 h and then increased again to reach a maximum of 76.5 mmol O2.h-1.kg-1 of DM at 200 h. It then decreased exponentially down to about 7 mmol O2.h-1.kg-1 of DM after 450 h. Physico-chemical and microbiological analysis showed that both wastes initial composition differed greatly. While both wastes contained about the same amount of insoluble COD, the sludge contained twice less soluble COD than MSW but twice more soluble and insoluble NTK. This observation was correlated with HPLC analysis that revealed a higher amino acid content of the sludge. Microbial analysis showed that the initial sludge contained about 3.6 107 bacteria and 6.5 102 fungi per mg of organic matter while MSW contained only 0.3 107 bacteria but 31 102 fungi per mg of organic matter. Coupling the characterization of the polymeric substances and carbohydrates molecular weights of the wastes at different times to both respirometric measurements and microbial communities' dynamics led to propose an interpretation of the waste organic matter aerobic biodegradation processes: the respirometric activity at the beginning of aerobic biodegradation is principally correlated with the amount of low-size molecules (less than 1KDa) that is rapidly consumed, probably by bacteria. When these initial small molecules are all consumed, the hydrolysis of large-size dissolved molecules and non-soluble solid organic matter became the source of nutrients for the microorganisms. Organic matter degradation in sludge was correlated with a 10 fold increase of the amount of fungi but did not dramatically affect the bacterial number. In the MSW however, both increases in oxygen consumption rate correlated with increases in bacterial numbers while the amount of fungi was multiplied by 100. Conclusion. This multidisciplinary approach is a first step in the understanding of the link between wastes initial composition and aerobic biodegradation kinetics. Future work will be to integrate these new data into respirometric mathematical models to improve our ability to simulate and design aerobic biodegradation processes.
keyword : DIGESTAT
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https://hal.inrae.fr/hal-02594433
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Submitted on : Friday, May 15, 2020 - 6:36:25 PM
Last modification on : Friday, November 27, 2020 - 3:54:03 PM

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  • HAL Id : hal-02594433, version 1
  • IRSTEA : PUB00030891

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P. Dabert, Karine Esteve, M. Launay, Rémi Dufourcq, A. Trémier. Respirometry, chemical and microbial community analysis of solid waste aerobic biodegradation. 7th International Conference ORBIT 2010, Jun 2010, Heraklion, Greece. pp.9. ⟨hal-02594433⟩

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