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Study of the feasibility of composting treatment for anaerobic digestion solid residues

Abstract : Waste production has constantly increased in recent years due to population expansion and industrial development. In order to face this crucial issue, environmental policies become more severe and regulate waste management and treatment. Biological treatments are developing as sustainable ways to manage organic wastes. These technologies actually contribute to reduce the volume of wastes and recycle the organic matter contained in wastes while generating a product that can be used as an organic fertilizer or soil improver. In particular, anaerobic digestion (AD) is rapidly growing since it allows the production of renewable energy (biogas) while treating wastes. Nevertheless, this technology is still facing some technical difficulties. In particular, AD residues are not fully stabilized: they present a residual biodegradability, complex organic elements such as ligno-cellulosic compounds that have not been degraded and total nitrogen is conserved and mineralised during digestion. The post-treatment of AD residues including a composting stage constitute an adequate post-treatment since it can stabilize their remaining organic matter. This work aimed at studying the feasibility of a composting treatment for AD residues. The determination of digestates residual biodegradability and the assessment of operational composting parameters allowed to predict the composting behaviour of several AD solid residues. Six digestates have been studied resulting from different materials: sludge from waste water treatment plant (WWTS), food-processing wastes (FPW), agricultural solid wastes (AW) and source selected organic fraction of municipal solid wastes (SS-OFMSW). Residual biodegradability and composting feasibility have been evaluated by the determination of physico-chemical and biological indicators. Chemical oxygen demand, total carbon and nitrogen content have been measured to illustrate the waste ability to be biodegraded. Measurements of the biological activity through respirometry have also been conducted to evaluate waste aerobic reactivity and biodegradation rates. Then, the prediction of composting operational parameters has been made based on respirometric tests. Indeed, oxygen consumption curves allowed the estimation of the temperature rising and the aeration conditions to apply during the composting process of AD residues. Theoretical global need in aeration supply to achieve biological stabilization has been estimated. The minimal air flow rate required to insure non limiting aerobic conditions during composting has also been calculated. The determination of the residual biodegradable potential finally led to estimate for each digestate the minimum time of composting to reach full stabilization. The determination of aerobic treatability parameters showed that digestates still showed biological reactivity. In some case, the remaining biodegradable organic matter content is comparable with products obtained at the end of the active phase of composting. Thus, maturation of these digestates may be sufficient to reach stabilization. Nevertheless FPW or AW for instance, presented residual biodegradability similar to raw wastes and though must be subjected to a complete composting post-treatment. AD residues might be post-treated by composting to insure optimal biological stabilization, but this composting process would be probably shortened in comparison with raw compostable wastes. The prediction of composting behaviour showed that AD would lead to moderate temperature rise that might involve hygienization issues if digestates appear to be still contaminated with pathogens. Besides, the determination of total aeration needs confirm the difference between several digestates residual biodegradability. Indeed, SS-OFMSW would require lower aeration supply to achieve full stabilization. Minimum air flow required at the beginning of AD residues composting process were comparable with certain raw organic wastes. Finally, the assessment of the minimum time required for biological stabilization confirmed that a composting post-treatment of digestates will be shorter than raw organic wastes typical composting. Composting trials of AD solid residues in 300-litre reactors will verify these assumptions. Furthermore, composting parameters such as oxygen consumption, temperature evolution or gaseous emissions, all followed at lab-scale, will lead to evaluate the environmental impact of an AD step by the comparison of non digested and digested wastes composting.
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Submitted on : Friday, May 15, 2020 - 6:36:04 PM
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  • HAL Id : hal-02594430, version 1
  • IRSTEA : PUB00030889



C. Teglia, A. Trémier, J.L. Martel. Study of the feasibility of composting treatment for anaerobic digestion solid residues. 7th International Conference ORBIT, Jun 2010, Heraklion, Greece. pp.8. ⟨hal-02594430⟩



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