Anaerobic degradation of the organic municipal solid waste together with manure. Part 1
The present project consists of introductory investigations of co-digestion of the organic fraction of municipal solid waste (OFMSW) together with manure. The investigations included characterization of OFMSW and preliminary experiments of the anaerobic degradation of OFMSW under thermophilic conditions.
This project will examine anaerobic digestion of organic municipal waste in co-digestion with manure. The content af xenobiotics in the waste can have an inhibiting effect on the anaerobic degradation and it must be ensured that the effluent from a biogas plant treating household waste meets the standards for the use of the effluent as a fertiliser. The content of xenobiotic compounds in the waste materials and their degradation potential in the biogas reactor will be evaluated. The project will include the following items: 1) Literature study to determine the characteristics of OFMSW found in other studies. Experimental data from the different Danish full scale plants using OFMSW in co-digestion with manure (biogas plants at Studsgård, Sinding, Vaarst-Fjellerad). 2) Characterisation of the composition of OFMSW by analytical methods. 3) Evaluation of the degradability of xenobiotics in selected OFMSW from two different sources together with manure by anaerobic digestion, focusing on the inhibiting effects and other important factors. This will be done by analysis of the effluent from the biogas plants and by laboratory batch experiments. The project should be seen as pre-investigations for the development of a stable and energy efficient biogas process of OFMSW together with manure. The results will estimate how efficient the degradation of xenobiotics has to be when treating household waste together with manure in biogas plants
Characterization of OFMSW was in particular concerning the content of xenobiotics while the anaerobic degradation of OFMSW was with focus to determination of biogas potential in batch experiments and methane yield, reduction of organic matter (VS) and process stability in reactor experiments. Regarding the content of xenobiotics, the concentration of nonylphenolethoxylates (NPE) and linear alkylbenzenesulfonates (LAS) was of minor significance. The main problem was the content of di(2-ethylhexyl) phthalate (DEHP). A concentration of DEHP as high as half of the threshold for the use as fertilizer (50 mg/kgTS) was measured in OFMSW before treatment. Since the dry matter (TS) content is reduced throughout the anaerobic degradation, the DEHP concentration per gram dry matter in the effluent will exceed the threshold if DEHP is not degraded in the process. The concentration of polycyclic hydrocarbons (PAH) in the collected OFMSW was only in one case close to the threshold level and the concentration in the effluent would exceed the threshold if PAH's are not degraded throughout the anaerobic degradation process. A biogas potential of OFMSW of 187 m3biogas/m3waste was determined both in batch and reactor experiment, which makes OFMSW a very attractive substrate for the use in biogas plants. No signs of inhibition were monitored in the degradation of pure OFMSW in batch experiments. In reactor experiments a stable degradation process could be established by increasing the ratio of OFMSW in the co-digestion mixture with manure. A methane yield of 350 lCH/4/kg VS with a VS reduction of 50-60% was obtained in the treatment of a mixture of OFMSW and manure in a ratio of 50:50% (on VS basis). When using 100% OFMSW diluted with tap water as reactor influent a methane yield higher than in the batch experiment was achieved with a VS reduction up to 80%. Analysis of DEHP and PAH indicates that DEHP is not degraded under thermophilic conditions while there is a partial reduction of PAH's
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