Anaerobic digestion of poultry slaughtering wastes
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|Tila||Julkaistu - 1999|
The feasibility of anaerobic digestion of poultry slaughterhouse wastes combined with wastes from a food packing plant was studied using semi-continuously fed, laboratory-scale, continuously-stirred digesters at 35°C and 55°C. Furthermore, factors affecting anaerobic digestion were studied using batch assays with digested material from the digesters. In the mesophilic digester, inoculated with mesophilic digester sewage sludge, and with a loading of up to 4.6 g volatile solids (VS) l-1 d-1 (a hydraulic retention time (HRT) of 18 days), the specific methane yield was 330 ml g-1 VS(added). Nitrogen in the feed was organic nitrogen with a slight amount of ammonium present, while ammonium nitrogen in the digested material accounted for 50 to 70% (up to 3.9 g l-1) of total nitrogen. The total solids and VS removals were 58 and 68%, respectively. With the highest loading, however, methane production was apparently curtailed at the end of the study period, and sustainability of a long-term operation of the process remains to be proven. In contrast, under similar conditions the digesters inoculated with mesophilic and thermophilic granular sludge both failed after 40 to 50 days of operation, their failure being due apparently to inhibition (unadapted inocula or overloading). The results show that up to 100 m3 of methane can be produced from ton (wet weight) of the waste mixture studied. The process may be inhibited by ammonium nitrogen and some other inhibitory compounds, most likely long-chain fatty acids.