ANAEROBIC CO-DIGESTION OF DAIRY CATTLE SLURRY AND AGRO-INDUSTRIAL FATS: EFFECT OF FAT RATIO ON THE DIGESTER EFFICIENCY

摘要

The objective of the study was to optimize the co-digestion of cattle slurry in the presence of fats from the food industry. A laboratory pilot plant operating continuously was used for the experimental study. Tests were carried out with only cattle slurry and with different fat ratio (0, 10, 25, 45 and 60%(w/w) of the feed COD as fats). In the case of using cattle slurry feed and OLR from 0.4 and 3.0kg VSm(-3)day(-1) (HRT between 125 days and 19 days), methane productivity versus OLR exhibit a linear relation reflecting optimum biodegradability of the organic matter. For OLR above 3kg VSm(-3)day(-1) (HRT less than 19 days), a break in the slope is observed expressing a decrease of the organic matter degradation rate. For HRT equal to 30 days, the results show that fat incorporation ratio lower than 25%(w/w) does not affect the digester operation while maintaining acceptable biodegradability of the fat. In contrast, with a fat ratio of 60%(w/w), the system became unstable and a significant decrease in the methane productivity was observed, due to an accumulation of undegraded Long Chain Fatty Acids (LCFA). The conclusion is that the fat ratio must be controlled to avoid the destabilization of digestion, and finally operational conditions are proposed for co-digestion.