a b s t r a c tThis study was carried out to assess the energy recovery potential from organic industrial by-products of a cattle slaughtering facility. There are several processes to convert organic material to energy; the technology of interest in this study was anaerobic digestion, the biological conversion of degradable organic material into methane. The scenario was initially confined to a full scale cattle slaughtering facility processing 3.28% of heads slaughtered in Ireland. The methane potential of dissolved air flotation sludge, paunch, soft offal as well as a mixed waste stream (combination of individual waste streams) was determined through a series of biochemical methane potential assays under mesophilic conditions. The methane potential of the characterised waste streams ranged from 49.5 to 650.9 mLCH 4 gVS À1 . The potential energy recovery from the mixed waste stream resulted in the prospective subsidy of 100% of the energy demands of the slaughtering facility as well as the energy demands for the production of the biogas. When investigating the impact of energy recovery from the entire sector the potential energy recovery equated to 1.63% of the final energy demands of the Irish industrial sector. This could potentially increase the RES in Ireland from 7.8% to 8.13% contributing to both RES-E and RES-H.
The effect of mandatory pasteurisation on Category 3 offals, according to the Animal By-Products Regulation (ABPR 1069/2009/EC), was determined using Biochemical Methane Potential (BMP) assays as well as kinetic and statistical analysis. Pasteurised and unpasteurised offals sampled from cattle, pig and chicken slaughterhouses were characterised and their specific methane yields (SMYs) and their bioavailability was assessed. The resultant SMYs were high (465-650mLCH4gVS(-1)) with no statistically significant increase in methane production identified due to pasteurisation. However, the kinetics of the biogas transformation processes highlighted increased bioavailability of the organics due to pasteurisation. This was brought to light by the change in maximum daily SMY from day 22 to day 1 for the cattle offal (p=0.001), day 17 to day 1 for chicken offal (p=0.025) and an increase of 18.8% in the maximum daily SMY of the pig offal on day 1 (p=0.003). The increased bioavailability of the offals manifested itself in two ways with the determining factor being identified as the physical characteristics of the fats i.e. particle size. Firstly reducing the hydrolytic lag phase for the cattle offal, λ=7.46-1.52days (p=0.013). Secondly, causing increased accumulation of Long Chain Fatty Acids to acute inhibitory levels in the chicken and pig offal indicated by increased lag phases λ=5.05-21.91days (p=0.012), λ=15.54-23.04days (p=0.007) respectively.
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