Anaerobic digestion of slaughterhouse waste in batch and anaerobic sequential batch reactors

This work focuses on the design of an effective treatment process for slaughterhouse waste management. Four different treatment sequences were proposed, based on aerobic and anaerobic technologies, as well as thermal and centrifugation pre-treatments. Biochemical methane potential tests were carried out to assess the viability in terms of biodegradability and biogas production of the anaerobic digestion units, which involved different substrates for each proposed process (raw slaughterhouse wastewater, thermal pre-treated slaughterhouse activated sludge, supernatant of thermal pre-treated slaughterhouse sludge, and co-digestion mixture of slaugh-terhouse wastewater and supernatant of thermal pre-treated slaughterhouse sludge). The obtained results showed that thermal pre-treatment is not effective by itself. However, if it is followed by centrifugation, organic matter removal is importantly improved. In addition, removal efficiency reached 76.0% when employing a co-digestion mixture. Kinetic analyses showed that the specific constant rate of the mixture was 1.5 times higher than with the sole supernatant. Afterwards, the co-digestion mixture was employed as a substrate for an anaerobic sequencing batch reactor working under a semi-continuous operational mode. The influence of organic load rate (OLR) on organic matter removal and biogas production was studied. The best operational OLR range was 1.16-2.16 kg/m3.d, achieving 87.8% of chemical oxygen demand removal and 0.23 L-CH4/L-digester.d of methane production rate. A faster organic load rate than 2.88 kg/m3.d led to bioreactor destabilisation. The obtained results were competitive against published studies that employed different anaerobic technologies and made progress towards the industrial implementation of effective technology in slaughterhouse facilities.