Anaerobic digestion of swine effluent: Impact of production stages

Methane capture and use from intensive livestock industries in Australia is relatively new and there is a lack of reliable kinetic data to design anaerobic systems both in Australia and internationally. This paper evaluates two parameters, degradability (BO) and apparent first order hydrolysis rate coefficient (khyd) from 5 different sites (one sampled twice), and six different pig growth stages. Hydrolysis rate was not significantly influenced by the production stage and was statistically similar at 0.1 d−1 and ranged from 0.06 d−1 to 0.3 d−1. However, degradability, as defined by estimated ultimate methane yield (referenced to standard temperature and pressure) per kg organics loaded varied substantially. Specifically, we found that the methane yields (per unit organic substrate (volatile solids) added) from finisher (470 ± 170 L kg−1), weaner (450 ± 150 L kg−1) and grower (460 ± 160 L kg−1) effluent streams were more compared to yields from dry sow (260 ± 120 L kg−1) and farrowing streams (380 ± 160 L kg−1). A possible indicator of the extent of degradation is the organic fraction of solids in the effluent. Variability in the degradation kinetics and chemical properties of the different effluent streams could be traced back to the differences in various industry management practices such as feed type, feeding techniques and effluent handling methods.

► Production stage of pig has an influence on the degradability of effluent stream.
► Effluent streams from dry sow and farrowing sheds degrade poorly.
► Effluent streams from weaner, grower and finisher sheds have better degradability.
► VS fraction is a possible indicator of the degradability of the waste.
► Feed type, feeding techniques and effluent handling methods can cause variability in degradability.