Recovery of energy and nutrient resources from cattle paunch waste using temperature phased anaerobic digestion

- Paunch waste contains 7.8 GJ energy, 13 kg N and 7 kg P per dry tonne.
- Temperature phased AD was a successful method of process intensification.
- Anaerobic digestion can reduce the wet mass of paunch solid waste by >60%.
- Crystallization recovered 85% P and 15% N from digested paunch liquor.
- An integrated process improved recovery to 95% P and >50% N from solid paunch waste.

Cattle paunch is comprised of partially digested cattle feed, containing mainly grass and grain and is a major waste produced at cattle slaughterhouses contributing 20-30% of organic matter and 40-50% of P waste produced on-site. In this work, Temperature Phased Anaerobic Digestion (TPAD) and struvite crystallization processes were developed at pilot-scale to recover methane energy and nutrients from paunch solid waste. The TPAD plant achieved a maximum sustainable organic loading rate of 1-1.5 kgCOD m−3 day−1 using a feed solids concentration of approximately 3%; this loading rate was limited by plant engineering and not the biology of the process. Organic solids destruction (60%) and methane production (230 L CH4 kg−1 VSfed) achieved in the plant were similar to levels predicted from laboratory biochemical methane potential (BMP) testing. Model based analysis identified no significant difference in batch laboratory parameters vs pilot-scale continuous parameters, and no change in speed or extent of degradation. However the TPAD process did result in a degree of process intensification with a high level of solids destruction at an average treatment time of 21 days. Results from the pilot plant show that an integrated process enabled resource recovery at 7.8 GJ/dry tonne paunch, 1.8 kg P/dry tonne paunch and 1.0 kg N/dry tonne paunch.

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