Proceedings

Abstract
Anaerobic digestion of food wastes is now well established in the UK. The greatest challenge for most operators is minimising the volume of digestate recycled to land as this is a loss centre. Because food waste has a high dry solids content and the digesters in the UK are ‘wet’ the feedstock must be diluted down to remove contaminants and facilitate pumping and mixing. Dilution increases the volume of digestate to transport therefore any strategy which minimises the addition of water is worthy of consideration.

This papers reviews the strategy of recirculating digestate back to the head of the process instead of using mains or borehole water. It evaluates the:
• impact upon ammonia levels in the digestate
• resulting potential for digester inhibition
• implications for odour generation
• impact upon PAS110 stability limits
• challenges facing operators wishing to dewater whole digestate

Keywords: organic waste digestion, ammonia inhibition, PAS110, digestate dewaterability