Pilot-scale testing of a leachbed for anaerobic digestion of livestock residues on-farm. (April 2016)

• Record Type: Journal Article
• Authors: Yap, S.D.; Astals, S.; Jensen, P.D.; Batstone, D.J.; Tait, S.
• Is Part Of: Waste management. Volume 50(2016)
• Page Start: 300
• Page End: 308
• Publication Date: 2016-04
• Subjects: Anaerobic digestion -- Leachbed -- Solid-phase -- Manure -- Straw -- Inoculation; Hazardous wastes -- Periodicals; Refuse and refuse disposal -- Periodicals; 363.728
• DOI: 10.1016/j.wasman.2016.02.031
• Languages: English
• ISSNs: 0956-053X

Abstract

Graphical abstract: Highlights: Pilot leachbeds compare leachate flow modes (trickling vs. flood-and-drain). Methane productivity is found to be insensitive to leachate flow modes. Leachbed performance was limited by microbial activity. Flood-and-drain mode mobilised unwanted non-degradable particulates into leachate. Trickling is to be preferred over flood-and-drain. Abstract: A leachbed is a relatively simple anaerobic digester suitable for high-solids residues and on-farm applications. However, performance characteristics and optimal configuration of leachbeds are not well-understood. In this study, two 200 L pilot-scale leachbeds fed with spent straw bedding from pigs/swine (methane potential, B0 = 195–218 L CH4 kg −1 VSfed ) were used to assess the effects of leachate recirculation mode (trickling vs. flood-and-drain) on the digestion performance. Results showed comparable substrate solubilisation extents (30–45% of total chemical oxygen demand fed) and methane conversion (50% of the B0 ) for the trickling and flood-and-drain modes, indicating that digestion performance was insensitive to the mode of leachate flow. However, the flood-and-drain leachbed mobilised more particulates into the leachate than the trickling leachbed, an undesirable outcome, because these particulates were mostly non-biodegradable. Inoculation with solid residues from a previous leachbed (inoculum-to-substrate ratio of 0.22 on a VS basis) hastened the leachbed start-up, but methane recovery remained at 50% of the B0 regardless of the leachate recirculation mode. Post-digestion testing indicated that the leachbeds may have been limited by microbial activity/inhibition. The high residual methane potential of leachate from the trickling (residual Bo = 732 ± 7 L CH4 kg −1 VSfed ) and flood-and-drain leachbeds (582 ± 8 L CH4 kg −1 VSfed ) indicated an opportunity for further processing of leachate via a separate methanogenic step. Overall, a trickling leachbed appeared to be more favourable than the flood-and-drain leachbed for treating spent bedding at farm-scale due to easier operation.