Abstract
The idea that storage can enhance manure quality as substrate for anaerobic digestion (AD) to recover more methane is evaluated by studying storage time and temperature effects on manure composition. Volatile fatty acids (VFA) and total dissolved organics (CODs) were measured in full scale pig manure storage for a year and in multiple flasks at fixed temperatures, mainly relevant for colder climates. The CODs generation, influenced by the source of the pig manure, was highest initially (0.3 g COD L−1d−1) gradually dropping for 3 months towards a level of COD loss by methane production at 15°C. Methane emission was low (<0.01 g COD L−1d−1) after a brief initial peak. Significant CODs generation was obtained during the warmer season (T > 10°C) in the full scale storage and almost no generation at lower temperatures (4–6°C). CODs consisted mainly of VFA, especially acetate. All VFAs were present at almost constant ratios. The naturally separated manure middle layer without sediment and coarser particles is suitable for sludge bed AD and improved further during an optimal storage time of 1–3 month(s). This implies that high rate AD can be integrated with regular manure slurry handling systems to obtain efficient biogas generation.
Highlights
Anaerobic digestion of manure can reduce greenhouse gas emissions (GHGE) and odors, produce renewable energy in the form of biogas, and enhance manure fertilizer quality [1]
Manure from the production stage Farrow and Wieners was collected from the manure channel in the barn and stored under controlled conditions at 11∘C, 15∘C, and 20–23∘C for 3 months to monitor the content of degradable organics in the liquid manure. 100 mL infusion glass bottles with rubber stopper and metal ring were used
The amounts of degradable organics in pig manure depend on the source of the manure and the storage time and temperature
Summary
Anaerobic digestion of manure can reduce greenhouse gas emissions (GHGE) and odors, produce renewable energy in the form of biogas, and enhance manure fertilizer quality [1]. The largest potential source of methane by AD of wet organic waste is manure, for example, ∼40% in Norway; only a small fraction of this is realized [2]. The main reason for this is the low energy density of manure, implying low production rates in continuous flow stirred tank reactors (CSTR) currently used for manure AD. Such solutions are not economically sustainable in Norway because the costs of construction and operation of such plants are larger than the value of the methane produced [2]. New process solutions for AD treatment of manure must be developed to realize the enormous total energy potential of this source
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