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Effect of feeding frequency on the anaerobic digestion of berry fruit waste. | LitMetric

AI Article Synopsis

  • On-site anaerobic digesters on small farms face challenges due to fluctuating feeding schedules, particularly with putrescible waste impacting stable digestion operations.
  • A study tested different feeding frequencies of rejected raspberries in 3L reactors over 350 days, finding that while specific methane yield remained consistent, the methane production patterns varied significantly across different feeding regimes.
  • The reactors failed when the organic loading rate was increased, highlighting that while digestion efficiency might be stable with varying feeds, rising organic levels can lead to acidification issues if alkalinity isn’t managed properly.

Article Abstract

On-site anaerobic digesters for small agricultural farms typically have feeding schedules that fluctuate according to farm operations. Shocks in feeding, particularly for putrescible waste can disrupt the stable operation of a digester. The effect of intermittent feeding on the anaerobic digestion of rejected raspberries was investigated in four 3L reactors operated in semicontinuous mode for 350 days at 38 °C with a hydraulic retention time of 25 days and an organic loading rate (OLR) of 1gVS/L/d. During the acclimatisation period (147 days) the organic loading was 5 feeds per week. The feeding regime of two reactors was then changed while maintaining the same OLR and HRT to one weekly feed event in one reactor and 3 equal feeds per week in another. The feeding regime did not significantly affect specific methane yield (369 ± 47 L/kgVS on average) despite very different weekly patterns in methane production. Volatile fatty acids (VFA) comprised >83 % of the organics in the effluent, while the rest included non-inhibitory concentrations of phenolic compounds (515-556 mg gallic acid/L). The microbial composition and relative abundance of predominant groups in all reactors were the archaeal genera Methanobacterium and Methanolinea and the bacterial phyla Bacteridota and Firmicutes. Increasing the OLR to 2gVS/L/d on day 238 resulted in failure of all reactors, attributed to the insufficient alkalinity to counterbalance the VFA produced, and the pH decrease below 6. Overall results suggests that optimal digestion of raspberry waste is maintained despite variations in feeding frequency, but acidification can occur with OLR changes.

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Source
http://dx.doi.org/10.1016/j.wasman.2024.02.011DOI Listing

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