Process upsets in a full-scale anaerobic digestion bioreactor: over-acidification and foam formation during biogas production

Abstract

Background: Biogas plays a worthwhile role as a renewable, storable energy source. Anaerobic digestion (AD) is the core process in biogas production. The two most common process upsets that occur during this biotechnological process in practice are over-acidification and foam formation. Several research projects have been carried out so far to identify the causes of these upsets and to develop early warning indicators. However, the relevant laboratory resultshave not yet been verified in practice. Accordingly, the aim of this work was to study the practical application of the published tools in the case of a full-scale biogas plant. Methods: A full-scale AD plant utilizing cattle manure and energy crops was sampled over a period of 12 weeks. During this time, over-acidification and foam formation occurred in the primary digester. Results: The sum of acetate, propionate and butyrate (VFA S ) and the ratios of VFA S to magnesium (VFA S /Mg), calcium (VFA S /Ca), and phosphorus (VFA S /P) were found to be good predictive tools to identify over-acidification for the given AD system. Their values increased by factors of 6 (VFA S /Mg and VFA S /Ca) and 13 (VFA S , VFA S /P) in the early overacidification phase. In contrast, the VFA/TIC ratio, which is a common indicator in practice, increased only by a factor of 2 during this phase. An ammonium-nitrate-urea solution proved to be an effective agent for foam suppression when sugar beet was used as a substrate. Its application showed no negative effect on the daily electricity production and the achieved long-term foam elimination. Conclusions: Several parameters were verified to be able to serve as an early warning indicator of over-acidification, but not one was found to be able to serve as an early warning indicator of foam formation in AD. Further research is needed to identify parameters with predictive potential for indicating foaming in AD.

A Review of the Chemistry of Anaerobic Digestion: Methods of Accelerating and Optimizing Process Efficiency

“…As such, high levels of skills and investments are required to keep it up and running. Considering this high sensitivity, any imbalances caused by over-accumulation of certain substances in the digestion process can easily lead to inhibition, and consequently to process failure [125]. The chemical aspect of AD described in this review suggests that it is as important as the microbiological aspect.…”

A Review of the Processes, Parameters, and Optimization of Anaerobic Digestion

“…Each stage of anaerobic digestion is carried out by different groups of microorganisms, each with their own respective environmental optimum; methanogenesis proves to be a particularly sensitive process, as it is carried out by a small class of strictly anaerobic archaea [ 21 ]. Considering the sensitivity of anaerobic digestion, the imbalances caused by the over-accumulation of certain intermediates in a digester can easily cause an inhibition or process failures [ 93 ]. As such, the design of single-vessel digester, continuous or otherwise, must be able to take into these factors in order to ensure efficient and thorough digestion, and there should exist methods by which potential upsets in digesters can be detected and rectified.…”

Current scenario of solid waste management techniques and challenges in Covid-19 – A review

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