Abstract
This review gives an overview of the current knowledge concerning the problem of foam formation in the process of anaerobic digestion in biogas plants that utilize renewable resources or biogenic waste material for biogas production. Process upsets in biogas production induced by foam formation can have a negative impact on the efficiency of biogas plants. The foam can block gas pipes and cause severe damage to the bioreactor equipment, ranging from a failure of the feeders to a damage of the roof of the biogas plant. The most common foam removal methods - stirring in the foam, adding anti-foaming agents, diminishing substrate feeding, and altering the biogas reactor management - are not always successful. However, the reasons for the excessive foam formation during the biogas production process have not yet been elucidated in detail. In contrast, foam building in the rumen of ruminants as a cause for bloat has been studied thoroughly. In general, the interaction between proteins, polysaccharides (mucilage), and small plant particles is assumed to be the crucial factor. As the fermentation process in the rumen has many similarities with the biogas production process, the current research results on bloat in ruminants are summarized and compared with the process of foaming in biogas plants.
Highlights
In order to achieve a sustainable energy production, a great number of biogas plants have been commissioned in Germany in the last decade
Some problems still occur during the biogas production process that can have serious consequences for the biogas plant operator
Excessive feeding of finely ground grain leads to foam formation in both biogas plant and rumen
Summary
In order to achieve a sustainable energy production, a great number of biogas plants have been commissioned in Germany in the last decade. Proteins play a crucial role in foam formation They occur in biogas plants as a consequence of both feeding and microbial activity. Frothy bloat in ruminants and consequences for biogas foam research Just as in biogas plants, gas in the rumen of ruminants is produced as a natural by-product of both digestive fermentation and acidification of bicarbonate [37]. This gas contains approximately 20% to 30% methane, 45% to 70% carbon dioxide, and trace amounts of nitrogen, oxygen, hydrogen, and hydrogen sulfide [37,38]. As the biogas plant is not equipped with such a complex self-regulating system, the knowledge, mindfulness, and intuition of the human operators of the biogas plant and upset-free process operation are important factors for an effective, ecological, sustainable, and durable operation of biogas plants
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