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What Are the Causes of Manure Foaming?

Manure foam is described as bubbles gathering at the top of pits storing liquid animal manure. These bubbles consist of up to 70 percent methane, which poses considerable risk of explosion as methane is flammable and explosive at a concentration of only 20 percent. Approximately 25 percent of U.S. animal farms experience manure foaming, 10 percent of which have more than 6 inches of foam. While specific reasons for manure foaming are unknown, researchers have identified some potential causes.

  1. Surface Active Agents

    • Surface active agents lower the surface tension of liquid manure, potentially causing foaming. These agents include surfactants, such as proteins, lipids and detergents, and bio-surfactants, such as polymers and microbial products. Surface tension is lowered as the hydrophilic or water-loving end of the agent enters the liquid, leaving the hydrophobic or water-averse end exposed to air. It is proposed that proteins are the most-effective agent at causing foaming as it is least biodegradable.

    Diet

    • The inclusion of dried distillers grains with solubles (DDGS) and other supplements in animal diets increases the amount of manure produced by up to 30 percent in some cases and may thus increase the possibility of foaming. DDGS contains nutrients, such as phosphorus, lysine and other crude protein and lipids, which adds to the presence of surface active agents.

    Characteristics of Manure

    • The physical and chemical characteristics of manure may also influence foaming. These characteristics include pH, alkalinity, volatile acid concentration and temperature. Cooler temperatures are associated with less foaming. The amount of water consumed by animals is also a factor, as less water results in an increase in surface active agents in manure, which would have otherwise dissolved.

    Methane Production

    • The accumulation of methane is also linked to manure foaming. Methane production is determined by the depth of the storage pit, microbe content and the presence or absence of oxygen. Inadequate ventilation causes gases to accumulate, thus increasing the possibility of manure foam formation. Thus continuous ventilation is recommended to prevent methane buildup.

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