This week I have had calls and conversations with producers from several locations in the Midwest regarding pits foaming thru the slats. While I’ve had an occasional call or conversation with a producer regarding the phenomenon in past years, the large number in one week is causing me to think about possible causes and solutions.
The callers have had 2 basic questions – what is causing the pits to foam and what do I do about the foam?
Let’s think about what is happening in manure pits. They are full of actively growing microorganisms that are giving off by-products of their metabolism as they feast on the ready source of nutrients available in the manure. Because the pits lack oxygen, the by-products of this metabolism are not always ‘user-friendly’, a polite way of stating that the by-products often have an offensive smell to many people.
If there was sufficient oxygen present in the pit, the by-products would be such things as carbon dioxide (CO2), nitrates (NO2) and sulfur dioxide (SO2). Because of the lack of oxygen as the final electron acceptor in the metabolic process, we end up with by-products such as methane (CH4), ammonia (NH3) and hydrogen sulfide (H2S). While ammonia is water soluble as ammonium (NH4+) if the pH is lower than 7.0, the other 2 products are gases that are emitted from the pit.
In a typical pit, when these gases erupt from the pit surface, they often form tiny bubbles that readily burst. However, in the pits that are foaming, something is causing the surface tension of the water surface to change. This means the thin layer of surface water atoms that forms the bubbles now has sufficient electrical and chemical bonding ability to cling together.
The increase in foaming in late fall is most likely a function of increased biological activity in the pit due to warmer conditions. The pits have had all summer to accumulate heat, and while there may have been some foaming occurring all summer, with the pit nearly full prior to fall pumping, foam is now coming up thru the slats into the pig zone. If we think about it, the pits are probably at their biological activity peak in late September and early October. I suspect that the foaming problems will decrease as the pits cool with the return of cold weather to the Midwest.
The immediate solution to the problem is to add a surfactant to the surface of the pit. An option would be the use of crop oils such as the ones routinely added to herbicide sprays. These disrupt the bonding and don’t allow the formation of the bubbles that make up the foam.
As to the cause of the increased foaming, are the pits more biologically active resulting in a greater release of gases from the pit, or is the surface tension of the pits different today? I don’t know the answer to this, but I think the answer may be related to our changing dietary ingredients.
In conversations with nutritionists in the past few days, everyone cites the increased use of distillers grains (DDGS) and the recent wide-spread use of phytase. Is their increased usage related to the foaming problem or is the foaming due to another variable that we haven’t accounted for? For example, I don’t know how crusting of the pit surface is affecting foaming – is foaming worse in pits that have a minimal crusting on the surface?