Managing Silage Effluent

08:18AM Sep 05, 2014

By: John Tyson, Agricultural Engineer, Penn State Extension

Fall is almost here and with that will come corn silage harvest. One common side effect of silage making is silage effluent. No matter our best efforts to harvest at the correct moisture and in a timely fashion, it happens. If you have a silo, upright or horizontal, you have some amount of silage effluent.

Where that effluent ultimately flows to is the issue. From a pollution potential standpoint, silage effluent ranks among the highest sources. A common measure of pollution potential is the biological oxygen demand (BOD). Simply stated this is the amount of oxygen needed to break down the product. Silage effluent often has a BOD around 50,000 mg of oxygen per liter of effluent, while raw domestic sewage runs about 500 mg/L. The actual numbers are not important here, the point is that silage effluent is 100 times as strong as raw sewage. For a better example, as little as one gallon of silage effluent can lower the oxygen content of 10,000 gallons of fresh water to a critical level with respect to fish survival. The nutrient concentration of silage effluent, in terms of N, P and K, is very similar to typical liquid dairy manure. The pH is typically in the 4.0 range which is another potential pollution problem and leads to the characteristic vegetation burns around silos.

So what can be done in terms of treatment/disposal? First, think about placement and preparation of the silo. Silos should be located away from open waterways and wells. An unused piece of pasture down by the stream may seem like a nice place for a bunker, right up until the stream becomes polluted. Proper preparation of the site will also help with collection and/or treatment of the effluent. Divert clean water away from the site and layout the site so on-site runoff will move toward a common point for collection and/or treatment.

To limit the treatment, try to minimize the amount produced. Basically this means ensiling at the proper moisture content. When stored at a dry matter content of 30% effluent flow is greatly reduced. Covering horizontal silos also helps reduce the prolonged flow of effluent.

But, even when properly located and minimized, there is still effluent to handle. There are several methods to handle effluent. Probably the most often used method is incorporation with a liquid manure system. Be very careful when mixing silage effluents with manure. Hydrogen sulfide and other poisonous gases are produced, and it should not be done if the storage is covered or under the barn. The second option is land application to a crop field or grass filter strip. However, effluent must first be diluted with water if applied to a growing crop; typically a 1-to-1 ratio will work. The effluent can also be directly applied to fields with a non-growing crop.

Treatment must be addressed on a case by case basis, because each farm is different. Help is available through the NRCS, Conservation District, and Extension. The consequences of ignoring the problem will not make it go away, and it can only get worse.