Commercial Composting: The Bruno Feeds Story

Most industrial or processing plants have by-products that with the right idea or partnership can be an asset instead of a liability. Bruno Feeds is no exception. Bruno Feeds is located just outside the village of the same name, 90 km east of Saskatoon. The facility makes feed pellets for a variety of livestock and pets. The processing leaves them with 240 to 350 tonnes per year of a grain-based residue called "finings". It was costing thousands of dollars a year to have the material hauled away. In December 2008, they contacted the Saskatchewan Waste Reduction Council (SWRC) to see if we could help them investigate the feasibility of composting and marketing the finings. SWRC had been looking for an industrial partner for its Sustainable Composting Project. The Bruno mill was a good fit.

SWRC staff person Larry Mullen helped Kim Smith, Doug Krentz and Roberta Lees from Bruno Feeds sort through their options. The finings were an interesting composting challenge. Initial tests indicated 7% total nitrogen and significant amounts of other useful plant nutrients. The same test also pointed to a potential problem with sodium levels at close to 1%. The physical nature of the finings also posed a challenge. The particles are very small and there were concerns that, without the right material mix, it would turn to dough when the necessary water was added. Dough is great for bread but not for composting, where a porous, fluffy mix is desired so that the microbes carrying out the process have access to oxygen from the air as well as water.

A plan was developed to create a compost mix of the finings, turkey manure, soil, gypsum and straw. The gypsum was added to help deal with the sodium content. The soil was present to attempt to hold onto the nitrogen content. This compost mix had higher than normal nitrogen levels. This was done in part to integrate these two nearby waste materials and also in hopes of producing a finished compost that would have a 5 to 6% total nitrogen and 2% phosphorus content. These nutrient levels would produce a product that would be worth moving some distance for field scale application.

In mid-June 2009, Larry Mullen and Doug Krentz created a 30 foot long pilot windrow. They built a static (unturned), passively-aerated, windrow in an unused barn. The building was big enough to allow a bobcat to operate and sheltered the windrow from drying winds. They began by laying down a base layer of twelve inches of straw. Then they laid down 30 feet of perforated sewer pipe on the straw base and covered it loosely with eight inches of straw. With the mill's bobcat, Doug premixed one tonne of finings and one tonne of grain dust, along with 2 tonnes of turkey litter and about 240 pounds (109 kg) of soil. This mix was placed over the length of pipe, leaving the ends of the pipe exposed. The pile was almost six feet high. Fifty pounds (23 kg) of gypsum was added to the compost materials as the windrow was built. Larry and Doug covered the windrow with an insulating layer of straw and then added water using 150 feet (46 meters) of soaker hose laid back and forth along the length of the pile. This gave complete coverage when the water was turned on. Six hours of continuous soaking wetted the pile to the desired moisture content: the material balled up in the hand, but no moisture dripped out when it was squeezed.

Microbial activity, measured by a rise in internal windrow temperature, started within days. Initial temperatures of 40 to 45C were a little lower than expected and caused some concern. A few days later, temperatures caused a different sort of concern as they rose to 78 to 80C. Ideal temperature at the early phase of composting is 50 to 60C; higher temperatures kill beneficial organisms and can result in spontaneous combustion. A timely watering reduced the temperatures to 60C. No other incidents of this sort occurred during the pilot period.

By mid-November, five months after construction, the windrow had returned to ambient temperatures. The material was sent for testing in late October. The good news was that the sodium level of the finished compost had dropped considerably, to 0.05%. The less favorable news was that the level of total nitrogen had dropped to 1.3%--relatively high for compost but below the hoped-for 5 to 6% range. It is likely that the nitrogen levels in the mix were simply too high and a mix that contained more straw or other accessible carbon would allow more of the nitrogen to be retained.

The story is not over. Generally speaking, the staff at Bruno Feeds is pleased with the pilot project. They've identified several potential markets for the compost and the mill is planning to move to a larger scale compost program in 2010. Dr. Jeff Schoenau, from the University of Saskatchewan, is carrying out growth trials using Bruno Feeds compost in plant growth chambers starting in late November 2009.

Thanks to the following people who provided thoughtful assistance at various stages of the Bruno Feeds pilot project:

• Dr. Katherine Buckley, Agriculture and Agri-Food Canada, Brandon
• Dr. Jeff Schoenau and Dr. Richard Farrell, Dept. of Soil Science, College of Agriculture and Bioresources, University of Saskatchewan, Saskatoon
• Grant Wood, Dept. of Plant Sciences, College of Agriculture and Bioresources, University of Saskatchewan, Saskatoon