DesignClinic

Design of an Affordable Silage Leachate Treatment System

Natural Resources Conservation Service

Natural Resources Conservation Service

2013-2014: In collaboration with the Natural Resources Conservation Service (NRCS) this team developed an affordable, scalable waste treatment system for use on small dairy farms.  The project was initiated by a design team during the 2011-2012 Design Clinic and continued by this team.

Silage leachate is the liquid effluent that results from fermenting high-moisture crop materials to produce food for farm animals. It is acidic and nutrient-rich and has high biological oxygen demand (BOD) so it cannot be applied directly to crop lands or allowed to discharge to local streams. The team investigated multiple ways to mitigate the contaminant levels in silage leachate. Experiments were conducted to test the ability of biochar, activated carbon, limestone, and gypsum to adsorb or react with components from the leachate. Both flow-through and stirred configurations were evaluated. None of the media reduced nutrients or BOD enough to allow discharge of the treated leachate to waterways, but a combination of limestone and gypsum increased the pH sufficiently to allow application on selected crops. A treatment system was designed to mix the leachate with gypsum and lime overnight and use an irrigation system to apply the treated effluent on land. Residual solids can be applied to crops with manure.

Deliverables resulting from this work included a final report detailing all experimental procedures and results, the recommended design, a cost estimate, and an explanation of implementation and maintenance requirements.