Techno-economic assessment of dairy manure granulation

Abstract. Continued growths in number of milking cows, milk productivity per cow and number of concentrated animal feeding operations (CAFO) are all leading to increases in quantity and concentration of manure. Under these conditions, poor manure management practices coupled with uncertainty in rain events pose a greater threat to the health of surrounding ecosystems, in addition to the economic loss of manure nutrients as runoff. This study presents a comprehensive model of granulation as an advanced processing alternative for dairy manure. Granulation offers an opportunity to improve manure characteristics, which facilitate precise land application and affordable transportation. Additionally, it could improve manure acceptability as organic fertilizer thus adding a revenue source to producers. The impacts of herd size, management practices, operating costs, and internal rate of return (IRR) on the minimum sale price (MSP) of granulated manure were quantified. Herd size was found to significantly impact MSP for herds below 10,000 cows. For herds of 1,000, 5,000 and 10,000 cows, the MSP were $559, $291, and $237 per metric ton of granulated manure. The process economics were evaluated in terms of breakeven distances, which correspond to transportation distances at which the cost of granulation equals the savings in transportation cost. Finally, process economics were evaluated in terms of unit mass of phosphorus (P) retained in the granulated manure. When considered as a technique to export P off eutrophic watersheds for sale as organic fertilizer, granulation may be competitive with other P-reduction technologies.