Manure management is a critical aspect of modern dairy operations. Mismanagement can result in contamination to local and regional watersheds that may have adverse environmental impacts. Because fresh manure has a high water content (~85%), direct use is typically limited to local direct land application as a carbon source for soil amendment and as low-quality fertilizer. However, this practice may not be a viable option for all operations, so the manure is often transported to treatment facilities at a considerable cost. This project focuses on the development of an on-site treatment process for the dairy manure that can produce a solid fuel source, liquid fertilizer, and high-quality reuse water, all of which can be used on-site or sold for profit.
This presentation will focus on the use of direct contact membrane distillation (DCMD) for the treatment of the aqueous byproduct of thermally treated dairy manure to concentrate nutrients and produce high-quality reuse water. Hydrothermal carbonization (HTC) was applied to wet dairy manure with hot compressed water to produce a solid, carbon-rich hydrochar and an aqueous, nutrient-rich byproduct. Once the solid fuel products have been removed, the hot aqueous stream serves as a feed to DCMD, where soluble nutrients (nitrogen and phosphorus) are concentrated for use as a liquid fertilizer and the distillate water can serve as high-quality reuse water. No heating is required for DCMD operation as the HTC liquid byproduct is received at an elevated temperature, thereby making the treatment of the liquid phase a very low-energy process. Preliminary results indicate >99% rejection of TOC and total nitrogen (TN) in the feed solution and >95% rejection of phosphorus, with concentration factors greater than 6 achievable. The coupling of DCMD with HTC offers a great low-energy opportunity for nutrient and water recovery from a traditional waste source.