(460d) Nutrient Recovery from Thermally-Treated Agriculture Waste Using Membrane Distillation

As the modern dairy industry continues to develop, the trend has consistently been a decrease in the number of operations, but an increase in the number cows at each operation. Considering that a single dairy cow produces ~150 pounds of manure each day, the amount of manure that can accumulate at these concentrated dairy operations is significant. Current manure handling methods involve temporary storage of manure and then land application as a low-grade fertilizer; however, this often results in the contamination or eutrophication of local and regional surface waters. When not used locally, the financial burden of transporting the manure to an off-site waste management facility can be overwhelming. Thus, a new management approach that treats the manure on the dairy is sought.

One such management method being developed utilizes an integrated hydrothermal carbonization (HTC)-membrane distillation (MD) process for treating dairy manure on-site. HTC is an energy densification process that converts organic waste material into a valuable solid fuel and a nutrient-rich aqueous product (HAP). The HAP is then treated using MD to concentrate the nutrients for use as a liquid fertilizer and produce a high-quality water for on-site reuse.

In this study, we evaluate the nutrient and water recovery potentials of MD when treating HAP. A bench-scale direct contact MD (DCMD) system was tested with feed temperatures ranging from 35-60°C and distillate (permeate) streams maintained at 25°C, resulting in water fluxes from 6-15 L/m²-hr. HAP from multiple HTC conditions were evaluated, and recoveries of total nitrogen (TN) and total organic carbon (TOC) were consistently >99%, and overall concentration factors >6 based on total volume were achieved. Because MD rejects nearly all of the nitrogen and carbon in the HAP, the final concentrated solution may be suitable for use as a liquid fertilizer while the high-quality distillate water may be recycled back to the HTC process or used elsewhere on-site. These preliminary results indicate that the combined HTC-MD process is a technically valid alternative to land application of manure or transport for off-site treatment.