(25f) Struvite Precipitation for Nitrogen Removal in Horse Manure for Gasification: Experimental Study and Economic Analysis

Animal manure is one of the most common kinds of waste in farming areas. Instead of direct disposing or burning, gasification is a more promising and cleaner way to harvest the energy from waste and reduce pollution at the same time. From previous study, addition of horse manure and chicken manure to woodchips could improve syngas production up to 40%. However, the nitrogen content inside the manure, taking up around 2-3 wt% in the sample, may course environmental or explosive concern for gasification. On the other hand, retrieving nitrogen from animal manure can be a significant source as fertilizers. From FT-IR tests, nitrogen was found to be in the form of ammonia mainly in the manure samples. Thus, struvite precipitation is considered as an excellent approach to remove ammonia and produce struvite at the same time.
 
In this work, horse manure from Singapore Turf Club was studied. Elemental analysis, FT-IR and TGA tests for the manure samples were conducted as feedstock characterization. Firstly, ammonia was leached out from manure samples using water at different ratios. After leaching, ammonia concentration could reach around 100 mg/L. For precipitation process, optimal experimental conditions, such as molar ratios of Mg²⁺ and PO₄^3- sources, mixing time and pH, were studied. Performance of different kinds of Mg²⁺ and PO₄^3- sources were compared. In the end, economic analysis of struvite precipitation process was also conducted to find the optimal solution for the whole process. The objective of this work is to find out the optimal experimental conditions for fully utilization of manure waste in a most cost-effective and high-yield way.