Selective Carbonization of N-Containing Compounds to Produce N-Doped Chars and Thermally Treated Dairy Manure
Creators: name: Mainali, Kalidas
Publisher: name: Washington State University
Year: 2025
Subjects: Phosphate adsorption
Protein
Pyridine
Pyrolysis
Selective carbonization
Stabilized intermediates
Agriculture engineering

description: Large quantities of N-containing wastes, such as food, animal, and yard spoils, are generated worldwide with limited management options. Although there are other biochemical technological alternatives, anaerobic digestion (AD) and composting are the most commonly used. AD is an excellent strategy to convert the energy contained in organic waste streams into methane. However, most of the nutrients (N, P) in the initial feedstock are released to the environment in a diluted liquid effluent that is difficult to transport away from the production site. Consequently, it is often applied to nearby fields already suffering from high N and P concentrations. Likewise, although composting is a useful waste management tool, it can negatively impact air quality. Special care is required to ensure a targeted N/C ratio; otherwise, an important fraction of N is released into the air in the form of ammonia and NOx. Thermochemical processing is explored as an alternative to these technologies. However, very little is known about the thermochemical behavior of N-contained molecules in blends with lignocellulosic materials. This dissertation contributes to understanding the reactions between N-containing compounds in acidic and basic environments and how these reactions can be used to design N-doped chars for phosphate adsorption and to manage dairy manure. The thermochemical reactions between model N-containing compounds such as lysine, melamine, dicyanamide (DCD), chitosan, and cellulose were studied. Experimental evidence of interactions between amine and ammonia from N-containing compounds and the carbonyl groups from cellulose through the Maillard reaction was observed. While cellulose blends with lysine and chitosan resulted in pyrrolic chars, DCD and melamine favored the formation of pyridinic chars. The impact of acid and basic carbonization conditions on char yield and N conversion efficiency was studied. H3PO4 catalyzes dehydration reactions, leading to higher quantities of char and the formation of pyrrolic N groups. The highest N conversion efficiency, close to 78 wt. %, was obtained at 500 °C with chitosan. NaOH favors the formation of pyridinic chars. The information gained in these studies was used to develop engineered chars from Douglas fir and chitosan to remove phosphates from aqueous effluents. A response surface methodology approach was used to identify processing conditions leading to high phosphate adsorption capacity. A biochar with an adsorption capacity of 112 mg/g was obtained at a carbonization temperature of 700 °C, a biomass/chitosan ratio of 1:1, and an MgCl2 concentration of 12 wt.%. A synergetic effect between N and Mg leading to high phosphate adsorption capacity was observed. Reactions mechanistic understanding gained in the first half of the dissertation was used to design an experimental program to identify the best thermal conditions to treat dairy manure/biomass blends. These carbonized solids are rich in N and P. A surface response methodology was used to identify processing conditions maximizing N conversion efficiency at douglas fir/manure ratio: 1:1, temperature: 260 °C, and an H3PO4 concentration of 2 wt. %.