Hydrothermal liquefaction enhanced by various chemicals as a means of sustainable dairy manure treatment

Because of the increase in concentrated animal feeding operations, there is a growing interest in sustainable manure management. In this study, hydrothermal liquefaction (HTL) of dairy manure enhanced by various chemicals (NH3·H2O, H3PO4, and glycerol) was proposed as a sustainable alternative for the dairy manure management. The applications of NH3·H2O and H3PO4 during HTL could significantly enhance the production of liquid chemicals. The addition of NH3·H2O or glycerol increased the amounts of non-polar toluene, xylene, and other benzene-contained compounds, while the use of H3PO4 produced high amounts of acids, pyridine, 3-methyl-pyridine, 2,6-dimethyl-pyrazine, 2-cyclopenten-1-ones, and phenols. The biochars produced via HTL showed a significant increase in the surface area/pore volume and relatively higher N, P, C, and other minerals, and may serve as a good soil amendment and nutrient source. The preliminary energy analyses showed that the energy consumption of this process might be reduced to 50% of the original energy content of the feedstock, and the energy payback period was about 3.5 years. Combining all advantages, HTL of dairy manure might increase the sustainability of the farming operation via producing energy products, fine chemicals, and biochars.