Roy Posmanik 1, Ran Darzi 1, Refael Glicksberg 1, Ariel Shabtay 2 and Miri Cohen-Zinder 2
1. Institute of Soil, Water and Environmental Science, ARO, Waste Management Section, Newe Ya’ar Research Center, Israel
2. Institute of Animal Science, ARO, Beef Cattle Section, Newe Ya’ar Research Center, Israel
Optimizing the feedlot energy balance
As global population continues to grow, with estimates predicting over 9 billion people by 2050, the world is facing an increasing demand for animal food products and the development of sustainable operation practices is required. With the majority of animal feed applied carbon secreted as feces, the conversion of livestock manure into energy products (i.e., solid and liquid fuels for heat, electric power and transportation) can enhance energy recovery from confined feedlots.
Hydrothermal treatment of livestock manure as a renewable energy resource
The study, published recently at one of the Royal Society of Chemistry’s journals Environmental Science: Water Research and Technology, is focusing on the conversion of livestock manure into energy products via hydrothermal liquefaction. Hydrothermal reactions, conducted at different temperatures (200–300 °C), were compared on the basis of conversion yields, carbon and energy recoveries and product quality.
Testing different temperatures to optimize the treatment
The results demonstrate how reaction temperatures affect the relative production of biocrude oil and hydrochar. Comprehensive analyses of both biocrude oil and hydrochar suggest that decarboxylation was the dominant mechanism involved in the reaction and was enhanced with temperature. With a relatively high carbon (67–74%) and low oxygen (13–18%) content, biocrude oil seems to provide a better platform to deliver recovered energy, with higher heating values of 30–35 MJ kg−1.
Energy return is 2-3 times higher than the energy invested
An overall energy balance, supported by a sensitivity analysis, demonstrated how the higher temperature enhanced the overall energy return. Twelve scenarios were used to estimate the daily net energy gained in feedlots of different sizes. All scenarios provided a positive energy balance with returned energy found to be 2 to 3 times higher than invested energy. The estimation presented herein highlights the feasibility of hydrothermal technology to return energy by multiple products and, hence, to provide a sustainable waste management practice in confined feedlots.