P. Somsila, U. Teeboonma, and S. Khabuanchalad, “A Two-Stage Anaerobic Digester of Pig Manure and Food Waste for Biogas Production with Heat Exchanger”, Eng. J., vol. 25, no. 10, pp. 123–132, Oct. 2021, doi: 10.4186/ej.2021.25.10.123.