Xue, Bai, Li Zifu, Wang Xuemei, He Xi, Cheng Shikun, Bai Xiaofeng, and Gao Ruiling. 2017. “Online Measurement of Alkalinity in Anaerobic Co-Digestion Using Linear Regression Method”. International Journal of Agricultural and Biological Engineering 10 (1). Beijing, China:176-83. https://ijabe.org/index.php/ijabe/article/view/2701.