Belmonte, M., C.-F. Hsieh, C. Figueroa, J. L. Campos, and G. Vidal. “Effect of Free Ammonia Nitrogen on the Methanogenic Activity of Swine Wastewater”. Electronic Journal of Biotechnology, vol. 14, no. 3, May 2011, https://preprints.pucv.cl/index.php/ejbiotechnology/article/view/v14n3-11.