Lukkhana Benjawan, Seung-Hwan Lee, and Thammarat Koottatep. “Nitrogen Removal in Duckweed-Based Ponds with Effluent Recirculation”. Agriculture and Natural Resources, vol. 42, no. 4, Dec. 2008, pp. 767-75, https://li01.tci-thaijo.org/index.php/anres/article/view/244514.