Nitrogen removal and power generation from treated municipal wastewater by its circulated irrigation for resource-saving rice cultivation Toru Watanabe, Takuma Mashiko, Rizki Maftukhah, Nobuo Kaku, Dong Duy Pham and Hiroaki Ito ABSTRACT This study aims at improving the performance of the cultivating system of rice for animal feed with circulated irrigation of treated municipal wastewater by applying a larger amount of wastewater, as well as adding a microbial fuel cell (MFC) to the system. The results of bench-scale experiments indicate that this modification has increased the rice yield, achieving the target for the rice cultivar used in the experiment. In addition, an assessment of protein content of the harvested rice showed that the value of the rice as animal fodder has improved. Compared with normal one-way irrigation, circulated irrigation significantly enhanced the plant growth and rice production. The direction of the irrigation (bottom-to-top or top-to-bottom) in the soil layer had no significant effect. This modified system demonstrated >96% for nitrogen removal from the treated wastewater used for the irrigation, with approximately 40% of the nitrogen being used for rice plant growth. The MFC installed in the system facilitated power generation comparable with that reported for normal paddy fields. The power generation appeared to be enhanced by bottom-to-top irrigation, which could provide organic-rich treated wastewater directly to the bacterial community living on the anode of the MFC set in the soil layer. Toru Watanabe (corresponding author) Takuma Mashiko Nobuo Kaku Hiroaki Ito Department of Food, Life, and Environmental Sciences, Faculty of Agriculture, Yamagata University, 1-23 Wakaba-machi, Tsuruoka, Yamagata 997-8555, Japan E-mail: to-ru@tds1.tr.yamagata-u.ac.jp Rizki Maftukhah Faculty of Agricultural Technology, Gadjah Mada University, Jl. Sosio Yustisai, Bulaksumur, Yogyakarta 55281, Indonesia Dong Duy Pham The United Graduate School of Agricultural Sciences, Iwate University, 3-18-8 Ueda, Morioka, Iwate 020-8550, Japan Key words | circulated irrigation, microbial fuel cell, municipal wastewater, nitrogen removal, power generation, rice fodder ABBREVIATIONS DO dissolved oxygen EC electrical conductivity MFCs microbial fuel cells MSD midsummer drainage ORP oxidation-reduction potential SPAD soil plant analysis development TN total nitrogen TOC total organic carbon INTRODUCTION In many areas worldwide, it has been recognized that urban wastewater is an important water resource. In addition, as wastewater is rich in the nutrients needed for plant growth, it is ideal for agricultural irrigation (Chung et al. ; Norton-Brandão et al. ). Reusing wastewater for agricultural irrigation brings about major economic, environmental, and social benefits, as water and nutrients are supplied simultaneously for crop production (Mateo- Sagasta et al. ), thereby reducing the need for and the cost of added fertilizer. In addition, the discharge of pollu- tants to surface water bodies ( Jiménez ) is avoided. On the other hand, municipal wastewater could have unde- sirable contents, such as inorganic matters, toxic chemicals, and pathogens that could pose health risks to the consumers and farmers (Singh et al. ; Hanjra et al. ). Rice is a major food crop worldwide, especially in Asia and Africa (Chapagain & Hoekstra ); however, the cul- tivation of paddy rice consumes significant volumes of water (Muramatsu et al. ). As rice plants grow by consuming 898 © IWA Publishing 2017 Water Science & Technology | 75.4 | 2017 doi: 10.2166/wst.2016.572 Downloaded from https://iwaponline.com/wst/article-pdf/75/4/898/455111/wst075040898.pdf by guest on 13 June 2020