Cultivation of rice for animal feed with circulated irrigation of treated municipal wastewater for enhanced nitrogen removal: comparison of cultivation systems feeding irrigation water upward and downward

Abstract

To achieve enhanced nitrogen removal, we modified a cultivation system with circulated irrigation of treated municipal wastewater by using rice for animal feed instead of human consumption. The performance of this modified system was evaluated through a bench-scale experiment by comparing the direction of circulated irrigation (i.e. passing through paddy soil upward and downward). The modified system achieved more than three times higher nitrogen removal (3.2 g) than the system in which rice for human consumption was cultivated. The removal efficiency was higher than 99.5%, regardless of the direction of circulated irrigation. Nitrogen in the treated municipal wastewater was adsorbed by the rice plant in this cultivation system as effectively as chemical fertilizer used in normal paddy fields. Circulated irrigation increased the nitrogen released to the atmosphere, probably due to enhanced denitrification. Neither the circulation of irrigation water nor its direction affected the growth of the rice plant and the yield and quality of harvested rice. The yield of rice harvested in this system did not reach the target value in normal paddy fields. To increase this yield, a larger amount of treated wastewater should be applied to the system, considering the significant amount of nitrogen released to the atmosphere.

Evaluation of Dissolved Greenhouse Gas Profiles in Paddy Fields Irrigated with Treated Sewage Effluent

“…The rice varieties used here were Bekoaoba (forage rice) and Akita-Sakekomachi (brewery rice). The adaptation of Bekoaoba to TSE-irrigated cultivation has been assessed in a previous study [5]. The transplant density was 18 stubbles per reactor.…”

“…For example, the water resource per capita in the Asian Pacific was estimated to be 2,970 m 3 y -1 in 2009, which is less than half of the global average (6,236 m 3 y -1 ) and exhibited a decreasing trend (3,455 m 3 y -1 in 1999) [4]. Therefore, TSE use in agricultural fields in this region, particularly paddy fields, has been strongly promoted [5][6][7].…”

Municipal Wastewater Irrigation for Rice Cultivation

“…For example, urea plant effluents, as a rich source of liquid fertilizer in concentrated forms, have adverse effects on rice and corn yields [2]. Also, oversupply of nitrogen may be resulted in overgrowth of rice plants, which triggers their lodging and reduces eating quality of rice due to increased content of proteins [39].…”

“…These difficulties in irrigation of treated wastewater gave us motivation to propose a new concept to cultivate rice for animal feed rather than for human consumption [39]. The rice cultivars used for animal feed have several advantages compared with those used for human consumption.…”

“…The bench-scale experiment (Figure 2) with dimension of 0.6 × 0.3 m revealed that cultivation of rice for animal feeding could remove three times the amount of nitrogen from the treated wastewater compared with rice cultivation for human consumption [39]. In addition, the experiment showed that upward irrigation called bottom-to-top irrigation, in which treated wastewater is supplied from the pipe fixed at the bottom of the field and then infiltrate up through soil layer to the surface, increased the nitrogen released to the atmosphere, probably because of enhanced denitrification.…”