Nitrogen removal and power generation from treated municipal wastewater by its circulated irrigation for resource-saving rice cultivation

Cai

et al. 2019

Water

Self Cite

To obtain a high rice yield and quality for animal feed without synthetic fertilizers, an experiment with bench-scale apparatus was conducted by applying continuous irrigation with treated municipal wastewater (TWW). Uniform rice seedlings of a high-yield variety (Oryza sativa L., cv. Bekoaoba) were transplanted in five treatments to examine different TWW irrigation directions (“bottom-to-top” and “top-to-top” irrigation) and fertilization practices (with and without P-synthetic fertilizers) as well as one control that simulated the irrigation and fertilization management of normal paddy fields. The highest rice yield (14.1 t ha−1), shoot dry mass (12.9 t ha−1), and protein content in brown rice (14.6%) were achieved using bottom-to-top irrigation, although synthetic fertilizers were not applied. In addition, this subsurface irrigation system could contribute to environmental protection by removing 85–90% of nitrogen from TWW more effectively than the top-to-top irrigation, which showed a removal efficiency of approximately 63%. No accumulation of heavy metals (Fe, Mn, Cu, Zn, Cd, Ni, Pb, Cr, and As) in the paddy soils was observed after TWW irrigation for five months, and the contents of these metals in the harvested brown rice were lower than the permissible limits recommended by international standards. A microbial fuel cell system (MFC) was installed in the cultivation system using graphite-felt electrodes to test the capacity of electricity generation; however, the electricity output was much lower than that reported in normal paddy fields. Bottom-to-top irrigation with TWW can be considered a potential practice to meet both water and nutrient demand for rice cultivation in order to achieve a very high yield and nutritional quality of cultivated rice without necessitating the application of synthetic fertilizers.

Section: Discussioncontrasting

confidence: 75%

Section: Introductionmentioning

confidence: 99%

Rice Cultivation without Synthetic Fertilizers and Performance of Microbial Fuel Cells (MFCs) under Continuous Irrigation with Treated Wastewater

Cai

et al. 2019

Water

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“…The high yield under Control treatment was thus attributed to the high dose of mineral fertilisers supplemented. However, in spite of zero use of mineral fertilizers, CSI treatment still produced a comparable yield that were much higher than the target of 8 t ha -1 for the variety Bekoaoba 17 and the average yield (7.3 t ha -1 ) obtained from conventional paddy elds in the same region 7 . The high yield obtained from CSI treatment was primarily attributed to the effective assimilation of the plant nutrients, especially the high concentrations of N (Table 2) derived from the irrigation TWW during the entire crop season 6 .…”

Section: Discussionmentioning

confidence: 84%

Methane Mitigation is Associated with Reduced Abundance of Methanogenic and Methanotrophic Communities in Paddy Soils Continuously Sub-irrigated with Treated Wastewater

Miyazawa

et al. 2021

Preprint

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Herein, we examined emissions of CH4 and the community structures of methanogenic archaea and methanotrophic bacteria in paddy soils subjected to a novel irrigation system, namely continuous sub-irrigation with treated wastewater (TWW). This system has recently been developed by our group to effectively reuse TWW for the cultivation of protein-rich rice. The results showed that despite not using mineral fertilisers, the wastewater reuse system produced a high rice yield comparable to that of a conventional cultivation practice and reduced CH4 emissions from paddy fields by 80%. During the reproductive stage of rice plants, when high levels of CH4 emissions from both treatments were observed, continuous sub-irrigation with TWW not only considerably inhibited the growth of methanogens in the lower soil layer, but also vastly reduced the abundance of methanotrophs in the upper soil layer, which was strongly consistent with the effective mitigation of CH4. The compositions of the examined microbial communities were not particularly affected by the studied cultivation practices. Overall, this study demonstrated that continuous sub-irrigation with TWW was an effective method to produce high rice yield and simultaneously reduce CH4 emissions from paddy fields, and it also highlighted the potential underlying microbial mechanisms of the greenhouse gas mitigation.

“…The TWW used for topdressing was collected from the effluent of the WWTP, which employed the standard activated sludge process followed by chlorine disinfection, showing annual average total suspended solids and biochemical oxygen demand of 3.1 and 4.7 mg L −1 , respectively 34 . Other basic properties of the TWW are as follows: pH of 7.2; EC of 64.8 mS m −1 , total N, P, and K contents of 24.8, 0.6, and 10.2 mg L −1 , respectively.…”

Section: Methodsmentioning

confidence: 99%

High yield of protein-rich forage rice achieved by soil amendment with composted sewage sludge and topdressing with treated wastewater

Ichikawa

et al. 2020

Sci Rep

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Aiming to promote low-cost production of protein-rich forage rice and resource recycling from wastewater treatment plants, a pot experiment was conducted to assess the possibility to substitute mineral fertilizers with composted sewage sludge (cSS) with/without top-dressing with treated municipal wastewater (TWW). Results indicated that a basal application of CSS at 2.6 g N pot −1 replaced conventional mineral fertilization of 1.3 g N pot −1 to produce comparable yields with the same rice protein content, although there might be a risk of increased As concentration in rice grains. Interestingly, CSS application at a reasonable dose of 1.3 g N pot −1 , followed by a topdressing with TWW resulted in 27% higher yield and 25% superior rice protein content relative to the mineral fertilization, with no risk of heavy metal(loid) accumulation in grains and in paddy soils. Here we demonstrated an appealing fertilization practice with zero use of mineral fertilizers in paddy rice cultivation, expectedly contributing towards sustainable rice farming and animal husbandry in Japan. Accelerated generation of sewage sludge and treated municipal wastewater (TWW) along with increasing limitations in availability of resources have required highly efficient and sustainable disposal practices for the sludge and TWW, triggering a rapid change of wastewater treatment plants (WWTPs) from stations for wastewater purification and pollutant removal towards facilities for recourse recovery 1. Rice farming demands large quantities of irrigation water and mineral fertilizers, which allows the great opportunity for recycling plant nutrients and water from WWTPs to reduce the dependence of the crop production on mineral fertilizers and other freshwater sources through soil amendment with sewage sludge and reuse of TWW. Aiming to substitute forage rice for imported feed-stuffs of unstable supply and a price highly dependent on global markets and to avoid the risk of rising production costs of domestic animal husbandry, adoption of forage rice cultivation is drawing increasing attention in Japan 2,3. In attempts to promote low-cost forage rice cultivation while recycling plant nutrients and water from WWTPs, we have developed new irrigation systems for effective reuse of TWW as a sole source of both water and plant nutrients to produce high grain yields of protein-rich rice without the need for mineral fertilizers 3-5. These TWW irrigation systems have proved highly beneficial and applicable to paddy fields located near local WWTPs, from which the effluent is supplied to paddy fields 3 ; however, they frequently face difficulties to attain an even distribution of TWW to paddy fields far from the WWTPs due to the rising cost of instalment of water-distributing pipes/channels. Hence, application of sewage sludge might be an alternative in those paddy fields owing to its abundance in organic matter and plant nutrients, especially N and P 6. Nevertheless, soil amendment of sewage sludge generally raises concerns of environmental and health risks du...