Sewage sludge can be turned into crop fertilizer
TOKYO >> As prices for raw materials continue to soar, the Japanese government is working toward using sewage treatment sludge as fertilizer.
Chemical fertilizers are ubiquitous on Japanese farms, but the country relies on overseas imports for related raw materials such as potassium chloride. Due to the ongoing war in Ukraine and other factors, prices for these materials have skyrocketed.
Producing domestic fertilizers can keep food prices down and protect the agricultural industry.
The government planned to include measures for domestically produced fertilizer in a comprehensive economic stimulus package assembled in November. Prime Minister Fumio Kishida had already sought measures to reduce Japan’s dependence on chemical fertilizers as part of a more resilient economic structure to tackle energy and food crises.
According to the Land, Infrastructure, Transport and Tourism Ministry, only about 10% of the roughly 2.3 million tons of sewage sludge discharged annually is used as fertilizer, after undergoing dewatering and fermentation. Farmers are hesitant to reuse sewage sludge in part because of concerns that heavy metals such as cadmium and mercury could concentrate in the wastewater. Additionally, factors such as its strong odor have hindered its acceptance.
The ministry has allocated more than $220,000 from its 2023 budget to expand the use of the fertilizer. The ministry plans to analyze its chemical makeup and publicize the safety of the fertilizer, which is rich in the nitrogen and phosphoric acid vital for growing crops.
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The appeal of fertilizers made from sewage sludge is their low cost. Saga City, for instance, processes all its sewage sludge into fertilizer, which sells for 1 cent per kilogram.
The Saga City Sewage Purification Center — which processes 20 million tons of sewage water annually — removes sludge from sewage water, dewaters it, then ferments it at 194 degrees Fahrenheit or hotter. The process kills bacteria and weed seed while eliminating odors. Each year, the center transforms about 8,000 tons of sludge into 1,400 tons of fertilizer.
According to the city government, the fertilizers sell out every year.
