A potential new source of fertilizer

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Abstract graphic. Credit: DOI: 10.1016 / j.scitotenv.2021.146648

A recently published study focuses on a new process for converting human waste from household septic tanks into phosphorus-rich fertilizer.

Professor of Biomedical and Chemical Engineering and Science Toufiq Reza, along with former Florida Tech researchers Nepu Saha and Kyle McGaughy and Sarah Davis at Ohio University, have published a new paper titled “Assessing hydrothermal carbonization as Sustainable Home Sewage Management for rural counties: A case study from Appalachian Ohio “published in August in the journal Total environmental science.

The main conclusions of the article are that hydrothermal treatment of septic tank waste, known as septic sludge, is economically viable and this treatment could reduce the cost of pumping septic sludge by up to 25%. Converting waste into usable fertilizer could also significantly reduce the demand for fertilizer in the study area, which for this research was rural Athens County, Ohio, a rural Appalachian county in the southeastern part of the ‘State. This work can also have major impacts in developing countries, a benefit that underpins some of Reza’s previous research.

For this study, waste is converted into fertilizer through a high temperature, high pressure process called hydrothermal carbonization (HTC). HTC is a thermochemical conversion technique that can transform wet biomass into energy and chemicals without pre-drying. So far, the process has produced material that shows potential to facilitate the growth of inedible crops, although Reza noted that more testing needs to be done to see if the fertilizer could be used for growing. food.

“The idea is that human sewage contains pathogens, and we have to kill them and sterilize them,” Reza said. “If we use high temperatures and high pressures, many of these pharmaceuticals in waste, such as antibiotics and the active ingredients in birth control pills, will be degraded.”

In addition to offering potential benefits to agriculture, this renewable approach could help homeowners financially. Almost 22 million American homes (about 25% of the total) use septic tanks. In Ohio, more than one million homes depend on their own treatment facility, with the percentage of homes equipped with septic systems being even higher in rural Appalachian areas. A study by the City of Athens Department of Health showed that over 25% of septic tanks in Ohio do not perform well or fail due to lack of understanding of the need for maintenance and / or expensive cleaning. To provide the cleaning service, sludge haulers may charge homeowners around $ 200 to $ 500, depending on the size and complexity of the tank. This is quite a significant cost for rural homeowners, who have median and average annual household incomes of $ 24,326 and $ 48,628, respectively.

“The idea was that instead of homeowners who might have a hard time paying for the sludge pumping costs, we could convert their burden into something valuable and useful locally. That way we could eliminate the sludge. pumping fee from the septic tank, with someone coming in, taking it and converting it to fertilizer and selling it to the local community, “said Reza.” That was the motivation: can we take this responsibility from the owners and become a profitable business? ”

This approach could also be good news for inland waterways. Sludge is considered dangerous because it can transmit disease and is high in nitrogen, phosphorus and potassium, which can lead to damaging nutrient runoff. Excessive amounts of nutrients in rivers and other bodies of water can cause harmful algal blooms and disrupt the reproductive endocrinology of fish.

In addition to testing the fertilizer for edible crop use, the researchers also plan to examine ways in which the septic tank waste disposal system would be implemented. Reza noted that an ideal situation would be to have a hydrothermal treatment plant near a sewage treatment plant, although in rural areas this is not always possible. One idea they have is a mobile unit that can pick up the waste, convert it into fertilizer, and then move on to the next house.

Reza and the researchers are also leading a related project in Ohio, funded by the Sugarbush Foundation, which focuses on “vector attraction reduction.” It examines whether wastewater treatment can reduce the number of flies and other insects. The next step is to design a pilot system and then seek approval from the United States Environmental Protection Agency.

Reza hopes that the projects’ focus on rural areas will lead to better renewable resource initiatives overall.

“If we develop each county and use its own resources, it will make their county sustainable and lead to a sustainable state,” he said. “Instead of developing cities, maybe we could develop rural counties sustainably, which will have a huge impact on the sustainability of the United States.”


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More information:
Nepu Saha et al, Evaluating Hydrothermal Carbonization as a Sustainable Management of Domestic Wastewater for Rural Counties: A Case Study from the Ohio Appalachians, Total environmental science (2021). DOI: 10.1016 / j.scitotenv.2021.146648

Provided by the Florida Institute of Technology

Quote: From Septic Tank to Sustainability: A Potential New Source of Fertilizer (2021, September 20) retrieved September 20, 2021 from https://phys.org/news/2021-09-septic-sustainable-potential-source- fertilizer.html

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