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FEC researches sludge use
sewage as fertilizer

Researchers Marta Guilherme Pires and Patrícia Mazzante do Nascimento: sludge improves the biological activity of the soil

The sludge generated by the domestic sewage treatment process is rich in nutrients and organic matter and is increasingly being considered a viable alternative for agriculture. The use of this material, with a series of advantages, reduces the use of chemical fertilizers – widely sold on the market – as proven by three research works, carried out at the Faculty of Civil Engineering (FEC) at Unicamp.

Rich in micro and macronutrients, such as nitrogen and phosphorus, sludge improves the biological activity of the soil. However, sewage sludge can contain contaminants and its application requires special care to avoid damage to the health of the population and the environment, warn Unicamp researchers.

The sludge used in the research was collected at the Riacho Grande Sewage Treatment Station, located in the municipality of São Bernardo do Campo, in Greater São Paulo. The treated waste ends up generating sewage sludge, a biological mass composed of microorganisms that feed on the organic matter found in the waste. In order not to become an environmental problem, researchers at Unicamp started working on research and discovered that sewage sludge is an efficient, cheap and less polluting fertilizer than chemical fertilizers.

Real Time – Marta Guilherme Pires, author of the thesis Assessment of the presence of pathogens in the stabilized liquid sludge from ETE (aerobic process) when applied to sandy – silty soil, says that the three works have the main purpose of monitoring the application of sewage sludge to the soil , with the aim of verifying whether or not the reuse of this type of material can be done and what are the problems of possible contamination.

“The application of sewage sludge to the soil can be done, without forgetting that the sludge may contain elements that could eventually cause soil contamination, such as pathogens or nitrogen that will end up being transformed into nitrate, and can be harmful to health. of the individual”, explains the researcher. In the case of pathogens, the main contaminations are those caused by Ascaris eggs, amoebas and Giardia.

Regarding the contamination of the water table with nitrate, a compound that can cause methemoglobinemia (a disease that affects the transport of oxygen by red blood cells) in newborn children who consume contaminated water.
“The World Health Organization (WHO) recommends values ​​of up to 10 mg of nitrate per liter of water”, says Patrícia Mazzante do Nascimento, author of the master's thesis Assessment of contamination of groundwater by nitrate and phosphorus after applications of liquid sewage sludge domestic soil. Patrícia also explains that an aerobic sewage treatment plant produces large quantities of sludge that need to be disposed of appropriately.

“We seek to evaluate sanitary parameters with a view to using sludge in agriculture and also in correcting degraded soils. The sludge contains nutrients that help improve the conditions of this soil, which can possibly be used for new plantings, reducing the need for the use of chemical fertilizers”, he says. Currently, sewage sludge has been tested on coffee and corn crops.

It is not recommended to use sludge on crops such as vegetables, for example, as there may be contamination through the ingestion of pathogens due to direct consumption of the product.

The other master's thesis, Application of liquid sanitary sewage sludge to soil: determination of fecal and total coliforms, by Andréia Ferraz de Campos, researched the incidence of total and fecal coliforms in surface soil and infiltrated liquid.

As a final result of the three surveys, it was concluded that the liquid sewage sludge application rate of 22,5 TS/ha per year proved to be the most appropriate in terms of the parameters evaluated, with regard to contamination of the groundwater and surface soil. . All research was supervised by professor Bruno Coraucci Filho, from the Faculty of Civil Engineering (FEC). (ARF)

 

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