#33 Asta: From feces to farm – closing nutrient loops

How to safely return nutrients in human feces to agricultural fields?

Asta Hooge Poulsen is a PhD fellow at Roskilde University and conducts research on nutrient recovery from sewage sludge for agricultural use. She studies how different sludge treatments impact the fitness of sludge for field application and its implications for soil health.

Department & Group: Department of Science and Environment, Environmental Dynamics, Roskilde University Plastic Society (Roskilde Environmental Plastic Society | Roskilde Universitet (ruc.dk))

Supervisors: Henrik Hauggaard-Nielsen, Gry Lyngsie and Kristian Syberg

Dissertation Title (as for now 😉):

Nutrient recirculation from urban to rural areas: Sludge – A gem in disguise?
Which sludge treatments favour soil health, efficiently remove contaminants like microplastics and contain wanted components like plant nutrients for farming systems.

Today, most wastewater treatments plants focus on releasing water clean enough for discharge into natural aquatic ecosystems. One important step in that treatment is separating the solid fraction (the sewage sludge) from the liquid fraction (the water). The sludge is often treated as waste, burnt and landfilled. However, the sludge contains organic matter and nutrients useful for agricultural fields, which is why interest in using it in agriculture systems grows. Some countries, like Denmark, already apply parts of their sludge to fields.

Why doesn’t everyone do it, if it can contribute to nutrient recycling?

Mostly because the sludge doesn’t only include useful nutrients but also problematic substances like microplastics, heavy metals, pharmaceuticals, and others.

In her research, Asta focuses on soil health, microplastics and societal barriers for using sludge as fertiliser. She looks at the microplastic-removal-efficiency of different sludge treatments at wastewater treatment plants and the effects sludge has on soil.

She does that by collecting sludge samples at wastewater treatment plants and by applying sludge to soil columns in her lab. In addition, she and her colleagues work on a risk assessment matrix that shall help estimate the adverse effects of applying sludge containing microplastics to agricultural lands.

She also talks to farmers to find out about their concerns and wishes for using sludge as fertiliser. She wants to build a bridge between the management of sludge at wastewater treatment plants and the farming sector and help them collaborate for mutual benefit.

Soil Health: Soil with properties favourable for agricultural production. Characteristics of a healthy soil in that context are: sufficient plant nutrients, a diverse population of microorganisms and species like earthworms and other soil-living insects, a crumbly structure – comparable to the one found in soils you can buy at a gardening center.

Asta’s publication:

Fate of Microplastics in Sewage Sludge and in Agricultural Soils

Sediment matters as a route of microplastic exposure: A call for more research on the benthic compartment

UN plastic treaty must mind the people: Citizen science can assist citizen involvement in plastic policymaking

Asta’s funding:  

The PhD is fully funded by Roskilde University. Between Department of Science and Environment and Department of People and Technology.

If you would like to get in touch with Asta, check LinkedIn or X @AstaHooge .

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