Sludge deposition calculation

An important source of engineered nanomaterial (ENM) releases into the environmental soil system is the deposition of sludge coming from sewage treatment processes. In many European countries, the sludge from waste water treatment plants (or sewage treatment plants, STP) is intentionally applied to agricultural land as a soil enhancer (because it is rich in nutrients and organic matter). This sludge may contain ENMs that were present in the waste water streams, stemming from industrial manufacturing processes or from household wash-off of cosmetics or sunscreens.

In the NanoFASE, ENM releases to waste water treatment have been calculated based on the emission model (Adam et al., 2018)

1. $$\small M_{STP}$$ - mass of ENM entering sewage treatment plants (STP)

2. $$\small TC_{STP}\rightarrow _{Sludge}$$ - transfer coefficient of ENM from STP to sludge

3. $$\small M_{Sludge} = M_{STP} \times TC_{STP}\rightarrow _{Sludge}$$ - mass of ENM in sludge

4. $$\small TC_{Sludge}\rightarrow _{Sludge}$$ - transfer coefficient from sludge to soil

5. $$\small M_{Sludge treated soil} = M_{Sludge} \times TC_{Sludge}\rightarrow _{Soil}$$ - mass of ENM in sludge-treated soil

Execution

The mass of ENM entering STPs is calculated in the upstream part of the emission model. The transfer coefficient of ENM from STP to sludge depends on the level of treatment (primary, secondary or tertiary) implemented in the STPs of the waste management system. This transfer coefficient was assessed based on the related scientific literature specific to each ENM. The transfer coefficient from sludge to soil corresponds to the application of sludge to agricultural land. All transfer coefficients are defined as probability distributions, enabling the consideration of several data sources in the definition of each flow. Total ENM present in deposited sludge is calculated on a per country basis distributed spatially across a grid by using arable land as defined in CORINE as a proxy.