Sewage sludge | Scoins.net | DJS

## Sewage sludge

You would n't think this would make an intersting topic, so read this:

Microplastics were detected in all samples taken from across the treatment process with concentrations ranging from 37.7–286.5 number of microplastics/g of sludge (dry weight). The microplastic load in the final biosolid products produced at the site ranged from 37.7–97.2 number of microplastics/g of sludge (dry weight). The wastewater treatment works in this study produces 900 tonnes of anaerobically digested sludge cake and 690 tonnes of lime stabilised cake per month. Based on the results from this study, the application of these biosolids to agricultural land as fertilisers can potentially release 1.61 × 10¹⁰ and 1.02 × 10¹⁰ microplastics in anaerobically digested and lime stabilised sludge respectively, every month (equivalent to the same volume as >20,000 plastic bank cards).  From

Q1. 1.61x10¹⁰ particles of microplastic are, on average in every tonne of digested sludge cake, which is then distributed onto farm land just from this wastewater treatment works. This treatment works produces 900 tonnes per month of this sludge cake and the UK produces around 85,000 tonnes a month

How many particles of microplastic are we imagining being added to the soil every month in the UK?

Q2.  A standard plastic bank card is, im millimetres, 85.6x53.98x0.76. Convert this to cubic metres.

Q3. The text says the volume of plastic added to the soil from this treatment plant is equivalent to more than twenty thousand credit cards. Convert this to cubic metres and then to litres and then choose an everyday object of about the same size.

Q4. Take your answers from the previous questions amd describe the volume of plastic going into the soil every month by this method.

We no longer do regular testing of soils for contaminants. Apparently we cannot afford it. One wonders if we can afford not to do that testing. If we are taking the plastics out of the waste water, why are we putting it back via the soil? For that matter, if thsi is happening with plastics, what else are we separating out of water and returning it to the environment? What else should we be doing?

Of course, you don't want this sort of question mixed with maths, but if we don't use the answers we get, where is the point?

A1.   1.61x10¹⁰ x 85000/900 = 1.52x10¹²

A2.   0.0856x0.05398x0.00076 = 3.511x10⁻⁶  m³

A3.   20,000 x A2 = 0.07m³ = 70 litres, about the same as a human (of 70kg). Also a large fuel tank, a small cupboard or a comfy chair.

A4.   A3 x 85000/900 = 6.63 m³ of plastic to the soil every month.

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