The Beloved threw a story at me that runs along similar tracks. Different scale, different chemical, different source, different problem, different outcome but . . . still about reducing the incommensurate to cash and thereby directly comparing apples and oranges. That's not so difficult actually, because they are both fruit. In the story above carbon is carbon is carbon, in this one nitrate is nitrate. And we really do not want the stuff in the water-supply.
pooo-eeee> charnel-house and then a poisoned watercourse where nothing lives.
The EU Water Framework Directive WFD / Wasserrahmenrichtlinie / Directive-cadre sur l'eau / Rámcové směrnice o vodě / Vesipuitedirektiivi [prev] is a set of evidence-based regulations that endeavour to keep European water within acceptable limits of insult from industrial, agricultural and domestic pollution. WFD encompasses a lot: pH, phenol, BOD, phosphates, nitrates.
Wessex Water had to reduce its discharge of nitrates into Poole Harbour by 40 tonnes a year. No fair, cried Wessex, there are 2,000 tonnes of nitrate added to the Harbour, so that 40 tonnes on our To Do List is only 2% of the total. Furthermore, it will cost our Malaysian masters £6 million to build new treatment plants which will incur a £400,000/yr running cost - that's £10,000 per tonne to process the waste water solution to the excess nitrate problem. They looked round the harbour for something on which to shift the blame. The graphic L shows that sewage treatment works STW's contribution is dwarfed by that of agriculture. Agricultural nitrates enter the water because farmers pay for fertiliser and spread it on their fields in unsuitable quantities and inappropriate times. Before it can be absorbed by the wheat, beet or ryegrass, the rain comes in and washes the investment into the local drains, rills, streams and rivers, eventually to Poole Harbour.
Wessex contacted Entrade to do some research and broker a deal with local farmers. That solution sounds good because it looks at nitrates as a catchment issue rather than a Wessex Water issue. In our everything can be monetized world, nitrate is nitrate, in the same way as €1 is $1.14. Entrade determined that, if farmers could be induced to plant cover crops over-winter when rainfall is highest, then that would demonstrably reduce fertilizer run-off. That would alsokeep the nutrient on the fields on which it had been spread and as a green manure provide better soil structure. And (although this wasn't factored in) promote microbial diversity in the soil. How to set the price? By auction! farmers bid for money from Wessex to encourage them to do manage their land a little differently. The price came down to £1.40 /kg N saved. I'm a bit out of my depth [so not in the shallows of Poole Harbour har har] here but I think that is equivalent to £6,360 /tonne NO3 saved. Which is less than the STW capital infrastructure solution at £10,000 /tonne.
Wessex can wriggle off the WFD hook and save a massive capital investment. My mother and her neighbours can continue to flush flush flush and pay for a bunch of Malaysians to deal with their ordures. If that sounds bit colonial it is; but the question is who is the coloniser and who the colonised?