Definitely not a poo bus

[whole diary]

[Red Squirrel]

Hold on - there's two things going on here, and getting mixed up: "bio" and "methane".

Who's getting these mixed up? I think Tim made a typo: his

But the combustion products are CH4...

should read 'But the combustion products of CH4...'; other than that I can't see any obvious source of confusion.

FTN makes an interesting observation:

To read the various news articles at face value, you would be forgiven for thinking that First will be taking hourly deliveries of food waste, and shovelling it into a giant machine, producing a special gas that is quite different from normal natural gas. Not so - biomethane is chemically identical to the fossil fuel version. First's refuelling plant will be connected to the gas national grid in much the same way as mu=y gas boiler is.... ...The gas from such plants is "bought" by First, then pumped into the national gas supply. First then turn on the tap and draw an equal amount from the same national supply, making this an accounting device, because the plant would be producing gas anyway. Again, I have no issue with the process, which solves more than one problem. Waste is used rather than buried, energy is produced, and greenhouse gases fall. It's the somewhat dishonest gloss put on the story that I object to. On the plus side, if we get too many gas buses to be able to fuel them all from biogas, we will be able to use the methane producedd by hydraulic fracturing of deep rocks.

An analogy. Some years ago, a French bottler of naturally sparkling water was found to have been removing the carbon dioxide from the spring water before transporting it to its distant bottling plant. Its explanation was that it expelled the gas into the atmosphere to make the water easier to transport to much closer to its customers. It then removed the same gas from the air and injected it back into the water - voila! It didn't go down well.

There's nothing dishonest about this - it's a mechanism we all use when we choose our energy supplier. They buy it wholesale and sell it retail. If you subscribe to a 'green energy' tariff, you won't be able to tell whether the electricity you use was generated using coal or wind, but you know that you are supporting sustainable sources.

[Tim]

I did make the typo.   

Making methane from poo is good of course, but just how good depends on what would have otherwise happened to the poo.   If the poo was going to be sent to an aerobic  sewage works where it was put in a tank and aerated until the bugs in the water respired all the poo to water and CO2 and heat then the only gain by making the poo into bio methane is that the heat is not wasted by used to do work and drive the bus forward.  The climate gain is equivalent to the cancelation of the damage which would have been done by the emissions produced by having the bus run on a fossil energy.

But if the poo was going to be sent to an anaerobic sewage works where it would mostly settle out into sludge which would then be land-filled and ferment over years in the landfill site releasing huge amounts of methane which escapes into the atmosphere where it is 200 times more potent a greenhouse gas than CO2 then then the poo bus scheme alternative delivers a huge climate gain (however note that the vast majority of this climate gain would have been provided by capturing the bio methane and burning it off in a big flare)

If the poo bus scheme ends up diverting poo from an aerobic treatment works to an anaerobic treatment work where it produces methane rather than CO2 and just 1% of that methane escapes accidentally into the atmosphere during production and transport than the poo bus scheme has a negative effect on climate.   

 

[TonyK]

Except that:

...the greatest advantage of biomethane over fossil fuels is the fact that it does not contribute to carbon dioxide emissions despite the fact that biomethane combustion produces this greenhouse gas as well. This is due to the fact that the utilization of biomethane is basically only utilization of energy which is released during the natural decomposition of organic matter. Carbon dioxide which is released into the atmosphere during biomethane combustion equals the amount of carbon dioxide that is emitted during natural decomposition of manure for instance.

Source: biomethane.org.uk

Excellent point, thank you Red Squirrel. I am now even more in favour. (Not MetroBust, obviously)

Thank you, FTN, for the clear but extensive explanation of the process in both chemical and financial terms. One little thing I'd quibble with though: "110 cleaner vehicles in Bristol won't clear the air overnight, but it's a start." Yes, but they will only do their little bit to clear the air to the extent that they replace rather than supplement dirtier vehicles. Though even if they are supplementary they still set an example and make available the refuelling station, as you point out.

As there aren't enough drivers in the Bristol area to move the existing fleet of buses slowly around the city, I would imagine that the non-MetroBust vehicles will be deployed in the usual way, displacing older vehicles that can be redeployed in smaller towns in place of even older vehicles. After several levels of similar cascade, the oldest in the fleet are sold abroad. When MetroBust finally gets going, the 30-odd new vehicles will displace those working on ordinary services which are no longer viable.

[Bmblbzzz]

Ah, the trickle-down effect in action in bus fleets and the great carbon economy!

[Western Pathfinder]

And at the same time these new cleaner burning buses will actually be scrubbing the air,so some more advantage to be had from the introduction  .

[Tim]

I'm am a bit wary of any scheme which increases the production, transport or handling of methane.  Methane is a massively powerful greenhouse gas in its own right and just a tiny fraction of it needs to be lost to the atmosphere for any climate benefits to be cancelled out.   It might be best just to take the poo and incinerate it to CO2 optionally using the heat for heating homes or generating electricity. 

I have the same concerns about the "dash for gas" in electricity generation.  Sure methane is a cleaner fuel than coal in power stations, but extracting it is a messy business with quite a lot lost to the atmosphere especially when you get it from fracking.

[Red Squirrel]

And at the same time these new cleaner burning buses will actually be scrubbing the air,so some more advantage to be had from the introduction  .

Not like in the old days... https://www.youtube.com/watch?v=drE3lgaTgTA

[CyclingSid]

I believe the First manager responsible used to run Reading Buses, so no shit there.