One thought on “Monday Message Board”

1. Greenwashed plastic tarmac vs. plutonium-eating bugs

   Facebook’s algorithm has fairly enough profiled me as a sucker for good news on green tech. Last week it served me up a typically unreferenced item on a successful project in Minas Gerais state in Brazil to add recycled plastic waste to bituminous road surfaces, at lower cost and an improvement in durability. Big win for the climate! Not for long.

   I checked it out. The tech is real; here’s a fat World Bank report from 2023: https://documents1.worldbank.org/curated/en/099003105242322144/pdf/IDU0743eda4a0091c049000acd506d2f0b9ae123.pdf It turns out this process is being actively developed in many countries, led in fact by India, the first one to adopt technical standards. There are heavyweight corporate backers including the notorious Dow Chemical. So far so good.

   How big a contribution can it make? Google AI is great for quick-and-dirty calculations. It says the world total length of roads is 65m km, of which 35% is is paved, 23 m km. The lifespan of a paved road is 10-30 years depending on traffic, let’s say 20 years on average. This is generous, as most roads carry only light traffic. This gives an annual demand for repaving of 1.14 m km. New roadbuilding and paving of dirt roads pushes this up, say to 1.5 m km. We aren’t going to get 100% of this with our plastic tarmac. We pencil in 33% – 500,000 km – as the prudent target and 50% – 750,000 km – as the stretch one. The standard plastic addition is 1 tonne per km, the highest claimed feasible use 4 tonnes/km. These ranges give an upper limit of 3 m tonnes a year and a prudent estimate of 500.000 tonnes.

   The world total of plastic waste is 400 mt/yr. So at best recycling it for road-building only uses up 0.75%, more likely 0.12 %. A minor contribution, worth including in the overall plan. For a major plastics producer like Dow, it’s patent greenwashing.

   What would a serious attack on plastic pollution look like? The current work on a global plastics treaty is better than nothing. but not much. A pair of “unrealistic” proposals that might make a difference:

   1. A global Pigovian plastics tax, weighted by damage, levied on producers like Dow, and fully hypothecated for mitigation.

   Argument: same as for GHGs.

   2. Shifting the priority from recycling to biodegradation.

   Arguments:

   (a) There are just too many different types of plastic for comprehensive recycling after use to be feasible. One good thing about the road-building plan is that up to a point you can use an unsorted mixture from the town dump, but this is unusual. Most recycling requires precise and expensive sorting: PET bottles here, LDPE there, PVC in a third bin, and WTF is this?

   (b) Biodegradation in contrast is a single broad metric, placed in the zero band of any plastics tax. It is much simpler to administer than credits for product-by-product recycling.

   (c) The strategy fits in with the existing logistics of the retail business. All food products have a defined shelf life, and the single-use packaging around them only needs to survive this with a safety margin (say 2x). When the food is sorted, you move on to the longer-life products like bottles of detergent. Refill comes in here.

   (d) If biodegradation works at all, it would scale easily with simple equipment, and should work out much cheaper than recycling.

   (e) Above all, biodegradation is nature’s way of recycling dead stuff. Why make macho chemical reactors, product by product, when you can ally (via GM) with greedy no-wage and freely reproducing bacteria and fungi, maybe working all at once in a single digester chain?

   Is this wishful thinking technically? I think not. There are hero bacteria that thrive in the nightmare environment of ponds or heaps of nuclear waste, actively collecting radioactive compounds. Some tap the energy for their own metabolism, others sequester them, yet others precipitate soluble compounds into insoluble minerals or metallic forms which are less toxic to humans or easier to recover. Some can even take up plutonium: oversize, radioactive, extremely toxic, and novel. The element does not exist in detectable quantities in nature, so this extreme adaptation took place, quite unaided, in the 81 years since the X-10 pilot production reactor went critical at Oak Ridge on 4 November 1943. Do you think that the vast bacterial kingdom, with a helping hand from legions of human biologists, will be defeated by mere microplastics, forever chemicals and composite wind turbine blades? https://asm.org/articles/2023/january/how-do-microbes-remove-radioactive-waste