The Recycling of The Future #2

Last week I wrote about ideas which have garnered a great deal for money for researchers to look into overhyped things which have proven themselves practically worthless time and again, until collective memory of their impracticality has faded.

I'm presently wondering if graphene will join this list. I'm pretty clear that the promises being made for it in the field of water treatment are simply ridiculous. The water sector however has its own track record of fads which come around again and again, most notably anything promising zero sludge yield. Perhaps we will over time fall for the academic hype around the supposed "promise" of graphene again and again, as we have with AI. Time will tell.

You'd think engineers and scientists would be proof against this phenomenon. How can there be fads and fashions in engineering and science? Why are some of the biggest mugs those "engineers" who consider their practice to be the application of the pure natural sciences? In my view, the answer is simple. Those who do not recognise the effect of emotion in human decision making are prone to being run by their emotions. In the case of these kinds of fads, they are prone to the wishful thinking which causes them to set aside any common sense or professional judgment they may have.

Let's take the example of "zero sludge yield". When we treat wastewater biologically, we are left with a sludge comprising the bugs we used to treat the wastewater, even if we have removed all solid material in the original water. There is a way in which we can get the bugs to eat themselves to some extent, reducing sludge yield. Whilst it is easy in a lab to produce results suggesting that a zero yield of sludge has been produced by a process, this is an artefact showing only the limitations of the lab test. This is practically impossible for reasons which are I hope obvious.

This does not however stop marketing departments extrapolating from such trials in promotional materials. Experienced engineers are extremely sceptical of such claims, having seen them many times before. This scepticism is professional judgment. Knowing what doesn't work is a far larger part of such judgment than knowing what does.

Zero sludge yield is of course a subset of the "circular economy" nonsense currently raking in research money and forming the basis of greenwash. The practical implications of thermodynamics tell any real engineer that there can be no true circular economy. I've seen discussions in which academic researchers in the field state that the only problem left to solve in that area is the economics. That is however 100% of the problem. Their research to date has shown that they can solve the problem in fairyland.

Any technology which aims to expend more resources on recovering mass or energy than you can buy that mass or energy for is of no practical use, and therefore of no professional interest to engineers. Even when a technology has the possibility of becoming economic in the medium to long term, those terms can be pretty long. The future in engineering is a long way off.

Let's go back to the claims being made for graphene in my sector. It is claimed that membranes can be made of graphene which will allow low-cost desalination to make cheap drinking water from seawater for poor nations. Firstly let's have a look at how long it has taken for membranes to become a practical part of water engineering. The first commercial membrane-based plant went in in Japan in 1962. This isn't however when researchers started looking at the possibilities in the lab. Reverse osmosis was first documented by researchers in 1748, almost 200 years earlier.

The claims made for graphene are based on the idea that headloss though a graphene membrane might be very low (though no-one has shown this in a practical application). There are however two or three obvious and practically insurmountable problems.

The first is that most of the pressure which must be overcome to push water through reverse osmosis membranes is osmotic pressure, the better part of 30 bar for a seawater feed. Trans-membrane pressure for a clean membrane is trivial, maybe 0.3 bar. It wouldn't matter if researchers produced a reverse osmosis membrane with zero headloss. Reverse osmosis of seawater would still have high operating costs, as even a perfect membrane would only save 1% of the required pumping energy.

The second is that the membrane must be capable of taking significant pressure in both directions if it is to have a reasonable working life. High-purity lab graphene is very strong indeed for a material one atom thick, but nowhere near strong enough for the job.

I was pretty sceptical of membranes when they first started being economically viable for certain applications. They were (and still are) expensive, and not all that robust. They are however a good technology in a certain niche. That niche in the case of reverse osmosis is mostly those places where oil is cheaper than water. Reverse osmosis is energy hungry, and always will be. Yes, there have been incremental reductions in price and headloss during my career, but it's never going to be the way to make cheap water, because it depends on overcoming osmotic pressure.

So I was right to be sceptical, and I could give examples of other membrane applications oversold on the basis of extrapolated lab results which turned out to be either useless, or far less practical than expected by wishful thinkers. And that's just membranes....

So recognise marketing material for what they are, no matter how much you wish they were true. It's what real engineers do.