Tune in from 2:20 pm with Jenny Seaton and ask me a question
Yesterday I made my latest appearance on today tonight. I had a lot of fun but inevitably with these type of segments some important details get left on the cutting room floor
In this case it happened with one of the things that was mentioned on the segment – how to stop mirrors fogging in your bathroom (or windscreens fogging in your car).
In the segment it said that you smear detergent over the mirror before you shower. That is correct, but the important detail that was missing is that you need to rub it until it becomes clear.
Obviously if you smear detergent across a mirror it will do just that – smear. To achieve the desired effect you must rub it with a dry cloth until it eventually clears – in other words, until all the water in the detergent evaporates.
And this will last for months. For months after this you will have a mis free mirror. It’s a remarkably simple and effective trick.
In broad terms there are two types of biodegradation – aerobic and anaerobic, with and without oxygen respectively.
By far the more common is aerobic, mainly because there is plenty of oxygen around and also aerobic biodegradation is fast. For this reason, this approach is used quite a lot industrially. Typically, an industrial waste treatment plant will involve a chemical dosing step, followed by a biodegradation plant. This normally simply involves a large vat with aerators. The aerators provide the oxygen for the bugs to do their stuff, and they successfully remove both the carbon (as CO2) and nitrogen (as N2). Essentially, aerobic digestors are pretty foolproof.
And these are used in sewage treatment plants – massive treatment vats with banks of aerators blast air through the waste day and night. These plants have a substantial amount of sludge, of course, and this sludge is tapped off at various points and sent to an anaerobic digestor. The anaerobic digestor consumes this solid sludge with about 96% efficiency, and converts it all to methane, ammonia, and hydrogen sulphide.
Interestingly, I recently heard of one of these facilities that is being set up commercially, using food waste, to generate methane that can be used as fuel to generate power.
So the world around us is an incredibly efficient biological reactor, using several mechanisms, to recycle pretty much everything.
Biodegradation is part of the cycle of life. There are certain elements in the world around us that are constantly being recycled. These days of course we all attempt to recycle rubbish where possible, but nature has already been doing it since time immemorial.
There are four cycles that you learn about when you study environmental chemistry – the carbon cycle, the nitrogen cycle, the oxygen cycle, and the sulfur cycle.
By far the most important of these is the carbon cycle. In nature, of course, carbon is the element of life. This is why in chemical terms, carbon chemistry is also known as organic chemistry – it is the chemistry of living tissue. So whether it is carbohydrates (lignin in trees), lipids (triglycerides present as either vegetable oils or animal fats, or proteins or enzymes, they are all carbon-based and will all degrade.
Perhaps the noticeable exception here is wood. Although some carbohydrates are very biodegradable (sugars and starches), there are some that aren’t, most noticeably wood. If it gets wet, of course, it degrades (this is what rotting is) but dry wood will last for a very long time.
The difference between the properties of the various carbohydrates is simply the types of linkages in the molecules’ carbon backbone.
But of course this is offset by the fact that wood burns, whereas other carbohydrates don’t. A simplistic representation of this may be:
CH2O + O2 = CO2 + H2O
That is, carbohydrate (wood) + oxygen = carbon dioxide + water.
Interestingly, if we reverse the process that happens when the wood burns, we come up with
CO2 + H2O = CH2O + O2
As it happens, this process is photosynthesis, the natural process that converts carbon dioxide and water into wood and oxygen. This is the simplest and most important process that is part of the carbon cycle.
Another example is something rotting, or “going off”. You know what happens – you’ve left the milk out and when you come to it, it is all puffed up and bloated. When you open the lid you are met with a blast of rancid smelling gas.
This gas is in fact due to Volatile Fatty Acids (VFAs) from the milk fats. In fact, any naturally occurring oil or fat will produce the same result when in contact with water and oxygen. And of course this process happens very quickly – milk that is not refrigerated will begin this process within 24h. In fact the degradation of oils and fats is probably the most rapid biodegradation process that there is. Tip a bottle of rancid milk out by your front door today, and within 3 or 4 days the rancid smell will have disappeared.
The process may be represented as (using acetic acid as a simple carboxylic acid):
CH3COOH + 2O2 = 2CO2 + 2H2O
Note that soil is probably the most efficient catalyst for this process that there is, as it is full of the bacteria that catalyse this process. It was very common during the American Cilvil War, for example, for weather and erosion to uncover naked skeletons of soldiers that had been buried in shallow graves only a few months hence.
One of the most commonly asked questions with regard to any chemical that is used in the marketplace is “is it biodegradable”?
This applies to insecticides, detergents, dry-cleaning fluids, herbicides and so on. And the reason is that today we have an understanding of ecosystems that we didn’t have 50 years ago, and the need for any chemical that we place into the environment to biodegrade, and therefore have no lasting impact on the environment.
50 years ago, the very opposite was the case. You see. another word for “biodegradable” is “unstable”. And back then, that was a bad thing. Back then we wanted chemicals to last for, well, forever if possible. When we sprayed a surface insecticide we wanted it to last forever. And this was the great advantage of DDT. As a chlorinated insecticide it was extremely stable (ie not biodegradable), and so it could be blasted here there and everywhere, knowing that we wouldn’t have to come back for a while.
But as time marched on, we started to realize that these chemicals were starting to accumulate in the environment, and in some cases they have caused disruption of ecosystems that was never originally intended.
So now you pretty much cannot use a chemical in the marketplace if it is not biodegradable. And this even applies to dry cleaning fluids. It used to be the case that when you had your clothes dry cleaned, the chemical of choice was 1,1,1-trichloroethane, a triply chlorinated solvent that was also contained in the original formula of Preen aerosol. That now is out the door, to be replaced by something that is biodegradable. I’m not sure how well these newer chemicals work, however, as I tend not to get things dry cleaned. One thing I do know, however, is that today’s Preen is not a patch on the old stuff. Tomorrow we’ll start lookin at exactly how biodegradation works in world around us.