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Monday, May 31, 2010

Neutralizing Oil Slicks

New oil finds are in ever deeper water which is both bad and good. Bad because the chance of accidents increases along with the difficulty of fixing them. Good because if there is an oil slick, it is generally further from any coast than shallower finds and hence will take more time to reach the shore. There is more time to neutralize the oil slick before it gets to beaches and wetlands. At present dispersants are used which in themselves are toxic and they simply disperse the oil through the water column. Their effect is more cosmetic than actual and the damage then occurs in deep water where most people don't see it.

It should be possible to accelerate the conversion of oil into single cell bacterial biomass out in the ocean before it hits the beach. This process occurs naturally in the oceans with natural oil seeps but the trick is to make it happen fast enough that no oil reaches shore and so that the exposure of wildlife to oil is as short a time as possible.  Single cell biomass is then utilized by a whole range of filter feeders. An oil slick could, ironically, increase the productivity of an area. Oil is an organic material, mainly consisting of carbon and hydrogen with some minor elements such as sulphur. Bacteria eat oil. They use it just as we do as a source of energy.   In the "Gulf Spill", scientists were amazed by how quickly bacteria ate up the oil.   Let me tell you about some work that was done on this subject back in the early 1980's.

The North-South oriented Gulf of Aqaba at the north end of the Red sea has an oil delivery jetty on its western shore. The prevailing wind is from the North and from time to time there is an oil spill from the jetty. Usually spills are relatively minor, consisting of a couple of tons of crude. The oil is blown south, coating the western shore. Keep that in mind for a moment.

Oil tankers when they have emptied their tanks go back to pick up another load. They pump enough sea water into their tanks to make the ship stable. When they get to the oil pick up point, they first pump this ballast water out of their tanks along with a considerable amount of entrained oil. This oil pollutes the sea by the oil pick up terminal and turns the nearby beach into asphalt.

Scientists at the University of Tel Aviv thought that they could solve the problem. It is known that there are bacteria that eat oil. For instance, they are found  in tanks of petrol, diesel and other hydrocarbons if there is some water in the tank. The bacteria grow in a film between the hydrocarbon and the water. So, in the expectation that such bacteria would be found where there is chronic oil pollution, scientists from the U of T took samples from the beach to the South of the oil terminal.

Back at the lab, the samples were put into flasks along with sea water.  Missing nutrients and a dollop of crude oil were added and the flasks were aerated. Oxygen is necessary as only aerobic biological processes are vigorous enough to utilize oil. Lo and behold, the oil was eaten up, converted to bacterial biomass and all the crude oil disappeared. Not a big surprise but very satisfying to see. Then they went on to the next stage.

They bulked up their bacteria culture to have a large inoculate and took it back to the Gulf of Aqaba. They persuaded one of the oil tanker captains to let them try an experiment. To one compartment of the tanker with its ballast water, they added the required nutrients that are missing in crude oil and put in an aerator to keep the mixture oxygenated. They then added the bacterial culture that they had bulked up in the laboratory. When they got to the oil pick up jetty, a week or so later, to every one's delight but no one's surprise, there was no oil slick when they pumped out the experimental compartment. The oil had been converted to bacterial biomass, which was available to local filter feeders and the tank was as clean as a whistle. But there was a surprise.

They took samples of the pumped out water back to the lab and what did they find. The bacteria in the water was a different bacteria than the one they had inoculated. Apparently, bacteria that eat oil are all around wherever oil is found and the bacteria they found in the ballast water was the one which could compete most effectively. There was no need to isolate special bacteria. All that was necessary was to add nutrients which are missing in oil and aerate. Incidentally, the existence of oil eating bacteria is not surprising. Oil has been leaking out of natural seeps for multi-millions of years and there has been sufficient time for bacteria to evolve to utilize this energy source. If this wasn't the case, we would see asphalt beaches wherever an oil seep made land fall*.

*Asphalt because the oil hits the beach, the lighter fractions evaporate and the remaining tar sticks the beach sand and stones together.

So what does this have to do with cleaning up an oil slick and especially one as huge as the present one in the Gulf of Mexico. We already have three of the four needed requirements, namely sea water and oil in contact and oxygen in the water and in the air above the slick. What we need is a way of delivering the needed nutrients to the oil slick. It is of no use to simply pour or spray nutrients onto the oil slick. They will dissolve in the water and disperse into the depths*. We need some sort of floating particle which oil sticks to (oil sticks to almost anything so this shouldn't be a problem) and the particle must be impregnated with the necessary nutrients. The nutrients mustn't be in too soluble a form such that they simply dissolve in the water and disperse. They also shouldn't be in such a refractory form that the bacteria can't get at them. Fortunately,over the Milena, bacteria have evolved to 'eat' virtually any naturally occurring material available. They can even cleave off the sugar molecules that make up cellulose. Here are some random thoughts on how the research might proceed.

* The other benefit of a particle relates to bacterial life style.  Bacteria, unlike photosynthetic single celled organisms hardly live free in the water at all.  They mostly live attached to a substrate in bacterial colonies.

First the Tel Aviv experiments must be repeated to determine which nutrients are needed and in what proportions to balance the energy and the few nutrients in the oil. This will be different for oil from different fields. For instance, so called sweet oil is very poor in sulphur.  Once this is determined, the work can commence.

A good place to start would be  to first analyze various crude oils for their nutrient composition and to analyze oil eating bacteria for their nutrient composition. Subtracting one from the other will give a first approximation of which nutrients are missing and in what proportions.  These quantities can be tweaked to achieve better results once the basic premise is proven.

The nutrient needed in the greatest quantities for any life is Nitrogen. It might be possible to use wool, feathers, shrimp/lobster/crab carapace waste or some other protinaceous substrate to provide the nitrogen. Protein is on average 16.5% nitrogen. Feathers from all the chickens plucked for our table might be a particularly good starting point since they have a hollow shaft which will provide flotation. It also might be possible to precipitate the necessary additional nutrients into the hollow shaft. The advantage here is that these protinaceous substances are not soluble in water and the bacteria have to cleave off the nitrogen. It is certain that there are bacteria in nature that can utilize wool, feathers and the protinaceous substrate in arthropod carapaces. Otherwise we would be waist deep in wool and feathers* which have been sloughed off/moulted ever since the demise of the dinosaurs and the ocean bottom would be covered with arthropod carapaces from their frequent moults and ultimate demise. Wool, feathers and arthropod carapaces don't accumulate and therefore are being used up. Cleaving the nitrogen off such refractory substances use up energy (and hence more oil).

* Actually we would be far deeper in feathers.  Apparently at least some dinosaurs also had feathers so there is another 250m years of accumulation.  In fact, all the Nitrogen of the atmosphere would have been converted into feathers.

However, other nutrients are also needed. Probably the next most needed one is Phosphorous and then possibly Iron which seems to be particularly lacking in sea water. Here we might be able to turn to a combination of scientists who dye cloth and to the makers of slow release fertilizers. Slow release fertilizers dissolve slowly in water which might be the solution and cloth dyers deposit colored materials inside fibers to give them their color. It just might be that a collaboration between these two disciplines will come up with the solution. The necessary nutrients might be precipitatable inside the protinaceous material of choice.  One might even use a foamed gelatine (again a source of nitrogen) with the necessary nutrients dissolved or suspended in it.

Each time a new substance is developed, it can be tested in an aerated tank of sea water with an oil slick on the top.

As for a delivery strategy, the way bacteria multiply can help. They Double each doubling period. (sorry for the tautology). The doubling period for some bacteria is measured in minutes. Others longer. Their growth is exponential. At first growth is almost imperceptible but quickly builds up to incredible levels as long as there is substrate remaining for them to feed on and oxygen for respiration. One might spread a light dusting of the material over the oil slick and let the initial log growth phase occur and then, a couple of days later, with a good culture of bacteria well established, hit the slick with a heavier treatment.

How do we get our nutrient delivery pieces to float? Firstly, the substance we use could be less dense than sea water. Such materials, though, are rare. Even cellulose* (wood) only floats because of entrained air spaces. Secondly we could use a substance with natural entrained air (feathers) or a manufactured product like corn puffs into which we entrain air. Thirdly, we could make the material into a thin flake. Even if the flake itself is denser than sea water, if oil clings to it, the combination of the flake and the oil might well be lighter than water.

*Cellulose is probably not a good material to use.  It is itself, chemically speaking, equivalent to oil.  That is a source of energy without nitrogen.

This material could probably also be used to treat beaches. Spread the material on an oil impregnated beach and trillions of bacteria will start to eat up the oil and turn it into carbon dioxide, water and bacterial biomass. Each tide will mix up the oil and the substrate and aerate it. If the substrate is also the source of nitrogen (any protinaceous material), it would also disappear. This would be a distinct advantage over using a floating particle of, for instance, plastic*,which would remain after the oil had been eaten up.

*Incidentally, the oceans today are full of tiny particles of plastic which are dispersed over tens of meters of the surface of the ocean.  This plus the relative nutrient richness of the Gulf (Mississipi feeds into it) may explain the very fast metamorphosis of oil into bacterial biomass which was observed.

I'm not saying that it will be easy to come up with the perfect material to solve the problem of oil in the ocean but it should be eminently possible with a little careful research. Necessary characteristics are:
1. It must float
2. It must deliver missing nutrients for the oil eating bacteria. Slow delivery would be acceptable but even better would be materials from which the bacteria have to actively cleave off the nutrients. Note that cleaving off the Nitrogen uses up energy (oil).
3. The material should be used up and disappear leaving no trace.
4. It should be cheap. This requirement is far down the list. The cost of not making the oil slick disappear is very expensive.
5. It would be good if a waste material such as crustacean carapaces, feathers from the poultry industry and so forth was used. (also far down the list of priorities)
6.There is  no need to impregnate the substance with suitable bacteria. Crude oil eating bacteria are ubiquitous.

*Some recent reports suggest that much of the oil from the blow-out is suspended in droplets in the water column. Some experiments carried out off the coast of Norway suggest that with deep oil releases there may be as little as 2% of the oil making it to the surface. Here an injection of nutrients in a soluble form might be the solution to convert this oil to bacterial biomass. However, with no source of oxygen (the air) such a move could make the water anaerobic as the bacteria use up the oxygen. Once the oxygen is used up, the consumption of oil ceases. Anaerobic processes are not sufficiently energetic to consume oil. Once this body of water reaches the surface, as long as there are spare nutrients left, the oxygen in the air will start the process going again. For deep water applications, there might be some way of incorporating an oxidizer that the bacteria could use.

** An interesting aspect of this problem is as follows. Assume that one treats the oil slick with somewhat less of a nutrient load than is necessary to consume the oil quickly. The bacteria top out of the sigmoid growth curve, become senescent and die. When they die, their nutrients are mineralized, available for other bacteria. As long as there is an energy source (unused oil) bacteria will continue to munch it up. If there is time available before the slick reaches land, it could be that a relatively low dose of our oil eating material would clean up all the oil.

***Bacteria, unlike single cell algae, hardly grow at all suspended in water. For the most part, they live in bacterial films attached to a substrate. With the particle we are designing with its contained nutrients there is no problem. The bacterial will form a film on the particle. However, if we do use a protinaceous substrate, the bacteria will consume it and then have no place to 'sit'. It might be worthwile to provide some sort of refractory particle which is easily cleaned up for the polishing stage following the main consumption of the oil. Actually, this may already exist in the water. Apparently the beaches of the world are continually grinding up plastic that reaches the shore and tides are taking this material back into the water. Continuous plankton samples taken by commercial ships crossing our oceans are showing more and more fine plastic suspended in the water. Oil sticks to plastic. Perhaps these particles will help with the consumption of oil spills as first stage bacteria die and release their nutrients into the water.

Note:  In New Scientist, Aug 7, 2010, p4 it is reported that the oil slick in the Gulf has disappeared far more quickly then expected.  The suggestion is that the area is already primed by suitable bacteria due to the natural seeps in the area.  It seems likely that there is also a sufficient concentration of nutrients in the water, possibly from the Mississippi river.  One wonders how fast an oil slick would disappear in waters which are cold, nutrient poor and without a history of oil seeps.


Nicole said...

I enjoyed reading your article. I have been turning many questions over in my mind since the BP tragedy. Have they found little life jackets for the bacteria yet? What about gelatin? It dissolves completely and floats, would be safe for the ocean and it's inhabitants. Would oil stick to it, I don't know. I'm not an avid jello eater, but I imagine it would. I wish it were that simple.

William Hughes-Games said...

Hi Nicole
I bet a jelatine based product would work. Gelatine is made from animal left overs like horses hooves and is Nitrogen rich.