Science Spin May 2009

Shocked bugs devour phosphorous

By Sean Duke

Phosphorous is a natural mineral mined from rock and used in fertilizers, detergents, and even Coca Cola. We humans need it as part of our diet, as our DNA, for example, is made up of a phosphorous backbone, and our bones contain a lot of phosphorous.

It is very useful, but it's running out, and also it causes pollution when it's used up.

Once phosphorous leaches into a lake or river systems it can cause 'eutrophication' - which is essentially the slow death of the lake. The lake is starved of oxygen and light due to the growth of algae micro-organisms that 'bloom' on top of the water surface. The algae thrive on the presence of phosphorous, causing a green film on the water.

Ireland has a significant problem with phosphorous said Dr McGrath: "There are 496 lakes in Ireland that have more phosphorous in them than there should be under European legislation. There are 37 to 40 per cent of rivers with the same problem."

The major source of phosphorous pollution is wastewater from domestic sewage. There other important place that it arises is in agricultural 'run-off' from lands where fertilizers have been used. The phosphorous, in both cases, can cause major problems.

Water companies use chemicals to remove phosphorous from wastewater. This involves dosing the water with iron chloride, or aluminium compounds to precipitate out phosphorous. The process works well enough, but it is, costly, and it causes another problem as it increase sludge by 30 per cent. This sludge bye-product must then, in turn be removed, and the options to do that are limited and expensive.

Solution

This all means that industry is crying out for a 'biological solution' for dealing with phosphorous, one that is chemical-free. There is a biological system on the market for dealing with phosphorous in wastewater, said Dr McGrath, but it was developed in the 1960s in South Africa, and has been shown not to work very well in wetter climates.

Dr McGrath's approach is to expose micro-organisms to 'shocks', such as acidic PH levels. What this achieves, he said, is that it tricks the micro-organisms to ingest phosphorous in the environment around them, and lock it up in a harmless form.

"It is like you jumping into the Atlantic on Christmas Day. As soon as you hit the water you take an intake of breath. But what some of these micro-organisms do is that when you shock them, instead of taking a breath, they take an intake of phosphorous. They store that inside themselves to protect against these (future) shock events."

Dr McGrath began by testing the shock technology at a small sewage treatment works, and then moved on to a full-scale trial at Mullaghglass, which is close to Lisburn, near Belfast. "That has given us some encouraging results. We have managed to increase P (phosphorous) removal to about 64 per cent. Normally a treatment works will remove about 40 per cent of the phosphorous that comes in."

The European Commission are pushing for 80 per cent of phosphorous to be removed from wastewater by treatment plants - by tightening its legislation under the Urban Wastewater Treatment Directive. Dr McGrath said that he has looked at applying another 'shock', on top of the acid shock, to micro-organisms that can achieve compliance with the legislation. He can't, at the moment, say more about this.

The use of micro-organisms which convert phosphorous pollutant into a safe, and useful form, can also provide a method for recycling of a scarce, useful commodity.