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How to Use This Nutrient-Rich By-Product of Daily Business? Opinion is Sharply Divided Over Sewage Sludge

Posted on: Monday, 20 March 2006, 09:00 CST

By Fordyce Maxwell

THERE is a lot of it about. We all do our bit and the result is that more than 150,000 tonnes a year of sewage sludge is produced in Scotland, with a 17 per cent increase forecast in the next 20 years.

As a specialist in the subject, and someone has to be, said a few years ago: "Sewage sludge is not everyone's cup of tea. But it's my bread and butter."

The problem is what to do with it. Unlike in the good old days of gardey-loo, ash or chemical toilets, chamber pots and night soil collection for vegetable crops, we now worry about pathogens and other nasties that might be lurking.

We all help produce it, but no one wants it - figuratively speaking or otherwise - in their backyard.

That has given Scottish Water a problem, as if it needed another in its present fragile, chairman-less state.

Theoretically, sewage sludge is an environmentally friendly by- product after the billion litres of waste water biologically treated by Scottish Water each day is returned to the environment. It can provide power as a pelleted fuel, or nitrogen, phosphate, potash and trace elements for crops and grass. It should fit in snugly with a society where recycling and good-life sustainability has increasing priority.

In practice, environmental groups, some scientists, politicians and those living anywhere near where sludge is spread, burned or land-filled complain.

Last year about 57,000 tonnes, 40 per cent of the Scottish total, was used as dried solids in land reclamation.

About 50,600 tonnes, 35 per cent, was burned as dried pellets for power generation; that is continuing on an interim basis only at Longannet because of concerns expressed by the Scottish Environment Protection Agency (SEPA).

And about 33,770 tonnes, 23 per cent of the total, was spread on farm land.

Most of the farm land sludge was treated, including by lime pasteurisation, to reduce bacterial content by 99 per cent. Some was spread after only basic treatment.

Scottish Water's proposal, out for consultation until late April, is to swing the balance to 48 per cent of sewage sludge used to generate power, about 47 per cent on farm land, and only about 4 per cent for land reclamation. Even if approved, much will depend on Scottish Executive funding. Meantime, the arguments about whether sewage sludge is a good thing or not continue.

Dr Tim Evans, formerly of Thames Water, now an independent consultant, is in no doubt. He told me: "Every one of us has a responsibility to stand up for sustainable development. Administrations, including the UK government and European Commission, have said that in most circumstances the use of biosolids [sewage sludge] on land with appropriate controls is the best practicable environmental option.

"It conserves organic matter, needed by the soil, which also reduces greenhouse gas emissions, and completes nutrient cycles.

"We shall never know everything about anything, but on the basis of what we know and the controls we have in place I believe that the use of biosolids on land within today's control programmes is safe."

Heavy metal deposits, "there for ever" as some critics claim, are not a problem, Evans said.

"These are now controlled at source. At a recent US conference the unanimous conclusion was that we have a grip on these, as we have on pathogens."

Any resistance to the use of sewage sludge on farmland by crop or livestock quality assurance schemes - either on instructions from supermarkets or trying to second-guess future requirements - is, Evans said, "deeply disappointing."

Jerry Mulders, an Edinburgh-based businessman who lives in what he thought would be a rural idyll in Ayrshire, could not disagree more.

In the few years since he moved to the Ayrshire countryside he has found himself surrounded by opencast mining, a wind farm and land being spread with 3,000 tonnes per hectare of sewage sludge.

"Sewage tends to be out of sight out of mind for most of us. We're encouraged not to think about what happens to it.

"But it can't all be mixed together successfully, domestic and industrial. Treatment does not eliminate pathogens. There are huge amounts of chemicals and heavy metals still there. No-one really knows what's in it. Then hundreds of tonnes an acre are spread on the land.

"If there are doubts, why put it on the soil? Copper poisoning, for example - it's for ever, to the end of the life of the planet."

Burning it is not much, if at all, better, Mulders said. That causes air pollution, which was the complaint made by SEPA about Scottish Power using Scottish Water waste - a constitutionally interesting conflict - at Longannet.

Mulders said: "SEPA, Scottish Water, local authorities, industries, the Executive - everyone is waiting for someone else. The biggest problem, I think, is that Scottish Water has to do something, but the Executive does not want to give it the money."

He argues his case remorselessly with regular presentations to MSPs at Holyrood, and he believes he is making progress.

He says: "Some MSPs want to do the right thing. All we want to do is make people think. There are so many unanswered questions."

Mulders tried to find some answers at the sewage treatment plant at Meadowhead, Ayrshire.

"First, there is a barrier to take out the Durex, tampons, and other solids. Then it goes into an aeration tank - a soup full of bacteria. Then the settling ponds, thickening and mechanical de- watering, to take it to 25 per cent solids," he explains.

"From Scottish Water's point of view, that is treated sewage sludge. Not from our point of view. The smell is bad, but what's in it is worse.

"We have to push, prod and cajole to find out what's going on. Scottish Water has a duty of care, SEPA has a health remit."

Rules on spreading sludge on any kind of land - farm, forestry, moorland - must be tightened, Mulders said.

"SEPA's role has to change. They must be able to go to a site and make someone stop. It should be able to enforce rules - a third warning means stop now and on-the-spot fine. The law must change to independent investigation, rigorous testing, sludge content known and understood.

"I would have no problems with sewage sludge going on to land in reasonable quantities if the content is known. But industrial waste must be separated from domestic and spreaders must have a full licence, with no exemptions."

Source: Scotsman, The

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