Data on the impact of recent EC legislation on water and sewerage has been slower to emerge in Scotland than in England and Wales. Scottish sewerage undertakers, the regional councils, are still deciding how to comply with last year's wastewater treatment Directive, particularly the requirement to phase out sea dumping of sewage sludge by 1998 (ENDS Report 194, pp 34-5).
A report produced by Consultants in Environmental Sciences (CES) for the Department of the Environment in 1990 (ENDS Report 182, pp 12-16) concluded that meeting the Directive in Scotland would involve capital expenditures of £480 million.
This estimate assumed that all other works required to bring sewerage and sewage treatment into line with current legislation had been carried out. But this has not been done. The Scottish water industry suffered the same chronic lack of investment during the 1980s as that south of the border, but without the debt write-off which accompanied privatisation.
Although the Scottish Office is aware that costs will certainly exceed the CES estimate, it has not produced revised figures. A conference in Glasgow on 16-17 March organised by the Institution of Water and Environmental Management and Scottish Enterprise provided the regional councils with an opportunity to air their own estimates.
Lothian Regional Council has calculated that it needs about £450 million to bring water and sewerage into line with current legislation. Strathclyde estimates that it needs £930 million, divided equally between water and sewerage and sewage treatment, over the next 15 years. This would require £90 million per year during the mid 1990s, double the allocations announced recently by the Scottish Office for the early 1990s.
For Scotland as a whole, Strathclyde believes that multiplying its own costings by a factor of five gives a reasonable estimate of the expenditure required. This suggests the total spend will be about £4.5 billion over the next 15 years.
The regional councils see little prospect of such sums being made available. The prospect is that Scotland will struggle to meet the EC deadlines for progressive upgrading of sewage treatment standards, beginning in 1998, by several years.
Costs are likely to rise for both industrial and domestic consumers. The steepest increases will be in trade effluent charges for businesses outside the Lothian and Strathclyde areas. Only the former has a trade effluent charging and control policy comparable to those in England and Wales. Until recently, Strathclyde kept trade effluent charges low to encourage new businesses.
Domestic customers can also expect that water charges, a component of the poll tax or council tax in Scotland, will rise to a level more comparable with those south of the border. In Lothian region, for example, the average cost per household is £93, well below the lowest figure in England and Wales - Thames Water's £125 average.
Companies discharging to sewer may face requests for capital contributions, particularly where their effluents make up a substantial proportion of the load on a sewage works. The quality of treatment required under the 1991 Directive depends on the size of the discharge from a works. Large trade effluents may take small sewage works above thresholds requiring more extensive treatment.
The sensitivity of waters to eutrophication will be a major factor in the cost equation. The classification of waters will determine the standard of treatment required. Following a report by the river purification boards, most coastal waters in Scotland have been provisionally designated as "less sensitive areas". The Directive permits only primary treatment of sewage discharged into such areas. Exceptions are the highland estuaries and the coast around Ayr and Stranraer, where secondary treatment would be the norm.
Four inland waters have also been provisionally identified as "sensitive areas", where tertiary treatment may be required. These are the rivers Almond and Teviot, South Calder water and Forfar loch, all of which receive large inputs of sewage effluent and other discharges.
Major investments will also be needed to provide an alternative disposal route for the 70% of Scotland's sewage sludge which is currently dumped at sea. Lothian and Strathclyde dump 73,000 dry tonnes of sludge annually in the Forth and Clyde estuaries.
Neither council has announced a new disposal strategy, but Lothian is likely to opt for incineration at its Seafield works in Edinburgh. Strathclyde is spending £400,000 on a six-month study on the options by a team of consultants comprising Watson Hawksley, Environmental Management, Crouch Hogg Waterman and the University of Strathclyde.
Incineration is the most likely route for the large volumes of sewage sludge produced in Glasgow. But Strathclyde Regional Council appears reluctant to adopt the technology, which is politically unpopular. Public protests have already been made against proposed clinical and possible sludge incinerator schemes in the city.
Other regions rely heavily on sludge disposal to farm land, which takes 20% of Scotland's total sludge production. Forestry, landfill and Central Region's sludge incinerator account for most of the remaining 10%.
Tayside Region has a policy of sludge digestion and disposal to agricultural land. Implementation of the wastewater treatment Directive will double its sludge production, but the council is confident that enough land exists to utilise all the region's sludge arisings, which includes the cities of Perth and Dundee.
Sludge use as a forest fertiliser shows scope for expansion. Only 3% of Scotland's sludge is disposed by this route, but a Water Research Centre report has estimated that 15% of current production could be used in this way within 10 miles of sludge sources.
New technologies discussed at the seminar included bacterial augmentation, which is being marketed as BactaPur by Water-shed Systems. The company claims to achieve a 30% reduction in sludge production and improvements in nitrification by adding improved bacterial strains to sewage treatment systems.
Solar aquatic technology, also marketed by Watershed, combines reed beds and bacterial augmentation to produce a multistage effluent treatment which eliminates sludge production. "Solar silos" are a particular feature of the system, comprising greenhouses which are used to support communities of bacteria, algae, plants, snails and fish which digest and absorb nutrients and contaminants.
Both technologies have been piloted in North America, and Watershed Systems intends to establish a trial scheme with Strathclyde Regional Council.