The government's assumption that imposing higher waste water treatment thresholds brings greater environmental benefit, must be challenged said water companies this week.
Government's interpretation of the Urban Waste Water Directive is more stringent than necessary, according to Anglian Water Group head of environmental regulation Dr Stephen Bolt.
The directive is part of a tranche of European Union legislation geared to cleaning up coastal waters.
Most sewage discharged into the sea is subject to primary treatment. In its application of the Urban Waste Water Directive, the UK government requires secondary treatment facilities to be built at all plants. Secondary treatment removes around 90% of viruses and bacteria present in sewage after primary treatment.
Utilities firms are providing the required equipment in their current round of capital spending. But the directive permits greater flexibility than allowed by the government, claims Bolt. It says levels of treatment must be suited to prevailing marine conditions, taking into account the volume and toxicity of sewage, length of outfall pipe, tides, currents and local biodiversity. This should allow for some variation of the level of treatment carried out before sewage is discharged into the sea.
A small but significant number of sewage plants, serving communities of 2,000 to 4,000, are being forced to install secondary treatment for no discernable environmental benefit, says Bolt. Worse, the huge amounts of energy consumed carrying out secondary treatment will result in large emissions of the greenhouse gas carbon dioxide.
Anglian is taking the lead in questioning the government's blanket requirement for secondary treatment, but other firms including Northumbrian Water and United Utilities are also looking at the trade off between marine and atmospheric pollution.
The argument was dismissed by environmental group the Marine Conservation Society.
Sewage discharged after only primary treatment dramatically reduces available oxygen, killing off benthic life forms such as star fish that live on the sea bed. This impacts on the food chain, says coastal pollution officer Kate Hutchinson.
An Environment Agency spokesman said a decision on whether or not to relax enforcement of directives lies with DEFRA and the European Parliament.