Municipal Wastewater

Public Sewers

The responsibility for treatment of sewage discharged to the public sewers in the United Kingdom rests with the Water Service Companies such as Thames Water and Anglian Water. Where a sewer exists, there is in general a right to connect to it, subject to the provisions of the Water Industries Act 1991.

The standards for treatment of sewage effluent were set by the Royal Commission of 1912, as 20 mg/l of BOD and 30mg/l of suspended solids. This assumed a minimum 8-fold dilution in the receiving waters.

The standard, known as the 'Royal Commission Standard' was the accepted target effluent quality for most of the last century, and is still generally the standard for package sewage treatment plants. The Royal Commission standard could be achieved by a percolating filter plant, and many remain in service to this day.

More recently, the effluent quality requirements have been increased, typically to 10/10 BOD/SS, with restrictions in the level of ammonia in the effluent. This has led to a switch away from percolating filters towards various forms of extended aeration for newer treatment works, and the fitting of additional treatment stages to older works.

A growing problem is the disposal of sewage sludge. Dumping at sea is now banned, and restrictions on land spreading are increasing. Sludge is now routinely 'digested' to reduce the pathogen content before disposal, but the quantities of sludge are vast and disposal is a major issue facing the industry.

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