asked Her Majesty's Government:

When they expect the majority of sewage treatment units in the United Kingdom to be converted to the fast activated sludge processing technique. [HL889]

There are many forms of activated sludge treatment. All sewage works serving more than a population of 2,000 receive at least secondary treatment which can be delivered through several techniques, of which activated sludge is one.

The Environment Agency has no policy requirements for a specific variant of urban waste water secondary treatment. Although the Environment Agency sets the standards that the discharge must meet, the choice of treatment technique rests with the operator.