DISCUSSION

Mr R. B. P. JAMES, Senior Partner, Pick, Everard, Keay and Gimson

Everyone is looking for opportunities to apply new or improved techniques as they become available and engineers have to admit that the guidance provided by the Water Pollution Research Laboratory under Dr Downing has been invaluable. It may be a reflexion of Mr Reeve's dictum on diminishing returns in§ 48 that the space occupied by reports on secondary treatment in Dr Downing's annual reports has diminished recently.

Nevertheless, it seems likely that there is a lot of work to be done on plastic media and rotating discs to which Mr Reeve refers in §§ 25 and 26. The engineering implications of changes in this field may yield something better than a diminishing return. Probably the only major economy to be introduced into the building of bacteria beds recently is the use of precast concrete wall units, but there may lie in the introduction of random packed plastic media into otherwise conventional systems hope for substantial savings in cost, especially in the cost of the massive civil engineering works now usually associated with the use of stone media.