Micro-Straining and Ozonization of
Water and Waste Water
DR. P. L. BOUCHER,  Civil Engineer
Glenfield and Kennedy Limited
London, England
INTRODUCTION
There have been many papers on micro-straining and its applications (1)
since the process was introduced first in England in 1945. Installations for water
clarification are in operation now in more than 30 countries, including over 70
plants in the U. S. A. and Canada.
Ozonization has been employed since the beginning of the present century for
water sterilization, principally in France, although there are also installations in
some 20 other countries. Recently, general interest in ozone has been increasing
following developments and new applications, some of which were dealt with at
the Sixth Congress of the International Water Supply Association in Stockholm,
Sweden in 1964 (2).
The combination of micro-straining with ozonization is relatively new and has
led to the development of the Microzon and Micellization/Demicellization processes, preliminary accounts of which were presented at the Water Treatment
Symposium at Adelaide, Australia, in 1965 (3).
The present paper is concerned with the latest use of micro-straining, combined with ozonization and, in certain cases with other processes, in water and
effluent purification. It presents specifically preliminary results from a pilot plant
investigation into the recovery of water from sewage effluent, currently under
study in the London area.
A brief review is first given of the separate processes involved.
MICRO-STRAINING
This process involves the use of high-speed, continuously back-washed, rotating drum filters, working in open gravity-flow conditions. The principal filtering
fabrics employed have apertures of either 35 microns or 23 microns, fitted on the
drum periphery. Drum headloss is between four and six ins. maximum and automation relates drum speed and backwash pressure to water conditions, through
headloss.
Sole Filtration
This is for waters free of colloidal turbidity and carrying only directly filterable microscopic solids. With subsequent sterilization, a highly economic water
purification system is provided, which has been widely applied. The largest example in the U.S.A., is at the Marston Lake Facility of Denver Water Board,
Denver, Colorado, for a flow capacity of 60 MGD. Twenty-three micron filtering
fabric is invariably employed for this application.
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