Developments in the Biological Treatment of Waste
Water Produced in Synthetic Resin Manufacture at
CIBA-GEIGY (U.K.) Limited, Duxford, Cambridge
K.G. SINGLETON, Manager
Effluent Treatment and Solids Waste Disposal Plants
CIBA-GEIGY (U.K.) Ltd., Plastics Division
Duxford, Cambridge, Great Britain
INTRODUCTION
The development of effluent treatment facilities at Duxford from 1951 to 1966 has been
previously reported (1, 2, 3,4) and although it is not the intention of this paper to cover the
same ground again in detail, a brief resume of the salient features of this development may
not be out of place.
The basic components of the wastewater have not changed significantly since 1951
when the first section of the diffused air activated sludge plant was commissioned. The
major contributors to the effluent load are still urea-formaldehyde resins, epoxy resins and,
to an increasing extent, phenol-formaldehyde resins. During 1958 a marked reduction in
the strength of the waste was achieved by modification of the resin manufacturing
procedure. For example, in 1956 the average BOD load was 3,300 lb/day, compared with
1,430 lb/ day in 1960, since then the BOD load has remained steady at about 9 lb/ton of
finished product.
Extensions to the diffused air activated sludge plant were carried out in 1956 and 1960.
Meanwhile experimental work was performed on both conventional and forced draught
percolating filters with a view to installing full secondary treatment. It was therefore in 1963
that two 90 ft diameter filters of conventional design were brought into use. The
improvement in quality of the final effluent discharged into the river Cam as a result was
considerable and between 1964 and 1969 it was rare for the BOD to exceed 10 mg/1.
With the continuing expansion of the production units, it was apparent by 1966 that
additional primary treatment facilities would soon be necessary. It had already been
established that the most effective form of treatment of the waste, which is essentially
bactericidal in character, was activated sludge followed by percolating filters.
Investigational work was therefore put in hand to compare various activated sludge
systems.
EXPERIMENTAL WORK
The existing primary stage plant operated with Activated Sludge Limited equipment
and as the load to the plant increased various modifications were effected. The original 4 in
diameter diffuser domes were replaced by 7 in domes; the 110 cfm blowers were replaced by
a 400 cfm blower and a further 800 cfm blower was added in 1966. Intended to operate solely
as a partial treatment plant, the design criteria catered for a 50% reduction in BOD at a load
of 1,750 lb/day. Although this load was exceeded in 1966, the BOD removal was
maintained at about 50 percent until 1968 when the load has risen to 3,000 lb/day.
Although basically a very dependable system, one serious shortcoming was the
rapidity with which the diffuser domes became clogged due to coatings of synthetic resin
precipitating from the wastewater being treated. This situation developed more regularly as
the plant became overloaded. It was considered necessary therefore, to examine other forms
of aeration which would not suffer in this way.
547