Use of Styrofoam for Trickling
Filter Covers
J. P. SHE AH AN, Engineer
Plastics Development and Service
The Dow Chemical Company
Midland, Michigan
INTRODUCTION
Population expansion, community and industrial growth are outrunning the
nation's water supply. In consequence, problems of liquid waste control, water
conservation, and pollution prevention are taking on new urgency. This urgency
is reflected in new legislation at all levels -- national, state, municipal.
Many waste disposal techniques are available to reduce pollution. Some are
diminishing in acceptability, others are not practical in all parts of the nation.
Disposal of raw waste in rivers and lakes is being discouraged or prohibited in most
states. Dilution runs the risk of producing odors or objectionable tastes in water
supplies. Ocean disposal is limited to industries and cities with easy access to the
seacoasts. Ponding is practical only if sufficient surface area is available. However, it is often used in conjunction with other techniques, although evaporation
of large liquid wastes is acceptable only in certain isolated areas. The greatest
opportunities for economic practical solutions to liquid waste problems rest in new
techniques and methods.
Biological Oxidation is effective for treating most wastes. The trickling filter
principle is used to support bacterial decomposition of suspended and dissolved
wastes.   It may require preliminary and secondary flocculation and settling.
HISTORY
The Dow Chemical Company through the Dow Industrial Services Division and
the Waste Water Treatment Groups have long been active in this area. Recently,
the plastics department has developed a method of enclosing space with a technique called "Spiral Generation" --an ingeneous system which can form singly or
doubly curved structures of rigid plastic foam. This concept is seen as a means of
economically justifying the use of covers over trickling filters to eliminate problems ranging from freeze-up to acceptable appearance.
The Spiral Generation method involves use of a specially designed machine
which bends, places, and bonds pieces of plastic foam together to a predetermined
shape. A variety of shapes can be produced by modifying and "programming" the
machine. In forming a dome the machine head is mounted on a boom which
swings around a pivot, like the hands of a clock, laying and bonding layer upon
layer of foam board in a rising spherical form.
The Waste Water Treatment Plant at Midland, Michigan, where Dow is located, provided an excellent facility for testing the installation and use of covered
trickling filters. The plant has two identical parallel systems allowing a performance comparison to be made by covering the primary and secondary trickling
filters of one system. Dow was interested in developing the comparative data to
determine if covers for trickling filters are justified on an efficiency basis and the
-  572 -