COMPARATIVE PHYSICO-CHEMICAL STUDY OF
INDUSTRIAL WASTEWATER TREATMENT BY ELECTROLYTIC,
DISPERSED AIR AND DISSOLVED AIR FLOTATION TECHNOLOGIES
Ernest R. Ramirez, Consulting Engineer
American Standard Inc.
Wayne, New Jersey 07470
INTRODUCTION
The technology of wastewater treatment is an unusual one. In general, it does not increase productivity; it does not improve the quality of the product; nor does it add to
profit. On the contrary, wastewater treatment generally is an expense which most plants
could well do without. As a result of these restrictions, many plants follow the theory
that the least expensive operation which wdl meet the needs for limitations on discharge
of wastewater is sufficient. Companies are not looking for frills or novel technology per
se, but rather a method of complying with the guideline limitations at the lowest possible cost.
Strangely enough, the lowest possible cost means different things to different plants.
Some plants place capital equipment costs as the most important, while others place
operation costs as more important.
In summary, each plant has adopted a method which suits its specific needs best.
Whde engineering practice would suggest that actually there exists only one wastewater
treatment choice for a given set of circumstances which would be the least expensive,
reality tells us that different plants see the problem differently, and that much confusion
reigns over the choices of wastewater treatment equipment.
The objective of this chapter is to supply enough quantitative data so that sanitary
engineers can best select the proper flotation technology avadable to meet their specific
goals.
HISTORY OF FLOTATION PROCESSES
In the literature one of the earliest references to flotation by bouyancy involves the
British patent in 1860. This process involves the addition of od to wastewater where the
lighter density of the oil surfaced impurities in the water itself.
The use of gas as of a bouyant media to treat wastewaters was first mentioned in a
German patent in 1877. In this concept gases were generated by the reaction of acids
with suspended sulfides and carbonates. Production of gases by electrolysis for wastewater treatment was first referred to in a British patent of 1 904. Vacuum generation of
gas bubbles is also first covered at approximately this time.
It was not until 1904 that U.S. patent 835,120 covered the concept of introducing gas
and creating gas bubbles by mechanical dispersion.
The use of gas sparging (through a porous bottom surface) is first applied in U.S. patent
1,104,755 issued in 1914. It was not untd roughly 1925 that dispersed air flotation of
minerals was fully utdized, and dispersed air flotation accompanied by frothing agents
was the principal industrial use of dispersed air flotation.
Numerous patents were issued in the United States on both electrolytic flotation and
dispersed air flotation in the 1920s.
699