Hydrolysis of Condensed
Phosphates in Wastewater
GARY W. HEINKE, Assistant Professor
Department of Civil Engineering
University of Toronto
Toronto, Ontario, Canada
JACK D. NORMAN, Associate Professor
Department of Chemical Engineering
McMaster University
Hamilton, Ontario, Canada
INTRODUCTION
Nutrient enrichment through pollution causes intense aquatic growth in many
of our lakes, which results in their deterioration for man's use. Phosphorus is suspected as possibly the most important element in this problem. Condensed phosphates
from detergents in wastewater are a major supply of phosphorus to surface waters.
They hydrolyze to orthophosphate, the form most readily available to plants and
organisms. The removal of phosphorus in treatment plants has therefore been suggested.
The chemical industry has carried out many studies on the rate of hydrolysis of
condensed phosphates in distilled water. However, few investigations have been made
on this effect in natural water and wastewater. The objective of this study is to
establish rates of hydrolysis of sodium tripolyphosphate, and to a lesser extent sodium
pyrophosphate, the most widely used condensed phosphates, in wastewater under
conditions of temperature, pH, and concentration levels occurring in the environment.
Comparison of rates found in wastewater to those of other media are presented.
THE ROLE OF CONDENSED PHOSPHATES
Condensed phosphates are used as builders in detergents because of the synergistic effect between moderate amounts of these inexpensive compounds and relatively low percentages of expensive surfactants. Phosphates may account for as
much as 50% by weight in detergents. Based on production figures for condensed
phosphates for the United States, Canada, and West Germany for 1966, population
figures, and an assumed wastewater generation of 80 gpcd, the contribution to
phosphorus in wastewater from detergents and human wastes are calculated, and
presented in Table I.
Detergents contribute more than twice as much phosphorus as human wastes,
based on United States figures. In Canada and West Germany, the contribution of
each are about equal. Discussions with representatives of the detergent industry on
the surprising difference between United States and Canadian figures on detergents
supported the figures presented, but did not come up with an explanation.   The
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