Philosophy and Methodology of
Metallic Waste Treatment
NOLAN A. CURRY, Senior Sanitary Engineer
Bureau of Industrial Wastes
New York State Department of Environmental Conservation
Albany, New York
INTRODUCTION
Since the days of early civilization, disposal of waste has been a major problem.
Ancient pollution was mainly organic in nature. Given time, decomposition by bacteria
and the beneficial action of oxygen and sunlight, these simple organic excrements and
refuse could be converted into harmless re-absorable elements and compounds.
Our sophisticated civilization is now producing toxic concentrations of metallic
pollution that cannot be handled adequately by natural forces. Such metals are generally
toxic in any soluble form and do not break down into harmless products. Many metals
retard or prevent both modern sewage treatment processes and the biodegration/purification provided by nature.
In the past, industry has tended to use dilution as the cheapest and easiest means to
reduce metal toxicity. The assimilative capacity of ground and surface waters has been
usurped to such an extent that some waters are no longer usable for many purposes. Natural reservoirs, where evaporation is the main exit, are showing steady increases in dissolved solids. Even the ocean, which some consider to be capable of infinite absorption,, is
showing signs of man's misuse. Waste containing metal pollution can be divided into two
classes. In each, the method of treatment to remove the metals is basically the same.
The first class would be those in which removal of only part of the metals provides
water suitable for reuse. Addition of chemicals used in the process, plus readjustment of
pH, is sufficient to permit complete reuse. This type of wastewater should be limited to,
essentially, no discharge. Processes are generally not affected by small quantities of the
metals acceptable for recycling, but excessive for discharge. This reuse and recycling
permits less complete removal of toxic metals at reduced expense.
The second major classification would be wastes produced by processes generating
by-products of soluble salts, whose build-up in solution makes the product unacceptable.
This type of waste is frequently found in the plating industry. Removal of the toxic metals
leaves the non-toxic soluble salts for disposition. If assimilation cannot be used, there is
the added problem of de-salination. Unless a usable by-product can be recovered, the
cost of such processes may require reassessment of the manufacturing operation.
METHODS OF REDUCING POLLUTANT DISCHARGE
This paper is concerned mainly with steps to be taken to reduce the amount of pollutant in a discharge, assuming that some discharge is required in the process. In any such
process, the amount of pollutant is the product of the amount of flow and of the concentration of the pollutant in the flow. Thus, reduction in either the flow or the concentration will reduce the pounds of pollution in the discharge. Seven rules are presented,
(see also Appendix A), based on this formula:
1.       Omit flows with a pollutant concentration lower than the concentration in equilibrium with the precipitate formed.
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