74   TECHNIQUES FOR FLUORIDE REMOVAL IN
INDUSTRIAL WASTEWATERS
C. Peter Varuntanya, Project Manager
Dennis R. Shafer, Project Engineer
Chester Environmental
Pittsburgh, Pennsylvania 15244
INTRODUCTION
Generation of fluoride containing wastes from the semiconductor industry is a result of chemical
etching in which hydrofluoric acid is used. Fluoride containing wastes from the steel or metal processing industries are a result of pickling by utilizing a mixture of nitric and hydrofluoric acid. Industries,
such as electroplating, glass manufacturing, and the aluminum industry typically generate fluoride
containing wastes as well.
For discharges resulting from the manufacture of semiconductors, U.S. Environmental Protection
Agency (U.S. EPA) has proposed the fluoride effluent limitations for any existing point source
subject to best available technology (BAT) and new sources subject to new source performance
standards (NSPS) in 40 CFR 469.17 as 32.0 mg/L for the daily maximum and 17.4 mg/L for the
average of daily values for 30 consecutive days, respectively. As for discharges resulting from the
manufacture of non-ferrous metals for surface treatment rinses in 40 CFR 471.92, BAT standards for
fluoride are 52.9 mg/off-Kg (daily maximum) and 23.5 mg/off-Kg (average of daily values for 30
consecutive days). [The term "off-Kg" means the mass of metal or metal alloy removed from a
forming operation at the end of a process cycle for transfer to a different machine or process.)
Most of the state regulatory agencies have subscribed to a uniform limitation of 1 mg/L for the
concentration of fluoride ion in surface waters to prevent mottling of teeth. Therefore, regulatory
agencies will be driven to allocate limitations to industrial facilities that will ensure a 1 mg/L fluoride
concentration in surface waters.
This paper discusses treatability studies utilizing several techniques for reducing fluoride-laden
industrial wastewaters based on limited plant operating data. The treatability studies were conducted
on the wastewaters of a semiconductor manufacturing facility and of a zirconium tube manufacturer.
BACKGROUND
As specified by its NPDES (National Pollutant Discharge Elimination System) permit, the zirconium manufacturer was required to meet a discharge limit for fluoride of 18.9 lb/day as a daily
maximum and 8.4 lb/day as a monthly average. The average flow from the facility was 0.07 MGD.
The maximum flow from the facility was 0.10 MGD. Based on a maximum flow, a concentration
limit of 10.1 mg/L was established as the objective for fluoride reduction in the treatability studies.
The semiconductor facility was under agreement with its permitting authority to limit its discharge
to 22.6 lb/day. The flow from this facility was 0.6 MGD. Therefore the objective of treatability
studies for this waste was to reduce the fluoride concentration to a maximum of 4.5 mg/L.
Both facilities generate wastewaters containing roughly 25 mg/L fluoride. The treatability studies
showed that fluoride can be reduced to nearly 1 mg/L using conventional treatment processes.
The treatability studies conducted in the laboratory were based on lime precipitation which is the
first stage of chemical addition. Upon formation of the calcium fluoride precipitate, other chemicals
were added sequentially; i.e., calcium chloride, alum, alum/sodium hexametaphosphate, and phosphoric acid. Use of lime precipitation followed by activated alumina was also performed.
48th Purdue Industrial Waste Conference Proceedings, 1993 Lewis Publishers, Chelsea, Michigan 48118. Printed in
U.S.A.
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