Activated Sludge Treatment of
Cyanide, Cyanate and Thiocyanate
F. J. LUDZACK, Chemist
R. B. SCHAFFER, Assistant Sanitary Engineer
Robert A . Taft Sanitary Engineering Center
U.S. Public Health Service
Cincinnati 26, Ohio
Cyanide, cyanate, and thiocyanate, separately or in combination with
other wastes, frequently are waste water problems. Several treatment methods
are available for cyanide; some lack the desired efficiency, others are difficult to control, and all have high operating costs. Little information is
available on the biological degradation ofcyanates. Thiocyanate pollution
has a long history but its characteristics commonly are misunderstood or
ignored; lower treatment efficiency follows. Since the three anions are related in chemistry, in industry, and in waste control, a group comparison
should bring out certain aspects of the individuals that might otherwise be unnoticed.
Research in this laboratory (1) demonstrated surface water degradation of
cyanide and associated wastes. Pettit and Mills (2) treated relatively high
concentrations of cyanide on percolating filters. Other investigations by the
same group followed (3,4) and more were in progress through 1959. Gurnham
(5) reviewed British research for the Purdue conference. Organisms associated
with cyanide degradation were characterized in cited material and by Tre-
lawney, et al (6). Nesbitt, Kohl, and Wagner (7) studied activated sludge
sustained on a mineral supplemented cyanide feed.
Chemical behavior of cyanates in water has been well documented.
Acidity affects the rate of cyanate hydrolysis, which is rapid at pH 1.0 and
negligible above pH 7.2. Resnick, Moore, and Ettinger (8) reviewed and re-
checked pH effects on hydrolysis rates and studied the effect of biological
degradation in surface water. Anaerobic action resulted in cyanate disappearance with ammonium formate as a likely first stage degradation product.
Aerobic cyanate degradation (8) was not detectable in river water (pH 7.2)
for 10 days. A recneck during this investigation showed negligible cyanate
degradation in river water for one month; two-thirds was destroyed in another
month.  Added cyanate at 90 days was degraded slowly after a negligible lag.
Arthur Key (9) reviewed thiocyanate waste studies cited (10,11,12) and
others. Both percolating filters and activated sludge caused thiocyanate degradation after acclimation. Test feeds generally consisted of a small percentage of gas works waste in sewage. Performance was affected by tar, phenol,
and ammonia in the feed as much as by thiocyanate. Thiocyanate sulfur
appeared in the effluent as ammonium sulfate. A high removal of SCN occurred in the top of a filter, whereas toxicity was evident at the start of
activated sludge aeration. After complete treatment, both processes produced
acceptable effluents. Badger and lackson (13) treated thiocyanate in spent
gas liquor successfully by activated sludge with 1:1 recirculation of the effluent.
Key's observation (9) on the greater tolerance of filters for shock loads
expressed   a frequently accepted theme.    It is more likely that differences
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