ADAPTATION OF AN INDUSTRIAL ACTIVATED SLUDGE PROCESS
TO THE REMOVAL OF CYANIDE
Dennis Harden, Graduate Fellow
Daniel D. Jones, Associate Professor
Joseph J. Gauthier, Associate Professor
Biology Department
University of Alabama
Birmingham, AL 35294
INTRODUCTION
Cyanide occurs in the wastewater of a variety of industries, particularly those involved in steel
production, metal plating, coal gasification and in the manufacture of chemicals, plastics, and
pharmaceuticals. Because of its toxicity, cyanide is generally removed from wastewaters by chemical
and physical methods, including alkaline chlorination, complexation, ozonation and electrolytic
oxidation, prior to biological treatment. A disadvantage of these processes is their cost.
It is known that cyanide can be degraded by microorganisms. Allen and Strobel [1] showed certain
cyanogenic fungi are capable of assimilating hydrogen cyanide. There have also been many reports of
microorganisms being resistant to cyanide [2,3,4]. Ware and Painter [5] isolated a strictly aerobic,
autotrophic actinomycete from percolating filters treating sewage that was capable of utilizing
concentrations of cyanide up to 150mg/l. It was a slow-growing organism and was unable to grow in
the presence of agar and peptone.
It has been reported that low concentrations of cyanide can be treated in trickling filter systems [6]
and activated sludge processes [7]. However, Raef [8] has pointed out that due to the chemical reactivity and volatility of cyanide, the validity of some of the early work on cyanide degradation may be
open to question. More recently, Gaudy et al [9] have shown, using a synthetic feed supplemented
with 10-20 mg/l cyanide, that extended aeration processes can effectively remove organic substrates
as well as ammonia and cyanide in a single-stage system. Cyanide did not accumulate in the sludge.
Up to 60% could be removed by air, stripping before it could be biologically degraded.
Wastewaters generated by the steel industry and coal gasification processes contain relatively high
concentrations of phenols, thiocyanate, cyanide and ammonia. If the concentrations of cyanide and
ammonia are first reduced by distillation, this wastewater can then be treated in a complete-mix
activated sludge process. Influent concentrations of 200 mg/l phenol, 250 mg/l thiocyanate, 50-100
mg/l ammonia and 1-2 mg/l cyanide can be successfully removed in a single-stage process [10].
Similarly, Wong Chong and Hall [ 11 ] showed in another study on the treatability of coke-plant wastewater, that both ammonia (about 200 mg/l) and free cyanide (40 mg/l) could be treated, at least for a
brief period, in a single stage system. Luthy et al [12] showed that influent cyanide levels of 100 mg/l
could be removed in a biological reactor receiving coal gasification wastewater diluted to one-third of
the original strength and pre-treated by lime aeration to strip ammonia.
When complete-mix activated sludge processes were first employed to treat steel industry wastewater, microorganisms from municipal waste treatment processes were used as the inoculum.
Although this population was not initially able to remove phenol, thiocyanate and the other
pollutants, microbial selection occurred over a period of several weeks, resulting in a mixed population able to withstand the physical conditions of the wastewater and to utilize the soluble components
as nutrients. The object of this research was to determine whether a mixed microbial population
already adapted to the treatment of stream-stripped coke-plant wastewater could be further adapted
to treat the higher concentrations of ammonia and cyanide found in nondistilled ammonia liquors.
Even partial by-passing of the steam stripping process would reduce the overall cost of treatment.
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