BIODEGRADATION OF CYANIDE: NITRITE INTERFERENCE
IN THE STANDARD TEST FOR TOTAL CYANIDE
J. C. Rapean, Senior Staff Research Chemist
R. A. Johnson, Senior Research Chemist
T. P. Hanson, Senior Research Engineer
WesthoUow Research Center
Shell Development Company
Houston, Texas 77001
INTRODUCTION
Shell Chemical operates a plant at Axis, Alabama for the manufacture of BLADEX®
Herbicide and atrazine. The BLADEX process produces a highly nitrogenous wastewater
which is treated in a dedicated plant involving the steps shown in Figure 1. In this scheme,
cyanide is removed by a reaction with formaldehyde. After hydrolysis, the wastewater is
stripped to remove ammonia, neutralized and dduted for biotreatment.
The biotreater is a conventional single-stage activated sludge system with a nominal
residence time of 48 hours. Air is supplied by four surface aerators. Secondary clarification
involves flocculation and settling. Phosphate is the only nutrient required since the organic
nitrogen compounds in the wastewater supply the required nitrogen.
Since start-up in August 1978 this treatment scheme has produced an effluent meeting
all NPDES requirements. As a consequence of the cyanide in the raw process waste, the
Alabama Water Improvement Commission imposed a limit on the discharge of cyanide of
0.87 pounds per day for the monthly average. At design flow rates, this corresponds to a
concentration of 0.12 mg/l. Until August 1979 routine monitoring of the effluent showed
cyanide concentrations well below this limit.
Toward the end of August, cyanide appeared in the effluent unexpectedly. Analytical
methods were checked between Shell laboratories and satisfactory repeatabUity and recovery
of "spiked" samples confirmed that the observation of cyanide was real. Figure 2 shows
typical cyanide and ammonia data for October. The only other observed change in plant
performance during this period was a decrease in the level of nitrification.
RAW  WASTE
v-
CYANIDE   ION
Ha SO
2300             ~~]
FORMALDEHYDE
CYANIDE
REMOVAL
HYDROLYSIS
AMMONIA
STB 1 PCJR
REQUIRED
■MM
0»T
MjSO,
NEUTRALIZER
BIOTREATER
TREATED W
)
ASTEWATEfl
Figure   t.  BLADEX  herbicide  wastewater  treatment-cyanide removal.
430