BIODEGRADATION OF ORGANOBISTHIOCYANATES

CHARLES CHI-SU CHOU, Purdue University

Abstract

The impact of three organobisthiocyanate biocides on a biological wastewater treatment system and the extent of biodegradation of the biocides were studied using a laboratory model continuous flow activated sludge system. The compounds tested were methylenebisthiocyanate (MBT), vinylenebisthiocyanate (VBT) and chloroethylenebisthiocyanate (CEBT); all of these have been applied to control nuisance microorganisms in industrial process waters. Radioactive organobisthiocyanates with ('14)C positional labelling in the thiocyanic carbons were applied at three levels, 0.3 mg/l, 1.0 mg/l and 3.0 mg/l. Liberation of ('14)C metabolic gas was measured and used as an indicator for organobisthiocyanate degradation. When unacclimated activated sludge was used MBT and VBT were substantially degraded at all levels tested, CEBT was degraded at low input levels but was more refractory at 3.0 mg/l. Acclimation of the biomass to MBT resulted in substantial improvement of the rate and extent of biodegradation. Acclimation to the biocide did not require extended period of exposure. Continued application of gradually increasing doses at MBT to the biological wastewater treatment reactor resulted in a bacterial population which reduced the level of MBT (20 mg/l) by 87-95%, however, approximately 50-65% and 2-9% equivalent of the input thiocyanic carbon (MBT) were identified in the reactor as inorganic thiocyanate and cyanide respectively. A search for bacteria implicated in the transformations of the organobisthiocyanates yielded a heterotrophic axenic culture which substantially converted each of the three organobisthiocyanates tested to inorganic thiocyanate which could be used as an alternate nitrogen source for NH(,3). Examinations of the ('14)C metabolic gas produced as a result of biodegradation of the three biocides by resting cells revealed that cyanide was the major component, although a small amount of ('14)CO(,2) was also released. Unacclimated activated sludge cells were shown to produce cyanide from MBT as the major metabolic gas either under resting cell conditions or growth conditions.

Degree

Ph.D.

Subject Area

Civil engineering

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