PARENT SESSION

2A - Mixture toxicity
Poster Hall
8:30 AM - Monday, 28 April 2003
Chair: Hermens, J.¹, ¹
Co-chair: Toy, R.², Backhaus, T.³, ^{2 3}

(MOP/78) Elimination of cooling water biocides in batch tests at different inoculum concentrations.

Gartiser, Stefan¹, Urich, Elke¹, ¹ Hydrotox GmbH, Freiburg, Baden-Württemberg, Germany

ABSTRACT- In Germany the discharge of cooling water is regulated in Annex 31 of the Framework regulation for wastewater. Here inter alia the blow down of recirculating cooling systems after a shock treatment with a biocidal substance is only allowed if the luminescent bacteria toxicity does not exceed GL =12 (GL= Lowest ineffective dilution factor, LID). Following the recommendation of the VCI-working group "Biocides in cooling systems" the elimination of biocidal effects usually is determined in batch tests with high inoculum density (activated sludge with 500 mg d.s./l). Within a research project supported by the German Environmental Agency (F+E 200 24 233) the input of cooling water chemicals was evaluated, identifying the chemicals from product information, calculating their loads from consumption data and investigating the basic characteristic data needed for an environmental hazard assessment. Additionally, water samples and products have been evaluated in several bioassays and the elimination of eight cooling water biocides has been determined at different inoculum concentrations (30-1000 mg d.s./l). The elimination of biocides showed that isothiazolinones and quarternary ammonium compounds were better removed with higher inoculum concentration due to their adsorption to activated sludge. In contrast, the elimination velocity for 2,2-dibromo-3-nitrilopropionamide (DBNPA) increased with increasing pH. For the oxidative biocide bromochlorodimethylhydantoin (BCDMH) only a weak dependence on inoculum concentration was observed, while Bronopol showed a distinct toxicity at low inoculum concentrations even after 8 days. The results reveal, that the test conditions for the determination of elimination must be clearly defined. Especially for directly discharged cooling water, results about ready biodegradation and/or elimination curves at lower inoculum concentrations that that proposed (i.e., 30 mg d.s./l corresponding to the test conditions of the OECD 301 "Ready biodegradability" tests) should be demanded.

Key words: biocides, cooling water, luminescent bacteria toxicity , elimination