Ecotoxicity and Biodegradability Assessment of Metalworking Fluids by Activated Sludge Bacteria

The main aim of this study was to evaluate toxicity of metalworking fluids to bacterial consortium of activated sludge according to OECD 209 (STN EN ISO 8192) and a potential of the same sludge to degrade a part of the fluids according to OECD 302B.

Toxic impact can affect different responses, particularly the inhibition of respiration measured from the oxygen consumption in a closed bottle. The degradation rate was calculated from COD according to the authors such as van der Gast and Ian Thompson (1, 2) who tested the degradability of some MWFs in bioreactors by measuring the COD. The lowest toxic MWF's were Cimstar 597 and Emulzin H (the highest tested concentration was below EC₅₀), then Zubora TXS (EC₅₀ - 11 349 mg l^-1), Aquamet LAK-E (EC₅₀ - 5 228 mg l^-1), Adrana D 407 (EC₅₀ - 4 351 mg l^-1) followed, and finally, Hocut 3380 (EC₅₀ - 2 339 mg l^-1) was assessed as the most toxic.

Important in this test (OECD 302B) is that the starting concentration of the tested substance must not decrease below 20% after 3 hours of cultivating. After that, it is impossible to distinguish biological degradation of organic matter from abiotic elimination from the suspension through adsorption. Tested were 8 MWFs of similar concentration and different addition of activated sludge - 0.25 g l^-1, 0.50 g l^-1 and 1.00 g l^-1. The test showed that, after the first 3 hours of cultivating, adsorption grew with the increasing amount of inoculums, except of Akvol B (the decrease of the starting concentration after the first 3 hours of cultivating was the lowest of all and below 20%). It can be stated that, according to the test basic conditions, all the tested MWFs have a potential to ultimate degradation.