Biodegradation of solvents in varnish waste water of an airscrubber from an automobile varnish shop

Abstract

The scrubber liquid of an automobile varnish shop, where varnish particle, pigments and resins are washed out, contains microorganisms, that are able to degrade the main compounds of the solvents in the waste gases, i.e. n-butanol, ethylbenzene and structural isomers of xylene, ethyltoluene and trimethylbenzene. The concentration of the compounds in the varnish waste water to be purified oscillated between 1000 and 1 ppm. The specific degradation efficiency could be increased 4 to 12 times by improvement in oxygen supply.

A further enhancement was achieved by continuous addition of organic solvents in the gas phase. During the cultivation the number of different microorganisms of the mixed culture in the scrubber liquid was reduced. The biological system was also very stable and not sensitive to fluctuation in the solvent supply. Differences in the degradation capacity of structural isomers take place at the same concentration of aromatic hydrocarbons. The elimination of 2- or 4-ethyltoluene and 1,3,5- or 1,2,3-trimethylbenzene were 10 to 25% lower than 3-ethyltoluene or 1,2,4-trimethylbenzene.