PRACTICAL EXPERIENCE WITH AN INDUSTRIAL BIOFILTER TREATING SOLVENT VAPOR LOADS OF VARYING MAGNITUDE AND COMPOSITION

A biofilter was installed to reduce levels of solvent vapours in air e xhausted from a rotogravure printing press. This air was first humidif ied and then passed through two filter beds in series which contained a mixture of mushroom compost, activated carbon, lime and polystyrene beads. The printing press employed different inks for which the solven ts included ethanol, ethyl acetate, n-propyl acetate, acetone, methyl ethyl ketone and toluene. The amount and composition of the solvent va pours in the exhaust air depended on the printing tasks undertaken. Br eaks in the supply of solvent to the filter occured during job changeo vers and press shut down. The performance of the biofilter under such varying operating conditions was studied. Maintaining moisture in the bed proved critical. Overall solvent removal efficiency was affected b y the nature of the solvent mixture, the relative solubility of indivi dual solvents and their relative biodegradabilities. No significant la g period was evident in biofilter performance when sudden changes in s olvent vapour composition occurred. It was inferred that the activated carbon's adsorptive properties were at least partly responsible for t his. Inferences drawn from observations during plant operation were us ed to gain insights into the relative importance of various physical, chemical and biological processes.