Ultraviolet treatment of microbially contaminated metalworking fluids using a thin film contactor

Microbially contaminated batches (0.2, 0.4 and 1.0 m(3)) of a commercial me talworking fluid (MWF) were irradiated with short-wave (lambda = 253.7 nm) ultraviolet light (UV) using a thin film contactor operating continuously a nd in total recycle. The MWFs were irradiated at a flowrate of 1.8 x 10(-2) m(3) sec(-1), at a UV dose of 44.5 mW-s cm(-3), in the form of enclosed un supported liquid films known as 'bells' which were generated with a nozzle of special design. A rapid decline in cell numbers from approximately 10(6) to 10(7) colony forming units (cfu) ml(-1) occurred within 6-8 hours for t he smaller batches and in 24 hours for the 1.0 m(3) batch. Thereafter, low microbial levels were maintained for up to 250 hours when the counts were s imilar to 100 cfu ml(-1). Prospects for the commercial UV irradiation of MW Fs ar-e discussed both in general terms and with particular reference to th in film contractors.