Online UV sterilization of cheese whey

The performances of single UV reactors (single coil or single conventional) and series UV reactor (two coil or two conventional) were investigated for the purpose of online sterilization of cheese whey. The sterilization efficiencies of the single reactors and the series reactors were studied at eleven flow rates (5, 10, 15, 20, 25, 30, 35, 40, 50, 60 and 70 mL/min) and five flow rates (35, 40, 50, 60 and 70 mL/min), respectively. The results showed that UV radiation can be used for cheese whey sterilization if the proper reactor design and flow rate are used. Although the flow was laminar in all the reactors (Re = 1.39-20.10), Dean's vortices were observed in coil reactors (De 1.09-15.41) which resulted in higher destruction efficiencies and increased heat transfer. The coil reactors achieved higher microbial destruction in a shorter retention time. The rate of microbial destruction was found to be exponential in single conventional reactor and polynomial in single coil reactor. For the reactors in series (coil or conventional), the microbial destruction followed an exponential trend. Increasing the flow rate from 5 to 70 mL/min decreased the microbial destruction efficiency from 99.40% to 31.58% in the single conventional reactor. Destruction efficiency in the single coil reactor increased from 60.77% at the flow rate of 5 mL/min to 99.98% at the flow rate of 30 mL/min and then decreased with further increases in flow rate reaching 46.2% at the flow rate of 70 mL/min. Destruction efficiency of 99.25% and 97.40% was achieved at the flow rate of 35 and 40 mL/min in the conventional reactors series while complete sterilization (100% efficiency) was observed in the coil reactor series at the flow rate of 35 and 40 mL/min, 48 and 42 minutes residence time respectively.; The temperature of the effluent decreased with the increase in flow rate in all the reactors. The maximum effluent temperatures in the single conventional reactor, single coil reactor, conventional reactor series and coil reactor series were 45.8, 46.1, 36.0 and 36.4°C, respectively. The results indicated that in all reactors, a major portion of heat was lost with cheese whey effluent while small losses occurred through the reactor wall and top. Heat generation increased with the increase in flow rate all reactors but the heat losses were more in coil reactors compared to conventional reactors due to the presence of helical coil. At the same flow rate, the amount of energy converted to UV was higher in series reactors than single reactors. The effective radiation decreased with the increase in flow rate (from 5 to 70 mL/min) in all reactors (from 52.82 KJ/h to 7.33 KJ/h in the single conventional reactor, from 49.20 KJ/h to 4.51 KJ/h in the single coil reactor, from 58.36 KJ/h to 41.75 KJ/h in the conventional reactor series and from 51.61 KJ/h to 36.00 KJ/h in the coil reactor series).; Fouling in the coil reactors was less compared to the conventional reactors. The total operating time in which 100% destruction efficiency is achieved prior to the advent of fouling was 25 minutes in the conventional reactor series and 198 minutes in the coil reactor series.