Study On Concentrating Fruit Juices And Oil Refining Wastewater By Multiple-effect Membrane Distillation

Multiple-effect membrane distillation (MEMD) process was applied toconcentrate fruit juices such as watermelon juice, pear juice, grapefruit juice andapple juice, which possessed characteristics of mild operation conditions, internal heatrecovery and high thermal efficiency. In this study, the effects of various processparameters on the MEMD performances were investigated for trans-membranepermeation flux and thermal energy efficiency which was described in terms ofperformance ratio (PR), and the parameters include feed-in temperature, heatingtemperature, feed-in flow rate and feed-in concentration. The experimental resultsshowed that, trans-membrane flux and PR increased with an increase of heatingtemperature; trans-membrane flux increased and PR decreased with an increase of thefeed-in flow rate. New squeezed fresh juices were about8.7°Brix, at the heatingtemperature of75℃, the mean trans-membrane flux was about3L/(m~2·h), and FRwas7. Besides, stability test was conducted by choosing apple juice as a model feed,and after two months, the value of trans-membrane flux and PR remained almost thesame. Another study was carried out on deeply concentrating oil refining wastewaterwhich had been pre-concentrated by reverse osmosis by using MEMD process. Theexperimental results showed that the wastewater could be concentrated by20timesand the recovery of freshwater could be more than95%. When hot water of95℃wasused as heating resources, the PR was6.8-10.2and trans-membrane flux was4.5-6.5L/(m~2·h) respectively. The electrical conductivity of the permeate water could be lessthan8.6μs/cm, and CODCrwas under40mg/L. The concentrated feed from could befurther treated by the conventional evaporation-crystallization devices to get wastesolid salt. In short, MEMD process which could be conducted without hightemperature and pressure provides a new way to the concentration of materials and thetreatment of waste water.