Separation of residual fatty acids from aqueous solutions using an agitated solution of protein and membrane filtration

摘要

Wastewaters from food processing plants often contain residual fatty acids in solubilized form.They are often difficult to separate by using ultrafiltration membranes due to their small size (approx 1 nm) and tendency to condense in membrane pores causing severe flux reduction.These difficulties can be overcome by binding fatty acids to large protein molecules so that the resulting complex can be easily retained on a membrane.Binding and filtration may be carried out in a single equipment such as an agitated column. The rate of mass transfer of the fatty acid molecules to the surface of protein molecules influences efficiency of separation and utilization of the protein in a continuous process.The mass transfer coefficient during filtration of fatty acid solutions through agitated protein solutions was studied using caprylate and bovine serum albumin as model fatty acid-protein system.An agitated cell fitted with a fully retentive membrane (30kDa nominal molecular weight cutoff) to the protein was used at 100 kPa.Fatty acid in the permeate was monitored by periodic analysis of permeate samples for organic carbon.A linear driving force model was used to evaluate the mass transfer coefficients. At pH 4.9 and stirring rate at 500 rpm,the mass transfer coefficient remains around 6 min~(-1) until approximately 60% of saturation of BSA,and then it rapidly drops.At low agitation (50 rpm) mass transfer coefficient gradually increased to 7.5 min~(-1) before a gradual decline,indicating involvement of other fatty acid retention mechanisms in addition to binding to protein in bulk solution.Under low agitation and pH,increased protein fouling and condensation of fatty acid in fouled layers of the protein could have resulted in apparent increase of the mass transfer coefficient and may provide a potentially effective process to remove large amounts of these residual fatty acids.