Abstract
In this Doctoral Thesis the feasibility of treatment with membrane
technologies to demineralize sweet whey from a cheese industry of
the Community Valenciana has been studied.
Nanofiltration is used to eliminate mineral salts from lactose, having
previously eliminated the proteins by ultrafiltration. Both proteins and
lactose can then be used as ingredients in a great variety of
products.
The experiments on membranes both in flat and spiral wounded
configuration have been conducted in a plant designed by the
Department of Chemical and Nuclear Engineering that is able to
operate with both modules. To determine all of the components in the
process, diverse analytical techniques have been used as atomic
absorption, UV-VIS spectrophotometer, ion chromatographic, etc.
The nanofiltration experiments have been carried out with model
solutions of whey and sweet whey. The first have been carried out
with four membranes NF200, NF270, Ds-5 DK and Ds-5 DL. From all of
them, the NF200 membrane have shown the biggest permeate flux
and solute retention values, and the Ds-5 DL membrane have shown
the lowest values. Nevertheless, both are susceptible for use in the
process of demineralization, so that they have been selected to study
their behaviour with the sweet whey.
The permeate flux obtained with the NF200 and Ds 5 DL membranes in
the experiments with the whey do not evidence significant
differences between themselves, but the higher solute retention are
for the NF200 membrane. Solute flux values of chloride ion are for the
NF200 and Ds 5 DL membranes 9,9 g/m2h and 32,42 g/m2h
respectively.
To increase the demineralization values obtained in the concentration
stage with Ds 5 DL membrane, an additional stage of diafiltration was
added. In the concentration stage both lactose and polyvalent ions
were concentrated up to 60 % approximately, while the monovalent
ions did it in 20 % for a factor of reduction of volume of 2. In the stage
of diafiltration, the percentages of demineralization were close to 20%
for polyvalent ions and between 70-95 % for monovalent ones with
losses of lactose around 10% for a factor of dilution of 2.06.
The final characteristics of the sweet whey treated by concentrationdiafiltration
offer concentrations around 65 % in lactose with a value
conductivity of 2500, that allow to obtain a revalued whey
(concentrate in lactose) reducing to the minimum the environmental
impact of wastewater with a pullback time of investment estimated
at around 2 years.
The results obtained with mathematic model (DSPM) in relation to the
lactose retention are in concordance with the results obtained
experimentally.