Development and Optimization of a Carbon Dioxide-Aided Cold Microfiltration Process for the Physical Removal of Microorganisms and Somatic Cells from Skim Milk

Diagram of the microfiltration experimental setup.

Permeate flux (a) and relative flux change (J/J_in; b) for cold microfiltration of raw skim milk under different cross-flow velocity (v) conditions. Error bars represent standard deviations. Transmembrane pressure = 69 kPa and t = 6±1°C. The water flux for these experiments was 987±104 L/(m²h).

Permeate flux (a) and relative flux change (J/J_in; b) for cold microfiltration of raw skim milk under different transmembrane pressure (TMP) conditions, at a constant cross-flow velocity of 7 m/s and t = 6±1°C. Error bars represent standard deviations. Water flux range: 1,079±101 L/(m²h).

Permeate flux (a) and relative flux change (J/J_in; b) for cold microfiltration of raw skim milk under different transmembrane pressure (TMP) conditions, at a constant cross-flow velocity of 7 m/s and t = 6±1°C for setup 2 (CO₂ counterpressure). Error bars represent standard deviations. The water flux for these experiments was 1,130±110 L/(m²h). For a TMP of 52 kPa, only 2 replicate measurements were performed.

Absolute values of the (a) flux and (b) flux relative to the flux obtained at a transmembrane pressure (TMP) of 69 kPa for microfiltration experiments carried out at different TMP, at a velocity of 7 m/s and t = 6±1°C. Error bars represent standard deviations. Closed symbols represent data obtained with setup 1 [membrane 2; water flux = 1,079±101 L/(m²h)], and open symbols represent data obtained with setup 2 [membrane 3; water flux = 1,130±110 L/(m²h)].

Effect of water flux on the initial permeate flux (J_in) in the cold microfiltration (MF) of skim milk. All MF experiments were performed with setup 1 (membranes 1 through 4), under optimal processing conditions: velocity = 7 m/s, transmembrane pressure in the critical pressure range (69 to 83 kPa), and t = 6±1°C. All data points represent single MF experiments.

Effect of microfiltration on the SCC of skim milk. Processing conditions: t = 6±1°C, velocity = 7 m/s, transmembrane pressure = 69 kPa. Run A: membrane 1; runs B and C: membrane 4. A minimum of 10 replicate measurements per sample were performed. Error bars represent standard deviations.

Correlation between separation yield (flux) and transmission of proteins into the permeate in the cold microfiltration (MF) of skim milk at t = 6±1°C. All data points represent single MF experiments.

Permeate flux in cold (6°C) microfiltration (MF) versus warm (53°C) MF of raw skim milk. All experiments were performed with setup 1 under optimal processing conditions (velocity = 7 m/s, transmembrane pressure = 69 kPa). Error bars represent standard deviations. Water flux values: 1,167 L/(m²h) for cold MF and 1,015 L/(m²h) for warm MF.

Scanning electron micrographs of a cleaned membrane surface (left) and of the fouling layer formed after cold skim milk microfiltration on the membrane surface of an inner channel (middle) and an outer channel (right).

Permeate flux (a) and relative flux (b) in cold microfiltration (MF) of raw skim milk, with and without CO₂ backpulsing. Experiments were performed with setup 2. Error bars represent standard deviations. Processing conditions: velocity = 7 m/s; transmembrane pressure (TMP) = 75 kPa (in the critical TMP range); t = 6±1°C; water flux = 889 to 945 L/(m²h).

Rate of flux decline for experiments performed with and without CO₂ backpulsing. Experiments were performed with setup 2. Processing conditions: velocity = 7 m/s; transmembrane pressure (TMP) = 75 kPa (in the critical TMP range); t = 6±1°C; water flux = 889 to 945 L/(m²h).