Case Study:
A novel Ultrafiltration Membrane for the Treatment of Dark Juices
The Challenge:
A Brazilian-based juice company seeks to achieve a microbiologically stable juice which can be stored, further processed or directly bottled without compromising on quality. Fruit juices have a complex composition due to the fact that it is a natural product and vary strongly depending on the harvest time and pre-treatment. The primary challenge lies in establishing a reliable and robust membrane filtration system that ensures consistent performance with predictable operational demands and cost-efficiency.
Conventional membrane filtration systems often face two critical limitations when processing dark (grape) juices: either a loss of the juice’s characteristic deep red color, or insufficient cleaning performance due to an inadequately suited membrane formulation. Each fruit juice presents a unique matrix composition – containing varying levels of fiber, pectin, starch, anthocyanins, and other colloidal or particulate substances – that significantly influence crossflow filtration behavior. As a result, lightcolored juices, such as apple juice, exhibit entirely different filtration characteristics compared to dark-colored juices like red grape juice.
For this specific application, selecting the appropriate membrane polymer and molecular weight cut-off (MWCO) is essential. Passage of healthy secondary metabolites including flavonoids and phenolic compounds is mandatory.
At CUT Membrane Technology GmbH, the core objective is to develop and manufacture membrane solutions that are precisely tailored to the specific requirements of such demanding juice filtration processes. The key performance criteria for the membrane system include:
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Clear, stable and particle-free permeate while secondary metabolites can pass the membrane barrier
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High cleanability of the polymeric membrane layer to restore initial flux values after each filtration batch, regardless of the varying raw juice composition
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Long-term mechanical and chemical stability of membrane modules under industrial production conditions
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Reduction of colloidal fouling by selecting the optimal membrane cut-off to balance retention and throughput
The Solution (Retrofitting the Filtration System)
The installed tubular crossflow filtration system is equipped with T-CUT MF 500-125 PVDF 107-3685 membrane modules, specifically developed for the treatment of dark juices such as grape juice. The system is engineered to handle elevated solid loads and complex juice compositions without compromising on filtrate quality or membrane integrity. Configuration of the system is 3 x 10 membrane modules in series and the operating pressure is set up to 6 bar inlet pressure.
Each membrane module provides an active filtration surface area of 5.2 m², resulting in a total installed membrane area of 156 m² per system. This configuration ensures sufficient membrane surface for high-volume batch processing while maintaining optimal footprint.
At production start-up, the system operated at an initial flux rate of 61 hL/h. Over the course of the batch filtration process, the flux rate remained at approximately 39 hL/h. When translated into membrane specific performance metrics, these values correspond to flux rates ranging between 39.1 LMH and 25.0 LMH. These outstanding flux values on sulfonated grape juice show that the membrane suits perfectly in this application.
To assess performance, representative samples were taken from both the raw juice and the permeate. Processing temperatures ranged from 18 °C to 30 °C while the initial turbidity in the feed stream was 256 NTU. During the first two hours of filtration, the turbidity raised to a value of 457 NTU. The permeate turbidity constantly remained as low as 0.02 NTU; thus, close to detection limit of the measurement device. The sugar content (°Brix) of the juice varied depending on the type of grape and specific harvest batch, with typical values ranging between 12 and 18 °Brix.
The Solution (Membrane Details)
CUT Membrane Technology GmbH utilizes a PVDF membrane recipe coated on a tubular membrane structure with an internal diameter of 12.5 mm (½ inch). The membranes are manufactured exclusively from food-grade compliant materials, ensuring full compatibility with hygienic and regulatory requirements in the food and beverage industries.
The membrane elements are designed with exchangeable membrane cores (“cartridge style”), which are housed in robust stainless-steel pressure vessels. This modular construction not only facilitates ease of maintenance and membrane replacement but also aligns with the company’s broader sustainability and waste-reduction strategy.
After several month of operation, an unchanged outstanding performance is reported by the customer.
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