Cross-Flow Membrane Filtration in Biochemical Production Processes

Many of the basic materials required for the production of biochemicals are obtained from renewable sources through fermentation. These materials include alcohols, organic acids such as lactic acid and citric acid, enzymes as well as biomonomers and biopolymers.

Figure 1 shows a basic process flow diagram of a fermentation process. Possible applications for membrane filtration technologies are marked in blue.

Figure 1: Basic diagram of a fermentation process.

Cross-flow membrane filtration technology plays an important role in subsequent processing stages for the production of high-purity biochemicals required for high-quality and competitive products. Membrane filtration systems are used for biomass separation, isolation of valuable substances, purification and pre-concentration.

Biomass Separation

Biomass separation through membrane filtration has a significant advantage in that a solid-free fermentation solution (filtrate) can be produced in a continuous and virtually maintenance-free process. Ceramic membranes are preferably used because they reject genetically modified organisms (GMOs) contained in the filtrate. Alternatively, combinations of centrifuges and membrane systems equipped with spiral wound modules can be applied.

Figure 2: Pilot plant with ceramic membrane modules.

 

Isolation and Purification of Valuable Substances

After biomass separation, valuable substances are isolated from the fermentation solution. For this purpose, ultrafiltration and nanofiltration are used in a two-stage fractionation process. Diafiltration water is often added to increase efficiency and purity.

Figure 3: Ultrafiltration system with polymer membranes.

Concentration

Membrane filtration systems can also be used for pre-concentration of large process streams prior to evaporation systems, particularly for low-viscosity aqueous solutions. This significantly reduces the operating costs of the evaporator.

Technology Behind Cross-Flow Membrane Filtration

In cross-flow membrane filtration technology, the product flows tangentially across the membranes (cross-flow), unlike conventional dead-end cake filtration. This allows for continuous operation over extended periods. Cross-flow membrane filtration is a pressure-driven technology with pore sizes ranging from 100 g/mol molecular weight to 5 microns. Depending on the application, different membranes and system configurations are possible.

Reverse Osmosis (RO)

Reverse osmosis is a high-pressure, energy-efficient process for water removal from process streams, concentration of low molecular weight compounds or purification of waste materials. Common applications include pre-concentration of streams prior to evaporation and treatment of process water.

Nanofiltration (NF)

Nanofiltration is a unique filtration process positioned between UF and RO, designed to separate low molecular weight compounds such as minerals and salts from complex process streams with high selectivity and efficiency. Typical applications include purification of fermented products, recovery of hydrolyzed proteins, concentration of sugars and purification of soluble dyes and pigments.

Ultrafiltration (UF)

Ultrafiltration is a selective separation stage used to concentrate and purify the environment of high molecular weight components such as proteins, carbohydrates and enzymes. Common application areas include purification of fermented products, removal and concentration of gelatin ash and fruit juice treatment.

Microfiltration (MF)

Microfiltration is a low-pressure process for separating suspended or colloidal compounds from high molecular weight dissolved solids. Applications include cell harvesting from fermentation media, protein separation, purification of sugar solutions and CIP chemical recovery. Various system configurations and membrane types allow for optimization of specific separation applications. Membrane types include both polymeric (spiral, tubular and corrugated fiber) and inorganic membranes (ceramic and stainless steel). The capacity to perform highly specific separations at low temperatures or ambient temperature without phase change makes membrane filtration a much more precise and cost-effective process solution compared to conventional methods in many applications. Benefits compared to other separation methods: proper separation of multiple streams, reduced risk of damage particularly to heat-sensitive products, no loss of nutritional value or clinical efficacy, low energy consumption, higher yields and flexibility in developing new products. GEA specializes in specially designed membrane filtration systems and complete process lines tailored to customer requirements. GEA operates test facilities including various pilot systems for product testing and development and optimization of liquid recovery processes. These tests enable the feasibility and effectiveness of recovery processes to be practically demonstrated before acceptance at the customer's facility. Pilot systems supplied by GEA in modules can be integrated into customer facilities for more comprehensive testing prior to full-scale production. Christian Entrup Process Engineer – Membrane Filtration GEA     İlker Damar Sales Manager Industrial Applications GEA Türkiye