An introduction to membrane separation in dairies
Service Is Key to Membrane Separation
Every dairy is different. Each plant is unique, producing custom products from complex organic streams. Although all dairies process milk, milk streams differ depending on individual factors such as the breed of the cows, their differing diets, and different environmental conditions. The dairy pool produces a very wide spectrum of products many of which have membrane filtration as a key process:
- Basic grades of milk, skim milk, and cream
- Cheeses of various types and flavors
- High-value proteins from sweet whey
- Added-value milk products, including extended shelf life (ESL) milk
- Functional food and nutritional products such as infant formula and nutritional bars
- Nutraceuticals such as sports and performance products
- Medical products for vaccines and wound healing
- Healthcare products such as shampoos and toothpastes
- Animal feeds
Cross-flow membrane filtration has become the accepted technology for isolating and concentrating many sensitive dairy components. It is a cost-effective means of producing very specific separations at low or ambient temperatures with no phase change. There are several basic technologies in widespread use:
- Reverse osmosis is an energy-efficient de-watering process often used to pre-concentrate dairy or food streams prior to evaporation.
- Nanofiltration can achieve very specific separations of low-molecular-weight components, used for recovery of hydrolyzed proteins, concentration of sugars, and de-ashing of dairy products.
- Ultrafiltration is used to concentrate and purify medium-to-high-molecular-weight components such as dairy proteins, carbohydrates, and enzymes.
- Diafiltration is often coupled with ultrafiltration for additional product recovery, using water injection to remove solubles and wash out low molecular weight materials.
- Microfiltration removes bacteria and spores from milk, separates suspended particles, and fractionates milk proteins, as well as recovering cleaning chemicals.
Separation membranes are made of various materials, with polymeric membranes being the most common and most cost-effective for typical dairy applications. Polymeric membranes are available in spiral wound for high-volume applications with minimal or no suspended solids. Tubular configurations are resistant to plugging, so are typically used where there are suspended solids or fibrous compounds. Hollow fiber polymeric membranes have an extremely high packing density and open channel design ideal for low-solid liquid streams where backwashing from the permeate side is required. For strength and resistance to extreme conditions of pH, temperature, or solvents, inorganic membranes of ceramic or stainless steel are the material of choice. Ceramic membranes are often used in microfiltration for bacteria and spore removal.
Typical applications for membrane separation in the dairy industry include:
- Production of high-value whey protein concentrate (WPC) and whey protein isolate (WPI)
- Protein standardization of milk prior to cheese production to increase yield
- Concentration and demineralization of whey to reduce energy costs
- Reduction of BOD/COD loading from evaporator condensate and permeate streams to reduce the cost of wastewater treatment
- Salt brine cleanup
- Removal of bacteria and/or spores from milk or whey
- Clean-in-place (CIP) caustic and/or acid clarification and re-use
The Cleaning Dilemma
Cleaning is a very important part of milk processing because milk spoils easily, producing toxins and bacteria. Because of the nature of the milk stream, processing plants get fouled and must be cleaned every day. There may be complex built-up products from the organic milk streams, making cleaning difficult. Often dairies pre-treat feed to minimize fouling.
Typical CIP systems require three factors for proper cleaning: turbulent flow, chemical concentration, and high temperatures. Most polymeric spiral membrane elements are temperature limited to 50°C (122°F). There are also pH limitations because the membrane material is most often cast onto a polyester backing. This backing is very easily hydrolyzed at high and low pH, so concentrated chemical cleaning is undesirable. Membranes are also somewhat limited by their structural integrity and ability to withstand the high velocity and turbulence of cleaning processes. So all three of the factors required for proper cleaning are limited.
Over the past ten years great advances have been made to make cleaning easier, and more gentle, while retaining its effectiveness. This has allowed the more widespread use of membrane separation and eliminated some of the cleaning problems. These new systems use a mild caustic with enzymes to help break down fouling molecules and chelators, and to hold broken-down products in solution.
In general membrane separation systems have a lower initial investment, but cleaning requirements make the operating costs higher. Cleaning procedures must be followed strictly with little deviation, so service is crucial to make sure dairy operators are running the plant properly and cleaning it adequately and according to guidelines.
Certain types of membranes can be cleaned with chlorine, but many, including polymeric membranes, will not tolerate chlorine treatment. Today’s dairy operations have segregated systems so chlorine cannot come into contact with polymeric membranes and cause damage.
The Essentials of Good Service
There are key elements that create a comprehensive service package from a filtration membrane supplier: training; oversight and optimization; replacement membranes; and process testing, development and design.
Training
When a membrane filtration process is first introduced into a plant it is essential for the supplier to provide comprehensive training for the operators covering process parameters and operation. Consistent operational procedures are essential to ensure the reliable performance of membrane separation systems so training will usually be provided at instillation. Once the system is running, GEA technicians will revisit regularly, throughout the plant’s operating life, to ensure that best practice is still being observed and, if not, corrective action is taken. This way optimum separation performance can be maintained.
Oversight & Optimization
The proper operation of a dairy separation process will prolong membrane life and enhance product quality. Membranes wear out gradually with constant use and the quality of the final product will deteriorate over time. For example, when concentrating dairy proteins the retained protein level can be as much as 99.5% at the beginning but may drop by as much as 1% over the subsequent week or two. The point at which the membrane should be replaced will depend on the retained protein level required, the value of the lost product, effluent requirements and other down-stream processes.
GEA works closely with its customers to decide upon the optimum time for replacement by making an economic analysis and balancing the lost profit against the membrane cost thereby allowing the dairy to maximize profits.
Replacement Membranes
Organic membranes have a limited life span and need to be replaced periodically, usually about once or twice a year depending on the processing rates and conditions. GEA stocks replacement membranes and works with each dairy’s service technicians to maintain a service replacement history and predict when new membranes will be needed.
If there is a catastrophic failure of a membrane - e.g. if a polymer membrane is improperly cleaned or subjected to extreme conditions - it is essential for membranes to be replaced quickly to minimize down time. Sometimes this can happen with little warning. GEA maintains central stores of membranes, has consignment stocks with manufacturers, and keeps replacement membranes at strategic customers' sites, to ensure the fastest possible response.
Process Testing, Development & Design
GEA works with clients right from the process development phase to help design market leading products manufacture them in the most efficient and sustainable way. Using its experience and know-how to guide customers GEA can help design and bring new products to market quickly and effectively. Pilot testing, for example, can establish the best way to isolate a particular compound from a process stream. GEA pilot plants are available at the company’s headquarters in Hudson, Wisconsin or may be hired for onsite trials.
If a customer wishes to establish a process without testing, GEA engineers can design a plant and generate a proposal based on capacity and product quality.
Service models for optimum operation
GEA uses its process expertise to develop predictive service programs for its customers. By maintaining its independence GEA is able to source membranes from the most appropriate suppliers for each application and to meet every customer’s needs. This independence, combined with GEA’s leading technology, provides a powerful service partner for dairy processors worldwide.
GEA has a membrane service program with three levels of service, designed to meet the needs of any dairy or other processor using membrane filtration. The three levels of service are: the Membrane Replacement Plan, the Membrane Service Agreement, and the Membrane Maintenance Program.
Membrane Replacement Plan
GEA will supply membranes that enhance process performance at a competitive price. Membranes can be supplied from stock at short notice if necessary. GEA has relationships with all major membrane manufacturers and can leverage its buying power for the best prices and maximum manufacturer warranties. The program includes visits by GEA's highly experienced service technicians, whose advice and recommendations can frequently help customers improve profit levels. This plan is available to any dairy, even those who originally bought from another supplier.
Membrane Service Agreement
In addition to the benefits of the Membrane Replacement Plan, this mid-level service from GEA provides service technicians and engineers to help the customer by performing process audits and making recommendations to optimize the performance of all filtration systems in the plant. The customer also has access to GEA's design and process engineering group for process advice and guidance.
Membrane Maintenance Program
This is the top level of service that includes all the features of the Membrane Replacement Plan with the additional benefit of a service contract, usually for three years. Under the contract GEA will provide a dedicated service technician to work with the customer in return for a monthly fee. The technician makes sure that all the membranes and process systems are perfect condition and operating appropriately. By constant observation the service technician can collect all the information needed to optimize replacement time and schedule work accordingly.
The program also provides a technician on call to provide instant help should the need arise.
By assuming the responsibility for handling problems under the program, it is in GEA’s best interest to make sure the technician keeps close watch on the plant’s operation and maintains a close working relationship with operators to ensure that best practice is observed at all times. The program also includes annual training for operators.
The Membrane Maintenance Program has a number of major advantages for the customer:
- The service company assumes the responsibility for membrane performance, and all membranes are kept operating at optimum levels for maximum profit
- The risk of membrane failure is shifted to the service company
- The customer has a fixed budget, converting the capital cost of membrane replacement to a monthly operating expense, simpler for accounting and budgeting
- As technology improves, GEA can recommend changes to improve operations
- The service program is customized for each individual client
It is GEA’s dedicated service technicians that provide the resource that allows the company to offer so many levels of customized service. Their primary job is to travel from plant to plant, maintaining facilities with membrane maintenance and other service agreements. These permanent personnel are trained experts, each with 10 -15 years of full time experience in servicing membrane separation systems. They work with membrane separations every day, loading membranes, training operators, reviewing process logs, and maintaining contact with customers. They are highly experienced so can diagnose most common problems by simply looking at a membrane. Service technicians also understand regulatory agency requirements and reporting and are familiar with process control systems.
All GEA service technicians come from practical technical backgrounds and have the skills, common sense, hands-on capabilities and mechanical minds that allow them to go into plants and diagnose problems. Each service technician covers a dedicated geographic area and builds close working relationships with customers in that area.
The service technicians are supported by a large process engineering department at the GEA headquarters in Hudson, Wisconsin. If there is an unusual problem, the process engineering section provides advice and support. The engineers will ask detailed questions to pinpoint a problem, and even make plant visits when necessary. This department also does development, process design, and sizing of new systems based on pilot plant data. Engineers will recommend portable pilot plants for testing at customer sites where needed.
Engineering, design, fabrication, and installation of membrane filtration systems are all very important. But the day-to-day operation, maintenance and servicing of a system are the keys to maintaining profit levels for dairy owners.
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