- Draw solutions and their recovery methods for dairy and food industries – a brief overview - June 16, 2018
- The future of forward osmosis commercialization - October 8, 2017
Currently, Forward Osmosis (FO) is well suited for applications in which water needs to be removed in a gentle manner (e.g. food processing and concentration of valuable such as flavors & fragrances and pharmaceuticals). The technology will be especially more applicable when smart draw solution (DS) systems become industrially available utilizing waste heat or solar thermal energy for draw regeneration (e.g. Membrane Distillation (MD) hybrid process). For more information please feel free to revisit my previous article “The Future of Forward Osmosis Commercialization“.
Before embarking on the overview it is worthwhile to mention that draw solution recovery for dairy/food industry is somehow easier than when the final product ends up in the draw solution like desalination process. For instance, in fruit juices, milk or skim milk concentration, we need to concentrate the feed stream in which water goes into the draw solution but water is not important for us as a product because our final product is our concentrated feed stream. It makes our draw solution regeneration easier rather than desalination.
Selection of draw solute for forward osmosis
The selection of a suitable draw solute plays a vital role in development of the FO technology, depending on the targeted application. Tailored draw solution not only improves the process efficiency but also saves significant costs regarding the draw solution recovery process.
Draw solutions applied in dairy/food industries
This overview provides a general view and a comprehensive summary of the application of different types of DS applied in dairy and food industries. Table 1 shows a list of state of the art investigations of FO application for food and dairy industries.
|Table1 – The latest progress summary of applied draw solutions in dairy and food industry|
|Draw Solution||Water Flux (LMH)||Type of membrane||Application||Scale||Recovery Method||Short Description||Ref.|
|Concentration(%,w/w)||An attempt was made to explore the use of mixed osmotic agent (sodium chloride and sucrose) solutions in order to overcome the drawbacks associated with sucrose solution (low flux) and sodium chloride solution (saltiness in juice) as osmotic agents.|
|0||6||0.44||Commercial/ Osmotek Inc.,||Pineapple Juice||Lab||NO|||
|2 M NaCl||15||HTI1/CA2||Orange Liquor||Lab||NO||The application of FO was performed well in dewatering complex slurry that has a high fouling propensity.|||
|4 M NaCl||22|
|6 M NaCl||7.5||Osmotek,
|Beetroot Juice||Lab||NO||Forward osmosis increased 57.1 fold the concentration of betalains content in beetroot juice, and 6.8 fold the anthocyanin content in grape juice.|||
|4 M NaCl||3.52||HTA/CTA3||Jaboticaba Juice||Lab||NO||FO preserved the nutraceutical and organoleptic characteristics of the jaboticaba juice, showing that FO is an interesting technique to be used as alternative in the food industry.|||
|1 M Nacl||15||Synthesized TFC Polyamide Membrane||Fructose Sugar||Lab||RO/NF||Economic estimation revealed that industrial production of crystalline sugar can be optimized through process integration involving fructose concentration up to a range of 16–20% by forward osmosis followed by evaporation and crystallization.|||
|1.5 M Nacl||22|
|2 M Nacl||27|
|2.5 M Nacl||29|
|Seawater Bittern Samples
|10-15||Synthesized TFC Polyamide Membrane||Sugarcane Juice||Lab||NO||The experiments were performed at room temperature and 1bar applied pressure at feed solution side using different bittern samples as draw solution.|||
|2 M NaCl||2.78||FO membrane, HTI
|Lab||NO||Concentrating sugar solutions is a common process used in the production of many food products that can be facilitated by FO process for either dewatering a high value product or concentrating waste streams prior to disposal.|||
|4 M NaCl||5.84|
|1 M NaCl||12-15||Synthezied hollow fiber TFC membrane||Whey Recovery||Lab||NO||This study validated the feasibility of FO-based whey concentration using high-performance hollow fiber membranes that were fabricated in-house. The investigation focused on the effects of various operating conditions on the concentration performance.|||
|1 M NaCl||6-7||Osmoteck||Sweet Lime Juice||Lab||NO||This study is the ultrasound-assisted forward osmosis process which resulted in higher water fluxes in case of sweet lime juice as well as raised extract containing anthocyanin. The degradation of rose anthocyanin due to ultrasound was found to be 1.82%.|||
|2 M NH4HCO3
|12||HTI/CA||Whey Concentration||Lab||NO||Usage of forward osmosis membrane was performed in application of whey concentration using NH4HCO3 draw solution.|||
|3 M NaCl||FO CTA/HTI
RO Composite Polyamid
Whey powder Production from Whey
|Lab||RO||Results have proved that prior to whey powder production, the integrated system could be effectively employed for whey concentrations up to a solid content of 25–35%.|||
|2 M NaCl||FO: HTI/ CTA,
RO: Composite Polyamid Hydranautics Inc.
Whey Powder Production from Whey
|Lab||RO||FO/RO in whey processing could also be effectively employed for all the investment intended for both water recovery and whey powder production.|||
|2 M NH4HCO3||Thermal decompo-sition /RO|
|0.5 M MgCl2||3.12||HTI/CTA||Struvite Recovery from
Digested Livestock Wastewater
|Lab||NO||Livestock wastewater contains a large amount of nutrients that are available for recovery. The results of this study have demonstrated the feasibility of nutrient recovery from livestock wastewater facilitated by FO treatment.|||
- Hydration Technology Incorporation
- Cellulose Acetate
- Cellulose Triacetate
As it can be seen from Table 1, listed following information was taken:
- It illustrates that FO membranes have a great potential to be improved and should be specialized for this process in order to successfully apply FO in food processing.
- There was no draw solution recovery in mentioned FO processes, and the researchers mostly tried to execute the first stage of the whole FO Process.
- Although the study of experimental performance of draw solution recovery has not comprehensively been conducted, a simulation of DS recovery has been done in the area of liquid concentration. Madhumala et al.  simulated the hypothetical commercial-process for concentration of fructose solution using a spiral-wound FO membrane module followed by evaporation and crystallization to reach a solid sugar product. For the solution recovery, the diluted DS can be fed to an RO/NF system to facilitate recycling of draw solution with concurrent recovery of water as a byproduct.
- Table 1 also shows that most of the membranes employed in this process are asymmetric that are made by cellulosic polymeric. The only commercially available FO membrane has been the asymmetric cellulose acetate membrane from Hydration Technology Innovations (HTI, Albany, OR) or asymmetric FO membrane developed by Osmotek, Inc. (Corvallis, OR, USA). However, applications of FO in food processing were limited to the existing commercial membranes in which most of them were designed for desalination process.
Draw solution recovery method mainly applied for other FO applications
Although there is not much research done around DS recovery in dairy/food industries based on Table 1, the draw recovery options available for pairing with FO for other applications of FO can be mainly categorized into thermal processes, membrane-based processes and responsive thermal draw solutes (Table 2).
|Table 2 – Classified technology for draw solution recovery for different FO applications|
|Thermal Process||Multi Stage Flash Distillation
Muliti-Vapor compression (MVC)
|Can recover the draw solution at a wide TDS range at the expense of high energy consumption from 30-60 kWh/m3|
Membrane Based Processes
|Nanofiltration (NF)||Hydraulic pressure driven processes that require no further introduction, They are well established desalting technologies used for various industrial applications.|
|Brackish Water Reverse Osmosis (BWRO)|
|Seawater Reverse Osmosis (SWRO)|
|Osmotically Assisted Reverse Osmosis (OARO)||OARO treats high salinity brines as a membrane-based process that uses equipment common in RO and FO. OARO brine treatment consumes less energy than evaporative processes. Detailed description |
|Disk Tube Reverse Osmosis (DTRO)||DTRO as a Conventionally process for landfill leachate treatment can apply up to 100 bar of osmotic pressure in the brine solution due to its unique module design.|
|Membrane Distillation (MD)||MD becomes an attractive option for draw recovery regeneration only when low quality waste heat is readily available in the plant due to inherent high-energy requirements|
|Responsible Thermal Process||Under an external thermal stimulus can be easily regenerated into ammonia and carbon dioxide||There are special responsive draw solutes such as ammonium bicarbonate draw system but faces drawbacks with high reverse solute flux and scaling issues which limit the scope of practical application.|
Based on this investigation, there is no preferred draw solute that is universally applicable to all forward osmosis applications. According to Ye Wee Siew, Business Development Executive Aquaporin Asia, when dealing with food applications, we are looking at draw solutes that have the following characteristics:
- Low reverse solute flux – no one likes a salty coffee, milk or fruit juice
- Cheap and readily available
- Relatively high osmotic pressure
- Low viscosity to avoid pressure build-up
- Easily recoverable
With the culmination of all the factors, there are some conclusions as follow:
- Combination of two components of sugar and salt as a draw solution in order to overcome the drawback of sucrose (low flux) and sodium chloride (salt migration) as osmotic agents during FO process. The literature indicated that the concentrated pineapple juice using mixed osmotic agent was found to be most preferable. For its recovery method based on the types of components, RO, NF can be used or membrane distillation would be an option.
- It is quite obvious from current overview that authors mostly have interest to apply NaCl solution as a draw solution in their investigation for food and dairy industries. Although NaCl provides high osmotic pressure, it has higher potential for reverse salt flux and this should be carefully evaluated especially when it comes to dairy and food industries. However, RO draw solution recovery method in whey processing could also be effectively employed for all the investment intended for both water recovery and whey powder production. It is also worthwhile to mention that in some products such as applications of FO in vegetable juice or some dairy products that needs to be added a certain rate of salt, the migration of salt or even sugar agent into the product is not considered because migration of salt resulted in improved quality of the product based on the quantity of revers salt flux and the standard quality of products .
- For water and wastewater applications, MgCl2 is the best choice due to its low scaling propensity and good FO performance potential where many mineral salt scaling counterparts are present based on A. Achilli and coworker’s investigation . They investigated more than 500 different inorganic compounds for their potential as draw solutes for forward osmosis applications and reached to short list of 14 candidates based on the selection criteria of draw solution. Also for applications with pure feed streams (e.g. food processing), KHCO3 and NaHCO3 are good choices because of their ability to deliver high water fluxes in combination with low reverse salt fluxes.
- To minimize draw solute build up in the final product, it is recommended to use forward osmosis membranes with as low reverse solute flux as possible.
- Once the selection of draw solute and its recovery method has been done, laboratory experiments can be conducted in order to evaluate the performance of the potential DS in terms of reverse salt diffusion, water flux and water recovery, which are the main parameters used to assess the performance of the whole FO process. We should always strive to keep re-concentrating and recovering the DS simple whenever possible at low-energy cost. Finally, the remaining DS should be tested at full-scale, and life cycle assessment should be conducted to assess the environmental impacts of each stage of the process. Definitely consideration of draw solution and its recovery method need further investigation as this is the concern of all universities and companies who wish to commercialize FO process but this overview would be a potential basis for further investigation.
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