Concentrate Management Modeling, Design, and Optimization
Project ID: 3464
Principal Investigator: Saied Delagah
Research Topic: Desalination and Water Treatment
Priority Area Assignments: 2011 (Advanced Water Treatment)
Funded Fiscal Years: 2011
Can reverse osmosis (RO) concentrate streams be further dewatered cost effectively to reduce the volume of concentrate in need of disposal and recover additional water trapped in the concentrate?
RO concentrate stream disposal costs add a considerable expense to capital and operation and maintenance (O&M) costs of RO plants. Reducing the volume of concentrate generated in desalination reduces this additional cost and frees additional untreated water trapped in the concentrate streams.
Can state-of-the-art process simulation software be used to accurately model concentrate handling unit operations that will be encountered in concentrate minimization and water reuse?
OLI software model is used in the oil and gas industry and is highly regarded for its electrolyte modeling capabilities. This model needs to be investigated in the water treatment field and verified to be used as a tool for predicting complex aqueous behavior in concentrate streams. Once verified, this tool can help in optimization of current processes and screening for new processes, such as DEWVAP used for concentrate minimization.
The Consortium for High Technology Investment on Water and Wastewater (CHIWAWA) has identified a computer aided decision tool as an area in need of further investigation. Concentrate management is the bottleneck in inland brackish desalination as land locked communities are realizing that concentrate disposal is holding up inland desalination plant development because a large amount of concentrate, 25 to 50% of feed water, is generated in desalination plants.
Need and Benefit
Membrane processes are becoming a technology of choice for the water purification industry. Purification of sea and brackish water creates new sources of water that enhance the nation's conventional water supplies. The mission of the Bureau of Reclamation is to manage, develop, and protect water and related resources in an environmentally and economically sound manner in the interest of the American public (Reclamation Web site). Desalination of water assists Reclamation in achieving its mission with greater success and is becoming critical for Reclamation to achieve its mission in managing and developing water.
The concentrate generated from membrane desalination contains the particulates and salts that were removed from the feed water. The volumes of these concentrate streams can be anywhere from 50% of the total feed for sea water desalination and up to 15% of the total feed for brackish water desalination. Disposal or management of these concentrate streams represents a significant waste disposal cost and loss of additional valuable water (15 to 50% of wasted concentrate) contained in the concentrate stream. Concentrate disposal is more difficult in inland areas where the ocean cannot be used as the ultimate disposal site. Costly evaporation ponds are used in inland areas to reduce the volume of concentrate.
Mickley, M. (2004) completed a membrane concentrate disposal study for Reclamation. He found that in 2004, there were 234 membrane desalination plants larger than 25,000 gallons per day in the U.S., and this number is predicted to increase rapidly in the future. About 40 of these plants are larger than 6 million gallons per day (MGD), and 90 of them are larger than 0.1 MGD. A minimum of 250 MGD (760 acre-feet per day) of concentrate was being disposed of in the U.S. in 2004, and that number has grown and will continue to grow as the U.S., especially in the West, is facing water challenges for its growing population. Recovery of 50% of the concentrate would have generated an additional 125 MGD of water and reduced the cost of disposal. The potential for cost savings and additional water recovery will only continue to grow as more desalination plants come on-line in the future years.
There is a need for minimization of the concentrate stream volume, which is achieved by placing the appropriate processes to induce the desired effect in the process stream. Water recovered from the precipitated salts can be recycled to the head of the treatment system, thereby increasing recovery of the whole process. Predicting complex aqueous water mixture behavior in different processes such as evaporation ponds, multi-stage flash, DEWVAP, or other evaporating processes leads to better selection of unit processes and their components.
Currently, no such tool has been verified that can model concentrate streams comprehensively and be able to predict their behavior as the concentrate streams are further dewatered and are reaching supersaturation points. The originality of our proposal is that rather than relying on all-or-nothing projects to test the core idea, we plan to first develop and evaluate the broad-based tools for performing virtual process design. Thus, costly further experimentation using unpromising conditions will be avoided.
Using the tools identified by this proposal, we can effectively contribute to meeting Reclamation and Science and Technology (S&T) program goals by facilitating the development and use of new scientific advances. More water can be recovered from feed water of desalination plants, and the reduced concentrate generated will have less disposal costs, therefore aiding Reclamation in achieving its mission.
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