1. Desalination for NYC? Energy In Sea Water In Fresh Water Out Reverse Osmosis Brine Out Nathan Winkler, E4160 Waste Management: Term Project, April 2011
2. Whining about the Brine Nathan Winkler, E4160 Waste Management: Term Project, April 2011
3. Brine Disposal Shoreline Discharge Deep Ocean Discharge 150 Miles to the Deep Ocean! Nathan Winkler, E4160 Waste Management: Term Project, April 2011
4. Salt Recovery & Zero Discharge Water Recovery Salt Brine In Salt Product Out Nathan Winkler, E4160 Waste Management: Term Project, April 2011
5. NYC RO with Salt Recovery NYC Water Consumption: 1,391 million m^3/yr Reverse Osmosis & Brine Recovery Energy Consumption (Semiat 2008, Kim 2011): 4 kWh/m^3 Water Price with RO Desalination and Ion-Exchange Salt Recovery: $4.10/100ft^3 Current Water Price (NYCDEP): $2.95/100ft^3 Increase in Water Price: 38% Recovered Salt Price (The Economist 2010): $30/tonne Estimated Plant Cost (15x Ashkelon): $3 billion Nathan Winkler, E4160 Waste Management: Term Project, April 2011
Editor's Notes
The picture shown here is of a newly constructed desalination facility for producing drinking water in one of the world’s most populous and wealthy cities. Before I explain which city, why it’s important, and what that means for New York, please guess which of the regions of the world, the desalination plant was built: 1)Middle East 2)Northern Europe 3)AustrailiaDid you guess the Middle East or Australia? Unfortunately for all of us, you’re wrong. The answer was London, England. That’s right, one of the world’s rainiest cities (click) doesn’t have enough fresh water for it’s inhabitants and they’re forced to rely upon desalination via reverse osmosis (click), which consumes seawater and energy and produces freshwater and brine. What does this mean for all of us? Fresh water supplies are no longer a concern limited to the world’s desert population, the issue has become a global concern. Even water-rich areas close to New York City, such as Cape May, NJ and Rockland County, NY have built or begun the planning for desalination plants to meet their water needs. This term project was focused on assessing the economic and environmental feasibility of meeting New York City’s water needs via desalination.
An important environmental impediment to installing desalination in NYC is environmental impact of brine disposal. Brine, is what’s left over after as much fresh water as possible has been separated from the original salt water (50% or more). The salt content of brine can be as much as 7 times the amount in the original seawater and as a result brine can have a devastating impact on the local aquatic environment. In Rockland County, New York, where Professor Somasundaran lives, public opposition to the construction of a desalination facility has been based on environmental concerns. And thus, far (click) the project has been prevented from going forward until an acceptable brine management plan is developed. What does this mean for NYC or any major city for that matter? It’s important to note that the water production rate for the Rockland County desalination plant is only 1/100 the current largest desalination plant in Ashkelon, Israel, and only 1/1000 the water consumption of NYC. This means that a brine management strategy would have to carefully developed for a large-scale desalination for NYC to be built and failure to manage brine effectively could make such a plant unfeasible.
Conventional brine disposal methods typically consist of discharging the brine into the ocean, either immediately offshore, or into the deep ocean via long pipelines. Near shore disposal has the greatest impact on aquatic life and local beaches due to the disruption caused to local ecosystems by a significant change in salinity. Given the scale of brine production by a potential NYC desalination system, and the level of public opposition that might be anticipated, near-shore brine disposal can be effectively ruled out as option.Deep ocean discharge can minimize the environmental impact by depositing the brine beyond the continental shelf, where the ocean’s capacity to handle the environmental effects is significantly greater. There are hurdles to implementing this in NYC. Constructing a pipeline out into the ocean is hardly a simple engineering task (click). The longest ocean discharge pipe in North America is currently about 2 miles. The distance between NYC and the continental shelf (click) is 150 miles. Thus deep ocean discharge of brine from NYC desalination would likely be an unparalleled feat of engineering, a maintenance nightmare, and prohibitively expensive.
There is an alternative to treating the brine as waste and that is to treat it as a raw material unto itself. Salt is routinely harvested from the ocean and certain high grades may sell for more than $100/tonne. There are several methods for harvesting salt from seawater and from brine. The flowchart displayed in the diagram is for a reverse osmosis ion exchange system, where the brine is pumped through success reverse osmosis membranes to concentrate the brine as much as possible and then finally passed through a solid resin containing hydrogen ions, which are exchanged for the sodium ions in the brine and thus remove the salt from the aqueous phase. In the case of a large-scale desalination facility, salt recovery and zero discharge may be the only way to avoid negative environmental impacts. The recovered salt would then provide an additional product to help pay for the plant.
Let’s assume NYC were to install a facility using Reverse Osmosis and Ion-Exchange desalination and salt recovery technology because these processes have proven to be the most cost effective in climates without significant solar energy. The water demand of NYC is about 1.4 billion cubic meters per year. The energy consumption of the process is roughly 4 kWh per cubic meter (click), the salt price is roughly $30 per tonne, and the cost of the plant is about $3 billion (click), which will then be spread over a 50 year plant life. This adds up (click) to a water price of $4.10 per 100 cubic feet, which is an almost 40% increase beyond the current rate. So is desalination feasible for NYC? An initial analysis suggests that with salt recovery and zero brine discharge, desalination is a real option for major coastal cities such as New York.
