Pitch
I propose to combine CHP biogas cogeneration systems in wastewater treatment plants to power water desalination systems.
Description
Summary
Methane gas is produced naturally within wastewater treatment plants due to the anaerobic reactions. Organic materials within wastewater undergo anaerobic microbial decomposition, a reaction in which microorganisms metabolize organic material in an oxygen-free environmental resulting in the production of biogas, a mixture composed of 55-75% methane (CH4) and 25-45% carbon dioxide (CO2).
The methane gas is then captured from the anaerobic digester and directed into a gasholder, a system referred to as a biogas cogeneration system. The average fuel value of the collected biogas is between 22-30 MJ/Nm^3 at higher heating values and 19-26 MJ/Nm^3 at lower heating values. This biogas is then converted into energy using an internal combustion gas microturbine CHP system. Microturbines burn gaseous fuels to create mechanical energy that turns an electrical generator. Such clean-burning, low-emission microturbines are ideally suited to use biogas from digesters as fuel for energy production. The CHP system produces enough heat to maintain proper heat within the anaerobic digesters, as well as generates enough energy to power water desalination systems.
Using reverse osmosis membrane technology for desalination requires a three-step process. The first step, pretreatment, requires .9-1.5 kWh/kgal (8-12% of total energy) to remove suspended material. The second step, reverse osmosis, is dependent on the salinity and temperature of the water input to determine energy consumption. The most energy intensive water input, seawater, requires 6.8-8.2 kWh/kgal (65-85% of total energy input) for reverse osmosis. Brackish and other waters would require less energy input. Lastly, post-treatment of permeate requires conditioning of the desalinated water with chemicals for buffering and stabilization prior to entering the drinking water supply. The fully processed water then enters the potable water distribution system.
What actions do you propose?
I propose implementing this system in existing wastewater treatment plants.
Who will take these actions?
This proposal can be implemented by renovating pre-existing wastewater treatment and desalination plants, or new facilities can be constructed. Facilities should be located near the water source being utilized for desalination to decrease transportation energy costs. The facility will need to have access to existing wastewater and drinking water systems.
Where will these actions be taken?
This system can be utilized in any country with a public wastewater treatment and water distribution system. It is ideal for communities prone to drought and water shortages, such as California.
How will these actions have a high impact in addressing climate change?
The energy-water nexus focuses on the intersection of energy and water usage. As the global population continues to increase at an exponential rate, the development of technologies that provide alternative sources for potable water and renewable energy is vital. According to a study conducted in southern California, water desalination systems consume an average of 14-19% of the total residential energy demand. The proposed integrated wastewater treatment and water desalination plant uses naturally free methane gas produced by the wastewater treatment to produce clean energy. While this energy could be sent back to the main energy grid, utilizing this energy for water desalination systems not only relieves the intensive energy demand such a system would impose on the energy grid, but offers an alternative source for drinking water.
What are other key benefits?
The desalination system can be used to turn a variety of different waters into potable drinking water, allowing the integrated system to work within a variety of environments. Desalination systems not only process seawater and brackish water, but can also turn agricultural run-off and aquaculture water back into usable water for the those industries.
What are the proposal’s costs?
The most cost effective way to implement this system is to build off of pre-existing wastewater treatment plants. The cost range of implementing a cogeneration system using CHP microturbines, depending on the facility, ranges from $275,000-$500,00.
The cost of installing a 60-120 kW reverse osmosis desalination system varies between brackish and saltwater systems. Assuming brackish water is the most common source for desalination systems, the average bid for a reverse osmosis system is $850,000.
Time line
- Government subsidies provided for technology development of integrated system (6-8 months)
- Ideally pre-existing wastewater treatment plants are targeted for integrated systems implementation (6 months)
- Government subsidies offered for installation and operation of integrated system in pre-existing and new facilities (begin installations after 1 year and continue to implement/improve integrated systems worldwide)
Related proposals
References
Desalination by reverse osmosis. (1997). Source Book of Alternative Technologies for Freshwater Augmentation in Latin America and the Caribbean. Retrieved April 21, 2015, fromhttp://www.oas.org/DSD/publications/Unit/oea59e/ch20.htm
Krishna, H. (2011). Introduction to Desalination Technologies. Retrieved April 21, 2015, fromhttps://www.twdb.texas.gov/publications/reports/numbered_reports/doc/R363/C1.pdf
Nemeth-Harn, J. (2012, January 1). Capital and O&M Costs for Membrane Treatment Facilities. Lecture conducted from Harn R/O Systems, Inc., Venice, FL. Fromhttp://www.harnrosystems.com/papers/capitalandomcostforro_presentation.pdf
Opportunities for Combined Heat and Power at Wastewater Treatment Facilities: Market Analysis and Lessons from the Field. (2011, October 1). Retrieved April 21, 2015, fromhttp://www.epa.gov/chp/documents/wwtf_opportunities.pdf
Seawater Desalination Costs. (2012). Water Reuse Association. Retrieved April 21, 2015, fromhttps://www.watereuse.org/sites/default/files/u8/WateReuse_Desal_Cost_White_Paper.pdf
Seawater Desalination Power Consumption. (2011). Water Reuse Association. Retrieved April 21, 2015, fromhttps://www.watereuse.org/sites/default/files/u8/Power_consumption_white_paper.pdf
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