We reported yesterday about Dr. Bretschger’s (J. Craig Venter Institute) MFC (microbial fuel cells) to recover energy from wastewater. Today, we’ll discuss a slightly different version, under development at Penn State University and for which results were recently published in Science.
Scientists know that by using reverse electrodialysis (RED), energy can be produced (as has been tested in the Netherlands). In conventional electrodialysis, electricity is employed to force ionic components (salts) from impure water (rendering the feed waters more pure), where the ions cross a membrane and are, therefore, captured. RED is the reverse process; it uses fresh water and seawater in alternating chambers of the device, which generates an electrical charge from the salinity gradient [difference in saline concentrations in the alternating cells]. (Come on, you remember that materials tend to diffuse from more concentrated solutions to lesser concentrated fluids. And, if a membrane stops the back diffusion, the separation can be permanent- and, in this case, generate electricity).
The Penn State group, headed by Dr. Bruce Logan (along with team members Drs. Kim and Cusick), knows that locating power plants contiguous to the sea is not the ideal choice, and the larger number of chambers required to generate significant power would be prohibitively expensive. So, they chose to use MFC to generate power from wastewater. And, instead of using seawater as the second fluid, they use ammonium bicarbonate as the basis of the saline solution (a solution which can also be regenerated, recycled, and reused in subsequent processes). This combination was chosen because they found insufficient power would be generated when using just wastewater alone.
Logan’s group’s results compared pretty favorably with the 13% energy recovery reported by Bretschger’s group (results linked above). Logan found they could produce 5.6 W/m2 of cathode (the negatively charged electrode) area. Without the ED stack, they produced about 20% of that energy. Without the ammonium bicarbonate, electricity production was almost halved to 3 W/m2 of cathode area. They also found they could recover about 30% of the energy in wastewater, with the chemical additive.
so are power plants using system this to produce electricity on a large scale now or in the near to come future?
shawn recently posted..And the Winner Is
Shawn…
This will probably never make sense for power plants per se. Instead, the goal is to provide the energy needed to treat the wastewater from this source. As such, the costs for treatment will be lower and the plants could be located more remotely without regard to power line accessibility.
Roy
It’s hard to see how ammonium bicarbonate and waste water can create clean water if you have one on each side of the cell or are they just using them both to create energy? I could make a potty joke somewhere in here, but someone might read my bad language and get steamed. Hey, we could use that for energy.
Ann recently posted..Marketing Ball Game — 2. Having the Right Mindset
The use of ammonium bicarbonate is to improve the energy developed. The microbes degrade the waste and produce electrons and protons which then combine with the saline solution. This is how the energy is produced, Ann.
Roy
OK, but it must really stink.
Ann recently posted..Marketing Ball Game — 2. Having the Right Mindset