Hydrogen producing, microbial electrolysis and desalination cell (MEDC)

Combining desalination, wastewater treatment, hydrogen production, and electricity generation

Since the mid 2000s researchers have been developing microbial electrochemical systems (MESs), including microbial fuel cells (MFCs) which generate bioelectricity from exoelectrogenic bacteria. Two types of MESs of particular interest are microbial electrolysis cells which use bacteria to create hydrogen and other gases and microbial desalination cells which use bacteria to remove salt from water.

Combining these two systems together creates a microbial electrolysis and desalination cell (MEDC). With this pairing, hydrogen gas can be concurrently generated while desalinating water, removing biowastes, and producing electricity.

When applying an additional power source to operate an MEDC, such as solar energy or a microbial fuel cell (MFC), the efficiency of a microbial electrolysis and desalination (MEDC) can be improved, allowing for even greater amounts of hydrogen generation, wastewater treatment, and salt removal.

The following discusses a theoretical continuous flow, renewable hydrogen producing, electricity generating, desalinating and wastewater treating, microbial electrolysis and desalination cell amplified by a microbial fuel cell, integrating Alicat mass flow controllers for liquid and gas flow regulation throughout the system.

Microbial electrolysis and desalination cell optimized by a microbial fuel cell for simultaneous renewable hydrogen production, electricity generation, wastewater treatment, and water desalination

Background info

In 2010 researchers developed a batch-flow MEDC capable of producing hydrogen while treating wastewater and desalinating water simultaneously. In this system, it was found that applying additional electricity increased the efficiency of the MEDC’s hydrogen generation and desalination.

Alternatively, researchers previously developed a continuous flow MFC powered MEC system and a continuous flow MDC system. By applying the electricity generated from the MFC to the MEC, additional hydrogen was produced.

Therefore, it is possible to combine these systems, allowing for a continuous or batch flow MEDC amplified by a MFC. In other words, it is possible to simultaneously generate electricity, treat wastewater, desalinate water, and produce renewable hydrogen by using these systems together.

Making a hydrogen producing MFC powered MEDC

An MFC powered MEDC works by firstly creating a continuous flowing biomass solution which is pumped from a wastewater reservoir to a MFC to produce bioelectricity. The bioelectricity produced by the MFC would be routed to the MEDC system, while the wastewater outflow would run as the inflow to the MEDC.

Instead of operating in batch mode, the MEDC could run continuously by flowing the wastewater solution through the microbial electrolysis cell (MEC) to generate hydrogen while a concurrent water line from an ocean water reservoir would run into the microbial desalination cell (MDC) to remove ocean salts. After this, the wastewater line would flow back into the microbial fuel cell, repeating over and over. At the same time, the ocean water would flow back into the desalination cell, also repeating over and over. The process would stop once the wastewater solution and ocean water solution are cleaned such that more hydrogen or salt removal is no longer possible.

After sufficient hydrogen production, wastewater treatment, desalination, and electricity production has occurred from enough cycling, the treated desalination outflow could be mixed with the treated wastewater into a final clean water reservoir. At this point, new wastewater and ocean water could enter the wastewater and ocean water lines, replacing the cleaned water. The hydrogen gas within the cleaned water could then be separated and stored, such as through a sparging process or via a pressure swing adsorption process. Remaining bioelectricity generated by the system could be stored in batteries.

System flow control

In research experiments of MESs, including microbial fuel cells, microbial electrolysis cells, and microbial desalination cells, the flow rates for all of these separate MESs could be precisely controlled by liquid mass flow controllers, such as LC-Series or CODA KC-Series.

Additionally, these systems can be automated in a control loop using electronic valves and Alicat mass flow controllers, ensuring that flow rates are optimized to maximize electricity generation, hydrogen production, wastewater treatment, and desalination.

Using totalizing and batching settings on Alicat’s liquid mass flow controllers such as CODA KC-Series or LC-Series, these systems can automatically cycle themselves or replace wastewater in batches.

Due to precise flow control, Alicat’s liquid mass flow controllers can also be used for custom biofluid mixing and testing for these systems. Thus, a wide range of standardized biowaste solutions could be researched and optimized to run through the system, increasing system efficiency.

Additionally, depending on system design, other important gases besides hydrogen could also be generated.

Alicat’s CODA KC-Series can be customized to include Coriolis meter-pumps to drive the flow throughout the system. Instead of needing to pressurize the wastewater solution inflow, Coriolis meter pumps can ensure that correct amounts of fluids could move through different parts of the system.

LC-Series specs and features include:

NIST-traceable accuracy up to ±2% of full scale  
Batching and totalizing options

CODA KC-Series specs and features include:

NIST-traceable liquid accuracy up to ±0.2% of reading or ±0.05% of full scale  
Batching and totalizing options
Pressure rated up to 4000 PSIA
Control range down to 40 g/h

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