the cathode chamber, and the electrical potential generated
between the anode and cathode drives the removal of salts,
heavy metals, and charged organic matter for water purification
and desalination. Electrical energy can be generated during ion
discharge from the electrodes, similar to a rechargeable battery.
The MCD process has been tested at lab- and pilot-scale, and
a mobile trailer system with a capacity of 5 gallons per minute
is being developed for field testing. Using actual produced
water obtained from Denver-Julesburg Basin, which has
chemical oxygen demand (COD) ranging from 1,100 to 2,600
mg/L and TDS ranging from 16,000 to 28,000 mg/L, the lab
systems were able to remove 10,200 to 66,240 mg TDS/L/day
and ~4,000 mg COD/L/day. In addition to water treatment,
the system generates 89 to 131 W/m
3
of electricity, which is
harvested and stored for powering online sensors.
The figure below shows the pilot system, developed by the
University of Colorado at Boulder, which is stackable and can
be mounted on a truck. The inset shows the water before and
after treatment. Preliminary techno-economic analysis shows
the MCD system is inexpensive to operate ($0.10 to 0.60/
barrel depending on treatment need) and credited with low
energy consumption; moreover, extra electricity and water are
produced due to the use of sodium percarbonate as an electron
acceptor.
The main value proposition of MCD is that it offers a
simpler solution for oil and gas water management because
it can simultaneously remove hydrocarbons, salts, and metals
in one reactor. This not only reduces system capital costs by
eliminating multiple units, but it also reduces operational costs
by reducing energy consumption and producing renewable
energy and water. MCD can also be integrated with other
treatment units with complementary functions, so overall
efficiency can be improved. For example, MCD has been
connected with electrocoagulation (EC), with EC removing
TSS while MCD removes COD and TDS. In the meantime,
MCD can provide the electricity needed by EC, making the
system energy-neutral. If further treatment is needed for
certain reuses, MCD can also be integrated with membrane
technologies such as reverse osmosis or forward osmosis to
provide high-quality effluent.
Challenges Ahead
While microbial electrochemical processes show good potential
for oil and gas wastewater treatment and reuse, there are many
challenges ahead. For extra-high-saline produced water like that
generated at the Marcellus Shale in Pennsylvania or the Bakken
formation in North Dakota, MCD may not be very efficient
due to its limitation on adsorption capacity; rather, it may serve
as a low-cost pretreatment for membrane distillation. Similar
to the cost of other desalination technologies, the cost of
TDS removal by MCD is still high for the industry compared
with deep well injection, so further development and new
incentives for external water reuse such as irrigation are needed
for possible market adoption. There are several new articles
covering the technology and market, and critical comments
from experts can be found there: Microbes Could Help Clean
Up After Fracking (CBS News) and New Technology Could
Make Treatment of Oil and Gas Wastewater Simpler, Cheaper
(University of Colorado Boulder). n
wateronline.com
n
Water Innovations
Electrical energy can be generated during
ion discharge from the electrodes, similar to
a rechargeable battery.
Dr. Zhiyong (Jason) Ren is an Associate Professor of Environmental Engineering at the University of Colorado at Boulder. He co-founded Bioelectric
Inc., a cleantech startup focusing on innovative water and energy solutions. An expert in microbial and electrochemical processes for energy and
environmental applications, Ren has been funded by NSF, DoD, EPA, and private sponsors to conduct water-energy R&D.; He has published more than
100 journal and conference articles and has filed four patent disclosures. His research findings have been featured by NPR, ABC, and CBS. More info is
available at http://spot.colorado.edu/~zhre0706/.
About The Author
27
PRODUCEDWATER
Clear results: The MCD pilot shown with influent- effluent comparison.