WASTEWATER TREATMENT WITH METHANOL DENITRIFICATION
What is denitrification?
Denitrification is a process involved in the treatment of wastewater. As wastewater is collected
in a treatment facility, it contains high levels of ammonia. Through a bacterial degradation
process this ammonia is converted into nitrates. If discharged into the environment, nitrates in
sewage effluent can have a devastating effect on water ecosystems. Denitrification refers to the
process of removing the nitrogen from the treatment facility discharge, through a combination of
chemical additives and bacterial degradation.
Why is denitrification important to America’s water resources?
Excess nitrogen causes an abundant growth of algae which feed off the nitrates in the water.
An overgrowth of algae doesn’t allow oxygen to penetrate deeper into the water, in essence
suffocating the fish and plant life below. Also, the alga prevents sunlight from reaching the
deeper, sub-surface waters. An extreme example of this occurrence can be found in the Gulf of
Mexico, where there is an 800 square mile “dead zone,” a result of over abundant nutrients
reaching the water due to insufficient wastewater treatment and agricultural run-off in the 32
states comprising the Gulf of Mexico wate rshed.
What makes methanol
denitrification?
a
valuable
tool
for
Methanol’s strength is in its chemical makeup. Known
as “wood alcohol,” methanol is a simple molecule
(CH3OH) that serves as a carbon source for bacterial
“bugs.” Accelerated by the addition of methanol,
anaerobic bacteria convert the nitrate to harmless
nitrogen gas, which is vented into the atmosphere.
Where is methanol being used for denitrification?
Today, 100 wastewater treatment plants around the
United States are using methanol in their denitrification
process. One of the larger plants in the country, the
Blue Plains Wastewater Treatment Facility, has had one of the best success stories related to
methanol denitrification. Blue Plains, which serves the metropolitan Washington, D.C. area,
releases nearly 350 million gallons of treated wastewater to the Potomac River each day. The
Potomac flows into the Chesapeake Bay, the largest estuary in the United States. As a result of
its size, the Blue Plains Wastewater Treatment Facility is the single largest point source of
nitrogen for the Bay, at 20 tons of nitrogen per day. Methanol denitrification helped to reduce
that number to 10 tons per day, half its original nitrogen discharge. The use of methanol
denitrification at Blue Plains has resulted in a 30% drop in nitrogen levels in the Chesapeake
Bay, from just one treatment plant.
Where does methanol come from?
The typical feedstock used in the production of methanol is natural gas. Methanol also can be
made from renewable resources such as wood, biomass crops, and methane gas from landfills
or wastewater treatment plants. The production of methanol also offers a market for the use of
remote natural gas, which is often flared, thus contributing significant greenhouse gas (CO2)
emissions.
In a typical methanol plant, production is carried out in two steps. The first step is to convert the
feedstock natural gas into a synthesis gas stream consisting of CO, CO2, H2O and hydrogen.
This is usually accomplished by the catalytic reforming of natural gas and steam. Partial
oxidation is another possible route. The second step is to catalytically synthesize liquid
methanol from the synthesis gas stream. Each of these steps can be carried out in a number of
ways depending on the desired application.
Can methanol be made from renewable resources, such as wood waste or landfill gas?
Yes. At the University of California-Riverside, researchers are operating a pilot plant using the
“Hynol Process” to convert sawdust into methanol. The process combines biomass and
hydrogen at high pressure and high temperature to produce a synthesis gas and, ultimately,
methanol. The researchers have demonstrated a carbon conversion efficiency of >85%, making
it feasible to produce methanol on a price competitive basis. In Columbus, Ohio, Alcohol
Solutions is building a commercial facility to produce methanol from landfill methane gas. A
typical landfill generates enough methane gas to produce 15,000 gallons of methanol per day,
or 5 million gallons per year.
How much does methanol denitrification cost?
In the example of Blue Plains, again one of the largest wastewater treatment facilities in the
country, methanol denitrification cost $100 million less then the closest alternative to methanol
denitrification. Also, the facility is experiencing a $1 million savings in plant operating costs as a
result of methanol denitrification. This all equates to a cost of about $0.50 to $0.60 per pound of
nitrogen removed for Blue Plains. Average nitrogen removal costs in the Chesapeake basin
have been reported to be about $4 per pound, according to EPA Chesapeake Bay Program
officials.
For More Information Contact:
www.savethebay.cbf.org
www.methanol.org