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Comment 4 for To collect comments on the public health evaluation document of the Scoping Plan. (sp-pub-health-ws) - 1st Workshop.


First Name: Allen
Last Name: Dusault
Email Address: adusault@suscon.org
Affiliation: Sustainable Conservation

Subject: Methane digester air quality impacts.
Comment:
My comments relate to the passage below from the draft AB 32
Scoping Plan - Public Health Evaluation. 

"The anaerobic digestion of human, animal, or wet organic wastes
produces a gas of 50 to 80 percent methane.This “biogas” can be
combusted to produce electricity. Anaerobic digesters must also be
controlled to limit emissions of NOx, particulate matter and carbon
monoxide, as digester gas-based electricity generation generates 22
times the amount of NOx and 9 times the amount of PM as electrical
grid natural gas power plants (per MWh).

This statement is inaccurate for several reasons.  First, digester
that combust biogas for electricity generation provide baseload
power that does not displace just central natural gas plants. 
They displace a mix of facilities that include biomass plants,
legacy natural gas plants (with higher emissions), coal fired
facilities, peaker plants, etc.  A recent analysis we conducted
showed the levels of emissions of NOx, PM and other pollutants
from CA generated electricity mix was much higher than the central
combined cycle natural gas plants. I believe CEC also has recent
analysis of the "average emissions" from this mix that would be
displaced. Importantly, nearly 20% of the mix of electricity we
consume comes from out of state coal plants.  I would presume that
CARB would not ignore those emissions when assessing public health
impacts.  Those impacts include NOx in some cases over 1000ppm. 
They also include mecury, lead and dioxin that is displaced by
biogas generated electricity. The public health and air quality
benefits of that displacement should be recognized.

There is one other major ommission that needs to be corrected. 
Biogas engines are powered by air pollutants.  That is they
consume not only methane but also H2S (a PM/SO2 precursor and
occupational hazard), VOCs and even some ammonia.  The amount of
H2S consumed is in the hundreds of tons a year.  And the amount of
VOCs consumed is nearly equivalent to the amount of NOx produced.
Your analysis doesn't recognize those public health and
environmental benefits.  It needs to.

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Date and Time Comment Was Submitted: 2008-10-10 12:24:34



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