What is anaerobic digestion
This is a biologic process
of decomposition that occurs in the absence of oxygen. When oxygen
is absent, the process generates methane that is captured for its
The process also generates a compost-like soil amendment.
How much will the digestion
facility cost to build?
Estimates from the preliminary
results from the feasibility study suggest an AD facility would cost around $40
million, including site preparation, permitting and a hefty 30% contingency
fee. However, the facility would
save the City money by allowing it to retire its sewage sludge incinerator ($2
million per year), avoid transportation costs, avoid an external waste disposal
fee, and sell the biogas ($1.4 million per year). Likely sources to pay for the facility would be the City’s
Refuse Fund, the City’s Calaveras Fund ($60 million in reserves for electricity
projects), PaloAltoGreen ($1 million per year), government grants and carbon
How much will this reduce
our greenhouse gas emissions?
This process could reduce City
emissions by up to 20,000 tons of CO2 per year, which is more than 2.5% of the
total emissions from all sources for the Palo Alto community. It would eliminate the incineration of
the sewage sludge from the wastewater treatment plant (6,000 tons per year) and
the waste ash from this process.
Why should this facility
be in Palo Alto?
Can't we have a regional solution for disposing of waste?
This facility would generate enough
renewable energy to power 1,400 homes and produce more than 15,000 tons of
compost each year, generating income of around $1.6 million per year and
diverting 20,000 tons of material from the landfill. Many people feel
Palo Alto should take care of its own waste and should not dump it
elsewhere. In this case it makes financial and environmental sense too,
especially when the facility is located next to the wastewater treatment plant,
the only possible location to allow us to retire our sewage sludge incinerator.
A truly regional solution would require enough capacity to handle all of the region's organic waste. Palo Alto (pop. 65,000) is less than 4% of the 1.8 million who live in Santa Clara County. Palo Alto generates 60,000 tons per year of organic waste annually. The planned San Jose facility will begin with 50,000 tons/year of capacity, and will grow to 150,000 tons/year. So that facility might be able to handle 15% of the County's total organic waste at most. If Palo Alto depends on that facility, we will be taking up precious capacity that could be used by other communities, including San Jose itself. Unless we build more facilities (such as the one proposed in Palo Alto), we simply won't have the capacity to handle all of our region's organic waste.
Palo Alto's wastewater treatment plant is already a regional facility handling sewage from Palo Alto, Mountain View, Stanford, Los Altos, Los Altos Hills and East Palo Alto, so the proposed dry anaerobic digestion and compost facility is already a regional solution. It is only the yard and food wastes which would be sourced from Palo Alto only.
Why does this facility have
to be on future parkland?
Other sites adjacent to the wastewater treatment plant were looked at but proved to be nonstarters due to cost or permitting. Only about 8% of the landfill would be utilized for the new facility; the remaining 92% would still be open space that can be turned into a park when money is available for that purpose. The income from the new facility could help the City pay for the parkland development. Currently there is no money to develop Byxbee into a park. The facility will generate revenue that could be used to develop the remaining 92% of the proposed park. Byxbee comprises 127 acres of the 1,940-acre Palo Alto Baylands.
Won't this facility affect wildlife?
Since the proposed site is currently a dump, it does not have much wildlife. The plant site is farther away from wetland habitat than the sewage treatment plant or the airport are. The digestion takes place in enclosed vessels.
Once the land is undedicated, can't it be used for anything the city council wants?
Why can’t City Council
decide this? Isn’t that their job?
This is a significant decision regarding our money, our waste, and our land. Furthermore, a vote of the people is required by law to repurpose the land needed for this facility since, although the land is currently a dump, it is slated to be added to the current Byxbee Park.
The Palo Alto Green Energy and Compost Initiative in Section 5 specifically restricts the use of any undedicated land at the landfill exclusively to an organic waste conversion facility. The initiative also states that if the facility is not built within ten years, the land reverts to parkland.
Do we need this industrial facility/power plant on what's been promised as parkland?
The conversion is done by microorganisms in enclosed vessels. The methane could be converted into electricity either through a small generator at the wastewater treatment plant or through state-of-the-art fuel cells. Currently there is no money to develop Byxbee into parkland. The facility will generate revenue that could be used to develop the remaining 92% of the proposed park. Byxbee comprises 127 acres of the 1,940-acre Palo Alto Baylands.
Aren't major public regulatory bodies on record against this plan?
The Parks and Recreation Commission determined such a facility would not be consistent with the Baylands Master Plan; the initiative provides language amending the Baylands Master Plan to make the anaerobic digestion facility a conforming use.
Will the technology work?
The Planning and Transportation Commission also determined an Anaerobic Digestion facility would not be consistent with the Baylands Master Plan, and they recommended that the City form a Blue Ribbon Task Force on composting to look at a long-term solution for organic waste processing. The Blue Ribbon Task Force determined that anaerobic digestion was the best solution for Palo Alto, and that the facility should be located next to the wastewater treatment plant so that it could retire the current sewage sludge incinerator and convert the sludge into methane (green energy). Seven of the nine Task Force members are strong supporters of the landfill location.
The Zero Waste Task Force created a zero waste strategy for Palo Alto which encourages expanded compost and composting businesses. The report was silent on the future location for composting in Palo Alto. A later Zero Waste Operations plan by city staff alluded to a regional composting solution, but that was issued after the Task Force disbanded.
All these groups are advisory boards to the City Council.
On April 5 the Council voted to commission a feasibility study to determine the pros and cons of siting an anaerobic digester on landfill land adjacent to the wastewater treatment plant.
Yes. There are more than 100 first-generation anaerobic digestion facilities in the United States, and more than 70 of the second generation, “dry” facilities running in Europe and elsewhere; examples here. A full-scale demonstration plant is operating in Canada need link, and several U.S. cities, including Santa Barbara, San Jose, and Sacramento, are evaluating vendors for new second-generation installations.
Will city residents see tax increases or increased garbage rates?
Once the land is undedicated, can't it be used for anything the City Council wants?
Residents should not see an
increase in municipal solid waste (MSW) pickup rates based on this project. To
the contrary, it will give the city control over the rates for yard and food
waste instead of being at the mercy of whichever entity we would send this to
if we don't handle it ourselves.
In general, MSW trucks pay a
tipping fee to drop off the garbage, recycling, or green materials they have
collected, as the compost trucks do now when they deliver yard trimmings to the
city's current compost operation. These fees help pay for the compost
The Palo Alto Green Energy and Compost Initiative specifically restricts the use of any undedicated land at the landfill exclusively to an organic waste conversion facility. The initiative states that the City Council may rededicate any unutilized portion of the property as parkland.
What is the geological composition of the soil at the site?
How would Palo Alto incorporate the digester into current systems of distribution to residents, or would entirely new infrastructure be required?
A little below the surface is mud, then a layer of crushed rock; the facility would have a concrete pad on top of that. The building won't be taller than the existing tanks at the wastewater treatment plant, so there won't be much sway. Structures in Foster City and Redwood Shores held up well in the 1989 earthquake, and this facility will be much more modern.
As for sea rise level, per page 4 of the Dry Anaerobic Digestion Facility Project Request for Information, September 24, 2010, "...the site is located in the Special Flood Hazard Area (Zone AE) with a base flood elevation of 10.5 feet above mean sea level (Datum NAVD88) show the 9-acre pad at elevations from 12 to 17 feet above mean sea level; therefore, the facility should not be subject to requirements for such a zone."
If Palo Alto does not build up and strengthen its levees, this area would be at risk of flooding from a high tide/climate change combination. The projected increase in sea/bay level rise is 16 inches by 2050 and 55 inches by 2100. However, much of Palo Alto (pretty much up to Middlefield Road) would be at risk, so the City will definitely invest in the infrastructure to protect lives and property. And if every community embraced anaerobic digestion, the impacts of climate change would be reduced.
That the generated compost would be a local resource, the methods of distribution should at least be as convenient as at the present. It is reasonable that distribution of finished compost might be incorporated into the same vehicles that collect the green waste. A Palo Altan would place clippings and food waste into the green bin, and find later in the day finished compost left for their reuse. However, the initiative only provides for the land for this project, and does not direct any future handling of compost.
The petition calls for 10 acres, the feasibility study is for 9 acres; what is the impact of this difference?
Will the anaerobic digestion facility be lit up at night thereby disrupting nocturnal wildlife?
The extra acre provided in the initiative allows for flexibility if the facility were to require additional area beyond the 9 acres considered in the feasibility study. The 10 acres was identified in preliminary designs by Harvest Power, and accommodates a capacity to separately process the biosolids from food and yard waste. The proponents of the initiatived judged the extra acre prudent until final designs are complete. Any extra land can be restored by Council to parkland.
The actual digestion process is an indoor operation, and would NOT pose a lighting impact. Therefore, beyond security lighting, there should be no additional lighting to pose an impact to nocturnal wildlife.
When I think of anaerobic digestion, I think "stinky". Will this smell bad?
No, the anaerobic digestion (AD) is done in a closed container so there are no odors. Furthermore, any venting from the containers is scrubbed in a bio-filter.
Will the AD facility be noisy?
The AD facility will not be any louder than the existing dump and wastewater treatment plant. Anaerobic digestion, a process by which microorganisms break down organic waste into methane and compost, takes place in enclosed vessels.
Won't it leak pollutants into the Bay and adjacent wetlands?
Anaerobic digestion takes place in enclosed vessels. In northern Europe such plants (and there are many) are frequently sited near residential areas. Normal design would specify berms that would limit any run-off or seepage or liquids from the digesters and receiving areas from escaping the facility.
Will the AD facility be unsightly?
Trees will screen the facility from the future park. A green roof is proposed for the facility, which would blend in with the future park and also help to block the view of the existing wastewater treatment plant.
If methane is a potent greenhouse gas, why would we advocate a project that produces methane?
Basically all biological degradation end in producing carbon dioxide. Combustion for power generation ends at the same point as well. In the oxygenated biological degradation process methane is not produced. Instead oxygen consuming bacteria convert the sugars and starches to carbon dioxide. An aerobic process offers no opportunity to yield usable energy. However, through an anaerobic degradation process we harvest methane. The anaerobic bacteria without oxygen cannot produce carbon dioxide (there is no oxygen), and instead produce methane. An anaerobic digester carefully harvests this methane in a way that prevents any leakage. So at this point we have methane to use for fuel.
Why would we choose to combust methane, and thereby emit more greenhouse gases?
While greenhouse gases are emitted through combustion of methane, there is an inherent benefit. First the carbon dioxide emitted by combusting methane from the planned anaerobic digester would be the same mass as emitted by the current aerobic bacteria in a compost process. Second, the biologically generated methane prevents the need to combust mined mineral methane (from inside the earth). When mineral methane is burned for energy new carbon dioxide is introduced to the atmosphere.