Post a New Topic
New study, same arguments in Palo Alto's compost debate
Original post made
on Jun 28, 2011
Palo Alto's heated debate over the future of local composting reignited Monday night, with both supporters and opponents of a new facility pointing to a newly released analysis to support their position.
Read the full story here Web Link
posted Monday, June 27, 2011, 9:56 PM
Like this comment
Posted by Cedric de La Beaujardiere
a resident of Barron Park
on Jun 29, 2011 at 12:09 am
Cedric de La Beaujardiere is a registered user.
I think we can all agree that sewage incineration is out: it will be is outrageously expensive to rebuild it, and emits a lot of green house gas. Both opponents and proponents of the initiative agree on this.
For the sewage, of the options evaluated in the study, that leaves either Dry or Wet Anaerobic Digestion (AD). (These correspond to cases 1a for Dry AD, and 1b, 1c, 2a & 3a for Wet AD.)
For the yard and food wastes, the study considered processing them in Dry AD (Case 1a), or sending yard to southern Gilroy for Composting (2a & 3a), and/or sending food to a Dry AD in San Jose (2a).
For reasons of cost competitiveness, I have focused on options 1a, 2a & 3a. The opponents to this initiative like 2a or 3a, because these would handle the sewage at the water treatment plant, keep this 8% of the landfill/park intact, and send the rest of our wastes "away".
The study considered three scenarios which affect costs, which are summarized on page 1 of Web Link
Under these Scenarios (Sc 1, 2, 3), these cases were estimated to have the following total 20-year costs:
20-year NPV (Millions $):
Case..... Sc 1..... Sc 2..... Sc 3 .... Description
1a............ 60........ 73......... 96 ...... local Dry AD for all our organics
2a............ 94........ 96......... 81 ...... Wet AD for sewage, Food sent to San Jose Dry AD, Yard sent to Gilroy for Composting
3a............ 89........ 91......... 77 ...... Wet AD for sewage, Food and Yard sent to Gilroy for Composting
In Scenario 1, Cases 2a, 3a cost 50% more than Case 1a.
In Scenario 2, Cases 2a, 3a cost 28% more than Case 1a.
In Scenario 3, Cases 2a, 3a cost 18% less than Case 1a.
Note that Scenario 3 has $908,000/year in rent for the Case 1a Dry AD on the landfill/Byxbee park site, inflating its cost by $11M over 20 years. It's not $18M because inflation means that the fixed-cost of rent deflates over time ($1 is worth more today than in 20 years), so when you add up all the future costs and bring them to their Net Present Value (NPV), it comes to $11M in today's dollars... Scenario 3 Case 1a would be $85M without rent.
I asked myself, why is it that cases 2a and 3a cost so much more than 1a, given that they're all doing forms of AD, and so I calculated how much of their costs come from exporting the food and yard wastes. I obtained the following results:
20-year NPV (Millions $) of exporting food and yard wastes (and percentage of total cost):
Case...... Scenario 1..... Scenario 2...... Scenario 3
2a............ 44 (47%)........ 44 (46%)......... 35 (43%)
3a............ 39 (44%)........ 39 (43%)......... 30 (39%)
Sending our wastes "away" will cost us tens of millions of dollars. While processing them locally will also have costs, the affordability of Case 1a hints that keeping our compost local may be more affordable, plus it retains a local source of compost, and a place where residents could dump their green waste after a big yard cleanup. This is why, if the citizens vote to make the land available, I encourage the City and Staff to study a combination of Wet AD for sewage at the existing treatment plant, and composting the digestate from the AD and other organics at the landfill site.