From my initial reading of this material, EBMUD used bench-scale digesters so they could more accurately measure the digestion performance and energy generation characteristics of the food waste stream. In normal operations, however, food waste would be (and currently is) co-processed with sewage. Thus, whatever contamination hits the biosolids in general will also affect the processed food wastes.
I think it is useful to segregate the energy recovery and biosolids questions. On energy recovery, to the extent that existing infrastructure can be used to dispose of food waste in an environmentally-responsible manner, it would seem a good thing. The basic trade-off is some additional water (to carry the food waste from disposals) versus separate organics collection at curbside (with labor, infrastructure, and fuel impacts). My guess is that the disposals win.
Biosolids quality is another issue, and seems driven by how well the POTW is run. Of particular importance is the quality of its pre-treatment program. Pretreatment forces industrial dischargers to pull chemical contaminants prior to discharging to the sewers. POTWs are all over the map on this, though my recollection is that EBMUD is considered in the top tier. If even they have trouble with biosolids quality (which they may not), an alternative method of organics collection might make sense. Perhaps others on your list know more of the details.
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>>> Ann Schneider <email@example.com> 6/8/2008 9:58 PM >>>
Hi ZWForum, CNRCC Energy & Climate Comm & GRRN:
Just curious but what is the general feeling in the greater recycling community about sending food waste to sewage treatment plants (POTWs publically operated treatment works) so energy can be recovered and the end product I assume used as a soil amendment. In the study just released below the food waste is kept separate from other materials entering the POTW so should be no cross contaimation with sewage sludge.
If this is a good idea, we may want to add this to suggestions we are sending to Cool Cities as a good way for gargage and energy to work together aka achieve both composting and energy goals and sustainability goals (handling things close to the source) by getting each communities POTW to add this type of process to their operations.
Chair, National Zero Waste Committee
--------- Forwarded message ----------
Date: Tue, 22 Apr 2008 12:37:01 -0700
Subject: Anaerobic Digestion of Food Waste Final Report Available
The US EPA, Region 9 Office of Pollution Prevention and Solid Waste is
pleased to announce the final report "Anaerobic Digestion of Food
In 2006 EPA Region 9 awarded a $50,000 grant to East Bay Municipal
District (EBMUD), a wastewater treatment facility in Oakland, California
to investigate anaerobically digesting food wastes from restaurants,
grocery stores and other food-handling facilities at a wastewater
treatment facility. EBMUD bench-scale digesters were fed only food
wastes, but were operated under a variety of conditions, varying
digester loading rates, temperature, and other parameters. The project
recovered significant quantities of energy from food waste as well as
high volatile solids reduction, showing the potential of diverting large
quantities of valuable food waste from landfills.
Please feel free to contact me if you have any questions.
U.S. EPA Region 9
Office of Pollution Prevention and Solid Waste
Recycling: It is not just about landfill diversion, it is about
replacing virgin material production which will significantly reduce
energy consumption and greenhouse gas emissions.