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Re-Imagining Wastewater as a Resource

posted Apr 15, 2011, 4:35 PM by Bob Wenzlau   [ updated Apr 16, 2011, 8:48 PM ]
Stanford University's Environmental Engineering program was invited to make recommendations toward Palo Alto's Long Term Waste Water Planning. A presentation by Dr. Craig Criddle of Stanford University was pivotal as it lays out a strategy whereby wastewater systems actually return green energy rather than being large energy consumers.  That's important, as the water pollution control plant is often a city's single largest energy consumer in electricity and gas.

How is this possible? In one respect it is simple, and applies the same methodology we are asking for the organic solids Palo Alto generates - its leaves, food waste and yard trimmings.  The wastewater, like the organic solids, would be treated anaerobically to yield energy, rather than the current aerobic/incineration process that requires enormous resource inputs.  Recall that the anaerobic process generates methane to be used as a "green" energy source, while aerobic processes consume oxygen and the energy yielded actually goes toward generating biomass (or sludge) that we now incinerate. A part of the current "aerobic" process is the incineration of the biosolids - an incinerator targeted for elimination by this campaign.

One of my Stanford classmates David Carmein, the Director of Design at Accio Energy, Inc., noted hat carbon dioxide is the product of the aerobic reactants, and that no useful work is harnessed in the process. "Each person's organic waste stream is part of their carbon load. It's nice to have a pathway, chemically and organizationally, that holds the potential to harness the stored energy and offset carbon use elsewhere."

As the wastewater treatment plant of the future emerges, and our campaign for anaerobic treatment of the organic solids succeeds, we will arrive at an integrated wastewater and organic treatment system that yields the City of Palo Alto significantly more energy. The new approach eliminates major energy consumption associated with the current methodologies. I liken this to merging two silos - the silo of "trash" with the silo "waste water" -- what emerges is a more appropriate view point - that all organics (solid or liquid) should be treated in an aligned and coordinated fashion. Reducing energy usage is a critical element to climate change.  Now not all the technology Stanford identifies is conventional, but much of it is, and allows implementation without fear of failure.  Dr. Criddle rightly identifies an approach of "baby steps" - moving and implementing the changes incrementally.  These "baby steps" should start now.

This emerging vision reinforces the confidence the campaign holds in the siting of our compost facility adjacent to the current wastewater plant. (Recall the Blue Ribbon Compost Task Force attempted to find another piece of land at the airport side of the water pollution control plant, and were thwarted by airport advocates.)  . In this vision, the same operator of the anaerobic digestion process for the liquids would be the same operator to manage the anaerobic processes for the solid organics -- an efficiency that would enhance operational effectiveness and lower overhead. Biologically combined operations generate advantageous synergies. Food waste appears to catalyze anaerobic processes for wastewater solids.  Conveniently the woody organics in yard trimmings provide a binder for the digested biosolids from the treatment of wastewater, and aid their final disposition as compost. The logic for this integration is compelling, and would certainly be economically validated as well. 

The remarks by Dr. Criddle, and joined by Dr. Perry McCarty reinforce confidence in the path this campaign has taken identifying land next to the water pollution control plant.  We will need land to accomodate the requirements of organics management, be they derived from waste water or placed into a compost bin for pickup.  We will need land to re-invent our waste water treatment systems -- one cannot turn it off to put in new anaerobic systems, instead one must build next to the old, and as such land would be needed.  We were short-sighted to let the land next to the waste water treatment plant be inadvertently converted to parkland, and we are wise to return it back for developing innovative sustainable methods.  

The vision we see in Palo Alto will and already is being extended elsewhere.  San Jose is incorporating the same mixed organics management in a project at their wastewater treatment plant. However, Palo Alto's vision can be more compelling as traditional aerobic treatment is replaced by energy yielding anaerobic processes. That is one of the important contributions Palo Alto brings to our region.

Therefore, please enjoy Craig's slides as he steps through the anaerobically based wastewater treatment plant (begin at slide 39), or watch a video cast of related remarks. We all appreciate Stanford's research capabilities and skills as a leader in environmental engineering -- we are lucky to be able to heed their input.