September 12, 2007 | General

Hard Problems, Simple Solutions

BioCycle September 2007, Vol. 48, No. 9, p. 18
Sally Brown

HOW simple things used to be. When I was young and didn’t finish the food on my plate, all that was at stake was the starving children in Africa. Fedex hadn’t been invented yet, so even as a child I realized that this was just a ploy to get me to eat more, rather than a realistic solution. And the corn husks and banana peels were garbage, not even a consideration that they could be anything else.
Now we are coming to understand that the earth is starving and we have an atmosphere that we’ve put on a gluttonous binge for the last 100 years. According to Rattan Lal, the President of the Soil Science Society of America, high volume production agriculture has robbed our soils of critical organic matter. The sustainability of this type of production is questionable. Our atmosphere is currently enriched with compounds such as carbon dioxide, methane and nitrous oxide, allowing it to heat up to record levels. The time has come to reexamine those leftovers. Once again, it is the United States, the land of plenty, that is largely responsible for all of the consumption driving the hunger on the surface and the excess up above. So how does food waste fit into this broader understanding?
Food waste consists of fixed carbon from the short-term carbon cycle (greenhouse gas neutral), nutrients and water. The fixed carbon has value both as an energy source and as a means to enrich our soils to grow more short-term fixed carbon (aka food). The nutrients also have value if they are added to soils. The water – well, the water can be viewed as a hindrance (for unleashing the energy in the food waste via combustion), or an asset (for unleashing the energy in the food waste via anaerobic digestion). In an ideal case, we would come to view this waste as an asset and work to take advantage of every potential source of value in this material. One possible scenario for this would be to capture the energy from the waste via anaerobic digestion followed by land application of the residuals from the digestion process. This would be a way to take advantage of all of the potential value from these materials as well as to completely eliminate them from the waste stream. For water engineers, there is even a term for this: “cascading,” which means using the water again and again.
What would this accomplish? From a broad perspective, a change in behavior like this could have a massive impact. At a recycling conference I attended recently, I heard a municipal official say that diverting all organics from landfills in California with the resulting decrease in landfill methane emissions would be the equivalent of neutralizing all of the car emissions in that state. There are an awful lot of cars in California and not all of them are Priuses. The power that could be generated from agricultural wastes alone in California was recently estimated to be 248 MWe. Water savings from use of the compost on high value crops could result in savings of approximately 1 ml per ha.
On one hand, this would not be such a tough thing to accomplish. We have the technology to do this. Anaerobic digestion with energy capture is a tried and true technology for the wastewater treatment sector. Composting followed by land application is also standard practice for a range of organic residuals. Many municipalities already have recycling programs where homes and businesses sort a portion of the MSW stream for recycling. Expanding preexisting programs to include organic wastes is just a matter of expanding an already accepted practice. Public acceptance of this is also not such an obstacle. As a result of efforts to divert organics from landfills, San Francisco has achieved a 20 percent (organics) diversion rate. A Danish study showed that participation in organics recycling programs increases with time and familiarity. Waste pick up schedules could be altered with more frequent collection for putrescibles, and less frequent pick ups for inert materials.
On the other hand, this type of change will require a concerted effort on multiple fronts if it has the potential to succeed. Success in diverting organics from landfills in Europe has been achieved through a combination of legislative initiatives and order of magnitude increases in tipping fees. In this country, we are not quite sure if the landfill is a good thing or a bad thing. Pressures from companies that own and operate landfills are strong on the side of the good thing. Although methane is a viable source of electricity, and anaerobic digestion of organics provides large quantities of this gas, this power comes at a higher price than electricity generated from coal. Some wastewater treatment facilities have excess digester capacity that is currently being used for food waste, but sufficient capacity does not exist to handle all of the food waste.
Now simple solutions are available for problems that are much more complex than when I was trying to avoid eating my supper as a child. However, the obstacles blocking the path to these solutions are complex and will require the cooperation of a range of players to be overcome.
Sally Brown is Research Associate Professor at the University of Washington, and a member of the BioCycle Editorial Board.

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