Friday, December 16, 2005

Biosolids, Politics and Character

Biosolids, aka domestic wastewater (sewage) treatment solids, is pretty interesting stuff, to me anyway. From a soil scientist's perspective it is chock full of good stuff: Essential plant nutrients and humic substances (humic acid, fulvic acid) beneficial to soil quality. Biosolids is superior to chemical fertilizers from both a crop production perspective and an environmental protection perspective.

This is not raw sewage solids or raw septic tank solids. This is the microbial biomass solids produced during the time the sewage is being treated, usually a 20-30 day process, prior to the treated liquid being discharged to a surface water body. These solids have about the same ratio of N:P:K:S present in soil microbial biomass.

Since the 1972 Clean Water Act, USEPA has been encouraging treatment facilities to give preferential consideration to recycling the soil property enhancing constituents in biosolids. These constituents were originally derived from crops grown on agricultural land and federal legislative intent is to see these materials recycled and put to beneficial use at their source. At the basis of this intent is a conviction that the overall benefits of beneficial use exceeds the added economic and regulatory burden placed upon the local and regional taxpayer and the wastewater treatment ratepayer.

Because of costs to transport material beyond the reach of urban sprawl, it would be cheaper to dispose of it in the ocean, or, for interior cities, in a landfill.

The constituents within biosolids are derived from nonrenewable resources and energy intensive processes and, being a regulated material under the authority of the federal government, cannot responsibly be allowed to be simply discarded when the opportunity for beneficial use is available. This policy makes more sense with each passing year.

Critics and skeptics of beneficial reuse on farm land abound, but fears of environmental degradation have yet to be borne out by events.

Once I had the opportunity in the 1980's to ask the then-President of the Washington State Farm Bureau why the American Farm Bureau Federation had a policy in opposition to land application of biosolids on farmland. He was a respected, retired soil scientist, and I asked for a science-based explanation. Instead, he explained that the national Farm Bureau was using their opposition to biosolids to persuade legislators to address burdensome regulation of farmers related to wetlands and surface water quality. They correctly recognized that Farm Bureau support was valuable and wanted a quid-pro-quo accommodation or to at least be able to make a statement.

You have to respect this point of view. It may not be science-based but its not off base either. That Farm Bureau fellow was just staying in character.

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rich said...

One of the fears I've heard from sustainable ag types regarding the use of biosolids is the possibility of heavy metals and/or radioactive components (from chemotherapy) in the product. That's well outside me area of expertise, though.

Not an issue on my farm (I'm too far from an urban center to use them, anyway), but I can see the concern in denser population areas.

Philip Small said...

I've also heard those fears. Many stem from legitimate concerns in the days before source control activism by the treatment plants. Source control involves requiring alternative manufacturing processes and redesigning the waste collection process to segregate wastes at the source. Before the source control campaigns of the 1970's, for example, dentists were washing mercury laden amalgam down the sink and printing firms were using high metal content (manganese and cobalt, if I recall correctly) inks and discharging the cleanup fluids.

Chrome finishing, lead from solder and fluxes, the list of processes where source control is necessary to achieve low-metal biosolids is long.

Use of medical radionuclides is highly regulated and release to a drain, or any similarly uncontrolled fate, is prohibited.

With few exceptions, biosolids' metals content now is low enough that it requires many years of land application, decades in some cases, for accumulation to be detected above the noisy data of soil background levels.

Source control means controlling peoples' behavior and I think this is where community heartburn over biosolids safety comes in. It is, as always, as much a question of social anthropology (who do we trust and why) as it is a question specific to the chemistry and biology of biosolids.

Farm Kid said...

First of all, Septic tank solids are NOT raw sewage! A septic tank is effectively a small, self contained version of a digester. These solids are not as far decomposed as a municipal treatment plants product, but they are not raw. Secondly, Heavy Metals are in fact a concern with Biosolids land application. Any reputable handling firm will take deep soil samples before, during and after application. There is a great deal of soil science that goes into determining the agronomic rate of application. Land application is a benefit for both the farmer, and for the municipality. We get what we eat from the land; we should return what is left.