Biosolids: Sludge Has Come a Long Way Since the 1980s

In Small Planet by Patrice Coleleave a COMMENT

Marketing and advertising professionals know the power of words. What you call something and the way you describe it go a long way toward building aversion, acceptance, or outright yearning for that thing. Somewhere along the way in the past 25 years, wastewater treatment professionals have learned to wordsmith the tools and products of their trade. One possible result is that something that used to be a source of citizen complaints has locally become the recipient of national awards.

The process most commonly used these days to treat municipal wastewater was developed by a couple of United Kingdom engineers early in the 20th century. They called the process “activated sludge,” and it uses beneficial bacteria and other microorganisms to clean up the water by absorbing the contaminants as food. The “sludge” part reflects the image of something collecting at the bottom of a container of some sort, which is exactly what happens in the clarifier of a typical wastewater treatment plant. The microbes that have just settled out of the water are pumped back to the aeration basin where they get some air and are “reactivated” to resume eating and reproducing.

Eventually there’s extra sludge that must be removed from the system. Those wee beasties that have given their all are pumped to a digester, the tank where they will die for lack of food. Time and heat in the digester kill most of any pathogens that remain. After most of the water is removed, the solids look and smell a lot like rich, brown soil.

Once upon a time, the landfill was the destination for most of this stuff that we now call “biosolids,” an equally descriptive but more appetizing name than “sludge.” But its value as fertilizer was obvious, and some municipalities and utilities started applying biosolids to pasture land they owned or where rural landowners would allow it. It made sense—it saved a lot of money and landfill space, and it turned a waste into a resource with beneficial use. Sometimes, though, the sight of certain kinds of trucks with certain logos going down rural roads would provoke suspicion and perceptions that, in turn, prompted angry calls to certain government offices. It could be tough to convince a caller that raw sewage wasn’t being spread around next door.

Then, as now, TDEC regulated land application of biosolids, and EPA was and still is encouraging its beneficial use. More than 25 years ago the guidelines for land application were much the same as now. The biosolids must have very low levels of heavy metals, pathogens, and other contaminants so as not to pose a risk to human health and the environment. The application site must be relatively flat and have certain kinds of soil. Buffers must be maintained around waterways and other sensitive areas. Soil must be periodically tested to make sure there’s no build-up of metals or certain other chemicals.

Even so, it was an uphill slog back in the 1980s to get broad public acceptance of the practice. Even TVA took a stand against it in refusing to allow a utility district to apply biosolids to land leased by TVA to the utility district. TDEC and EPA assurances that the biosolids and the site were ideal for land application failed to allay TVA’s fears of future environmental liability.

Fast forward to 2016, and KUB’s biosolids are in big demand. KUB has land-applied biosolids for decades, but in 2011 it got some serious bragging rights in the form of platinum certification by the National Biosolids Partnership. KUB’s program is one of only 34 in the nation with the highest NBP certification, and it’s the only one in Tennessee besides Chattanooga. The certification process is totally voluntary and costs KUB additional time in rigorous reviews and third-party audits, but it provides that much more reassurance to the public and the area farmers who collectively receive close to 30,000 tons of biosolids each year, saving them about $90,000 in fertilizer costs.

The platinum certification was renewed in 2014, and that same year the Kentucky-Tennessee Water Environment Association presented KUB with an award for Beneficial Use of Biosolids. KUB’s biosolids are registered as a fertilizer with the state Department of Agriculture, and 100 percent of those biosolids are recycled on hay and pasture lands. The demand outstrips the supply.

A lot goes into making sure this end-product of wastewater treatment is as clean as it needs to be for beneficial use. Beginning with the end in mind, KUB’s industrial pre-treatment program makes sure that no industrial or other source of wastewater is sending enough heavy metals, oils, or certain other chemicals to the sewer to build up and persist in the biosolids. The other concern for quality is that the biosolids have very few disease-causing organisms. KUB produces Class B biosolids, which must be monitored for quality every 60 days, but KUB monitors more frequently than that. They also use a third-party contractor, Synagro, to get the biosolids to farmers and use best management practices to land apply.

Farmers say biosolids improve their soil, and they are saving big by not needing to buy commercial fertilizer. At least 20 farms in Jefferson, Knox, and Loudon counties receive KUB biosolids, and KUB reports little or no public objection. We will probably never know how much difference the semantic switch from “sludge” to “biosolids” made in gaining public acceptance of its beneficial use, but it’s certainly a nicer name for something that does so much for us.

Patrice Cole's Small Planet educates readers on local issues pertaining to environmental quality and sustainability. Topics include particular threats to natural resources, public policy with local impacts, and advances in environmental science. She has 25 years of professional experience in environmental science and sustainability. She has also taught biology, ecology, environmental planning, and sustainability at the University of Tennessee and Pellissippi State Community College. Cole earned a master’s degree in planning and a Ph.D. in ecology and evolutionary biology at UT.

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