The Poop on Biosolids
Readers continue to write with concerns about composted biosolids and Bloom. To calm your concerns, I’ll lead you through the processes that make fully treated biosolids safe to use in your food garden.
Since the early 1980s, thousands of tons of composted biosolids have been sold and used in the Baltimore-Washington, D.C., area and surrounding states. All made according to EPA and USDA specifications, Compro (biosolids treated at D.C.’s Blue Plains Wastewater Treatment Plant); Orgro (made at Baltimore Back River Wastewater Treatment Plant); and Earthlife, (made at City of Philadelphia Wastewater Treatment) have been used effectively by home gardeners, landscapers and growers of nursery and greenhouse crops.
I have been involved in conducting research growing numerous crops using composted biosolids from all three major producers in this region. In addition to ornamentals, I have grown and eaten fruits and vegetables from compost-amended soils. I have reviewed numerous research manuscripts that support the use of biosolids compost in horticulture. Even agronomists who have studied the effects of biosolids and composted biosolids in the production of cattle feed and grain crops have reported no adverse effects when biosolids are used properly.
To be cleared for composting, biosolids must reach Class A standards. At Class A, all nutrients and heavy metals are below EPA allowable levels. Wastewater facilities submit samples for testing monthly to keep this certification.
During composting, PFRP (Processed Further to Reduce Pathogens) standards must be achieved, meaning the composting materials are maintained at 150 degrees for 10 consecutive days. Achieving these temperatures is not difficult because at the middle stage of composting temperatures often reach 180 degrees. EPA also requires that equipment used for loading the composting system be independent of the equipment used for moving the finished compost.
The microorganisms at work in composting are bacteria, fungi and actinomycetes, which destroy organic and even inorganic compounds. Scientists at the Biological Waste Management Laboratory have used composting to destroy PCBs in contaminated soil. I have used composting to destroy dioxins in bleach-contaminated paper-mill sludge.
The metals of greatest concern are lead and cadmium. Unless the biosolids come from Flint, Michigan, the lead levels in Class A biosolids are far below EPA standards in Compro, Orgro and Earthlife. The same is true for cadmium.
The system used for making Bloom is even more aggressive. First the biosolids are steam sterilized under pressure; then they are digested by anaerobic organisms, which are more aggressive in destroying compounds than aerobic organisms.
The roots of plants are selective in what they absorb. Plant roots can only absorb minerals; they do not absorb compounds and chemicals. In soils containing more than three percent organic matter, heavy metals such as lead and cadmium become fixed, thus making them unavailable for absorption. Much of this research was published by Dr. Rufus Chaney, a research scientist of worldwide reputation, at USDA Beltsville. He did most of his lead studies in lead-contaminated soils in Baltimore. I had the honor of working with Dr. Chaney while associated with the Biological Waste Management Laboratory.
Skeptics who have forwarded warnings against biosolids, please note the distinction between raw biosolids, whose use I do not advocate, and composted and processed further biosolids.
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