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Using Biosolids, Composts, and Tailor-Made Biosolids Mixtures in Remediating Urban and Brownfield Sites and Other Metal-Contaminated Soils

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Our research on beneficial use of biosolids has been shown in laboratory and field studies that amendment of urban soils can reduce plant uptake of soil Pb and the bioavailability of Pb in ingested soil. Similar remediation is achieved by biosolids plus limestone at Pb, Zn, and Cd contaminated soils at Superfund Sites. Further, by combining other byproducts of agriculture, industry and urban industries with biosolids, and processing to fit the end use (composted or stabilized as needed), we have illustrated the use of “Tailor-Made Biosolids Mixtures” to inactivate soil Pb in urban soils and remediate dead soils.

High Fe, P, and fertility of biosolids amended soils aid in precipitation and adsorption of soil Pb, and adsorption of soil Cd, Zn, and other elements. In the case of Pb, we have conducted soil feeding tests to measure the effectiveness of biosolids constituents and processing on bioavailability of Pb in the amended soils. For urban soils from Baltimore, bioavailability of Pb has been reduced by as much as 60% at 30 days after adding 224 t/ha of high Fe biosolids or composted biosolids. Other research has shown that part of this reduction in bioavailability is the formation of chloropyromorphite, a very insoluble Pb mineral. Thus the remediation effectiveness is expected to only increase w ith time as precipitation is more complete. The low solubility of both Pb and Pin soils slows the precipitation reaction, but the high Fe and P in the biosolids provides strong selective adsorption of metals such as Pb.

Urban soils are statistically Pb contaminated by many sources. Houseside soils with 5% Pb have been found even in rural settings when high Pb paint fell onto soil. Historic automotive and stack emission Pb also contributes to urban soil Pb. Most US children who have excessive blood-Pb live in older center cities w here their environment is high in Pb, although interior paint Pb remains the most important source of excessive Pb absorption. Thus remediation of soil Pb can be achieved at little cost by incorporation of composted Fe rich biosolids and seeding or sodding. Superfund addresses the soil Pb risk of only a small fraction of US children because urban soil Pb does not come from a know n industrial source. The combination of high fertility and improved soil condition and water holding capacity from the biosolids amendment supports strong cover with turf grasses, making soil transfer to children much more difficult. Using composted (and some other treated) biosolids products rich in Fe and P (Class A disinfection) in urban soils can provide important public health benefits by reducing Pb risk from urban soils.

This same approach is effective in remediation/revegetation of risks at hazardous smelter contaminated soils, mine wastes, and many metal contaminated soils and industrial wastes. In cooperation with EPA's Superfund Emergency Response Team, we have tested use of mixtures of biosolids with alkaline byproducts (wood ash; coal ash; limes) and wood byproducts rich in carbon, for revegetation of Superfund sites at Palmerton, PA, Kellogg, ID; Leadville, CO; and Joplin, MO; as well as smelter slags in Katowice, Poland. Very effective and persistent revegetation has been demonstrated at sites where traditional hydroseeding with limestone and fertilizer has been ineffective; one can get grasses started by the hyrdroseeding approach, but w hen the first hot dry period hits the site, these plants die quickly. On adjacent plots with Tailor-Made biosolids mixtures, grasses and legumes thrived. The semisolid mixture was surface applied on up to 100% slopes, and was not eroded by rainfall. The reaction of wood ash or fly ash with biosolids causes some “setting up” such that rainfall does not cause erosion before plants become established; yet water percolates through the mixture well, and roots grow thru the layer and enter the contaminated soil as soon as pH is raised. For surface deposited metals from smelter contamination of mountain soils (up to 100% slopes), surface application was highly effective in reducing metal phyto- and bio-availability. The limestone equivalent of the mixture can be leached down the soil profile if the mixture contains both limestone and biodegradable organic matter, while inorganic limestone products do not penetrate to neutralize subsurface acidity. Making the rooting depth calcareous is an important part of persistent remediation of high Zn soils. We have achieved effective revegetation on mine waste and smelter slag with over 10,000 mg Zn/kg soil. The high phosphate in these mixtures supplies P for precipitation of Pb, and having enough left over to support plant growth; particularly for eroded forest sites, most phosphate is lost from erosion of the organic layer and the soils are very phosphate deficient with the high soil Zn inhibiting root growth to get P. Plants accumulate far lower metal concentrations on the amended soils, such that the biomass is a safe forage for lifetime consumption by livestock or wildlife. Where deep deposits of acid generating minew astes require revegetation, incorporation of limestone equivalent and biosolids products is more likely to be successful than surface application because a larger rooting volume can be made non-phytotoxic. Thus a new market for biosolids has been demonstrated which provides great public benefit and illustrates that metals in biosolids are part of the solution to metal contaminated sites, not an important soil contamination problem.

Document Type: Research Article


Publication date: January 1, 2001

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