Physical Characteristics of Alkaline Stabilized Sewage Sludge (N-Viro Soil) and Their Effects on Soil Physical Properties
The N-Viro process for alkaline stabilization of municipal sewage sludge combines dewatered sludge with one or more alkaline industrial byproducts and destroys pathogens by a combination of high pH, heat, and drying. The final product, N-Viro Soil, is a soil-like material that is being used as an agricultural lime substitute, soil amendment, and soil substitute. Physical characteristics of 28 N-Viro Soils were determined and compared to those of mineral soils. The N-Viro Soils have an average solids content of 62%, particle density of 1.96 Mg/m3, bulk density of 0.59 Mg/m3, and total porosity of 70%. Mean moisture retention was 66, 58, 34, and 31% (v/v) at saturation, 5.9, 33, and 1.5 MPa, respectively. Available water content was 27% by volume (60 cm water tension, 1.5 MPa). Noncompacted and compacted saturated hydraulic conductivities were high, 3 × 10−2 and 9 × 10−4 cm/s, respectively. Mean weight diameter (MWD) of water stable aggregates was 2.0 mm. Fifty-six percent of the materials were >2 mm in diam., almost all of this (88%) in sizes <16 mm. Of the <2-mm fraction, 69% was >0.5 mm. The N-Viro Soils have a shrinkage of 58%, and Atterberg liquid limit, plastic limit, and plasticity index of 76, 64, and 18% water (w/w), respectively. The N-Viro Soils are similar in physical attributes to those of medium to fine textured, porous soils with granular, stable aggregates, and nonplastic consistency. The moisture retention characteristics are those of a fine textured soil dominated by fine pores and low to medium available water holding capacity, and these materials are highly permeable, even when compacted. N-Viro Soil was applied to the Miamian silt loam (fine, mixed, mesic Typic Hapludalf) in the field at a rate of 500 Mg/ha (dry solids), and changes in physical properties were measured 1 yr after application. All effects of N-Viro Soil were statistically significant (P = 0.01), except total porosity, 33 KPa moisture holding capacity, 0.5- to 0.25-mm water stable aggregates, and pocket penetrometer measurements, and all of the effects were beneficial.
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