Physical Characteristics of Alkaline Stabilized Sewage Sludge (N‐Viro Soil) and Their Effects on Soil Physical Properties

Abstract

AbstractThe 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.