Chemical Composition of Sewage Sludges and Analysis of Their Potential Use as Fertilizers

TLDR

Sewage sludge varies by city and contains trace metals, so knowing its composition is essential before land application. The study surveyed more than 250 sludge samples from about 150 treatment plants across eight states, measuring 30 chemical constituents. Analysis revealed that N, P, and K levels were relatively consistent, while heavy metals such as Pb, Zn, Cu, Ni, and Cd varied widely; median concentrations ranged from 4.2–4.8 % N to 540–1,890 mg kg⁻¹ Pb/Zn, and applying sludge at 100 kg N ha⁻¹ would require less than 1 % of agricultural land.

Abstract

Abstract A regional survey of sewage sludge composition was conducted by obtaining data for 30 constituents in > 250 sewage sludge samples from approximately 150 treatment plants located in 6 states in the north‐central region and 2 in the eastern region. Computation of the mean and median values indicated that N, P, and K levels were within a relatively narrow range, whereas these statistics demonstrated that Pb, Zn, Cu, Ni, and Cd concentrations were extremely variable. Median concentrations for anaerobically digested sewage sludges were as follows: N, 4.2; P, 3.0; K, 0.3%; Pb, 540; Zn, 1,890; Cu, 1,000; Ni, 85; and Cd, 16 mg/kg, and for aerobically treated sludges: N, 4.8; P, 2.7; K, 0.4%; Pb, 300; Zn, 1,800; Cu, 970; Ni, 31; and Cd, 16 mg/kg. Based on population and sludge production estimates, < 1% of the agricultural land would be required for application of sewage sludge at a rate of 100 kg available N per ha in most of the states considered. The heterogeneous nature of sewage sludges produced by different cities and the presence of potentially harmful trace metals necessitates a knowledge of the chemical composition of each individual sewage sludge prior to land application.