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Sewage Sludge Proteins: I. Extraction Methodology

Cropping Systems and Water Quality Research Unit, USDA-ARS, Columbia, MO 65211;

K. A. Barbarick

Dep. of Agronomy, Colorado State Univ., Ft. Collins, CO 80523.

P. Azari

Dep. of Biochemistry, Colorado State Univ., Ft. Collins, CO 80523.

L. E. Sommers and D. G. Westfall

Dep. of Agronomy, Colorado State Univ., Ft. Collins, CO 80523.

^* Corresponding author.

ABSTRACT

The extraction and quantitation of sewage sludge proteins is a pre-requisite to evaluating their role as labile C and N sources in sludge-amended soil. The objective of this study was to develop extraction methodology for the routine quantitation of sewage sludge proteins. Seven sewage sludges were obtained and prepared by oven drying at 55 °C followed by extensive grinding and mixing to produce homogenous samples. Proteins were extracted using H₂O, 10% (v/v) Triton X-100 (a non-ionic detergent), and 1 M NaOH, and they were analyzed using the Lowry protein assay with bovine serum albumin standards. Protein contents of extracts ranged from (in g kg^–1, dry wt. basis): (i) H₂O, 1.3 to 24; (ii) 10% Triton X-100, 3.6 to 59; and (iii) 1 M NaOH, 53 to 280. Water and detergent-extractable proteins were less than, and base-extractable proteins were within, literature values reported for total sludge proteins. The coefficients of variation (CV) for each extractant and all sludges were, with one exception, below 6%. The three methodologies provided precise and reproducible data for the extraction of sewage sludge proteins. The detergent extraction procedure is recommended for routine use because of its shorter extraction time.