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Research article2015Peer reviewed

Urea for Sanitization of Anaerobically Digested Dewatered Sewage Sludge

Nordin, Annika; Olsson, Jesper; Vinnerås, Björn

Abstract

When recycling sewage sludge to agriculture, the risk of disease transmission must be taken into account. Sanitizing treatment prevents disease transmission by reducing dissemination of pathogens early in the reuse chain. Sanitization is commonly achieved by heat treatment of sludge, for example, by prepasteurization before anaerobic digestion or by thermophilic anaerobic digestion. This study evaluated ammonia treatment of anaerobically digested dewatered sewage sludge at pilot scale (65 ton) by urea addition at 0.85% and 1.6% wet weight compared with storage without ammonia addition over 145 days of treatment during the Swedish winter, with ambient temperatures below 0 degrees C. Addition of 1.6% urea reduced indicator organisms Enterococcus spp. and Escherichia coli to below the detection limit of 100 and 10 cfu/g, respectively, within 3 months of treatment, whereas the 0.85% urea treatment did inactivate E. coli but not Enterococcus spp. within the study period (145 days). In the control, both indicator bacteria were still present at the end of the study period. Thus, 1.6% treatment with urea is a promising low cost on-demand option for sludge sanitization and can be performed at considerably lower cost than heat treatment.

Keywords

sewage sludge; urea; pathogen; treatment; biosolids; indicator organism; sanitization

Published in

Environmental Engineering Science
2015, Volume: 32, number: 2, pages: 86-94
Publisher: MARY ANN LIEBERT, INC