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Electronic Journal of Biotechnology
Universidad Católica de Valparaíso
ISSN: 0717-3458
Vol. 5, No. 3, 2002, pp. 216-227
Bioline Code: ej02035
Full paper language: English
Document type: Research Article
Document available free of charge

Electronic Journal of Biotechnology, Vol. 5, No. 3, 2002, pp. 216-227

 en Operation of a slow rate anaerobic digester treating municipal secondary sludge
Benatti, Cláudia Telles; Tavares, Célia Regina Granhen; Filho, Benedito Prado Dias & Moitinho, Maria da Luz Ribeiro

Abstract

This study was designed to evaluate the performance of a slow rate anaerobic digester in treating secondary sewage sludge received from one local municipal wastewater treatment plant. The digester was fed by secondary sewage sludge without any previous thickening. A series of three independent batch experiments was investigated at an operation time of 60 days. The total solids (TS) in the influent sludge contained a percentage of organic matter of 59, 63 and 54%, a concentration of volatile suspended solids (VSS) of 23.7, 29.2 and 27.8 g L-1 and a chemical oxygen demand (COD) of 51.8, 32.9 and 65.7 g L-1 for the three experiments, respectively. The operation of anaerobic digestion was stable, with no noticeable scum or foaming problems. The COD reduction in each experiment reached 29, 21 and 45% in the sludge and 95, 85 and 82% in the supernatant. The microbial indicators were surveyed by sampling the sludge throughout the digester operation and counting the number of bacteria in the sampled sludge. Counted bacteria included the total culturable, the total and fecal coliform groups, Pseudomonas aeruginosa check for this species in other resources and fecal streptococci. The percentage removal of the indicator bacteria was higher for fecal streptococci (99.9%) than for coliform bacteria (96.3%), which in turn was higher than for P. aeruginosa (95.6%). Parasitological analysis was also performed on multiple sludge samples by determination of protozoa and helminth eggs. Protozoa ( Eimeria check for this species in other resources and Entamoeba check for this species in other resources ), helminth eggs ( Ascaris check for this species in other resources , Trichuris check for this species in other resources , Toxocara check for this species in other resources , Hymenolepis check for this species in other resources ) and mites were detected in the influent sludge, and particularly among the helminth eggs, only Trichuris was detected in the effluent sludge.

Keywords
anaerobic digestion, enteric bacteria, enteric protozoa, sewage sludge, stabilisation

 
© 2002 by Universidad Católica de Valparaíso -- Chile
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