Academic journal article Journal of Environmental Engineering and Science

Autothermal Thermophilic Aerobic Digestion (ATAD)-Part II: Review of Research and Full-Scale Operating Experiences

Academic journal article Journal of Environmental Engineering and Science

Autothermal Thermophilic Aerobic Digestion (ATAD)-Part II: Review of Research and Full-Scale Operating Experiences

Article excerpt

Abstract: Autothermal thermophilic aerobic digestion (ATAD) is an exothermic process where sludge is subjected to temperatures greater than 55 [degrees]C for at least 4 hours, over 6-10 days. Organic solids are degraded and the heat released during the microbial degradation is used to bring the process temperature within the thermophilic range. It produces a biologically stable product, achieving a reduction in biomass, while using smaller digesters, compared to mesophilic aerobic and anaerobic digestion. There are no regulatory requirements in North America and Europe for the reduction of the volume of total solids in sludge processing. However, a reduction in the volume of material for final disposal has cost benefits. By virtue of the residual mass, volume reductions are easily made through dewatering or dehydrating steps following ATAD. Despite the apparent advantages of ATAD, limited information on the process is available in the literature. Concerns still exist about documented cases of odour issues, problems with sludge dewaterability, foaming, excess use of polymers and high-energy consumption. This article presents some relevant bench-scale and pilot ATAD study data, with appropriate discussion. It also assembles information from a range of sources and provides an insight into actual application and experiences with full-scale ATAD.

Key words: aerobic, animal wastes, autothermal, class A biosolids, municipal sludge, thermophilic digestion, waste treatment.

Resume : La digestion aerobie thermophile adiabatique est un procede exothermique dans lequel les boues sont soumises a des temperatures superieures a 55 [degrees]C pour au moins quatre heures sur une periode de 6 a 10 jours. Les solides organiques sont degrades et la chaleur liberee durant la degradation microbienne est utilisee pour amener la temperature du proce de dans la plage thermophile. Ce procede genere un produit biologique stable, reduisant la biomasse, tout en utilisant des digesteurs plus petits par rapport aux digestions mesophiles aerobies et anaerobies. Il n'y a aucune exigence reglementaire en Amerique du Nord ou en Europe touchant la reduction de volume des solides totaux dans le traitement des boues. Toutefois, une reduction du volume de materiel pour la deposition finale presente des avantages financiers. Les reductions de volume sont facilement atteignables par des etapes de deshydratation apres l'ATAD. Malgre les avantages evidents de l'ATAD, la litterature ne contient que peu d'information sur ce procede. Des preoccupations existent toujours concernant certains cas documentes sur les questions d'odeurs, des problemes de potentiel de deshydratation des boues, la formation de mousse, l'utilisation excessive de polymeres et une forte consommation d'energie. Le present article aborde certaines donnees d'etudes ATAD pilotes et en laboratoire ainsi qu'une discussion appropriee. Il rassemble egalement de l'information provenant de diverses sources et fournit aperc u de l'utilisation et des experiences reelles avec des ATAD a pleine echelle.

Mots-cles : aerobie, dechets animaux, adiabatique, biosolides de classe A, boues municipales, digestion thermophile, traitement de dechets.

[Traduit par la Redaction]

Introduction

Urban and industrial wastewater treatment plants produce sludge and it must be treated so that pathogens and vector attraction conditions are reduced to safe levels before final disposal. Cost-effective and innovative solutions to the problem incurred by sludge disposal are continuously in demand. The principal objective of biological sludge treatment is to produce biosolids that can be safely reused. Sludge digestion processes reduce the mass of solids by biologically oxidizing the readily digestible organic fraction and transforming the sludge into slow release fertilizers and soil conditioners. In Canada, this addresses the key principals of recovery and reuse in The Natural Step[TM] program (Kelly 2006). …

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