DIGESTION EFFECTS ON DEWATERABILITY OF THERMOPHILIC AND MESOPHILIC AEROBICALLY DIGESTED BIOSOLIDS
Experience from full-scale operations revealed that autothermal thermophilic aerobic ATAD (digestion) results in deterioration of biosolids dewatering properties, and increased costs of biosolids conditioning. This paper presents findings of a laboratory study on effects of feed sludge characteristics, sludge retention time of digestion, and digesting temperature on dewaterability of thermophilic and mesophilic aerobically digested municipal biosolids. Parallel bench-scale reactors were operated at 60°C and 22°C, respectively, to digest primary, secondary, and mixtures of primary and secondary sludge for up to 30 days. This study found that thermophilic aerobic digestion significantly deteriorated dewaterability of the secondary sludge, but had less effect on the primary and the mixed sludge. Mesophilic aerobic digestion had gradual and continued effects that deteriorated dewaterability of all types of sludge. Sludge retention time was not a predominant factor for effects of thermophilic digestion on dewaterability, but was important in the effects of mesophilic digestion. Thermophilic digestion resulted in rapid deterioration in dewaterability of the secondary sludge, which was accompanied by rapid increase in amounts of soluble proteins, polysaccharides, and phosphate. For mesophilic digested biosolids, deterioration in dewaterability appeared to have a strong correlation with the amounts of soluble proteins and polysaccharides. Thermophilic digestion also resulted in smaller and finer biosolids flocs than mesophilic digestion, which might contribute to the deteriorated dewaterability and increased demands of conditioning polymers.
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Document Type: Research Article
Publication date: 01 January 2001
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