Abstract
The efficacy of volatile fatty acid (VFA) production in thermophilic aerobic digestion (TAD) of primary sludge was investigated under 3 aeration conditions. The HRT and SRT of the pilot scale 2 stage TAD process was 6 d. The average total solids in the primary feed sludge was 1.7%. A 294°C-day operation resulted in an average total solids destruction of 29%. The microaerobic condition (air flow rate of only 0.126 V/V/h) gave the highest VFA concentration at 950 mg/l. The transition condition (air flow rate of 0.28 V/V/h) produced considerably less VFA at 80 mg/l. The aerobic condition (air flow rate of 0.6 V/V/h) produced negligible amounts of VFA. Acetate constituted 81% out of the total VFA concentration. Propionate constituted the second largest fraction at 11%. VFA production was concluded to be a function of aeration. Decreasing or increasing the aeration rate resulted in a simultaneous proportionate change in VFA production.
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