Characterization of sludges for predicting anaerobic digester performance

Area of Science:

• Environmental Engineering
• Biotechnology
• Wastewater Treatment

Background:

• Sludge management is a critical aspect of wastewater treatment.
• Understanding sludge biodegradability is essential for optimizing digestion processes.
• Primary sludge and waste activated sludge have different degradation characteristics.

Purpose of the Study:

• To determine the ultimate biodegradability of primary sludge and waste activated sludge.
• To evaluate existing models for predicting sludge degradation.
• To develop an improved model for waste activated sludge digestion.

Main Methods:

• Batch anaerobic digestion tests were conducted over 123 days.
• Primary sludge and waste activated sludge were used as substrates.
• Wastewater models were employed to predict particulate COD fractions.
• A first-order decay function was used to model endogenous decay.

Main Results:

• Primary sludge biodegradability could be predicted using the inert fraction of particulate COD from wastewater models.
• A model assuming equivalent biodegradability of particulate COD components characterized waste activated sludge for the first 60 days.
• After 60 days, endogenous product decay occurred in waste activated sludge, described by a first-order decay function (k=0.0075 d(-1)).
• Continuous flow digesters (SRTs 30-60 days) showed ~10% higher VSS destruction with the modified model.

Conclusions:

• Wastewater models can predict primary sludge anaerobic biodegradability.
• Waste activated sludge requires a modified anaerobic digestion model that includes endogenous decay after 60 days.
• The modified model improves predictions of VSS destruction in continuous flow digesters.