Explore the sludge stabilization process in sludge drying bed by modeling study from mesocosm experiments

Area of Science:

• Environmental Engineering
• Wastewater Treatment
• Biotechnology

Background:

• Sludge drying beds (SDBs) are an effective alternative to conventional sludge treatment.
• Sludge hydrotexture changes during dewatering complicate direct SDB process modeling.
• Activated sludge models (ASMs) use cell decay theories for biokinetic process descriptions.

Purpose of the Study:

• To propose a novel modeling strategy for simulating sludge stabilization in SDBs.
• To separate sludge dewatering and solids stabilization into independent processes for modeling.
• To compare the death-regeneration concept and endogenous respiration theory for sludge digestion.

Main Methods:

• Developed a two-step modeling strategy: sludge dewatering followed by sludge solids stabilization.
• Compared two established cell decay theories (death-regeneration and endogenous respiration) within the ASM framework.
• Analyzed effluent total COD, NH4-N, NO3-N, and sludge layer composition.

Main Results:

• Both cell decay theories adequately modeled effluent parameters and sludge composition but differed in effluent COD composition.
• Natural aeration was insufficient for complete nitrification of NH4-N released by cell decay.
• Sludge digestion kinetics are adaptable, suggesting the use of lumped biokinetic values.
• Lowered dewatering rates increased biodegradable COD, while higher loading rates increased effluent COD and NH4-N.
• Sludge layer formation was found to reduce biodegradable COD leaching, contrary to expectations.

Conclusions:

• The proposed modeling strategy effectively simulates deposited sludge digestion in SDBs.
• Separating dewatering and stabilization provides a robust approach to SDB process modeling.
• Understanding sludge layer dynamics is crucial for optimizing SDB treatment efficiency.