Nitrogen transformations during aerobic/anoxic sludge digestion

Area of Science:

• Environmental Engineering
• Wastewater Treatment
• Microbial Ecology

Background:

• Aerobic digestion is a common wastewater treatment process.
• Controlling pH and improving effluent quality are ongoing challenges in aerobic digestion.
• Nitrogen transformations significantly impact wastewater treatment efficiency.

Purpose of the Study:

• To compare nitrogen transformations in aerobic digestion versus aerobic/anoxic (A/A) digestion.
• To evaluate the impact of sludge residence times (SRTs), temperatures, and anoxic cycles on A/A digestion performance.
• To assess the potential of A/A digestion for pH control and enhanced supernatant quality via endogenous nitrate respiration (ENR).

Main Methods:

• Laboratory-scale experiments were conducted to simulate aerobic and A/A digestion processes.
• Process performance was analyzed under varying operational parameters: SRT, temperature, and anoxic cycle duration.
• Key parameters measured included solids reduction, total nitrogen removal, and specific ENR rates.

Main Results:

• Both aerobic and A/A digestion achieved comparable solids reduction.
• A/A digestion demonstrated superior pH control through ENR and improved supernatant quality compared to aerobic digestion alone.
• Optimal performance was observed at 10 d SRT, 30°C, and a 50% anoxic cycle, yielding 43.7% volatile suspended solids reduction and 33.7% total nitrogen removal.

Conclusions:

• Incorporating anoxic phases into aerobic digestion (A/A digestion) is a viable strategy for enhancing wastewater treatment.
• A/A digestion effectively utilizes endogenous nitrate respiration for pH stabilization and improved effluent quality.
• The A/A process offers a promising alternative for efficient nitrogen removal and overall sludge digestion.