[Calcium carbonate precipitation in UASB reactors with different substrates].

Area of Science:

• Environmental microbiology
• Wastewater treatment technologies
• Biogeochemical processes

Context:

• Calcium carbonate precipitation is a significant challenge in treating calcium-rich industrial wastewaters using anaerobic digestion.
• Upflow anaerobic sludge bed (UASB) reactors are widely employed for organic wastewater treatment.
• Understanding factors influencing precipitation is crucial for optimizing reactor performance.

Purpose:

• To investigate the influence of different organic substrates on calcium carbonate precipitation in UASB reactors.
• To evaluate the impact of substrate-induced precipitation on sludge characteristics and reactor efficiency.
• To correlate sludge microstructure with calcium carbonate precipitation patterns.

Summary:

• Two lab-scale UASB reactors treated calcium-rich wastewater (800 mg/L Ca+) with either acetic acid or glucose/soluble starch as substrates at an organic loading rate of 9 kg COD/(m³·d).
• Acetic acid wastewater resulted in significantly higher calcium precipitation (up to 65%, averaging 25%) compared to glucose/starch wastewater (approx. 7.5%).
• Sludge ash content increased substantially, particularly in the acetic acid reactor (to 70%), but COD removal efficiency remained high (~90%) in both reactors throughout 180 days of operation.
• Scanning Electron Microscopy (SEM) revealed substrate-dependent differences in granular sludge microstructure, explaining the varied calcium carbonate precipitation rates.

Impact:

• Demonstrates that substrate selection is a critical factor in managing calcium carbonate precipitation in UASB systems.
• Highlights the resilience of UASB reactors to high sludge ash content, maintaining high organic matter removal.
• Provides insights into the microstructural basis of precipitation, aiding in the design and operation of anaerobic treatment for challenging wastewaters.