Engineering Evaluation Case: A Landfill-Leachate Ammonia Stripper Scales After pH Is Raised for Better NH₃ Removal
Raising pH is a common way to improve ammonia stripping because it shifts more ammonium toward volatile NH₃.
Leachate and industrial wastewater can also contain significant:
- calcium;
- magnesium;
- alkalinity.
The same high-pH condition that improves ammonia stripping can therefore create mineral precipitation.
Project Situation
Consider a packed ammonia stripper treating landfill leachate.
The process adjusts pH upward before the tower.
Initial ammonia removal improves.
After several weeks:
- white mineral scale forms;
- distributor openings block;
- bed pressure drop rises.
Chemistry Improvement Creates a Fouling Side Effect
High pH changes more than ammonia speciation.
It can also change the solubility of minerals in the wastewater.
Possible precipitates can include:
- carbonate-related scale;
- magnesium-containing solids.
Heating and Aeration Can Intensify the Change
Air stripping removes:
- ammonia;
- CO₂.
CO₂ removal changes carbonate chemistry further.
Therefore, the liquid composition evolves as it travels through the tower.
Scale Can Form Inside the Bed
The incoming water may be clear.
Precipitation begins only after:
- pH adjustment;
- aeration;
- CO₂ removal.
The packing therefore becomes the surface where the new solid appears.
Open Packing Provides More Tolerance
Larger passages can extend operating time.
But if the water is strongly supersaturated, scale formation continues.
Pretreatment May Be the Real Solution
Depending on water chemistry, the plant may need to evaluate:
- softening;
- solids removal;
- different pH strategy.
Engineering Takeaway
Optimizing ammonia chemistry can simultaneously worsen mineral chemistry.