Salt risk is a key limiting factor in high-dose sewage sludge land application

Area of Science:

• Environmental Science
• Soil Science
• Ecological Restoration

Background:

• Land application of sewage sludge is a cost-effective disposal method.
• High sludge addition can improve soil quality and act as a soil substitute in ecological projects.

Purpose of the Study:

• Evaluate sewage sludge as a substrate for slope ecological restoration.
• Identify factors limiting higher sludge application rates.

Main Methods:

• A 150-day pot experiment with tall fescue (Festuca arundinacea).
• Assessed substrate properties (salts, heavy metals), plant growth, and element enrichment at 10%, 30%, and 50% sludge ratios.
• Utilized Random Forest and Structural Equation Modeling for analysis.

Main Results:

• Increased sludge addition raised salt and heavy metal levels.
• Early growth inhibition was linked to salt stress, not heavy metal toxicity.
• Mature plants showed decreased concentrations, improved resistance, and resumed normal growth.

Conclusions:

• Sewage sludge can be used for slope restoration, but salt stress is a key limitation at high doses.
• Application rates exceeding 30% (w/w) should be avoided unless pre-treated to mitigate risks.