Greywater-induced soil hydrophobicity

Area of Science:

• Environmental Science
• Soil Science
• Water Resource Management

Background:

• Greywater (GW) reuse is promoted for freshwater conservation in irrigation.
• Research and regulations primarily address GW health risks, overlooking environmental impacts.
• Soil hydraulic properties may be affected by GW irrigation.

Purpose of the Study:

• To investigate GW's potential to induce soil hydrophobicity.
• To determine the degree and persistence of GW-induced soil water repellence.
• To assess the impact of GW treatment levels on soil properties.

Main Methods:

• Fine-grained sand was wetted with freshwater (control) and three model GW solutions (raw, treated, highly treated).
• Samples underwent five cycles of wetting, incubation (5°C or 30°C), and drying (60°C).
• Capillary rise, contact angle (CA), and surface tension were measured after each cycle.

Main Results:

• Soil water repellence, indicated by CA, increased with GW concentration, peaking with raw GW incubated at 5°C.
• No treatment created definitively "water-repellent soil" conditions.
• Raw GW-coated sand released surface-active compounds, reducing water surface tension.

Conclusions:

• Untreated GW might induce sub-critical soil water repellence in sand.
• This effect is temporary and sensitive to biodegradation and washing processes.
• GW irrigation's impact on soil hydraulics requires careful consideration of treatment levels and environmental conditions.