Modeling effluent distribution and nitrate transport through an on-site wastewater system

Area of Science:

• Environmental Engineering
• Soil Science
• Hydrology

Background:

• On-site wastewater systems (OWS) are crucial for wastewater treatment before environmental release.
• OWS performance depends on soil properties, effluent quality, and system design.
• Simulation models can enhance the evaluation of OWS impacts on subsurface environments.

Purpose of the Study:

• To evaluate the efficacy of a subsurface drip irrigation system (SDIS) using sequential batch reactor effluent (SBRE).
• To simulate soil water potentials (Psi(s)) and nitrate (NO(3)) migration within and downslope of the SDIS.
• To validate the HYDRUS-3D model's capability in simulating wastewater transport in soil.

Main Methods:

• Utilized an existing SDIS dosed with SBRE.
• Employed a two-dimensional HYDRUS-3D code for simulations.
• Measured and simulated Psi(s) and NO(3) concentrations at 55-cm and 120-cm depths.

Main Results:

• Simulated and measured Psi(s) indicated consistently unsaturated soil conditions.
• Simulated and measured NO(3) concentrations were comparable at both depths.
• High agreement (R² ≈ 0.97) between measured and simulated data validated the model's performance.
• Unsaturated conditions limited the migration of concentrated nitrate plumes.

Conclusions:

• HYDRUS-3D accurately simulates SBRE flow and nitrate transport in soil.
• SDIS with SBRE shows potential for mitigating soil and site limitations in OWS.
• The model's accuracy supports its use in assessing OWS impacts and reducing environmental degradation.