New conceptual model for soil treatment units

Formation of multiple hydraulic zones during unsaturated wastewater infiltration

Mengistu Geza, Kathryn S. Lowe, Deborah N Huntzinger, John E. McCray

Research output: Contribution to journalArticle

4 Citations (Scopus)

Abstract

Onsite wastewater treatment systems are commonly used in the United States to reclaim domestic wastewater. A distinct biomat forms at the infiltrative surface, causing resistance to flow and decreasing soil moisture below the biomat. To simulate these conditions, previous modeling studies have used a two-layer approach: a thin biomat layer (1-5 cm thick) and the native soil layer below the biomat. However, the effect of wastewater application extends below the biomat layer. We used numerical modeling supported by experimental data to justify a new conceptual model that includes an intermediate zone (IZ) below the biomat. The conceptual model was set up using Hydrus 2D and calibrated against soil moisture and water flux measurements. The estimated hydraulic conductivity value for the IZ was between biomat and the native soil. The IZ has important implications for wastewater treatment. When the IZ was not considered, a loading rate of 5 cm d-1 resulted in an 8.5-cm ponding. With the IZ, the same loading rate resulted in a 9.5-cm ponding. Without the IZ, up to 3.1 cm d-1 of wastewater could be applied without ponding; with the IZ, only up to 2.8 cm d-1 could be applied without ponding. The IZ also plays a significant role in soil moisture distribution. Without the IZ, near-saturation conditions were observed only within the biomat, whereas nearsaturation conditions extended below the biomat with the IZ. Accurate prediction of ponding is important to prevent surfacing of wastewater. The degree of water and air saturation influences pollutant treatment efficiency through residence time, volatility, and biochemical reactions.

Original languageEnglish (US)
Pages (from-to)1196-1204
Number of pages9
JournalJournal of Environmental Quality
Volume42
Issue number4
DOIs
StatePublished - 2013

Fingerprint

Ponding
Infiltration
vadose zone
Wastewater
infiltration
Hydraulics
hydraulics
Soil moisture
Soils
wastewater
soil
Wastewater treatment
Hard facing
soil moisture
Hydraulic conductivity
Water
saturation
Fluxes
flux measurement
Air

ASJC Scopus subject areas

  • Environmental Engineering
  • Pollution
  • Management, Monitoring, Policy and Law
  • Waste Management and Disposal
  • Water Science and Technology

Cite this

New conceptual model for soil treatment units : Formation of multiple hydraulic zones during unsaturated wastewater infiltration. / Geza, Mengistu; Lowe, Kathryn S.; Huntzinger, Deborah N; McCray, John E.

In: Journal of Environmental Quality, Vol. 42, No. 4, 2013, p. 1196-1204.

Research output: Contribution to journalArticle

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