Numerical modeling of unsaturated flow in wastewater soil absorption systems

Deborah N Huntzinger, John E. McCray

Research output: Contribution to journalArticle

36 Citations (Scopus)

Abstract

It is common practice in the United States to use wastewater soil absorption systems (WSAS) to treat domestic wastewater. WSAS are expected to provide efficient, long-term removal of wastewater contaminants prior to ground water recharge. Soil clogging at the infiltrative surface of WSAS occurs due to the accumulation of suspended solids, organic matter, and chemical precipitates during continued wastewater infiltration. This clogging zone (CZ) creates an impedance to flow, restricting the hydraulic conductivity and rate of infiltration. A certain degree of clogging may improve the treatment of wastewater by enhancing purification processes, in part because unsaturated flow is induced and residence times are significantly increased. However, if clogging becomes excessive, the wastewater pond height at the infiltrative surface can rise to a level where system failure occurs. The numerical model HYDRUS-2D is used to simulate unsaturated flow within WSAS to better understand the effect of CZs on unsaturated flow behavior and hydraulic retention times in sandy and silty soil. The simulations indicate that sand-based WSAS with mature CZs are characterized by a more widely distributed flow regime and longer hydraulic retention times. The impact of clogging on water flow within the silt is not as substantial. For sand, increasing the hydraulic resistance of the CZ by a factor of three to four requires an increase in the pond height by as much as a factor of five to achieve the same wastewater loading. Because the degree of CZ resistance directly influences the pond height within a system, understanding the influence of the CZ on flow regimes in WSAS is critical in optimizing system design to achieve the desired pollutant-treatment efficiency and to prolong system life.

Original languageEnglish (US)
Pages (from-to)64-72
Number of pages9
JournalGround Water Monitoring and Remediation
Volume23
Issue number2
StatePublished - Mar 2003
Externally publishedYes

Fingerprint

unsaturated flow
Wastewater
Soils
wastewater
modeling
soil
Ponds
pond
Hydraulics
hydraulics
Infiltration
infiltration
Sand
silty soil
sand
pollutant
Silt
Organic chemicals
Hydraulic conductivity
Biological materials

ASJC Scopus subject areas

  • Water Science and Technology

Cite this

Numerical modeling of unsaturated flow in wastewater soil absorption systems. / Huntzinger, Deborah N; McCray, John E.

In: Ground Water Monitoring and Remediation, Vol. 23, No. 2, 03.2003, p. 64-72.

Research output: Contribution to journalArticle

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