Journal
ENVIRONMENTAL TECHNOLOGY
Volume 34, Issue 10, Pages 1341-1347Publisher
TAYLOR & FRANCIS LTD
DOI: 10.1080/09593330.2012.746737
Keywords
septic effluent; soil chemical properties; subsurface drip disposal; vertisols; wastewater
Categories
Funding
- Alabama Agricultural Land Grant Alliance (AALGA)
- Alabama Water Resources Research Institute (AWRRI)
- Department of Biosystems Engineering at Auburn University
- Department of Agronomy and Soils at Auburn University
- Department of Civil Engineering at Auburn University
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The operation of onsite septic effluent disposal without considering seasonal moisture changes in drain field conditions can be a major cause of the failure of conventional septic systems. This study addressed this issue from a soil hydraulic perspective by using real-time drain field soil moisture levels to limit septic effluent disposal in a vertisol via subsurface drip irrigation. A prototype system was field-tested in a Houston clay soil and results describe the subsequent impact on selected soil chemical properties. After one year of hydraulic dosing with a synthetic wastewater, soil total carbon and nitrogen concentrations increased, but no increase in soil total phosphorus concentration was observed. Soil NO3-N leaching potential was noted, but soil NH4-N concentrations decreased, which could be ascribed to NH4-N nitrification, fixation within clay sheets and NH3 volatilization. Soil K+, Mg2+ and Na+ concentrations increased in soil layers above the drip lines, but decreased in soil layers below drip lines. Soil electrical conductivity accordingly increased in soil layers above drip lines, but the range was significantly lower than the threshold for soil salinity. Although the moisture-controlled effluent disposal strategy successfully avoided hydraulic dosing during unfavourable wet drain field conditions and prevented accumulation of soil salts in the soil profile beneath the drip lines, soil salts tended to accumulate in top soil layers. These adverse effects warrant system corrections before large-scale implementation of subsurface drip irrigation of effluent in similar vertisols.
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