Effect of Loading Rate and Soil Amendments on Inorganic Nitrogen and Phosphorus Leached from a Wastewater Soil Absorption System1
- R. L. Uebler2
Permissable wastewater loading rates for ground absorption sewage disposal systems in North Carolina are currently estimated from an on-site characterization of soil texture and structure; but, after the trenches of the system are dug, the actual ability of the soil to absorb the applied wastewater may be far less than the estimated loading rate due to smearing of the trench-soil interface. This study was designed to evaluate the effects of wastewater loading rate and soil amendments proposed to help overcome the detrimental effect of soil smearing on wastewater treatment by a soil absorption system.
Three loading rates, 7.5, 11.3, and 15.0 L m−2 d−1, were tested and two soil amendments, cement and lime, were compared with a control. The amendments were added to the soil on a 5% by-weight basis. Three absorption trenches, 3.0 m in length, were dug for each loading rate-soil amendment combination. Soil water samples were obtained monthly for 12 months from ceramic cups placed 15 and 30 cm below the trenches. Water samples were analyzed for NH4+-N, NO3+-N, soluble P, chloride and pH.
Concentrations of NH4+-N, NO3−-N, and soluble P varied significantly with the time of sampling. Transformation of NH4+-N to NO3−-N was enhanced by the soil amendments, indicating that the aeration status of the soil near the trenches was improved by the amendments. The effect of the amendments was most noticeable during the spring recovery period as aeration status was increasing from winter minimums. Higher NO3−-N levels for the cement as compared with the lime in spring suggest that cement may be a more effective amendment than lime. The lowest loading rate had significantly higher concentrations of NO3−-N during the spring months. Soluble P levels increased linearly from 0.1 to 0.9 mg L−1 over the first year operation of the system.Please view the pdf by using the Full Text (PDF) link under 'View' to the left.
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