LAGOON SEALING AND FILTER CAKES

Abstract

A recent study presented a two-layer (liner and seal) unsaturated model to predict the flux from lagoons. The modelpredicted that flux is not related to liner thickness, is only weakly related to the saturated hydraulic conductivity of the liner,and is primarily controlled by the hydraulic conductivity of the seal. In this study, we evaluated those predictions bymonitoring the flux of dairy waste through eight intact soil monoliths (silt loam) with large macropores. After applying a 2.3 mcolumn of dairy waste (2.3% total solids) to the top of the monoliths, a seal developed within 2 d, and the leakage continuedto decrease for the remaining 83 d of the test. The average leakage rate after 85 d was 0.70 mm d-1, and an average of 218 mmof waste infiltrated into the monoliths. Small holes drilled into the sides of the monoliths, just below the soil surface, failedto fill with liquid, which demonstrated that the soil was unsaturated and therefore was not limiting the leakage rate. Theamount of waste required to initially seal the monoliths did not correlate to the seal growth rate, which also implies that thesoil contributed little to the seal growth rate or leakage rate after seal development. A plot of cumulative waste infiltrationversus the square root of time showed a strong linear relationship (R2 = 0.996), which suggests that the phenomenon of dairywaste sealing a soil is analogous to filter cake growth. Long-term studies with other soil and waste types are needed to confirmthe findings of this research.