DISPOSAL OF SEWAGE EFFLUENT AND BIOSOLIDS IN EUCALYPTUS PLANTATIONS: A LYSIMETER SIMULATION STUDY

Abstract

Reduced soil leaching under nutrient-rich sewage effluent irrigation and biosolids compost application was tested as means to control leaching of nutrients, organic carbon, heavy metals and enteric bacteria. Two-hundred liters, sand-packed lysimeters were either applied with biosolids compost (at rates equivalent to 125 and 625 Mg/ha) or not applied, and 3-times daily surface drip irrigated with either oxidation ponds effluents or fertilized fresh water. Irrigation peaked at nearly 60 L/day·lysimeter. Lysimeters were planted with a Eucalyptus camaldulensis tree, and leaching of planted lysimeters was either intermittent or at leaching fraction (LF) of 0.2. Without a tree the LF was near 1. Results from the 2nd year of the experiment are presented. The trees resisted the increasing salinization of the soil solution caused by the combination of low LF and frequent irrigation. Applied nitrogen was nearly completely intercepted in the soil-tree system, which was less efficient with respect to phosphorus. The fate of P in the studied system was governed by uptake and precipitation, the latter probably being retarded by low Ca and Mg activities (despite their overall high concentrations). Leaching of heavy metals was minimal even at the heavy biosolids application rate. Counts of fecal coliforms in the leachates were most often nil under LF 1, yet they were substantial under low leaching. Still, the overall recoveries of the bacteria in the leachate corresponded to the LF in a bell-shaped pattern, with maximum recoveries of 5-40% at LF 0.2. The main parameter that positively correlated with this recovery pattern was the leachate BOD. Hence, the simulation study showed that inasmuch as the trees withstood elevated salinity levels and the soil-plant system effectively intercepted organic and inorganic pollutants and bacteria, yet its long term sustainability (in terms of salinization and sodicity) should not be overlooked. 433 I. Twardowska et al. (eds.), and Water Pollution Monitoring, Protection and Remediation, 3–23.