Biosolid recycling to enhance carbon sequestration in mountainous Lebanese conditions

In Lebanon, the great majority of wastewater is dumped wildly into streams, wells or the sea. Eventually treated sludge will be produced across the country and disposed of, to a great extent, on land. This disposal obeys rules and regulations in most countries. In this work, on the results of the application of a biosolid on the carbon balance in two contrasting soils are reported. The biosolid that originated from a small plant treating domestic wastewaters did not contain high concentrations of heavy metals. Biosolids were applied in two levels (S1: 3.75 tons ha-1 and S2: 7.50 tons ha-1) to a loamy sand (Kfarhim) and a calcareous loam (Baakline). The incorporation in early October was immediately followed by the sowing of a barley cover crop. Sludges increased the barley production in the fast draining loamy sand only. In parallel, the in-situ decomposition studied during the rainy seasons gave a carbon loss of 21.8% (Baakline) and 29.1% (Kfarhim) of the initial sludge C. In the short-term, studies showed that 15 to 31 % of the carbon of biosolids will remain in soils. This could significantly contribute to carbon sequestration, particularly in slowdraining soils.