Soil wetting-drying and water-retention properties in a mine-soil treated with composted and thermally-dried sludges

摘要

The main objective of this study was to analyse how different sewage sludges influence soil wetting and drying dynamics. Three composted and three thermally-dried municipal sludges from different wastewater plants located in Catalonia (NE Spain) were mixed with a mine-soil obtained from a limestone quarry. Measurements of the time required to reach zero contact angle (t(CA) = 0 degrees) and water holding time (WHT) provided information on the time required for a mine-soil to reach its complete wettability and the residence time of water stored between -0.75 and -25 MPa of soil suction, respectively. One month after sludge amendments, one composted and one thermally-dried sludge significantly increased t(CA)= 0 degrees. WHT was increased in the mine-soil treated by composted sludges (50.6% by Blanes' sludge, 65.5% by Manresa's sludge and 52.5% by Vilaseca's sludge) one month after sludge amendments. The amount of water retained in the mine-soil was increased by all composted sludges and one thermally-dried sludge after one month (by 42.3% with Blanes' sludge, 42.3% with Manresa's sludge, 65.7% with Vilaseca's sludge and 23.9% with Mataro's sludge) and one year after sludge amendments and at a small suction. Increments in WHT corresponded with the amount of water retained so the time-scale of soil water availability should also be considered. The t(CA)= 0 degrees. value was modified mainly by increments in carbon stock and microbial biomass, while the WHT was modified mainly by increments in pH and electrical conductivity. Under similar air-drying conditions, mine-soil treated with composted sludges retained more water for longer compared with thermally-dried sludges.