Aluminium and manganese leaching and retention in two contrasting soils treated with aluminium-based sludge water in a column experiment

Liquid waste (sludge water (SW)) from treatment of drinking water contains impurities which pose disposal challenges. Irrigation with SW could be a solution for the Morton Jaffray Water Works. This study was conducted to determine the effects of SW dilution on aluminium (Al) and manganese (Mn) concentrations in (a) leachates from columns with either clay or a sandy loam soil and (b) different depths in the columns. The columns were leached with tap water (control) and 25, 50, 75 and 100% of the original SW concentration and the leachates were analysed for pH, electrical conductivity (EC), Al, and Mn. The sectioned soils (0–5, 5–10, 10–15 cm depths) were analysed for pH, exchangeable acidity, extractable Mn and total Al and Mn. Leaching with undiluted SW significantly increased EC and Al and Mn concentrations and lowered pH in leachates of the first four and two leaching events in the clay and sandy loam soils, respectively. The last two to four leaching events released additional Mn. Higher SW concentrations significantly increased retention of Mn, Al, extractable Mn and acidity, and lowered pH in the soils. In practice, irrigation with SW may retain the pollutants and acidify the soil, increasing Mn mobility, potentially causing leaching and phytotoxicity.