Leachate Quality from Acidic Mine Spoil Fertilized with Liquid Digested Sewage Sludge

Abstract

AbstractThe leachate quality from an acidic mine spoil was upgraded by the addition of liquid digested sludge. Mixing liquid sludge with acidic spoil material (pH 2.5) at a w/w ratio of 1:37 (61 metric tons/ha, dry basis), reduced leachate constituents as follows: total acidity, 17%; Al, 99%; Fe, 80%; and soluble salts, 41% for this 110‐day study. During this period leachate showed increases in: NH3‐N, 1689%; SO4, 49%; Zn, 1941%; and Mg, 827%. The pH of this leachate increased immediately to 4.6 (check column remained near 2.5) and continued with a gradual neutralization. The mixing of sludge with this spoil material at a w/w ratio of 1:18 (122 metric tons/ha, dry basis) was the second most efficient for water amelioration. This leachate had an immediate pH increase of 4.5 and an eventual increase to pH 8, a 99% reduction in Al, an increase in NH3‐N by 3131%, and total P by 1069% over the check column leachate. A third ratio of sludge to acidic soil of 1:37 mixed in the top quarter of the column showed the least leachate amelioration, but after 30 days of leaching, nitrification began in this column, indicating aerobiosis and a pH of > 5.4 in a part of the soil column. The columns were leached 1 hour/day with 1.36 cm of aerated deionized water so that unsaturated flow occurred during a part of each day.