Abstract:
Rehabilitating coal gasification ash dumps by amendment with
waste-activated sludge has been shown to improve the physical
and chemical properties of ash and to facilitate the establishment
of vegetation. However, mineralization of organic N from sludge
in such an alkaline and saline medium and the effect that ash
weathering has on the process are poorly understood and need to
be ascertained to make decisions regarding the suitability of this
rehabilitation option. This study investigated the rate and pattern of
N mineralization from sludge in a coal gasification ash medium to
determine the prevalent inorganic N form in the system and assess
the effect of ash weathering on N mineralization. An incubation
experiment was performed in which fresh ash, weathered ash, and
soil were amended with the equivalent of 90 Mg ha−1 sludge, and
N mineralization was evaluated over 63 d. More N (24%) was
mineralized in fresh ash than in weathered ash and soil, both of
which mineralized 15% of the initial organic N in sludge. More
nitrification occurred in soil, and most of the N mineralized in ash
was in the form of ammonium, indicating an inhibition of nitrifying
organisms in the ash medium and suggesting that, at least initially,
plants used for rehabilitation of coal gasification ash dumps will take
up N mostly as ammonium.
