Assessment of heavy metal removal efficiencies by naturally fermented and a. niger fermented pineapple wastes from contaminated sewage sludge

Abstract

Heavy metals in sewage sludge can pose a long term environmental risk due to their toxicity,
non-biodegradability and consequent persistence, This study assessed the efficiencies of
various organic extractants such as naturally fermented and A�pergillus niger (A. niger)
fermented raw liquid from pineapple wastes, in the chemical extraction process, to extract Cr,
Cu, Pb, Ni and Zn, from anaerobically digested sewage sludge in Thailand. Pineapple wastes
are a good source of sugar and protein and have been utilized experimentally in the
production of citric acid by fennentation with the fungus A. niger. Comparison of the
extraction efficiencies of these extractants with commercial citric acid was also investigated at
two hours leaching time and pH 3 and greater. Results of the study revealed that at pH
approaching 4, A. niger fermented liquid seemed to exhibit the best removal efficiency for
practically all metals studied, attaining as much as 72% removal for Zn, 70% for Ni, 50% for
Cr and 37% for Cu, although effectivity of removal seemed to be less apparent for Pb. The
most readily solubilized metal seemed to be Zn with the most removal of 92% attained by
naturally fermented raw liquid, The effectivity of removal by A. niger fem1ented liquid may
be due to the presence of citric acid and other carboxylic acids as confirmed by the HPLC and
IR studies of the fem1ented liquid, Moreover, variation in metal removal efficiencies may be
attributed to the fonns of metals in the sludge, as evidenced by chemical speciation studies
using sequential chemical extraction procedure, with metals predominantly in the
exchangeable and oxidizable phases showing ease of leachability,