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

Dominica Del Mundo Dacera,Sandhya Babel

doi:10.15626/eco-tech.2007.043

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 ofvarious 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 wastesare a good source of sugar and protein and have been utilized experimentally in theproduction of citric acid by fennentation with the fungus A. niger. Comparison of theextraction efficiencies of these extractants with commercial citric acid was also investigated attwo hours leaching time and pH 3 and greater. Results of the study revealed that at pHapproaching 4, A. niger fermented liquid seemed to exhibit the best removal efficiency forpractically all metals studied, attaining as much as 72% removal for Zn, 70% for Ni, 50% forCr and 37% for Cu, although effectivity of removal seemed to be less apparent for Pb. Themost readily solubilized metal seemed to be Zn with the most removal of 92% attained bynaturally fermented raw liquid, The effectivity of removal by A. niger fem1ented liquid maybe due to the presence of citric acid and other carboxylic acids as confirmed by the HPLC andIR studies of the fem1ented liquid, Moreover, variation in metal removal efficiencies may beattributed to the fonns of metals in the sludge, as evidenced by chemical speciation studiesusing sequential chemical extraction procedure, with metals predominantly in theexchangeable and oxidizable phases showing ease of leachability,

Highlights

Wastewater treatment plant operations generate large amounts of residual sludge, which pose serious problem in their final disposal due to the presence of toxic substances such as heavy metals
Some research have been conducted on the utilization of these wastes, this enonnous quantity of discarded material has not been utilized efficiently, The wastes are still currently disposed of into the environment at a considerable cost for transportation and environmental degradation, research on the alternatives for utilization of these wastes is still of interest, This study investigated the efficiency of using naturally fennented and A, niger fennented raw liquid from pineapple wastes in the extraction of Cr, Cu, Pb, Ni and Zn from anaerobically digested sewage sludge, with commercial citric acid as a reference
The sludge sample was taken from the sludge treatment facility at Nongkhaem, in Bangkok, Thailand, which receives dewatered sludges mainly from five central wastewater treatment facilities under the Bangkok Metropolitan Administration (BMA), This treatment facility employs anaerobic digestion for sludge treatment and uses filter press to dewater the treated sludge prior to disposal mostly by landfill, The BMA sludge sample collected was analyzed in terms of its physical and chemical characteristics, including heavy metals content according to the Standard Methods for the Examination of Water and Wastewater [14], Heavy metals were analyzed using flame atomic absorption spectrophotometer (AAS Hitachi Z-8230) after

Summary

Introduction

Wastewater treatment plant operations generate large amounts of residual sludge, which pose serious problem in their final disposal due to the presence of toxic substances such as heavy metals. Kalmar ECO-TECH '07 KALMAR, SWEDEN, November 26-28, 2007 basis, especially for metals such as cadmium (Cd), chromium (Cr), copper (Cu), lead (Pb), nickel (Ni) and zinc (Zn) [I, 2], One of the various technologies used in the extraction of heavy metals from contaminated sewage sludge is chemical extraction. Some research have been conducted on the utilization of these wastes (such as for animal feed, alcohol, vinegar and wine production), this enonnous quantity of discarded material has not been utilized efficiently, The wastes are still currently disposed of into the environment at a considerable cost for transportation and environmental degradation, research on the alternatives for utilization of these wastes is still of interest, This study investigated the efficiency of using naturally fennented (without A. niger) and A, niger fennented raw liquid from pineapple wastes in the extraction of Cr, Cu, Pb, Ni and Zn from anaerobically digested sewage sludge, with commercial citric acid as a reference. Extraction efficiencies were observed at various pH conditions and two hours contact time, Chemical speciation studies were done to detem1ine the fonns of metals in sludge which affects extraction efficiency

Methods

Results

Conclusion