Sources of adsorbable organic halogens (AOX) in sludge of Gaza

Average concentrations of adsorbable organic halogens (AOX) in sludge from the Gaza Strip reached 600 mg kg(-1) which currently represents a major limiting factor for sludge application in agriculture. This study aims to identify the main sources of AOX in Gaza where the area is small with limited industrial activities. The results showed that the AOX in effluent sludge is formed mainly inside the treatment plant. Although the plant receives AOX wastewater of only 85 mu g l(-1), this value increased five fold inside the plant to an average of 400 mu g l(-1) in the effluent wastewater. On the other hand, the sludge from the first sedimentation pond showed an AOX concentration of 213 mg, kg(-1) and increased in the final sedimentation pond to 500 mg kg-1. The AOX concentration in three month old sludge was 130 mg kg(-1). The textile and detergent industries are the major AOX producing industries in Gaza, with an average AOX of 40000 mu g l(-1) in their effluent wastewater. These values do not represent a significant AOX pollution load to the treatment plant because these industries are very limited and their effluents are diluted before entering the municipal treatment plant. Industrial activity decreased in 2006 to less than 70% of the previous four years. Consequently, the AOX in the industrial effluent decreased from 150 000 to 40000 mu g l(-1) over the same time period. Sludge from these industries showed 1300 mg kg(-1) AOX for the past four years and only 400 mg kg(-1) in 2006. Moreover, the AOX in the influent wastewater discharged to the treatment plant decreased from 320 to 85 mu g l(-1) for the same period. This study revealed that the major AOX is formed inside the treatment plant and especially in the anaerobic facilities. There was no correlation between the AOX concentrations in the sludge and the wastewater at the same location. Moreover, there was no correlation between the AOX in sludge/wastewater and dissolved oxygen, pH and chloride in that treatment plant. (C) 2007 Elsevier Ltd. All rights reserved.