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Abstract
Given the dramatic population increase, the problem >! wastewater collection, treatment, and disposal become one of the most serious basic challenges Alexandria City faces. One of the adverse effects of population growth is the increase of wastewater and sludge quantities produced by the city. The sludge produced is dewatered at a central mechanical dewatering facility at the West Treatment Plant, and the produces i dewatered sludge, which is about 362.8 tons/day is transported by trucks to a disposal site (Site 9N) near Amriya. The sludge has until recently been spread on land at this site on a dedicated basis as a means of disposal, although a pilot composting facility was also established on the site. Dedicated land disposal ceased in late 1998 with the establishment of full scale composting.
Unfortunately, sludge contains contaminants (principally heavy metals) and pathogens, the concentrations of which largely depend on the quality of industrial effluent discharged to the sewer and on the general health of the population. Consequently, sludge needs to be treated and managed appropriately to optimize its beneficial use \vhile avoiding potentially adverse impacts on the environment and human health.
Sludge landfill could be one of the sludge stabilization in well as final disposal methods. Stabilized sludge could be used as fertilizer if its constituents do not exceed any of the law limits. At the same time trenches could be reused again, -vhicb optimize required land area needed.
The aim of this study was to: 1-Assess the stabilization of sludge achieved at variable depths and for variable anaerobic stabilization time. 2-Assess the biological,, chemical and physical changes which take place during the stabilization with emphasis on heavy metals speciation between the solid and the leachate in order to evaluate its suitability for further use as a conditioner or fertilizer. 3-Evaluate the volume of leachate and gases generated in a simulating unit in the laboratory to the variable depth and stabilization time. 4-Evaluate the public health safety and environmental impacts of applying the proposed system.
To achieve this aim, a pilot unit was installed to assimilate a part of the landfill site, the unit was 210 cm length, and 60 cm for the two side length. The study stalled by filling the pilot unit by about 0.5 cm3 of dewatered sludge. It lasted for one yea! starting from September 2002 till September 2003 to cover the effect of the seasonal variations. The unit was designed to monitor and to track the changes that may take place in the sludge, leachate and gas characteristics versus time. Tested sludge was divided into three layers (A, B, and C), the thickness of each was 60 cm and each one was covered with )un soil to assimilate the applicable landfill cells.
This test had been repeated for another sample for one hh.’v year to assess the gas production, which had been prohibited during the first test. Sampling and analysis plan was built to collect more samples during the first two months of th t-.’st then longer sampling