Abstract:
Leather is one of the prospective industries of Bangladesh. Bangladesh annually exports millions of dollars worth of leather goods to some 70 countries, including Australia, U.S. and Japan. At the same time, this is one of the industries in Bangladesh, which causes alarming environmental pollution. In this study, an attempt has been taken to analyze the use of tannery sludge in a suitable sludge stabilization process to reduce the heavy metal concentration in it. For this purpose, solidification, a stabilization process that involves mixing the waste with a binder to reduce the contamination leachability by physical and chemical means, was used to assess the stabilization of heavy metals present in the sludge. The main objective of this study is to assess the likelihood of stabilization of the heavy metals in tannery sludge with the concrete mix and to assess the usability of the sludge mixed concrete in construction work.
To conduct the study, raw sludge sample was collected from Apex Tannery and the preselected properties of the raw sludge were determined. The heavy metal contents of the sludge sample were determined in terms of total Cadmium (Cd), Lead (Pb), Chromium (Cr) and Copper (Cu). Subsequently, the sludge was mixed with cement, aggregates to prepare concrete specimen, and left to solidify for 28 days. The compressive strengths as well as other physical properties and chemical constituents of the mixes were determined to analyze their performance.
During the study, 0%, 1%, 5%, 10%, 15%, and 20% of sludge were used by weight of cement replacing equal weight of the sand to prepare the mix. The sludge sample was oven dried, powdered and sieved to achieve a uniform gradation. 0.50 water/ cement ratio was used for all the mixes. Concrete Strength decreased with the increasing addition of sludge on the mixes. The result showed that the sludge/ cement ratio up to 5% met the requirement for both physical and chemical properties. The repeatability test also confirmed initial test results found for 5% of sludge/ cement addition in concrete. In both cases 15% compromise of strength was founded compared to the sludge free concrete.
The TCLP test results of the crushed concrete showed that the high concentration of chromium and the lead contents of the raw sludge were stabilized to desired range. A remarkable amount of stabilization was taken place for all ranges of sludge addition in concrete.
