Abstract:
Dyeing Sludge (DS) has the potential to become a serious environmental burden for Bangladesh in future with very limited safe disposal options. One potential way for the disposal and stabilization of DS is by incorporating it in clay bricks. However, it must be ensured first that the essential engineering properties of bricks are not diminished and leaching of harmful materials does not occur because of incorporation of sludge as a brick constituent. In this study, laboratory experiments have been performed to assess the engineering properties of sludge-amended clay bricks as well as to determine the leaching potential of toxic heavy metals from such bricks. The goal was to explore the viability of DS as a brick constituent and determine the effectiveness of such bricks as a safe option for sludge management.
Clay bricks were prepared with different proportions of sludge (10%, 20%, 30%, 40% and 50% by weight) in a brick kiln and its suitability as a construction material was assessed based on its strength, water absorption, firing shrinkage, weight loss on ignition and bulk density. Results of the tests indicated that the sludge proportion is the key factor in determining the brick quality. Increasing the sludge content in bricks resulted in a decrease in compressive strength. The compressive strength of DS bricks reduced considerably from 25.6 MPa to 9.93 MPa when DS content increased from 0% to 50%. The addition of 50% sludge into the mixture reduces strength approximately 61.2% compared with the control bricks though all the DS bricks have been found to meet both the Bangladesh and ASTM requirements for building construction material.
Water absorption of bricks depends on sludge content also. Water absorption was increased with the increase of sludge addition raw 11.4% bricks absorbed 12.8% of dry weight where brick that is made of 50% DS absorb 25.2% of water.
Also, total shrinkage and weight loss in burning were compared with raw brick which shows that total shrinkage did not vary that much however the weight loss in burning varied from 10.8% to 24.3% in case of raw brick to 50% DS brick.
The TCLP test results indicated that the leaching behavior of several targeted heavy metals (As, Cd, Cr, Cu, Hg, Ni, Pb and Zn) analyzed in this study for all samples have been found to be insignificant and far below the USEPA regulatory limits. the leaching concentration of As, Cr, Cd, Cu and Pb are reduced by 92.6%, 97.5%, 91.3%, 85.6% and 96.9%, respectively in case of 10% sludge amended bricks with respect to the original sludge.
The recommended proportion of sludge in brick making can be 10% (by dry weight) for producing good quality bricks. Also 20% and 30% sludge brick can be a viable option for light weight brick. Results from this study indicate that textile dyeing sludge can be sustainably stabilized in clay bricks.
