Stabilization of liming sludge in brick production: A way to reduce pollution in tannery

Abstract

In leather processing, hair burning liming operation is employed to remove the hair/wool, epidermis, fat, grease, and non-structural proteins. The discharged wastewater from the hair burning step produces the most of the sludge in the tannery which is a hazardous waste that has a serious impact on the environment. Thus, managing of the liming sludge has become a great challenge for the leather industry. Using liming sludge as a raw material in building materials has the potential to reduce environmental pollution. In this novel work, building bricks were made under field conditions, where liming sludge (w/w) were incorporated by 2%, 4%, 6%, 8%, 10%, and 12%, and fired in a kiln at 1000 °C. Results reveal that 6% liming sludge incorporated fired brick showed the best engineering properties, microstructure, and chemical characteristics. It also offered the best properties such as compressive strength (ASTM C 67-02c), area shrinkage (ASTM C326), weight loss, bulk density, and water absorption (ASTM C373-88) which were found to be 27.50 MPa, 5.03%, 7.79%, 2.18 g/cm3, and 10.46%, respectively. Moreover, Fourier-Transform Infrared (FT-IR) spectroscopy and Scanning Electron Microscope (SEM) analysis showed that liming sludge content has a profound effect on the structure of fired bricks. The Netherlands tank (NEN 7345) and Toxicity Characteristic Leaching Procedure (TCLP) (USEPA 1311) leaching test results exhibited insignificant leachability of metals from the sludge incorporated fired bricks. Hence, the utilization of liming sludge as an ingredient for producing construction materials will reduce the pollution loads of tannery industries.