Textile ETP sludge characterization and assessment of solidification options

Abstract

The textile and apparel industries are one of leading industrial sectors in Bangladesh economy. In FY 2018-2019 this sector contributed about 84% of total foreign exchange earnings of Bangladesh. At present, textile wet processing units of Bangladesh is consuming approximately 217 million m3 of water per year and generating about fifty thousand metric tons of suspended solid per year as by product. Characteristics of TES (Textile Effluent Sludge) vary depending on textile production processes and recipes (knit, woven, denim dyeing, etc) and effluent treatment techniques (chemical, electro-coagulation, biological: aerobic, anaerobic, anoxic, etc). Depending on characteristics, there could be different options for TES management. This study presents a comparison of different physico-chemical properties as well as elemental analysis of different kinds of TES. Typical textile sludge was found to have moderate to high (60-90%) moisture content, pH (7.2-8), calorific value (~1400-4900 Kcal/Kg). Higher volatile organic contents (30-56%), higher electrical conductivity (2730-4300µS/cm), and total dissolved solids (1208- 1958 mg/L) were found in biological sludge as compared with physico-chemical-biological sludge and electro-coagulation biological sludge. In order to find functional and sustainable solutions for the disposal of textile sludge, an alternative solution could be solidification/stabilization (S/S) technique. In the solidification of M25 grade concrete, electrochemical coagulation process treated knit sludge was adopted to replace the sand at weight ratio ranging from 0% to 30%. The compressive strength test results for 28 days cured concrete shows 33 MPa, 29 MPa, 18 MPa, 13 MPa for 0%, 10%, 20% and 30% sludge addition respectively. Thus, TES of up to 10% can be added effectively with the cement to prepare concrete specimens of desired compressive strength. The leaching study conducted for the sludge based concrete reveals quite low concentration of heavy metals (Pb, Cu, Ni) compared to the standards specified by USEPA. This indicates the potential of sludge as building material without the possibility of heavy metal contamination to surrounding. Analysis of sub-base materials prepared from TES through S/S technique showed moderate California Bearing Ratio (CBR) test values (4.1-8.3%) and negligible leaching potential. So, TES can be applied as alternative sub-base materials in roads and pavements with further research.