Management of chemical sludge generated from textile wastewater treatment plants

Abstract

This study attempted towards finding an environment friendly and cost effective solution for management of chemical sludge. The chemical sludge samples were collected from various CETPs and subjected to characterization studies for physic0-chemical parameters, toxicity and microstructural aspects. Solidification/Stabilization (S/S) of chemical sludge was carried out using two binder systems i.e. Ordinary Portland Cement (OPC) and Portland Pozzolona Cement (PPC) so that it can be utilized in the construction material. Evaluation of solidified samples was carried out in terms of physical engineering properties such as unconfined compressive strength, block density and chemical properties in terms of leachability of heavy metals. The toxicity assessment of solidified samples was carried out using fish bioassay. The microstructural examination of solidified samples was also performed using X- ray diffraction (XRD) and scanning electron microscopy (SEM). The characterization studies revealed that sludge was alkaline in nature with pH in the range of 8.02 to 9.0 with high electrical conductivity values varying from 0.21 to 0.66 S/m. The total dry solids in the sludge were varying from 33.35 % to 94.60 % and volatile solids were 34.30 % to 48.37 % of the total solids. The values of Total Organic Carbon (TOC) were also varying to a large extent ranging from 1.23 % to 17.82 %. The concentrations of heavy metals Cr, Cu, Ni, Zn, Cd, Co and Pb in the raw dried sludge as well as leachate were found to be less than the prescribed limits. The concentration range for heavy metals on dry weight basis were; Cu (39.81 to 389.83 mg/kg), Ni (23.73 to 88.75 mg/kg), Total chromium (32.00 to 316.33 mg/kg), Cd (4.25 to 5.41 mg/kg), Co (12.12 to 13.46 mg/kg), Pb (20.31 to 52.04 mg/kg) and Zn (73.48 to 386.94 mg/kg). The hexavalent chromium was found to be below detection limit (BDL), The oxides such as SiO2, Al2O3, Fe2O3, MgO and SO3 were present in significant amount.