Biological sludge from textile dyeing effluent treatment plant – Characterization, combustion simulation and its impact on air pollution

• Characterization reveals that the sludge is within the PCB standards stipulated for landfilling. • Combustion simulation shows a heat recovery potential of 5.42 kWh (19.512 MJ)/kg of sludge. • Greenhouse gases of 26.51 mmol NOx , 1.123 mmol SOx , and 30.56 mmol CO 2 /gm of sludge generated. • NOx and SOx generated is approximately 4000 and 1500 times greater than EPA guidelines, respectively. • Open combustion contributes to unmonitored air pollution, demanding regulated disposal methods. The textile effluent sludge obtained from Effluent Treatment Plants (ETP) poses a critical challenge due to its increasing annual production. When in real time the biological sludge is openly burnt in boilers leading to unmonitored emission, such traditional methods do not address the problems associated with air pollution and the removal of toxic substances. This study primarily focuses on assessing and quantifying the impact of the current disposal methods by characterization and combustion simulation of the biological sludge generated from an Individual Effluent Treatment Plant (IETP) in Tirupur, Tamil Nadu, India. The standard testing procedures from APHA (American Public Health Association), American Society for Testing and Materials (ASTM), and Indian Standards were followed for the ultimate and proximate analysis of the sludge, indicating that results are well within the limits for landfilling. Furthermore, TGA-DTG (Thermogravimetric Analysis and Derivative Thermogravimetry) showing considerable mass loss around 273 °C and 639 °C along with SEM/EDX (Scanning Electron Microscopy/ Energy Dispersive X-Ray Analysis) confirming the presence of elements like C, O, Na, Si, S, Cl and Ca was carried out. The combustion simulation process was done using Aspen plus software, to analyze the heat recovery potential and NOx, SOx , CO 2 generated from the sludge. By simulating the biological sludge through combustion process under specific heat recovery conditions, it was determined that approximately 5.42 kWh (19.512 MJ ) of heat can be obtained per kilogram. Besides having a considerable heat recovery potential, each gram of incinerated feedstock resulted in the generation of NOx = 26.51 mmol, SOx = 1.123 mmol, and CO 2 = 30.56 mmol . Comparing the obtained test results with the Pollution Control Board guidelines for emission from boilers the simulation result is approximately 1500 and 4000 times more than the stipulated SOx and NOx limits respectively. This research empirically proves that the open burning of the sludge from the IETPs increases the risk of air pollution through uncontrolled emission. Hence emphasizing the critical need for combustion techniques that incorporate controlled emissions or advanced thermo-chemical remediation strategies.