Toward Sustainable Municipal Wastewater and Sludge Treatment: Simulation of Technological Processes

Abstract

Municipal wastewater sludge (MWS), an inevitable byproduct of municipal wastewater treatment plants, presents environmental and regulatory challenges due to its high biodegradable organic matter content. This study integrates real municipal wastewater characterization with process simulations to provide a predictive framework for evaluating treatment performance, scalability, and sustainability, advancing previous approaches to MWS stabilization and solidification (S/S). The main objective is to produce a nonhazardous solidificate that meets regulatory standards and is suitable for safe reuse or disposal. Simulations were conducted using HSC Chemistry and SuperPro Designer, incorporating characterization, process parameters, and thermodynamic properties to determine material flows. Simulation results indicate that the addition of 38% calcium oxide (CaO) yields a solidificate with 14.5% residual moisture and a final mass of 69.9% of the initial MWS. The solidificate is composed primarily of Ca(OH)₂ (27.3%), CaCO₃ (36.8%), and inorganic oxides (2.9%), exhibiting characteristics suitable for safe disposal or potential reuse. Experimental investigations, including the application of the solidificate as a partial replacement for fine aggregate in concrete, along with material characterization and unconfined compressive strength (UCS) tests, confirm the simulation predictions and demonstrate the practical applicability of the treated material. A screening life cycle assessment (LCA) estimated a climate change impact of 0.36 kg CO₂-eq per kg of MWS, with CaO production being the main contributor. Techno-economic assessment demonstrated economic viability at 10 K t/year of MWS capacity, with a payback period of 12 years. Sensitivity and scenario analyses confirmed the robustness of the process under varying operational and financial conditions. Overall, this study demonstrates the feasibility of an integrated MWS treatment approach combining simulation, experimental validation, environmental assessment, and techno-economic evaluation. The proposed S/S approach provides a pathway toward sustainable waste management by reducing emissions, enhancing resource efficiency, enabling safe material recovery, and ensuring regulatory compliance, while maintaining economic viability.