The Role of Alternate Oxic–Anoxic Cycles in Full-Scale Sludge Stabilization for Energy Savings

Sludge management constitutes a significant share of the operational costs in wastewater treatment. Given the financial and bureaucratic challenges associated with implementing new technologies, process optimization often represents the most feasible approach for existing facilities. This study presents the results of four full-scale batch stabilization tests conducted in the aerobic sludge stabilization unit of a wastewater treatment plant in northern Italy. The objective was to evaluate the potential of alternating oxic–anoxic cycle stabilization in terms of the energy consumption and sludge treatment performance. Operational parameters were monitored and evaluated. Stabilized and dewatered sludge samples, as well as the liquid fraction from the dewatering process, were collected and analyzed. Energy consumption was continuously monitored. Data were normalized and a comparative model was developed to evaluate performance against traditional continuous aeration, using results from previous tests. The findings indicate that alternating cycle stabilization achieved comparable stabilization efficiency to continuous aeration, with an energy demand of about one-third of that required for continuous aeration. Additional benefits of the alternating cycle strategy included improved nitrogen removal and enhanced sludge dewaterability. This experimental study demonstrates how full-scale functional testing in existing treatment units can support process optimization within a circular economy framework, contributing to reduced resource consumption and an improved sludge quality.