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The characterization of sludge settling is important in determining the operating performance of the secondary clarifier and also evaluating the purification efficiency of wastewater treatment plants. Many models have been proposed to explain the activities of settling velocity and illustrating the relationship between settleability characteristics. The aim of this research was to present a model for the settling velocity as a function of the stirred specific volume index at 3.5 g/L (SSVI3.5), based on the Vesilind function, the solids flux theory, and the experimental data. Using this model gives an important performance improvement after calibration of the different settleability parameters.Practitioner points Batch settling tests are some of the most interesting source of information to determine the sedimentation velocities and their characteristics. The modeling as an optimum operation of wastewater treatment plants is widely used for design, optimization, and management of installations. The characterization of sludge settling is important in determining the operating performance of the secondary clarifier. The characterization of sludge settling is necessary to evaluate the purification efficiency of wastewater treatment plants.

A simple formulation of rigid polyurethane foams (RPUFs) is presented for obtaining a material, with good thermal insulation and long-term stability, based on the different hydrocarbon blowing agents (HBAs). The obtained formulation is prepared from isocyanate and polyol for construction application or appliances. A method and a particular experimental approach have realized to replace hazardous blowing agents (chlorofluorocarbons (CFCs) and hydrochlorofluorocarbons (HCFCs)) with other less harmful agents to improve the thermal resistance of this polymer. The obtained results are very encouraging in certain foams prepared from HBA and provide excellent performance.

The study of secondary settler modelling, which aims to establish the main model (one-dimensional-1D model), which is involved in some fundamental processes of the hydrodynamic behaviour of this liquid/solid separation unit and to engender variations of the sludge blanket height as a function of the operating parameters and maintaining of the municipal wastewater treatment plant of Setif. The objective of this research is focused on solid/liquid separation in the secondary settler by attempting a mathematical model that allows us to evaluate the sedimentation velocity as a function of the sludge settleability parameters.