The primary activity of Premifab d.o.o. is the distillation of waste organic solvents. Distillation is a process that separates liquids based on their different boiling points, resulting in two products. The primary product is the distillate, which can be used as a new, purified product, while the secondary product is the distillation sludge, which remains after the distillate has been removed. This sludge contains non-volatile components and residual organic solvents, classifying it as hazardous waste. Due to its beneficial properties arising from its composition, the distillation sludge has potential further applications and thus requires additional characterization. This approach supports a circular economy and reduces the need for traditional waste disposal. Calorimetry is a scientific method used to measure the amount of heat released or absorbed during chemical reactions, physical changes, or thermal processes. Spectrophotometric analysis is a method for quantitatively measuring the concentration of substances in a sample based on the absorption of light at specific wavelengths. Method verification ensures that the chosen analytical method performs the intended tests or measurements reliably, precisely, and adequately. High concentrations of sulfates and nitrates can negatively impact industrial processes, particularly in the paint and coatings industry and the construction industry. This study verified methods for the spectrophotometric analysis of sulfates and nitrates from the eluate obtained by burning the distillation sludge in a calorimeter. Both methods proved suitable for determining the mass fractions of sulfates and nitrates in samples of distillation sludge. The low mass fraction of sulfates in distillation sludge from the automotive industry and the low mass fraction of nitrates in distillation sludge from the processing industry indicate potential for further use. Thus, waste once again becomes a product, aligning with the principles of a circular economy.