The pre-treatment of sludge has gained a lot of attention for treating and handling waste, especially in wastewater treatment plants. Different technologies are being investigated to improve how waste can be reduced, a certain type of pre-treatment used is Free Nitrous Acid (FNA). This technology has been used as a chemical pre-treatment in the anaerobic digestion process to improve the fermentation/hydrolysis stage. The effect of utilizing different doses of the FNA pre-treatment was investigated for this study, and the effect of the pre-treatment on the characteristics of thickened waste activated sludge (TWAS) were identified. It was observed that as the doses of FNA increased, the concentration of soluble chemical oxygen demand (SCOD) increased, with the highest values noticed at an FNA concentration of 0.7 mg N/L for both experiments. The volatile suspended solids (VSS) decreased as the doses of FNA increased, the highest decrease in VSS was observed at FNA dose of 2.8 mg N/L.