Chemical pre-treatment includes the addition of alkaline (ALK) agents, acidic agents and a strong oxidant. These chemicals can disintegrate the complex extracellular polymeric substances matrix in waste activated sludge as well as promote cell lysis. Alkali pre-treatment has been widely used for lignin breakdown in biomass. The basic principles of the alkali hydrolysis are based on solvation and saponification, which induce depolymerization and cleavage of lignin–carbohydrate linkages, accordingly rendering the uneasily biodegradable substances more accessible to the extracellular enzyme. In addition, the ALK treatment of organic material has been reported to induce swelling of particulate organics, making the substrate more susceptible to enzymatic attack. As a result, biodegradability may be significantly enhanced. Ozonation is a widely reported chemical sludge treatment technology. Ozone chemically reacts with the sludge and destroys microorganism cell components. Sludge ozonation is the combined chemical effect of direct and indirect ozonation.