Chemical pre-treatment includes the addition of alkaline (ALK) agents (e.g., NaOH), acidic agents (e.g., H2SO4) and a strong oxidant (e.g., O3). These chemicals can disintegrate the complex extracellular polymeric substances (EPS) matrix in waste activated sludge (WAS) as well as promote cell lysis. These treatments are applied to secondary sludge or mixtures of primary and secondary sludges, as depicted in Figure 6.1. A short introduction of the different chemical pre-treatments is given as follows. Flow sheet including a chemical pre-treatment in the sludge line. https://s3-euw1-ap-pe-df-pch-content-public-u.s3.eu-west-1.amazonaws.com/9780429437960/42a06879-e040-4470-99e3-a165ed585427/content/fig6_1_B.tif"/>