TA and EF Pretreatment of WAS. The

TA and EF Pretreatment of WAS. The expected effect of TA and EF pretreatment on sludge was the release of organic materials, with interest focused on solubilisation of COD, polysaccharides, proteins, and VSS, thus enhancing hydrolysis in order to improve biogas potential of sludge. Table 1 showing the characteristics of sludge samples indicates the improvement of EF pretreated sludge quality for subsequent biological treatment in comparison to raw and TA pretreated Sludge. Soluble COD (4 g/L) and NTK (2.61 g/L) concentrations were higher in EF pretreated sample in comparison to raw and TA pretreated WAS. It can be noted that EF could contribute to the solubilisation of sludge, but it did not degrade the organic compounds greatly [26]. The pH of EF pretreated sludge was increased to value in the range of neutrality, which is favorable for anaerobic post-treatment. Indeed, in the case of TA pretreatment, an alkaline pH was obtained which requires a correction prior biological treatment. The increase of soluble COD for the both pretreatment methods indicated that they have the potential to damage excess sludge structure and cell membranes and to release extracellular and possibly intracellular compounds with high solubility. EPS are composed of proteins (PN) and polysaccharides (PS), and the solubilisation of these compounds reflects the disintegration degree of sludge [27]. In this study, proteins, polysaccharides, and VSS concentrations were considered the main parameters for evaluation of sludge disintegration.