Optimization of the preparation process of biological sludge adsorbents for application in water treatment

The objective of this study was to optimize the preparation of treatment plant wastewater sludge adsorbents for application in water treatment. The optimal adsorption capacity was obtained with adsorbents prepared by pyrolysis at 700°C for 3h. We studied the effect of binder type on the adsorbents, finding that their textural properties were not substantially affected by the addition of phenolic resins but their surface area was reduced by the presence of clayey soil. Analysis of the composition of surface groups in these materials revealed: (i) a high concentration of basic surface groups in non-activated pyrolyzed sludge, (ii) an increase in the concentration of basic surface groups after chemical activation, (iii) no modification in the concentration of carboxyl or basic groups with the addition of binding agent before the activation, and (iv) total disappearance of carbonyl groups from sample surfaces with the addition of humic acid or clayey soil as binder. All these adsorbents had a low C content. The capacity of these sludge-derived materials to adsorb methylene blue, 2,4-dichlorophenol, tetracycline, and (Cd(II)) was studied. Their adsorption capacity was considerably increased by the chemical activation but reduced by the pre-activation addition of a binding agent (humic acid, phenolic resin, and clayey soil).