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The excess of activated sludge generated in municipal wastewater treatment plants constitutes one of the challenging problems facing modern society. The high-water content of this waste makes difficult the transport, disposal, and management of these solids. In this work, activated sludge excess from a secondary clarifier has been dehydrated by means of a combination of temperature and hydrogen peroxide treatment. Three main operating variables have been considered to affect sludge dewaterability and filterability. Temperature (120–180 °C), hydrogen peroxide dose (0.01–0.03 M), and treatment time (20–60 min) influence have been assessed by completing a 15-run Box Behnken experimental design. Different output variables (water content, resistance to filtration, sedimentation volumetric index, extracellular polymeric substances, etc.) have been monitored. Generally, temperature seems to be the most influencing parameter to obtain a dehydrated sludge with acceptable management/disposal characteristics (sludge volume reduction and filterability). In line with the concept of circular economy, an attempt has been conducted to obtain a sustainable biosorbent from the dehydrated sludge generated in the previous stage. Optimum conditions of carbonization and activation revealed that the solid obtained at 400 °C by using ammonium nitrate as activation agent was the most efficient absorbent to eliminate some model compounds from water (namely, phenol, ofloxacin, and diuron); however, a clear improvement margin in the synthesis is foreseen. [ABSTRACT FROM AUTHOR]

Synthesis of activated carbon by chemical activation results in materials with high surfaces areas and pore volumes (e.g., >1800 m 2 /g and >1 cm 3 /g). The main problems are the large amount of chemical required and the waste water created. To solve these problems, we have studied the recycle of KOH, focusing on the impacts of impurities originating in the starting materials and transferring to the solution used for washing the product. After activation of petroleum coke and carbon black, potassium was recovered in an aqueous solution including mainly KOH and K 2 CO 3. The higher the fraction of the more active form of potassium (i.e., KOH), the higher the level of activation in subsequent experiments. The presence of sulphur increased the fraction of KOH recovered. Full recovery of potassium was achieved using HNO 3 in the washing solution, but this acid also dissolved others species, such as Si and Al, that were detrimental for carbon activation. [ABSTRACT FROM AUTHOR]