Sewage sludge as source of activated carbon for the removal of endocrine disrupting chemical in wastewater

Sewage sludge is an unavoidable consequence of wastewater treatment (WWT). Increasing legislation has propagated sludge production whilst limiting disposal options. WWT effluent contains many trace contaminants, one group of significant concern being endocrine disrupting chemicals (EDCs). Their removal is becoming a priority. Sludge is a potentially valuable material which offers opportunities for reuse and valorisation. This research has undertaken an in depth and rigorous study of the optimization of sludge carbonization and activation to produce inorganic-carbonaceous adsorbents akin to activated carbon. The resulting sludge based adsorbents (SBAs) have been comprehensively evaluated for their adsorption of EDCs using bisphenol A (BPA). This data has enabled a fundamental analysis of SBA-EDC adsorption processes and the proposal of an adsorption mechanism. SBA production using various European sludge types was undertaken, to produce high performance SBAs based on surface area (SA) and EDC adsorption. Key research findings were: • SBAs can be produced from most types of municipal sludge, except lime added sludge. • Carbonized or carbonized/steam activated SBAs presented low SA (270_m2/g) and BPA adsorption capacity (87 mg/g) when compared to chemically activated SBAs. • K2CO3 was the best chemical reagent in producing high SA up to 1979 m2/g and BPA adsorption of 714 mg/g. • FeCl3 is a very attractive chemical reagent in giving high BPA adsorption and SBA yield of 119_mg/g and 59.3_%, respectively. • Bisphenol A adsorption fitted well with Langmuir, Freundlich and Temkin equations with the best fit depending on the production conditions (temperature, time, activating reagent). • BPA adsorption by SBAs generally depend on SA and pore volume, with surface chemistry also influencing adsorption, especially for chemically activated SBAs. • The SBAs produced from K2CO3 activation outperformed all commercial activated carbons (CACs); the best SBA outperformed the best CAC by nearly 2-fold indicating the significant potential of SBAs as effective adsorbents for WWT effluents.Open Acces

Application of sludge-based carbonaceous materials in a hybrid water treatment process based on adsorption and catalytic wet air oxidation

This paper describes a preliminary evaluation of the performance of carbonaceous materials prepared from sewage sludges (SBCMs) in a hybrid water treatment process based on adsorption and catalytic wet air oxidation; phenol was used as the model pollutant. Three different sewage sludges were treated by either carbonisation or steam activation, and the physico-chemical properties of the resultant carbonaceous materials (e.g. hardness, BET surface area, ash and elemental content, surface chemistry) were evaluated and compared with a commercial reference activated carbon (PICA F22). The adsorption capacity for phenol of the SBCMs was greater than suggested by their BET surface area, but less than F22; a steam activated, dewatered raw sludge (SA_DRAW) had the greatest adsorption capacity of the SBCMs in the investigated range of concentrations (<0.05 mol L−1). In batch oxidation tests, the SBCMs demonstrated catalytic behaviour arising from their substrate adsorptivity and metal content. Recycling of SA_DRAW in successive oxidations led to significant structural attrition and a hardened SA_DRAW was evaluated, but found to be unsatisfactory during the oxidation step. In a combined adsorption–oxidation sequence, both the PICA carbon and a selected SBCM showed deterioration in phenol adsorption after oxidative regeneration, but a steady state performance was reached after 2 or 3 cycles