Simple and eco-friendly thermal regeneration of granular activated carbon from the odour control system of a full-scale WWTP: Study of the process in oxidizing atmosphere

Abstract

Adsorption by granular activated carbon (GAC) is an efficient, reliable, and well-established technique for treating malodours in wastewater treatment plants (WWTPs). However, when the lifespan of GAC is over, it becomes a hazardous industrial waste, which is mostly discarded in landfills. In the framework of a sustainable economy, this work proposes an oxidative thermal regeneration of GAC from the odour control system of an urban WWTP for reuse, mainly as an odour adsorbent in WWTPs, avoiding the use of high-cost inert atmosphere and complex additional post-treatments. In this sense, GAC, from two deodorization points of the abovementioned facility, the pretreatment header (P1 sample) and sludge dewatering (P2 sample), has been characterized in depth, both before and after its regeneration. Previous characterization has shown that GAC regeneration conditions depend on the nature of adsorbed odorants after the same operating time, while post-regeneration characterization has proven the recovery of the GAC’s original properties. Thus, specific surface area (SBET) values above 550 m2/g have been reached for both P1 and P2, considerably exceeding the pristine sample (P0) value of 406 m2/g. Furthermore, the microporous structure was also recovered in both samples, highlighting the case of the almost non-porous P1 sample, whose micropore volume exceeded 1.27 times the value of the P0 sample (0.180 cm3/g) after regeneration. On the basis of the above, and taking into account the good regeneration efficiencies reached (72–98%), the oxidative thermal regeneration at temperatures no higher than 350 °C can be a simple and sustainable alternative to revalue GAC used in WWTPs.