Powdered activated carbon full-scale addition to the activated sludge reactor of a municipal wastewater treatment plant: Pharmaceutical compounds control and overall impact on the process

Powdered activated carbon (PAC) dosing to a conventional activated sludge (AS) reactor is a low-investment option for controlling pharmaceutical compounds (PhCs) in municipal wastewater treatment, but its advantages and limitations in real operating environments are not fully assessed. A 3-week PAC-AS full-scale test was conducted in an oxidation ditch plant to assess PAC impact on effluent quality (PhCs, dissolved organic carbon (DOC) and other parameters), energy consumption, sludge production and costs. DOC-normalized PAC doses of 0.7-2.6 mgPAC/mgDOC significantly reduced recalcitrant PhC discharge (e.g. by 63-83 % for carbamazepine and 67-69 % for diclofenac), the higher dose yielding a more reliable effluent quality. Effluent quality for total phosphorus, colour, organic matter and transmittance was also enhanced and no interference with nitrification, oxidation-reduction potential or dissolved oxygen in the oxidation ditch was observed, resulting in no energy consumption increase. PAC had no impact on effluent turbidity and mixed liquor suspended solids settleability, showing a positive effect on dewatered sludge dry weight and ultimately a 7-9 % increase on final sludge production. After stopping PAC dosing, PAC remaining in the return sludge presented adsorption capacity for some PhCs until it was completely out of the system. Estimated costs for PAC addition to AS-reactor compare favourably with literature data for PAC and GAC post-treatment and similarly with post-ozonation.