To what extent may pharmaceuticals and pesticides be removed by PAC conventional addition to low-turbidity surface waters and what are the potential bottlenecks?

Pilot runs of powdered activated carbon/coagulation/flocculation/sedimentation (PAC/CFS) were conducted to investigate the removal of 19 pharmaceutical compounds and 9 pesticides as a function of their properties. PAC addition impact on the clarification effectiveness of low-turbidity surface waters was also explored. Four sets of operating conditions tested different PAC types, doses and contact times. Removals of 65?79 % for total pharmaceuticals and 73?83 % for total-pesticides were achieved with 3-9 mg/L of a mesoporous PAC or with 20-24 mg/L of a microporous PAC. Microcontaminants? key properties for adsorption were charge, hydrophobicity and aromaticity. For low-hydrophobicity compounds, positively charged functional groups and low surface polar area and/or high number of aromatic rings acted as adsorption enhancers. The positively charged compounds were better removed than the negatively charged ones, an effect stronger for the negatively charged PAC. Results show PAC dose reduced to half/one-third using an adequate PAC and to one-quarter/one-eighth with additional 1-h contact time. PAC dose saving is crucial, for economic and environmental reasons and for PAC/CFS effectiveness. PAC addition, particularly above 10 mg/L PAC, hampered the clarification of the low turbidity waters studied towards residual turbidity, aluminium and aerobic endospores, and may require a reliable downstream filtration to retain PAC fines.