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

Hybrid Process of Adsorption/Coagulation/Ceramic MF for Removing Pesticides in Drinking Water Treatment—Inline vs. Contact Tank PAC Dosing

“…They were spiked into two surface waters feeding PAC/coagulation/ceramic MF pilot (Table 1). According with our previous results with an identical pool of pesticides, though with other PAC in PAC/CFS application [11], different amenabilities to PAC adsorption are expected from those nine pesticides. The percentile distribution of removal efficiencies was therein represented and dimethoate and bentazone were amongst the compounds presenting less amenability to adsorption (P < 33), while chlortoluron, diuron, linuron and tebuconazole were amongst those more amenable to adsorption compounds (>P67).…”

“…Our previous work studying PAC adsorption of pharmaceutical compounds and a similar pool of pesticides in the same concentration range, though with a different PAC and conventional application [11], showed no correlation between compounds' removal efficiency and their initial concentration (C0) for all conditions tested. This was in agreement with several other studies concluding that, in natural waters and below a sufficiently low C0 value, the residual percentage concentration of microcontaminants is not a function of C0 for any activated carbon [11]. Therefore, even though different initial concentrations of pesticides were observed, this aspect mainly affects their outlet concentrations, and no relevant impact on removal efficiencies is expected for the concentration ranges studied.…”

“…Overall, in natural waters, PAC seems to be more efficient for the adsorption of neutral hydrophobic or positively charged compounds [11,28,29], the latter apparently through microcontaminants-PAC-NOM electrostatic interactions [28][29][30]. For low-hydrophobicity compounds, positively charged functional groups and low surface polar area and/or high number of aromatic rings seem to act as adsorption enhancers [11,27]. The influence of PAC contact time on microcontaminants' removal was shown to depend on microcontaminants' characteristics and NOM-microcontaminants competition, some compounds benefiting with contact time increase, others not being affected [29].…”

“…Powdered activated carbon (PAC) based solutions are amongst the best available technologies for controlling organic microcontaminants in conventional water treatment plants (WTPs) due to PAC high adsorption ability for a wide range of microcontaminants [7][8][9][10], high flexibility and easy implementation, simultaneously avoiding the potential formation of undesired by-products with unknown toxicity (sometimes more toxic than the parent compounds). A reliable downstream filtration is nevertheless required to retain PAC fines, particularly in challenging conditions for coagulation to occur, such as low turbidity/low organic matter/low alkalinity waters [11]. The hybrid PAC/coagulation/ceramic microfiltration (MF) process is a very appealing barrier for upgrading conventional water treatment plants.…”

“…Microcontaminants' affinity for adsorption seems to depend not on a solute single parameter but on several properties determining the microcontaminants-PAC-NOM interactions, amongst them, hydrophobicity, charge, size, aromaticity and polarity [8,11,[27][28][29]. Overall, in natural waters, PAC seems to be more efficient for the adsorption of neutral hydrophobic or positively charged compounds [11,28,29], the latter apparently through microcontaminants-PAC-NOM electrostatic interactions [28][29][30]. For low-hydrophobicity compounds, positively charged functional groups and low surface polar area and/or high number of aromatic rings seem to act as adsorption enhancers [11,27].…”