The influence of natural organic matter on the adsorption of microcystin-LR by powdered activated carbon

In this study, microcystin-LR (MC-LR) adsorption to four different types of powdered activated carbon (PAC) was evaluated to provide insight into the use of PAC to treat water containing MC-LR. MC-LR adsorption to the four PAC types (wood, coal blend, bituminous coal, and coconut shell) was studied in equilibrium and kinetic batch experiments utilizing a model water with different natural organic matter (NOM) concentrations (0, 5 and 10 mg L -1) and pH (5.2, 8.5 and 9.5). The effect of NOM type was evaluated by comparing MC-LR uptake in model water amended with Suwannee river fulvic acid or a NOM extracted from a natural water experiencing an algal bloom. The results demonstrated that the wood-based PAC removed MC-LR at the highest rate and to the greatest extent, which likely reflects that wood-based PAC typically contains a greater proportion of mesopores than the other types of PAC in this study. MC-LR removal was significantly reduced in the presence of NOM, with the impact being slightly higher for the algal-derived NOM compared to Suwannee river fulvic acid. MC-LR removal decreased with decreasing pH in the presence of NOM, but increased with decreasing pH in the absence of NOM. This suggests competition with NOM not only varies depending upon the source of NOM, but also on the solution pH as NOM interactions with PAC will vary with pH. Thus, properly determining PAC doses to treat MC-LR must account for the presence of NOM as well as the pH-dependent interactions of NOM with PAC as these interactions strongly influence MC-LR adsorption.