The cyanotoxin saxitoxin is increasingly detected in drinking water sources, resulting in increased concern regarding its removal during drinking water treatment. Powdered activated carbon (PAC) is often utilized by utilities to supplement conventional treatment to improve the removal of cyanotoxins from water. However, studies of PAC removal of saxitoxin are limited; for example, it remains a question as to which PAC type performs well when treating saxitoxin. In addition, there exists uncertainty over what comprises an appropriate dosage of PAC to efficiently removed saxitoxin. In this study, we compared the adsorption of saxitoxin by four types of PAC (wood, coconut, coal blend and bituminous coal) via isotherm and kinetic experiments. Experiments were conducted in batch-mode using synthetic water, which mimics the source water characteristics of surface water in Ohio, with 1 or 5 ppb of saxitoxin and 0.05 – 1.2 mg/L PAC. For the isotherm experiments, samples were mixed with different amounts of PAC and after mixing for three days the equilibrium toxin concentrations were analyzed after sample filtration by enzyme-linked immunosorbent assays. For the kinetic experiments, samples were collected at predetermined time intervals for a 3-day timeframe. Our results show that wood-based PAC adsorbed the greatest amount of saxitoxin and bituminous coal-based PAC adsorbed the least. Under the tested PAC dosage and initial toxin concentration, coal blend and coconut-based PACs exhibited similar toxin removal that was intermediate between the wood- and bituminous coal based PACs. Isotherms fits to the saxitoxin adsorption show the wood and bituminous-coal based PACs were well described with a linear isotherm, while the other two PACs were better fit to a Freundlich isotherm. The kinetic results show that wood-based PAC adsorbed saxitoxin rapidly and appeared to reach equilibrium in 8 hours. However, the adsorption of saxitoxin onto coconut-, coal blend- and bituminous coal-based PACs required 24 hours to achieve equilibrium. The wood-based PAC has the highest volume of mesopores and micropores, and thus the results suggest the volume of pores on PAC play an important role on adsorbing saxitoxin.

Adsorption of saxitoxin onto powdered activated carbon: The influence of carbon type

2019 Spring National Meeting

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