Removal of saxitoxins from drinking water by granular activated carbon, ozone and hydrogen peroxide — implications for compliance with the Australian drinking water guidelines

摘要

In a laboratory-scale trial, we studied the removal of saxitoxins from water by ozone, granular activated carbon (GAC) and H_2O_2, and considered the implications of residual toxicity for compliance with the Australian drinking water standards. Cell-free extracts of Anabaena circinalis were added to raw, untreated drinking water obtained from a water supply reservoir to provide a toxicity of 30 μg (STX equivalents) l~(-1). Ozone alone, or in combination with H_2O_2, failed to destroy the highly toxic STX and GTX-2/3, and only partially destroyed dc-STX, and the low-toxicity C-toxins and GTX-5. In all cases, the toxicity of the water was reduced by less than 10%. GAC removed all of the STX, dc-STX and GTXs, but only partially removed the C-toxins. However, the residual toxicity was reduced to the suggested Australian drinking water guideline concentration of 3 μg (STX equivalents) l~(-1) without O_3 pre-treatment. Modelling the spontaneous chemical degradation of residual C-toxins following treatment shows that residua! toxicity could increase to 10 μg l~(-1) after 11d due to formation of dc-GTXs and would then gradually decay. In all, residual toxicity would exceed the Australian drinking water guideline concentration for a total of 50 d.