Comparing PAC/UF and conventional clarification with PAC for removing microcystins from natural waters

Abstract

PAC/UF was investigated for removing M. aeruginosa cells and microcystins from natural waters and its performance was compared with the conventional clarification with PAC addition (PAC+C/F/S). Ozonated and clarified waters from Tavira's Water Treatment Plant were used. Both processes achieved an absolute removal of chlorophyll-a, but greater turbidity and microcystins (intra and extracellular) removals were reached by PAC/UF. With PAC/UF, 10 mg/L PAC resulted in a cycle-averaged concentration of microcystins in the permeate (0.72 μg/L MC-LR_eq) below the WHO guideline value, while the water quality obtained with 15 mg /L PAC+C/F/S was far beyond that guideline value. However, the occurrence of cell lysis during UF (with subsequent release of microcystins and UV_254nm absorbing substances) and the preferential removal of high molar mass compounds by coagulation yielded better UV_254nm removals by PAC+C/F/S. Natural organic matter showed a small impact onto microcystins removal, with greater effect of some algogenic compounds, but especially of high concentrations of humic and tannic-like compounds.

Keywords:

• PAC/UF
• Clarifi cation
• Microcystins
• AOM
• NOM