Abstract

In this study, the simultaneous removal of inorganic turbidity and organics was investigated at alkaline pH to avert the need for pH adjustment and overdosing. It was aimed to compare the doses for conventional and enhanced coagulation; and consequently, arrive at optimized coagulation where both had synergistic maximum removal. High basicity PACl was used to coagulate simulated waters prepared by humic acid (HA) and kaolin. The removal of turbidity, TOC, DOC and UV254 was evaluated. The impact of varying input concentrations of HA and turbidity on doses was studied. The enhanced coagulation doses were higher than conventional ones. However, with an increase in input TOC, the difference between enhanced and conventional doses narrowed. The doses for optimized coagulation ranged from 2 to 9 mg Al/L. At optimized coagulation, the removal of TOC, DOC and UV254 varied from 30–85%, 30–89% and 73–91% respectively. FTIR spectroscopy revealed the presence of Si-O-C bond. The interactions of unsaturated bonds of hydrophobic organics to inorganic clay were possibly favoured over hydrophilics. HA agglomeration reduced coagulant consumption as the input TOC increased. It was concluded that instead of stoichiometric approach, modified dosing approach can be applied for limiting underdosing and overdosing while ensuring maximum removal of impurities.

HIGHLIGHTS

  • Simultaneous optimized removal of inorganic turbidity and dissolved and particulate organic matter.

  • Doses for enhanced coagulation were higher than that for conventional coagulation.

  • Modified dosing approach avoids underdosing and overdosing.

  • With an increase in input TOC and turbidity the difference between the dose for enhanced and conventional coagulation narrowed.

  • Favoured interaction of hydrophobic organics over hydrophilic organics revealed by FTIR spectroscopy.

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Supplementary data