Abstract:
Humic substances are major part of NOM (Natural Organic Matter) contamination in
surface water. It adds color to water, transports heavy metals, precursor of carcinogenic
DBPs formation and also act as a substrate for bacterial growth in water distribution
system. Many advance technologies and disinfection procedures are being practiced for
removing humic acid and pathogens from drinking water, but they are costly and posing
severe environmental effects. Conventional water treatment process includes
coagulation-flocculation using alum as chemical coagulant due to its cost effectiveness
and easy availability. To improve efficiency of coagulation-flocculation and
sedimentation, it is necessary to study floc properties in detail. In this study two
synthetic feed waters (SFWs) have been prepared, one with humic acid (SFW-1) and
other with humic acid incorporating E. coli (SFW-2). Optimum coagulant dose of 70
and 60 mg/L has been found for SFW-1 at pH 10.25±0.5 before coagulation and SFW-
2 at pH 7.5±0.5 respectively. Floc characteristics i.e., floc size and fractal dimensions
(Df) have been studied on coagulation at 150 rpm for 2 minutes with three flocculation
regimes of high, medium and low Gtmix conditions for both SFWs i.e., 117660, 57564,
16713 respectively. After that settling time of 30 minutes has been provided in each
condition. Largest average floc size was 395.1± 44.8 μm for SFW-1 and 498.2±29.7
μm for SFW-2 and highest Df was 2.64±0.04 for SFW-1 and 2.70±0.05 for SFW-2
achieved at medium Gtmix condition before 30 minutes of settling for both SFWs. This
study may ultimately beneficial for improving water quality in treatment plants that
plays a main role in achieving SDG 6 ‘clean water and sanitation’ target 6.1 ‘safe and
affordable drinking water for all’.
