Abstract:
Stormwater runoffs are one of the primary causes for deteriorating water quality in the Nainital Lake,
India – a prominent tourist attraction and the sole drinking water source for the habitants of Nainital
City. Treatment of fluctuating runoffs and contaminant influxes before mixing with the lake’s water
by conventional methods would require a large land footprint, which is a big constraint in the Nainital
because of the hilly region. Ballasted sand flocculation (BSF) technology requires much less land
footprint; a full-scale 1 MLD capacity pilot plant was applied for treatment of stormwater runoffs of
the Nainital Lake. Twenty-eight storm events were monitored for runoff characterization and for
evaluating the performance of BSF technology. The runoff water showed marked variation especially
for total suspended solids (TSS), total phosphorus (TP), chemical oxygen demand (COD), biochemical
oxygen demand (BOD), total coliform (TC) and fecal coliform (FC) with maximum concentrations of
964 mg/l, 2.35 mg/l, 520 mg/l, 299 mg/l, 21 × 105 MPN/100 ml and 14 × 104 MPN/100 ml. The
performance analyses results of the pilot plant revealed that the contaminants including trace metals
in the stormwater runoff were reduced appreciably and the pollutant removal efficiencies were
found to be largely unaffected by fluctuation of the influent contaminants’ concentration.
