Abstract:
The ready-made garment (RMG) sector has become one of the largest manufacturing sectors in
Bangladesh. Among various RMG industries, denim-washing factories are water intensive and
utilize a wide variety of chemicals and dyes. In this study an assessment of chemical dosing
optimization in the primary treatment unit for a denim garment washing plant has been done for
various water quality parameters.After finding the optimum dosing for different chemicals a
sensitivity analysis has been conducted to find the effective combined dosing both for removal
efficiency of selected water quality parameters and economic point of view. For this, chemical
dosing optimization has been done for alum, ferrous sulfate and polymer with controlled pH
condition.This is because pH controlling increases the removal efficiency. A comparison between
the optimum dosing and half of the optimum dosing has been conducted to find the sensitivity
for removing selected water quality parameters. It was observed that, even after reduction of
chemical dosing by 50%, removal efficiencies for color, turbidity, TSS, COD, and BOD5 did not
seem to decrease significantly. Based on the observations from the above mentioned
analysis,combined dosing of different concentartions for alum, ferrous sulfate and polymer were
carried out to find the removal efficiencies. It was found that combination of chemicals provided
better removal efficiencies than individual chemical dosing. Polymer and alum dosing provided
better removal efficiencies for different water quality parameters. Dosing with combination of
chemicals, having polymer and alum also provided better removal results. Ferrous sulfate
provided least removal efficiencies for most of the water quality parameters when compared to
other individual chemicals. Combinations having ferrous sulfate in them also provided relatively
less removal of various water quality parameters. A cost analysis for that different combined
dosing was also carried out to determine the possible effective dosings. The cost analysis will
facilitate respective ETP management of denim washing factories with selection of combined
dosing of chemicals, which is function of the overall design of ETP (i.e. primary, secondary and
tertiary units) and willingness to pay for primary treatment stage.
