Abstract:
The rise in the number of industries in Bangladesh, including textile-dyeing operations, has
seriously increased water pollution in the country. The effluent treatment plants (ETPs) are based
on a combination of two or more treatment methods: physical, chemical and biological.The aim
of this study is to assess the treatment efficiency of textile waste by chlorination and evaluation
of possible THM formation. The influent and effluent characteristics and efficiency of ten
chlorine based treatment plants were investigated in this study. The concentrations of untreated
effluent was found ranged between BOD5:96 -242mg/l, COD: 225-800mg/l, TDS: 228-2040mg/l,
TSS: 15-110mg/l, Color 382- 205 (Pt-Co unit). All the treated effluents do not meet the
standards set as per Schedule 12-B of the Environmental Conservation Rules -1997 (ECR-1997,
Bangladesh). Chlorine oxidation of untreated sample of textile waste water by commercially
available bleaching powder solution as the source of chlorine was done in the laboratory. The
effect of chlorine dose was observed. It is found that 1 to 1.5 kg chlorine is required for 1 kg
BOD removal. The effect of contact time was also assessed and it is evident that 20 min contact
time is enough for chlorination process.
The concentrations of Trihalomethane (THM) in the treated effluent were assessed since these
disinfection byproducts are suspected to cause cancer, liver and kidney damage in human fetus.
The concentration of THM was measured and the presence of THMs was confirmed in this
study. However, the concentration of THMs in treated water sample was found below the WHO
concentration where the effluents contain a lower value of DOC. The effect of pH and dissolved
organic carbon (DOC) and chlorine dose on the concentration of THMs was assessed. It is
assessed that trihalomethanes formation increase significantly with increasing pH but it is
independent of THM when the concentration of THM is 150ppb and above. The pH value is 8.5
at 150 ppb concentration of THM. Finally curves have been generated in Matlab software to find
out the concentration of THM for different chlorine dose, pH and DOC values. The
concentrations of THM in the outlet stream of different ETPs can be found out using these
curves. The results are very close to the practical measured values.
