| dc.description.abstract | Industries in Dhaka, Bangladesh, play a significant role in polluting the waterways. Although effluent treatments plants are required by law for many of the industrial sites, these are in many cases not well monitored and often not used. The result of the lack of effluent treatment is that many of these industries are releasing large amounts of wastewater into the water untreated. There are many issues due to water pollution in Dhaka relating to human health, ecological health and reduction in agricultural production, for example. To improve water quality in the area policies and approaches need to change. Although some parameters have been monitored in the past, there are substances which are potentially overlooked. By modelling emissions from industries, pollution hot spots could be analysed in the area, based on the substance loads industries add to the waterways. Subsequently, the effect of adding industries onto the existing sewage system in Dhaka was modelled to assess the impact this would have on substance load added by industrial effluent in the study area.
The first step in modelling industrial effluent emissions in Dhaka’s waterways was categorising the industries for use in the emissions model. The resulting categories textile, tanneries and paper mills were selected based on their wastewater quantity and quality. A further division was made for the textile category, consisting of dyeing, printing, washing and mixed wet processes. Substances also needed to be selected for modelling, which was based on literature data availability and consequences for ecological and human health. The selected substances were arsenic, cadmium, chlorine, nitrate, sulphate and tannins. The wastewater production per individual industry was used as input in the model in combination with typical substance concentrations in the effluent to calculate the substance load.
The emissions model results in substance loads emitted spatially. The industrial effluent locations were then assigned to sub-catchments, which were defined by using a digital elevation map. Using the digital elevation map the outfall points for wastewater from industries were also estimated, to show where the modelled substance load would enter the waterways. Pollution hot spots could subsequently be defined as the outfall points with large substance loads for each of the substances. From the modelled loads the industrial categories which contributed most to the substance loads could also be shown.
Validation of the model was based on the concept of a substance balance. Modelled discharge values for the main stretches of river were combined with substance concentrations measured at various points in the study area. The loads were calculated and compared for nitrate and sulphate, which were the only substances with available concentration data. Although the validation was not fully realised, the next steps were indicated for improving the validity of the model for further use.
The scenario analysis looked at the effects on the substance loads added to the waterways by industries and what the impact would be of connecting the industries to the sewers for the Pagla wastewater treatment plant. The results from this analysis showed this would have very little impact on substance load addition to waterways, with all reductions being under one percent of the total load in the study area. | |
