Changing climate: Waste water management in Dhaka city
Rainwater harvesting system should be installed in buildings to recharge groundwater and to supply water for at least the household or outdoor use e.g., toilet flushing, laundry and garden, etc
A.K.M. Saiful Islam
On the 22nd March, we observed the world water day with a reminder that one of the biggest challenges of the 21st Century will be the climate change and its impact on water resources. This years theme was waste water in supporting the sustainable development goal (SDG) 6.3. Providing clean water and sanitation is the one of 17 Global Goals of SDG that needs to be ensured by 2030. This theme is very important for Bangladesh particularly the urban areas like Dhaka city.
Water supply system of Dhaka city
According to its latest report, Dhaka WASA is currently capable of producing 2420 MLD (million liters per day) of water against the daily demand 2250 MLD of the city dwellers. A total of 78 per cent of this water comes from underground sources and the rest 22 percent from surface water. However, groundwater level of the city is declining by 2 to 3 meters per year due to continuous abstraction of water. WASA has planned to establish additional mega Water Treatment Plants: one at Jashaldia having a capacity 450 million liters water per day to treat water from the river Padma and the other one at Gandharbpur having a capacity 500 million liters water per day to treat water from the river Meghna.
However, these plants will take many more years to be built and our dependency on the groundwater will be continues. Under the changing climate, increasing variability of the rainfall and changes in the fresh water flows, it is expected that water supply of mega city Dhaka will be under pressure in the future. Therefore, during this transition period of shifting dependability for water supply in the city from groundwater to surface water, conservation of water and improving efficiency of the supply system are essential. At present the systems loss of WASA is about 22% which can be further reduced. Rainwater harvesting system can be installed to the slum dwellers of Dhaka city using simple and low cost technology.
In a recent study of the University of Nottingham, researchers showed that using 100m2 roof areas of Dhaka city, 33% water demand can be met by rain water harvesting. Roof water could be used directly for aquifer replenishment to reduce the groundwater mining. Conservation and protecting of wetlands will increase the groundwater recharge. Conserving the flood plains of the rivers and wetlands are allowing not only groundwater recharge but also reducing flood peaks, reducing summer heat, providing breeding and feeding grounds for fish and wildlife habitats. A recent study conducted by the scientists of Rajshahi University showed that water bodies and lowlands of Dhaka city decreased by 32.57% and 52.58%, respectively during 1960 and 2008.
Solid and wastewater management system of Dhaka City
Primary causes of the pollution of the surrounding rivers of Dhaka city are: i) disposal of untreated industrial waste from tanneries, dying industries and other chemical industries, ii) disposal of untreated domestic waste water in the open water bodies, iii) dumping of solid wastes in the open water bodies and rivers, iv) urbanization, v) deforestation, vi) illegal encroachment of wetlands and rivers etc. According to the latest report of WASA, the only waste water treatment plant, Pagla Sewage Treatment Plant, can treat only 40,000 cubic meters of wastewater. WASA has a plan to improve its capacity so that it can use its full capacity of treating 1.2 lakh cubic meters of wastewater. Untreated domestic wastewater and un-authorized connections from the Septic tanks are finally discharged into the surrounding rivers of Dhaka city. However, unless drastic and coordinated actions to reduce water pollution are taken, Dhaka will always remain somewhere in the list of topmost polluted cities.
A few suggestions
A few suggestions can be provided to cope up with the upcoming challenges of urbanization and the threats of climate change.
1. We must stop illegal encroachment in the wetlands, natural canals and rivers.
2. Developing coordinated and integrated solid waste management systems including solid waste disposal system for Dhaka city.
3. We must ensure proper treatment of domestic waste and removal of unauthorized connection of domestic sewer into the open water bodies.
4. ETP must be installed and made operational for treating the waste water from the tannery, dying and other chemical industries.
5. Rainwater harvesting system should be installed in buildings to recharge groundwater and to supply water for at least the household or outdoor use (e.g., toilet flushing, laundry and garden etc.).
6. We should stop installation of any new groundwater pump inside Dhaka city.
7. New water treatment plants should be designed to treat water only from the surface water sources.
8. Awareness should be built to conserve water and system loss of WASA should be reduced.
9. Drains and canals should be cleaned before monsoon to drain out the excess runoff of the city.
Many scientific studies revealed that climate change will increase variability of rainfall in terms of quantity, timing, spatial distribution, intensity and frequency.
Therefore, we must think about proper utilization, conservation and management of natural water sources. Integrated and coordinated efforts based on appropriate adaptation planning can reduce the risks of climate change and its associated threats to environment, water resources and ecosystems.
The writer is a professor of the Institute of Water and Flood Management at the Bangladesh University of Engineering and Technology, Bangladesh. Email: [email protected]
