ENVIRONMENTAL degradation is taking place in the capital city and all over Bangladesh due to uncontrolled discharge of liquid and solid waste in our environment from domestic, commercial and industrial sources. The stakeholders are unable to address the problem due to lack of proper planning, lack of finance, inadequate institutional capability as well as political interest. In the Global Liveability Survey by the Economic Intelligence Unit, Dhaka has been branded as the most unliveable city out of 140 cities of the world.
Dhaka is surrounded by four major rivers — Buriganga, Sitalakhya, Turag and Balu. These rivers are polluted with heavy metals. The surface water treatment plants operated by Dhaka WASA are not equipped to remove the heavy metals because the plants are operated by conventional (rapid sand filters) method. Besides, the rivers are used as the source of surface water treatment plants and the same water is also a source of household use. Four different industries around the Dhaka use the water from these rivers for processing their productions and then discharge the effluent containing heavy metals into the rivers. Most of the industries in these clusters either do not have rudimentary effluent treatment facilities. As a result, the effluent quality in most cases violates the Environmental Quality Standards of Bangladesh.
Dhaka City has the highest density of population in the world (44,000/Sq. Km.). Considering a population of 16 million, the water demand is approximately 230 crore l/day (500/IMGD). Of the total requirement 22 percent is met by four surface water treatment plants and the remaining 78 percent from ground water extraction. The system pressure is below 1 bar (33 Ft. head of water) and some areas have zero pressure and depend mainly by sucking water from the WASA water main through booster pumps. During 1970-1972 Dhaka WASA constructed three one-million-gallon steel tanks at different locations of the city in order to boost the system pressure. These tanks were designed in the USA and provided with altitude valves. These valves operate on system pressure. When the system pressure is high after midnight, the altitude valve opens through system pressure and the excess water is stored in the tank. During the peak consumption hours after 5 AM the altitude valve opens under system pressure in order to meet the excess demand of the system. The tank is said to be floating on the system and functions as a balancer. But the present water network of Dhaka WASA cannot be operated in the absence of a well-designed and strong distribution system.
In designing any water supply and sanitation project it is considered that 70 per cent of the water returns back as spent water/waste water (sullage and sewage) and if it remains unaddressed the spent water is bound to create environmental pollution. In Dhaka WASA, of the total water and sewer connections, approximately 80 per cent is water connection and the rest 20 per cent is sewer connection, which indicates water connection is increasing at a faster rate than sewer connection which is not desirable in maintaining an environmental friendly living area.
The average human body waste is 17,000 tons/day. The water carriage sewerage system is available mainly in south Dhaka. According to a study of Improved Sanitation Services study the pipe borne sewerage system was present in about 20 per cent urbanised area of the city. The existing only sewage treatment plant (Oxidation lagoon) of Dhaka WASA at Pagla is treating a daily average of 45,000 Cu.m /day. The pollution load on the environment due to domestic sewage is enormous. A stabilisation pond with limited infrastructure was provided for the city but ultimately the system never functioned properly due to deficiency in pipe diameter, pipe gradient, blocked/broken manhole, improper design of manhole cover and inefficient operation and maintenance of the treatment plant and network. In other words, human waste management system is in a dire state.
The situation of industrial waste management is no different. There are nine clusters of industrial areas in Dhaka. In addition to these clustered areas, there are many sources of industrial wastes and some are toxic containing heavy metals like Lead, Mercury, Chromium, Aluminium and Cadmium. Several of the industries which are located in the clusters require large volume of industrial water. Principal amongst these are the textiles (dyeing & printing) and tannery industries. Both these industrial sectors are the major sources of pollution due to high discharge levels of organic and inorganic chemical compounds associated with the dyeing and tanning process. Most of the industries in these clusters either do not have or have rudimentary / inadequate treatment facilities. As a result the effluent quality in almost all case violates the environmental quality standards of Bangladesh.
According to an industrial survey, the biochemical oxygen demand and dissolved oxygen levels in all the rivers are beyond acceptable limits, as such the surface water quality situation in Dhaka watershed is generally unacceptable for drinking water purpose. Particularly, the presence of heavy metal indicates that a conventional surface water treatment plant (rapid sand filter) cannot be recommended, unless other very costly design for removal of heavy metals is applied. It is known that there are laws and different regulatory authorities in Bangladesh to control the industrial pollution. Unfortunately, the authority concerned and jurisdiction of various agencies in this issue is not clearly defined and laws are not strictly enforced. Further, political influence cannot be overruled when discussing the illegal establishment of industries and their defiance of maintaining guidelines.
The Dhaka City Corporation has not been able to make any remarkable improvement in the solid waste management of the capital city. Solid waste collection started in the city in 1830. Since then two improvements have been achieved: firstly, the abolition of bullock carts and switching to refuse collection vehicles. The other improvement is night time collection in the old city. The introduction of demountable containers system without properly designed primary collection technique has become a white elephant for the DCC.
In solid waste collection/management there is no unique solution, because the method of primary collection is very much dependent on the locality. The component primary collection is very critical particularly in the developing countries where people are less conscientious of their responsibilities. In the absence of a well thought out primary waste collection strategy, the demountable container system introduced by DCC failed.
Basic principal operation in solid waste management consists of three distinct phases as far as the technology is concerned: primary and secondary collection, transportation and disposal/treatment. The primary collection is the most critical in designing sound waste disposal system in terms of physical work and the beneficiary is directly involved in achieving reasonable/progressive collection efficiency. The other components are within the control of the executing authority. In designing a mega city solid waste management plan the most important component is to conduct a baseline survey. The data obtained through the baseline survey shall be used to prepare the preliminary design, which will obviously produce a financial focus in order to prepare a final design and execute the project by the DCC.
The DCC is unable to offer the expected level of services with the existing capacity and trend of waste management. The existing projection of future generation rate indicates that by the year 2020 it may exceed 32 thousand tons/day, which in turn will require over 200 acres/yr of landfill area. In addition to a technically sound plan for solid waste management, as suggested by experts, the DCC may consider a community based solid waste management system involving recycling and composting in conjunction with sanitary land filling with possible provision for transfer station to account for long distance of landfill sites. For a green Dhaka, the problem of solid waste management needs immediate attention.
Mohammad Shamsuzzoha is a retired engineer.
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