Integrated approach for ultimate disposal of municipal solid wastes

Abstract

Dhaka, the capital of Bangladesh, is one of the fastest growing metropolises of the world with an annual average growth rate of 3.72 percent. In the Dhaka City Corporation (DCC) area of 360 sq. km, the present population is estimated to be 7 million. Approximately 3500 - 4000 metric tons of solid wastes are generated per day, with an average generation rate of 0.5 kg/cap/day. The primary objective of the research work has been to develop an 'Integrated Approach' for ultimate disposal of solid wastes of Dhaka City and compare its technical and economic aspects with those of conventional sanitary landfill approach. The research was expected to develop an environmentally sound and economically affordable method for the ultimate disposal of solid wastes from urban areas that should be applicable for large metropolitan cities as well as small to medium towns of Bangladesh. For ultimate disposal of solid waste conventional sanitary landfill, as well as an integrated approach comprising recycling, composting and land filling was designed and compared technically and economically. Energy recovery from solid waste employing incineration was also assessed. In Integrated Approach, primary collection was assUmed to be operated by rickshaw van from households and linked to secondary collection through community transfer station. Community transfer station was designed for both demountable container truck and open truck for collection of solid wastes. The organic part of the collected waste is to be processed to produce compost and inorganic non-reusable part disposed of by landfill. Conventional sanitary landfill was designed with primary collection by handcart and secondary collection by open or demountable container truck with or without transfer station. Leachate control and landfill gas management systems were also considered. Analysis was done dividing the whole DCC area as 5-study zone, 3-study zone and single study zone. Considering 3-study zone, the cost analysis shows that the annual cost of Integrated Approach employing recycling, composting and small-scale land filling was about 58% cheaper than the conventional sanitary landfill. It was assumed that secondary collection was operated by demountable container truck with community transfer station. However, when DCC area was assumed to be divided into 5-study zone, annual cost of Integrated Approach was found to be marginally higher compared to 3- study zone and when the DCC area was consider as a single zone and land filling done at a single place, the annual cost increases but still remains far less than the conventional sanitary land filling. In each case, the annual costs slightly increase, when open truck is considered for secondary collection. The net unit income excluding all expenses of Integrated Approach in 3-zone case was found to be Tk.620 per ton of generated waste. However, for 5-zone and single zone case the net unit income was about Tk.600 per ton of generated waste. But, there was no economic return from conventional sanitary landfill. Land requirement for 'Integrated Approach' has been estimated to be only 10% of that required for conventional sanitary land filling. That means, the land required for conventional sanitary land filling for 10 years, might be utilized for more than 100 years if 'Integrated Approach' is adopted for the disposal of same quantity of waste. Energy recovery option from present municipal solid waste was also considered and it was found that only 5 -10 MW electricity could be produced from wastes (as received) generated daily in Dhaka City, which is very insignificant, compared to the daily demand. All these analyses performed in the present study lead to the conclusion that solid waste management of Dhaka City employing the proposed Integrated Approach of recycling, compo sting and small-scale land filling will be appropriate and most profitable.