Water saving technology for recycling wastewater

摘要

The abstraction of groundwater for irrigation, industrial use and in public water supplies continues to increase day by day throughout the world in general and Bangladesh in particular. The area of irrigated land that used groundwater increased from 6% of the total irrigated land during 1972-1973 to about 91% of the total irrigated land during 20032004. Such use of groundwater especially for irrigation and public water supplies have caused lowering of ground water level, drying up the surface water sources and salt water intrusion in coastal belt of the country. In such situation many countries are moving towards a formal recognition of the role of the technological options that reclaim and save water for supplementing existing sources of fresh water for irrigation. Thus the use of biogas technology and duckweed based pond systems for the treatment of sewage, greywater and organic wastes preserves the nutrients in effluent, which are recycled back into aquaculture pond and/or to agricultural field with valuable nutrients and supply renewable energy from biogas plants. These systems reclaim water and hence save huge amount of fresh water for irrigation and aquaculture purposes. Recently there has been growing interest in application of biogas technology especially in Bangladesh. Presently around 25 thousand biogas plants have been operating in Bangladesh. Attempt has been made by different Government and Non-Government organisations to construct biogas plants at different households, communities, poultry farms and institutions for improving socio-economic and overall environmental conditions of target communities, particularly for better rural livelihoods. The use of this technology is also most widespread in Asia and the Pacific region. In China around 118 million households use biogas, about 4 million biogas plants have been operating in India, and successful programmes have been established in Nepal (around 16 thousand operational plants) and Vietnam (about 23 thousand operational plants). This study clearly demonstrates that the planned use of wastewater to agriculture and/or aquaculture, appears to be an environmentally sound ecological sanitation option for proper management of sewage, greywater, and organic wastes in developing countries in general and Bangladesh in particular, and makes a significant contribution towards saving a vast quantity of fresh water. This study evaluates the cost-effectiveness and performance of the proposed technological options as practised in Bangladesh. An attempt is also made to highlight the potential of water saving technologies in Bangladesh context, and to identify problems and research needs in this prospective field.