The Danish International Development Assistance agency has funded a project in Bhutan which includes a water supply component in six urban centres, a sewerage component in the two largest cities plus associated institutional development. The project includes the implementation of an extensive water-borne sewerage system and associated wastewater treatment. The treatment process adopted was waste stabilisation pond technology due to the low associated construction, operations and maintenance costs and low requirements for technical skills hence contributing to financial and O&M sustainability of the project, as well as meeting the water quality requirements for the receiving waters. Since essentially all available land is utilised in the country, the locations of the treatment plants are adjacent to rivers which are fast flowing, leading to a risk of severe erosion conditions during the monsoon season. In order to protect the treatment plant structure, river training was necessary. The high elevation of the country also has consequences for the design and operation of the plants. The wastewater treatment process includes a train of anaerobic, secondary facultative and maturation ponds, lined with a high density polyethylene liner. This paper describes the project as implemented, focusing on the wastewater treatment plants and the hurdles required to be overcome to ensure sustainable operation of the waste stabilisation pond treatment plants, in particular overall design of the system, the re-design required due to the loss of land occasioned by the intense monsoon rains in the south of the country prior to construction of river training works, the training required for the local staff from the operations and maintenance authorities and the financial aspects of the project. The project is discussed within a broader framework of Danish development aid in the country which covers the health, environment and the public health infrastructure sectors. Lessons learnt from the project are discussed.

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