Dar population poses a big problem By Zephania Ubwani, Arusha THE CITIZEN Many waste stabilisation ponds (WSPs) in Dar es Salaam are heavily overloaded because of the increasing population in the city, an expert has said. This has led to untreated liquid waste over spilling to surrounding areas from the ponds, posing a health hazard to people, he explained. Dr Karoli Njau of the University of Dar es Salaam (UDSM) said hundreds of thousands of people living in the informal settlements do not use the facility. He told an experts meeting here that many of the ponds currently serving the city of over four million people were constructed many years ago to serve the small population of those days. The problem has been compounded by poor maintenance of the existing waste water treatment facilities, especially from residential homes and industries. He said the situation was grim in the major city and other municipalities and its solution needed the quick intervention of relevant authorities. WSPs are artificially made ponds connected to sewage systems in urban areas, mainly for disposal of waste matter from toilets and industrial plants. Although for many years considered the most appropriate technology for waste water treatment in Tanzania, they were later to be joined by constructed wetlands (WCs). The latter are more or less similar structures like WSPs. However, they are operated and maintained to employ ecological aspects of waste water treatment through the planting of vegetation tolerant to flooding and made to imitate natural systems in treating water. Dr Njau, who is currently the vice chair of the Waste Stabilisation Ponds and Constructed Wetlands Research Group being coordinated by the UDSM, however, said Moshi municipality had performed well in waste water treatment compared to other municipalities in the country. "Most of the waste water treatment ponds in Dar es Salaam are heavily overloaded," he told a training workshop for environmental and municipality engineers on how application of the technology could be improved. Some of the largest ponds for liquid waste treatment in Dar es Salaam are located at the UDSM. But the university don admitted that they were constructed to serve a population of less than 5,000 people only. "Currently the UDSM has a population of over 20,000 and keeps on growing. Those ponds can no longer serve that number of people," he told experts at a workshop on constructed wetlands.