Waste stabilization ponds in Tanzania by Michael Yhdego the remaining 76 per cent use pit It is claimed that waste stabilization ponds latrines.6 However, 70 to 80 per provide an efficient, inexpensive and appropriate cent of Tanzania's industries are concentrated in Dar es Salaam, and form of wastewater treatment for developing the wastewater from industries such countries. On the basis of negative experiences as breweries and textile plants is in Tanzania, Michael Yhdego disputes this claim. discharged into the Indian Ocean without any form of on-site IN TANZANIA, waste 0 There was a scarcity of funds and treatment. 5 stabilization ponds (WSPs) are used skilled operational supervision. During the mid-1960s and the extensively in the treatment of Furthermore, the effluent from beginning of the 1970s, WSPs were domestic and industrial wastes; ponds had already polluted some constructed to treat wastes from about 20 ponds are located in the rivers; for example, the Ubungo semi-urban residential areas, country's main urban centres. It has ponds in Dar es Salaam and the industrial sites and institutions such been claimed that WSPs are an Arusha ponds badly polluted the as the university and army camps. efficient, effective, inexpensive and Msimbazi and Themi Rivers, There are now nine ponds in the appropriate wastewater treatment respectively. city. in comparison with conventional Table 1 presents a summary of treatment methods.! ,2,3 They the population, areas served, net require little maintenance and the Dar es Salaam ponds pond areas and type of system used. effluent is largely free from The city of Dar es Salaam is located The data are based on the author's pathogenic and parasitic along the Indian Ocean and is the observations and research over the organisms.4 These factors make major industrial, commercial and period from May 1985 to October WSPs an apparently attractive institutional centre of Tanzania. 1986. His findings were correlated treatment system, if sufficient land The central business area and the with two other major surveys. is available on which to build them. high- and medium-density A number of interesting points A survey carried out in several residential areas around the city emerge from Table 1. Firstly, urban areas over 1985 and 1986 centre are served by a sewerage anaerobic ponds were not however, showed that the majority system; this reaches 12.8 per cent incorporated into the pond systems. of the pond systems in Tanzania of the city's population. The sewage Secondly, the net pond area did not were either not working at all, or is discharged through an ocean take into account the incremental else performing poorly, for various outfall which is defective and too development of the area. Thirdly, reasons: short. The large quantity of industrial wastes were supposed to o Standard design formulas were untreated sewage has generated a be treated by ponds; yet the adopted without considering high level of biological pollution in Ubungo industrial area, for local environmental factors, with Tanzania's coastal waters, and instance, does not have facilities for the result that ponds were not reports of fungal infections caught the removal of heavy metals and designed with proper care. by people bathing along the dyes. Finally, no feasibility study o The lack of maintenance and polluted beaches of Dar es Salaam was carried out on alternative desludging had adversely are widespread.3 combinations of ponds which might affected the ponds' performance Of the people not served by a minimize capital and operational and turned them into breeding sewerage system, 11 per cent use costs. sites for mosquitoes. septic tanks and soakage pits while Design The ponds were designed by engineering firms from the United Kingdom and Denmark, and the designers' criteria, approach and methods varied from firm to firm. Assumptions were based on the firms' experience in similar projects, not necessarily in hot climates, as well as their own expertise. At the time that the Dar es Salaam ponds were designed and constructed, there was no central authority to verify the designs before construction. Today, despite the absence of data on the methods used in the design of the ponds, it is necessary to point out just why A burst sewage pipe near a WSP encourages mosquito breeding. the pond systems failed. To begin 10 WATERLINES VOL.8 NO.1 JULY 1989 Table 1. Pond locations and specifics Pond Population Net pond Pond system Areas served designed area to serve (hectares) eDt Airport! Not DSM airport Airwing available 0.8 F,M (2 units) Airwing staff SHORT COURSES houses (less than three months) Buguruni 13,000 3.2 F,M (3 units) Buguruni suitable for professional staff development working for voluntary agencies, area government and local government, Lugalo 20,000 5.2 F,M (7 units) Military barracks and international organizations in developing countries Mgulani 10,999 1.5 F,M (3 units) Police, army and marine barracks 10/12 week Msasani 19,500 3.7 F,C (4 units) Mikocheni, Kijitonyama and DIPLOMA COURSES Regent estate o Community water supply and Ubungo Not Not F,M,ST Ubungo sanitation available available (5 units) industrial area o Community technology for rural development Ukonga Not Not F (1 unit) Prison and o Groundwater development available available officers training o Infrastructure (or low income college urban housing University 4,975 1.7 F,M (7 units) University of Dar o Water analysis & quality es Salaam Vingunguti Not 4.5 F,M (4 units) Industrial area OTHER SHORT available COURSES Practical water supply and KEY o sanitation (6 weeks) F = Facultative pond C = Chlorination pond M = Maturation pond ST = Settling tank o Disaster relief & refugees* o Irrigation & water resources* o Planning and management for with, the engineering firms failed from the local city council to the urban services to carry out a thorough study of regional government and back for * planned for 1980 essential factors such as the past 20 years. It is worth temperature, climate, infiltration, highlighting the following points: soil and other design factors. Most o When the Dar es Salaam city of the ponds were designed using council resumed responsibility in Gloyna or McGarry and Pescod July 1978 there were major systems, and this uncritical operational problems both in the eDt approach to the methods, and their sewerage and the pond systems. adaptation in Tanzania without It was impossible to maintain the ALSO consideration of environmental ponds as many of the factors, was the cause of the total components were broken and /2-month and 2-year MSc courses deterioration of the ponds. The would require major assumptions made by the engineers rehabilitation before they could AND had little relevance to Tanzania. resume operating. individual programmes of any o The people and industries served duration to suit special by the sewerage and pond requirements Operation and systems are supposed to pay a maintenance certain sum of money for their services. However, nothing had A proper management and been collected for many years, maintenance programme is due to the shifting responsibility, essential if a pond system is to be and, as a result, no finance was eDt operated efficiently. Maintenance available to run and maintain the work consists of good pond- systems. For industries who Enquiriesto Professor Jon Pickford keeping, making repairs to helped maintain the WSPs, their or Mrs. Rowena Steele embankments, cutting down weeds industrial waste was and grass and periodic desludging. indiscriminately dumped into the WEDC The operation and maintenance of WSPs, totally ignoring their LoughboroughUniversity of facultative and maturation ponds chemical and toxic properties. Technology, Leicestershire LEI I 3TU, was not carried out in Dar es o There is a shortage of local England Phone:0 (44) 509 222390 Salaam, mainly because the professionals in the city and town Telex: 34319 UNfTEe G responsibility for the sewerage councils - such as public health Fax:0 (44) 509 610231 system and ponds has been shifting engineers - who could approve WATERLINES VOL.8 NO.1 JULY 1989 11 practical point of view, a minimum operation and maintenance distance of 500m from housing areas problems. With regard to the design has proved satisfactory; if anaerobic method and construction, ponds are incorporated, a minimum Tanzania's technological distance of one kilometre is infrastructure is not yet equipped recommended.2 to modify or rectify a technology, The siting of ponds in Dar es whether it is called appropriate or Salaam was somewhat haphazard. capital intensive. The WSPs of Mgulani, Msasani, The Dar es Salaam experience Buguruni and Ubungo are located has shown that waste stabilization at 10m, 15m, 20m and 5m ponds will totally deteriorate if respectively from the nearest there are inadequate funds, houses. All these ponds are management and technical breeding places for mosquitoes; competence to operate and they produce foul smells and attract maintain them. Even after the flies. The direction of prevailing rehabilitation of some of the ponds, winds (during the day and at night- the newly established Department time) was another factor not given of Sewerage and Sanitation is facing A partially overgrown malfunction- proper consideration. problems: the familiar shortage of ing waste stabilization pond. technicians, transport, equipment and funds. a the designs prepared by the Assessment of the overseas consultants. technology There is a great deal of literature References on the design of ponds and the Compared to conventional 1. Mara, D.O., Sewage treatment removal of organic matter and treatment methods, pond systems in hot climates, John Wiley and pathogenic organisms, but no do not need sophisticated Sons, London, 1976. manuals giving guidelines on the technologies and energy 2. Arthur, J.P., 'Notes on the operation and maintenance of pond requirements for operation.