East African wastewater treatment and reusage

Beijing Municipal Research Institute of Environmental Protection and Tongji University recently issued Research report of Sino-Africa wastewater treatment cooperation, to analyze status quo of wastewater treatment and reuse in Africa.

One common problem that East African countries face is shortage of water resources. This shortage is compounded by the lack of basic facilities for water purification and sewage treatment, as well as underdevelopment of relevant technologies, leading to large amounts of discharge of untreated or partially treated sewage into the environment and causing a deterioration of the quality of limited clean water resources.

In Kenya, for instance, the main source of municipal sewage is from domestic uses, schools and restaurants, while industrial wastewater comes primarily from manufacturing such as pulping and paper-making, sugar, tanning, and etc. Nowadays a majority of sewage plants operate with out-dated technologies and deficient handling capacity, which causes direct discharge of large volumes of raw sewage or inadequately treated sewage.

Data from the sewage treatment database of Kenya in 2004, shows that there are 58 systems of sewage treatment in total, 52 of which adopt the technology of stabilization ponds including anaerobic, facultative and aerobic process (Table 1.2). This situation results mainly from limited funds for sewage treatment and supply of energy source, but in the long run shortcomings like overload, sedimentation of sludge and poor performance of disinfection make it difficult to meet national standards. Ruai and Kariobangi, two sewage treatment plants located in Nairobi, the capital of Kenya, with a daily handling capacity of 80,000 m3 and 12,000 m3, respectively serve as examples of the inadequacy of the situation.

Table 1.2 Sewage treatment systems in Kenya in 2004

Results of analysis about influent and effluent samples of these two sewage plants in 2010.10~12 have shown a less than optimal situation. COD, BOD and TSS of ultimate effluent of these two sewage treatment plants are far greater than the national standard, indicating their treatment process should be improved urgently (Table 1.3).

In 2003, Kenya, Tanzania and Uganda, reached an agreement on sustainable development which aims at protection of water quality of the Victoria Lake region by soft constraint on sewage discharge by neighbor countries, since researches have indicated a trend of deterioration of water quality in Victoria Lake. Kisumu, one of the port cities near the Lake, as well as a major city of Kenya, has served as a pathway for sewage discharge into Victoria Lake. 4000m3 of sewage are generated per day, but there is a huge gap toward full treatment since existing treatment plants can only handle 17,800 m3. Only 8% of city regions are served by sewage pipe network, leading to a huge volume of sewage discharge into Winam Gulf. Two sewage treatment plants, Kisat and Nyalenda Lagoons, have to undertake all treatment of sewage from the whole city.

Table 1.3 Water Quality of Influent and Effluent of Ruai and Kariobangi Sewage Treatment Plant, Nairobi (* indicates exceeding discharge standards)

In terms of quantities of wastewater treated; in 2011, Kisat WWTP treated an average of 5,371m3/day at an efficiency of 79% while Nyalenda treated an average of 4695 m3/day at 43% efficiency. The average amount of wastewater treated was 10,066 m3/day at an average capacity efficiency of 56.5%. In 2012, Kisat WWTP treated an average of 6,105 m3/day at an efficiency of 89% while Nyalenda treated an average of 5,653 m3/day at 52% efficiency, the average amount of wastewater treated was 11,788 m3/day at an average capacity efficiency of 66%.

This study was conducted for a period of two years from January 2011 till December 2012, using both quantitative and qualitative data collection methods. A literature review of related reports and documents, site visits, observations and interviews with major stakeholders were conducted. Actual wastewater sampling and analysis were also carried out, both at Kisat conventional wastewater treatment plant and Nyalenda lagoons in Kisumu. Comparing with national water quality standards of Kenya (Table 1.4), it is shown that BOD, COD and TSS of final effluent did not satisfy related standards, but all go into Victoria Lake via Kisat River and Winam Gulf.

Nyalenda lagoon is not lined, and it is possible that there is infiltration of groundwater which diluted the pollutants in the wastewater. The high concentration of COD in Kisat is due to the industrial wastes in the influent.

Table 1.4 Water Quality in Kisat wastewater treatment plant and Nyalenda wastewater treatment plant, 2012.12

Note: * means value exceeding the discharge standard.

Dandora sewage treatment plant situated in Nairobi, Kenya has been constructed in two stages in 1970 and 1990 respectively. Its treatment capacity is 90,000 m3 per day with stabilization pond treatment process covering 200 acres. The flow path is as shown in Figure 1.4.

Influent of this sewage plant includes wastewater from sugar, coffee and other industries, thus its COD is around 2,000 mg/L. The high value of COD and low efficiency of grit removal (resulting from electricity shortage) often cause poor performance of subsequent aerobic pond and with resultant COD of effluent exceeding 500 mg/L. The level of nutrient is also very high and contribute to algal bloom. For industrial wastewater with such a high COD value, biochemical process is much more promising for its treatment efficiency with less occupied area as compared with technology like artificial wetlands. There is therefore a strong need for a treatment process with high efficiency and low energy input in Africa. In addition wastewater quality discharge standards on industries that discharge into municipal drainage system in order to control COD influent to treatment plant and to achieve better treatment effects can also be drawn up and implemented by the African countries.

Current technology of sewage reuse makes it possible to utilize treated wastewater for agricultural irrigation, industrial cooling and toilet cleaning. Hindered by facilities and technology, there are few related examples in East Africa. At present, countries in East Africa are witnessing rapid urbanization and population growth, which create huge pressure on water resource due to the increasing demands of domestic, agricultural and industrial applications. Sewage treatment and reuse are of great importance for the improvement of local water environment. Most East African countries share a similar history: their initial sewage treatment plants were built by colonialists at that time; after their independence, economic development is relatively slow, and the existing sewage plants are faced with the dilemma of limited and inadequate treatment equipment and out-dated technology.