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1.Brief introduction on China-UNEP-Africa water project
The research group has studied the water resources and water environment in Africa under the auspices of China-Africa International cooperation projects supported by The Ministry of Science and Technology. The group members have done a lot of research in Libya, Egypt, Tanzania, Zambia, Kenya, Uganda and other African countries, and understood water distribution of some main countries in Africa and the processes and problems of water treatment basically. At present the group are researching African water treatment technology and engineering design, and received some African students to enter the group and engage in related work.
Professor Fengting LI was appointed by the Ministry of Science and Technology of the People’s Republic of China (MOST) as the team leader of expert committee of UNEP-MOST-Africa project. Professor Li was recognized by the United Nations Office for his special Contribution to South-South and Triangular Cooperation in 2013. Professor Li was the Special Coordinator for South South Cooperation of United Nations Environment Programme (UNEP) during 2014 to 2015.
2.Demonstration project on drinking water treatment in Nairobi
Ngethu treatment plant is the largest urban water plant in East Africa, located in the Nairobi Kenya. The water plant was built in 1971, designed by the British. Ngethu treatment plant has three phases, I, II, and III (completed in 1997) with the scale of 440,000 tons of water per day, accounting for 83% of the total water supply in Nairobi. It owns the traditional water treatment processes as shown in Fig.1. The source of Ngethu water treatment waters is Chania River while the existing coagulants are aluminum sulfate imported from South Africa.
Recently, the fluctuation of water quality in Chania river is caused by global climate change and specific season conditions change between dry season and rainy season in eastern Africa. The rain rush into raw water so heavily that turbidity increased rapidly with fluctuations as shown in Fig.3. The turbidity goes as high as about 1000 NTU from dozens of NTU within several hours. The water treatment plant can not be in the stable operation in such drastic fluctuations and sometimes even suspend the water supply due to substandard water quality. Therefore, Ngethu water treatment plant optimization is imperative.
The system optimization, which including process optimization and operational optimization, aims to lower running cost and achieve efficient operation in the premise of water supply safety. Namely, system optimization could efficiently avoid the gap between initial design and actual operation Ngethu water treatment plant is such a kind of example, in which actual operation condition is further beyond the initial design since turbidity of raw water under rainy season goes as high as 1000 NTU. The system cannot work well and substandard treated water is caused by turbidity fluctuations within 3~4 hours which is beyond the water treatment capacity and emergency operations response time.
polyaluminum chloride (PAC) has been widely used in China especially meeting the processing requirements under the current turbidity fluctuations. Therefore PAC is recommended as an alternative to aluminum sulfate. Considering the economic costs and control requirements of residual monomer content, PAM, one polymer flocculants, is not recommended in the short term in Africa.
According to the continuous 120 hours monitoring, it was found that:
1) It is conducive to solve the influent turbidity flocculation in rainy season in Africa replacing aluminum sulfate by poly aluminum chloride (PAC). It can also reduce the effluent turbidity and colority, guaranteeing the safety drinking water and avoiding water-break because of high turbidity.
2) Despite of the flocculation of raw water, the effluent in phase 1 (PAC) is better than that in phase 3 (aluminum sulfate). The turbidity in phase 1 is lower than that in phase 3.
3) When using PAC as the coagulant, the turbidity is usually within 2 NTU, far lower than the local standard in Kenya (< 5 NTU). However, when using aluminum sulfate, there is some time that not only the effluent cannot reach the standard, but also most the effluent turbidity is near the upper limit without sufficient safety margin. In other words, it cannot guarantee the quality of effluent.
4) PAC not only reduces the dosage and the cost, but also saves water, energy and labors. In addition, the back-wash times become less. In this way, finally, it can reduce the comprehensive cost.
Ngethu waterworks in Nairobi, Kenya
Demonstration project in Ngethu waterworks in Nairobi, Kenya
Professor Fengting Li is investigating drinking water treatment in Nairobi
Prof. Fengting Li and Doctor Hongtao Wang are investigating RUVU water plant in Tanzania
Green Hill, blue cities, an ecosystem approach to water resources management for African cities, by UNEP and
Professor Fengting LI is the coordinating editor
UNEP-CHINA-AFRICA COOPERATION PROGRAMME Enhancing the Role of Ecosystem Management in Climate Change Adaptation
Professor Fengting Li is one of the editors