Conceptual approach for an energy-autonomous water treatment system for developing countries ─Case study of Kenya rural areas─

Water and energy are very essential commodities needed for the well-being of both flora and fauna and also for the country’s economic growth and development. The United Nations’ (UN) sustainable development goals (SDGs) advocate for availability and sustainable management of water and sanitation for all (SDG 6). Similarly, SDG 7 on the other hand champion for access to affordable, reliable, sustainable and modern energy for all by 2030. Despite these committed efforts, nearly 2 billion people worldwide still lack access to safe drinking water with around 800 million living in Sub-Saharan Africa (SSA). Similarly, nearly 700 million people worldwide still lack access to electricity, with close to 80% of the population living in the SSA. Globally, urban areas are well supplied with improved water sources and grid connection than rural areas. Rural areas in developing regions such as SSA suffer the most from lack of access to both improved water supply and energy provisions. This has led to increased cases of water related deaths and poor health related issues arising from consumption of contaminated surface water and excessive use of fossil fuels in the low- and middle-income countries. This dissertation study aimed to presenting a conceptual approach for an energy-autonomous water treatment system for developing countries with case study of Kenya’s rural areas. To achieve this objective, the study involved a publication based structured approach (cumulative dissertation) to undertake four specific objectives namely (i) to conduct literature research on the state-of-the-art of hydrokinetic turbine technology (HKT) in developing countries, (ii) to develop and experimentally test the laboratory performance of HKT, (ii) to experimentally test the field performance of the HKT and (iii) to develop a low-tech water pretreatment system operated by the HKT. The first specific objective was achieved through a review article on the status of HKT in Africa and is presented in chapter 2. The second specific objective was achieved by conducting laboratory experiments to assess the performance of the HKT at the laboratory settings. This investigation involved the assessment of four varied flow augmentation structures namely: nozzle 1, nozzle 2, nozzle 3 and Diffuser_type 1 for acceleration of flow towards the rotor. The flume experiment was conducted by increasing the flow in the flume from 90-150 l/s with a 10 l/s incremental steps. This resulted to a measured approach flow velocity (velocity of flow in the flume) of 0.166-0.253 m/s respectively. At an approach flow velocity of 0.166 m/s, the accelerated flow was found to be 0.611, 0.687, 0.538 and 0.480 m/s for nozzle 1, nozzle 2, nozzle 3 and diffuser_type 1 respectively. Nozzle 2 had the best enhancement of the approach flow velocity with a factor of 4.139. Similarly, nozzle 2 performed well in accelerating the flow with a factor of 1.124, 1.277 and 1.431 when compared to nozzle 1, nozzle 3 and diffuser_type 1 respectively. At an approach flow velocity of 0.166 m/s in overflow condition, the loaded output voltage registered was found as: Nozzle 1 (6.522 ± 0.110 V AC; 7.133 ± 0.181 V DC), diffuser_type 1 (5.345 ± 0.130 V AC; 5.452 ± 0.060 V DC), nozzle 2 (7.091 ± 0.177 V AC; 8.009 ± 0.096 V DC) and nozzle 3 (6.144 ± 0.027 V AC; 6.647 ± 0.056 V DC). The third specific objective was achieved by conducting fieldwork experiments to assess the performance of the developed HKT at real life environments. Nozzle 2 was chosen due to its exemplary performance and reproduced for fieldwork investigation in Kenya. Two distinctive flow velocities of 0.800 m/s and 1.200 m/s were measured during the times of field investigation. An average output voltage of 9.605 ± 0.089 V AC and 10.282 ± 0.053 V DC (equivalent to 11.543 ± 0.021 W) was registered for the flow velocity of 0.800 m/s. Similarly, average output voltage of 17.224 ± 0.195 V AC and 17.715 ± 0.186 V DC (equivalent to 37.129 W) was measured for the flow velocity of 1.200 m/s. An average performance based on water to wire efficiency of 0.97 was realized for the entire system. The fourth specific objective was achieved by conducting a laboratory performance of a horizontal roughing filtration (HRF) process as a low-cost pretreatment option. This is intended to be adopted for surface water pretreatment before the subsequent application of slow sand filtration (SSF) process. The HRF was fed with synthetic water of turbidity in the range of 300-450 NTU. The system was operated at filtration rates ranging between 0.35-2.00 m/h. The effluent turbidity ranged between (8.85 ± 2.98) -(25.02 ± 2.84) NTU with an average removal efficiency of 94%. Operating the HRF at 0.35 m/h produced the most desirable effluent for instant SSF influent. Other filtration rates were good enough for an effluent that can be fed into the SSF in accordance to the WHO’s guidelines. The study provides detailed conceptual approach on the research and development (R&D) undertaken to develop a low-cost HKT for power generation by harnessing the kinetic flow of rivers. A low-cost surface water pretreatment system was also setup and tested and found to be viable for use in providing access to safe drinking water. The overall project combines the work on hydropower utilization using simple hydrokinetic turbines and the method investigated for water treatment, in that the energy generated by the turbine can be used to operate the water treatment plant. However, both components (turbine and water treatment) can also be used/operated separately/independently.