Life Cycle Assessment of a small scale, solar driven HVR water purification system

Abstract: Water purification systems have made access to drinking water easier by treating water sources which previously could not be used for drinking. Such systems however require energy and materials to build and operate which means they have environmental impacts. This thesis performs a cradle to grave life cycle assessment of a solar driven HVR water purification system used to treat contaminated groundwater in Odisha, India. The system has three subsystems each with different components – a water purification subsystem that uses an air gap membrane distillation (AGMD) process to purify ground water to produce drinking water, a solar photovoltaic subsystem to provide electricity and a solar thermal subsystem with evacuated tube collectors to provide hot water. The timeframe of the study is 15 years and the chosen functional unit is 590 m3 of drinking water produced over 15 years. The environmental impacts of the system are evaluated using the ReCiPe Midpoint (H) impact assessment method and the life cycle is modelled in the software SimaPro using the Ecoinvent database for inventory data. A comparison is then made between the lifecycle impact of a solar driven HVR water purification system and a grid driven HVR system as well as a water purification system with conventional end of life treatment and a system with state of the art end of life treatment. Along with the lifecycle impact, the levelized cost of water of the water purification system has also been calculated. The results show that within the entire system the solar PV subsystem has the highest impact due to the high electricity consumption during silicon purification for manufacturing the solar panels. The solar thermal subsystem has the next highest impact with the biggest contributor being the manufacturing of glass tubes for the solar collectors. The water purification subsystem has the least impact with the highest share due to use of acetic acid during its use phase for maintenance. The modelling results focus on four impact categories and show the following life cycle impacts - global warming potential : 27 180 kg CO2eq, human carcinogenic toxicity : 2 412 kg 1.4-DCB eq, marine ecotoxicity : 2 662 kg 1.4-DCB eq, freshwater ecotoxicity : 1 967 kg 1.4-DCB eq. The grid operated system shows a lifecycle impact 70 to 170 times higher across these four impact categories compared to the solar driven system. This is due to the high share of fossil fuels in the Indian electricity grid. The state-of-the-art end of life treatment shows a 17% and 22% reduction in freshwater as well as marine ecotoxicity impacts of the system compared to conventional end of life treatment with negligible impacts on global warming and human carcinogenic toxicity. The levelized cost of water calculations show that the system with its current runtime of 6 hours when run using solar energy or the grid is not economically competitive compared to bottled water in India. A sensitivity analysis is then performed to evaluate the sensitivity of lifecycle impact to maintenance frequency and the lifetime of components and the sensitivity of the levelized cost of water to discount rate and the production cost of AGMD modules. The analysis shows that only the lifetime of components has a significant influence on the life cycle impactof the system, the maintenance frequency has a significant impact on freshwater and marine ecotoxicitywhile the discount rate and production cost of AGDM modules has no impact on the levelized cost of water. In conclusion the findings of this thesis agree with the major findings of previous studies done on the topic and adds to the limited knowledge in the literature on the life cycle impact of solar powered AGMD systems.