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Abstract: A pump can be used as turbine and has good application in micro-hydropower schemes. Pump as turbine (PAT) is one of the best alternatives for fulfilling the energy demands and providing the electricity in remote and rural areas. In this study a review on the work done in the area of pump working as turbine has been explained. Based upon the literature survey, analytical, experimental and computational works on pump as turbine have been discussed. Several methods for predicting the behaviour of pumps in turbine mode have been developed but no method is appropriate for the entire range of specific speeds. Computational fluid dynamics (CFD) is also used to study the reverse operation of centrifugal pumps, but still results are not yet acceptable. [Copyright &y& Elsevier]

Hydropower is considered as one of the most convenient and popular renewable energy technologies and its capacity is growing rapidly throughout the world. Its rapid deployment also comes up with various environmental issues which cannot be neglected at a glance. Previous studies had imposed questions about its sustainable nature and now it becomes important to think about the sustainability of hydropower projects so that the technology would grow effectively in future. This paper reviews the status of research on environmental assessment of hydropower projects. The factors which affect the environmental impacts associated with hydropower generation are also explored. It is found that environmental impact assessment of hydropower projects must be performed considering all aspects and factors which affects the environmental impacts associated with hydropower projects. Most of the previous studies are focused on the estimation of GHG emissions so it is necessary to give emphasis on other environmental impacts like acidification, land use, energy consumption etc. and also consider biomass decomposition in submerged land. In fact it is not worthy to predict the sustainability of hydropower projects without considering almost all biophysical impacts associated with them. The paper also compares large and small hydro considering all sustainability assessment factors. Small hydropower projects are considered as a good alternative to control the problems associated with large hydropower projects but still many studies found that so many issues are associated with small hydro as well which cannot be neglected completely. Image 1 • Factors that influence the environmental impacts of a hydropower plant are summarized. • Current status of research related to sustainability assessment of hydropower projects is discussed. • Comparison among Large and Small Hydropower in respect of sustainability is provided. • Improvements required in the future research in order to obtain more realistic and useful results are outlined. [ABSTRACT FROM AUTHOR]