Vertical-axis wind turbines (VAWTs) are receiving more and more attention as they involve simple design, cope better with turbulence, and are insensitive to wind direction, which has a huge impact on their cost since a yaw mechanism is not needed. However, VAWTs still suffer from low conversion efficiency. As a result, tremendous efforts are being exerted to improve their efficiency, which mainly focus on two methods, regardless of whether the study is a CFD simulation, a field test, or a lab test experiment. An active approach involves modification of the rotor itself, such as the blade design, the angle, the trailing and leading edges, the inner blades, the chord thickness, the contra-rotating rotor, etc., while the second approach involves passive techniques where the flow is directed to optimally face the downwind rotor by mounting guiding vanes such as a diffuser or other shapes at the upwind position of the rotor. Among all the techniques undertaken, the counter-rotating wind turbine (CRWT) rotor technique seems to be the most effective, with an output comparable to that of horizontal-axis wind turbines (HAWTs), while the Savonius rotor has received more attention compared to other VAWT designs. Apart from technological issues, it has also been suggested that geographical issues, such as proper site siting of a wind turbine rotor at a particular location where a uniform flow can be guaranteed, are of paramount importance to ensure an effective conversion capacity of wind turbines. Thus, this study has successfully highlighted the latest improvements in augmentation methods and has established a solid foundation for future research aimed at improving the efficiency of VAWTs.

Vertical-axis wind turbines (VAWTs) are receiving more and more attention as they involve simple design, cope better with turbulence and are insensitive to wind direction which has a huge impact on the cost since the yaw mechanism is not needed. However, VAWTs still suffer from low conversion efficiency. As a results tremendous efforts are exerted to improve its efficiency which mainly focus on two methods regardless of whether the study is a CFD simulation or a field test or lab test experiment. An active approach which involves the modification of the rotor itself such as the blade design, angle, trailing and leading edges, inner blades, chord thickness, contra-rotating rotor, etc. While the second approach involves passive techniques where the flow is directed to optimally face the downwind rotor by mounting a guiding vane such as a diffuser or other shapes at the upwind position of the rotor. Among all techniques undertaken, the CRWT rotor technique seems to be the most effective with an output even comparable to that of Horizontal Axis Wind Turbines (HAWT), while the Savonius rotor received more attention compared to other designs of VAWTs. Apart from technological issues, it was also suggested that geographical issues such as proper site siting of the wind turbine rotor at a particular location where a uniform flow could be guaranteed is of paramount importance to ensure an effective conversion capacity of wind turbines.

Membrane bioreactors (MBRs) have been extensively applied to municipal wastewater treatment. Nevertheless, MBRs cannot eliminate nutrients to an adequate level without extra operation units and intensive chemical supplies. Furthermore, low temperatures destroy the performance of the MBR process. In this work, a pioneering anammox membrane electro-bioreactor (MEBR/anammox) system was designed and operated at a constant flow rate of 7L/d with continuous monitoring of sludge liquor temperature (8–22 °C). The MEBR/anammox worked with a sludge retention time (SRT) of 20 days and a hydraulic retention time (HRT) of 24 h. It was found that temperature variations did not significantly influence the effluents quality in terms of nutrients and COD. At lower operating temperatures, the effluent concentrations of $\mathrm{N}{\mathrm{H}}_4-\mathrm{N}$, TN, $\mathrm{P}{\mathrm{O}}_4-\mathrm{P}$, and COD in the MEBR-anammox were 0.77 mg/L, 6.42 mg/L, 0.80 mg/L, and 24.95 mg/L, respectively. The corresponding removal efficiencies were 94.46%, 88.62%, 95.60%, and 90.76%, respectively. Taken together, the implementation of a low/periodic direct current (DC) of 14.85 A/m² and anammox process inside the MBR, achieving a MEBR/anammox, was found to enhance the efficacy of the treatment system, improve sludge properties and increase membrane fouling control in low-temperature milieus compared to traditional MBR. The MEBR/anammox system, introduced in this work, establishes an innovative wastewater technology that minimizes the footprint, capital and operating expenditures of the plant. In addition, this system could open new prospects for the treatment of municipal sewage in cold regions.