# Design and Optimization of Piezoelectric-Powered Portable UV-LED Water Disinfection System
## 1 Introduction  
Environmental pollution has been threatening human life with the increase of industrial areas and population. Although sufficient and clean water accessibility is recognized as a human right by the UN General Assembly [1], 785 million people lack even a basic drinking-water service. Even microbiologically polluted drinking water causes 485,000 diarrdeaths each year [2]. Thus, the improvement of effective water treatment systems as well as innovative approaches, particularly for inactivation of pathogenic microorganisms in water, is of great importance for human well-being and prosperity [3]. Over the last decades, various water cleaning methods have been developed to overcome this problem. The most common one is chemical water disinfection, also known as conventional disinfection. However, the systems based on chemical water disinfection have some disadvantages, such as inefficiency to destroy some specific microorganisms, difficulties in the storage or transportation of chemical ingredients, harmful sediments that remain after the chemical process, the corrosive effects of chemical reactions on the system (need for maintenance). As an alternative, another method is using ultraviolet (UV) disinfection to have microbiologically clean water. Many studies have shown that UV radiation can influentially kill and deactivate pathogenic microorganisms [4, 5]. Therefore, UV disinfection has several advantages compared to chemical water disinfection, including lack of chemical addition and harmful disinfection by-products formation, as well as its effectiveness on chemical-resistant bacteria [6]. In literature, there are many water disinfection systems utilizing UV radiation and they can be evaluated in two different aspects: electrical power source and UV light source. Certain UV water disinfection systems use photovoltaic panels [7, 8], and the electric network as an electrical power source. Photovoltaic-panel-powered systems typically require photovoltaic (PV) cells-based solar energy which makes them fragile and so unsuitable for extreme conditions. Battery-powered systems have a very limited lifetime due to the capacity of battery cells, or size and weight constraints of the battery. Furthermore, batteries may not be stable in extreme temperature conditions and they can pollute the water [9]. Therefore, UV water disinfection systems powered by electrical battery cannot be used effectively in the field. In this regard, piezoelectricity may pave the way for powering portable UV disinfection systems. Piezoelectricity could be an effective energy harvesting mechanism for powering portable UV water disinfection systems. It may simply generate the required energy by applying mechanical stress, for example, simply shaking or vibrating by the user [10]. Various piezoelectricity energy harvesters have been developed and tested so far, such as a walking charger based on piezo-electric material [11], lead-zirconate-titanate (PZT) material, the Quick Pack (QP) actuator, the macro-fiber composite (MFC) for recharging batteries [12], and piezoelectric energy harvesters based on vibration [13]. To some extent, even natural vibrations can be used to supply the required power for UV water disinfection systems. On the other hand, the type of the UV light source also plays a critical role in UV water disinfections. Generally, UV water disinfection systems may use UV mercury lamp [14], or concentrated sunlight [15] or UV light-emitting diode (LED) [16]. UV mercury lamp-based systems have some disadvantages, including large physical size, narrowband radiation, toxic ingredients (mercury) and high energy consumption [17]. Sunlight-powered water disinfection systems require continuous sunlight, and should be large in physical size to generate the required energy levels. Besides, the optical components of these systems are fragile and inappropriate for harsh environments.