Although dissolved air flotation (DAF) has been successfully adopted for water and wastewater treatment, the fundamental characteristics of the process have not been fully investigated. According to recent theoretical work on DAF, bubble size is one of the most important factors that affect the efficiency of the process, with better removal efficiency when the sizes of both bubbles and particles are similar. In this study, a newly developed particle counter method (PCM) was introduced to measure particle sizes. To confirm its usefulness, the results were compared with those from image analysis. Then, using PCM, the size of bubbles in DAF was measured under various pressure conditions which are known to affect the bubble size the most (from 2 to 6 atmospheres). The bubble size decreased as the pressure increased up to a pressure of 3.5 atmospheres. Above this critical pressure, the bubble size did not decrease with further increases in pressure. According to these experimental results, it is not only costly, but also unnecessary, to maintain a pressure above 3.5 atmospheres if the goal is only to generate smaller bubbles.
In the era of ubiquitous service, the new service opportunity is closely related to user. User-centric approach takes into account user context in new service development. However, attempts to apply user context is insufficient to identify opportunities, since the opportunity is at least user's potential needs, which are not satisfied yet. In response, this paper proposes a "user-centric service map" to visualize existing services based on a priori dictionary of potential needs and investigates the vacuum to take concrete shape of the opportunities. At first, a potential needs dictionary is constructed as location, event and objective. Next, the service map is developed based on the evaluation of existing services from Apple App Store for each dimension. Finally, a new service opportunity is identified by analyzing the characteristics of vacuums of the service map and exploring how to satisfy the vacuums using related services for reference.
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