Abstract
Passive screen intake systems provide a higher degree of reduction in impingement and entrainment compared to open-ocean intake structures, such as channel and velocity cap intake systems. The system consists of a wedgewire screen structure with a conveyance pipeline to the plant facility and a pumping station. Commonly, the screen structure contains a semi-automated cleaning system that uses bursts of compressed air. Passive screen intake systems exclude a large part of the marine biota by using a relatively small screen aperture and a low inflow velocity. Screen slot aperture is commonly less than 3 mm and depends on environmental regulations pertaining to the specific site location. The range in design intake velocities through the screen ranges from 10 to 15 cm/s, again depending on local regulations. The current motion across the screen structure also sweeps small organisms off the screen and helps exclude them from entrainment into the inflowing water. The degree of environmental impact on entrainment of ichthyoplankton is greatly dependent on the design of the passive intake system and the current velocity. Some environmental impacts occur when constructing the connecting pipeline across or beneath the seabed and surface zone of the shoreline. Passive screen intake systems can provide a high-capacity SWRO plant with the required feed water. However, when the passive screens are located offshore, there is some complexity in the maintenance of the screens that can limit use of the technology.