What are the Criteria for Designing Seawater Reverse Osmosis Systems?
When designing something, such as a machine, program, or process, there are always some important factors to consider in determining the validity of the design.
For the past decade, water and wastewater treatment methods have focused on developing solutions to the epidemic of water scarcity, with a further focus on sustainability.
One of the criteria to consider when designing a SWRO system is that of the seawater uptake process and the concentrated brine drainage process flow back into the sea. Another important criterion to consider when designing a SWRO system is the planning of the pre-treatment process based on the water quality at each location.
Below is a brief explanation of why these above processes are so important and some of the ways you can handle them-
Ingestion: The main concern with ingestion is the potential for exposure and migration of marine life.
Entrain: Trapping one substance into another.
In this context, ingest refers to a larger organism that attaches to the mesh screen around the entrance. Entrainment, on the other hand, is a small creature that can traverse the web. Together they simply refer to the collective removal of marine organisms by the uptake system.
There is still no definitive numerical evidence that impingement and entrainment cause significant changes in the surrounding ecosystem. This is because it is difficult to evaluate. However, these impacts and entrainment issues with traditional mesh inlet screen systems can lead to significant increases in operating costs. These operating costs are associated with associated chemical costs due to sieving, increased energy consumption of suction pumps, and fluctuations in water quality.
There are several ways to deal with collisions and entanglements-
1: Location and Design of Coves
Coves can be located in areas with low biological productivity or low levels of marine life. The cove can also be designed with a higher recovery rate. This means less water needs to be drawn from the sea. A special slow inlet allows marine organisms to escape the induced flow from the inlet pump and reduce sediment/sludge uptake from the seafloor. This process helps avoid entanglement and collisions.
2: Intake Types
When planning a SWRO system, there are different types of intake sockets, which can be divided into two main groups: surface and underground.
The most common cove systems are surface coves, including deep-sea coves, land coves, and offshore coves. Because they are open directly to the ocean, they combine location, barriers and deterrence to reduce impact and entanglement. The underground cove is below the seabed, so it does not cause shock or drags and has the added benefit of natural filtration by sand. Such a system includes 4 types of wells and 2 types of galleries.
3: Barriers and Deterrence
It can be as easy as installing a wall or barrier to keep fish out of catch. Barriers, such as nets, travellers, and passive screens, physically prevent organisms from getting too close to the entrance. Detergents prevent marine life from approaching by targeting avoidance responses such as air bubbles, flashing lights, sound generators, and speed limits.
Brine Concentrate Emission is the purpose of the emission system and is an integral part of the SWRO design. As with ingestion, the main concern about saltwater discharge is the potential harm to marine life from increased salinity in saltwater spills. Concentrated salt water is denser than the average seawater. Therefore, when salt water is drained, it sinks to the seabed. This increases the local salt content of the ocean and can adversely affect organisms that are sensitive to changes in the composition of the surrounding water.
Here are some options for improving drainage system:
Rather than pumping all the brine concentrate from a single pipe, diffusers can be placed in series along the pipe to facilitate mixing and prevent brine from settling on the seabed. There is also a special slow diffuser that can improve the diffusion and dilution of brine over a wider area.
Salt water is dangerous because it is concentrated, but salinity decreases when diluted with more water. Diluted water can be obtained from sewage treatment facilities, power plant cooling towers, or purified wastewater from other industrial resources if near these facilities.
3: Tunnels and drains
These systems are a large network of pipes buried under a thin layer of sand. By spreading the brine in this way, the brine is slowly reintroduced over a wide area and the mixing can occur naturally.
Zero Liquid Discharge (ZLD)
These systems are becoming more and more popular in many industrial SWRO plant design applications. However, it can be costly to operate. Reusing seawater desalination emissions using the ZLD system requires a thermal evaporation process due to the salinity of the effluent. Subsequent crystallization processes will be required to extract and dry the salt from this brine for sale accordingly.