In a containerized
From time to time there may be reasons why you would not retrofit a normal freshwater maker package to your machinery room. You may need the freshwater supply only for a limited time period, or there could be a case where there are practical limitations preventing such installation. In these cases, a containerized system on deck may be the ideal solution.
In a containerized system all parts and equipment are installed and fixed inside the container, including pre-treatment, post-treatment and all piping and cabling.
Reverse Osmosis Container Interface points will be:
- Sea water in
- Potable water out (to tank)
- Waste water out
- Freshwater supply for flushing
- Electric supply
- Pilot air supply
Problems With Reverse Osmosis
Scaling occurs on RO membranes when the concentration of scale-forming species exceeds saturation, producing additional solids within the RO feedwater. Scalants include such chemical species as calcium carbonate, calcium sulfate, barium sulfate, strontium sulfate, and reactive silica. Since these species have very low solubilities, they are difficult to remove from RO membranes. Scaling decreases the effectiveness of the membranes in reducing the solids and causes more frequent cleanings. A scale on a membrane provides nucleation sites that increase the rate of formation of additional scale.
Methods to minimize scaling
Magnesium hydroxide tends to absorb silica, another scalant. Another softening procedure involves zeolite in an ion exchange process.
Often used with acidification, or by itself, are antiscalants. Antiscalants are chemicals added to wastewater to minimize scale carbonate or sulfate based scale. They consist of acrylates and phosphonates which inhibit the precipitation of carbonate or sulfanates.
Methods to prevent fouling
The second problem with reverse osmosis is with the fouling of membranes. Fouling occurs when suspended solids, microbes and organic material deposit on the surface of the membrane. Another problem is from colloidal sulfur, which when oxidized from H2S can foul RO membranes.
Coagulation is one technique that neutralizes the negative surface of the suspended solids, allowing the particles to cometogether. These large particles are then easy to remove from the water using filtration. The most common coagulants used are cationic polymers, inorganic salts, and aluminum and iron salts. Inorganic solvents tend to form large particles, while catonionic polymers require much less product for coagulation. Similar to coagulation is the clarification method, which destablizes suspended particles through charge neutralization. This is generally done by oxidizing iron and manganese and physically removing the precipitates in the manganese greensand bed.