The most common mistake when designing any water treatment plant is to make unnecessary assumptions and miss the small details that make all the difference. A Reverse Osmosis (RO) plant needs to be designed correctly for the feed water, and as the saying goes, any RO plant is only as good as the pre-treatment.
1. Feed Water
When installing a Reverse Osmosis plant it is important that a full analysis is completed of the feed water quality and the operating conditions of the proposed plant. In installing a Reverse Osmosis plant, key factors should be focused to establish good RO performance. Download this RO Guide for key factor cheat-sheet.
2. Feed Water Temperature
The volume and quality of the treated water from an RO plant can vary widely depending on the temperature of the feed water going into the plant, something to keep in mind if you are looking at installing an RO plant in the hottest parts of the world. In some cases it is necessary to cool the water prior to the reverse osmosis membranes. To verify that the plant will achieve your requirements it is recommended to complete membrane simulations at different temperatures.
3. Chlorine (Cl2)
Because chlorine will damage RO membranes you need to know if your raw water contains chlorine. If you are treating scheme or potable water for a high purity application it will almost certainly have chlorine that needs to be removed prior to the RO membranes. Chlorine can be removed by filtering the chlorinated water through activated carbon, or dosing with an antioxidant. It’s always best to have a chlorine analyser ORP meter prior to the RO membranes, that will shut the plant down if any chlorine gets through the pre-treatment so that you don’t damage the membranes.
Iron in the feed water will also damage and block RO membranes. Many RO plants are installed to treat bore water supply, which can be quite high in iron. It is important that the iron content is checked before the RO is installed. If the iron is high this can be removed with pre-treatment options including aeration and filtration or DMI filtration depending on how much iron is present.
5. Feed Water Hardness
Other forms of industrial water filter systems are used to remove excess ‘hardness’ (generally calcium & magnesium), which have the potential to cause scaling of plumbing and other undesired effects. Anti-scalents can be dosed to reduce the scaling impact of calcium and magnesium, or softening processes involve Ion Exchange, whereby calcium and magnesium ions are replaced with sodium ions, or Nano Filtration (NF).If this is not the case the RO membranes will very quickly become fouled and recovery rates will be reduced.
6. Pre RO Filtration
Filtration is frequently used as ‘pre-treatment’ of raw water, in order to remove suspended solids prior to desalination via Reverse Osmosis (RO). The type of pre-filtration required will depend on the level of suspended solids in the feedwater, turbidity and silt density index. Typical RO pre-treatment systems include Multimedia Filtration (MMF), Ultra Filtration (UF), or cartridge filtration.
7. CIP Cleaning / Membrane Services
In an effort to reduce costs many RO units are installed without the facility to clean the membranes. This can be a false economy as very often users end up replacing RO membranes. As membrane fouling is inevitable, even with the highest quality inlet water; effective cleaning maintenance and monitoring is required. An effective CIP process will clean the membranes without damaging them. The performance of the CIP will depend on the velocity of the CIP solution across the reverse osmosis membranes, the chemicals used and the temperature.
MAK Water has over 25 years’ of experience in the design, manufacture and maintenance of RO plants, as a result can supply a system exactly tailored to your needs. We work collaboratively with each client to review site specific requirements and define the best treatment process in order to ensure regulations are met. Whatever the requirement is, we have a solution ready to implement.
MAK Water designs and manufactures a range of RO plants, including:
- Sea Water Reverse Osmosis (SWRO)
- Brackish Water Reverse Osmosis (BWRO)
- Brackish Water Reverse Osmosis – Basic (BWROB)
- Demineralised Water Reverse Osmosis (DWRO)
View our project experience here.