Desalination What is it? How does it work? What is involved? Why do I need it? What do I need to do?
Desalination is Reverse Osmosis Filtration • The word desalination is an adopted general term for reverse osmosis filtration. • It is actually membrane filtration by rejection. • It is rejection of the undesired excess mineral base ion in a water supply that is not suitable for use as desired. • It will also remove trace and toxic elements • How is Reverse Osmosis achieved? • It is achieved applying pressure to a flow of water forcing it through a tightly wound semi permeable composite material wrapped around a perforated rod. • This is housed in a pressure chamber. • The passage of water is held back from open flow through the material by a valve control or flow restrictor at the reject or other end.
Reverse osmosis process • The pressure drop between the feed end and the reject end forces only the finest water through into what is called the product tube and this is called the permeate. • The excess mineral base flows through the reject. This is the concentrate of rich mineral content which goes to drain called just that, concentrate. • It is the osmotic pressure difference between the permeate and the concentrate within the housing or chamber that creates the osmotic pressure effect, reverse osmosis. • The feed water can flow back through the semi permeable membrane as pressures vary thus the true term osmotic pressure
How does it work? • Pressure is applied to the front of the reverse osmosis membrane and forced through the wrap by placing a seal called a brine seal between the outer membrane and the vessel. • Pressure is applied to feed side of the membrane. • On a simple household system, tap pressure is often enough. • Domestic reverse osmosis systems are limited to about 800-1200ppm total salts feed water and will generally reduce the salts level to better than 10% , or 80ppm.
Percentage Rejection • This table gives a clear picture of the rejection of excess unwanted minerals, trace and toxic elements. • It must be understood that this is a guide only
Whole of house reverse osmosis filtration • This is commonly called desalination. • We use reverse osmosis membranes and these are typically called 4040’s are over a metre long and about 300mm wide. • These can produce up to from as low as 1.5 litres per minutes to 4 litres per minute depending on feed water quality
Class of feed water • The class of feed water really impacts on the production. • The higher the salts level in ppm, the lower the production. 6000ppm can reduce the production down to 2 or even lower to 1.5 litres per minute or we lift the pressure to compensate. 1500ppm up to 3000ppm can easily produce around 4 lpm.
Desalination • Historically desalination plants can be oversized, cumbersome, slow to build and overpriced. • They are often hard plumbed in ABS (high pressure plastic and special glues) that pushes up the cost and time needed to build. They need bigger frames and are a space waste. • Panel mount pressure gauges are used that require water to be plumbed to them, more cost.
Desalination controls • The electric controls of many designs remain cumbersome , outdated and fall short of making life easier for the user. • Pre-filtration is often externally built and mounted using more room. • Chemical dosing is often inaccurate. • Manuals of operation are difficult to follow. • The owners are all too often left in the dark as to “How does it all work?
Introducing Modern Desalination • Compact – the size of a large refrigerator • Built quickly – One day • Simplicity • Very advanced equipment controls that make everything look as it is – simple • Highly protective – good levels of safety equipment • Installation generally in one day and easy training The First Generation Water Doctor desalination plant
Stylish, simpler, more compact! • In that size as shown we can fit • From 2 Up to 10 membranes if required. • From 1 up to 2 system pumps • Two pre-filters • 1 or 2 chemical dose pumps as required. • Complete automatic system start with compact simple software control. • Modem control is an option so that we or you can monitor the operation and the machine will dial us when a fault occurs. Adds about $1500.00 in costs at the moment.
The base desalination unit • Two membranes • One system pump • Two pre-filters • One chemical dose pump • Standard software control • Produces 7000 litres of quality water or more
The most popular unit • Three membranes • One system pump • Two pre-filters always • Chemical dose pump • Software control • Produces up to 17,000 litres per 24 hour day
Each component in more detail • 316 Stainless Steel frame and face plate • All metal fittings in stainless steel • Chemical dosing pumps(1 or 2) • Pre-filters. • System pump • Membranes • Flow meters • Plumbing • Control panel • Safety protection • Option to go modem and dial in • Software operation
Chemical dosing • Why do we need this? • Calcium and magnesium are hardness ions and both will block and destroy membranes quite quickly. Calcium will deposit on the membranes surface when mixed with oxygen and the flow will slowly die off. The pressure rises and the machine stops producing permeate water. This is called scaling. • Both iron and manganese have no place in a membrane and either remove them prior or control them. We do this chemically.
Dosing • We use a computer controlled dose pump for ease of use and accuracy that powers off the control panel and shuts off with the panel. • The anti-scalent is one of the worlds best and is diluted down for use. Auto dose pump
How does anti-scalent work? • We use a chemical compound that is harmless to handle generally called anti-scalent. Quite essential in membrane filtration to keep membranes flowing. • The chemical wraps the ions, trace elements, and toxics into an inert bundle and takes them through the membranes reject side only and out harmlessly. Yes, quite clever, but this does have limitations.
Limits!!! • If the calcium and magnesium levels are high, the iron level is high and other items that cause damage such as silica, barium, boron, strontium, etc., then you may stretch the friendship too far and stress the membranes for performance and then scale starts to form where it should not be and production drops off. • We seek to avoid that problem. • We can accurately identify these issues early and apply extra pre-treatment, as and if required.
Second Chemical • There is a trace element that is difficult to detect but can be very damaging and needs simple chemical dosing to stop it causing damage. It is Iodine. • Iodine is a very high oxidiser and will rapidly destroy membrane surfaces. • We dose with a reducing agent that converts it to a harmless salt and it is no longer a problem. This does a require second dose pump and another chemical
Sediment filtration • Extremely fine sediment filtration must be used in any desalination system to clean the water supply to high levels of at least 1 to sub micron levels. • We use two 20” filters that are 4.5”wide for good filter coverage and flow. • We use a 5 micron absolute rated filter cartridge followed by a 1 or .35um pleated.
The pre-filters • We use high quality commercial grade filter housings that simply will not break. We do apply high pressures to them at times so this is essential. • We use an accurate, high quality string wound sediment filters that do not collapse. • We then follow this with a pleated .35um. This is an excellent combination for this work. It really cleans the water to the level needed.
Filters Membrane housings Filter housings
Carbon filtration not required • Carbon filtration is not required for desalination work except where it is used against chlorinated supplies. • Chlorine will destroy membranes very quickly.
Lowara Stainless Steel pumps • High quality well backed vertical mulit – stage system pumps built in 304 stainless steel or 316 with very nasty water.
Higher pressures • We need to lift the pressure up quite high for membrane filtration. For low energy membrane filtration from as low as 130 psi right up to 220psi for higher pressure brackish membranes. • High energy membranes simply needs more horsepower in the pump to achieve that pressure level. • Typically we start at 1.5KW then 2.2KW pumps and up to 3-4KW when using 10 or more membranes. The power draw requirements are always much less when on 3 phase power supplies
The membranes • The reverse osmosis membranes are the heart of the system. We can use low or high energy, the former is less power produces more water at less pressure and will take 3000ppm down to 150ppm. • We also supply only membranes with anti-fouling ability. This is quiet a critical decision designed to protect your investment
Water Softener • We can add an iron removal water softener for pre-treatment when the iron is a real problem or a variety of other measures to stop or control when some elements are in excess and likely to cause problems. • This is applied to the ensure that feed water quality is high enough and controlled for membrane filtration. • The standard must be quite high. Typicalwater softener set up
Flow meters • These are a simple affair and measure the production of water and the amount rejected by a floating piston movement.
Plumbing • Perhaps the simplest yet more advanced and lower cost method of construction. • High pressure flexible hose is used throughout the plants for efficiency in building and operation to avoid friction losses. • High quality 316 Stainless Steel fittings are used • Quality low pressure plastic push fit permeate and reject hose and fittings. • Simple hose connections for feed in, reject to drain and product water. • Allows for flexibility of change when required.
Safety systems protection • The system pump through to the membranes needs protection for failure in water flows to prevent pump burnout. • We fit three electronic pressure transducers to perform these functions that feed back to the software controls. • Low and High pressure transducers protect either end of the membranes and pump.
Software control • The software starts and stops the machine automatically. • The digital display shows filter pressure, system pressure and reject pressure but is optioned to go further. • Standard format provides re-start ability and auto re-start off a tank float switch. • Night rate starts are built in the program Control Panel
Software display start up • At the start, once the button is pressed, the software opens a control valve and then flow commences. • A 120 second count down follows allowing water to flow through the membranes and eventually out through the reject and product flow meters. • This can be pressure off the bore pump or a feed pump and can start the bore if required. • This requires a secondary low volt control and cabling to the power supply.
Systemstart • Once the 120 second count is completed, the system will attempt to start the main pump and all associated equipment involved. • If successful, the screen will display the pressure readings expressed in kpa. • The machine is running. • When the tank being fed is full, the machine will switch off and display Tank Full.
Systemfaults • If the filters become blocked or the feed pressure drops below an accepted level of safety, the control panel will switch off and display Low Pressure Filter. Change the filters. • If the membrane system or reject pressure goes above the maximum safe level, then the machine will again switch off and display High Pressure. Call us!
Modem Option • We can offer many options, the newest being modems to be fitted in to allow us or the owner to dial in to view panel display, and to re-start remotely. • The modem will also dial out to notify of any fault. • We are also looking to adapt digital salt readings on the same display that are at the moment on a separate display.
Filterchanges • We make sure that the pre-treatment is sufficient in most normal cases and filter changes need then to occur about every month. • With poor quality water this can increase to weekly. • We offer a chemical cleaning service to keep both filters and membranes alive and clean which can be quite a costs saving. • Many desalination plants do not need this but where iron is present, may require it.
Chemical top ups and service • We supply a 60 litre plastic drum and top up the diluted mix about every three months if the customer requests. • We supply enough anti-scalent chemical for at least 12 months. • At this time the dose pump is checked to make sure that it is holding prime and this can be checked at the same time with filter changes. Very simple task.
Waterquality • We have added on line salt sensors that will indicate performance in and out. • Is the water potable? • In most cases as good as rainwater if the output salts level is low at less than 100ppm. • It is recommended that permeate water stored in tanks be disinfected by a simple ultra violet system as it is being pumped for use and consumption. This make it bacteria free.
How to order • We start with the water sample and or site visit, then we process the sample • Await results, then upon receipt, design, quote and send out proposal for acceptance • Upon deposit, build the plant to suit, test in factory, deliver, install, connect all services, commission and operate. • Train users/owners/manual of operations
Installations • The desalination plants are like any equipment once under cover will last longer. • We need to site visit assess the distance from the bore to the proposed site of the plant • The distance then to the storage tank • The layout of the shed or the shed to be built, power, etc. • How far we need to run plumbing, float switches, etc. • Excavation as required for plumbing and pumping and drainage.
ServiceLife of Equipment • Dosing pumps are serviced bi-annually and need low cost seal replacements • Filter elements will last as long as the duty is applied and the cleaner the feed water the longer the life expectancy. Filter costs are as per table in separate document. We supply enough usually to cover the first year of use. • Membrane life can be from 3 to 5 years. Costs as per table as filters. • Chemical anti-scalent is as per table, we start off with 20 Litres of chemical.
Plantowner service • The plant is fully commissioned • We encourage the owners to record readings and track performance • Charts are offered and commenced. • We encourage these to be maintained. • Filter changes and chemical top ups are encouraged by owners or we can be contracted.
Training • We then train the owner or staff or simply provide the support. • Laminated signs are displayed • The operating manual is handed over. • Job completed but phone support is always available.