Reverse Osmosis Process
Natural osmosis occurs when two fluids of different salinity are separated by a semipermeable membrane. The fluid with the lower salinity will pass through the membrane until the salt solution becomes equal on both sides of the membrane.
If pressure is exerted on the higher salinity solution the membrane allows desalinated, de-mineralized water to pass into the pure solution whilst it rejects the dissolved impurities, a process known as ‘reverse osmosis’ (RO).
The Pall Disc Tube (DT) module system is a membrane device designed to ensure molecular and ionic separation of the whole spectrum of pollutants in all aqueous environments: from suspended matter to the smallest ions, including colloids, bacteria, viruses and organic matter.
The Disc Tube module consists of a stack of molded ABS spacing discs separating membrane cushions which are formed from three octagonal layers which are welded to each other, ultrasonically at their periphery.
The unique configuration of the Disc Tube module offers numerous advantages over traditional spiral or tubular membrane modules.
- Open channel configuration
- High turbulances of the feed stream
- Reduced risks of clogging or crystallization
- Evenly distributed and self-cleaning hydraulic circulation
- More effective cleanings
- Minimization of cross-flow rate
- Extended range of cut-off for nanofiltration membranes (500 g/mole, 270 g/mole) and for reverse osmosis (high flow rates, Standard 100 g/mole, high rejection)
Why the Disc TubeTM RO Module has become the preferred module for leachate treatment?
Open Channel Technology
- Less susceptible to fouling and scaling
- Modules are easy to clean
- Suitable for silt density index (SDI) up to 5/15
- Module can be opened
- Module and membranes can be investigated
- Single membranes can be tested for best cleaning procedure
- Single membranes can be investigated at lab (EDX, Microscope)
Features of Pall DT Reverse Osmosis Systems
- Modular expandable design with one or multiple stages
- Recovery rates achievable by DT modules with staged RO Pressure (Base 18mS/cm)
- High pressure units maximize permeate yield (Recovery Rate)
- Mobile containerized units or in situ installation options
- No mechanical chemical pre-treatment necessary
- Small footprint
- Installation complementary to existing treatment plants
- ‘Plug & Play’ installation with short start-up period
- Capacity ranges from 1 – 25 m3/h per line
- Short or long-term rental opportunities
- Economic module exchange
- Worldwide service
What are the main challenges in the leachate treatment process?
- COD in landfill leachate is partially not biodegradable (“Hard COD”)
- COD cannot be reduced sufficiently by classical Biological treatment, e.g. in public WWTP’s
- High ammonia and total nitrogen contents require utmost treatment efficiency
- Salt content and heavy metals cannot be eliminated by conventional treatment methods
|Conclusion:||Reverse Osmosis is the only technology, capable of reducing almost all parameters!|
Characteristics of Pall's DT RO Systems for Landfill leachate treatment
- Best quality of product water (permeate)
- Small footprint
- Reliable at variations of quantity and quality
- Switch On / Switch Off operation possible
- ‘Plug & Play’ installation
- Treated leachate (permeate) can be discharged back to the environment or can be utilized for irrigation or process water.
- Modular, flexible construction
More than 220 Pall installations for leachate treatment are in operation worldwide!
Range of Applications
- Treatment of landfill leachate
- Cleaning of industrial waste waters
- Desalination of brackish water or sea water at ends of production of potable water
- Targeted molecular separation
Pressure Range (bar): 75 90 120 160
Recovery Rate (%): 80 85 90 93-95
|Units||Medium Pressure Modules||High Pressure Modules||Special Design|
|Feed flow rate range (min. - max.)||l/h||250 -1600||400 - 1500|
|Feed flow in operation||l/h||500 - 1200|
|Maximum temperature (cleaning)||°C||45|
|Maximum temperature (operation)||°C||40|
|Maximum operating pressure||bar||75||90||75||90||120||160|
|Operating pressure in filtration||bar||30 - 70||40 - 90||30 - 70||40 - 90||90 - 120||80 - 150|
|Pressure vessel external diameter||mm||214||218||214||218||224||234|
|Pressure vessel internal diameter||mm||202|
|Number of discs per tube||U||170||210||170||210||210|
|Total surface per tube||m²||7.65||9.45||7.65||9.45|
|Weight of a module (empty)||kg||58||74||66||82||72||88||120|
|Weight of a module (operation)||kg||64||80||74||90||80||96||128|
|Watertight flange||Polyoxymethylene (POM)|
|Pressure flange||Stainless Steel|
In leachate treatment and most waste water applications as a rough design value, the average output per module is 3 m³/day of pure water with a mean conversion rate varying from 75 % at medium pressure to 90 - 95 % at high pressure.
Value for DTGE Modules with Raw water conductivity is 10 - 15 ms/cm @ 25 °C