PT/DT Modules - RO/NF

Rochem’s Plate Tube Type Membrane Modules has many Operational advantages over the other Membrane Systems available in the market. A flat membrane Module uses patented concept of a membrane cushion stack with completely open feed channels in combination with straight through feed flow.

The vertical placement of Modules in combination with feed air / water flushing allows membrane cleaning and a stable operation for long periods without use of chemical cleaning agents.

“The key for a proper and reliable operation of RO membranes is in the pretreatment”.

Conventional technologies may have a number of pretreatment stages as follows:
a. Chlorine dosing
b. Coagulant dosing
c. Polyelectrolyte dosing
d. Coarse Filtration
e. Fine filtration
f. Antiscalant dosing
g. De-Chlorination
h. Micron Filtration (Upto 5µ)
i. Acid-dosing

The above pre treatment is necessitated due to inherent bio-fouling, colloidal fouling and scaling that is prevalent due to the peculiarity of construction of these membrane types.

To overcome these problems which plagued the Reverse Osmosis desalination technology until the mid 1980’s, ROCHEM developed their state of art Plate and TubeTM module after considerable research and trials. The main feature of such membrane configuration is the steady continuous waste water velocity over all sections of the membrane surface and the big channels between the membrane and the Plate surface which means an open-channel-operation.

ROCHEM’s PT membrane module has been conceived for tackling this exact difficulty of Spiral wound and Hollow film fiber membranes to purify waste water.


Rochem Plate Tube Module

The problems of conventional configurations, the configurations that reflect ease of manufacture rather than operational effectiveness, have been overcome by the state of art Plate and tube membranes module technology in all applications ranging from waste water desalination to industrial waste water treatment.

It is constructed from a series of octagonal membrane cushion separated by a series of plastic spacer Plates. The Plate support the membrane cushions but leaves an open channel flow path through module. The flow path is radial and gets reversed in 180° to flow over other side of cushion. This flow path repeats for each membrane in stack. The resultant turbulence due to reversal eliminates the concentration polarization minimizing scaling & fouling.

Configuration Characteristics Plate & Tube Spiral Hollow Fiber
Packing density Moderate High Highest
Permeate flux High High Low
Pretreatment Moderate High Highest
Suspended Solid build up Moderate High Highest

Having superior constructional features, the PT Modules also score on Operational Aspects and are far simpler to operate due to absence of elaborate stages of pretreatment of raw water.

The Plate Tube Membrane system can be used with simple backwash Sandfilter and cartridge filters of 10 micron. Any permanent wastewater pre-treatment by chemicals at various points is not required. A higher silt density index SDI-blocking factor of 15 only means that the system has to be cleaned less frequently, normally once every 4 weeks.

The cleaning circuit for the Plate Tube membrane is included in every plant and can be handled simply without any special knowledge demand from operating staff.

Advantages of Constructional Configuration in ROCHEM’s Plate Tube Module:


a. Open channel feed flow path

  • An Open Channel Feed Flow Path Reduces the need for Pretreatment and Reduces the Possibility of Fouling
  • The Plate Tube has an Open Channel of 1mm
  • A Conventional Module has a 3 - 7 Micron Channel
  • The Plate Tube has 1500% Greater Clearance
  • The Plate Tube Allows for More Complete Cleaning

b. Short flow path

  • Flow Reversal Causes Turbulence, Turbulence Reduces Polarization Concentration
  • The Plate Tube has a 3 Inch Flow Path between Flow Reversals
  • A Conventional Module has a 40 Inches Flow Path

c. Minimal areas of no flow

  • Zones of No Flow Increase the Rate of Fouling and Catch Bacteria and Colloidal Material
  • Contact with the Membrane Creates Zones of No Flow
  • The Plate Tube has Minimal Contact with Membrane Surface
  • The Feed Spacer In a Conventional Module has Tremendous Contact with the Membrane Surface

The PT module offers additional unique advantages over other types of membranes:

  1. Simplified prefiltration: Can smoothly operate with waters having Silt Density Index (SDI) of 15-20 as against 3-5 and turbidity of 4-5 NTU as against maximum 1 NTU tolerated by other membrane modules.

  2. No chemical operating costs: No chemical pretreatment is required for wastewater applications and also other difficult water qualities.

  3. High recovery rates: High recovery rates (i.e. m3 of Permeate produced/100m3 of feed pumped in) are typically achieved with PT. This means a lower energy consumption per unit pure water produced, and contributes towards lower pumping and maintenance costs in the case of PT.

  4. Longer Membrane Life: The Membrane is open channel type and raw water-flow in series. Due to fluid dynamics obtained with this design the suspended solids carried in the feed water do not clog or easily settle over the membrane surface.
    Thus, it can accept much worse waters than the SW/HFF types other types as is evident from threshold values of Silt Density Index (SDI) and Turbidity (NTU) as under:

                                     SDI (% per min)                  Turbidity (NTU)
    HFF                                  1 - 3                                           1
    SW                                    1- 3                                           1
    PT (Rochem)                  20                                              5

    It is known fact that makers of hollow fibre or spiral wound membrane system offer a 3 years to 5 years guarantee for the membranes’ life. This will be more or less an optical illusion because this guarantee is based on the operation of natural wastewater with a SDI-factor less than 3. Normally, Natural wastewater will be aggressive against the membranes’ material. But the guarantee will only cover the durability of the membranes’ material against all substances inside natural clean wastewater, and not a clogging of a membrane which will be the responsibility of the operator. Therefore such guarantees are of little help or value to the operator and maintainer.

  5. Lower membrane replacement costs: Conventional membrane elements are life-wasteled at manufacture so the complete element must be replaced at relatively high cost, but the PT module system offers the possibility of replacing individual sheets of membrane at a fraction of the cost.

  6. Better Chemical Cleaning: PT Configurations have design features which minimize fouling to a level where in situ chemical cleaning restores original membrane performance and provides a long operating life; SW and HFF membranes with inherently constricted flow passages are prone to heavy fouling which is only partially handled by chemical cleaning and thus have a pronounced tendency to choke and have limited operating life.

  7. Lower Maintenance Cost: With PT Module, even after the expected life, it is possible to identify the damaged membranes and replace only these membrane envelopes, rather than the total set in the stack. In SW or HFF types, which are factory - wasteled for life, the whole module is to be rejected. Thus the replacement cost of membranes is significantly higher for SW and HFF types compared to PT.

  8. Low Operating Costs: The above points, reduced pretreatment and longer membrane life, clearly show that the operating costs of the plant are significantly lower than the SW /HFF configurations.

  9. Easy Access to All Components including membranes: Modules can easily be opened up to permit exchange or inspection of each membrane sheet. (This is not possible in SW/HFF, since these are factory wasteled)

  10. Compact and Modular construction: The unique design offers versatile features like superior flux, smaller foot print, easy handling, ease of scalability, replacability and isolation in case of fault.




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