Location 

Tasmania, Australia

Source

River water

Application

Potable water

End-user

Taswater

Capacity

60 m3/hr

INTRODUCTION

When surface water is used for production of potable water, removal of Natural Organic matter (NOM) is important. NOM must be removed for several reasons like e.g.: organoleptic properties , preventing formation of carcinogenic disinfection by-products such as Trihalomethanes (THM’s) and biological after growth in the potable water distribution network.

With surface water as source for potable water the traditional method of water treatment is physical chemical treatment followed by chlorination. 

challenges

Traditional water treatment has several draw backs:
  • High consumption of chemicals and consequently production of a large volume of sludge to be treated and disposed of.
  • Clarifiers and media filters take up a large foot print.
  • Generation of disinfection by-products: Trihalomethanes (THM’s), Haloacetic Acids (HAA’s) and bromate
  • Requirements for micro biological safety are becoming more strict, especially with regards to viruses and cysts
  • Some feed water sources observe a decrease in water quality (browning) and are becoming more and more difficult to treat

Several alternative treatment steps have been explored:
  • High pressure membrane technology, such as nanofiltration
    - Extensive pretreatment required, discharge of concentrate with increased hardness
  • Low pressure membranes, assisted with coagulation
    - Addresses only micro biology, organics removal similar to conventional technology
  • Ion exchange
    - Does not address micro biology, discharge of brine solution

Methods

An ideal membrane would combine the strengths of hollow fiber membranes with those of high pressure membranes: minimum pre-treatment requirements, chemical free removal of dissolved organics and a good barrier for micro biology. 

Pentair X-Flow started development of a new hollow fiber nanofiltration membrane. The following goals have been set for development of this new membrane:
  • Single step reduction of dissolved organics without the need for coagulant dosing.
    Target is >50% removal of NOM and >70% of color 
  • Robust barrier for micro biology
    Target is >99.99% removal of bacteria and viruses 
  • Versatile and easy to clean membrane
    Target is a backwashable, chlorine tolerant membrane with open channels that do not block 

Pentair X-Flow did identify a material (modified Poly Ether Sulphon) that allowed for a single step spinning process of a membrane without a thin film top coating. The mechanical stability of this material allowed for production of unsupported hollow fibers with excellent mechanical properties (high burst and collapse pressure).

The membrane has been validated under NSF61 and NSF419. Size exclusion for all microbiology, including viruses.

An additional benefit is the very low retention for dissolved inorganics: typical retention for hardness is 20%. Valuable minerals are not being removed from the potable water, furthermore it facilitates concentrate discharge. 

This hollow fiber nanofiltration is marketed by Pentair X-Flow as HFW1000 Membrane Element. The figure below shows a comparison of TOC retention of UF, assisted with coagulation and hollow fiber NF, for different process settings.



Comparison

results

Following a successful pilot test, the membrane module has been installed in a fullscale system in Tasmania – Australia. Design capacity for the system is 60 m3/hr. Water source is rive water, low in hardness, alkalinity and conductivity and moderately high in dissolved organics. During storm events the water observes high turbidity and bacteriological contamination. 
The water treatment plant is co-located with an irrigation scheme. This allows for a shared river water intake, furthermore NF backwash waste is reused as irrigation water, thus eliminating the need for wastewater treatment or a sewer connection.

Besides nanofiltration membrane skids the following pre- and post treatment has been installed to ensure continuous supply of excellent drinking water:
  • Feed strainer to protect the membranes from ingress of harmful matter 
  • Granular Activated Carbon to remove small organics 
  • CO2 dosing and calcite contactors for control of corrosiveness 
  • UV treatment as second microbiological barrier 
  • Chlorine and fluoride dosing for transport safety and dental protection 

Impression of location

nanofiltration performance summary


units feed water  HFW PERMEATE final outlet 
 Turbidity NTU 1.3 - 1.4 0.020 - 0.027 0.06 - 1 
 Color (true)
Hazen 45 - 50 2  
pH
 -
6.0 - 6.5  same
7.8 - 8 
 DOC
mg/l 5  < 450
 1
 Total THM
mg/l
 < 80  < 5

CONCLUSIONS

Hollow Fiber Nanofiltration successfully combines the strengths of low pressure membranes (hollow fiber) and high pressure membranes (spiral wound): robust, backwashable, chlorine resistant and no need for coagulant dosing. It also offers the possibility of integrity testing according to LT2ESWTR specifications and membrane repair by fiber pinning. 

This new Hollow Fiber Nanofiltration membrane allows for chemical free one-step production of potable water from surface water high in organics and micro biology. Especially in environmentally sensitive locations, where handling and discharge of chemicals is restricted, the hollow fiber nanofiltration provides significant benefits

Wastewater from the Hollow Fiber Nanofiltration does not contain any chemicals or increase in minerals and can therefore potentially be discharged back to the environment without further treatment.

Besides the first operational plant another two full scale plants that employ Hollow Fiber Nanofiltration for potable water production are currently under construction in Tasmania.

Pentair logo

As part of its separation into a new pure play water company, a new Pentair website has launched. Please visit the new Pentair.com to learn more about our exciting new company and your favorite brands!