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Microfiltration

The Joyce Road treatment plant was the first public water supply plant in New Zealand to use microfiltration technology.

Water FiltrationAt the heart of the microfiltration system are millions of tiny straws all less than 1 millimetre across.  These are held in bundles of 20,000 in long tubes.  The tubes are held in units of 90 called "skids".  There are 10 such skids at the Joyce Road plant. 

Raw water enters the tubes and passes from the outside to the inside of the straws through tiny holes in the fabric.  These holes are so small that Cryptosporidium oocysts, which are only 5/1000th of a millimetre across, get trapped on the outside of the straws with other particles in the water.  The clean water passes out through the core of the straws, out of the tubes, and on to the next stage in the treatment process.

Every so often the inflow of water is switched off and high pressure air is pumped into the straws.  The air goes in the opposite direction to the water, from the inside of the straw to the outside. This dislodges the particles which were trapped on the outside wall of the straw.

The whole filter is then flushed out with water which carries the particles away to a sludge lagoon.  There the sludge settles out and the thickened sludge is spread on adjacent farmland owned by the Council.

The use of microfiltration means that the amount of chemicals needed to treat the water can be minimised.  A small amount of chemicals are used when there are heavy rains in the catchment which make the water highly discoloured.  Chlorine is added after the microfiltration units to maintain the quality of the water while it is piped to the homes and businesses around Tauranga.

At Oropi treatment plant there are 108 tubes in each skid and there are 9 Skids.  Microfiltration is the same treatment as Joyce Road, only Oropi does not have a lagoon system for wastewater.  Oropi has a backwash clarifier and is operated as a continuous batch unit.  This continuous process includes:

  • continuous feed from backwash tank and from pretreatement desludging systems (i.e flashmixer and clarifier) entering a sludge recovery plant
     
  • water is treated, recycled back to the plant and the sludge is pumped through a centrifuge and into a sludge bin and taken away for land fill

Joyce Road treatment plant

Oropi Road treatment plant

 


Last Reviewed: 11/04/2017