REVERSE OSMOSIS UNIT – Aigeira Landfill site

UW-tech has delivered the UW-BOX RO Unit for the leachate treatment of Aigeira Landfill site at Peloponnese, Greece. The total capacity of the unit is 4,5m3/hr incoming leachate for treatment.

All the components of the unit is fitted in a 40 feet standard size container. This container is placed in the premises of the leachate treatment plant and is connected to the rest of the equipment of the treatment unit. The main stages of the process of the reverse osmosis are:

  • pH adjustment of the incoming leachate stream with the use of sulfuric acid
  • Filtering of the incoming leachate through sand and cartridge filters. After the filtering stage, solids larger than 1 micron are removed from the stream
  • With the use of high pressure pump, in order to increase system’s pressure to the desired level, the filtered leachate is being pressed through the reverse osmosis membranes. This action creates one stream of permeate and one of concentrate. Permeate is gathered in an intermediate tank for further treatment, while the concentrate is sent back to the landfill. In order to prevent the clogging of the filtering area, a recirculation pump is used, in order to create a turbulent flow inside the reverse osmosis modules.
  • From the intermediate tank, the permeate of the first stage passes through a cartridge filter and then using a high pressure pump, for the second stage, it passes through the membranes of the second pass. Again, there are two effluents, one permeate and one concentrate. The permeate of the second stage is the final product of the unit, and the concentrate, since its quality is good (it’s the concentrate of an already treated stream in the first pass) is recirculated in the initial pH adjustment tank. Like in the first pass, the use of a recirculation pump for the second pass, creates turbulent flow which prevents the membranes from clogging.
  • In order to flush the membranes after every use and to extend their lifetime and maintain high standards performance, the unit comes with a fully equipped and automated chemical cleaning/ flushing system.

The unit, is composed of reverse osmosis modules. Each module includes one semi permeable membrane which is which is rolled in a spiral way. This semi permeable membrane is divided in two sheets and between them is a plastic grid which drives the permeate in a central collecting perforated pipe. Outside this “sandwich” there is another one separating grid, in which the permeate flows. The module has a cylindrical shape since the membranes and the grids are rolled on the outside surface of the perforated pipe. The leachate enters the cylinder from its base, passes through the separating grid that is around the membranes and one part of it passes through the membrane. This permeate then moves through the inner grid and finally is collected by the perforated pipe as clean stream. The rest of the leachate which did not pass through the membrane, ends up to the other side of the module and is collected as concentrate and been rejected.

Picture 1 Aspect of the entrance of the RO container

Picture 2 Aspect of the inside of the container. On the left and the right side there are the RO modules

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