Puurwaterfabriek

Puurwaterfabriek

NWTR has developed and owns the Puurwaterfabriek which opened in Emmen in 2010. This is where treated wastewater from Emmen’s wastewater treatment plant is processed into ultra-pure water. The output can be as much as 10,000 m3 daily. Ultra-pure water is so pure that even the minerals and chalk normally present in drinking water are removed. The Puurwaterfabriek is the world's largest EDI (electrodeionization) facility.

NAM purchases the ultra-pure water. The company converts this to steam, which it then injects into the Schoonebeek oil fields to render the thick, viscous oil more fluid. By 2036, it has been estimated, 120 million barrels will be extracted using this technique. When boiling ultra-pure water, no chalk deposits are left behind to damage expensive installations, such as turbines and pumps. The ultra-pure water is pumped to the NAM heat and power station in Schoonebeek via two pipelines. The contract with NAM is expected to run for 25 years.

Origins

Oil in the Schoonebeek oil field is particularly thick and viscous. Due to this, NAM gave up extracting in 1996. Pumping it up using traditional nodding donkey pumps had become just too unprofitable. More recently however, new techniques were introduced, including horizontal sectioning in combination with steam injection, which made extraction once again a viable economic proposition. Expectations are that the Schoonebeek oil fields will produce up to 120 million barrels by 2036. This is nearly 50% of what NAM extracted between 1947 and 1996. Further information on oil extraction can be found on the NAM website..

Design

The innovative combination of purification techniques utilised in the Puurwaterfabriek is unique. Process technologists from WLN (a WMD subsidiary company) together with engineers from WMD and the Velt and Vecht have water authorities developed and designed the process used in the Puurwaterfabriek. This was the result of utilising a smart combination of existing and innovative techniques. The various parts of the process taken together deliver considerable quality improvement; the whole in this case being more than the sum of the parts. The purification process has been positively assessed by external, internationally recognised technologists. Witteveen+Bos engineers and consultants drafted the engineering details and specifications.

Sustainability

The Puurwaterfabriek aims to be an environmentally friendly enterprise. The facility is sustainable in a number of ways:

  • Sustainable construction: the plant was constructed in a sustainable manner. For example, the concrete floor was poured using a mix which included crushed concrete from demolished structures.
  • Prevention of dehydration: the source material is wastewater. Wastewater is an ideal alternative to groundwater or surface water. Not extracting groundwater provides an excellent fit with Drenthe Province's anti-dehydration policy. Surface water is of varied quality and is often limited in supply during drier periods.
  • Minimal use of chemicals: The latest water purification methods have been adopted in the technical design, created in cooperation with nationally recognised technologists. The process is intended to minimise the use of chemicals.
  • Limited discharge to the surface water: rinse water and water used for cleaning is reused or returned to the wastewater treatment facility to be treated for a second time. Wastewater is better cleaned, which benefits the quality of the surface water. This process also prevents at least 30 tonnes of sewage sludge being deposited into the surface water annually and considerably reduces the amount of phosphates being discharged.
  • Efficient energy use: producing steam for extracting oil is heavy on energy use. To counter this, NAM has invested in its own heat and power station to generate electricity and heat. Electricity generated is also used in the Puurwaterfabriek to power the pumps and the various processes. To facilitate this, a 10kV cable connecting the NAM heat and power station and the Puurwaterfabriek was installed at the same time as the pipeline for the ultra-pure water was laid.

Technology

To remove all floating particles, nutrients and salts from treated wastewater, a comprehensive sequence of purification steps is put in place. Follow these steps of purification techniques beneath the image on top of this page.

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Prins Willem Alexander opent Puurwaterfabriek

Prince Willem Alexander opens Puurwaterfabriek

The plant is unique in the world due its chosen source, its production size and the innovative combination of purification techniques.

 

Water supply

Effluent from the Emmen wastewater treatment plant meets the quality standards and demands for discharging as surface water. If there is no or insufficient treated wastewater available, as a temporary measure water can be drawn from the Hoogeveen canal. And even if this source becomes unavailable, drinking water can be used.

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The water is pumped to the Pure-Water plant from the wastewater treatment plant

 

Filtering

Rotary screens remove the larger impurities and objects, such as leaves and hairs. A brushing mechanism ensures the screens are automatically kept clean and clear. The filtered waste together with the rinse water is collected in a buffer, from where it is returned to the wastewater treatment plant.

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Rotary screen to remove larger impurities in the water from the wastewater treatment plant

 

Ultra-filtration

An ultra-filtration installation removes the insoluble substances from the effluent. Cassettes containing strong membrane straws are submerged in the dirty water. The water is vacuum pumped from the basin through the walls of the straws. Any waste is caught by the exterior walls of these membrane straws. A condensed layer of waste builds up in the basin. This waste is returned to the Emmen wastewater treatment plant via a buffer. The straws are made from PVDF (micro filtration); a material particularly resistant to sodium hypochlorite which is used for cleaning the straws. The straws are aerated from below, causing them to move, preventing any waste from clinging or building up on their surfaces. Another advantage is the low level of flux: 20 litres per m² per hour. A process which does not require chemicals such as flocculation agents, nor a pH correction. The clean water is then passed to the next step of the purification process.

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Video van het ultrafiltratie-proces

View the video on the ultra-filtration process

 

Biological activated carbon filter

This step in the purification process is required to prevent biological pollution (bio-fouling) of the membranes of the reverse osmosis. By adding oxygen, a favourable environment for bacteria is created in the activated carbon filter, which convert nutrients into water and carbon dioxide. Bio-fouling in the membranes is thus considerably reduced. The rinse water and the superfluous bacteria (biomass) are returned to the wastewater treatment plant for treatment. The carbonated filter is a two step process: a pre and a follow-up filter. These filters have a filtration speed of 10 m³ per hour and 5 m³ per hour respectively. A screen removes any small activated carbon particles before the water is piped to the buffer. At this stage the water is almost of potable quality.

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The biological activated carbon filter removes nutrients for bacteria and consists of five identical lines of two filters

 

Reverse osmosis

Membrane installations for reverse osmosis remove any minerals. The pressure chambers are 6 meters in length. The total purification surface is 40,000 m2; approximately the dimension of eight football fields. During purification, approximately 20% of concentrate moves to the surface water. Adding anti-scaling prevents fouling of the membranes. Reverse osmosis happens in two stages; both installations are connected in a circuit.

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Video van het omgekeerde osmose-proces

View the video on the reverse osmosis process

The installation for reverse osmosis

 

Electrodeionization

Removal of any remaining minerals (ions) takes place with the electrodeionization treatment. This step is a new development in the field of water purification: a combination of membrane filtration and ion exchange.

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cedi

View the video on the electrodeionization treatment

 

Transport

Transport pumps push the ultra-pure water through 7 kilometres of polypropylene pipeline to the NAM location. There the water is stored in tanks with a capacity of 10,000 m³ ultra-pure water. This is enough for at least one day.

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Transport pumps get the water to the NAM location