Arbejdsrapport fra Miljøstyrelsen, 19/2005 – Rensning for nitrat og pesticider i små vandforsyningsanlæg

Rensning for nitrat og pesticider i små vandforsyningsanlæg

Summary and conclusions

On behalf of the Danish Environmental Protection Agency, the Geological Survey of Denmark and Greenland, GEUS; has made investigations which show that a major part of the private wells are polluted with pesticides. Furthermore, a major part of the wells are polluted with nitrate and/or micro organisms. Drinking water purification in local homes and buildings may be an alternative.

The aim of this project is to evaluate novel plants for treatment of pesticides and/or nitrate at local water supplies (private wells). The plants are evaluated in terms of possible future application in Denmark.

The most detailed experience regarding local water treatment for pesticides and nitrate is from authorities and research institutes in the US and Germany. Therefore, know-how was collected by visiting authorities in the US and Germany as well as by visiting plants in Germany. Also a literature search was conducted at the DTV (Technical Knowledge Centre of Denmark), etc.

The report describes that important guidance for implementation of local water treatment plants is given in the US /Ref.7/, and that these local plants are being tested and approved according to the standards: /Ref.14,15,16,17,18 and 19/.

In Germany, the installation and operation of local plants is approved by the local authorities, who also plan and supervise the monitoring activities. Local plants are being tested and approved according to the American standards previously mentioned.

The conclusion of the report is that POU (Point-Of-Use) plants should not be applied in Denmark, whilst POE (Point-Of-Entry) plants may be useful in Denmark. A POE plant should be placed in cool premises (alternatively connected to a cooler – particularly the water storage tank), non-freezing, and with easy access for monitoring and maintenance.

It has not been possible to get a clear survey of production costs. This is partly due to various ways of presenting costs and partly due to various conditions relating to the disposal of wastes.

In the chapter “Diskussion” of this report, the possible costs of application in Denmark are estimated. The total estimated price is in the range from DKK 22 to 92/m³ (euro 3-12) and depend greatly on which solutions are selected for waste handling. A probable price is 30-35 kr/m³ (euro 4-5).

It is recommended only to test POE plants in Denmark.

Two important processes for local water supplies are ion exchange and nanofiltration/reverse osmosis. For ion exchange, the pH value may be lower than 7, which is the Danish requirement for drinking water. For nanofiltration/reverse osmosis, the hardness may be lower than 5°dH, and the conductivity may be lower than 30 mS/m, both of which are the Danish requirements for drinking water.

A pilot plant to reduce/remove pesticides should include the following main processes:

Activated carbon (GAC) and UV treatment
Nanofiltration

A pilot plant to reduce/remove nitrate should include the following main processes:

2 ion exchangers in parallel
Reverse osmosis

A pilot plant to simultaneous reduction/removal of pesticides and nitrate should include the following main processes:

Reverse osmosis

These processes should be tested with the following types of raw water:

Soft water with iron and manganese (which requires pre-treatment)
Soft water without iron and manganese
Hard water with iron and manganese (which requires pre-treatment)
Hard water without iron and manganese

The nitrate concentration could be for instance 100 mg/l. The pesticide concentration could be for instance 0.5 µg/l. The pesticides can be one compound or mixtures of the compounds mentioned in section 1.2.

Thus, it is suggested to conduct the following series of measurement:

4 processes · 4 water types · 1 nitrate concentration · 1 pesticide content = 16 series of measurement.

The monitoring program should, at least, be planned to comprise raw water analyses as well as treated water analyses for “Extended control” and “Pesticides”.