Dutch agencies set requirements for use of purified wastewater

Dutch scientists have created a framework that can be used when looking into the reuse of water on food crops.

The National Institute for Public Health and the Environment (RIVM), Wageningen University and Research (WUR) and the Netherlands Food and Consumer Product Safety Authority (NVWA) have defined a set of minimum quality requirements that purified wastewater must meet for use in agriculture and horticulture. A testing framework was developed to limit the negative consequences for people, plants, and animals.

In dry summers, there may not be enough water to irrigate agricultural and horticultural crops. Purified wastewater is a potential solution but may still contain chemicals and pathogens.

Since 2020, European Union legislation has promoted the use of purified urban wastewater for irrigation in times of drought. The Netherlands implemented this law in 2023. The EU regulation has four quality classes (from A to D), with an associated maximum of E. coli for each one.

Water can contain a range of pathogens, including bacteria such as Salmonella, viruses like norovirus, and parasites such as cryptosporidium.

E. coli as an indicator
A risk assessment has been carried out for bacteria and viruses that are harmful to humans. The measure chosen is the number of E. coli in wastewater. The amount of E. coli is a key indicator of pathogenic microorganisms that can be transmitted via feces. The maximum permissible E. coli level in water depends on if the crop type is to be consumed raw or cooked, and the irrigation method, such as leaf spray irrigation.

For large-scale use of treated wastewater as irrigation water in agriculture and horticulture, further removal of E. coli, and pathogenic microorganisms, is necessary. This can be done with additional purification, such as disinfection or filtration.

Scientists said the concentration of pathogens cannot be predicted on the basis of indicators. This means a quantitative risk assessment based on the presence of pathogens is not possible. A risk assessment based on indicator organisms is possible, but requires a lot of data and can only be done under a large number of assumptions.

Eating a crop that has been irrigated with treated wastewater could lead to illness. The magnitude of risk depends, among other things, on the type of crop, cultivation method (e.g. above or below ground), irrigation method, and microbiological quality of the irrigation water.

For many chemicals, existing standards have been used that limit the maximum amount of the substance in water. Limit values have been established for the safe consumption of vegetable and animal products, so purified wastewater can safely be used for irrigation. These values have been compared with existing standards on chemicals. 

Further research will involve a study of the risks of chemicals and pathogens to sources of drinking water. Scientists will also assess the risk to local residents and passers-by from the inhalation of water droplets released during spray irrigation.

(To sign up for a free subscription to Food Safety News, click here.)