Dutch research sets requirements for the safe use of purified wastewater for irrigation
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 joint forces to define a set of minimum quality requirements that purified wastewater must meet for use in agriculture and horticulture.
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 some chemicals and pathogens, such as bacteria and viruses, that are harmful to humans, plants or animals.
Since 2020, European Union legislation has promoted the use of purified urban wastewater for irrigation in times of drought. The Netherlands implemented this legislation in 2023. Dutch researchers take now a step further with a study that focuses on the development of an assessment framework to ensure that humans, plants and animals are sufficiently well protected.
New criteria for chemicals and pathogens
Although there are already standards for the presence of various chemicals in water, with this new study, researchers have now established limit values for the safe consumption of both vegetable and animal products, so that purified urban wastewater can be used for irrigation safely. These risk limits have been compared with existing standards, with the most stringent one dictating the maximum permissible level for a chemical. This was needed because there were no food safety standards for wastewater.
As for pathogens, the risks associated with types that are harmful to humans and crops have been identified. The number of E. coli (‘poop bacterium’) in wastewater has been the chosen measure due to the prevalence of this bacterium. The amount of E. coli is a key indicator of pathogenic micro-organisms that can be transmitted via faeces. The maximum permissible E.coli level in water depends on whether the vegetable type is to be consumed raw or cooked, and whether there is a leaf spray irrigation.
Pathogens are also common in the soil, however, the number of additional pathogens in purified wastewater is negligibly small. The only identified risk concerns greenhouse horticulture. This is because crops are often grown in sterile environments where even small amounts of additional pathogens have the potential to cause harm.
Further research
The next phase of this research will involve a study of the risks of chemicals and pathogens to sources of drinking water. In addition, researchers will assess the risk to local residents and passers-by from the inhalation of water droplets released during spray irrigation.
