Dutch scientists have created a framework that can be used in research into water reuse for food crops.
The National Institute for Public Health and the Environment (RIVM), Wageningen University and Research (WUR) and the Dutch Food and Consumer Product Safety Authority (NVWA) have set of minimum quality requirements that purified wastewater must meet for use in agriculture and horticulture. An assessment framework has been developed to limit the negative consequences for humans, plants and animals.
In dry summers there may not be enough water to irrigate agricultural and horticultural crops. Treated wastewater is a possible solution, but it can still contain chemicals and pathogens.
Since 2020, European Union legislation has promoted the use of treated 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 amount of E. coli for each class.
Water can contain a range of pathogens, including bacteria such as Salmonella, viruses such as 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 number of E. coli in the wastewater was chosen as a benchmark. The amount of E. coli is an important indicator of pathogenic microorganisms that can be transmitted through feces. The maximum allowable E. coli content in water depends on whether the crop is to be consumed raw or cooked, and on the irrigation method, such as foliar spray irrigation.
For large-scale use of treated wastewater as irrigation water in agriculture and horticulture, further removal of E. coli and pathogenic micro-organisms is necessary. This can be done with additional purification, such as disinfection or filtration.
Scientists say that the concentration of pathogens cannot be predicted based on indicators. This means that 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 performed under a large number of assumptions.
Eating a crop irrigated with treated wastewater can lead to illness. The extent of the risk depends, among other things, on the type of crop, the cultivation method (for example above or below ground), the irrigation method and the 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 plant and animal products, so that treated wastewater can be safely used for irrigation. These values have been compared with existing standards for chemicals.
Further research will include a study of the risks of chemicals and pathogens to drinking water sources. Scientists will also assess the risk to local residents and passers-by from inhaling water droplets released during sprinkler irrigation.
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