Checking disinfector regularly is not a luxury

2 November 2020

"More than half of the water samples we analyze to check that disinfectors are working properly turn out to have high plate counts," says Jan Hardeman, greenhouse horticulture specialist at Eurofins Agro.

The aerobic plate count is an indicator of the quantity of bacteria and fungal spores present in the water. Hardeman reached his conclusion based on the results of 500 water samples taken by Eurofins Agro last year. In Dutch greenhouses all drain and irrigation water has  to be reused. However, recirculated water can contain various pathogens, such as fungi, bacteria, and viruses. With this in mind, many growers have installed disinfection units.

Hardeman: “These units require significant investments. We often hear growers say: ‘A disinfector is so expensive. But it will be very effective.’ However, the question is whether that is always the case. A DisinfectorCheck from Eurofins Agro provides you with an answer to the question 'Have the bacteria and fungi in the water been adequately killed off?' If not, the disinfector is not working properly and measures have to be taken."

Sterile sampling

For a microbiological check to determine whether a disinfector is working properly, a sample is taken from the taps immediately upstream and immediately downstream of the disinfector. This must be done in sterile conditions. The samples are then chilled and transported in sterile bottles to the Eurofins Agro microbiology lab, where the analysts determine the aerobic plate count (the total number of bacteria and fungi).

The results of the samples upstream and downstream of the disinfector are compared with each other to check whether the disinfector is working properly. The results are sent to the grower within five working days of the sample being received at the lab. The report states the number of live bacteria and fungi in CFU/ml (colony-forming units per ml).

Eurofins Agro compared the results of 500 samples from greenhouse growers. Of these, it was found that almost 40% had a CFU of more than 500/ml, and almost 30% had a CFU that was even higher than 1000/ml.

“Extremely high counts can have various causes,” Hardeman says. “For example, a UV disinfector may not be killing off the bacteria or fungi properly if the transmission value of the water is too low. It should be at least 75%. Also, the equipment could be wrongly configured, or it may not have undergone annual maintenance. Old UV lamps are often less effective. Another possibility is that other water is being used or that the water quantity passing through the disinfector has been changed. That can also reduce the effectiveness of the disinfector, because the sizing is wrong.”

DNA Multiscan

The Eurofins Agro DisinfectorCheck is suitable for all types of disinfectors. It is accredited by the Dutch Accreditation Council to ISO 17025. This proves that analysis performs to extremely high standards of reliability in accordance with the guidelines.

“The check is a snapshot,” Hardeman emphasizes. “The report provides a picture of the total number of bacteria and fungi. So you don’t know whether they are pathogens or not.” In addition to a DisinfectorCheck, Hardeman therefore recommends having a DNA analysis performed on the dirty drain water to establish which microorganisms are present in the cropping system. The Eurofins Agro DNA Multiscan is an effective tool for this.

In addition, Hardeman says, it can be helpful to have the DisinfectorCheck performed at least four times a year. This way, any glitches in the equipment can be traced promptly and future problems can be avoided.