Towards a water-wise world Annual report 2014

Mapping Aeromonas regrowth 

Applied research for Evides Waterbedrijf

1 November 2014BTO

Within the “Biological Activity” theme of the water sector’s joint research programme (BTO), the focus is primarily on the quantification and characterisation of microbial processes in the production and distribution of drinking water. By including KWR assistance in the in-company research of Evides Waterbedrijf, KWR makes its microbiology expertise available to help the water company solve some complex questions.

Within the BTO programme, Evides Waterbedrijf has dedicated most of its Tailored Research budget to the problems related to the regrowth of Aeromonas in the distribution system. “We observe an increase of this regrowth indicator during distribution,” says Jan Bahlman, process technologist at Evides Waterbedrijf. Aeromonas regrowth has appeared at 3 of the 4 sites where the company uses surface water from the Brabantse Biesbosch as its drinking water source. “We want to know why one of the plants does not have the problem and to understand the different factors responsible for this regrowth phenomenon in order to be able to take the right operational measures.”

Adapt fast

To answer the question, one has to identify the characteristics of the water treatment and of the distribution system that might be related to the Aeromonas regrowth. The water company includes KWR assistance directly in their research program. “For the Dutch water companies KWR is a centre of microbial expertise in the field of regrowth ,” according to Bahlman. “It’s a pleasure to work with KWR researchers because they can translate their knowledge to our daily practice.” Wim Hijnen, the KWR microbiologist assigned for this research project of Evides Waterbedrijf, agrees that this ‘KWR assistance at location’ is working out very well. “This construction is of mutual interest. Since I spend time at the client location, I can explain the ideas behind our research more thoroughly. At the same time, we can better tailor the research to the client’s wishes. We can adapt faster, which adds value to what we do.”

Slowly biodegradable compounds and ozone

At the site without Aeromonas regrowth, the concentration of slowly biodegradable compounds in the drinking water, assessed with new methods designed by KWR, was lower than in the drinking water at the other sites. This suggests that these compounds are correlated to the Aeromonas regrowth problem. Application of the oxidative ozone disinfection process is one of the possible explanations for this lower concentration of slowly biodegradable compounds at this regrowth-free plant. Since the water company has decided to switch from ozone to UV disinfection at all of the plants, there was a concern that this would result in Aeromonas regrowth at this regrowth-free plant. “Our joint research of 2014 has shown this concern is unfounded,” says Hijnen. “Ozone is not a significant barrier for these slowly biodegradable compounds in the water and the transition from ozone to UV will not increase Aeromonas regrowth.”

“Since I spend time at the client location, I can explain the ideas behind our research more thoroughly”


After the search for possible causes in the drinking water production at the water company for the Aeromonas regrowth, next year the research will be more focussed on the influence of the distribution system. Hijnen explains: “We know that to understand all factors involved in regrowth we have to look further than only water quality. We must also consider the configuration of the distribution system, in which materials, flow rates and the contact times of the drinking water with the pipes can vary considerably. The configuration of a distribution system of a city like Rotterdam with regrowth problems is different from the configuration of the distribution system at the countryside without Aeromonas regrowth. Aeromonas regrowth is caused by a complex of factors.”

© 2018 KWR Watercycle Research Institute

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