Bioregeneration of activated carbon filter systems for treatment of washing water contaminated with crop protection agents

From 2027 onwards, the European Water Framework Directive stipulates the aim of achieving near-zero emissions of plant protection agents into surface water. This includes the emission of crop protection agents from farmyards. To meet this target, farmers in the Netherlands must install a cleaning facility to prevent contamination of farmyard water by, for example, filling and cleaning sprayers with crop protection agents. This facility must remove at least 95% of the crop protection agents present in the washing water. The risk of new point contamination of the soil and groundwater should thus be eliminated.

At present, various methods are already being used to purify wash water, for example by using a so-called Fytobac. This is a system that collects the wash water and evaporates it, leaving the crop protection agents behind in the Fytobac packet and (partially) breaking it down. Filter systems based on granular activated carbon (GAC) are not yet widely used, because these systems become saturated after some time and have to be replaced. This involves considerable costs. However, activated carbon filters are seen as the most effective and safest solution to this problem. For this reason Bioclear earth, in cooperation with Broos Water bv, has looked into the possibility of postponing the saturation point of the filter by using pesticide-degrading microorganisms. These bacteria and fungi must ensure that the substances adsorbed by the activated carbon are broken down and become available for adsorption again. This process is known as bioregeneration.

Can bioregeneration increase the lifespan of granular activated carbon filters?

In order to investigate whether bioregeneration can extend the lifespan of GAC filters, several types of test arrangements were made on a laboratory scale. Among others, the difference between activated carbon enriched with pesticide-degrading microorganisms and activated carbon that has not been enriched has been studied. The tests were carried out with the widely used metribuzin, a herbicide that is often found in surface water and farmyard water. The degradation of metribuzin was monitored under various conditions such as different pH values, anaerobic and aerobic conditions and biological stimulation. Since this scenario will occur in practice, we also looked at how the filter system works when it is shut down for a number of days.

The results on a lab scale are very promising. It appears that 75% to 80% of the adsorption capacity can be recovered in a relatively short time. The tests show that bio-regeneration is possible with the help of bacteria that already occur naturally in the washing water. Further inoculation with bacteria specially selected for this purpose (bioaugmentation) provides additional security for extending the life span of the filter system. Even temporary shutdown of the system did not cause any problems and, under the right conditions, further bio-regeneration of the activated carbon took place.

From lab scale to full scale

Meanwhile, a pilot project has been started to test the bio-regeneration of full-scale granular activated carbon filtration with representative washing water, which not only contains metribuzin. For this purpose, 3000 litres of rinse water were collected with agents used in, among others, potato and flower bulb cultivation. The rinse water was analysed to determine which substances and concentrations we were dealing with. Furthermore, we were able to find a suitable test location at an agricultural contractor to test the system.

What are the advantages of this system?

When using a traditional activated carbon filter, the filter pack needs to be replaced approximately once a year. The prognosis is that with a bioregenerative GAC filter this will only be necessary once every 5 to 10 years. That is a huge cost reduction. An additional advantage is that less water needs to be used because the purified water can be reused to clean equipment.

If you would like to know more about the possibilities of this system, please contact Freek van den Heuvel.

This research has been made possible thanks to LTO Noord and the Union of Water Boards' Emission Reduction Budget for Open Crops and Livestock Farming.

Freek van den Heuvel
Consultant water quality and phytoremediation