Reducing contamination of drinking water at the source with surprisingly affordable technology

In the effort to ensure safe, clean drinking water for all, global testing leader ALS is helping study how to reduce pesticides in agricultural run-off, which can leech into drinking water sources, with the use of woodchip bioreactors.

Woodchip bioreactors were initially investigated for their effectiveness in removing excess nitrate from agricultural run-off. Nitrate removal from drinking water is critical because ingesting high levels of the chemical can lead to potential health impacts including respiratory illness, thyroid problems, adverse pregnancy outcomes and some cancers. 

In the European Union, reducing high levels of nitrate in groundwater has been a target of policy since the adoption of the Nitrates Directive. Fertilisers are a main source of nitrate concentrations in groundwaters in the EU, where an estimated 80% of the nitrogen discharge to the EU aquatic environment stems from agriculture.¹ 

Implementing woodchip bioreactors at the edges of agricultural fields has been shown to remove ~5 –90% percent of nitrates from water run-off, and due to the relative simplicity of the technology and its ability to reduce nitrate at the source, woodchip bioreactors have proven an effective alternative to costly technologies required to filter nitrate from already contaminated water.² 

This increasing use of woodchip bioreactors in farms around the world to remove nitrate from field run-off has also given rise to studies of their potential usefulness for removing other contaminants, such as pesticides. Research Project ELIPES, a three-year study that concluded at the end of 2025, conducted in the Czech Republic by ALS in partnership with several Czech research institutions, has confirmed the effectiveness of woodchip bioreactors for pesticide reduction in agricultural runoff.

How do woodchip bioreactors reduce water contamination?

A woodchip bioreactor is a passive, inexpensive and relatively simple technology that operates by channeling water through a woodchip-filled bed, which serves as a long-term source of bioavailable organic carbon. This process promotes heterotrophic denitrification, or the conversion of nitrates by microbes into gaseous nitrogen.

Additionally, the surface above a woodchip bioreactor is typically covered in grass, so they also function as essential drainage systems in agricultural landscapes. Woodchip bioreactors are highly durable and low maintenance, with a proven operational lifespan of 10 to 15 years, and they have no adverse effects on field drainage or crop production.

ALS leads research project on using woodchip bioreactors to reduce pesticides in agricultural run-off

In 2024, ALS reported on the initial findings of Research Project ELIPES – part of a broad study of pesticides in agricultural soils and surrounding surface waters across Central Europe. Project ELIPES, the first phase of which (ELIPES I) concluded at the end of 2025, leveraged ALS’ environmental monitoring expertise to monitor the efficacy of denitrifying woodchip bioreactors for the simultaneous removal of both nitrates and pesticides found in surface runoff from agriculturally active areas in Europe.

The pilot bioreactor monitored in ELIPES I featured a custom cylindrical tank installed partially underground, filled with poplar woodchips, and flooded with water. Powered by a solar panel due to its remote location, water was continuously supplied from a nearby watercourse using a maintenance-free gravity method. A throttle valve at the pipe outlet regulated water flow, enabling control of the hydraulic retention time for optimal bioreactor performance. 

Samples were collected weekly at the inlet and outlet of the bioreactor. In total, about 350 pesticide residues in water and 300 in soil were tested using the LC-MS/MS technique. 

Initial results showed that the pilot bioreactor achieved an average pesticides removal efficiency of 30%, with lower performance observed during the start-up phase and winter, without any modifications to its composition or microflora.

The goal of ELIPES I was to suggest the ideal operating conditions of woodchip bioreactors for maximum facilitation of the natural processes of microbial degradation of pesticides, or to identify ways to effectively support these processes by active intervention in the physicochemical composition of the bioreactor and its microflora.

“This project holds the potential to deliver promising results in the elimination of unwanted agricultural pollution, which could subsequently be applied in everyday practice,” explained
Kateřina Riddellová, Laboratory Manager, Environmental Services, ALS in Prague, Czech Republic.

What are the results of project ELIPES research? 

In ALS’ report on the conclusion of ELIPES I at the end of 2025, the pilot plant was shown to deliver an average denitrification efficiency of 56% (in places up to 86%), achieved over its more than two years of operation, and a significant reduction in the content of key pesticide substances on average around 30%. The effectiveness, robustness and ease of operation of the system in the field underscore the high potential of the solution for farmers, stream managers and water managers.³

Kateřina explains that ELIPES I demonstrates how woochip bioreactors “remove agricultural pollution directly at its source at minimal cost, protecting the environment while also avoiding the need for costly investments in water treatment plant technologies.” Results obtained in ELIPES I will be presented at professional conferences and in communication with representatives of organizations responsible for promoting the installation of bioreactors.

However, before putting these bioreactors into practice for pesticide removal, the project report clarifies that it’s necessary to deepen knowledge about their functioning.

To enable this understanding, a planned follow up project, ELIPES II, has been funded by The Ministry of Agriculture of the Czech Republic through 2030. In this next phase, the project will transition from pilot-scale verification to a comprehensive full-scale solution in an intensively farmed agricultural landscape. A larger, ground-mounted reactor with an expanded spectrum of monitored pollutants - including drugs and antibiotic resistance genes (ARG). 

To optimize the efficiency of the new bioreactor, the existing pilot-scale bioreactor implemented within ELIPES I will also be operated and tested in parallel with it, with the same poplar chip filling. In addition to monitoring pharmaceutically active substances, the expanded monitoring will also include an overview of the spread of ARG from runoff water from arable land.

“In the short term, the project will enable farmers on drained soils to install affordable equipment to reduce nitrogen and pesticide levels, which will operate without the need for energy and maintenance,” Katerina explains. 

“In the long term, the project can contribute to reducing the costs of drinking water treatment and meeting the key regulatory target of a 50% reduction in pesticide concentration in agricultural runoff by 2030.”⁴

To learn more about Project ELIPES and ALS’ comprehensive environmental testing services, email us