# Bioaugmentation has temporary effect on anaerobic pesticide biodegradation in simulated groundwater systems

## TL;DR

Bioaugmentation temporarily improves pesticide breakdown in groundwater systems, but its effects fade over time.

## Contribution

Demonstrates the temporary effectiveness of bioaugmentation in enhancing pesticide biodegradation under different redox conditions.

## Key findings

- Bioaugmentation achieved 100% 2,4-D removal efficiency for 100 days in simulated groundwater systems.
- 2,4-D removal was higher under iron-reducing than sulfate-reducing conditions.
- Microbial community shifts were observed after the first bioaugmentation but not after the second.

## Abstract

Groundwater is the most important source for drinking water in The Netherlands. Groundwater quality is threatened by the presence of pesticides, and biodegradation is a natural process that can contribute to pesticide removal. Groundwater conditions are oligotrophic and thus biodegradation can be limited by the presence and development of microbial communities capable of biodegrading pesticides. For that reason, bioremediation technologies such as bioaugmentation (BA) can help to enhance pesticide biodegradation. We studied the effect of BA using enriched mixed inocula in two column bioreactors that simulate groundwater systems at naturally occurring redox conditions (iron and sulfate-reducing conditions). Columns were operated for around 800 days, and two BA inoculations (BA1 and BA2) were conducted in each column. Inocula were enriched from different wastewater treatment plants (WWTPs) under different redox-conditions. We observed a temporary effect of BA1, reaching 100% removal efficiency of the pesticide 2,4-D after 100 days in both columns. In the iron-reducing column, 2,4-D removal was in general higher than under sulfate-reducing conditions demonstrating the influence of redox conditions on overall biodegradation. We observed a temporary shift in microbial communities after BA1 that is relatable to the increase in 2,4-D removal efficiency. After BA2 under sulfate-reducing conditions, 2,4-D removal efficiency decreased, but no change in the column microbial communities was observed. The present study demonstrates that BA with a mixed inoculum can be a valuable technique for improving biodegradation in anoxic groundwater systems at different redox-conditions.

The online version contains supplementary material available at 10.1007/s10532-023-10039-0.