WOODCHIPS BARRIERS FOR ATRAZINE AND NITRATE REMOVAL; EFFECT OF BIOCHAR AMENDMENT

Atrazine is the second most commonly used herbicide in the United States. It is very persistent in the environment; thus, it is frequently detected in reservoirs. In this study, we investigated the removal of atrazine by woodchips barriers in aerobic and anaerobic conditions. We also investigated the effect of biochar amendment on atrazine removal. Woodchips already have applications as substrate for the denitrifying bioreactors, since they provide organic matter and anaerobic conditions for denitrification.

Twelve flow-through chambers were constructed and filled with woodchips and woodchips and biochar (1:1 by volume). Synthesized drainage water flowed through the aerobic and anaerobic chambers and contained two levels of nitrate-N; 1.5 and 11.5 mgL^-1, two levels of atrazine; 20 and 50 µgL^-1, and 2 mgL^-1 phosphorus-P. Samples from the effluent were collected and analyzed for nitrate-N, phosphorus-P and atrazine.

Results showed a co-removal of atrazine and nitrate-N in short retention times in anaerobic conditions. In 4 hours, anaerobic woodchips chambers removed 65 % of nitrate-N and 35 % of atrazine. The removal of atrazine and nitrate-N increased with increasing retention time to 72 hours, and reached to 55% and 100 %, respectively. Addition of biochar increased atrazine removal by 40%. Aeration and nitrate level did not impact atrazine removal. In aerobic conditions, the removal of nitrate was coupled with the uptake of phosphorus, which is an indicator of cell assimilation, and is not a strong pool for nutrients. Although adsorption was the main factor for atrazine removal, atrazine metabolites were detected at the effluent of the chambers. The effluent of the anaerobic chambers contained hydroxyatrazine while the effluent of the aerobic chambers contained atrazine desethyl.