Assessment of Woodchip Bioreactor Characteristics and Their Influences on Joint Nitrate and Pesticide Removal

Abstract

We constructed a bench-scale continuous-flow (8 L total volume, 4.3 L/day) woodchip bioreactor and operated the reactor under field-like conditions to evaluate joint pesticide and nitrate removal. The continuous-flow reactor achieved 83.5 ± 8% diuron removal and 61.6 ± 11.9% imidacloprid removal with a 24 h hydraulic retention time (HRT). We designed a sequencing-batch reactor configuration (8 L total volume) to evaluate the impact of an aerobic phase on denitrification and pesticide removal performance. The sequencing-batch reactor achieved 89.2 ± 8.8% nitrate removal with a hydraulic retention time (HRT) of 12 h, while the continuous-flow design achieved 55.6 ± 9.1% nitrate removal with a 12 h HRT. There was no significant difference between pesticide removal between sequencing-batch and continuous-flow reactor types (p = 0.655 and p = 0.316 for diuron and imidacloprid removal, respectively). Kinetic batch tests revealed sorption, not microbial degradation, as the main mechanism of removal for both diuron and imidacloprid under denitrifying conditions. Imidacloprid removal ranged from 440.4 to 532.0 ng/gwoodchip (dry mass) and diuron removal between 468.6 and 553.8 ng/g-woodchip (dry mass) over 24 h. The bench-scale evaluation of pesticide behavior in woodchip bioreactors highlights the need to improve microbial degradation in such best management practices for pesticide removal.

Evaluation of woodchip‐bioditch reactors as a nutrient reduction conservation strategy

“…This lower NO 3 − reduction rate could be attributed to differences in condition and age of the reactors, considering anoxic conditions are preferred for denitrification (Payne, 1973;Seitzinger, 1988). However, in a bench-scale continuous flow woodchip bioreactor (8-L total volume), Wrightwood et al (2022) reported 55.6 ± 9.1% NO 3 − removal within a 12-h HRT, which is within the range observed in the current study.…”

Degradation of imidacloprid by Phanerodontia chrysosporium on wood chips for stormwater treatment

“…Sorption of imidacloprid to wood chips has been observed previously with 440–532 ng g −1 wood chips sorbed in one day and no significant sorption noted afterwards. 25 This value was lower than our observed average of 1185 ng g −1 d −1 sorption measured in the first seven days. Although the day 14 concentrations are anomalous, day 7 concentrations did not vary significantly from day 21 or day 28 values ( p = 0.31, 0.33).…”

“…Sorption of imidacloprid to wood chips has been observed previously with 440-532 ng g −1 wood chips sorbed in one day and no significant sorption noted afterwards. 25 This value was lower than our observed average of 1185 ng g −1 d −1 sorption measured in the first seven days.…”

“…52 Sorption of imidacloprid to filter media, such as wood chips or biochar, could allow for increased opportunity for fungal biodegradation, even in systems with shorter residence times. 25,26 Although current designs of bioretention cells are not intended for fungal degradation as a designed process, our results suggest fungal bioremediation could augment imidacloprid removal in similar systems.…”

“…Wrightwood et al observed 56.2% imidacloprid removal due to sorption to wood chips in 12 hours. 25 In another study, a comparison of sand and biochar-amended sand filters revealed that sand filters alone were ineffective in removing imidacloprid, while biochar-amended sand filters removed up to 100% of imidacloprid in two hours. 26 However, sorption-based treatments merely remove, not degrade, contaminants, posing concerns about longevity and contaminated media management.…”