Location: Cool and Cold Water Aquaculture ResearchTitle: Denitrifying bioreactor clogging potential during wastewater treatment Author
|Christianson, Laura - Freshwater Institute|
|Lepine, Christine - Freshwater Institute|
|Sharrer, Kata - Freshwater Institute|
|Summerfelt, Steven - Freshwater Institute|
Submitted to: Water Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/30/2016
Publication Date: 8/31/2016
Citation: Christianson, L.E., Lepine, C., Sharrer, K.L., Summerfelt, S.T. 2016. Denitrifying bioreactor clogging potential during wastewater treatment. Water Research. 15:147-156.
Interpretive Summary: Nutrients discharged from aquaculture facilities, in particular nitrogen and phosphorus, can cause eutrophication when released into adjoining watersheds. Waste treatment technologies that are simple, cost-effective, and provide efficient nutrient removal need to be developed and optimized for fish farming applications. In the present study, the potential for woodchip bioreactors to remove nitrate, phosphorus, and suspended solids from an aquaculture effluent was investigated under varying hydraulic retention times. The near-optimum hydraulic retention time for nitrate removal was approximately 24 hours. However, high levels of suspended solids in the aquaculture effluent caused plugging and hydraulic problems within the woodchip bioreactors, primarily around the bioreactor inlet, when operated at shorter hydraulic retention times. This research provides information that will influence the future design and operation of woodchip bioreactors, particularly those used to treat wastewater from aquaculture facilities. This research adds to a growing knowledge base that indicates that wood chip bioreactors are a simple, yet viable water treatment technology for organic-rich aquaculture effluents.
Technical Abstract: Chemoheterotrophic denitrification technologies using woodchips as a solid carbon source (i.e., woodchip bioreactors) have been widely trialed for treatment of diffuse-source agricultural nitrogen pollution. There is growing interest in the use of this simple, relatively low-cost biological wastewater treatment option in waters with relatively higher total suspended solids (TSS) and chemical oxygen demand (COD) such as aquaculture wastewater. This work: (1) evaluated hydraulic retention time (HRT) impacts on COD/TSS removal, and (2) assessed the potential for woodchip clogging under this wastewater chemistry. Four pilot-scale woodchip denitrification bioreactors operated for 267 d showed excellent TSS removal (greater than 90%) which occurred primarily near the inlet, and that COD removal was maximized at lower HRTs (e.g., 56% removal efficiency and 25 g of COD removed per m3 of bioreactor per d at a 24 h HRT). However, influent wastewater took progressively longer to move into the woodchips likely due to a combination of (1) woodchip settling, (2) clogging due to removed wastewater solids and/or accumulated bacterial growth, and (3) the pulsed flow system pushing the chips away from the inlet. The bioreactor that received the highest loading rate experienced the most altered hydraulics. Statistically significant increases in woodchip P content over time in woodchip bags placed near the bioreactor outlets (0.03 vs 0.10%P2O5) and along the bioreactor floor (0.04 vs. 0.12%P2O5) confirmed wastewater solids were being removed and may pose a concern for subsequent nutrient mineralization and release. Nevertheless, the excellent nitrate-nitrogen and TSS removal along with notable COD removal indicated woodchip bioreactors are a viable water treatment technology for these types of wastewaters given they are used downstream of a filtration device.