Denitrifying bioreactor inflow manifold design influences treatment of aquacultural wastewater

Authors: LEPINE, CHRISTINE - Freshwater Institute; CHRISTIANSON, LAURA - University Of Illinois; MCISAAC, GREGORY - University Of Illinois; SUMMERFELT, STEVEN - Superior Fresh

Submitted to: Aquacultural Engineering
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/11/2019
Publication Date: 11/12/2019
Citation: Lepine, C.A., Christianson, L., Mcisaac, G., Summerfelt, S. 2019. Denitrifying bioreactor inflow manifold design influences treatment of aquacultural wastewater. Aquacultural Engineering. 88:102036. https://doi.org/10.1016/j.aquaeng.2019.102036.
DOI: https://doi.org/10.1016/j.aquaeng.2019.102036

Interpretive Summary: Land-based recirculating aquaculture is subject to point-source effluent regulations. The industry recognizes the need for cost-efficient nitrogen remediation in order to meet discharge requirements. Denitrifying woodchip bioreactors have previously demonstrated to be an effective nitrogen removal system, though the system lifespan may be less than desired due to the high-strength nature of treating aquacultural wastewaters. This study assessed two different influent manifold designs in regard to overall system performance. Operating under a variety of influent conditions the bioreactors generally did not demonstrate performance differences regardless of manifold design. However, under the highest concentrated wastewater tested, the experimental manifold outperformed the traditional-use manifold with a 10% increase in removal efficiency for both nitrate and total suspended solids. Additionally, this is the first publication to report on aquacultural-use bioreactors through an entire second year of operation with systems removing 17-25 mg NO3-N per m3 per day. Regardless of manifold design, this study demonstrated that bioreactors could perform effectively under continuous operation for extended periods, removing substantial amounts of nitrate, which might otherwise exceed a facility’s discharge permit. For recirculating aquaculture operations with higher concentration wastewater, the experimental manifold design may extend system performance over a traditional manifold design.

Technical Abstract: Recirculating aquaculture systems (RAS) facilities subject to point-source effluent regulations need to implement cost-effective N remediation for their wastewater outflows. Relatively low-cost denitrifying “woodchip” bioreactors can effectively remove N from aquaculture effluents for at least one year, but there remain questions about bioreactor lifespan for such high-strength wastewaters. Four pilot-scale bioreactors (L x W x D; 3.8 x 7.5 x 0.61 m), two with a conventional single distribution inflow manifold and two with an experimental multiple-header, feed-forward distribution manifold, were operated over 784 d to observe second-year N removal performance and to determine if the manifold design can influence bioreactor effectiveness. The study also quantified performance metrics for chemical oxygen demand, total suspended solids, and phosphorus. Manifold style did not have notable impact on bioreactor performance when treating wastewater under the facilities’ normal operating conditions, but the multiple distribution style demonstrated an approximately 10% increase in both nitrate and total suspended solids removal efficiency over the single distribution manifold toward the end of the study when bioreactors treated higher strength wastewater. Additionally, bioreactor performance in both manifold designs decreased from an average of 92% total suspended solids removal efficiency under normal operating conditions to less than 76% when treating the high strength wastewater. The bioreactors provided N removal rates of 17-25 g NO3-N m-3 d-1 during the second year of study, demonstrating woodchip bioreactors can effectively treat aquaculture effluent for at least two years without major detrimental impacts due to potential clogging.