Integrating activated sludge membrane biological reactors with freshwater RAS: Preliminary evaluation of water use, water quality, and rainbow trout Oncorhynchus mykiss performance

Authors: DAVIDSON, JOHN - Freshwater Institute; SUMMERFELT, STEVE - Freshwater Institute; Schrader, Kevin; GOOD, CHRISTOPHER - Freshwater Institute

Submitted to: Aquacultural Engineering
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/26/2019
Publication Date: 9/29/2019
Citation: Davidson, J., Summerfelt, S., Schrader, K.K., Good, C. Integrating activated sludge membrane biological reactors with freshwater RAS: Preliminary evaluation of water use, water quality, and rainbow trout Oncorhynchus mykiss performance. Aquacultural Engineering. 2019;87:102022. https://doi.org/10.1016/j.aquaeng.2019.102022.
DOI: https://doi.org/10.1016/j.aquaeng.2019.102022

Interpretive Summary: Activated sludge membrane biological reactors (MBRs) were evaluated for their potential in conserving water usage and on enhancing water quality in recirculating aquaculture systems (RAS) used to grow rainbow trout. Water conservation was determined to be the main benefit of incorporating MBRs into RAS while further studies are needed to verify improvement of water quality variables such as denitrification efficiency and the reduction of common off-flavor compounds.

Technical Abstract: Onsite research indicates that activated sludge membrane biological reactors (MBRs) are an effective waste treatment technology for aquaculture effluents. MBRs produce a filtered permeate that is nearly free of dissolved nutrients, organics, and solids; therefore, this technology could be well-suited for integration within the process control loop of recirculation aquaculture systems (RAS). A four-month study was carried out to evaluate the feasibility of incorporating single-vessel MBRs within freshwater RAS while culturing rainbow trout Oncorhynchus mykiss. Triplicate RAS with and without MBRs (controls) were evaluated; mRAS and cRAS, respectively. System backwash water of mRAS was processed and retained within MBRs which allowed increased water recycling, while cRAS utilized standard dilution rates to limit nitrate accumulation. On average, mRAS required six and a half times less makeup water. Mean daily water replacement of the RAS volume for mRAS and cRAS was 1.2 ± 0.4 and 7.8 ± 0.5 %, respectively (P < 0.05). A range of water quality concentrations were significantly greater in mRAS including: chloride, carbon dioxide, heterotrophic bacteria count, pH, nitrate-nitrogen, total ammonia-nitrogen, total phosphorous, and true color, as well as dissolved concentrations of calcium, copper, magnesium, and sulfur. Alkalinity and ultraviolet transmittance levels were significantly lower in mRAS. These culture environment differences did not affect rainbow trout growth, feed conversion, or survival (P > 0.05). In addition, concentrations of common off-flavor compounds (geosmin and 2- methylisoborneol) in water and fish flesh were not affected by MBR presence. Improvements for future MBR integration with RAS were realized including optimization of MBR permeate rates, increased RAS water exchange through the MBRs, and infrequent supplementation of a carbon source to enhance denitrification efficiency and alkalinity recovery. Overall, incorporating MBRs within RAS resulted in substantial water savings and was biologically feasible for rainbow trout production.