Skip to main content
ARS Home » Northeast Area » Leetown, West Virginia » Cool and Cold Water Aquaculture Research » Research » Publications at this Location » Publication #160336
Title: AEROBIC TREATMENT OF GRAVITY THINKENING TANK SUPERNATANT

Author
item Brazil, Brian
item SUMMERFELT, STEVE - FRESHWATER INSTITUTE

Submitted to: Aquacultural Engineering
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/25/2005
Publication Date: 2/2/2006
Citation: Brazil, B.L., Summerfelt, S. 2006. Aerobic treatment of gravity thinkening tank supernatant. Aquacultural Engineering. 34:92-102.

Interpretive Summary: Improved treatment strategies for aquaculture effluent streams produce cleaner primary discharges but also generate secondary flows, some of which contain high concentrations of dissolved nutrients and suspended solids. This secondary flow is often stored and used as fertilizer. However, this strategy is not applicable in all areas. For some areas, additional treatment is necessary so that the high nutrient effluent can be disposed. In the current study, this secondary stream was treated aerobically at different flow rates to determine the impact of treatment time on effluent quality. Organic constituents measured as soluble BOD, DOC and COD were easily removed at efficiencies of 91%, 87%, and 75%, respectively, across all treatment times. Simultaneously, reductions in TAN and dissolved phosphorous of 88% and 64, respectively, were achieved. In contrast, nitrate and TSS concentrations, increased across all HRTs. Nitrate production reflected the conversation of ammonia, while TSS increases resulted from the accumulation of algae and particulate matter in the basin. The results demonstrate that aerobic treatment can achieve significant organic and nutrient reductions at the times studied. However, this treatment strategy did not allow for direct discharge of effluent because of the elevated algae concentrations. Thus, a final filtration step in necessary for algae harvesting to meet TSS discharge limits.

Technical Abstract: Aerobic treatment of the supernatant overflowing an aquaculture manure thickening tank was studied in replicated circular tank reactors (500 L) at 1, 3, and 6 day hydraulic retention times. Additionally, the effects of temperature and day length on effluent quality were examined by conducting the study during summer and winter months. Supernatant collected from off-line gravity thickeners was delivered to the reactors for treatment. Changes in the influent stream characteristics were a result of seasonal variations, most likely reflecting biological activity occurring within gravity thickeners. Organic carbon constituents were readily removed during aerobic treatment. Soluble BOD concentrations were decreased an average 91% and 82% across all HRTs during the summer and winter phases, respectively. Soluble COD and soluble DOC removal efficiencies varied from 75% to 87% across all treatments during both study phases. TAN removal efficiency increased with increasing HRT with an 87% removal efficient achieved at the 6d HRT under summer temperatures. However, the highest TAN removal efficiency, 57%, achieved during the winter phase was observed at the 3d HRT. With respect to nitrite and nitrate concentration, effluent from the 1-day HRT treatment possessed the lowest levels under both temperature conditions. TSS concentrations increased within the aerobic treatment vessels as soluble wastes were converted into heterotrophic micro-organisms and algae cell material. TSS increases within the aerobic treatment vessel suggest that an additional treatment process may be necessary to meet final effluent suspended solids standards when employing this strategy.