Biological denitrification using poly(butylene succinate) as carbon source and biofilm carrier for recirculating aquaculture system effluent treatment.

Nitrate removal is essential for the sustainable operation of recirculating aquaculture system (RAS). This study evaluated the heterotrophic denitrification using poly(butylene succinate) as carbon source and biofilm carrier for RAS wastewater treatment. The effect of varied operational conditions (influent type, salinity and nitrate loading) on reactor performance and microbial community was investigated. The high denitrification rates of 0.53 ± 0.19 kg NO3(-)-N m(-3) d(-1) (salinity, 0‰) and 0.66 ± 0.12 kg NO3(-)-Nm(-3) d(-1) (salinity, 25‰) were achieved, and nitrite concentration was maintained below 1mg/L. In addition, the existence of salinity exhibited more stable nitrate removal efficiency, but caused adverse effects such as excessive effluent dissolved organic carbon (DOC) and dissimilation nitrate reduce to ammonia (DNRA) activity. The degradation of PBS was further confirmed by SEM and FTIR analysis. Illumina sequencing revealed the abundance and species changes of functional denitrification and degradation microflora which might be the primary cause of varied reactor performance.

[Model of regularity of ammonia transformation along marine biological aerated filter].

This study investigates the biological aerated filter (BAF) of a marine recirculating aquaculture system, which is important to remove harmful ammonia and organics. A model, characterizing the ammonia transformation along the BAF, was established on the basis of the principle of adsorption and the first order reaction bio-film. Experiments were performed and verified the effectiveness of the proposed model. The target BAF was packed with bamboo ring for 70 cm high. Study under the conditions [pH 7.1-7.6, DO 5-7 mg x L(-1), gas water ratio about 20 : 1, organic load about 4 g x (m3 x h)(-1)] shows that ammonia is removed significantly under the 10 cm height of medium, while less ammonia is removed between 10-70 cm. Experimental results confirm that the model predicts the ammonia concentration along the BAF accurately with a low influent ammonia concentration, but the predicted value is slightly lower than the true value with a high influent ammonia concentration. Study on ammonia concentration along the BAF reveals that the effluent ammonia concentration increases along with either the increment of the influent ammonia concentration or the reduction of the hydraulic retention time.