Hongxin Tan

Effect of dissolved oxygen on heterotrophic denitrification using poly(butylene succinate) as the carbon source and biofilm carrier.

The effect of dissolved oxygen (DO) on heterotrophic denitrification using poly(butylene succinate) as the carbon source and biofilm carrier was evaluated in a lab-scale experiment. Aerated, low-oxygen, and anoxic treatment groups were set up, which had average DO concentrations of 5.2±1.0, 1.4±1.2, and 0.5±0.3 mg L(-1), respectively. The NO3(-)-N and total nitrogen (TN) removal rates in the aerated group (37.44±0.24 and 36.24±0.48 g m(-3) d(-1), respectively) were higher than those in the other two groups. There was no significant difference between the low-oxygen and anoxic groups for the NO3(-)-N or TN removal rate. Accumulation of NO2(-)-N reached 5.0 mg L(-1) in the aerated group; no nitrite accumulation was found in the other two treatment groups. Bacterial communities of the low-oxygen and anoxic groups showed high similarity and were significantly different from those of the aerated group.

Effect of dissolved oxygen on nitrate removal using polycaprolactone as an organic carbon source and biofilm carrier in fixed-film denitrifying reactors.

Nitrate-nitrogen (NO3(-)-N) always accumulates in commercial recirculating aquaculture systems (RASs) with aerobic nitrification units. The ability to reduce NO3(-)-N consistently and confidently could help RASs to become more sustainable. The rich dissolved oxygen (DO) content and sensitive organisms stocked in RASs increase the difficulty of denitrifying technology. A denitrifying process using biologically degradable polymers as an organic carbon source and biofilm carrier was proposed because of its space-efficient nature and strong ability to remove NO3(-)-N from RASs. The effect of dissolved oxygen (DO) levels on heterotrophic denitrification in fixed-film reactors filled with polycaprolactone (PCL) was explored in the current experiment. DO conditions in the influent of the denitrifying reactors were set up as follows: the anoxic treatment group (Group A, average DO concentration of 0.28±0.05mg/L), the low-oxygen treatment DO group (Group B, average DO concentration of 2.50±0.24mg/L) and the aerated treatment group (Group C, average DO concentration of 5.63±0.57mg/L). Feeding with 200mg/L of NO3(-)-N, the NO3(-)-N removal rates were 1.53, 1.60 and 1.42kg/m(3) PCL/day in Groups A, B and C, respectively. No significant difference in NO3(-)-N removal rates was observed among the three treatments. It was concluded that the inhibitory effects of DO concentrations lower than 6mg/L on heterotrophic denitrification in the fixed-film reactors filled with PCL can be mitigated.

Removal of geosmin and 2-methylisoborneol by bioflocs produced with aquaculture waste

Geosmin and 2-methylisoborneol (MIB) are two of the most common odorous compounds that critically affect the quality of fish. In the current study, the solid fish waste from a recirculating aquaculture system (RAS) was used as the substrate to produce bioflocs in suspended growth reactors (SGRs). The removal efficiency of geosmin and MIB by the bioflocs was investigated under in situ and in vitro conditions. The highest removal rates for geosmin and MIB in the SGRs were 187.00xa0±xa00.23 and 170.91xa0ng L−1 d−1, respectively. Under the in vitro experimental conditions, 90.30xa0% of the geosmin and 72.93xa0% of the MIB were removed from the aqueous phase by the bioflocs within 48xa0h of incubation. It was found that the decay of these odorous compounds by the bioflocs was mediated by both chemical/physical sorption and biological degradation. Moreover, the addition of these odorous compounds did not affect the treatment efficiency of the reactors and had no adverse influence on the crude protein content of the bioflocs. Thus, using biofloc technology (BFT), SGRs can be used to reuse the nitrogen in fish waste and to remove geosmin and MIB from the culture water efficiently.

Enhancement of Anaerobic Digestion to Treat Saline Sludge from Recirculating Aquaculture Systems

The effectiveness of carbohydrate addition and the use of ultrasonication as a pretreatment for the mesophilic anaerobic digestion of saline aquacultural sludge was assessed. Analyses were conducted using an anaerobic sequencing batch reactor (ASBR), which included stopped gas production attributed to the saline inhibition. After increasing the Cu2009:u2009N ratio, gas production was observed, and the total chemical oxygen demand (TCOD) removal efficiency increased from 75% to 80%. The TCOD removal efficiency of the sonication period was approximately 85%, compared to 75% for the untreated waste. Ultrasonication of aquaculture sludge was also found to enhance the gas production rate and the TCOD removal efficiency. The average volatile fatty acid (VFA) to alkalinity ratios ranged from 0.1 to 0.05, confirming the stability of the digesters. Furthermore, soluble chemical oxygen demand (SCOD), VFA, and PO4 3− concentrations increased in the effluents. There was a 114% greater gas generation during the ultrasonication period, with an average production of 0.08u2009g COD/L·day−1.

Effects of Inoculated Bacillus subtilis on Geosmin and 2-Methylisoborneol Removal in Suspended Growth Reactors Using Aquacultural Waste for Biofloc Production

Geosmin and 2-methylisoborneol (2-MIB) are two of the most common taint compounds that adversely affect the quality of aquacultural animals. In the present study, 94% of geosmin and 97% of 2-MIB in suspended growth reactors producing bioflocs (SGRs) with aquaculture waste were removed after inoculation with Bacillus subtilis, significantly higher than that of control SGRs (70% of geosmin and 86.4% of 2-MIB). The lowest concentrations of geosmin and 2-MIB achieved in the effluent of the SGRs were 2.43 ± 0.42 ng/l and 2.23 ± 0.15 ng/l, respectively. The crude protein content of the bioflocs produced in the SGRs was 35 ± 4%. The NH4(+)-N and NO2(-)-N concentrations in the effluent of the reactors were 1.13 ± 0.21 mg/l and 0.42 ± 0.04 mg/l, respectively. These results suggest that inoculated with Bacillus subtilis, SGRs have a better performance to reuse the nitrogen in fish waste and to remove geosmin and 2-MIB from the culture water efficiently.

Effects of Temperature on Inorganic Nitrogen Dynamics in Sequencing Batch Reactors using Biofloc Technology to Treat Aquaculture Sludge

Abstract As a new aquaculture technology, biofloc technology (BFT) makes it possible to minimize water exchange and convert the nitrogen in aquacultural waste into biofloc, which can be a natural fish food within the culture system. In the current study, biofloc bacteria were employed to treat sludge from a recirculating aquaculture system under four different temperatures (15, 20, 25, and 30°C) in three sequencing batch reactors (SBRs) per temperature. Ammonium reduction was seen on days 19, 17, 13, and 17 for the 15, 20, 25, and 30°C groups, respectively, indicating that the biofloc bacteria started to convert ammonium to microbial biomass on that day. The nitrite concentration remained below 6.5xa0mg/L for each group except the 30°C group, in which the value reached 13.88xa0mg/L. The nitrate concentration remained below 4.5xa0mg/L for each group. An ammonia nitrogen removal study revealed that all SBRs could remove a total ammonia nitrogen (TAN) concentration of 10xa0mg/L in 6xa0h without increasing the nitrite ...

Effect of Low Salinity on Jade Perch Scortum barcoo Performance in a Recirculating Aquaculture System

Abstract The jade perch Scortum barcoo is a new species in the developing freshwater finfish grow-out sector. In this study, the effects of salinity (0, 5, and 10‰) on growth and several physiological indicators of jade perch were investigated. Salinity did not have a significant effect on mean weight gained, condition factor, and feed efficiency of the fish, but it significantly affected their specific growth rate during the 28-d experiment. The levels of serum alanine transaminase and triacylglycerol did not differ significantly among the three treatment groups, but salinity did significantly affect serum cortisol level and serum lysozyme activity. Despite the elevation in circulating cortisol induced by saline conditions, growth of jade perch was not negatively affected, and the specific growth rate suggested an improved growth rate in fish held in 5‰ salinity water. Received May 31, 2011; accepted December 5, 2011

Nitrate removal efficiency and bacterial community of polycaprolactone-packed bioreactors treating water from a recirculating aquaculture system

A denitrification reactor packed with polycaprolactone (PCL) as a carbon source and biofilm carrier was developed to remove nitrate nitrogen (NO3−−N

Growth, digestive activity, welfare, and partial cost-effectiveness of genetically improved farmed tilapia (Oreochromis niloticus) cultured in a recirculating aquaculture system and an indoor biofloc system

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