The investigation of the interaction between fluorescent carbon dots labeling silk fibroin using a fluorescence microscope-surface plasmon resonance system.

The use of fluorescent carbon dots (CDs) as highly precise biolabeling probes has been widespread in the fields of live cell imaging and protein labeling due to their small size and excellent photoluminescence ability to accurately target specific molecules with surface chemical properties. However, there was a lack of research on the interaction between CDs and labeled molecules. In this work, we presented a novel investigation strategy, the fluorescence microscopy-surface plasmon resonance (FM-SPR) system, which combined the use of fluorescence microscopy and wavelength modulation surface plasmon resonance to study the interaction between CDs and labeled molecules in real-time. Using this system, simultaneously recorded the SPR signals and the fluorescence images on the surface of the FM-SPR sensor chip. We observed the dynamic curve and fluorescence images of the interaction between green emissive nitrogen-doped carbon dots (N-CDs) and silk fibroin (SF) in real-time. The kinetic parameters, the quantitative analysis, and the investigation of the binding could be achieved. The results showed a strong linear relationship between the change in SPR signals and the concentration of N-CDs, with a linear coefficient of 0.99913. The linear detection range was 2.5 µg/mL-100 µg/mL, and the real lowest detection limit reached 0.5 µg/mL. Additionally, the green fluorescence points in the imaging region on the FM-SPR sensor chip increased with the concentration of N-CDs, which was consistent with the change in SPR signals. Using this system we also acquired the association rate and dissociation rate of N-CDs to SF which were 2.65 × 10-5/s and 1.52 × 10-5/s, respectively. This demonstrated the effectiveness of our method in quantitatively analyzing SF labeled with N-CDs.

A novel multitrophic biofloc technology for duckweed and Megalobrama amblycephala integrated culture: Improving nutrient utilization and animal welfare.

Biofloc technology (BFT) is an eco-friendly aquaculture model that utilizes zero-exchange water. In this study, we investigated the integration of duckweed into BFT in an effort to enhance nitrogen, phosphorus, and carbon utilization and to improve animal welfare for cultivating Megalobrama amblycephala. The experiment spanned 75 days, comparing a group of M. amblycephala supplemented with duckweed (DM) to a control group (CG) with no supplementation, where duckweed consumption relied solely on the feeding behavior of the fish. The concentrations of nitrate, total nitrogen, and phosphorus accumulation were lower in the DM than in the CG from day 45 onwards, with differences of 16.19, 26.90, and 1.45 mg/L, respectively, at the end of the experiment. The DM showed simultaneous increases of 5.77, 11.20, and 5.07 % in the absolute utilization of nitrogen, phosphorus, and carbon, respectively. The abundance of TM7a (10.27 %), linked to nitrate absorption, became the dominant genus in the water of the DM. Additionally, the abundance of Cetobacterium, associated with carbohydrate digestion, was significantly higher in gut of the DM (23.83 %) than in the gut of CG (1.24 %, P < 0.05). Supplementing the diet of M. amblycephala with duckweed improved digestion and antioxidant enzyme activity. Transcriptome data showed that duckweed supplementation resulted in an increase in the expression of genes related to protein digestion and absorption and carbohydrate metabolism in M. amblycephala, and analysis of the significantly enriched pathways further supported improved antioxidant capacity. Based on the above results, we concluded that as M. amblycephala consumes more duckweed, the differences in nitrogen and phosphorus levels between the DM and CG would continue to increase, along with a simultaneous increase in fixed carbon. Thus, this study achieved the goal of recycling BFT resources and improving animal welfare by integrating duckweed.

Performance of feeding black soldier fly (Hermetia illucens) larvae on shrimp carcasses: A green technology for aquaculture waste management and circular economy.

Over 944 thousand tonnes of shrimp carcasses are produced worldwide during the shrimp production cycle, and black soldier fly larvae (BSFL) are a potential solution for this shrimp carcass accumulation. In this study, we evaluated the performance of BSFL feeding on shrimp carcasses. Six combinations of wheat bran and shrimp carcass powder (with replacement increments of 20 %) and one whole shrimp carcasses treatment were tested. The bioconversion rate (27.15 ± 3.66 %; p = 0.001), crude protein (55.34 ± 1.27 %; p < 0.001), and crude lipid (14.37 ± 1.86 %; p = 0.007) values of BSFL reared on whole shrimp carcasses were significantly higher than those of BSFL reared on wheat bran. Increasing the shrimp carcass amount in the feeding media resulted in significant increases in BSFL docosahexaenoic acid (with the highest value occurring for BSFL reared on whole shrimp carcasses; 1.46 ± 0.09 %; p < 0.001). Conversely, BSFL docosahexaenoic acid was not detected for BSFL reared on wheat bran. The detected heavy metal concentrations in BSFL were below the limits of the published international guidelines for animal feed. In the obtained BSFL, Salmonella was not detected, and the mould count was <10 CFU/g. The total bacterial count (Lg transformation) of obtained BSFL ranged from 7.88 to 8.07 CFU/g, and no significant differences among all treatments (p = 0.424). Overall, this study demonstrates that BSFL-based bioconversion presents a resource recovery technology for converting shrimp carcasses into high-value nutritional biomass.

A lightweight network for traffic sign recognition based on multi-scale feature and attention mechanism.

Traffic sign recognition is an important part of intelligent transportation system. It uses computer vision and traffic sign recognition technology to detect and recognize traffic signs on the road automatically. In this paper, we propose a lightweight model for traffic sign recognition based on convolutional neural networks called ConvNeSe. Firstly, the feature extraction module of the model is constructed using the Depthwise Separable Convolution and Inverted Residuals structures. The model extracts multi-scale features with strong representation ability by optimizing the structure of convolutional neural networks and fusing of features. Then, the model introduces Squeeze and Excitation Block (SE Block) to improve the attention to important features, which can capture key information of traffic sign images. Finally, the accuracy of the model in the German Traffic Sign Recognition Benchmark Database (GTSRB) is 99.85%. At the same time, the model has good robustness according to the results of ablation experiments.

Ecytonucleospora hepatopenaei n. gen. et comb. (Microsporidia: Enterocytozoonidae): A redescription of the Enterocytozoon hepatopenaei (Tourtip et al., 2009), a microsporidian infecting the widely cultivated shrimp Penaeus vannamei.

The microsporidian Enterocytozoon hepatopenaei from Penaeus vannamei (EHPPv) was redescribed on the basis of spore morphology, life cycle, pathology, and molecular character. Compared with the Enterocytozoon hepatopenaei isolated from Penaeus monodon (EHPPm), described by Tourtip et al. in 2009, new features were found in EHPPv. Electron microscopy demonstrated that EHPPv was closely associated with the nucleus of host cell. The merogony and sporogony phages were in direct contact with the cytoplasm of host cells, whereas some of the sporoblasts and the spores were surrounded by the interfacial envelope. Mature spores of EHPPv were oval and monokaryotic, measuring 1.65 ± 0.15 µm × 0.92 ± 0.05 µm. Spores possessed many polyribosomes around a bipartite polaroplast and the polar filament with 4-5 coils in two rows. Phylogenetic analyses showed all Enterocytozoon hepatopenaei isolates shared a common ancestor. Based on the morphological and molecular analyses, we propose the establishment of a new genus Ecytonucleospora and transferring Enterocytozoon hepatopenaei to the genus Ecytonucleospora, retaining the specific epithet hepatopenaei that Tourtip et al. proposed in recognition of their first research, as the new combination Ecytonucleospora hepatopenaei n. comb. Furthermore, it was suggested Enterospora nucleophila, Enterocytozoon sp. isolate RA19015_21, and Enterocytozoon schreckii be assigned into this new genus.

Impacts of Nile Tilapia (Oreochromis niloticus) exposed to microplastics in bioflocs system.

Microplastics (MPs) are abundant in aquaculture water, including in bioflocs aquaculture systems. Compared with other aquaculture systems, biofloc technology systems have the richest microbes and are beneficial to cultivated organisms. Therefore, this study provides a comprehensive assessment of the potential effects of MPs on aquaculture organisms in bioflocs systems. Here, Nile Tilapia (Oreochromis niloticus) were exposed to MPs (polystyrene; 32-40 µm diameter) with 0, 80 items/L (30 µg/L), and 800 items/L (300 µg/L) for 28 days in a bioflocs aquaculture system. The results showed that the MPs generally had no apparent effect on water quality, tilapia growth, or digestive enzyme activity. However, MPs accumulated the most in the liver (5.65 ± 0.74 µg/mg) and significantly increased the hepato-somatic index of tilapia and reduced the crude protein and lipid of tilapia muscle (p < 0.05). The levels of the antioxidant enzymes catalase and glutathione S-transferase increased significantly in response to MPs (p < 0.05). In contrast, MPs did not affect the content of glutathione, glutathione peroxidase, oxidized glutathione, and malondialdehyde, or the enzyme activity of Na+/K+-ATPase. Moreover, using an improved integrated biomarker response index, growth performance was found to be less responsive to MPs than to oxidative stress and digestive activity. Exposure to MPs did not significantly influence the microbial communities of the bioflocs and tilapia guts (p < 0.05). These results suggest that MPs barely affected tilapia in the bioflocs system. This study contributes to the evaluation of the ecological risk of MPs in aquaculture systems and a better understanding of the integrated response of cultivated vertebrates to MPs in biofloc technology systems.

A modification of nested PCR method for detection of Enterocytozoon hepatopenaei (EHP) in giant freshwater prawn Macrobrachium rosenbergii.

The microsporidian Enterocytozoon hepatopenaei (EHP) has become a critical threat to the global shrimp aquaculture industry, thus necessitating early detection by screening. Development of a rapid and accurate assay is crucial both for the active surveillance and for the assessment of shrimp with EHP infection. In the present study, a distinct strain of E. hepatopenaei (EHP Mr ) was found in Macrobrachium rosenbergii. The SWP1 gene analysis revealed it was a new genotype that differed with the common strain isolated from the Litopenaeus vannamei (EHP Lv ). A nested SWP-PCR method was modified to fix the bug that the original inner primers could not recognize the EHP Mr strain. The redesigned inner primers successfully amplified a product of 182 bp for both the EHP Mr strain and the EHP Lv strain. The new primers also had good specificity and high sensitivity, which may serve as an alternative for EHP genotyping. This study provided a method for detection of EHP in the biosecurity of Macrobrachium rosenbergii farming, and the developed protocol was proposed for the routine investigation and potential carrier screening, especially for molecular epidemiology.

Dietary effects of aucubin on growth and flesh quality of grass carp (Ctenopharyngodon idellus) based on metabolomics.

This aim of this study was to investigate the effects of dietary aucubin on the growth, flesh quality, and metabolomics of grass carp (Ctenopharyngodon idella). Five diets were designed with the aucubin inclusion of 0 (control diet), 0.2, 0.4, 0.6, and 0.8 g/kg (Auc-0.2, Auc-0.4, Auc-0.6, Auc-0.8) and were fed to grass carp with an initial body weight of 17.0 ± 0.2 g for 60 d. The results indicated that dietary aucubin did not significantly affect the growth performance of grass carp (P > 0.05). Compared to the control, dietary supplementation with 0.2 to 0.8 g/kg aucubin increased flesh hardness, chewiness, the activities of superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx), and the contents of total free amino acids (TFAA) and n-3 polyunsaturated fatty acids (n-3 PUFA) (P < 0.05). The contents of malondialdehyde (MDA) and lactic acid (LD) in the flesh were significantly decreased by the addition of 0.4 to 0.6 g/kg aucubin and by the addition of 0.6 to 0.8 g/kg aucubin (P < 0.05), respectively, while the content of delicious amino acids (DAA) was significantly enhanced by the addition of 0.4 to 0.8 g/kg aucubin (P < 0.05). Moreover, the contents of collagen and C22:6n3 (DHA) in the flesh of the Auc-0.8 group were significantly higher than those of the control (P < 0.05). In the metabolomics profiling of flesh, 133 and 135 named differential metabolites were identified in the Auc-0.4 and Auc-0.8 groups, respectively, compared to the control, and these metabolites were found to be involved in the second-grade pathways of "lipid metabolism" and "amino acid metabolism". Regarding gene expression, the mRNA levels of CuZn-SOD, CAT, COL1A1, COL1A2, Smad4, and FAS in flesh were upregulated in the Auc-0.4 and Auc-0.8 groups, and the expression levels of GPx, Nrf2, and TGF-ß1 mRNA were also upregulated in the Auc-0.8 group (P < 0.05). In summary, dietary aucubin did not promote growth, but improved the flesh quality of grass carp, which might be associated with the TGF-ß/Smad and Nrf2 pathways. The recommended supplementation level of aucubin in the diet of grass carp was 0.6 to 0.8 g/kg.

Aucubin is an iridoid glycoside that is widely distributed in green plants and exhibits various biological activities such as antioxidant, anti-inflammatory, and protecting the liver. In previous studies, we explored the effects of different dietary levels of iridoids including geniposide and geniposide acid, on the flesh quality of grass carp. As aucubin shares a similar chemical structure to that of geniposide and geniposide acid, it was speculated that aucubin might exhibit the same function of promoting flesh quality in fish. Our study was conducted to explore the effects on the growth and flesh quality of grass carp. We found that dietary aucubin did not affect the growth of grass carp but improved flesh quality by increasing the contents of collagen, free amino acids, and n-3 PUFA; increasing the activities of CAT, SOD, and GPx; and decreasing the contents of MDA and PC in flesh, which might be associated with the TGF-ß/Smad and Nrf2 pathways.

Nucleospora hippocampi n. sp., an Intranuclear Microsporidian Infecting the Seahorse Hippocampus erectus From China.

The life cycle, ultrastructure, and molecular phylogeny of a new intranuclear microsporidian, Nucleospora hippocampi n. sp., infecting the intestine of the Hippocampus erectus, were described. The histopathology revealed an extensive infection, mainly in the columnar epithelium of the intestinal mucosa layer. The enterocytes were the important target cell for Nucleospora hippocampi n. sp. infection. Transmission electron microscopy results showed that this microsporidian developed directly within the host cell nucleoplasm. In the intranuclear life cycle, the transformation from meront to sporogonial plasmodium was recognized by forming electron-dense disc structures, which were considered the polar tube precursors. The microsporidian showed the typical morphological characteristics of the family Enterocytozoonidae in the formation and development of spore organelles prior to the division of the sporogonial plasmodium. According to wet smear observation, eight spores were generally formed in a single host nucleus. Mature spores were elongated ovoids that were slightly bent and measured 1.93 × 0.97 µm. The isofilar polar tube was arranged in 7~8 coils in one row. Phylogenetic analysis of its small subunit ribosomal DNA sequences demonstrated that the parasite belonged to the Nucleospora group clade. The histological, ultrastructural, and molecular data support the emergence of a new species in the genus Nucleospora. This is the first report of Nucleospora species in Asia and threatened syngnathid fishes.

Metal-Organic Framework-Intercalated Graphene Oxide Membranes for Selective Separation of Uranium.

Design and construction of a membrane that can achieve selective separation of uranium from spent fuel or seawater is a big challenge in the field of separation science. In this work, 1,3,5-benzenetricarboxylic acid (BTC) and three different nitrates (Zn/Ni/Cu) were used to prepare metal-organic frameworks (BTC-MOFs) with different pore sizes, and then, BTC-MOFs were intercalated into the interlayers of graphene oxide (GO) for preparing the composite membranes which presented selective separation of uranium with strong acid resistance. Composite membranes prepared by Zn/Ni/Cu-BTC-MOFs and GO can achieve the separation between ions of different valence states, and their permeability and selectivity depend on the membrane thickness, the acidity of driving solution, and the pore sizes of MOFs. Importantly, Cu-BTC-MOF-intercalated GO membranes can not only achieve the selective separation of Th4+ and UO22+ with a selectivity of ≈6 but also induce the ultra-high selectively separation of UO22+ and Ce3+ because the rejection rate of Ce3+ is about 100%. Moreover, the Zn-BTC-MOF-intercalated GO membrane shows an excellent selectivity of Th4+ and UO22+ with a selectivity of ≈25, and it may also achieve selective separation of uranium from seawater.

Nitrogen-doped nanoporous graphene induced by a multiple confinement strategy for membrane separation of rare earth.

Rare earth separation is still a major challenge in membrane science. Nitrogen-doped nanoporous graphene (NDNG) is a promising material for membrane separation, but it has not yet been tested for rare earth separation, and it is limited by multi-complex synthesis. Herein, we developed a one-step, facile, and scalable approach to synthesize NDNG with tunable pore size and controlled nitrogen content using confinement combustion. Nanoporous hydrotalcite from Zn(NO3)2 is formed between layers of graphene oxide (GO) absorbed with phenylalanine via confinement growth, thus preparing the sandwich hydrotalcite/phenylalanine/GO composites. Subsequently, area-confinement combustion of hydrotalcite nanopores is used to etch graphene nanopores, and the hydrotalcite interlayer as a closed flat nanoreactor induces two-dimensional space confinement doping of planar nitrogen into graphene. The membrane prepared by NDNG achieves separation of Sc3+ from the other rare earth ions with excellent selectivity (∼3.7) through selective electrostatic interactions of pyrrolic-N, and separation selectivity of ∼1.7 for Tm3+/Sm3+.

A Nanoporous Graphene/Nitrocellulose Membrane Beneficial to Wound Healing.

Adequate treatment of skin wounds is vital to health. Nitrocellulose bandage as a traditional wound dressing is widely used for wound healing, but its limited air permeability and poor sterilization need to be improved for enhancing the actual efficacy. Here, nanoporous graphene (NPG) is used to mix into nitrocellulose for preparing a composite membrane, which exhibits a moderate transmission rate of water vapor, excellent toughness performance, and good biocompatibility. Moreover, the membrane shows an excellent broad-spectrum antibacterial property (>98%, Escherichia coli; >90%, Staphylococcus aureus) and can reduce the risk of microbial infection for the body after trauma. Importantly, after using the nanoporous graphene/nitrocellulose membrane, the wound closure percentage reaches 93.03 ± 1.08% at 7 days after the trauma, and the degree of skin tissue recovery is also improved significantly. Therefore, this study develops a highly efficient wound healing dressing, which is expected to be used directly in clinics.

Performance of a recirculating aquaculture system using biofloc biofilters with convertible water-treatment efficiencies.

To achieve high water-treatment efficiencies and simplify the setup of recirculating aquaculture systems (RAS), this study examined the use of suspended growth reactors (R1 and R2) based on biofloc technology (BFT) as water-treatment biofilters. Moreover, the conversion of the heterotrophic R1 biofilter to a nitrifying role was investigated. During RAS operation using heterotrophic BFT biofilters, R1 and R2 simultaneously controlled total ammonium nitrogen, nitrite (NO2--N), nitrate (NO3--N), soluble reactive phosphate (SRP), and alkalinity, with relevant functional microbes including denitrifying bacteria (DNB), phosphorus accumulating organisms (PAOs), denitrifying PAOs (DNPAOs), glycogen accumulating organisms, ammonia oxidizing bacteria, and nitrite oxidizing bacteria. To achieve low concentrations of nitrogen, phosphorus, and save carbon sources, we were able to quickly convert R1 into a nitrifying BFT biofilter by stopping carbohydrate addition. Although there were dominant relative abundances of DNB, PAOs, and DNPAOs in the converted R1, the lack of carbon sources resulted in continuous rise of NO3--N in the effluent, stable NO2--N removal efficiency, and absence of SRP removal after 40 h. However, R2 retained the previous NO3--N and SRP removal efficiencies with carbohydrate addition. This indicated that this novel RAS using BFT biofilters achieved simultaneous nitrogen and phosphate removal, and that the convertible water-treatment efficiencies of BFT biofilters could be controlled by carbohydrate addition. This approach could simplify the RAS setup and meet real-time water quality demands.

Highly Selective Separation of Rare Earth Elements by Zn-BTC Metal-Organic Framework/Nanoporous Graphene via In Situ Green Synthesis.

Rare earth elements (REEs) are used widely in devices of many fields, but it is still a troublesome task to achieve their selective separation and purification. Metal-organic frameworks (MOFs) as an emerging porous crystalline material have been used for selective separation of REEs using the size-selective crystallization properties. However, so far, almost all MOFs cannot be used directly for selective separation of REEs in strong acid via solid-state adsorption. Herein, a zinc-trimesic acid (Zn-BTC) MOF is grown by solid synthesis in situ on ZnO nanoparticles covering nanoporous graphene for preparing Zn-BTC MOF/nanoporous graphene composites with strong acid resistance. The adsorption capacity of the resulting composites to REEs is highly sensitive to the ionic radius, which may be attributed to the fact that the REE ions coordinate with O to form a stable structure. The selectivity of Ce/Lu is ≈10,000, and it is extremely important that the selectivity between adjacent REEs (e.g., Nd/Pr) is as high as ≈9.8, so the composite exhibits the best separation performance so far. This work provides a green, facile, scale, and effective synthesis strategy of Zn-BTC MOF/nanoporous graphene, which is hopefully applied directly in the separation industries of REEs.

Preparation of Vortex Porous Graphene Chiral Membrane for Enantioselective Separation.

Chiral materials are usually the key to the separation of chiral membranes. In this work, we propose a new strategy that chiral porous graphene membrane can be fabricated from nonchiral porous graphene by mechanical stirring to induce vortex structure. Porous graphene with controlled, nanosized pores was synthesized by a newly designed, one-pot process directly from graphite as opposed to graphene oxide. Then porous graphene was immobilized on ultrafiltration membrane through filtering while stirring to form porous graphene membrane, which was applied for enantioselective separation toward DL-amino acids: for example, the separation factor of l-/d-phenylalanine reached 4.76. Interestingly, we first observed that the front and back sides of the porous graphene membrane exhibited opposite optical activities.

Linking heterotrophic bacterioplankton community composition to the optical dynamics of dissolved organic matter in a large eutrophic Chinese lake.

Elucidation of the linkages between the bacterial community composition and chromophoric dissolved organic matter (CDOM) in lake ecosystems is critical for the understanding of the inland water carbon cycling. Despite substantial research into the relationship between the bacteria community and the bulk DOM pool, knowledge of the specific relationship between the optical dynamics of DOM and the bacterioplankton community in lake ecosystems is still poor. We investigated the linkages between the optical dynamics of DOM and bacteria composition in shallow eutrophic Lake Taihu, China. Redundancy Analysis (RDA) indicated that besides water temperature and phytoplankton biomass, also CDOM was an important factor determining the composition of the bacterial community. Generalized Additive Models (GAM) showed that terrestrial humic-like C1 and tyrosine-like C4 were the key factors explaining the abundance of the main bacterial clades. C1 was closely correlated with Verrucomicrobia, Actinobacteria, Alphaproteobacteria, Betaproteobacteria and Planctomycetes, and C4 was closely related to the latter two and to Bacteroidetes. At family level, the dominant families - Pelagibacteraceae (Alphaproteobacteria) and Gemmataceae (Planctomycetes) - were related to both allochthonous and autochthonous CDOM fluorophores but responded differently to the various CDOM components. Tryptophan-like C2 was significantly and positively correlated with Gemmataceae and Ellin6075 (Acidobacteria). Additionally, we found that the biomasses of Cyanophyta, terrestrial humic-like C1, tryptophan-like C4 and C5 were significantly related to the richness of heterotrophic bacterioplankton. Our results provide new insight into the relationship between bacteria and DOM optical dynamics although the mechanisms leading to these relationships need further experimental investigations.

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.

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.

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 C : N 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 0.08 g COD/L · day(-1).

[Kinetic Characteristics of Degradation of Geosmin and 2-Methylisoborneol by Bacillus subtilis].

The earthy and musty odor problem in aquaculture systems has been a worldwide problem, especially in freshwater aquaculture systems. Geosmin (GSM) and 2-methylisoborneol (2-MIB), the most common causative agents of the off-flavor in fish, are lipophilic secondary metabolites of cyanobacteria, actinomycetes, and other microorganisms. The odor threshold concentrations for 2-MIB and GSM are approximately 9-42 ng x L(-1) and 4-10 ng x L(-1), and 600 ng x kg(-1) and 900 ng x kg(-1) in the aquaculture water and fish, respectively. With such a low odor threshold concentration, the off-flavor compounds greatly reduce the quality and economic value of aquatic products. This renders the fish, especially some valuable fish produced in recirculating aquaculture systems (RAS), unmarketable. The study reported the kinetic characteristics of degradation of GSM and 2-MIB by Bacillus subtilis and discussed the impacts of the initial concentration of GSM and 2-MIB (T1, T2) and inoculation amount (T1, T3 ) on the biodegradation rate. The result demonstrated that these two compounds could be degraded by B. subtilis effectively and the biodegradation rate reached more than 90% in T1, T2 and T3 treatments. The biodegradation of these two compounds behaved as a pseudo-first-order kinetics with rate constants (K) in the range of 0.14-0.41. K values indicated that the degradation rate was dependent on the inoculation amount but the start concentration of GSM and MIB. The degradation kinetics showed the maximum specific rate value (u(max)) and the Monod constant (K(s)) were 0.311 and 1.73, however, 2-MIB degradation process did not meet the Monod microbial growth equation (R2 = 0.781).