Electro-coalescence in step emulsification: dynamics and applications.

Step emulsification is a low-shear method to produce monodispersed microdroplets by spontaneous breakup of dispersed fluid at a spatial "step". As a semi-open microfluidic system, controllable coalescence of multiple components in step emulsification has not been achieved. Here, we use a low voltage to control the coalescence position of flow tips in the terrace. By investigating the interaction between the coalescence behavior and the hydrodynamics of the drop formation, we numerically predict the shape evolution of the flow tips and give a semi-empirical model to calculate the sizes of droplets by the flow rates and the voltage. Furthermore, we explore the capabilities of the electro-coalescer based on step emulsification. To trigger the coalescence in the wide reservoir, the clogging problem in precipitate-producing reactions is avoided. Besides, the low-shear nature of step emulsification also facilitates the production of multilayered droplets.

Optimized aeration strategies for nitrogen removal efficiency: application of end gas recirculation aeration in the fixed bed biofilm reactor.

Aeration strategy played an important role in reactor performance. In this study, when superficial upflow air velocity (SAV) decreased from 0.16 to 0.08 cm s-1, low dissolved oxygen concentration (DO) of 2.0 mg L-1 occurred in reactor. The required depth for anoxic microenvironment in biofilm decreased from 902.3 to 525.9 µm, which enhanced the growth of denitrifying bacteria and total nitrogen (TN) removal efficiency. However, decreasing aeration intensity resulted in insufficient hydraulic shear stress, which led to weak biofilm matrix structure. Mass biofilm detachment and reactor deterioration then occurred after 87 days of operation. An end gas recirculation aeration strategy was proposed to separately manipulate DO and aeration intensity. Low DO and high aeration intensity were simultaneously achieved, which enhanced the metabolism of denitrifying bacteria (such as Flavobacterium sp., Pseudorhodobacter sp., and Dok59 sp.) and EPS-producing bacteria (such as Zoogloea sp. and Rhodobacter sp.). Consequently, high TN removal performance (82.1 ± 2.7%) and stable biofilm structure were achieved.

The impact of DO and salinity on microbial community in poly(butylene succinate) denitrification reactors for recirculating aquaculture system wastewater treatment.

The interactions between environmental factors and bacterial community shift in solid-phase denitrification are crucial for optimum operation of a reactor and to achieve maximum treatment efficiency. In this study, Illumina high-throughput sequencing was applied to reveal the effects of different operational conditions on bacterial community distribution of three continuous operated poly(butylene succinate) biological denitrification reactors used for recirculating aquaculture system (RAS) wastewater treatment. The results indicated that salinity decreased OTU numbers and diversity while dissolved oxygen (DO) had no obvious influence on OTU numbers. Significant microbial community composition differences were observed among and between three denitrification reactors under varied operation conditions. This result was also demonstrated by cluster analysis (CA) and detrended correspondence analysis (DCA). Hierarchical clustering and redundancy analysis (RDA) was performed to test the relationship between environmental factors and bacterial community compositions and result indicated that salinity, DO and hydraulic retention time (HRT) were the three key factors in microbial community formation. Besides, Simplicispira was detected under all operational conditions, which worth drawing more attention for nitrate removal. Moreover, the abundance of nosZ gene and 16S rRNA were analyzed by real-time PCR, which suggested that salinity decreased the proportion of denitrifiers among whole bacterial community while DO had little influence on marine reactors. This study provides an overview of microbial community shift dynamics in solid-phase denitrification reactors when operation parameters changed and proved the feasibility to apply interval aeration for denitrification process based on microbial level, which may shed light on improving the performance of RAS treatment units.

Simultaneous ammonia and nitrate removal in an airlift reactor using poly(butylene succinate) as carbon source and biofilm carrier.

In this study, an airlift inner-loop sequencing batch reactor using poly(butylene succinate) as the biofilm carrier and carbon source was operated under an alternant aerobic/anoxic strategy for nitrogen removal in recirculating aquaculture system. The average TAN and nitrate removal rates of 47.35±15.62gNH4-Nm(-3)d(-1) and 0.64±0.14kgNO3-Nm(-3)d(-1) were achieved with no obvious nitrite accumulation (0.70±0.76mg/L) and the dissolved organic carbon in effluents was maintained at 148.38±39.06mg/L. Besides, the activities of dissimilatory nitrate reduction to ammonium and sulfate reduction activities were successfully inhibited. The proteome KEGG analysis illustrated that ammonia might be removed through heterotrophic nitrification, while the activities of nitrate and nitrite reductases were enhanced through aeration treatment. The microbial community analysis revealed that denitrifiers of Azoarcus and Simplicispira occupied the dominate abundance which accounted for the high nitrate removal performance. Overall, this study broadened our understanding of simultaneous nitrification and denitrification using biodegradable material as biofilm carrier.

Evidence for anaerobic ammonium oxidation process in freshwater sediments of aquaculture ponds.

The anaerobic ammonium oxidation (anammox) process, which can simultaneously remove ammonium and nitrite, both toxic to aquatic animals, can be very important to the aquaculture industry. Here, the presence and activity of anammox bacteria in the sediments of four different freshwater aquaculture ponds were investigated by using Illumina-based 16S rRNA gene sequencing, quantitative PCR assays and (15)N stable isotope measurements. Different genera of anammox bacteria were detected in the examined pond sediments, including Candidatus Brocadia, Candidatus Kuenenia and Candidatus Anammoxoglobus, with Candidatus Brocadia being the dominant anammox genus. Quantitative PCR of hydrazine synthase genes showed that the abundance of anammox bacteria ranged from 5.6 × 10(4) to 2.1 × 10(5) copies g(-1) sediment in the examined ponds. The potential anammox rates ranged between 3.7 and 19.4 nmol N2 g(-1) sediment day(-1), and the potential denitrification rates varied from 107.1 to 300.3 nmol N2 g(-1) sediment day(-1). The anammox process contributed 1.2-15.3% to sediment dinitrogen gas production, while the remainder would be due to denitrification. It is estimated that a total loss of 2.1-10.9 g N m(-2) per year could be attributed to the anammox process in the examined ponds, suggesting that this process could contribute to nitrogen removal in freshwater aquaculture ponds.

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.

Optimization of factors with C/N ratio and flocs biomass concentration in simulated aquaculture bio-flocs systems by response surface methodology.

The TAN (total ammonia nitrogen) removal efficiency was investigated in simulated aquaculture bio-flocs technology systems. The response surface methodology that was applied with a central composite rotational design and two key operational parameters, flocs biomass concentration and C/N ratio was varied in order to evaluate the system performance and achieve the optimal operational conditions in this study. A polynomial linear regression model was found to quantitatively describe the relationship between the two variables and response values with adequate fitness in the simulate aquaculture bio-flocs systems. The results showed that flocs biomass concentration and operational C/N ratio both had significant impacts on the response objectives, as well as the interactions between them. The optimal results attained from the model indicated that more than 90% TAN removal efficiency was achieved when the flocs biomass concentration and C/N ratio were around 2.0-2.5 (volatile suspended solids, g/l) and 13-16, respectively.

Study on the flocs poly-ß-hydroxybutyrate production and process optimization in the bio-flocs technology system.

The bio-flocs technology (BFT) was applied in the sequencing batch reactor (SBR) to treat aquaculture wastewater for flocs poly-ß-hydroxybutyrate (PHB) accumulation with alternant anaerobic and aerobic conditions. The statistical modeling approach was used to evaluate system performance and to optimize the flocs PHB yield at batch mode. The results show that all variables have significant impact on the response objective, as well as the interactions of the C/N ratio with the flocs biomass concentration (VSS) and anaerobic time, respectively. By process optimization, approximately 150-200 PHB/VSS (mg·g) of flocs PHB yield was achieved in the range of 4-7g/l of flocs biomass concentration, 15-18 of the C/N ratio and 50-85min of anaerobic time in the BFT systems. The results demonstrated that a suitable flocs PHB yield can be obtained via optimizing the ex-situ operating strategy, which have potential prebiotic value and practical implication for the sustainable aquaculture.

[Denitrification and kinetic characteristics using biodegradable polymers as carbon source and biofilm carrier].

The PBS material that in the form of insoluble biodegradable polymers pellets was investigated as the solid carbon source and the biofilm carrier for nitrate removal from wastewater. The denitrification of nitrate removal and kinetic process were carried out in a packed-bed reactor in order to remove nitrate in recirculation aquaculture system. The experimental results indicated that the optimal influent loading rate was in the range of 0.107-1.098 kg/(m3 x d), when the water temperature was (29 +/- 1) degrees C and the influent nitrate concentration was in the range of 25-334 mg/L. The maximum nitrate volumetric removal rate of 0.577 kg/(m3 x d) was achieved at the influent loading rate of 1.098 kg/(m3 x d). When the influent loading rate exceeded 1.098 kg/(m3 x d), the nitrate volumetric removal rate was declined. The kinetic experimental results show that the denitrification rate of PBS as the solid carbon source and the biofilm carrier corresponds to first-order kinetics. Based on the kinetics characteristics, constants n and K used in Eckenfelder model were deduced, which can be successfully applied for the prediction of effluent nitrate concentration. The two groups' predictive values and actual values were analyzed by using SPSS 16.0 software for Paired-Samples t test analysis. The Paired-Samples t test analysis indicates that the corresponding p > 0.05 values are 0.553 and 0.632, which proved that no significant differences exist between the predictive values and actual values of the model.