Aeration Strategies Research Articles

Membrane aerated biofilm reactors for mainstream partial nitritation/anammox: Experiences using real municipal wastewater

This study investigated the potential of Membrane-Aerated Biofilm Reactors (MABRs) for mainstream nitrogen removal via partial nitration/anaerobic ammonium oxidation (anammox). Four laboratory-scale MABRs were operated with real municipal wastewater characterized by low concentrations of nitrogen (varying between 31 and 120 mg–NH4–N L−1) and the presence of biodegradable organic carbon (soluble COD (sCOD) between 7 and 230 mg-O2 L−1). Two reactors were operated with different aeration strategies (intermittent vs. continuous), the other two with differences in biomass retention (recirculation or removal of detached biomass). Keeping a constant HRT caused instabilities due to difficulties with setting the optimal oxygen flux for the respective surface loadings (1.6–6 g–NH4–N m−2 d−1). Operating the MABRs with a constant surface loading (2 g–NH4–N m−2 d−1) resulted in higher and more stable total nitrogen (TN) removal independent of the aeration strategy. The intermittently aerated MABR improved from an average TN removal of 23%–69%, the continuously aerated MABR from 20% to 50% TN removal. Independent of the feeding strategy, the continuously aerated reactor removed slightly more ammonium (80–95%) compared to the intermittently aerated reactor (74–93%).Limiting the oxygen supply by intermittent aeration proofed successful to favor partial nitritation and anammox. Continuous aeration did not achieve stable suppression of nitrite oxidizing bacteria (NOB). Of the removed ammonium, approx. 26% were left in the effluent as nitrate (only 10% with intermittent aeration).Recirculation of the detached biomass resulted in reattachment onto the biofilm or membrane surface. This recirculation led to significantly higher biomass retention times and thus to better performance. Removing detached biofilm from the reactor caused a slightly lower TN removal of 33% compared to 45% with reattachment, while average ammonium removal was 58% compared to 63%, respectively. Scouring events had a significant impact on the overall operation, resulting in short term losses of TN removal capacities of 50–100%.The microbial community composition was different depending on the aeration strategy and biomass retention. The continuously aerated reactor contained significantly more AOB than the intermittently aerated MABR. The reactor with biomass retention contained less ammonium oxidizing bacteria (AOB), compared to the reactor with low biomass retention. In all MABRs, anammox bacteria established in the biofilm after an initial drop in abundance.

An investigation of performance of a conventional U type loop-seal for CFB reactors with side and bottom aerations

Experiments were carried out in a circulating fluidized bed (CFB) system. The riser has a cross sectional area of 100×100mm2, while the supply and recycle chambers of the loop-seal have the same cross-sectional areas. Sand having a Sauter mean diameter of 310μm was used as bed material. Throughout the experiment, the superficial air velocity of the riser and the height of the solid particles in the storage column were kept constant. Four types of loop-seal categorized by their aeration scheme were investigated: aeration at the bottoms of supply and recycle chambers with side aeration at the supply chamber wall (USRQS), aeration at the recycle chamber bottom with side aeration at the supply chamber wall (URQS), aeration at the supply chamber bottom with side aeration at the recycle chamber wall (USQR), and aeration at the bottoms of supply and recycle chambers with side aeration at the recycle chamber wall (USRQR). The relation between the solid circulating rate and the side aeration flow rate was modeled as a saturated function. The results show that the URQS and the USQR types provide the same initial solid circulation rate, which is higher than for the conventional U type loop-seal. For a certain fluidization number, the loop-seals with side aeration provide higher solid circulation rate and require lower total aeration flow rate. The loop-seal with side aeration at the supply chamber wall tends to provide higher solid circulation rate and sensitivity of the circulation rate. For a certain solid particles height in the storage column, the maximum solid circulation rate was restricted by the flow through the horizontal passage.

Evaluation of nitrogen removal and the microbial community in a submerged aerated biological filter (SABF), secondary decanters (SD), and horizontal subsurface flow constructed wetlands (HSSF-CW) for the treatment of kennel effluent.

To ensure microbial activity and a reaction equilibrium with efficiency and energy saving, it is important to know the factors that influence microbiological nitrogen removal in wastewater. Thus, it was investigated the microorganisms and their products involved in the treatment of kennel effluents operated with different aeration times, phase 1 (7h of continuous daily aeration), phase 2 (5h of continuous daily aeration), and phase 3 (intermittent aeration every 2h), monitoring chemical and physical parameters weekly, monthly microbiological, and qualitative and quantitative microbiological analyzes at the end of each applied aeration phase. The results showed a higher mean growth of nitrifying bacteria (NB) (106) and denitrifying bacteria (DB) (1022) in phase with intermittent aeration, in which better total nitrogen (TN) removal performance, with 33%, was achieved, against 21% in phase 1 and 17% in phase 2, due to the longer aeration time and lower carbon/nitrogen ratio (15.7), compared with the other phases. The presence of ammonia-oxidizing bacteria (AOB), the genus Nitrobacter nitrite-oxidizing bacteria (NOB), and DB were detected by PCR with specific primers at all phases. The analysis performed by 16S-rRNA DGGE revealed the genres Thauera at all phases; Betaproteobacteria and Acidovorax in phase 3; Azoarcus in phases 2 and 3; Clostridium, Bacillus, Lactobacillus, Turicibacter, Rhodopseudomonas, and Saccharibacteria in phase 1, which are related to the nitrogen removal, most of them by denitrifying. It is concluded that, with the characterization of the microbial community and the analysis of nitrogen compounds, it was determined, consistently, that the studied treatment system has microbiological capacity to remove TN, with the phase 3 aeration strategy, by simultaneous nitrification and denitrification (SND). Due to the high density of DB, most of the nitrification occurred by heterotrophic nitrification-aerobic. And denitrification occurred by heterotrophic and autotrophic forms, since the higher rate of oxygen application did not harm the DB. Therefore, the aeration and carbon conditions in phase 3 favored the activity of the microorganisms involved in these different routes. It is considered that, in order to increase autotrophic nitrification-aerobic, it is necessary to exhaust the volume of sludge in the secondary settlers (SD), further reducing the carbon/nitrogen ratio, through more frequent cleaning, whose periodicity should be the object of further studies. Graphical abstract.

Effects of Aeration Strategy on Denitrifying Performance of Activated Sludge Processes in Treating Low-Carbon-Source Municipal Wastewater

In this study, the effects of aeration strategy on nitrogen removal performance of activated sludge processes in treating low-carbon-source municipal wastewater were investigated. Two aeration strategies (continuous aeration (CA) and intermittent aeration (IA)) were evaluated, and the long-term performance of activated sludge processes employing these strategies in treating wastewater with C/N=3 were analyzed. The results demonstrated that the total nitrogen removal efficiency in CA was 17.92% higher than that in the IA process. Meanwhile, the carbon source utilized in nitrogen removal in CA was 44.29% higher compared with the IA process. Furthermore, the results of 16S rRNA sequencing showed that relative abundances of denitrifying bacteria in CA and IA were 5.86% and 2.06%, respectively, suggesting that the CA process has better denitrification ability when treating low-carbon-source wastewater. In addition, 16S rRNA sequencing gene prediction was utilized to analyze the in-depth mechanisms. The results demonstrated that genes involved in membrane transport, carbohydrate metabolism, and cell composition were more highly expressed in CA. The enhancement of metabolic activity under continuous aeration strengthened microbial carbon source utilization. Therefore, the activated sludge process under continuous aeration was more efficient in treating low-carbon-source municipal wastewater. This study provides ideas for low-carbon-source municipal wastewater treatment.

Aeration strategy in the intensive culture of tambaqui, Colossoma macropomum, in the tropics

As the demand for fish increases and limitations are placed on water use, intensification in closed aquaculture systems could help to increase its sustainable production. The Amazon region stands out for its stable warm climate with fast-growing and resilient fish. This study evaluated the efficacy of two aeration regimes on intensive rearing of tambaqui, Colossoma macropomum, in six 46.4-m3 concrete-wall earthen bottom ponds, with no water exchange. Two aeration regimes were tested: (1) emergency aeration (EA), in which the aeration system was activated with dissolved oxygen (DO) levels below 3 mg L−1; (2) supplemental aeration (SA), with 8 h of aeration every night, and also during days with low solar radiation. Water quality, fish performance and health (haematological and parasitological indicators), aeration use and cost were assessed. Juveniles (44.39 ± 9.72 g, mean weight ± SD) were stocked in six concrete-wall ponds with earthen bottoms at 32,300 ha −1 and fed commercial feed (36–32% crude protein) for 17 weeks (122 days). Mean values of the water quality parameters showed no difference between treatments, but occurrences of hypoxia were significantly higher in SA (31 hypoxias with DO <2 mg L−1 and 11 extreme hypoxias with DO <0.5 mg L−1) than in EA (5 and 0.6 occurrences, respectively). Significantly more erythrocytes were observed in the fish in SA than in EA, which indicates a response to a low DO concentration. The parasitological analyses revealed 100% prevalence of Monogenoidea (Dactylogyridae) in animal gills, with higher abundance in the SA fish. All treatments showed high fish survival rate (99.6 ± 0.8% for EA; 99.3 ± 1.2% for SA) and low FCR (1.22 ± 0.1 for EA; 1.32 ± 0.1 for SA), but weight gain, specific growth rate and yield were higher (p < .05) and water use and energy cost was lower (p < .05) for EA. In conclusion, the aeration strategy influenced hypoxia frequency and aeration cost, resulting in superior fish performance and health conditions and lower energy cost in EA, which suggests this strategy to be more beneficial for tambaqui production than SA.

Mainstream partial nitritation/anammox with integrated fixed-film activated sludge: Combined aeration and floc retention time control strategies limit nitrate production

Implementation of mainstream partial nitritation/anammox (PN/A) can lead to more sustainable and cost-effective sewage treatment. For mainstream PN/A reactor, an integrated fixed-film activated sludge (IFAS) was operated (26 °C). The effects of floccular aerobic sludge retention time (AerSRTfloc), a novel aeration strategy, and N-loading rate were tested to optimize the operational strategy. The best performance was observed with a low, but sufficient AerSRTfloc (~7d) and continuous aeration with two alternating dissolved oxygen setpoints: 10 min at 0.07–0.13 mg O2 L−1 and 5 min at 0.27–0.43 mg O2 L−1. Nitrogen removal rates were 122 ± 23 mg N L−1 d−1, and removal efficiencies 73 ± 13%. These conditions enabled flocs to act as nitrite sources while the carriers were nitrite sinks, with low abundance of nitrite oxidizing bacteria. The operational strategies in the source-sink framework can serve as a guideline for successful operation of mainstream PN/A reactors.

A novel two-stage aeration strategy for Bacillus thuringiensis biopesticide production from biowaste digestate through solid-state fermentation

A novel aeration strategy has been developed at lab and bench-scale for Bacillus thuringiensis (Bt) derived biopesticides production through solid-state fermentation, using a mixture of digestate and biowaste as substrates. A Box-Behnken design was performed to select key parameters of the spore production process, being temperature and biodegradability the factors with a significant effect. Further tests confirmed the importance of oxygen content for spore production. Thus, a two-stage aeration strategy consisting of a microaeration phase followed by a high-rate aeration period was developed and tested. The production strategy was validated in a 22-L reactor using two different strains (Bt kusrtaki, Btk, and israelensis, Bti), demonstrating the robustness of the protocol. Maximum production of 1.3 × 108 spores g-1 dry matter for Btk and 4 × 108 spores g-1 dry matter for Bti were obtained, representing a final yield of 5 and 29 spores produced per initial CFU, respectively.

Production of Raw Starch-Digesting Amylolytic Preparation in Yarrowia lipolytica and Its Application in Biotechnological Synthesis of Lactic Acid and Ethanol.

Sustainable economy drives increasing demand for raw biomass-decomposing enzymes. Microbial expression platforms exploited as cellular factories of such biocatalysts meet requirements of large-volume production. Previously, we developed Yarrowia lipolytica recombinant strains able to grow on raw starch of different plant origin. In the present study, we used the most efficient amylolytic strain as a microbial cell factory of raw-starch-digesting (RSD) amylolytic preparation composed of two enzymes. The RSD-preparation was produced in fed-batch bioreactor cultures. Concentrated and partly purified preparation was then tested in simultaneous saccharification and fermentation (SSF) processes with thermotolerant Kluyveromyces marxianus for ethanol production and Lactobacillus plantarum for production of lactic acid. These processes were conducted as a proof-of-concept that application of the novel RSD-preparation supports sufficient starch hydrolysis enabling microbial growth and production of targeted molecules, as the selected strains were confirmed to lack amylolytic activity. Doses of the preparation and thermal conditions were individually adjusted for the two processes. Additionally, ethanol production was tested under different aeration strategies; and lactic acid production process was tested in thermally pre-treated substrate, as well. Conducted studies demonstrated that the novel RSD-preparation provides satisfactory starch hydrolyzing activity for ethanol and lactic acid production from starch by non-amylolytic microorganisms.

Bioreactor Simulation with Quadratic Neural Network Model Approximations and Cost Optimization with Markov Decision Process

The efficient operation of activated sludge type wastewater treatment plants is an ongoing topic for the utility providers, where electric energy consumption shares are high, giving cca. 30 % of total operational costs. Intervention methods for intensification include fine tuning of aeration settings, sludge removal and the adjustment of recirculation rates. In order to analyze the effects of various process control strategies, activated sludge models (ASM) are used for the purpose of biokinetic modeling. In practice, most model simulators do not incorporate optimization and necessary auto-calibration of the latter, due to high computational demand of timeseries evaluation. In this paper, a new mathematical model is presented, which makes biokinetic simulations suitable for the use in decision support systems. Namely, the ASM model is approximated with a computanional inexpesive quadratic model solution, fed into a set of mass-balance corrected neural networks. Cost optimization is achieved with Markov decision process model. The developed method was illustrated for a case of Hungarian, large wastewater treatment plant. It was proven, the model is able to find better aeration schemes for the plant in aspect of cost of operation and nitrogen removal efficiency. The model can be used to find cost-optimal policies under arbitrary defined conditions. As a benefit, results can be implemented into industrial logic controllers.

Modelling hexadecane uptake strategies of a rhizospheric bacterial consortium under different hydrodynamic draft-tube airlift reactor conditions

In this study, an analysis of the hydrodynamic effects on the hexadecane (HXD) uptake strategies of a bacterial consortium in an airlift bioreactor was performed using mathematical modelling. The model was developed by considering the capacity of the consortium to consume HXD either directly, through direct interfacial contact (DC) or through uptake of emulsified forms (EF). The model was fitted to experimental data (0.822 < R2< 0.996) under three different aeration strategies, which involved constant and variable superficial gas velocities. For the rhizospheric bacterial consortium used, DC was the primary HXD uptake strategy, which increased in magnitude as superficial gas velocity (Ug) increased (90.8–97.66%). Our findings revealed that both the DC strategy and microbial growth are sensitive to cell hydrophobicity, HXD droplet diameter and the morphological composition of the consortium, which was reflected by the increase in bacterial density on the surface of the HXD droplets, decreased in HXD droplet size and high oxygen uptake values predicted by the model. Furthermore, the model was implemented to simulate the effects of bacterial hydrophobicity and the morphological composition of the consortium on HXD uptake, which showed that DC increased as bacterial hydrophobicity associated with the bacillar shape of bacteria increased.

Mathematical modeling of oxygen control in biocell composting plants

We propose an optimal control problem to determine the best aeration strategy for aerobic biodegradation in a composting cell. The goal is to minimize the deviation of the oxygen level from its reference value for the entire duration of the biodegradation process. The mathematical model includes several chemical phenomena, like the aerobic biodegradation of the soluble substrate by means of a bacterial biomass, the hydrolysis of insoluble substrate and the biomass decay. The oxygen and the optimal mechanical aeration time profiles are obtained and discussed. Finally, the plant performance is evaluated in absence and presence of external aeration by means of several specific indices.

Effect of Intermittent Aeration in a Hybrid Vertical Anaerobic Biofilm Reactor (HyVAB) for Reject Water Treatment

Water from anaerobic sludge dewatering (reject water that is recycled to the inlet main process treatment) from the Knarrdalstrand municipal wastewater treatment plant in Porsgrunn, Norway, contains 2.4 g/L of total chemical oxygen demand (TCOD) and 550 mg/L NH4-N (annual average). The high concentration of ammonium causes disturbances in the mainstream physical and chemical processes, while only a small fraction of the organics is biodegradable. A pilot-scale hybrid vertical anaerobic biofilm (HyVAB) reactor combining anaerobic and aerobic treatment was tested for reject water treatment to reduce process disturbances. The pilot HyVAB was prepared for the study with continuous aeration of the aerobic part of the reactor for 200 days, while two intermittent aeration schemes were applied during the three-month test period. Ammonium removal efficiency increased from 8% during the continuous aeration period to 50% at the end of the test when a short (7 min) aeration cycle was applied. COD removal was close to 20%, which was mainly obtained in the anaerobic stage and not significantly influenced by the aerations schemes. Simultaneous partial nitrification and denitrification were established in the biofilm that alternated between aerobic and anoxic conditions. The observed high ammonium removal is explained by two alternative shortcut processes via nitrite. The lack of biodegradable organics in the aerated stage suggests that most of the nitrogen removal was via the anammox pathway (autotrophic denitrification). The HyVAB, combining an anaerobic sludge bed and an intermittently aerated biofilm, appears to be an efficient process to treat high ammonium containing reject water.

Application of unsupervised learning and process simulation for energy optimization of a WWTP under various weather conditions.

This paper outlines a hybrid modeling approach to facilitate weather-based operation and energy optimization for the largest Italian wastewater treatment plant (WWTP). Two clustering methods, K-means algorithm and Gaussian mixture model (GMM) based on the expectation-maximization (EM) algorithm, were applied to an extensive dataset of historical and meteorological records. This study addresses the problem of determining the intrinsic structure of clustered data when no information other than the observed values is available. Two quantitative indexes, namely the Bayesian information criterion (BIC) and the Silhouette coefficient using Euclidean distance, as well as two general criteria, were implemented to assess the clustering quality. Furthermore, seven weather-based influent scenarios were introduced to the process simulation model, and sets of aeration strategies are proposed. The results indicate that incorporating weather-based aeration strategies in the operation of the WWTP improves plant energy efficiency.

Limited simultaneous nitrification-denitrification (SND) in aerobic granular sludge systems treating municipal wastewater: Mechanisms and practical implications

Simultaneous nitrification-denitrification (SND) is, in theory, a key advantage of aerobic granular sludge systems over conventional activated sludge systems. But practical experience and literature suggests that SND and thus total nitrogen removal are limited during treatment of municipal wastewater using AGS systems. This study thus aims at quantifying the extent and understanding the mechanisms of SND during treatment of municipal wastewater with aerobic granular sludge (AGS) systems. Experiments (long-term and batch-tests) as well as mathematical modelling were performed. Our experimental results demonstrate that SND is significantly limited during treatment of low-strength municipal wastewater with AGS systems (14–39%), while almost full SND is observed when treating synthetic influent containing only diffusible substrate (90%). Our simulations demonstrate that the main mechanisms behind limited SND are (1) the dynamics of anoxic zone formation inside the granule, (2) the diffusibility and availability of electron-donors in those zones and (3) the aeration mode. The development of anoxic zones is driven by the utilisation of oxygen in the upper layers of the granule leading to transport limitations of oxygen inside the granule; this effect is closely linked to granule size and wastewater composition. Development of anoxic zones during the aerobic phase is limited for small granules at constant aeration at bulk dissolved oxygen (DO) concentration of 2 mgO2 L−1, and anoxic zones only develop during a brief period of the aerated phase for large granules. Modelling results further indicate that a large fraction of electron-donors are actually utilised in aerobic rather than anoxic redox zones – in the bulk or at the granule surface. Thus, full SND cannot be achieved with AGS treating low strength municipal wastewater if a constant DO is maintained during the aeration phase. Optimised aeration strategies are therefore required. 2-step and alternating aeration are tested successfully using mathematical modelling and increase TN removal to 40–79%, without compromising nitrification, and by shifting electron-donor utilisation towards anoxic redox conditions.

Improve biotransformation of crude glycerol to ethanol of Enterobacter aerogenes by two-stage redox potential fed-batch process under microaerobic environment

Ethanol production from crude glycerol under microaerobic condition was optimized. The aeration rate in the reactor was controlled using redox potential (ORP) as to replace a conventional oxygen sensor that became insensitive at low oxygen concentration. The performance of Enterobacter aerogenes TISTR1468 in a batch reactor using a simple medium (crude glycerol and tuna condensate (GT) medium) was evaluated on various aeration strategies: continuous aeration at 0.5 vvm; controlled aeration at −350 mV and −400 mV ORP; and no aeration. The 72-h batch fermentation showed that a more reductive environment (lower aeration and ORP value) increased ethanol concentration and yield, but decreased the ethanol productivity. No-aeration fermentation with the lowest ORP value achieved the highest ethanol production (18.78 g L−1) and yield (0.94 g-ethanol.g-glycerol−1). A more oxidative environment (higher aeration and ORP value) fasten the specific growth rate (μ), but ethanol concentration and yield decreased. The optimum specific ethanol production rate (qp) and glycerol consumption rate occurred at ORP of −400 mV and −350 mV, respectively. When the ORP was very low, the μ decreased following substrate depletion, but this phenomenon was not observed at higher ORP value, an evident that adequate oxygen supply could maintain cell viability.Fed-batch with two-stage aeration strategy (−350 mV and −400 mV ORP) acquired higher ethanol production (30.31 g L−1) than fed-batch with single-stage aeration (25.95 g L−1) and batch process (12.33 g L−1).This study has revived the potential of crude glycerol biotransformation to ethanol and opened up opportunities for optimization of related microaerobic systems other than ethanol.

Sensor-mediated granular sludge reactor for nitrogen removal and reduced aeration demand using a dilute wastewater.

A sensor‐mediated strategy was applied to a laboratory‐scale granular sludge reactor (GSR) to demonstrate that energy‐efficient inorganic nitrogen removal is possible with a dilute mainstream wastewater. The GSR was fed a dilute wastewater designed to simulate an A‐stage mainstream anaerobic treatment process. DO, pH, and ammonia/nitrate sensors measured water quality as part of a real‐time control strategy that resulted in low‐energy nitrogen removal. At a low COD (0.2 kg m−3 day−1) and ammonia (0.1 kg‐N m−3 day−1) load, the average degree of ammonia oxidation was 86.2 ± 3.2% and total inorganic nitrogen removal was 56.7 ± 2.9% over the entire reactor operation. Aeration was controlled using a DO setpoint, with and without residual ammonia control. Under both strategies, maintaining a low bulk oxygen level (0.5 mg/L) and alternating aerobic/anoxic cycles resulted in a higher level of nitrite accumulation and supported shortcut inorganic nitrogen removal by suppressing nitrite oxidizing bacteria. Furthermore, coupling a DO setpoint aeration strategy with residual ammonia control resulted in more stable nitritation and improved aeration efficiency. The results show that sensor‐mediated controls, especially coupled with a DO setpoint and residual ammonia controls, are beneficial for maintaining stable aerobic granular sludge.Practitioner points Tight sensor‐mediated aeration control is need for better PN/A.Low DO intermittent aeration with minimum ammonium residual results in a stable N removal.Low DO aeration results in a stable NOB suppression.Using sensor‐mediated aeration control in a granular sludge reactor reduces aeration cost.

Roles of biochar media and oxygen supply strategies in treatment performance, greenhouse gas emissions, and bacterial community features of subsurface-flow constructed wetlands

Biochar-based subsurface-flow constructed wetlands (CWs) with intermittent aeration (IA) or tidal flow (TF) oxygen supply strategies were established to treat domestic wastewater. The results showed that biochar achieved higher nutrient removal and lower greenhouse gas (GHG) emissions than ceramsite while supporting more diverse bacterial communities and higher abundances of functional taxa. Both IA and TF effectively enhanced nutrient removal, though the latter was more efficient and practical, and aeration conditions greatly influenced nutrient removal efficiency. GHG emissions were decreased by IA but were slightly increased by TF. Both oxygen supply methods significantly shaped the biofilm microbial communities and influenced biodiversity and richness, with observably higher proportions of potential nitrifiers and denitrifiers present in aerated CWs. Overall, biochar-based CWs operated with oxygen supply strategies provide superior treatment of decentralized wastewater.

Induction of β, ε-carotene-3, 3′-diol (lutein) production in green algae Chlorella salina with airlift photobioreactor: interaction of different aeration and light-related strategies

The impact and interaction of light irradiance strength (light intensities), lighting cycle (photoperiod), and aeration rate on biomass concentration and lutein production efficacy of the microalga Chlorella salina in a closed laboratory-scale airlift photobioreactor were investigated via the response surface method. Among the factors assessed, light intensity and aeration rate had significant influence on cell concentration, though a concurrent increment in light intensity noticeably decreased the lutein content. All the parameters were observed to be statistically significant. Best operating conditions for the growth of alga was evaluated to be as follows: light intensity, 200 μmol m−2 s−1; photoperiod, 12:12 h L D; and the aeration rate, 3 lpm. These conditions could substantially enhance the microalgal growth rate (0.82 day−1) and biomass production (665.89 mg). Specific lutein productivity and a recovery of 9.73 mg/L/day were achieved at a day light cycle of 16 h. According to the results of the experimental design, the optimum conditions led to a twofold increase in biomass and lutein productivity compared with unoptimized condition.

Effect of intermittent aeration mode on nitrogen concentration in the water column and sediment pore water of aquaculture ponds

Nitrogen in pond sediments is a major water quality concern and can impact the productivity of aquaculture. Dissolved oxygen is an important factor for improving water quality and boosting fish growth in aquaculture ponds, and plays an important role in the conversion of ammonium-nitrogen (NH4+-N) to nitrite-nitrogen (NO2−-N) and eventually nitrate-nitrogen (NO3−-N). A central goal of the study was to identify the best aeration method and strategy for improving water quality in aquaculture ponds. We conducted an experiment with six tanks, each with a different aeration mode to simulate the behavior of aquaculture ponds. The results show that a 36 hr aeration interval (Tc = 36 hr: 36 hr) and no aeration resulted in high concentrations of NH4+-N in the water column. Using a 12 hr interval time (Tc = 12 hr: 12 hr) resulted in higher NO2−-N and NO3−-N concentrations than any other aeration mode. Results from an 8 hr interval time (Tc = 8 hr: 8 hr) and 24 hr interval time (Tc = 24 hr: 24 hr) were comparable with those of continuous aeration, and had the benefit of being in use for only half of the time, consequently reducing energy consumption.

Application of an innovative front aeration and internal recirculation strategy to improve the removal of pollutants in subsurface flow constructed wetlands

The pollutant removal performance of traditional horizontal subsurface flow (HSSF) constructed wetlands (CWs) is limited because of the dissolved oxygen (DO) supply is insufficient. The aeration of HSSF CWs usually improves their pollutant removal performance, but a high DO induces the accumulation of nitrate-nitrogen (NO3−-N) and suppresses the improvement of total nitrogen (TN) removal. In this study, an integrated solution that involved in-tank front aeration and internal recirculation (FAIR) was used to improve the pollutant removal performance of HSSF CWs. Based on the experimental results, the FAIR system significantly increased the removal efficiencies of biochemical oxygen demand (BOD) from 53.8–76.0% to 82.0–91.7% and reduced the BOD concentration in the effluent to below 10 mg L−1. The removal efficiency of ammonia-nitrogen (NH3–N) increased from 15.1–78.3% to 98.5–98.6% while the removal efficiencies of the total Kjeldahl nitrogen (TKN) of the control and FAIR HSSF CWs were 18.2–77.1% and 93.5–94.3%, respectively. HSSF CWs with FAIR outperformed aerated HSSF CWs in the removal of NH3–N and TKN. The effects of two recirculation flow ratios (Rr = recirculation flow rate/influent flow rate), 14.3 and 3.0, on the improvement of pollutant removal performance were investigated. The lower Rr did not significantly affect the improvement of BOD, NH3–N, and TKN, but a higher Rr resulted in more severe accumulation of NO3−-N. The removal efficiency of TN in control HSSF CWs ranged from 20.4% to 75.5%, and in the FAIR HSSF CW was 71.6% for Rr = 14.3 and 81.3% for Rr = 3.0. However, the FAIR system did not enhance the removal performance of total phosphorus, suggesting that the DO level and internal recirculation were not dominant mechanisms for the removal of phosphorous. The easy maintenance of the FAIR system made it a superior modification for improving the pollutant removal performance of HSSF CWs.