Photosynthesis Of Microalgae Research Articles

Role of extracellular polymeric substances on nutrients storage and transfer in algal-bacteria symbiosis sludge system treating wastewater

This study reported the role and significance of extracellular polymeric substances (EPSs) on nutrients storage and transfer in an algal-bacteria symbiosis sludge (ABSS) system for wastewater treatment, and the novel algae-based sequencing batch suspended biofilm reactor (A-SBSBR, Ra) was selected as model of ABSS system. Results showed that compared to conventional SBSBR, the EPS of Ra performed better storage for NO2–-N, NO3–-N, total phosphorus and PO43− -P, with increase ratios of 43.7%, 36.0%, 34.1% and 14.7% in sludge phase and 174.0%, 147.4%, 150.4% and 122.0% in biofilm phase, respectively. The analysis of mechanisms demonstrated that microalgae active transport and uptake for divalent cations could enhance their local concentrations around ABS flocs and partially neutralized negative charge of EPSs, and more anions related to nutrients were absorbed in EPSs. Moreover, O2 produced by microalgae photosynthesis enhanced bacteria activity and improved the production of EPSs in both sludge and biofilm phases.

Salinity reduction of brackish water using a chemical photosynthesis desalination cell.

In this study, a chemical photosynthesis desalination cell (CPDC) was investigated for saltwater desalination. The cell consisted of three main parts: (1) an anodic compartment where the oxidation reaction occurs, releasing electrons, (2) a cathode compartment where the required soluble oxygen is provided by microalgae photosynthesis, and (3) an electrodialysis desalination cell installed between the cathode and anode. In the anode, a novel idea was adopted to shorten the desalination duration and increase the salinity rate using a chemical oxidation reaction in combination with the biocathode. The CPDC contributed to the carbon dioxide biological sequestration (reducing air pollution), produced microalgae biomass as a source of renewable energy and generated electricity. In the investigated CPDC, microalgae were used to supply the required oxygen solution as an electron acceptor. The metal anode-microalgae biocathode battery could provide the required energy for electrodialysis. In addition, some extra electricity was generated with a maximum excess power density of 32.4W/m3 per volume of the net anodic compartment, 16.2W/m3 per volume of the net cathodic compartment, and 3.07W/m2 of membrane surface area. This study confirms the benefits of microalgae as a sustainable biocathode in microbial desalination cells (MDCs) to supply electron acceptors in an environmental-friendly manner. Compared to photosynthetic microbial desalination cells (PMDCs), the CPDC decreased the desalination time by a factor of about 4. Besides, the NaCl removal was about 69% for 12g/L NaCl concentration in the CPDC, higher than other MDCs. In addition, as a new operational factor, the internal resistance variations were determined by electrochemical impedance spectroscopy in different case studies. The results demonstrated for the first time the possibility of applying a new desalination cell (i.e. CPDC) for water desalination and power generation which only uses a source of chemical reaction and microalgae photosynthesis without the need for an external power source.

Performance of different microalgae-based technologies in nutrient removal and biogas upgrading in response to various GR24 concentrations

Microalgae-based technology is an emerging strategy for the simultaneous purification of nutrients in biogas slurry and CO2 in biogas. To evaluate effects of synthetic analogue of strigolactone (GR24) concentration on removal efficiency, mono-cultivation of microalgae and co-cultivation of algae with fungus or activated sludge were performed in a photobioreactor. The GR24 concentration of 10−9 M was contributed to the optimum growth characteristics, photosynthetic performance and purification effects in the co-cultivation system of Chlorella vulgaris with activated sludge. The optimal growth rate and mean daily productivity for Chlorella vulgaris were 0.419 ± 0.04 d−1 and 0.342 ± 0.029 g L−1 d−1, respectively. The photosynthetic performance parameters Fv/Fm, PIABS, ΨO, and ΦEO were 0.89 ± 0.08, 6.89 ± 0.62, 0.97 ± 0.09, and 0.69 ± 0.06, respectively, indicating that GR24 with a concentration of 10−9 M was more helpful for photosynthesis of microalgae. Moreover, the maximum removal rate of chemical oxygen demand (COD), total nitrogen (TN), total phosphorus (TP) and CO2 were obtained by the induction of 10−9 M of GR24, which were 77.33 ± 7.25%, 78.86 ± 7.51%, 78.12 ± 7.57% and 69.33 ± 6.86%, respectively. This research therefore provides an effective strategy for wastewater bioremediation and high-quality biogas energy acquisition.

Strategies for decreasing the O2 content in the upgraded biogas purified via microalgae-based technology

Microalgae-bacteria consortium based technology using a High Rate Algal Pond (HRAP) interconnected to an Absorption Bubble Column (ABC) has emerged as an environmentally friendly promising option to upgrade biogas. However, the oxygenic photosynthesis of microalgae induces oxygen contamination in upgraded biogas, which could limit its further applications. Several strategies were proposed to favor the oxygen desorption and oxygen uptake in parts and accessories of the upgrading system. The effect of the volumetric ratio liquid recirculation rate/biogas rate (L/G = 5.0, 1.0 y 0.5) was evaluated in conjunction with the application of a novel accessory called Open Trickling Column (OTC). The O2 content in upgraded biogas was around 2.1%v, attaining CO2 removal efficiencies around 90%, at L/G ratio of 1.0 during diurnal and nocturnal periods. The inclusion of an OTC at the previous L/G, enhanced 54% the removal of O2 by stripping and uptake compared with the basal condition. Mass balances of H2S and methane showed that L/G > 1.0 favored the complete oxidation of H2S but promoted the loss of methane in dissolved form. Additionally the effect of increasing linear velocity of liquid broth in the lab-scale HRAP (from 15 cm s−1 to 20 cm s−1) showed to improve the O2 stripping with a consequential increase of biomass concentration under steady-state (from 0.7 to 1.4 g L−1) besides achieving O2 content in the upgraded biogas around 1.5%v.

Current understanding and challenges for aquatic primary producers in a world with rising micro- and nano-plastic levels

The impacts of micro- and nanoplastics (MNPs) on aquatic animals have been intensively studied; however, the extent and magnitude of potential effects of MNPs on aquatic primary producers are poorly understood. In this study, we quantitatively analyzed the published literature to examine the impacts of MNPs on growth, photosynthesis, pigments, and metabolism of aquatic microalgae. MNPs negatively affected growth of microalgae but usually had a high EC50 (>25 mg/L). However, positively charged MNPs had a much lower EC50 (<1 mg/L). MNPs lowered maximum photochemical efficiency of photosystem II (Fv/Fm) with the effect increasing with concentration of MNPs but diminishing with exposure time, and also reduced chlorophyll a content to enhanced extent with increased MNPs concentration. MNPs induced relatively higher changes in superoxide dismutase (SOD) and malondialdehyde (MDA) levels in marine algae than in freshwater algae. Reactive oxygen species (ROS) levels increased with MNPs concentration and exposure time while SOD levels first increased and then decreased with increasing MNPs concentration. Macrophytes were found to be able to trap MNPs via multiple mechanisms. Future work should focus on the mechanisms behind MNPs impacts on primary productivity and global carbon cycle, and the combined effects of MNPs with other environmental factors.

Modeling of photosynthesis and respiration rate for microalgae–bacteria consortia

In this article, the influence of culture conditions (irradiance, temperature, pH, and dissolved oxygen) on the photosynthesis and the respiration rates of microalgae-bacteria consortia in wastewater treatment was analyzed. Specifically, some short photo-respirometric experiments, simulating outdoor raceway reactors, were performed to evaluate the response of microalgae, heterotrophic bacteria, and nitrifying bacteria to variations in environmental parameters. Results demonstrate that irradiance is the most dominant variable to determine microalgae photosynthesis rates. However, reduction in microalgae activity was not observed at higher irradiance, ruling out the existence of photoinhibition phenomena. Related to heterotrophic and nitrifying bacteria, their activities were strongly affected by the influence of temperature and pH. Moreover, the effect of dissolved oxygen concentrations on microalgae, and bacteria activities was studied, displaying a reduced photosynthetic rate at dissolved oxygen concentrations above 20 mg/L. Data have been used to develop an integrated model for each population (microalgae, heterotrophic bacteria, and nitrifying bacteria) based on considering the simultaneous influence of irradiance, temperature, pH, and dissolved oxygen. The models fit the experimental results in the range of culture conditions tested, and they were validated using data obtained by the simultaneous modifications of the variables. These individual models serve as a basis for developing a global biologic microalgae-bacteria model for wastewater treatment to improve the optimal design and management of microalgae-based processes, especially outdoors, where the cultures are subject to variable daily culture conditions.

The mechanism of a new type of modified clay controlling Phaeocystis globosa growth

Phaeocystis globosa is a harmful algal bloom (HAB) species worldwide. Using modified clay (MC) to control HABs and to mitigate their adverse effects is currently a commonly used method in China. In this paper, the effects of oxidized composite modified clay (OXI-MC) on P. globosa were studied from different perspectives. The results show that the OXI-MC could effectively remove P. globosa and inhibit both the growth of residual algal cells and the formation of new colonies. The P. globosa algal biomass removal efficiencies after 3 h reached 90% at a dose of 0.1 g/L, and the number of colonies with different particle sizes was greatly reduced. Compared with those of the control, the superoxide dismutase (SOD) activity, catalase (CAT) activity, and malondialdehyde (MDA) content of the residual algae significantly increased, indicating that OXI-MC caused oxidative stress in the algal cells. In addition, we evaluated the effects of OXI-MC on the photosynthesis of residual microalgae and found that the maximal photochemical efficiency of photosystem II (PSII) under dark adaptation (Fv/Fm) and actual photochemical efficiency of PSII (ΦPSII) decreased, severely damaging the photosynthesis efficiency, implying that OXI-MC effected the photosynthesis system of P. globosa. The results of this study clarify that OXI-MC could remove the most of algal cells and break up the colonies of P. globosa by collision, flocculation, and releasing active substances, as well as inhibit effectively the growth and colony formation of residual P. globosa by causing oxidative stress, reducing photosynthesis activity, accelerating the degradation of polysaccharides, and inhibiting the formation of colonies.

Effect of water accommodated fractions of fuel oil on fixed carbon and nitrogen by microalgae: Implication by stable isotope analysis.

Effect of water accommodated fractions (WAF) of #180 fuel oil on fixed carbon and nitrogen in microalgae was studied by stable isotopes. Platymonas helgolandica, Heterosigma akashiwo and Nitzschia closterium were exposed to five WAF concentrations for 96h. The δ13C value of microalgae was significantly lower than that of the control group, indicated that carbon was limited in the WAF concentrations. The δ13C value of microalgae appeared peak valley at 48h in control group, corresponding to the enhanced capacity in carbon fixation during microalgae photosynthesis. The physiological acclimation capacity of microalgae was revealed by the occurrence time when the δ13C value was in peak valley, and thus the physiological acclimation capacity of microalgae decreased in the order of Nitzschia closterium>Heterosigma akashiwo>Platymonas helgolandica. Principal component analysis (PCA) were applied to the δ13C value in order to verify the "hormesis" phenomenon in microalgae. The δ13C value could discriminate between stimulatory effects at low doses and inhibitory effects at high doses. In addition, the present study also investigated the effect of the nitrogen on microalgae growth. Because microalgae could still absorb the NO3-N and release of NO2-N and NH4-N in present study, the nitrogen cycle in microalgae was in the equilibrium status. The δ15N value in microalgae exhibited no obvious change with the increasing of WAF concentrations at the same time. However, due to the enrichment of nitrogen, the δ15N value first increased gradually with the time and finally was stable. Overall, the fractionation of carbon and nitrogen stable isotopes illustrated that the effect of carbon on the growth of microalgae was more prominent than nitrogen. Stable isotopes was used to investigate the influence of WAF on fixed carbon and nitrogen in microalgae growth, providing a fundamental theoretical guidance for risk assessment of marine ecological environment.

Linking lipid accumulation and photosynthetic efficiency in Nannochloropsis sp. under nutrient limitation and replenishment

Oleaginous microalgae can accumulate large amounts of storage lipids that have many potential applications such as in the production of biodiesel and health products. All of the energy for the synthesis of lipids in microalgae is derived from photosynthesis. To date, however, the quantitative relationship between photosynthesis and lipid accumulation rate in microalgae is still unclear. In this study, Nannochloropsis sp. was selected to explore this relationship by investigating changes in lipid accumulation, photosynthetic efficiency, and the electron transport chain under nutrients limitation and replenishment. The results of the study demonstrated that lipids were the main form of storage of carbon and energy for this microalga. The alternative electron transport chain played an important role in photo-protection and lipid accumulation. The photosynthetic efficiency of this microalga showed a strong correlation with lipid accumulation rate (R2 = 0.959), with higher photosynthetic efficiency translating to higher lipid accumulation rates during the lipid accumulation stage of the growth cycle. The results of the present study indicated that nutrient depletion might not be the best signal to understand when microalgae begin to accumulate oil, as it appears that photosynthetic efficiency also has a large role in the rate of oil accumulation. Additionally, the study shows that excessive light might not be needed in later stages of growth for lipid accumulation, which in turn would alleviate the damage to microalgae caused by strong light making large-scale cultivation more cost-effective.

Mixotrophy in green microalgae grown on an organic and nutrient rich waste.

Vinasse is a waste from the alcohol industry that can support microalgal growth because of its mineral and organic contents. Growing microalgae on waste can be a means of its remediation and decrease culture costs. The physiological knowledge of microalgae on waste can generate subsidies to increase biomass productivity. However, few studies have explored the photosynthetic metabolism of microalgae on complex matrices such as vinasse. In the present research, we investigated some physiological aspects related to photosynthesis and growth of several microalgae in centrifuged and diluted vinasse. The species investigated were Chlamydomonas sp., Chlorella sorokiniana, Chlorella vulgaris, Desmodesmus spinosus, Haematococcus pluvialis, Monoraphidium sp., Scenedesmus quadricauda and Tetraselmis gracilis. Daily cell density, in vivo chlorophyll a and final cellular biovolumes (96h) were monitored to infer about population growth. Maximum and operational photosynthetic yields (ϕM and ϕ'M), photochemical (qP) and non-photochemical (NPQ) quenchings, light saturation curves and related parameters (α, rETRm and EK), as well as theoretical carbon fixation were evaluated using pulse amplitude modulated fluorometry (PAM). The results showed that chlorophyll a, photochemical (qP) and non-photochemical (NPQ) quenchings were not affected in vinasse, but photosynthetic yields, light curves parameters and autotrophic carbon fixation decreased. Connecting these results to the increase in productivities in vinasse lead us to the rationale that mixotrophic metabolism was supporting microalgae growth on the waste. This study offers important insights into the understanding of microalgal photosynthetic physiology on complex organic wastes, generating subsidies for optimization of biotechnological use of vinasse related to microalgae production.

The influence of microalgae on vegetable production and nutrient removal in greenhouse hydroponics

Abstract: The effect of microalgae on plant growth and nutrient removal was assessed for three vegetables (arugula, purple kohlrabi and lettuce) grown entirely using nitrate-rich synthetic wastewater in greenhouse hydroponics. Results showed that the response of the vegetables to microalgae varied. Microalgae had a negative effect on arugula growth, but in the purple kohlrabi and lettuce groups, there were no negative effects or even an increase in vegetable production. The dissolved oxygen (DO) and microalgae biomass concentrations in the group with microalgae added were relatively higher. pH increased because of microalgae photosynthesis and decreased due to NH3–N removal processes. The presence of microalgae, especially Chlorella vulgaris addition, can significantly improve the removal rate of total dissolved solids, total nitrogen (TN), and total phosphorus (TP), but not COD. The contribution of each vegetable and microalgal consortia on the N or P removal in greenhouse hydroponics was different. The P removal efficiency were satisfactory in all groups, especially in the natural microalgae treatment where P removal rate reached more than 98%. In some cases, vegetable hydroponics could be upgraded with microalgae co-cultivation which could be an ecofriendly and economically sustainable production system.

Mechanisms of cetyltrimethyl ammonium chloride-induced toxicity to photosystem II oxygen evolution complex of Chlorella vulgaris F1068

Microalgae photosynthesis is sensitive to coexisted contaminates in aquatic environment, thereby causes adverse effect on algal growth and nutrients uptake. Here, we investigated the photosynthetic toxicity mechanism of cetyltrimethyl ammonium chloride (CTAC)-induced on a green microalga Chlorella vulgaris F1068 (C. vulgaris F1068). Results showed that CTAC reduced the algal growth rate, nutrients removal efficiency and weakened the photosynthetic performance. Meanwhile, the efficiency of oxygen evolution complex (OEC) and oxygen evolvement rates stressed by CTAC were significantly declined to 90.48% and 58.48% of the control (without CTAC), respectively. In addition, atomic force microscopy (AFM) detected the damage of PSII-OEC morphology and structure by CTAC. Furthermore, proteomic analysis showed that 41% of proteins were in the chloroplast thylakoid membranes which function in photosynthesis. The activity of oxygen-evolving enhancer protein 2 (OEE2 or PsbP) involved in electron transfer was significantly inhibited by CTAC, which down-regulated 15.14-fold in the presence of 0.6 mg/L CTAC. These results indicated that photosynthetic inhibition of CTAC mainly occurred in the PSII-OEC. This study provided a new perspective of the photosynthetic response in evaluation of environmental bioimpacts of surfactants on microalgae.

Enhancing Stability of Microalgae Biocathode by a Partially Submerged Carbon Cloth Electrode for Bioenergy Production from Wastewater

The electricity output from microbial fuel cell (MFC) with a microalgae assisted cathode is usually higher than that with an air cathode. The output of electricity from a photosynthetic microalgae MFC was positively correlated with the dissolved oxygen (DO) level in the microalgae assisted biocathode. However, DO is highly affected by the photosynthesis of microalgae, leading to the low stability in the electricity output that easily varies with the change in microalgae growth. In this study, to improve the electricity output stability of the MFC, a partially submerged carbon cloth cathode electrode was first investigated to use oxygen from both microalgae and air, with synthetic piggery wastewater used as the anolyte and anaerobically digested swine wastewater as the catholyte. When the DO levels dropped from 13.6–14.8 to 1.0–1.6 mg/L, the working voltages in the MFCs with partially submerged electrodes remained high (256–239 mV), whereas that for the conventional completely submerged electrodes dropped from 259 to 102 mV. The working voltages (average, 297 ± 26 mV) of the MFCs with the 50% submerged electrodes were significantly (p &lt; 0.05) higher than with other partially or completely submerged electrodes. The associated maximum lipid production from wastewater was 250 ± 42 mg/L with lipid content of 41 ± 6% dry biomass. Although the partially submerged electrode had no significant effects on lipid production or nitrogen removal in wastewater, there was significant improvement in the stability of the electricity generated under variable conditions.

Life-cycle assessment of biohythane production via two-stage anaerobic fermentation from microalgae and food waste

A life-cycle assessment was performed to evaluate the energy conversion characteristics and environmental impacts of industrial-scaled biohythane (i.e., biohydrogen and biomethane) production via two-stage fermentation from microalgae and food waste. The results showed that for the entire system, the ratio of net energy input to net energy output was 0.24. Biomass pretreatment and microalgae cultivation were the dominant energy consumption processes, corresponding to a consumption of 53.8% and 16.6% of total energy input, respectively. The net greenhouse gas emissions per upgraded biohythane for the entire system were 124 g CO2-eq MJ−1, whereas the absorption of carbon sources by microalgae photosynthesis corresponded to 49 g CO2-eq MJ−1. The dominant emissions were generated by electricity production (41.6%), CO2 release in pressurized water (27.8%), and energy recovery (19.8%). According to the nutrient balance analysis, 55.3% of nutrients in the liquid fermentation effluents, including carbon, nitrogen, and phosphorus sources, were recycled to maintain the microalgae growth conditions. Additionally, the uncertainties caused by changes in the key parameters and the lack of critical processes were quantitatively analysed.

Antioxidant and Photoprotection Networking in the Coastal Diatom Skeletonema marinoi.

Little is known on the antioxidant activity modulation in microalgae, even less in diatoms. Antioxidant molecule concentrations and their modulation in microalgae has received little attention and the interconnection between light, photosynthesis, photoprotection, and antioxidant network in microalgae is still unclear. To fill this gap, we selected light as external forcing to drive physiological regulation and acclimation in the costal diatom Skeletonema marinoi. We investigated the role of light regime on the concentration of ascorbic acid, phenolic compounds and among them flavonoids and their connection with photoprotective mechanisms. We compared three high light conditions, differing in either light intensity or wave distribution, with two low light conditions, differing in photoperiod, and a prolonged darkness. The change in light distribution, from sinusoidal to square wave distribution was also investigated. Results revealed a strong link between photoprotection, mainly relied on xanthophyll cycle operation, and the antioxidant molecules and activity modulation. This study paves the way for further investigation on the antioxidant capacity of diatoms, which resulted to be strongly forced by light conditions, also in the view of their potential utilization in nutraceuticals or new functional cosmetic products.

Electrochemical method for dissolved oxygen consumption on-line in tubular photobioreactor

A new electrochemical tubular photobioreactor is designed for the efficient cultivation of chlorella, alongside eliminating the inhibition of the growth of microalgae caused by the high dissolved oxygen content. With the aid of anion-exchange membrane alkaline fuel cell, the dissolved oxygen in the photobioreactor which is produced by the photosynthesis of microalgae can be consumed and the energy consumption of photobioreactor can be reduced. Besides, the effects of different components and operating parameters on the efficiency of dissolved oxygen removal and the cell performance have been detailed investigated. The experiment results are shown as follows. First, by applying the double-cylinder alkaline direct glucose fuel cell to consume the dissolved oxygen of the microalgae suspension in the tubular photobioreactor on-line, the dissolved oxygen content rapidly decreases from over 20.0 mg L−1 to 10.72 mg L−1 below within 45 min. Second, the efficiency of dissolved oxygen consumption and cell performance increase significantly by using the bimetallic catalyst Pt-Ru as the cathode catalyst in the double-cylinder alkaline direct glucose fuel cell compared with the mono-metallic cathode catalyst by adopting Pd and Pt. Third, it exists an optimal cathode catalyst loading (1.5 mgPtRu·cm−2) to consume the dissolved oxygen with the fuel cell yielding the best performance.

Toxicity of BDE-47, BDE-99 and BDE-153 on swimming behavior of the unicellular marine microalgae Platymonas subcordiformis and implications for seawater quality assessment

Polybrominated diphenyl ethers (PBDEs), a class of brominated flame retardants, have been extensively applied and eventually leached into the surrounding environment. Marine microalgae are not only the dominant primary producers of marine ecosystem, but also food source for aquaculture. PBDEs have been found to remarkably inhibit growth, photosynthesis and metabolism of marine microalgae. However, whether they also affect swimming behavior of marine motile microalgae remains unknown. We chose BDE-47, BDE-99 and BDE-153 as model PBDEs, and the unicellular marine green flagellate, Platymonas subcordiformis, as test organism to figure out this issue. After two-hour exposure, motile cells proportion (MOT), swimming velocity (VCL, VAP and VSL), and swimming pattern (LIN and STR) of P. subcordiformis were measured via computer assisted cell movement tracking. Results suggest that the three PBDEs not only reduced motile cells proportion and swimming velocity, but also altered swimming pattern. BDE-47 was more toxic than BDE-99, followed by BDE-153, indicating their toxicity decreased as bromination degree increases. Swimming ability of P. subcordiformis was even completely arrested when BDE-47 and BDE-99 at 32 μg/L. The impairment of swimming ability by PBDEs might thereby hinder growth and survival of marine microalgae, and subsequently threaten marine ecosystem and aquaculture industry. More importantly, this study implies that marine microalgae swimming behavior test is more efficiency and sensitive than traditional marine microalgal bioassays, like growth and photosynthesis tests. We suggest that although future work is needed, swimming behavior analysis of P. subcordiformis with MOT, VCL and VAP as endpoints can be developed as a low-cost, convenient, fast, reliable and sensitive method for seawater quality assessment.

A novel light source provided by photobacteria to improve the growth of microalgal biofilm

Attached microalgae cultivation for biomass/bioenergy production has been proposed these decades to avoid the energy-intensive harvest process. However, the external light could only propagate <200 μm in biofilm, which inhibits the growth of microalgae in deep layer. In this paper, the possibility of using inner light emitted by mix-cultured photobacteria for attached microalgae growth was investigated. The luminance of photobacteria gradually increased along with their growth. However, it would fade after approximately 14 h in one-time feed cultivation, which could be recovered by refreshing medium. By scattering photobacteria in the middle of microalgae, light emitted from photobacteria could be utilized for the photosynthesis of microalgae. It was found that the involvement of photobacteria could promote the algal biofilm growth from 9.6 mg to 11.5 mg under the natural condition for a 7-day cultivation, which needed to be further strengthened.

Using co-occurrence network to explore the effects of bio-augmentation on the microalgae-based wastewater treatment process

Microalgae-bacteria consortia is considered to be an efficient way to improve wastewater treatment. However, the interactions between microalgae and bacteria were not clear. In this study, commercially available bacterial inoculum were used as bio-augmentation to improve the performance of microalgae-based wastewater treatment. Co-occurrence network analysis was used to investigate the interactions between microalgae and bacteria. Results showed that bio-augmentation could increase both microalgal growth and wastewater treatment efficiency. Microalgal biomass increased by 1.2 times. Removal efficiencies of total organic carbon, ammonium nitrogen and total phosphorus increased by 5.27%, 3.41%% and 5.74%, respectively. Decreasing trends for Cyanobacteria and Salinarimonas but increasing trends for Cyclobacteriaceae were observed in the microalgal culture system with bio-augmentation. Greater variations of microbial community were found in the treatment without bio-augmentation. Co-occurrence network analysis showed that the main functions of microbial community in the treatment with bio-augmentation were both nutrient removal and organic pollutant degrading. For the treatment without bio-augmentation, main function of microbial community was nutrient removal. It indicated that bio-augmentation increased the number of organic degrading bacteria, such as Bacillus and Paenibacillaceae. The interactions between these bacteria and microalgae promoted the degradation of organic pollutants in the wastewater, providing sufficient inorganic carbon sources for the photosynthesis of microalgae and thus promoting the growth of microalgae and the removal of nitrogen and phosphorus from wastewater.

Enhancement of wastewater treatment efficiency through modulation of aeration and blue light on wastewater-borne algal-bacterial consortia

Since few studies have investigated the nitrification and assimilation of nitrogens by algal-bacterial consortia, this study aimed to evaluate the effects of supplementary aeration and blue light on nitrogen removal and biomass growth of algal-bacterial consortia in real domestic wastewater. When blue light was weakly irradiated (500 μmol m−2 s−1), it was found that supplementary aeration enhanced ammonia removal from 38.5% to 96.3% and algal growth from 72.5 mg algae L−1 to 345.3 mg algae L−1 by providing oxygen for nitrification and inorganic carbon for photosynthesis of microalgae. It was also observed that ammonia was consumed first and then nitrate produced by nitrification was assimilated, indicating that diauxic growth of consortia on nitrogen sources occurred. Thus, it was expected that nitrogen removal could be enhanced by lowering nitrification and denitrification loads. Moreover, intense blue light was found to accumulate nitrite by selective photoinhibition of nitrite oxidizing bacteria (NOB) of which c-type cytochrome is known to be photo-bleachable at 408 nm. From these results, it was concluded that favorable conditions for growth and nitrogen removal by algal-bacterial consortia in real wastewater could be established by controlling aeration and light intensity.