Algal-bacterial Symbiosis Research Articles

Effect of light intensity on nitrogen removal, enzymatic activity and metabolic pathway of algal-bacterial symbiosis in rotating biological contactor treating mariculture wastewater.

An algal-bacterial symbiosis (ABS) system was developed on a rotating biological contactor treating mariculture wastewater, and its nitrogen removal, enzymatic activity and metabolic pathways were investigated under different light intensities. The nitrogen removal efficiency increased when light intensities ranged from 20 to 80 μE/(m2·s) but declined under 100 μE/(m2·s). Higher enzymatic activities under 80 μE/(m2·s) facilitated nitrogen conversion, light utilization, ATP supply and photosynthesis. Reactive oxygen species accumulation activated antioxidant pathways under 20 and 100 μE/(m2·s). Functional bacteria including Sedimentitalea, Thauera and Dechloromonas as well as Chlorella sorokinian, Dunaliella, Pleurosira laevis and Microcystis were enriched under 80 μE/(m2·s). Abundant photosynthesis-related genes (petC, Lca3/4 and atpH/A) supported energy supply and electron transport. Conversely, lower proportions of IDH3, gltB, and acnA/B under 20 and 100 μE/(m2·s) hindered tricarboxylic acid cycle, reducing NADPH and energy production. These results enhance the understanding on the effect of light intensity on ABS system treating mariculture wastewater.

Optimization of microalgal-bacterial consortium flocculation through chitosan-diatomite composite materials: A sustainable approach to biomass harvesting

Chitosan-based flocculants are emerging as a promising technology for microalgae harvesting. However, the implementation of cost-effective and sustainable chitosan-inorganic composites within algal-bacterial symbiosis (ABS) systems for harvesting microalgal-bacterial consortiums (MBC) is still underdeveloped. This study addresses this gap by synthesizing and evaluating chitosan-diatomite composite materials (CTS/DTE), with a focus on their concentration impact on MBC flocculation. Optimal biomass production and flocculation performance were achieved at a CTS/DTE concentration of 60 mg/L during MBC co-culture. Comprehensive characterizations revealed that the largest particle size significantly contributed to superior flocculation efficiency. This efficacy was primarily attributed to the synergistic effects of net trapping and adsorption cross-linking, facilitated by the unique interaction between CTS and DTE. These interactions not only enhanced the bond between the flocculant and microalgal cells but also promoted the structural stabilization of the MBC flocs. Additionally, tryptophan-like proteins in the extracellular polymeric substances (EPS), as identified through three-dimensional fluorescence (EEM) analysis, were found to be the primary contributor to the hydrophobic properties of MBC flocs, significantly enhancing their adhesion and aggregation thermodynamics. Collectively, this research elucidates innovative strategies and provides both theoretical and practical insights for the efficient and cost-effective harvesting of MBC, underscoring the potential of CTS/DTE composites in enhancing the sustainability of ABS systems.

Start-up phase performance evaluation of a pilot-scale sequential anaerobic-aerobic hybrid algal-bacterial suspended growth reactor for the domestic wastewater treatment

This study evaluated the start-up phase performance of an 80-cubic-meter pilot-scale anaerobic-aerobic hybrid algal-bacterial reactor treating real domestic wastewater operated at 24 h hydraulic retention time. The aerobic chambers of the reactor were inoculated with heterotrophic bacterial biomass and mixed microalgal culture. Blue light-emitting-diode (LED) lights were provided in the aerobic chambers to facilitate algal photosynthesis. The influent chemical oxygen demand (COD), total nitrogen (TN), and phosphorus (P) values were 241 ± 45 mg/L, 26.8 ± 4.2 mg/L, and 6.7 ± 0.9 mg/L, respectively. After thirty days of operation, the effluent COD, TN, and P values were observed to be 26.7 ± 6.5 mg/L, 15.6 ± 0.73 mg/L, and 4.45 ± 0.16 mg/L, respectively. The sludge volume index of the mixed liquor was 43 mL/g, indicating high settleability. During the operation, an increase in the chlorophyll to biomass ratio was observed, which implies that the algal-bacterial symbiosis might have played a role in simultaneous carbon and nitrogen removal from the domestic wastewater.

Microbial succession and enrichment of antibiotic resistance genes during algal-bacterial biofilm purification of aquaculture wastewater

This study involved the establishment of algal-bacterial biofilms on the surface of carbon fiber-based artificial aquatic plants, utilizing algal-bacterial symbiosis for the purification of aquaculture wastewater. The algae-bacteria consortium exhibited strong photosynthetic activity, as indicated by the chlorophyll a + b content (0.918 ± 0.029 mg/g carbon fiber (CF)). Particularly, during the initial 7 days, algal-bacterial biofilm displayed robust water purification activity and capacity, with a significant reduction in total phosphorus (TP) of 39.44 % ± 2.43 % observed. The microbial community of the biofilm was diverse, primarily dominated by Proteobacteria, Cyanobacteria, Actinomycetota, and Planctomycetota. Among these, Proteobacteria were in the highest abundance ranging from 39.18 % to 40.61 %. Changes in Cyanobacteria, driven by nutrient level alterations, not only impacted species abundance but also posed a risk of promoting the spread of antibiotic resistance genes (ARGs). Through the complex interactions among biological communities, 15 types of ARGs have been enriched on the algal-bacterial biofilm, among which Multidrug, Bacitracin, Aminoglycoside, and Glycopeptid have a higher abundance. Contigs and network analysis indicate that Nannocystis, Sphingorhabdus, and Polynucleobacter are the key hosts and it is found that their abundance will increase during the purification of water quality by the algal-bacterial biofilm. This study highlighted the risk of ARG transmission in aquaculture effluent treatment with algal-bacterial biofilms.

Toward nitrogen recovery: Co-cultivation of microalgae and bacteria enhances the production of high-value nitrogen-rich cyanophycin

The algal-bacterial wastewater treatment process has been proven to be highly efficient in removing nutrients and recovering nitrogen (N). However, the recovery of the valuable N-rich biopolymer, cyanophycin, remains limited. This research explored the synthesis mechanism and recovery potential of cyanophycin within two algal-bacterial symbiotic reactors. The findings reveal that the synergy between algae and bacteria enhances the removal of N and phosphorus. The crude contents of cyanophycin in the algal-bacterial consortia reached 115 and 124 mg/g of mixed liquor suspended solids (MLSS), respectively, showing an increase of 11.7 %–20.4 % (p < 0.001) compared with conventional activated sludge. Among the 170 metagenome-assembled genomes (MAGs) analyzed, 50 were capable of synthesizing cyanophycin, indicating that cyanophycin producers are common in algal-bacterial systems. The compositions of cyanophycin producers in the two algal-bacterial reactors were affected by different lighting initiation time. The study identified two intracellular synthesis pathways for cyanophycin. Approximately 36 MAGs can synthesize cyanophycin de novo using ammonium and glucose, while the remaining 14 MAGs require exogenous arginine for production. Notably, several MAGs with high abundance are capable of assimilating both nitrate and ammonium into cyanophycin, demonstrating a robust N utilization capability. This research also marks the first identification of potential horizontal gene transfer of the cyanophycin synthase encoding gene (cphA) within the wastewater microbial community. This suggests that the spread of cphA could expand the population of cyanophycin producers. The study offers new insights into recycling the high-value N-rich biopolymer cyanophycin, contributing to the advancement of wastewater resource utilization.

Optimizing aeration intensity to enhance self-flocculation in algal-bacterial symbiosis systems

Effectuating optimal wastewater treatment via algae-bacterial symbiosis (ABS) systems necessitates the precise selection of aeration intensity. This study pioneers an in-depth investigation into the interplay of aeration intensity on the microalgal-bacterial consortia's self-flocculation efficacy and the overall treatment performance within ABS systems. The research provides evidence for a direct association between aeration intensity and biomass proliferation, indicating enhanced pollutant removal efficiency with escalated intensities (1.0 and 1.5 L min−1), though the variance lacks statistical significance. The peak self-flocculation efficacy of the microalgal-bacterial consortium (82.39% at 30 min) was manifested at an aeration intensity of 1.0 L min−1. The meticulous analysis of biomass properties showed the complexity of self-flocculation capacity in the consortium, which involves a dynamic interplay of several pivotal factors, including floc size, zeta potential, and EPS content. In situations where these factors pose conflicting influences, the determining factor emerges as the dominant influencer. In this study, the optimal aeration intensity was identified as 1 L min−1, shedding light on the critical threshold for ABS system operation. This study not only enriches the understanding of microalgal-bacterial wastewater treatment mechanisms but also fosters innovative strategies to enhance the performance of such systems.

Amoxicillin degradation and high-value extracellular polymer recovery by algal-bacterial symbiosis systems

Algal-bacterial symbiosis systems have emerged as sustainable methods for the treatment of new pollutants and the recovery of resources. However, the bio-refinery of biomass derived from microalgae is inefficient and expensive. In order to simultaneously degrade antibiotic and recover resources efficiently, two algal-bacterial symbiosis systems were constructed using Pseudomonas aeruginosa (alginate overproduction) and Bacillus subtilis (poly-γ-glutamic acid overproduction) with amoxicillin-degrading-microalga Prototheca zopfii W1. The optimal conditions for W1 to degrade amoxicillin are 35 °C, pH 7, and 180 rpm. In the presence of 5–50 mg/L of amoxicillin, W1-P. aeruginosa and W1-B. subtilis exhibit higher amoxicillin degradation and produce more extracellular polymers than W1 or bacteria alone. The metabolomic analysis demonstrates that the algal-bacterial symbiosis enhances the tolerance of W1 to amoxicillin by altering carbohydrate metabolism and promotes the production of biopolymers by upregulating the precursors synthesis. Moreover, the removal of amoxicillin (10 mg/L) from livestock effluent by W1-P. aeruginosa and W1-B. subtilis is greater than 90 % in 3 days, and the maximum yields of alginate and poly-γ-glutamate are 446.1 and 254.3 mg/g dry cell weight, respectively. These outcomes provide theoretical support for the application of algal-bacterial symbiosis systems to treatment of amoxicillin wastewater and efficient production of biopolymers.

Effects of simulated extreme precipitation flooding on the degradation of anaerobic digestion effluent by algal-bacterial symbiosis system

Precipitation is directly affected by global warming among different extreme climate types. The moisture-holding capacity of the atmosphere increases by 7% with a temperature increase of 1 °C. A higher moisture content results in frequent and violent rainfall events, and the frequency and intensity of heavy rainfall and flooding events in certain countries and regions is gradually aggravated. Simulated extreme precipitation experiments with precipitation intensities of 50, 100, and 200 mm and precipitation time on 3th, 6 th, and 9 th day were set to study the effects of extreme precipitation and flooding events on the degradation performance of open algae–bacteria symbiotic (ABS) system for anaerobic digestion effluent (ADE). The experimental results showed that the precipitation time had an obvious impact on the open algae–bacteria symbiotic system. The daily COD (chemical oxygen demand) degradation rates in the algae–bacteria symbiotic system on the fourth day decreased from 12.64% (unaffected by precipitation) to 2.94, 2.38, and 1.90%, respectively, under the conditions of rainfall on the third day and precipitation intensities of 50, 100, and 200 mm. At the end of the experiments, the COD contents in the ADE increased from 355.09 mg/L (unaffected by precipitation) to 435.77, 413.67, and 403.54 mg/L, respectively. The degradation effects of COD, TN (total nitrogen), and TP (total phosphorus) in the open algae–bacteria symbiotic system were affected by extreme precipitation (200 mm) and flooding. On the third day of the heavy rainfall event, Actinobacteria, Proteobacteria, and Bacteroidetes were the most dominant phyla in the samples of the symbiotic system between algae and bacteria. Among them, the abundance of Proteobacteria and Bacteroidetes was the highest, accounting for 15.33, 21.33 and 19.97%, respectively. As the symbiotic system operated stably, their proportions decreased to 13.58, 12.13, and 17.85% on the ninth day. At the class level, the abundance of Beta-proteobacteria and Gamma-proteobacteria was relatively high in the samples of the symbiotic system. On the third day of the heavy rainfall event, they accounted for 8.99 and 7.11%, respectively. With the stable operation of the system, their proportions showed a decreasing trend, and on the sixth and ninth days, they were 7.03% and 6.01, 4.87 and 4.39%, respectively.

Rapid establishment of algal-bacterial granular sludge system by applying mycelial pellets in a lab-scale photo-reactor under low aeration conditions: Performance and mechanism analysis

Light-driven algal-bacterial granular sludge (ABGS) is an innovative low-carbon technology with significant merits in treating municipal wastewater, but how to shorten the photogranulation process, especially under low aeration conditions, is largely unknown. Herein, two strategies were proposed to accelerate the start-up of the ABGS system in photo-sequencing batch reactors (PSBRs) with a low superficial gas velocity of 0.5 cm/s. Compared to directly dosing mycelial pellets (MPs), applying MPs to flocculate algae and using the formed algal-mycelial pellets (AMPs) as carriers enhanced the establishment of the algal-bacterial symbiosis. The ABGS system developed rapidly within 20 days, with a large particle diameter (mean diameter of 321 μm) and excellent settleability (SVI30 of 55.4 mL/g). More importantly, this system could be stably operated for at least 100 days, mainly attributed to the reinforced secretion of protein with unique secondary structure and elevated hydrophobic functional groups. As for the reactor performance, the average removal efficiencies of the ABGS system were 97.8% for organic matter, 80.0% for total nitrogen, and 84.4% for phosphorus. The enrichment of functional bacteria and algae, and the up-regulation of functional genes and enzymes involved in electron production and transport processes likely drove the transformation of the pollutants, underlining the inherent mechanism for the excellent nutrient removal performance. This study provides a promising approach to solve the problem of a long ABGS start-up period and unstable granular structure under low aeration conditions, which is significant for achieving effective wastewater treatment without energy intensive aeration.

Enhancement of nutrients removal and biomass accumulation of algal-bacterial symbiosis system by optimizing the concentration and type of carbon source in the treatment of swine digestion effluent

The algae-bacteria symbiosis system (ABS) is used to effectively solve the problems of low carbon/nitrogen (C/N) ratio, low biodegradability and high ammonia toxicity in swine digestion effluent. This study examined the effects of the concentration and type of carbon source on ABS in the pollutants removal especially ammonia. When C/N ratio was 30:1 and carbon source was sodium acetate, the ABS was most conducive to the removal of nitrogen, phosphorus and COD, and to the accumulation of biomass and lipids. To make the wastewater discharge meet the relevant standard, the ABS + mono-cultivation of algae reprocessing system (MAS), was applied to actual swine digestion effluent. Through adjusting the C/N ratio in ABS to 30:1, the biomass concentration was 2.06 times higher than that of raw wastewater, and the removal efficiencies of NH4+-N, TN, TP and COD increased by 1.43, 1.46, 1.95 and 1.28 times, respectively. The final concentrations of NH4+-N, TN, TP and COD after the treatment of ABS (C/N ratio of 30:1) + MAS, were 16.98 ± 1.07 mg L−1, 18.72 ± 1.81 mg L−1, 0.48 ± 0.01 mg L−1 and 263.49 ± 11.89 mg L−1, respectively, reached the Chinese discharge standards for livestock and poultry wastewater. Bacterial community analysis showed that the dominant species of the ABS (C/N ratio of 30:1) was Corynebacterium (genus level). This study revealed that adjusting the concentration and type of carbon source was helpful to the nutrient cycling and resource utilization of ABS, indicating a feasible technique for treating high ammonia nitrogen digestate.

The sustainable utilization of anaerobic digestion effluents treating in suspended filler algae assisted systems

Significant amounts of anaerobic digestion effluents (ADE) containing high concentration of inorganic salts (source of nitrogen and phosphorus) and hardly degradable organic matter are produced during the generation of biogas using livestock manure. Without appropriate treatment, the imbalanced carbon to nitrogen ratio may lead to severe pollution of the environment. Considering different environmentally friendly processes such as recycling, energy regeneration, and sustainable development, suspended fillers were added to traditional algal-bacterial symbiosis (ABS) systems. In the present research, three systems including suspended filler algae assisted bio-reactor (SFA-PBR), no filler algae assisted bio-reactor (NFA-PBR), and single activated sludge system (ABS) were examined. Changes in bacterial communities were analyzed using high throughput sequencing. In addition, the mechanisms of ADE degradation in the presence and absence of suspended algae fillers were studied by comparing their effect on the degradation of COD (chemical oxygen demand), TN (total nitrogen), AN (ammonia nitrogen), and TP (total phosphorus). Systems where the ratio of active microalgae to bacteria was higher promoted the interaction between the two types of microorganisms, accelerating the stability of the ABS. Thus, the daily COD degradation rate in the stage was still high. Flora such as microalgae and bacteria were embedded in the filler spheres, which increased the microorganisms resistance to the poor environment induced by high concentrations of inorganic nutrients and organic matter present in the ADE. This favored the sustainable water utilization of ADE. After the treatment in the SFA-PBR system, the COD degradation rate was 75.32 %. The effluent COD concentration was 334.21 ± 39.18 mg/L. TN and AN degradation rates were 89.34 and 91.32%, respectively. The TN and AN concentrations in the effluent were 35.42 ± 2.65 and 29.97 ± 2.65 mg/L, respectively. The degradation rate of TP was 95.39 %. The effluent TP concentration was 0.86 ± 0.18 mg/L. The Chao diversity and ACE index values in the SFA-PBR system were higher than those of other groups. This result further supports the conclusion formulated with the Shannon diversity index result. Specifically, the effective sequence in the SFA-PBR system group presented a higher degree of homogeneity and abundance.

Symbiotic treatment of ammonia-nitrogen wastewater by algae and activated sludge: effects of algae and sludge inoculation rates

ABSTRACT A symbiotic microalgal-bacterial system may be an optional technology for wastewater treatment. It was composed of microalgae and activated sludge and established in the SBR to explore the effect of different dosing ratios of algae and sludge on the removal of nitrogen and phosphorus from simulated wastewater containing ammonium. It can be seen from the result that varied algae–sludge dosing ratios had a higher removal effect on COD removal, but the difference was not significant. The algal-bacterial symbiosis system had a 100% removal rate for ammonium removal on the 8th day. Relatively speaking, the removal of nutrients and related mechanisms vary with environmental conditions (inoculation rate). In general, when the additive ratio was 5:1 (algae: AS), the removal rate of TN and TP was the highest, reaching 53.85% and 85.13% in the shortest time (14 days), among them, the removal rate of ammonium and COD was 100%, and the reduction rates of Nitrite nitrogen and Nitrate nitrogen were 362.99% and 73.42%, respectively. In addition, 16S rDNA gene analysis results demonstrated that the microbial community in the reactor with algal sludge inoculation ratio of 5:1 had differences in three stages of the initial reaction, the middle reaction and the end of the reaction. Comamonadaceae, Flavobacterium, Paenarthrobacter, Mesorhizobium, Nitrobacter were enriched during the reaction operation.

Efficacious bioremediation of heavy metals and radionuclides from wastewater employing aquatic macro- and microphytes.

Cytotoxic, mutagenic, and carcinogenic contaminants, such as heavy metals and radionuclides, have become an alarming environmental concern globally, especially for developed and developing nations. Moreover, inefficient prevalent wastewater treatment technologies combined with increased industrial activity and modernization has led to increase in the concentration of toxic metals and radioactive components in the natural water bodies. However, for the improvement of ecosystem of rivers, lakes, and other water sources different physicochemical methods such as membrane filtration, reverse osmosis, activated carbon adsorption, electrocoagulation, and other electrochemical treatment are employed, which are uneconomical and insufficient for the complete abatement of these emerging pollutants. Therefore, the application of bioremediation employing aquatic macrophytes and microphytes have gained considerable importance owing to the benefits of cost-effectiveness, eco-friendly, and higher energy efficiency. Thus, the present review aims to enlighten the readers on the potential application of algae, cyanobacteria, plant, and other aquatic micro- and macrophytes for the elimination of carcinogenic metals and radioactive isotopes from wastewater. Additionally, the use of transgenic plants, genetically modified species, algal-bacterial symbiosis for the enhancement of removal efficiency of mutagenic contaminants are also highlighted. Furthermore, species selection based on robustness, mechanism of different pathways for heavy metal and radionuclide detoxification are elucidated in this review article.

Novel shortcut biological nitrogen removal using activated sludge-biofilm coupled with symbiotic algae

This study evaluated a novel shortcut biological nitrogen removal (BNR) method using activated sludge-biofilm coupled with microalgae in a photo-sequencing batch biofilm reactor (PSBBR) for treating high ammonia nitrogen (NH4+-N) wastewater. Results showed that the symbiotic microalgae supplied oxygen and an additional organic carbon source for bacteria. The consortium achieved high nitrogen removal efficiency (> 90%) and had the potential to lower the operating cost when used for treating biogas slurry (BS). It saved more than 50% of the external carbon source and reduced about 78% of oxygen demand compared with the conventional BNR process. Nitrogen was removed mainly through shortcut nitrification-denitrification (SCND) (> 80%) and biological assimilation (6.8%) in the PSBBR. The algal-bacterial symbiosis improved the species richness but reduced the microbial diversity of the biofilm. Nitrosomonas with an abundance of 19.81% was the dominant ammonia-oxidizing bacteria (AOB) in the biofilm, while Thauera with an abundance of 45.03% played a leading role in denitrification. This study concurrently indicated that algae and activated sludge coupling increased the nitrous oxide (N2O) emission in the shortcut nitrogen removal process.

The ecological network approach to algal-bacterial relationships: Review and prospects

<p indent=0mm>Algae and bacteria numerically dominate oceanic and freshwater planktonic communities. They play a central biogeochemical role in the marine ecosystem, including producing biomass to support aquatic food webs, cycling nutrients and trace elements, and decomposing organic matter. Algae and bacteria synergistically affect each other’s physiology and metabolism and have coexisted ever since the early stages of evolution that revolutionized many aspects of life on Earth. The relationship between algae and bacteria influences ecosystems and represents all conceivable modes of interaction from mutualism to parasitism. The interactions between these two groups of plankton, and the influence of their interaction on each other and on a global scale have, therefore, become the focus of recent research interest. Previous studies have summarized a variety of algal-bacterial interactions and aimed to reveal the essence of those interactions. However, it is clear that their interactions are diverse and not static, and can be initiated and broken in response to environmental and developmental cues. Traditional research methods have been unable to reveal the complexity behind algal-bacterial symbiosis. As microbial omics technology has developed and the influence of global change on marine ecosystems has become apparent, the research perspective on algal-bacterial relationships has gradually risen to the level of systemic ecology. The rapid-blooming of high-throughput sequencing technology and the ability to analyze big data offer new opportunities for a thorough study of algal-bacterial interaction. Ecological networks are prominent among these new methods: They can integrate multiple types of information and might represent systems-level behavior. Network theory methods are powerful approaches for quantifying relationships between biological components and their relevance to phenotypes, environmental conditions or other external variables within a system. In this paper, we review the research advances in the algal-bacterial ecological network based on big data. We begin by introducing the network parameters and attributes commonly used in ecological network analysis and review the existing network modeling methods in microbial studies and algorithm features and application scenarios. By comparing some common algorithms or software, researchers can choose appropriate network construction methods when confronted with different data characteristics. Next, the ecological network analysis used in the study of algal-bacterial relationships is presented at multiple layers from taxonomy to function (e.g., molecular and metabolic networks). The problems and experiences encountered during research into algal-bacterial relationships are then discussed. For example, when focusing on the interaction between host and microorganism, the time/space shift correlations among the variables will lead to wrong conclusions, including false-positive or false-negative results. We also attempt to introduce metabolic and dynamic biological networks into the study of the algal-bacterial relationship to reveal further the mechanism of their interaction from the perspectives of function and causality. Finally, our novel proposal to establish a knowledge network database of algal-bacterial interactions and a graphic database of photosphere biological profiles is discussed. We highlight the need for microbial ecological network inference and suggest strategies to infer networks more reliably. Our study aimed to explore the holistic information behind algal-bacterial relationships and provide new cues for further revealing the molecular mechanisms of algal-bacterial interactions.

Algal–bacterial symbiosis for nutrients removal from wastewater: The application of multivariate data analysis for process monitoring and control

The application of algal–bacterial symbiotic interaction as a low-cost and environment-friendly alternative for wastewater treatment was investigated in this research. In this context, a photobioreactor working under sequencing batch mode (SBR) was used. It consists of three basins of 200 L which were fed with pre-treated domestic wastewater. Following the adaptation period, and according to the obtained results, a synergistic interaction between algal and bacterial cultures was developed, which ultimately lead to enhance the removal of different pollutants. During daylight cycles, the dissolved oxygen concentration was around 6 mg/L, which promoted aerobic microbial activities to degrade organic pollutants such that more than 60% of the COD was removed. Additionally, more than 40% and 90% of the nitrogen (NH4+-N) and phosphorus were removed, respectively. Based on multivariate data analysis, it was noticed that there is a high positive correlation between DO and NO3− (i.e. 0.97), such that, any increase in the DO was associated with an increase in NO3−, whereas, a high negative correlation (i.e. -.092) between DO and COD was observed. Generally, the obtained results hold great promise for future process development regarding pollutants removal and the positive contribution in reducing greenhouse gas emissions as reactor mechanical aeration was totally replaced by algal photosynthesis.

Mechanism of contaminant removal by algae-bacteria symbiosis in a PBR system during the treatment of anaerobic digestion effluents

Large volumes of anaerobic digestion effluents (ADEs) are generated by intense livestock and poultry farm activities. If untreated, these effluents represent a threat to the environment. Previous data have indicated that microalgae are able to grow in photobioreactors (PBR) where high concentrations of inorganic salts are present. In the present research, algae-assisted sequencing batch photo-bio-reactor (A-SBPBR) with single micro-algae systems and single activated sludge systems were developed. We studied the effects of the treatments on different parameters including COD, TN, AN, and TP. We analyzed changes in bacterial community diversity using the high-throughput sequencing analysis. The degradation mechanism of the ADEs was studied by means of algal-bacterial symbiosis. Experimental results indicated that contaminants were efficiently removed from the ADEs when using the A-SBPBR. After treatment, the degradation rates of COD, TN, AN, and TP were 73.78%, 80.67%, 89.74%, and 95.39%, respectively. The outlet concentrations of COD, TN, AN, and TP were 355.09 ± 17.90, 83.97 ± 9.37, 35.42 ± 2.65 and 0.87 ± 29 mg/L, respectively. In the initial stage of the process (day 1), the most abundant bacteria present in the ABS (algal-bacterial symbiosis system) included proteobacteria, bacteroidetes, actinobacteria, acidobacteria and chloroflexi. Among these, those with the highest abundance values were proteobacteria and bacteroidetes. Abundance values were 24.33% and 19.97%, respectively. A-SBPBR contained various microorganisms including aerobic bacteria, fungus, and chlorella. In a reciprocal interaction, bacteria and microalgae were able to use each other´s metabolites. Under intermittent aeration conditions, organic C, N, and P present in the macromolecules were converted to smaller species. C was transformed to CO2 and organic C. In addition, N and P stayed as part of small molecules that were used by aerobic bacteria and fungus. When ABS operation reached stability, hydrolytic acidifying bacteria, which belonged to acidobacteria, were able to degrade different organic compounds including saccharides.

Comparison of algae growth and symbiotic mechanisms in the presence of plant growth promoting bacteria and non-plant growth promoting bacteria

Culturing algae with bacteria has been explored as a means of promoting algal growth and altering algal biochemical composition. Plant growth promoting bacteria (PGPB) are of particular interest given their ability to produce phytohormones that are bioactive in microalgae. However, many non-plant growth promoting bacteria also promote algal growth. The objective of this study was to test the benefits of a model PGPB versus non-PGPB in a side-by-side study, evaluating improvement in algal growth rates and impacts on biomass composition. Three green microalgae strains were tested with three strains of bacteria: Azospirillum brasilense (a model PGPB), Escherichia coli (a non-PGPB), and Bacillus megaterium (a potential PGPB). A. brasilense produces the auxin phytohormone indole-3-acetic acid. A. brasilense promoted growth in two of the three algae strains by 39–69% but did not promote growth in Chlorella sorokiniana (strain UTEX 2805). E. coli promoted growth in all three algae strains by 16–64%. That the non-PGPB, E. coli, performed as well as the PGPB, A. brasilense, suggests the importance of symbiotic mechanisms that are ubiquitous among many bacteria. One such mechanism, cell-to-cell O2-CO2 exchange, may have been important given significant consumption of algal photosynthate by bacteria. B-vitamin exchange is another widespread mechanism of algal-bacterial symbiosis. The riboflavin metabolite, lumichrome, was detected in low concentrations in co-cultures of A. brasilense (0.4–0.6 ng/mL) and E. coli (5.5–13 ng/mL). These concentrations of lumichrome were found to provide small but statistically significant growth benefits for C. sorokiniana UTEX 2805 and Auxenochlorella protothecoides.

Microalgal–Bacterial Synergistic Interactions and Their Potential Influence in Wastewater Treatment: a Review

Microalgae, as the most promising raw material for biodiesel, can absorb and transform N, P, and organic matter in wastewater into cell components such as oil, carbohydrate, and protein. The cultivation of microalgae in wastewater provides the possibility to realize harmless treatment and resource utilization of wastewater and reduce the cost of microalgal culture. Whether in a single microalgal culture process or wastewater system, there always be a large number of bacteria interacting with microalgae, forming a complex microecological system. Although microalgal–bacterial coculture system is feasible features for the higher biomass production and better nutrient adaptability from wastewater, the precise understanding of interaction and coexistence in water bodies is still unclear. Some major challenges are to develop sustainability in the microalgal–bacterial coculture system due to the incomplete knowledge about the mechanism of communication, algal growth promotion, and effect of microalgae on the indigenous bacteria in wastewater. In the present review, nutritional interaction and signal transduction, two main interaction models of algae and bacteria, and the effect of synergism of these two models on microalgal system are summarized. Moreover, the impact of algal–bacterial coculture on algal growth and removal of pollutants in wastewater treatment process was expounded systematically to develop highly efficient consortium systems by covering the sustainability limitations. This work would provide guidance for the establishment of efficient algal–bacterial symbiosis system in the wastewater with complex microecology and nutrient environment to improve the accumulation of microalgal biomass and reduce the cost of microalgal culture.

Evaluation of the effect of reaction time on nutrients removal from secondary effluent of wastewater: Field demonstrations using algal-bacterial photobioreactors.

Real field demonstrations to assess the removal efficiency of nutrients and organic matter from domestic wastewater were carried out using algal-bacterial photobioreactors. The reactors which consisted of three basins of 200 L were fed with secondary effluent of domestic wastewater and operated under natural day light/dark cycles. The results demonstrated that reaction time (RT) has a substantial role on the whole process performance. Whereas inoculation with nitrifiers affected the process only in some aspects. The enhancement in the dissolved oxygen production rate (1.15 mg O2. L−1.h−1) was in alignment with growing higher algal biomass concentrations due to the increase in RT. COD removal rates were significantly increased (p < 0.05) with increasing the RT, and removal rates of 27%, 46% and 50% were obtained under RTs of 2, 3 and 4hrs. respectively. Meanwhile, 30%, 84% and 95% of the phosphorus was removed under the same studied RTs. No significant effect was recorded due to the addition of nitrifying bacteria on the removal of both COD and phosphorus. Ammonium (NH4+-N) removal rates were also increased with increasing RT and by the addition of nitrifiers, such that removal rates of 13%, 21% and 31% were obtained in basins inoculated with nitrifiers, but 11%, 14% and 19.5% were obtained in non-inoculated basins under RT of 2, 3, and 4 hrs. respectively. These results provide some new insights into algal-bacterial symbiosis systems under real field conditions which could be helpful for further process development.