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The optimization of wastewater treatment technologies using biological processes is no longer limited to improving the removal of organic matter and nutrients, as it is possible to reduce area and energy consumption, and recover value-added by-products. In this context, the microalgae–bacteria consortium is an alternative for reducing costs, as microalgae produce the oxygen required by bacteria to oxidize organic matter through photosynthesis. Additionally, it is possible to extract different by-products such as lipids, biofertilizers, biogas, alginate-type exopolymers, and others. Furthermore, bioflocculation occurs naturally through the adhesion of microalgae to the surface of bacterial flocs, without the addition of chemical products. This review discusses the main systems that utilize the microalgae–bacteria consortium, the metabolism of the microalgae–bacteria consortium, and its performance in removing organic matter and nutrients, as well as the effect of operating conditions on the physical properties of the biomass. Among the highlighted systems are sequencing batch and single-batch reactors, high-rate ponds, and continuous flow reactors. Among the systems discussed in this work, the sequential batch reactor configurations found better biomass formation and production of extracellular polymeric substances and the continuous flow reactors showed lower installation and operating costs. From this perspective, the potential for full-scale application of each system can be evaluated once the optimum operating conditions have been defined and the limitations of each system have been understood. [ABSTRACT FROM AUTHOR]

BACKGROUND AND OBJECTIVES: The utilization of stabilization pond system for landfill leachate treatment is hindered by its requirement for expansive land areas and extended retention periods. Although the system effectively removes organic compounds, its ability to eliminate nutrients such as nitrogen and phosphorus is comparatively limited. Consequently, the leachate subjected to treatment often falls short of meeting the mandated standards for effluent quality. In response to this challenge, a research study was undertaken to investigate the potential of utilizing a consortium comprising microalgae and bacteria in the treatment of landfill leachate. METHODS: The microalgae, bacteria, and leachate utilized in this study were sourced from a leachate treatment facility located at the Aceh regional domestic waste management unit in Blang Bintang, Aceh Besar, Indonesia. The two glass photobioreactors were operated batchwise, where the first was provided with a combination of air and carbon dioxide, and the other was solely exposed to air. The pollutant removal efficacy in the leachate effluent was assessed through the measurements of chemical oxygen demand, ammonia, nitrate, nitrite, and phosphate concentrations. Subsequently, macroscopic identification of microalgae and bacteria species was also conducted. FINDINGS: Utilizing a consortium of microalgae and bacteria has demonstrated efficacy in treating leachate, resulting in a notable reduction of contaminants within the effluent. The symbiotic association between microalgae and bacteria in the context of leachate waste treatment is evident. The bacteria's metabolic actions result in carbon dioxide emission, which subsequently serves as a substrate for the photosynthetic activities of the microalgae. The microalgae facilitate the transfer of oxygen, produced through photosynthesis, to the bacteria to support their metabolic processes. Therefore, introducing exogenous carbon dioxide to the consortium yields minimal discernible effects, given that the bacteria adequately fulfill the carbon dioxide requirements of the microalgae. This discovery enhances the efficacy of leachate treatment techniques by leveraging the utilization of pre-existing mixed cultures of microalgae and bacteria found in leachate facilities. CONCLUSION: This study evaluated the microalgae-bacteria consortium's effectiveness in reducing leachate pollutants. The consortium exhibited a significant capability, achieving a 75 percent reduction in chemical oxygen demand and successfully eliminating a range of contaminants. Additionally, it demonstrated effective removal of nitrogen compounds such as ammonia, nitrate, and nitrite, with removal rates reaching 75 percent. Notably, the consortium showed a 99 percent removal rate for phosphate compounds. Even with the introduction of carbon dioxide, the pollutant removal remained consistently high, suggesting that the addition of carbon dioxide did not significantly influence the overall process. [ABSTRACT FROM AUTHOR]

BACKGROUND AND OBJECTIVES: The utilization of stabilization pond system for landfill leachate treatment is hindered by its requirement for expansive land areas and extended retention periods. Although the system effectively removes organic compounds, its ability to eliminate nutrients such as nitrogen and phosphorus is comparatively limited. Consequently, the leachate subjected to treatment often falls short of meeting the mandated standards for effluent quality. In response to this challenge, a research study was undertaken to investigate the potential of utilizing a consortium comprising microalgae and bacteria in the treatment of landfill leachate.METHODS: The microalgae, bacteria, and leachate utilized in this study were sourced from a leachate treatment facility located at the Aceh regional domestic waste management unit in Blang Bintang, Aceh Besar, Indonesia. The two glass photobioreactors were operated batch-wise, where the first was provided with a combination of air and carbon dioxide, and the other was solely exposed to air. The pollutant removal efficacy in the leachate effluent was assessed through the measurements of chemical oxygen demand, ammonia, nitrate, nitrite, and phosphate concentrations. Subsequently, macroscopic identification of microalgae and bacteria species was also conducted.FINDING: Utilizing a consortium of microalgae and bacteria has demonstrated efficacy in treating leachate, resulting in a notable reduction of contaminants within the effluent. The symbiotic association between microalgae and bacteria in the context of leachate waste treatment is evident. The bacteria’s metabolic actions result in carbon dioxide emission, which subsequently serves as a substrate for the photosynthetic activities of the microalgae. The microalgae facilitate the transfer of oxygen, produced through photosynthesis, to the bacteria to support their metabolic processes. Therefore, introducing exogenous carbon dioxide to the consortium yields minimal discernible effects, given that the bacteria adequately fulfill the carbon dioxide requirements of the microalgae. This discovery enhances the efficacy of leachate treatment techniques by leveraging the utilization of pre-existing mixed cultures of microalgae and bacteria found in leachate facilities.CONCLUSION: This study evaluated the microalgae-bacteria consortium’s effectiveness in reducing leachate pollutants. The consortium exhibited a significant capability, achieving a 75 percent reduction in chemical oxygen demand and successfully eliminating a range of contaminants. Additionally, it demonstrated effective removal of nitrogen compounds such as ammonia, nitrate, and nitrite, with removal rates reaching 75 percent. Notably, the consortium showed a 99 percent removal rate for phosphate compounds. Even with the introduction of carbon dioxide, the pollutant removal remained consistently high, suggesting that the addition of carbon dioxide did not significantly influence the overall process.

The optimization of wastewater treatment technologies using biological processes is no longer limited to improving the removal of organic matter and nutrients, as it is possible to reduce area and energy consumption, and recover value-added by-products. In this context, the microalgae–bacteria consortium is an alternative for reducing costs, as microalgae produce the oxygen required by bacteria to oxidize organic matter through photosynthesis. Additionally, it is possible to extract different by-products such as lipids, biofertilizers, biogas, alginate-type exopolymers, and others. Furthermore, bioflocculation occurs naturally through the adhesion of microalgae to the surface of bacterial flocs, without the addition of chemical products. This review discusses the main systems that utilize the microalgae–bacteria consortium, the metabolism of the microalgae–bacteria consortium, and its performance in removing organic matter and nutrients, as well as the effect of operating conditions on the physical properties of the biomass. Among the highlighted systems are sequencing batch and single-batch reactors, high-rate ponds, and continuous flow reactors. Among the systems discussed in this work, the sequential batch reactor configurations found better biomass formation and production of extracellular polymeric substances and the continuous flow reactors showed lower installation and operating costs. From this perspective, the potential for full-scale application of each system can be evaluated once the optimum operating conditions have been defined and the limitations of each system have been understood.

BACKGROUND: With the rapid development of society, a large amount of wastewater and pesticides enter the water bodies globally, posing a threat to both the environment and the health of people and other living things. In this paper, an algal strain Scenedesmus sp. was isolated from a municipal wastewater treatment plant (WWTP); its interaction effect with wastewater bacteria on the removal of IMI and conventional pollutants in municipal wastewater was evaluated. RESULTS: In this study, an algae‐bacteria system was constructed with municipal wastewater, with the aim of exploring the removal effects and mechanisms of the consortium system on Imidacloprid (IMI, 20 mg L−1 and 60 mg L−1) and conventional nutrients from municipal wastewater. The results showed that no IMI was removed under 20 μmol m−2 s−1. However, under 60 μmol m−2 s−1, more than 90% of IMI was removed in the algae‐wastewater group (AWG) with Scenedesmus sp.; this value is much higher than the 50.4% (20 mg L−1) and 36.1% (60 mg L−1) achieved by the wastewater group (WG) without Scenedesmus sp. Meanwhile, the removal efficiency of nitrogen was 82.3% (20 mg L−1) and 71.9% (60 mg L−1) in AWG, both of which are higher than the 73.4% and 59.1% in WG, respectively. Moreover, Scenedesmus sp. TXH has a strong resistance to IMI and 4 degradation products (including IMI‐urea, 4(5)‐hydroxy‐IMI, Nitrosimine, and a substance with m/z of 176) were found in AWG. CONCLUSION: Using consortium to treat municipal wastewater containing IMI is an effective and safe way. © 2022 Society of Chemical Industry (SCI). [ABSTRACT FROM AUTHOR]

The present study demonstrates a promising approach for production of bio-crude oil via hydrothermal liquefaction of microbial biomass grown in large-scale open raceway pond. Three key attributes to achieve process feasibility are co-cultivation of microalgae and bacteria resulting in high biomass titre, utilization of paper industry wastewater as cheap source of nutrients and water, and one-step direct conversion of biomass into bio-crude oil. High biomass titre of 4 g L−1 with 90% of COD removal efficiency was achieved, depicting robust performance of the microalgae-bacteria consortium in industrial wastewater and under fluctuating environmental condition. Statistical optimization resulted in highest bio-crude oil yield of 21.7 (%, w/w) under optimal temperature, biomass loading and reaction time of 299.7 °C, 16.1 (%, w/v) and 65 min, respectively. Bio-crude oil with energy recovery of 43% and heating value of 33.1 MJ kg−1 reflects 81.7% and 73.4% heating value of biodiesel and diesel, respectively. While high percentage of hydrocarbon content in bio-crude oil indicates good oil quality, the presence of significant esters fraction might offer resemblance to biodiesel. Lower H/C ratio and higher O/C ratio in comparison to diesel indicate requirement of upgradation of bio-crude oil before it can be realized at commercial scale. [ABSTRACT FROM AUTHOR]

Featured Application: Inoculation strategies for microalgae and bacteria consortium for the treatment of paper pulp industry effluents with an increase in biomass sedimentation and algae biomass recovery. The microalgae–bacteria consortium is a promising and sustainable alternative for industrial wastewater treatment, since it may allow good removal of organic matter and nutrients, as well as the possibility of producing products with added value from the algae biomass. This research investigated the best bacterial and microalgae inoculation ratio for system start-up and evaluation of removing organic matter (as chemical oxygen demand (COD)), ammoniacal nitrogen (NH4+–N), nitrite nitrogen (NO2−–N), nitrate nitrogen (NO3−–N), phosphate phosphorus (PO43−–P) and biomass formation parameters in six photobioreactors with a total volume of 1000 mL. Reactors were operated for 14 days with the following ratios of pulp mill biomass aerobic (BA) and Scenedesmus sp. microalgae (MA): 0:1 (PBR1), 1:0 (PBR2), 1:1 (PBR3), 3:1 (PBR4), 5:1 (PBR5), and 1:3 (PBR6). Results show that COD removal was observed in just two days of operation in PBR4, PBR5, and PBR6, whereas for the other reactors (with a lower rate of initial inoculation) it took five days. The PBR5 and PBR6 performed better in terms of NH4+–N removal, with 86.81% and 77.11%, respectively, which can be attributed to assimilation by microalgae and nitrification by bacteria. PBR6, with the highest concentration of microalgae, had the higher PO43−–P removal (86%), showing the advantage of algae in consortium with bacteria for phosphorus uptake. PBR4 and PBR5, with the highest BA, led to a better biomass production and sedimentability on the second day of operation, with flocculation efficiencies values over 90%. Regarding the formation of extracellular polymeric substances (EPS), protein production was substantially higher in PBR4 and PBR5, with more BA, with average concentrations of 49.90 mg/L and 49.05 mg/L, respectively. The presence of cyanobacteria and Chlorophyceae was identified in all reactors except PBR1 (only MA), which may indicate a good formation and structuring of the microalgae–bacteria consortium. Scanning electron microscopy (SEM) analysis revealed that filamentous microalgae were employed as a foundation for the fixation of bacteria and other algae colonies. [ABSTRACT FROM AUTHOR]

The use of microalgae and bacteria as a strategy for the startup of bioreactors for the treatment of industrial wastewater can be a sustainable and economically viable alternative. This technology model provides satisfactory results in the nitrification and denitrification process for nitrogen removal, organic matter removal, biomass growth, sedimentation, and byproducts recovery for added-value product production. The objective of this work was to evaluate the performance of microalgae and bacteria in their symbiotic process when used in the treatment of paper pulp industry wastewater. The experiment, lasting fourteen days, utilized four bioreactors with varying concentrations in mgVSS/L of microalgae to bacteria ratio (R1-100:100, R2-100:300, R3-100:500, R4-300:100) in the startup process. Regarding the sludge volumetric index (SVI), the results show that the R1 and R2 reactors developed SVI30/SVI10 biomass in the range of 85.57 ± 7.33% and 84.72 ± 8.19%, respectively. The lipid content in the biomass of reactors R1, R2, R3 e R4 was 13%, 7%, 19%, and 22%, respectively. This high oil content at the end of the batch, may be related to the nutritional stress that the species underwent during this feeding regime. In terms of chlorophyll, the bioreactor with an initial inoculation of 100:100 showed better symbiotic growth of microalgae and bacteria, allowing exponential growth of microalgae. The total chlorophyll value for this bioreactor was 801.46 ± 196.96 μg/L. Biological removal of nitrogen from wastewater from the paper pulp industry is a challenge due to the characteristics of the effluent, but the four reactors operated in a single batch obtained good nitrogen removal. Ammonia nitrogen removal performances were 91.55 ± 9.99%, 72.13 ± 19.18%, 64.04 ± 21.34%, and 86.15 ± 30.10% in R1, R2, R3, and R4, respectively. [Display omitted] • Microalgae and bacteria symbiotically initiated bioreactor start-up. • Initial inoculation concentrations were critical for photogranule development. • High total nitrogen removal efficiency in all bioreactor configurations. • Optimal setup boosts biomass and pigment. • Microalgae-bacteria consortium facilitated the production of valuable bioproducts. [ABSTRACT FROM AUTHOR]

The livestock sector is responsible for a significant amount of wastewater globally. The microalgal-bacterial consortium (MBC) treatment has gained increasing attention as it is able to eliminate pollutants to yield value-added microalgal products. This review offers a critical discussion of the source of pollutants from livestock wastewater and the environmental impact of these pollutants. It also discusses the interactions between microalgae and bacteria in treatment systems and natural habitats in detail. The effects on MBC on the removal of various pollutants (conventional and emerging) are highlighted, focusing specifically on analysis of the removal mechanisms. Notably, the various influencing factors are classified into internal, external, and operating factors, and the mutual feedback relationships between them and the target (removal efficiency and biomass) have been thoroughly analysed. Finally, a wastewater recycling treatment model based on MBC is proposed for the construction of a green livestock farm, and the application value of various microalgal products has been analysed. The overall aim was to indicate that the use of MBC can provide cost-effective and eco-friendly approaches for the treatment of livestock wastewater, thereby advancing the path toward a promising microalgal-bacterial-based technology. [Display omitted] • Integrating microalgae cultivation with wastewater treatment offers potential. • Interaction in the microalgae-bacteria consortium is crucial to improve treatment. • External, internal, and operating factors influence the whole system. • Mechanisms of two organisms are the core of the removal effect and outcomes. • The microalgae are the best candidates for a green economy. [ABSTRACT FROM AUTHOR]

Technologies based on microalgae-bacteria seem to be sustainable options for wastewater treatment and reuse, with lower costs than conventional biological treatment technologies. Furthermore, they can generate added-value products produced from algae biomass. Among other advantages, the consortium bacteriaalgae produce photosynthetic oxygen through the microalgae, which can be used by aerobic bacteria for oxidizing organic matter and nitrogen, thus reducing the need for introducing artificial oxygen. In this review paper, the main systems that use microalgaebacteria consortium are discussed. Microalgae-bacteria present advantages in the removal of organics, nitrogen and phosphorus, when compared with conventional biological treatment systems (e.g., activated sludge, percolating filters and ponds), and are able to produce final effluents for reuse (e.g., in agricultural irrigation, industry or aquifer recharge) and excess of microalgae that can be converted to added-value products such as biogas and biofuels. Attention is given to the innovative aspects of applying photobioreators to the treatment and reuse of pulp and paper effluents and fiber-waste-based recycling wastewaters, which seems to open a new opportunity for the pulp, paper and recycling paper industries. [ABSTRACT FROM AUTHOR]

Growth comparisons were made between a microalgal consortium and Scenedesmus sp. cultivated in treated wastewater (TWw) enriched with 1 mL·L–1 Bayfolan Forte fertilizer (BM), TWw enriched with (NH4)2HPO4 (PAM), TWw enriched with NH4HCO3 (BCAM), tap water with piggery wastewater (PEM), tap water with piggery wastewater digestate (PDM), and raw wastewater (Ww). Nitrogen (N) content in the media, except for TWw, was adjusted to 80 mg·L–1 N (NH4+-N and NO3–-N). Unconventional low-cost media with lower nutrient contents (BM and TWw) showed adequate productions of biomass and lipids. PEM was the most advantageous medium, showing the highest biomass productivity with the consortium (191.25 ± 6.25 g·L–1·d–1) and a lipid productivity of 36.75 ± 9.90 mg·L–1·d–1. The fatty acid profile was composed mainly of C16 and C18. PAM, PEM, and PDM showed a higher proportion of saturated fatty acids (60%–69%), whereas the composition of unsaturated fatty acids was in the range of 31% to 38%. In PEM and PDM the removal of NH4+ was 100%; however, there were NH4+ losses (as NH3) due to volatilization (46%). Unconventional media, especially Ww, are an option for growing microalgae.

Growth comparisons were made between a microalgal consortium and Scenedesmus sp. cultivated in treated wastewater (TWw) enriched with 1 mL·L-1 Bayfolan Forte fertilizer (BM), TWw enriched with (NH4)2HPO4 (PAM), TWw enriched with NH4HCO3 (BCAM), tap water with piggery wastewater (PEM), tap water with piggery wastewater digestate (PDM), and raw wastewater (Ww). Nitrogen (N) content in the media, except for TWw, was adjusted to 80 mg·L-1 N (NH4 +-N and NO3 --N). Unconventional low-cost media with lower nutrient contents (BM and TWw) showed adequate productions of biomass and lipids. PEM was the most advantageous medium, showing the highest biomass productivity with the consortium (191.25 ± 6.25 g·L-1·d-1) and a lipid productivity of 36.75 ± 9.90 mg·L-1·d-1. The fatty acid profile was composed mainly of C16 and C18. PAM, PEM, and PDM showed a higher proportion of saturated fatty acids (60%-69%), whereas the composition of unsaturated fatty acids was in the range of 31% to 38%. In PEM and PDM the removal of NH4 + was 100%; however, there were NH4 + losses (as NH3) due to volatilization (46%). Unconventional media, especially Ww, are an option for growing microalgae. [ABSTRACT FROM AUTHOR]

[Display omitted] • PMW (10%) was successfully remediated by a diatom-bacteria consortium. • COD, TN and TP in PMW (10%) was reduced by 82%, 94% and 96%, respectively. • Chaetoceros muelleri could inhibit the growth of Malaciobacter in the PMW. • An outdoor experiment confirmed the remediating performance in a continuous mode. Hypersaline pickled mustard wastewater (PMW), a typical food wastewater with high nutrient content, was successfully bioremediated via the co-treatment of Chaetoceros muelleri and indigenous bacteria in this study. Chemical oxygen demand, ammonia nitrogen, total nitrogen and total phosphorus in 10 % PMW could be effectively reduced by 82 %, 90 %, 94 % and 96 %, respectively, after 12 days treatment. Oxygen species activities, malondialdehyde content, microalgal biomass, photosynthesis and extracellular polymeric substances were characterized during the treatment to determine the responses of the consortium when exposed to different concentration of PMW. Microbial community analysis demonstrated a significant increase in the relative abundance of Halomonas and Marinobacter in the 10 % PMW after 12 days treatment, which was beneficial for nutrients recycling by the diatoms. Meanwhile, C. muelleri was effective in reducing the relative abundance of potentially pathogenic bacteria Malaciobacter. In conclusion, the work here offers a promising and environmentally friendly approach for hypersaline wastewater treatment. [ABSTRACT FROM AUTHOR]

The microalgae–bacteria consortium is a promising and sustainable alternative for industrial wastewater treatment, since it may allow good removal of organic matter and nutrients, as well as the possibility of producing products with added value from the algae biomass. This research investigated the best bacterial and microalgae inoculation ratio for system start-up and evaluation of removing organic matter (as chemical oxygen demand (COD)), ammoniacal nitrogen (NH4+–N), nitrite nitrogen (NO2−–N), nitrate nitrogen (NO3−–N), phosphate phosphorus (PO43−–P) and biomass formation parameters in six photobioreactors with a total volume of 1000 mL. Reactors were operated for 14 days with the following ratios of pulp mill biomass aerobic (BA) and Scenedesmus sp. microalgae (MA): 0:1 (PBR1), 1:0 (PBR2), 1:1 (PBR3), 3:1 (PBR4), 5:1 (PBR5), and 1:3 (PBR6). Results show that COD removal was observed in just two days of operation in PBR4, PBR5, and PBR6, whereas for the other reactors (with a lower rate of initial inoculation) it took five days. The PBR5 and PBR6 performed better in terms of NH4+–N removal, with 86.81% and 77.11%, respectively, which can be attributed to assimilation by microalgae and nitrification by bacteria. PBR6, with the highest concentration of microalgae, had the higher PO43−–P removal (86%), showing the advantage of algae in consortium with bacteria for phosphorus uptake. PBR4 and PBR5, with the highest BA, led to a better biomass production and sedimentability on the second day of operation, with flocculation efficiencies values over 90%. Regarding the formation of extracellular polymeric substances (EPS), protein production was substantially higher in PBR4 and PBR5, with more BA, with average concentrations of 49.90 mg/L and 49.05 mg/L, respectively. The presence of cyanobacteria and Chlorophyceae was identified in all reactors except PBR1 (only MA), which may indicate a good formation and structuring of the microalgae–bacteria consortium. Scanning electron microscopy (SEM) analysis revealed that filamentous microalgae were employed as a foundation for the fixation of bacteria and other algae colonies.

Wastewater discharges into the environment without adequate treatment is a problem still unresolved. That is why alternative technologies, such as applying static magnetic field (SMF), are currently being sought. The objective of this research was to evaluate the effect of a 47.23 mT SMF on the removal of nitrogen (N), phosphorus (P), and the growth of a Chlorella microalgae-bacteria consortium grown in piggery wastewater under different photoperiods. SMF application increased culture productivity, with maximum values of 0.030 g/ Ld−1 in cultures exposed to SMF in a 16:8 h light/dark photoperiod and 0.038 g/ Ld−1 for the 24:0 h light/dark photoperiod. Furthermore, SMF application increased the microorganisms' photosynthetic efficiency (QY), regardless of the photoperiod used. No significant differences were observed on day 21 regarding nutrient removal between the treated and control cultures. Removal percentages of 93.41 % N and 95.56 % P were obtained for the cultures exposed to SMF in the 16:8 h light/dark photoperiod, and 94.78 % N and 95.59 % P for cultures exposed to SMF during the 24:0 h light/dark photoperiod. In general, SMF acts mainly on the growth of microorganisms. • SMF application increased microalgal culture productivity. • SMF increased the microorganism's photosynthetic efficiency, regardless of the photoperiod. • 93 % of N and 96 % of P were removed for the cultures exposed to SMF in the 16:8 h light/dark photoperiod. [ABSTRACT FROM AUTHOR]

Highlights • Microalgae could grow on nutrients in the liquid fraction of agro-digestate. • Microalgae could grow outdoor under sub-optimal climatic conditions for 200 d. • Stable nitrification was established and supported by oxygen from photosynthesis. • Approximately 7 ± 3% of N was assimilated by microalgae while 61 ± 24% was nitrified. • The raceway reactor was slightly more effective than a bubble-column photobioreactor. Abstract This paper addresses the efficiency of a microalgae-based agricultural digestate treatment at pilot-scale in an outdoor raceway pond (880 L, pH-dependent CO 2 dosage) and in a bubble column (74.5 L, air-bubbling). Specifically, nitrogen removal, evolution of the algae-bacteria consortium, and the actual process applicability in the Po Valley climate are discussed. The performance of the two reactors varied seasonally. The average algal productivity in the raceway was 32.4 ± 33.1 mg TSS·L−1·d−1 (8.2 ± 8.5 g TSS·m−2·d−1) while in the PBR it was 25.6 ± 26.8 mg TSS·L−1·d−1; the average nitrogen removal was 20 ± 29% (maximum 78%) and 22 ± 29% (maximum 71%) in the raceway and in the column, respectively. Nevertheless, nitrification had a key role as 61 ± 24% and 52 ± 32% of the nitrogen load was oxidized in the raceway and in the column, respectively. [ABSTRACT FROM AUTHOR]

Abstract A sustainable process was demonstrated towards production of biomass feedstock coupled with wastewater treatment. Sustainability was endeavored to be achieved via symbiotic growth of microalgae and bacteria coupled with utilization of wastewater as cheap source of nutrient and water. The best microalgae-bacteria consortium comprised of two microalgae Chlorella sorokiniana strain DBWC2 & Chlorella sp. strain DBWC7 and two bacteria Klebsiella pneumoniae strain ORWB1 & Acinetobacter calcoaceticus strain ORWB3. When the consortium was characterized on artificial wastewater and raw dairy wastewater, a significant improvement in the microalgal growth, total biomass titer, chemical oxygen demand (COD), and nitrate removal efficiency was observed as compared to microalgae alone. Total biomass titer, nitrate removal, COD removal efficiency was found to be 2.84 g L−1, 93.59%, 82.27% and 2.87 g L−1, 84.69%, 90.49% in artificial wastewater and raw dairy wastewater respectively. The selected microalgae-bacteria consortium may be a potential platform towards sustainable production of microbial biomass using wastewater. Graphical abstract Unlabelled Image Highlights • Sustainable biomass production using microalgae-bacteria consortium on wastewater • Artificial wastewater (AWW) & raw dairy wastewater (RDWW) was considered for study. • Biomass (g L−1): 2.84 for AWW and 2.87 for RDWW • Nitrate and Chemical Oxygen Demand (COD) removal efficiency for AWW: 93.5% & 82.27% • Nitrate and COD removal efficiency for RDWW: 84.69% & 90.49% [ABSTRACT FROM AUTHOR]

Adoption of microalgae-sourced products depends on the economic feasibility. In the case of fatty acids, it is crucial to obtain high lipid yield, especially in the form of storage lipids (TAGs). However, the production of these lipids often comes into competition with the microalgae biomass, resulting in a decrease in growth. A microalgae culture integration project was conducted in an industrial park in Canada in order to cultivate microalgae from park’s wastewaters and then obtain products from the biomass. Different deficiencies and stresses were tested to evaluate what condition allowed the induction of the highest lipids accumulation without compromising the growth of microalgae. The results showed that the medium controlled to pH 7.0 allowed reaching the largest amount of extracted lipids (28 ± 4.3%). Companies involved in this project could be able to make significant savings by the reduced wastewater treatment costs and by not adding expensive nutrients in culture. [ABSTRACT FROM AUTHOR]

[Display omitted] • Chlorella sorokiniana AK-1 can effectively treat raw dairy manure wastewater. • Addition of acclimated bacterial cultures enriched from dairy manure improved treatment efficiency. • Bacterial process was effective for carbon removal, while microalgae process showed efficacious nitrogen removal. • COD, BOD, TN, NH 3 -N and TP removal efficiencies were 84.3%, 97.8%, 90.2%, 99.1%, and 100%. • High diversity was observed in the bacterial community during wastewater treatment. The major objective of this study was to develop a functional microalgae-bacteria consortium for the treatment of dairy manure wastewater (DMW). Chlorella sorokiniana AK-1 was selected as the proficient microalgal strain for treating unsterilized DMW. AK-1 was directly grown in 50% raw DMW, and the addition of an acclimated mixed bacterial culture enriched from dairy manure improved treatment efficiency. Culture conditions for DMW treatment using the AK-1 mixed bacterial consortium were optimized as follows: 50% raw DMW, 0.4 g/L mixed bacterial inoculum on day 1, followed by 0.1 g/L AK-1 inoculum on day 3, and further incubation for 3 days. The achieved removal efficiencies for COD, BOD, TN, NH 3 -N, and TP were 84.3%, 97.8%, 90.2%, 99.1%, and 100%, respectively. Bacterial 16S rDNA sequencing was conducted to analyze the shift in the bacterial community during wastewater treatment. In DMW, Firmicutes emerged as the dominant phylum, whereas Proteobacteria took over after microalgal inoculation. Additionally, Actinobacteria and Bacteroidetes were consistently present in all samples. Interestingly, Patescibacteria and Planctomycetes were found in varying proportions. At the species level, the predominant bacteria identified during the treatment process were Rhizobiaceae , Sericytochromatia _ unclassified , Pirellula _sp, Owenweeksia , Devosia _ unclassified , Acinetobacter _ towneri , and Acinetobacter _ unclassified. Despite the significant diversity of the microbial community among the different processes, optimal microalgal biomass production and maximum nutrient removal efficiencies were achieved using this designer microalgae-bacteria consortium. [ABSTRACT FROM AUTHOR]

To reduce the anthropogenic nutrient loading into natural waterways, onsite wastewater treatment is essential for households without access to municipal sewer systems. However, many conventional septic tanks significantly underperform the centralized wastewater treatment. In the present study, a novel illuminated septic tank inoculated with the consortium of microalga Chlorella vulgaris and aerobic bacteria was developed by modifying the conventional configuration. The inclusion of microalgae facilitated aeration inside the septic tank through photosynthetic oxygen evolution, and the microalgae-bacteria consortium enhanced the wastewater treatment performance. With the operation at 15 ℃ and a hydraulic retention time of 2.5 days, the lab-scale algae-assisted septic tank significantly decreased the concentrations of ammonium-nitrogen (NH 4 +-N), soluble phosphorus (P), total P, and total chemical oxygen demand by 54%, 65.2%, 78.5%, and 90.7% in the discharged effluent, respectively (p < 0.05), whereas the conventional septic tank without microalgae did not exhibit any treatment of NH 4 +-N or soluble P and the total P removal efficiency was lower by 50%. Meanwhile, the photosynthetic activity of microalgae altered the gas composition in the tank headspace by consuming carbon dioxide, emitting oxygen, and inhibiting the evolution of methane, which further benefited the aeration requirement and contributed to the mitigation of greenhouse gas emissions from septic systems. [Display omitted] • A novel illuminated septic tank was developed for onsite wastewater treatment. • A consortium of algae and bacteria was inoculated in the illuminated septic tank. • Illuminated septic tank achieved significantly higher P & N removals than control. • O 2 generated from microalgal photosynthesis facilitated aeration and nitrification. • Greenhouse gas emissions were remarkably reduced from algae-assisted septic tank. [ABSTRACT FROM AUTHOR]

Respirometric techniques are useful tools to evaluate bacterial activities in activated sludge processes due to their fast execution and the possibility to obtain several kinetic parameters from a single test. Using such techniques in microalgae-bacteria consortia treating wastewater could allow a better understanding of mutual interactions between the microbial populations as a function of environmental parameters. This work aims at developing and testing a novel experimental respirometric protocol to determine oxygen uptake rates and oxygen production rates by a microalgae-bacteria consortium. The defined protocol is characterized by alternating light/dark regimes and by dosing substrates/inhibitors to selectively activate/inactivate microalgal and bacterial metabolisms. The protocol was then applied on microalgal and bacterial consortia, which were grown on the liquid fraction of black water from biogas plants fed on agricultural and municipal waste sludge. Results elucidate the presence and activity of microalgae and nitrifying bacteria in the tested systems, suggesting that the respirometric tests could be included into monitoring procedures of photobioreactors/algal ponds. [ABSTRACT FROM AUTHOR]

Heavy metals in industrial wastewater are hazardous, not easily biodegradable, and can be enriched in the food chain. This will lead to serious global environmental problems. Traditional physicochemical heavy metal remediation treatments have limitations, including high costs and secondary contamination. However, biosorption is an effective and affordable way for treating wastewater containing heavy metals. A large specific surface area of microorganisms makes them attractive as biosorbents for the removal of heavy metals. In particular, more benefits exist for heavy metal adsorbents when microalgae and bacteria are combined. The combined system biological adsorption method of microalgae and bacteria is an ideal method for the remediation of large volume and low concentration heavy metal wastewater. The reuse of biological biomass of algae and bacteria resources can also be achieved. Therefore, it has very promising application prospects. This present review aimed to discuss the removal of heavy metals from wastewater using presently applied conventional treatments followed by the treatment using consortia of microalgae-bacteria, modes of microalgae-bacteria consortia system, the advantages of microalgae-bacterial consortia as biosorbents, the mechanisms of biosorption for heavy metals and the factors affecting the biosorption efficiency of heavy metals. Moreover, the feasibility of industrial applications and the potential product applications of harvested microalgae-bacterial consortia were also discussed. This review is foreseen to bring significance to industrial stakeholders including engineers, environmental technologists and business entities in developing and investing in more effective ways of bioremediating heavy metals from wastewater, for overall environmental sustainability. [Display omitted] • Microalgae-bacteria consortium is promising to bioremediate heavy metals. • Mechanisms of biosorption for heavy metals and its applications are discussed. • Factors are light intensity, pH, temperature, coexisting ions, and heavy metal concentrations. • Microalgae-bacteria consortium is highly efficient in biomass value-added products. [ABSTRACT FROM AUTHOR]

Microalgae-bacteria biomass was digested through anaerobic digestion (AD) to produce biogas. Since microalgae typically have a more resistant cell wall than activated sludge (AS), its anaerobic biodegradability is limited. Therefore, three different pre-treatment techniques were evaluated for their effect on anaerobic biodegradability, especially of the extracellular polymeric substances (EPS). Firstly, heat at 70 °C for 1.5 h. Secondly, exposure to a mixture of commercially available enzymes (cellulase, α-amylase and protease), and thirdly, adding crude hydrolytic enzymes extracted by ultrasonication from a highly loaded anaerobic digestion cascade reactor. The first and third treatments had better effects than enzymatic pre-treatment with commercial enzymes, improving anaerobic biodegradability, the solubilisation of organic matter and increasing the methane production rate by 78 and 21 %, respectively. The EPS content of microalgae-bacteria biomass was considerably lower than reported for WAS, and about 40–50 % of the EPS consisted of proteins and polysaccharides. The hydrolysis of proteins and polysaccharides was quantified, and its effect on AD was discussed. A COD balance showed that the increase of soluble COD is due to the conversion of tightly bound EPS into loosely bound and soluble EPS but also due to the release of organic matter from cellular material. Although all pre-treatments increased the soluble organic fractions, especially those corresponding to EPS, none significantly improved the overall methane yield. Nevertheless, the methane production rate increased after thermal and pre-treatment with hydrolytic enzymes, which could result in smaller and more efficient anaerobic reactors. • Pre-treatments resulted in the solubilisation of microalgae-bacterial biomass. • 40–50 % of microalgae-bacterial EPS consisted of proteins and polysaccharides. • Microalgae-bacterial biomass contained less EPS than reported by activated sludge. • Solubilisation also corresponded from the release of cellular compounds. • Thermal treatment and hydrolytic enzymes increased the methane production rate. [ABSTRACT FROM AUTHOR]

The performance of a full-scale photobioreactor (PBR) for the treatment of olive washing water (OWW) was evaluated under different HRTs (5–2 days). The system was able to treat up to 3926 L OWW day −1 , and consisted of an activated-carbon pretreatment column and a tubular PBR unit (80 tubes, 98.17 L volume, 2-m height, 0.25 m diameter). PBR was an effective and environmentally friendly method for the removal of phenols, COD, BOD 5 , turbidity and color from OWW (average efficiencies 94.84 ± 0.55%, 85.86 ± 1.24%, 99.12 ± 0.17%, 95.86 ± 0.98% and 87.24 ± 0.91%, respectively). The diversity of total bacteria and microalgae in the PBR was analyzed using Illumina-sequencing, evaluating the efficiency of two DNA extraction methods. A stable microalgae-bacteria consortium was developed throughout the whole experimentation period, regardless of changes in HRT, temperature or solar radiation. MDS analyses revealed that the interplay between green algae ( Sphaeropleales ), cyanobacteria ( Hapalosiphon ) and Proteobacteria ( Rhodopseudomonas , Azotobacter ) played important roles in OWW bioremediation. [ABSTRACT FROM AUTHOR]

The ciprofloxacin treating via microalga and its microalgae-bacteria consortium was investigated for discussing the potential application of microalgae-mediated bioremediation. As results, the maximum removal efficiency of ciprofloxacin by pure microalgae and the consortium was 87.5 ± 3.5 % (5 mg/L) and 96.1 ± 0.07 % (40 mg/L), respectively. The consortium enhanced the degradation rate to 0.81 d−1 compared with the pure microalgae (0.27 d−1). To reveal the symbiotic mechanism, extracellular polymeric substances, pigments contents, antioxidant enzymes and symbiotic bacterial community were analyzed. The malondialdehyde content in the pure microalgae (1622.6 ± 38.7 nmol/mg protein) was higher than that in the consortium (298.34 ± 2.4 nmol/mg protein), and there were obvious chlorophyll b accumulations (approximately 90 %) in consortium. In addition, the symbiotic bacteria had a positive effect on microalgal secretion of fulvic acid-type components. As mechanism, symbiotic bacteria improved ciprofloxacin biodegradation by reducing cell damage and secreting fulvic acid. The presence of Phycisphaeraceae and Rhizobiaceae , nitrogen fixation bacteria, in the consortium suggest that improvement of ciprofloxacin biodegradation might be associated with nitrogen co-metabolism as well. Collectively, this work elucidates the mechanism of enhancing elimination of ciprofloxacin via microalgae-bacteria consortium and accelerates development of microalgae-mediated aquaculture tailwater bioremediation. [Display omitted] • Defense mechanism was discussed based on antioxidant enzyme and pigment contents. • Bacteria induced fulvic acid secretion that promoted ciprofloxacin elimination. • The symbiotic bacterial diversity was analyzed by high-throughput sequencing. • POD played a crucial role in intracellular ciprofloxacin degradation. [ABSTRACT FROM AUTHOR]

The dissolved oxygen (DO) concentration in water streams is one of the most important and critical quality parameters in aquaculture farms. The main objective of this study was to evaluate the potential of two Continuous Flow Granular Reactors, one based on Partial Nitrification-Anammox biomass (Aquammox CFGR) and the other on Microalgae-Bacteria biomass (AquaMab CFGR), for improving dissolved oxygen availability in the recirculation aquaculture systems (RAS). Both reactors treated the extremely low-strength effluents from a freshwater trout farm (1.39 mg NH 4 +-N/L and 7.7 mg TOC/L). The Aquammox CFGR, removed up to 68% and 100% of ammonium and nitrite, respectively, but the DO concentration in the effluent was below 1 mg O 2 /L while the anammox activity was not maintained. In the AquaMab CFGR, bioaugmentation of aerobic granules with microalgae was attained, producing an effluent with DO concentrations up to 9 mg O 2 /L and removed up to 77% and 80% of ammonium and nitrite, respectively, which is expected to reduce the aeration costs in fish farms. [Display omitted] • Microalgae-Bacteria granules greatly succeeded over PN-AMX granules. • PN-AMX granules facing recirculating aquaculture effluents lost their anammox activity. • Aerobic granules bioaugmentation with microalgae favoured the treatment process. • Microalgae attachment to granules allowed their retention in the continuous flow system. • Treated effluents meet the requirements for water recirculation in the aquaculture farm. [ABSTRACT FROM AUTHOR]

[Display omitted] • C. sorokiniana AK-1 can form a stable consortium with wastewater-derived bacteria. • Small microalgal inoculum size was sufficient to promote growth in the presence of bacteria. • Semi-batch mode attained higher biomass and nutrient removal. • A novel two-stage process with an initial bacteria-only startup phase is employed. • The effluent of full-strength wastewater treatment met the discharge standards of Taiwan. This study aimed at developing an eco-friendly and effective treatment for swine wastewater (SWW) using a designer microalgae-bacteria consortium. A functional algal bacterial consortium was developed with SWW-derived bacteria and Chlorella sorokiniana AK-1. Light intensity (300 µmol/m2/s) and inoculum size (0.15 and 0.2 g/L for microalgae and bacteria) were optimized. Semi-batch operation treating 50 % SWW resulted in a COD, BOD, TN, and TP removal efficiency of 81.1 ± 0.9 %, 97.0 ± 0.7 %, 90.6 ± 1.6 % and 91.3 ± 1.1 %, respectively. A novel two-stage process with an initial bacterial start-up stage followed by microalgal inoculation was applied for attaining stable organic carbon removal, in addition to satisfactory TN and TP removal. Full strength SWW was treated with this strategy with COD, BOD, TN, and TP removal efficiencies of 72.1 %, 94.9 %, 88 %, and 94.6 %, respectively. The biomass consisted of 36 % carbohydrates, indicating a potential feedstock for biochar production. In addition, the effluent met the standards for effluent discharge in Taiwan. [ABSTRACT FROM AUTHOR]

The studies on the removal of Neonicotinoids pesticides (NNIS) and their degradation products have attracted more and more attention. However, the simultaneous removal of pesticides and conventional pollutants remain inadequately understood. In this study, a green alga strain Scenedesmus sp. TXH was isolated from a wastewater treatment plant and the microalgae-bacteria system was constructed with municipal wastewater. The removal effect of consortium system on Imidacloprid (IMI)/Thiacloprid (THI) and conventional nutrients was employed. Results showed that Scenedesmus sp. TXH achieved 71.24 % and 9.71 % removal of IMI and THI in wastewater under 100 μmol m−2 s−1 of light intensity, much higher than the 55.54 % and 2.71 % without inoculating Scenedesmus sp. TXH. The removal efficiency of the two pollutants was obviously different, which may be attributed to the different functional groups of pollutants. Meanwhile, a much faster removal of conventional pollutants (TDN, TDP and sCOD) occurred in algae-wastewater group. Based on the identified products from mass spectrometer, the main reaction pathways were found and products have lower toxicity evaluated by Ecological Structure-Activity Relationship (ECOSAR) program. This study provided valuable information for the development of NNIS removal with microalgae, which could further enhance the feasibility of microalgae applications in removing NNIS and conventional pollutants. [Display omitted] • Algae-bacteria consortium removed 71.24 % of IMI and 9.71 % of THI. • More than 80 % and 90 % of TDN and TDP were removed by algae-bacteria consortium. • The main way of removing pesticide by algae-bacterial consortium was biodegradation. • More degradation products of THI were detected in algae-bacteria consortium. • Scenedesmus sp. TXH can be used as a promising species for IMI/THI treatment. [ABSTRACT FROM AUTHOR]

[Display omitted] • Supply of co-substrate to algae-bacteria consortia enhances antibiotics degradation. • Co-substrate improved SDZ degradation more significantly than SMX degradation. • Co-substrate induced the secretion of microalgal EPS with high protein ratios. • Supplementation of co-substrate could decrease peroxide damage to cells. • The symbiotic bacterial diversities were analyzed by high throughput sequencing. Both co-cultivation and co-substrate addition strategies have exhibited massive potential in microalgae-based antibiotic bioremediation. In this study, glucose and sodium acetate were employed as co-substrate in the cultivation of microalgae-bacteria consortium for enhanced sulfadiazine (SDZ) and sulfamethoxazole (SMX) removal. Glucose demonstrated a two-fold increase in biomass production with a maximum specific growth rate of 0.63 ± 0.01 d−1 compared with sodium acetate. The supplementation of co-substrate enhanced the degradation of SDZ significantly up to 703 ± 18% for sodium acetate and 290 ± 22% for glucose, but had almost no effect on SMX. The activities of antioxidant enzymes, including peroxidase, superoxide dismutase and catalase decreased with co-substrate supplementation. Chlorophyll a was associated with protection against sulfonamides and chlorophyll b might contribute to SDZ degradation. The addition of co-substrates influenced bacterial community structure greatly. Glucose enhanced the relative abundance of Proteobacteria , while sodium acetate improved the relative abundance of Bacteroidetes significantly. [ABSTRACT FROM AUTHOR]

• Ecotoxicological effects of SDZ and SMX on the microalgae-bacteria consortium were evaluated. • Intracellular antioxidant enzymes and pigments were influenced by SDZ and SMX. • EPS was shown to be associated with granule formation in presence of SDZ. • The bacterial community in the presence of SAs was identified by high throughput sequencing. • CAT and POD played a crucial role in intracellular sulfonamides biodegradation. Antibiotics in wastewaters (e.g., sulfonamides (SAs)) are not effectively removed by the conventional bacterial processes. In this study, a microalgae (Scenedesmus obliquus)-based process was evaluated for the removal of SAs. The maximum removal efficiency of sulfadiazine (SDZ) and sulfamethoxazole (SMX) by the consortium was 5.85% and 40.84%, respectively. The lower SDZ biodegradation efficiency could be due to the difference in the lipophilic degree related to cell binding. The presence of SAs did not significantly inhibit the biomass production of the consortium (1311–1952 mg/L biomass) but led to a 36–51% decrease in total polysaccharide content and an increase in microalgae's protein content, which caused granule formation. The presence of SMX and SDZ resulted in an increase in lipid peroxidation activity with a 6.2 and 23.5-fold increase in malondialdehyde content, respectively. Rhodobacter and Phreatobacter were abundant in the consortium with SAs' presence, while alinarimonas , Catalinimonas and Cecembia were seen in their absence. [ABSTRACT FROM AUTHOR]

Highlights: [•] Microalgae-bacteria consortium was cultivated in the landfill leachate. [•] The TN was removed by 90% in medium with 10% leachate spike ratio. [•] Maximum lipid productivity and carbon fixation was 24.1 and 65.8mgL−1 d−1. [•] Humic substances in the landfill leachate were decomposed. [ABSTRACT FROM AUTHOR]

There is great controversy regarding the best substrate (fresh or anaerobically digested swine slurry) for the development of microalgae-bacteria consortia. This study aims to elucidate the best substrate by assessing biomass productivity, microorganism predominance, and their ability for organic matter removal. In addition to the different substrates, different operational conditions and influent strengths were evaluated. Increasing organic matter content when favourable temperature and illumination conditions were present improved biomass production. However, these conditions were not favourable for microalgal growth, but they were favourable for bacteria. Regardless of the operational conditions, reactors fed with fresh slurry not only resulted in the highest biomass productivity, but also the greatest removal of total and soluble chemical oxygen demand (COD). On the other hand, reactors fed with digested slurry showed biomass productivity and COD removal values lower than those obtained for reactors fed with fresh slurry, most probably due to the recalcitrant nature of the former. Nevertheless, digested slurry was the substrate more appropriate for microalgae growth under harsh operational conditions (16 °C and 9-h illumination) at low influent strength and optimum operational conditions (30 °C and 24-h illumination) at higher influent strength. [ABSTRACT FROM AUTHOR]

[Display omitted] • Microalgae-bacteria consortium was resistant to CTC up to 80 mg/L. • Biosorption and enzymatic degradation were the major CTC removal mechanism. • Monod model was applied for the enzymatic degradation of CTC. • Symbiotic bacteria were analyzed by Biolgo Eco plate and sequencing. • Symbiotic bacteria diversity was enhanced in the presence of 40 mg/L CTC. Microbial removal of Chlortetracycline (CTC) at low CTC concentrations (in the order of 10–20 mg/L) has been reported. In this study, a novel microalgae-bacteria consortium was developed for effective CTC biodegradation at higher concentrations (up to 80 mg/L). The microalgae-bacteria consortium is resistant to up to 80 mg/L CTC, while the pure microalgal culture could only tolerate 60 mg/L CTC. CTC removal in the initial 12 h was primarily via biosorption by the microalgae-bacteria consortium and the adsorption capacity increased from 61.71 to 102.53 mg/g biomass in 12 h. Further, CTC biodegradation by the microalgae-bacteria consortium was catalyzed by extracellular enzymes secreted under antibiotic stress. The symbiotic bacterial diversity was analyzed by high throughput sequencing. The aerobic bacteria Porphyrobacter and Devosia were the dominant genera in the consortium. In the presence of CTC, a microbial community shift occurred with Chloroptast , Spingopyxis, and Brevundimonas being the dominant genera. [ABSTRACT FROM AUTHOR]

[Display omitted] • Flue gas transportation and wastewater pretreatment are added production cost. • Risks and uncertainties need to be analysed along with economic feasibility. • Algae-bacteria consortium as useful wastewater treatment and energy production. • Mature developments of technologies are required towards commercialization. • Co-products aid in reducing production cost and sustaining the project profits. Climate change due to increasing CO 2 emissions from industries with severe environmental pollution from wastewater due to rising global population and production plants. Current approaches in treating wastewater and flue gases are expensive processes requiring high operating costs. Hence, efficient strategies to utilize flue gases and simultaneously treat wastewater is in desperate need to tackle the current situation. One of the potential solutions is to cultivate microalgae-bacteria consortium using industrial flue gas and wastewater, where the nutrients and organic matters within flue gas and wastewater are consumed for the growth of microalgae-bacteria consortium. The production of biomass from the consortium can be further transformed into sources of biofuel, valuable metabolites and animal feed. This review explores the mechanisms of CO 2 mitigation and phycoremediation through microalgae-bacteria consortium along with possible future prospects. [ABSTRACT FROM AUTHOR]

The effects of water depth, operational and environmental conditions on bacterial communities were analyzed in microalgal-bacterial outdoor photobioreactors treating urban wastewaters from March to August 2014. Three raceway photobioreactors inoculated with Scenedesmus sp. and with different water depths (20, 12, and 5 cm) were used at different dilution rates (0.15, 0.3, 0.4, and 0.5 d−1). A thin-layer reactor with 2 cm water depth and operated at 0.3 d−1 was used as a control. The results showed that biomass productivity increased as water depth decreased. The highest biomass productivity was 0.196 gL−1d−1, 0.245 gL−1d−1, and 0.457 gL−1d−1 for 20, 12, and 5 cm depth raceway photobioreactors, respectively. These values were lower than the maximum productivity registered in the control reactor (1.59 gL−1d−1). Bacterial communities, analyzed by high-throughput 16S rRNA sequencing, were not affected by water depth. A decrease in community evenness was related to a decrease in nutrient removal. Hetetrotrophs and phototrophs, mainly from the family Rhodobacteraceae , dominated bacterial diversity. The community changed due to increasing temperatures, irradiance, and organic carbon, ammonia, and phosphate contents in the photobioreactor-influent as well as, microalgae inhibition and higher organic carbon in the effluent. The photobioreactors shared a core-biome that contained five clusters of co-occurring microorganisms. The bacteria from the different clusters were taxonomically and ecologically different but functionally redundant. Overall, the drivers of the community changes could be related to abiotic variables and complex biological interactions, likely mediated by microalgae excretion of organic substances and the microorganisms' competence for substrates. [Display omitted] • Biomass productivity increased as the depth of cultivation decreased. • No influence of water depth on bacterial community structure. • Strong influence of temperature, irradiance and nutrients on bacterial communities. • The PBRs core biome was dominated by heterotrophic and phototrophic bacteria. • Microalgae excretion of organic substances could modulate bacterial communities. [ABSTRACT FROM AUTHOR]

The aerobic formers of Exiguobacterium and Bacillus licheniformis were screened to construct a Chlorella -bacteria consortium for the piggery wastewater treatment. The optimal consortia of Chlorella - Exiguobacterium (C.v - E.x) and Chlorella - Exiguobacterium / Bacillus licheniformis (C.v - E.x/B.l) were designated to purify wastewater scaled-up in a column photobioreactor. The results showed that the rates of contaminant removal and cell growth of the Chlorella -bacteria consortium were all higher than those of the axenic Chlorella system and pure bacterial system. The C.v - E.x consortium had the best purification effect, and the concentrations of total phosphorus (TP) and ammonia nitrogen (NH 4 +-N) were reduced to 1.8 mg L−1 and 35.0 mg L−1 after 12 days, respectively. The final removal rates of total nitrogen (TN), TP, NH 4 +-N, and chemical oxygen demand (COD) were 78.3%, 87.2%, 84.4%, and 86.3%, respectively, and these levels were below the wastewater discharge standard (GB18596-2001, China). The mutualistic interactions between Chlorella and its coculture bacteria were explored by detecting total inorganic carbon (TIC), net photosynthetic activity (NPA), dissolved oxygen (DO), pH, and nitrogen-related enzyme activity. The results showed that the C.v-E.x consortium had a higher NPA (70.8% increase), DO concentration (172.4% increase), and TIC concentration (71.0% increase) and maintained a low pH 9.3 compared with the axenic C. vulgaris system. Therefore, the synergistic interactions of cell growth promotion and the exchange of carbon and oxygen between microalgae and bacteria were identified. The detection of nitrogen-related enzymatic activities in the photosynthesis pathway of Chlorella demonstrated that Exiguobacterium obviously improved the activities of nitrate reductase (NR), nitrite reductase (NiR), glutamine synthetase (GS), and glutamate synthetase (GOGAT) by 94.2%, 57.5%, 58.6%, and 79.4% , respectively. This result indicated that cocultured bacteria might secrete some metabolites as enzyme activators, and there was a synergistic mechanism in the enzymology between microalgae and bacteria. The research provides a reference for the wastewater resourceful treatment by microalgae-bacteria consortia. • Exiguobacterium and Bacillus licheniformis were screened to construct a Chlorella -bacteria consortium. • The Chlorella - Exiguobacterium consortium had the best purification effect on piggery wastewater. • The concentration of TN, TP, NH 4 +-N and COD meet the wastewater discharge standards within 12 days. • The synergistic interactions of cell growth promotion and carbon-oxygen exchange were explored. • Exiguobacterium obviously improved the nitrogen-related enzymatic activities of Chlorella. [ABSTRACT FROM AUTHOR]