Microalgae Consortium Research Articles

The Effect of Chemical Sulfide Oxidation on the Oxygenic Activity of an Alkaliphilic Microalgae Consortium Deployed for Biogas Upgrading

The oxygenic photosynthetic activity (OPA) of an alkaliphilic microalgae consortium was evaluated at different concentrations of dissolved sulfide under room temperature and well-defined conditions of irradiance and pH in a tubular closed photobioreactor. The kinetic assays showed that it was optimal at a sulfide concentration of 3.2 mg/L under an external photosynthetically active radiation of 50 and 120 μE/m2 s together with a pH of 8.5 and 9.2. In contrast, the oxygenic photosynthetic activity was insignificant at 15 μE/m2 s with a pH of 7.3, both in the absence and presence of sulfide. Consecutive pulse additions of dissolved sulfide evidenced that the accumulation rate of dissolved oxygen was decreased by the spontaneous chemical oxidation of sulfide with dissolved oxygen in alkaline culture media, mainly at high sulfide levels. At 3.2 mg/L of sulfide, the oxygenic photosynthetic activity was improved by around 60% compared to the treatment without sulfide at external irradiances of 120 μE/m2 s, 30 °C, and pH of 8.5 and 9.2. Additionally, an even higher OPA enhancement (around 85%) was observed in the same previous conditions but using 16 mg/L of sulfide. Thiosulfate was the major end-product of sulfide by oxic chemical reaction, both in biotic and abiotic assays with yields of 0.80 and 0.68, respectively.

Nitrification of anaerobic digestate using a consortium of microalgae and nitrifiers in an open photobioreactor with moving bed carriers

A consortium of microalgae and nitrifiers has attracted attention as an alternative to the expensive traditional nitrification process. A possible obstacle to achieving this is the inhibition of nitrifiers under strong light irradiation. This study evaluated the effect of moving bed carriers on anaerobic digestate nitrification in an open photobioreactor inoculated with microalgae and nitrifiers under an incident light intensity of 1000 μmol photons m−2 s−1. The results showed higher specific nitrification activity in the carrier-added photobioreactor (103.6 mg-N g-TSS day−1) than in one in which no carrier was added (11.7 mg-N g-TSS day−1). The empirical equations for determining the light intensity at different depths in the photobioreactor showed a significant contribution by carriers in attenuating the incident light intensity. This is due to the large light attenuation caused by the carrier (1.09 cm−1). The average light intensity inside of the photobioreactor decreased considerably in the carrier-added photobioreactor (342 μmol photons m−2 s−1), whereas it did not decrease in the one with no added carrier. It was found that specific nitrification activity was significantly negatively affected by average light intensity inside of the reactor, and not by incident light intensity, by combining the results from different studies including ours. This study demonstrated, for the first time, the effectiveness of adding moving bed carriers in photobioreactors to mitigate light inhibition of nitrifiers in a consortium of microalgae and nitrifiers.

Versatile method to obtain protein- and/or amino acid-enriched extracts from fresh biomass of recalcitrant microalgae without mechanical pretreatment

The aim of the study was to develop a sequential alkaline-enzymatic method to obtain protein- and/or amino acid-enriched extracts from fresh biomass of recalcitrant microalgae without any supplementary pretreatment. The effects of the initial biomass concentration, the use of freeze-dried or fresh biomass, enzyme dosage, processing procedure (two-step and single-step, with and without pH control) and species were studied. The method was evaluated with a consortium of microalgae isolated from a landfill leachate and was tested on other recognized recalcitrant microalgae such as Chlorella vulgaris, Nannochloropsis gaditana and Scenedesmus obliquus. The approach includes alternative pathways, provides high extraction yields of proteinaceous material and produces protein- and/or hydrolyzed peptide-enriched extracts with different amino acid compositions (e.g., a pathway without pH control achieves a yield of 81% of total protein and a concentration of 29 mg mL−1 of proteinaceous material). The versatility in processing procedures and the range of products obtained, along with applicability to different microalgal species, make this method an interesting option for algae biomass treatment. Furthermore, the high yield and simplicity from a technological point of view, gives it a great potential for process development and encourages further research for a wide variety of applications, such as feed, biostimulants, culture media, bulk chemicals, and biogas.

Natural Pigments and Biogas Recovery from Microalgae Grown in Wastewater.

This study assessed the recovery of natural pigments (phycobiliproteins) and bioenergy (biogas) from microalgae grown in wastewater. A consortium of microalgae, mainly composed by Nostoc, Phormidium, and Geitlerinema, known to have high phycobiliproteins content, was grown in photobioreactors. The growth medium was composed by secondary effluent from a high rate algal pond (HRAP) along with the anaerobic digestion centrate, which aimed to enhance the N/P ratio, given the lack of nutrients in the secondary effluent. Additionally, the centrate is still a challenging anaerobic digestion residue since the high nitrogen concentrations have to be removed before disposal. Removal efficiencies up to 52% of COD, 86% of NH4+-N, and 100% of phosphorus were observed. The biomass composition was monitored over the experimental period in order to ensure stable cyanobacterial dominance in the mixed culture. Phycocyanin and phycoerythrin were extracted from harvested biomass, achieving maximum concentrations of 20.1 and 8.1 mg/g dry weight, respectively. The residual biomass from phycobiliproteins extraction was then used to produce biogas, with final methane yields ranging from 159 to 199 mL CH4/g VS. According to the results, by combining the extraction of pigments and the production of biogas from residual biomass, we would not only obtain high-value compounds, but also more energy (around 5–10% higher), as compared to the single recovery of biogas. The proposed process poses an example of resource recovery from biomass grown in wastewater, moving toward a circular bioeconomy.

Omega fatty acids production in an isolated native Chlorella sp. from northeast Mexico with improved growth using urine as nutritive medium

The production of essential fatty acids (Omega 3, 6, 9) from microalgae consortia and from Chlorella sp., using urine as a culture medium, was analyzed in this study. These microorganisms require a supply of nutrients and light to stimulate their growth; and through variations of these factors, it is possible to improve lipid synthesis, fundamental elements for the production of value-added products. The BG11 culture medium was replaced with a urine-based medium (MOB) to cultivate a microalgae of the genus Chlorella sp, native to the State of Nuevo Leon. The growth of the microalgae in MOB was increased when compared to its growth in BG11. An improvement was also observed in the production of fatty acids and proteins, where the cultivation of Chlorella sp. with the urine medium (MOB) showed an average production (%) of 17.22% saturated fatty acids (SUFA's), 22.03% of monounsaturated fatty acids (MUFA's) and 60.73% of polyunsaturated fatty acids (PUFA's), demonstrated also in the high concentrations of mainly linoleic and linoleic fatty acids in the microalgae. This work, shows that human urine as a culture medium, provides enough nutrients to increase the production of biomass and oils; therefore, the use of this organic residue as a nutritive medium can be considered a suitable source for the production of essential fatty acids

Assessing Domestic Wastewater Effluent with a Battery of Bioassays after Treatment with a Specific Consortium of Microalgae and Different Flocculation Methods

Wastewater stabilization ponds (WSP) are a common method to treat wastewater before release. The purpose of the current study was to find the most inexpensive coagulation and flocculation reagents to use during harvesting of WSP algae from effluent so that water without algae can be generated for irrigation purposes. In the study, the toxicity of effluent from the algae-based WSP system after treatment with alum and chitosan was investigated. The chemical composition of the resultant supernatants was tested in conjunction with a battery of bioassays (Daphnia magna, Allium cepa, Lactuca sativa and Triticum aestivum). The bioindicator organisms were exposed to varying concentrations of the supernatant resulting from harvesting the algae biomass with chitosan (0.368 g/L chitosan) and aluminium sulphate (9.96 g/L powder). Alum was lethal to D. magna, while chitosan did not seem to affect the Daphnia test specimens. Undiluted chitosan supernatant and 100% alum resulted in minimal inhibition of the rate of T. aestivum seed germination, while both resulted in significant inhibition of the L. sativa seed germination rates. Similarly, minimal effects were found for the root growth in T. aestivum, with significant root growth inhibition observed in L. sativa and A. cepa. In A. cepa, clear differences were observed in the inhibition of root growth when the two reagents were compared. The alum and chitosan supernatants had a total carbon, iron and sulphate concentration of 327.78 mg/L, 0.12 mg/L and 68.44 mg/L and 182.04 mg/L, 0.16 mg/L and 166.80 mg/L, respectively. Based on the test specimens’ response, chitosan as flocculation method was less toxic when compared with alum coagulation, even though both algae harvesting methods changed the chemical composition of the algae-treated water.

Bio-oil production by catalytic solvent liquefaction from a wild microalgae consortium

Due to the increase in greenhouse gas emissions by combustion of fossil fuels, new alternatives for obtaining clean energy have been investigated. In this work, a wild microalgae consortium, grown in treated wastewater, was used to produce bio-oil by catalytic solvent liquefaction process. Tetralin and zeolite HZSM-5 (Si/Al = 80) were employed as a reaction medium and catalyst, respectively. The effect of H2 pressure and reaction time on biocrude yield, conversion of biomolecules, and the type of generated chemical compounds in the bio-oil were investigated, and reaction schemes were proposed. The best reaction condition was at 120 min and 760 psi, where a bio-oil yield of 51 wt% was obtained and high percentage of the original protein content was converted. The main type of compounds in the produced bio-oil were oxygenated (~ 50 chromatographic area %) and nitrogenated (~ 18 area %) compounds. H2 pressure is an important variable to process proteins, lipids, and simple carbohydrates. Despite the high protein content in the feedstock, a relatively low nitrogen content of 1.2–1.5 wt% was found in the resultant bio-oil, which has an estimated HHV of 32–33 MJ/kg.

Influence of period light on cultivation of microalgae consortium for the treatment of tannery wastewaters from leather finishing stage

Wastewater from the leather finishing step in tanneries contains high nutrient loads and toxic compounds, such as dyes, acids, toxic metals among others. To our best knowledge, for the first time, the influence of light period on the treatment of wet-end and finishing leather wastewaters with a microalgae consortium containing mainly Tetraselmis sp. was investigated. In this work, a microalgae consortium present the ability to grow well in this kind of tannery wastewater and was used for reducing nitrogen, phosphorus, ammonium, chemical and biochemical oxygen demands. Additionally, the wastewater presents high turbidity, which has an influence on the penetration of light, during the cultivations. Therefore, the influence of the illumination period was also studied: continuous light (24-light), 12 h light/dark (12-light) and without light (0-light); in addition to the influence of compositions, 50% and 75% of raw wastewater. The maximum concentration of biomass in the wastewater was observed in the 24-light culture: 50R50S (1.40 gL-1) and 75R25S (1.04 gL-1), with maximum removals of total nitrogen (71.74%), total phosphorus (97.64%), total organic carbon (31.35%), chemical oxygen demand (56.70%), biological oxygen demand (20.68%) and ammonium (100%). These results show that this microalgae consortium is a promising alternative treatment for wastewaters of the leather wet-end and finishing steps.

Development of bioplastics from a microalgae consortium from wastewater

Nowadays, as the world population is in need of creating alternative materials that can replace conventional plastics, microalgae biomass may be identified as a viable source for producing more environmentally friendly materials. Scenedesmus sp and Desmodesmus sp are the main components (~80%) of a microalgae consortium (MC) that first has been used to remove Nitrogen and Phosphorus from wastewater. The potential to develop bioplastic materials from MC considering its relatively high protein content (~48%) has been assessed in the present manuscript, using as a reference a commercial biomass rich an Arthrospira specie (AM) also present in the studied consortium.Bioplastics were obtained through injection moulding of blends obtained after mixing with different amounts of glycerol, and eventually characterized using Dynamic Mechanical Thermal Analysis (DMTA), water immersion and tensile tests. All bioplastics displayed a glass transition temperature around 60 °C, showing a thermoplastic behavior which is less pronounced in the CM based bioplastics. This would imply a greater thermal resistance of bioplastics produced from the biomass harvested in wastewater. Moreover, these bioplastics showed a lower ability to absorb water when immersed, due to the lower deformability displayed in the tensile tests. The mechanical properties of all samples, independently of the nature of the biomass, were improved when the presence of the biomass was higher.Therefore, results here presented prove the potential of valorisation of microalgae consortia used in the effective treatment of wastewater through the development of bioplastic materials.

Upgrading of microalgal consortia with CO2 from fermentation of wheat straw for the phycoremediation of domestic wastewater

Algae have been considered as a best feedstock for combating CO2. In the present study, two mixed microalgal cultures i.e. MAC1 and MAC2 were evaluated in batch mode with an extraneous supply of CO2 from the fermentation of wheat straw. Both the mixed cultures displayed promising CO2 sequestration potentials of 287 and 263 mg L−1d−1, respectively. The removal efficiencies in terms of ammonium, phosphate, chemical oxygen demand, and nitrate were found to be 87%, 78%, 68% and 65%, respectively. Enriching the tolerance of the microalgal consortia to CO2 supply and wastewater as the nutrient source significantly enhanced the lipid production for both the microalgae consortia. Lipid contents of MAC1 and MAC2 were observed to be 12.29 & 11.37%, respectively while the biomass yield from both the consortia was 0.36 g L-1. Total chlorophyll and protein contents of MAC1 and MAC2 were 14.27 & 12.28 µgmL−1 and 0.13 & 0.15 mgmL−1, respectively. Both the consortia found to have significant potential for CO2 sequestration, wastewater remediation and biofuel production.

Kinetic characterization and modeling of a microalgae consortium isolated from landfill leachate under a high CO2 concentration in a bubble column photobioreactor

Abstract Background The determination of kinetic parameters and the development of mathematical models are of great interest to predict the growth of microalgae, the consumption of substrate and the design of photobioreactors focused on CO2 capture. However, most of the models in the literature have been developed for CO2 concentrations below 10%. Results A nonaxenic microalgal consortium was isolated from landfill leachate in order to study its kinetic behavior using a dynamic model. The model considered the CO2 mass transfer from the gas phase to the liquid phase and the effect of light intensity, assimilated nitrogen concentration, ammonium concentration and nitrate concentration. The proposed mathematical model was adjusted with 13 kinetic parameters and validated with a good fit obtained between experimental and simulated data. Conclusions Good results were obtained, demonstrating the robustness of the proposed model. The assumption in the model of DIC inhibition in the ammonium and nitrate uptakes was correct, so this aspect should be considered when evaluating the kinetics with microalgae with high inlet CO2 concentrations. How to cite: Saldarriaga L F, Almenglo F, Ramirez M, et al. Kinetic characterization and modeling of a microalgae consortium isolated from landfill leachate under a high CO2 concentration in a bubble column photobioreactor. Electron J Biotechnol 2020;44. https://doi.org/10.1016/j.ejbt.2020.01.006 .

Effects of different light conditions on ammonium removal in a consortium of microalgae and partial nitrifying granules

Ammonium removal by a coupling process of microalgae (Chlorella sorokiniana) with partial nitrifying granules was evaluated in batch reactors illuminated in a wide range of light intensities (0, 100, 450, and 1600 μmol photons m−2 s−1). Ammonium oxidation performance for different light exposure time showed that the granules had a light stress tolerance at 1600 μmol photons m−2 s−1 for up to 12 h, but continuous illumination induced severe inhibition on nitrifying bacteria thereafter. Ammonium removal efficiencies at the end of tests were 66%, 62%, 5%, and −10% (due to ammonification) for 0, 100, 450, and 1600 μmol photons m−2 s−1, respectively. The nitrogen mass balance shows co-occurrence of microalgal growth taking up 24% of fed ammonium and nitrifying bacteria oxidizing 38% of fed ammonium at 100 μmol photons m−2 s−1, while both nitrification and microalgal growth are inhibited at light intensity above 450 μmol photons m−2 s−1. In comparing results from this study with previous results, it was found that the ammonium removal pathway, i.e., nitrification or microalgal uptake, is regulated more strongly by daily average light intensity than by instantaneous light intensity. Empirical model equations to estimate the oxygen balance in consortium reactors categorized the effect of daily average light intensities on process performance as follows: (i) below 27 μmol photons m−2 s−1: insufficient oxygen for nitrification; (ii) 27 to 35: sufficient oxygen for nitrification via nitrite; (iii) 35 to 180: sufficient oxygen for nitrification via nitrate; (iv) above approximately 200–300: oversaturated dissolved oxygen, excess free ammonia and/or intensive light inhibitions.

Optimization and scale-up of an LED-illuminated microalgal photobioreactor for wastewater treatment.

The use of light-emitting diode (LED)-illuminated photobioreactors with microalgae has been extensively studied for wastewater treatment. Most studies have used isolated microalgae species; however, this practice does not match the reality of conditions in wastewater treatment plants. Operational conditions that promote greater growth of algal biomass and that remove pollutants most effectively are disputed in the literature. In this context, LED-illuminated photobioreactors with microalgae were evaluated using multivariate analysis in order to optimize removal of pollutants (nitrogen, phosphorus, and carbonaceous organic matter). Three variables were evaluated: operating time, LED wavelength, and luminous flux intensity. A microalgae consortium was used in the photobioreactor. In addition to the LED-illuminated photobioreactors, control photobioreactors illuminated by sunlight were also operated. Using the results obtained in the optimization, a scaled-up reactor approximately 8.5 times larger in volume was operated to evaluate if the behavior would be maintained. The best operational conditions for the removal of pollutants were observed in LED-illuminated photobioreactors operated under a light intensity of 700 μmol·m-2s-1 for 15 days. Under these conditions, it was possible to remove 89.97% of carbonaceous organic matter, 86.50% of nitrogen, and 30.64% of phosphorus. The scaled-up photobioreactor operated with similar performance.

Hydrogen producer microalgae in interaction with hydrogen consumer denitrifiers as a novel strategy for nitrate removal from groundwater and biomass production

Low-soluble and hazardous hydrogen gas which is used in current water denitrification processes was substituted by microalgae as a novel approach for biological nitrate removal. Bioremediation of nitrate-contaminated groundwater was evaluated by three batch cultures of hydrogen consumer denitrifiers (HCD), microalgae, and HCD-microalgae consortium at a similar inoculated total biomass of about 0.025 g. Microalgae contained three species of Chlorella vulgaris, Ettlia sp., and Chlamydomonas reinhardtii with an initial cell number of 60 × 104 cell/mL and subsequently C. vulgaris as dominant strain. High nitrate concentration of about 221 mg/L was entirely removed in hydrogen-injected denitrification bioreactor containing HCD in <24 h with N removal rate of 86 mg/L/d. However, it released sCOD into the environment and did not remove phosphorus efficiently. The consortium of HCD and microalgae could offset the lack of hydrogen for dissimilation of nitrate and produced N removal rate of 78 mg/L/d at lowest HCD/microalgae inoculated mass ratio of 0.26. Microalgae played the main role for assimilation of phosphorus and mitigation of the produced sCOD in both photobioreactors containing microalgae alone or their consortium with HCD. The maximum biomass productivity of 0.32 g/L/d and settling efficiency of 0.6 were obtained at highest inoculated HCD/microalgae mass ratio of 2.33. However, the performance of the consortium in terms of nitrate removal was better in lower ratio of HCD/microalgae, which can be applied in large-scale application.

Production of lipids from psychrophilic microalgae present in antarctic glaciers for the synthesis of biofuel

Microalgae had a negative impact on the overall sensory quality. Psychrophilic microalgae live in extremely cold environments, their growth increases because they have enzymes in their structure that only adapt to temperatures below 0 ° C. For this reason, the Sustainable Chemistry Laboratory of the Central University of Ecuador, together with the Ecuadorian Antarctic Institute (INAE), made an expedition in the Greenwich, Roberts, Dee, Barrientos and Antarctic Towers where several microalgae consortia were collected, where 15 samples from Greenwich Island and Roberts were analyzed at 21 days at different temperatures, from which the genera Chlorella sp, Chlorococcum sp and Stichococcus sp. Subsequently, isolation was made in Petri dishes to obtain monoalgal cultures. Each of the isolated genera was massified in a volume of 5 mL until reaching a volume of 250 mL in modified M1 medium at a temperature of 4 ° C and 24 ° C, 5000 lux and a photoperiod of 12:12 hours. The Bligh &amp; Dyer method was used for the extraction of lipids. The values of the lipid concentration showed that the genus Chlorella sp is the highest concentration with a value of 0.2802 mg / mL at 4 ° C and a value of 2.6704 mg / mL at 24 ° C on the 22nd day of its exponential phase in comparison with the genera Chlorococcum and Stichococcus sp.

BIORREMEDIACIÓN EFICIENTE DE EFLUENTES METALÚRGICOS MEDIANTE EL USO DE MICROALGAS DE LA AMAZONÍA Y LOS ANDES DEL ECUADOR

Mining operations in the south of Ecuador have increased their activity in the last decades due to the great auriferous wealth of the region. Nevertheless, gold extraction involves processes that cause dangerous impacts to the environment, such as the release of metal ions and inorganic compounds, which are discharged into aquatic systems or to the earth’s surface, interacting adversely with various organisms. Due to this problem, the aim of this research was to evaluate the removal efficiency of mercury, phosphates, sulfates, and nitrates from the gold mining wastewater through a phytoremediation process. The study collected and applied microalgae species of the Andes and the Ecuadorian Amazon such as Pleurococcus sp., Scenedesmus sp., and Chlorella sp. The adaptation of the microalgae was evaluated, as well as the absorption capacity of the pollutants of the wastewater collected from one of the gold processing plants located on the riverside of the Calera River, province of El Oro. The microalgae strains were cultivated individually and as a consortium in photobioreactors for the treatment. The physical and chemical parameters of the wastewater and the treated water were characterized. The results determined that all the treatments were efficient, since the concentration of contaminants was considerably reduced. Pleurococcus was the genus of microalgae with the highest percentage of mercury removal, with 86 %, while in the removal of sulfates, phosphates, and nitrates, the microalgae consortium achieved results greater than 76 %, 93 % and 97 %, respectively. Thus, the use of isolated microalgae on the lacustrine systems of the Andes and the Ecuadorian Amazonia represents a promising source of germplasm for environmental bioremediation applications.

Plant and microalgae consortium for an enhanced biodegradation of sulfamethazine.

Pharmaceutical contamination in diverse water resources has been recognized as an emerging concern in environment because of its wide distribution and adverse effects on aquatic microorganisms and human health. Plant remediation with augmentation of microorganisms is a cost-effective and environmentally friendly approach toward an efficient treatment of pollutants, which can be easily applied in situ. (Bio)degradation of sulfamethazine (SMZ) by Iris pseudacorus, microalgal consortium, and plant-microalgal consortium was investigated. I. pseudacorus and microalgae could remove 63.5, and 25.8% of 1 mg SMZ L-1, respectively, whereas, the plant-microalgal consortium achieved 74% removal. The identified intermediates extracted after plant remediation indicated (bio)degradation of SMZ was through ring cleavage, hydroxylation, and dehydroxylation. Pigment content (total chlorophyll and carotenoid) of I. pseudacorus was significantly influenced by SMZ stress. A phytoreactor (20 L) constructed with I. pseudacorus achieved 30.0% and 71.3% removal of 1 mg SMZ L-1 from tap water and nutrient medium. This study has provided a better understanding of the metabolic mechanisms of SMZ in plants and showed the potential development of a plant-microalgal consortium as an advanced technology for treatment of these emerging contaminants. Graphical abstract.

Novel shortcut biological nitrogen removal method using an algae-bacterial consortium in a photo-sequencing batch reactor: Process optimization and kinetic modelling

This study evaluated a novel shortcut nitrogen removal method using a mixed consortium of microalgae, enriched ammonia oxidizing bacteria (AOB) and methanol utilizing denitrifier (MUD) in a photo-sequencing batch reactor (PSBR) for treating ammonium rich wastewater (ARWW). Alternating light and dark periods were followed to obtain complete biological nitrogen removal (BNR) without any external aeration and with the addition of methanol as the sole carbon source, respectively. The results showed that influent NH4+ was oxidized to NO2− by AOB during the light periods at a rate of 8.09 mg NH4+-N L−1h−1. Subsequently, NO2− was completely reduced during the dark period due to the action of MUD in presence of methanol. The high activities of ammonia monooxygenase (AMO) and nitrite reductase (NIR) enzymes revealed the strong role of AOB and MUD for achieving shortcut nitrogen removal from the wastewater. The reduced activities of nitrate reductase (NR) and nitrite oxidoreductase (NOR) at a high concentration of DO, NH4+ and NO2−in the system further confirmed the nitrogen removal pathway involved in the process. The biomass produced from these experiments showed good settling properties with a maximum sedimentation rate of 0.7–1.8 m h−1, a maximum sludge volume index (SVI) of 193 ml g−1- 256 ml g−1and floc size of 0.2–1.2 mm. In order to describe the growth and interaction among the algae, AOB and MUD for nitrogen removal in the system, the experimental results were fitted to four metabolic models, which revealed best fit of the experimental data due to the models based on algae-AOB and algae-AOB-MUD activities than with the other two models.

Viability of combining microalgae and macroalgae cultures for treating anaerobically digested piggery effluent

Algal phytoremediation represents a practical green solution for treating anaerobically digested piggery effluent (ADPE). The potential and viability of combining microalgae and macroalgae cultivation for the efficient treatment of ADPE were evaluated in this study. Bioprospecting the ability of different locally isolated macroalgae species illustrated the potential of Cladophora sp. to successfully grow and treat ADPE with up to 150 mg/L NH4+ with a biomass productivity of (0.13 ± 0.02) g/(L·day) and ammonium removal rate of (10.23 ± 0.18) mg/(L·day) NH4+. When grown by itself, the microalgae consortium used in this study consisting of Chlorella sp. and Scenedesmus sp. was found to grow and treat undiluted ADPE (up to 525 mg/L NH4+) with an average ammonium removal rate of 25 mg/(L·day) NH4+ and biomass productivity of (0.012 ± 0.0001) g/(L·day). Nevertheless, when combined together, despite the different cultivation systems (attached and non-attached) evaluated, microalgae and macroalgae were unable to co-exist together and treat ADPE as their respective growth were inversely related to each other due to direct competition for nutrients and available resources as well as the negative physical interaction between both algal groups.

Photorespiration in an outdoor alkaline open-photobioreactor used for biogas upgrading

The rates of oxygenic and carbon fixation photosynthetic processes of a microalgae consortium were simultaneously evaluated under steady-state performance in an bench scale alkaline open-system exposed to outdoor conditions in Mexico City. A synthetic methane-free gaseous stream (SMGS) similar to biogas was used as inorganic carbon source and model of biogas upgrading. The microalgae CO2 fixation rates were calculated through a novel methodology based on an inorganic carbon mass balance under continuous scrubbing of a SMGS similar to biogas, where the influence of pH and temperature time-depended oscillations were successfully incorporated into the mass balances. The oxygenic activity and carbon fixation occurred at different non-stoichiometric rates during the diurnal phase, in average carbon fixation predominated over oxygen production (photosynthesis quotient PQ≈ 0.5 mol O2 mol−1 CO2) indicating photorespiration occurrence mainly under dissolved oxygen concentrations higher than 10 mg L−1. The oxygen and inorganic carbon mass balances demonstrated that photorespiration and endogenous respiration were responsible for losing up to 66% and 7% respectively of the biomass grew at diurnal periods under optimal conditions. In favoring photorespiration conditions, the microalgae biomass productivity (CO2 effectively captured) can be severely decreased. A kinetic mathematical model as a function of temperature and irradiance of the oxygenic photosynthetic activity indicated the optimal operation zone for this outdoor alkaline open-photobioreactor, where irradiance was found being the most influential parameter.