Production of carbohydrates and polyhydrohybutyrate by cyanobacteria grown in wastewater

Cyanobacteria are prokaryotic aerobic photosynthetic microorganisms with the capacity to remove nutrients from wastewater and synthesize a large variety of bioactive compounds and valuable byproducts. Among those valuable byproducts, glycogen (carbohydrates) and polyhydroxybutyrates (PHB) are receiving increasing interest due to their potential as biofuel substrate and as bioplastic, respectively. The main objective in this PhD thesis was to cultivate and select cyanobacteria from a mixed microalgae culture for carbohydrates and PHB production. In order to fulfil that main goal, the thesis was divided in two parts. The first consisted in evaluating the effect of nutritional and operational conditions on the selection and grow of wastewater-borne cyanobacteria in a mixed microalgae consortium fed with in secondary effluent and digestate. While the second was focused in the accumulation of carbohydrates and PHB throughout different strategies based on nutrients and carbon limitation. In the first part, digestate diluted with secondary effluent wastewater was used to select a culture dominated by cyanobacteria from an initial mixed microalgae consortium in pilot scale (30 L) and lab scale (3L) closed-photobioreactors (PBRs). Through several essays, the PBRs were operated at different nutrients loadings (paying attention on N and P ratios and concentrations) and hydraulic regimes (i.e. continuous, semi-continuous and sequencing batch) in order to find conditions appropriated for cyanobacteria dominance over other wastewater-borne microorganisms (mainly with green microalgae). During approximately one year of operation, the effect of nutrient variations in the influent and their ratios on the culture composition and biomass concentration was evaluated in a semi-continuous PBR operated at 10 days of HRT/SRT. The results evidenced that cyanobacteria species dominated over green algae when the influent had non-limited carbon conditions, N:P ratios between 16:1-49:1 (molar basis) and low phosphorus loads. Under these conditions, cyanobacteria were able to reach an average biomass production of 0.08 g L-1 d-1. Subsequently, short term studies testing operational strategies were performed in order to remove green algae also tolerating phosphorus limiting conditions. These strategies consisted on sequencing batch operation. According to the results, a sequencing batch operation consisting in a HRT of 6 days and SRT of 10 days provided suitable conditions to remove unsettled green algae Scenedesmus sp. and to improve cyanobacteria dominance until reach 70% of the total population. While increasing the biomass production to 0.12 g L-1 d-1. On the contrary, lower HRT and SRT led to high volumetric loads that promoted the presence of other microorganisms (diatoms and protozoa) and bacterial activity. In the second part, the cyanobacteria dominated culture previously obtained was submitted to different strategies to accumulate polymers. Among these, nutritional conditions (N and P limitation) and luminic (permanent light and light/dark alternation) were found to be a promising strategies to reach PHB content up to 6.5% and carbohydrates content of 75% in N limitation under light/dark alternation in batch test performed along two weeks. Subsequently, this time needed of accumulation was reduced through the adaptation of cyanobacteria to feast and famine regimes. Consisting in the submission of the biomass to a period of carbon availability and a subsequent absence of carbon. With the application of this procedure the culture was able to reach similar PHB and carbohydrates concentrations in less than 2 days. In addition, these results indicated that carbon uptake and the consequent polymers production from cyanobacteria can be enhanced through carbon and nutrient feeding strategies.Las cianobacterias son microorganismos fotosintéticos aeróbicos procarióticos con la capacidad de eliminar nutrientes de las aguas residuales y sintetizar una gran variedad de compuestos bioactivos y subproductos valiosos. Entre esos subproductos, el glucógeno (carbohidratos) y el polihidroxibutirato (PHB) están recibiendo creciente interés debido a su potencial como sustrato de biocombustible y como bioplástico, respectivamente. El objetivo principal de esta tesis doctoral fue cultivar y seleccionar cianobacterias de un cultivo mixto de microalgas para la producción de carbohidratos y de PHB. Para cumplir ese objetivo principal, la tesis se dividió en dos partes. La primera consistió en evaluar el efecto de las condiciones nutricionales y operativas en la selección y crecimiento de cianobacterias nativas de aguas residuales. Mientras que la segunda parte se centró en la acumulación de carbohidratos y PHB através de diferentes estrategias basadas en limitación de nutrientes y de carbono. En la primera parte, se consideró el efecto de las condiciones nutricionales y operativas en la selección y el crecimiento de cianobacterias nativas de aguas residuales cultivadas en aguas residuales secundarias y en digestato. En estaparte, las cianobacterias se seleccionaron de un consorcio inicial mixto de microalgas que trataban aguas residuales. En primer lugar, se evaluaron los efectos de los nutrientes (e.g., concentraciones, ratios y cargas) en un estudio a largo plazo realizado en un fotobiorreactor (FBR) a escala piloto (30L) operado en modo semicontinuo. Los resultados de esta sección evidenciaron que las especies de cianobacterias nativas en aguas residuales Aphanocapsa sp., Chrooccocus sp. y Pseudanabaena sp. fueron capaces de dominar sobre las algas verdes Chlorella sp. y Stigeoclonium sp. en un FBR piloto semicontinuo. Su dominio se logró bajo condiciones de carbono no limitado, relaciones N:P entre 16:1-49:1 (basemolar) y bajas cargas de fósforo inorgánico (IP) (~0.25 mgLd-1). Bajo estas condiciones, un cultivo dominado por cianobacterias fue capaz de alcanzar un promedio de producción de biomasa de 0.08 gL-1d-1. Por último, se llevaron a cabo estudio sacorto plazo en FBRs a escala de laboratorio (3L) para evaluar el efecto de las condiciones operacionales (e.g., regímenes hidráulicos, tiempo de retención de sólidos (TRS), tiempo de retención hidráulica (TRH)). Los resultados indicaron que el un TRH de 6 días y un SRT de 10 días proporcionaron condiciones adecuadas para eliminar las algas verdes suspendidas, tolerantes a bajos niveles de IP (e.g., Scenedesmussp.), y mejorar la concentración de cianobacterias de 2% hasta 70% de la población total, mientras que aumenta la producción de biomasa a 0.12 gL-1d-1. Por el contrario, la reducción de TRH y TRS afectó negativamente a la dominancia de las cianobacterias, favoreciendo el dominio de las algas verdes y una mayor actividad bacteriana. En la segunda parte, el cultivo dominado por cianobacterias obtenido previamente fue sometido a diferentes estrategias para acumular polímeros. Entre estas, las condiciones nutricionales (limitación de nitrogeno (N) y fósforo (P)) y lumínicas (luz permanente y alternancia de luz/oscuridad) se encontraron como estrategias prometedoras para alcanzar un contenido de PHB de hasta el 6,5% y un contenido de carbohidratos del 75% en condiciones de limitación de N y alternancia de luz/oscuridad, en doce días de incubación. Posteriormente, este tiempo necesario de la acumulación se redujo mediante la adaptación de las cianobacterias a regímenes de festín y hambre. Esta estrategia consiste en la alternancia de períodos con disponibilidad de carbono y una posterior ausencia de carbono durante el cultivo. Con la aplicación de esta estrategia, el cultivo acumuló similares cantidades en solo 24h de incubación bajo condiciones aeróbicas iluminadas

Production of carbohydrates and polyhydrohybutyrate by cyanobacteria grown in wastewater

Cyanobacteria are prokaryotic aerobic photosynthetic microorganisms with the capacity to remove nutrients from wastewater and synthesize a large variety of bioactive compounds and valuable byproducts. Among those valuable byproducts, glycogen (carbohydrates) and polyhydroxybutyrates (PHB) are receiving increasing interest due to their potential as biofuel substrate and as bioplastic, respectively. The main objective in this PhD thesis was to cultivate and select cyanobacteria from a mixed microalgae culture for carbohydrates and PHB production. In order to fulfil that main goal, the thesis was divided in two parts. The first consisted in evaluating the effect of nutritional and operational conditions on the selection and grow of wastewater-borne cyanobacteria in a mixed microalgae consortium fed with in secondary effluent and digestate. While the second was focused in the accumulation of carbohydrates and PHB throughout different strategies based on nutrients and carbon limitation. In the first part, digestate diluted with secondary effluent wastewater was used to select a culture dominated by cyanobacteria from an initial mixed microalgae consortium in pilot scale (30 L) and lab scale (3L) closed-photobioreactors (PBRs). Through several essays, the PBRs were operated at different nutrients loadings (paying attention on N and P ratios and concentrations) and hydraulic regimes (i.e. continuous, semi-continuous and sequencing batch) in order to find conditions appropriated for cyanobacteria dominance over other wastewater-borne microorganisms (mainly with green microalgae). During approximately one year of operation, the effect of nutrient variations in the influent and their ratios on the culture composition and biomass concentration was evaluated in a semi-continuous PBR operated at 10 days of HRT/SRT. The results evidenced that cyanobacteria species dominated over green algae when the influent had non-limited carbon conditions, N:P ratios between 16:1-49:1 (molar basis) and low phosphorus loads. Under these conditions, cyanobacteria were able to reach an average biomass production of 0.08 g L-1 d-1. Subsequently, short term studies testing operational strategies were performed in order to remove green algae also tolerating phosphorus limiting conditions. These strategies consisted on sequencing batch operation. According to the results, a sequencing batch operation consisting in a HRT of 6 days and SRT of 10 days provided suitable conditions to remove unsettled green algae Scenedesmus sp. and to improve cyanobacteria dominance until reach 70% of the total population. While increasing the biomass production to 0.12 g L-1 d-1. On the contrary, lower HRT and SRT led to high volumetric loads that promoted the presence of other microorganisms (diatoms and protozoa) and bacterial activity. In the second part, the cyanobacteria dominated culture previously obtained was submitted to different strategies to accumulate polymers. Among these, nutritional conditions (N and P limitation) and luminic (permanent light and light/dark alternation) were found to be a promising strategies to reach PHB content up to 6.5% and carbohydrates content of 75% in N limitation under light/dark alternation in batch test performed along two weeks. Subsequently, this time needed of accumulation was reduced through the adaptation of cyanobacteria to feast and famine regimes. Consisting in the submission of the biomass to a period of carbon availability and a subsequent absence of carbon. With the application of this procedure the culture was able to reach similar PHB and carbohydrates concentrations in less than 2 days. In addition, these results indicated that carbon uptake and the consequent polymers production from cyanobacteria can be enhanced through carbon and nutrient feeding strategies.Las cianobacterias son microorganismos fotosintéticos aeróbicos procarióticos con la capacidad de eliminar nutrientes de las aguas residuales y sintetizar una gran variedad de compuestos bioactivos y subproductos valiosos. Entre esos subproductos, el glucógeno (carbohidratos) y el polihidroxibutirato (PHB) están recibiendo creciente interés debido a su potencial como sustrato de biocombustible y como bioplástico, respectivamente. El objetivo principal de esta tesis doctoral fue cultivar y seleccionar cianobacterias de un cultivo mixto de microalgas para la producción de carbohidratos y de PHB. Para cumplir ese objetivo principal, la tesis se dividió en dos partes. La primera consistió en evaluar el efecto de las condiciones nutricionales y operativas en la selección y crecimiento de cianobacterias nativas de aguas residuales. Mientras que la segunda parte se centró en la acumulación de carbohidratos y PHB através de diferentes estrategias basadas en limitación de nutrientes y de carbono. En la primera parte, se consideró el efecto de las condiciones nutricionales y operativas en la selección y el crecimiento de cianobacterias nativas de aguas residuales cultivadas en aguas residuales secundarias y en digestato. En estaparte, las cianobacterias se seleccionaron de un consorcio inicial mixto de microalgas que trataban aguas residuales. En primer lugar, se evaluaron los efectos de los nutrientes (e.g., concentraciones, ratios y cargas) en un estudio a largo plazo realizado en un fotobiorreactor (FBR) a escala piloto (30L) operado en modo semicontinuo. Los resultados de esta sección evidenciaron que las especies de cianobacterias nativas en aguas residuales Aphanocapsa sp., Chrooccocus sp. y Pseudanabaena sp. fueron capaces de dominar sobre las algas verdes Chlorella sp. y Stigeoclonium sp. en un FBR piloto semicontinuo. Su dominio se logró bajo condiciones de carbono no limitado, relaciones N:P entre 16:1-49:1 (basemolar) y bajas cargas de fósforo inorgánico (IP) (~0.25 mgLd-1). Bajo estas condiciones, un cultivo dominado por cianobacterias fue capaz de alcanzar un promedio de producción de biomasa de 0.08 gL-1d-1. Por último, se llevaron a cabo estudio sacorto plazo en FBRs a escala de laboratorio (3L) para evaluar el efecto de las condiciones operacionales (e.g., regímenes hidráulicos, tiempo de retención de sólidos (TRS), tiempo de retención hidráulica (TRH)). Los resultados indicaron que el un TRH de 6 días y un SRT de 10 días proporcionaron condiciones adecuadas para eliminar las algas verdes suspendidas, tolerantes a bajos niveles de IP (e.g., Scenedesmussp.), y mejorar la concentración de cianobacterias de 2% hasta 70% de la población total, mientras que aumenta la producción de biomasa a 0.12 gL-1d-1. Por el contrario, la reducción de TRH y TRS afectó negativamente a la dominancia de las cianobacterias, favoreciendo el dominio de las algas verdes y una mayor actividad bacteriana. En la segunda parte, el cultivo dominado por cianobacterias obtenido previamente fue sometido a diferentes estrategias para acumular polímeros. Entre estas, las condiciones nutricionales (limitación de nitrogeno (N) y fósforo (P)) y lumínicas (luz permanente y alternancia de luz/oscuridad) se encontraron como estrategias prometedoras para alcanzar un contenido de PHB de hasta el 6,5% y un contenido de carbohidratos del 75% en condiciones de limitación de N y alternancia de luz/oscuridad, en doce días de incubación. Posteriormente, este tiempo necesario de la acumulación se redujo mediante la adaptación de las cianobacterias a regímenes de festín y hambre. Esta estrategia consiste en la alternancia de períodos con disponibilidad de carbono y una posterior ausencia de carbono durante el cultivo. Con la aplicación de esta estrategia, el cultivo acumuló similares cantidades en solo 24h de incubación bajo condiciones aeróbicas iluminadas.Postprint (published version

Prevalencia de sensibilización a proteínas de la leche de vaca en niños con dermatitis atópica en un centro de referencia para la atención de enfermedades alérgicas

La dermatitis atópica (DA) es una enfermedad inflamatoria, crónica y recidivante de la piel que afecta con mayor frecuencia la población pediátrica. En el grupo de edad pediátrico, la alergia a las proteínas de la leche de vaca (APLV) es la alergia alimentaria más común entre los niños menores de dos años y también en este grupo está reconocido que se asocia con otras enfermedades atópicas. Existen opiniones distintas en cuanto a la relación de la dermatitis atópica con alergia a alimentos, las cuales varían desde considerar que no juega un papel importante, hasta el considerar la alergia alimentaria como la principal responsable de las exacerbaciones de la DA en algunos pacientes. El objetivo de este estudio fue determinar la prevalencia de sensibilización a la proteínas de la leche de vaca en los niños con dermatitis atópica de un centro de referencia y de esta forma valorar su potencial papel como factor de riesgo en el desarrollo de dicho trastorno de la piel. Se incluyó de forma prospectiva a todos los pacientes menores de 5 años que acudieron a consulta al Centro Regional de Alergia e Inmunología Clínica, quienes contaran con diagnóstico de dermatitis atópica definida por criterios clínicos de Hanifin y Rajka captados durante los meses de agosto a noviembre del 2015. Se aplicaron pruebas epicutáneas para leche entera, caseína, α-lactoalbúmina y β-lactoglobulina. Se 2 recabaron variables y practicaron pruebas para proteína de la leche de vaca en 24 niños con edad máxima de 5 años que reunieron criterios clínicos de dermatitis atópica. Se identificó una prevalencia de sensibilización (positividad para cualquiera de los antígenos) de 37.5%, (9 de 24). Se identificó α-lactoalbúmina como la proteína para la que se identificó la mayor frecuencia de reacciones positivas, con 7 pacientes (29.1%). En orden decreciente de frecuencia, fue seguida por β-lactoglobulina, con 6 pacientes (25%), caseína con 5 pacientes (20.8%) y leche entera con 4 pacientes (16.6%). Se identificó una diferencia significativa (P=0.04) entre la mediana de tiempo de exposición a la lactancia materna de los pacientes sensibilizados, con 7 meses, (RIQ de 3 a 12) vs 1.5 meses (RIQ de 0.75 a 6) para los no sensibilizados. Los pacientes no sensibilizados mostraron una frecuencia más alta de síntomas gastrointestinales, con un 73% (11 de 15) vs 44.4% (4 de 9) de los sensibilizados. Conclusión: La prevalencia de sensibilización a proteínas de leche de vaca en niños con dermatitis atópica en un centro de referencia de enfermedades alérgicas del Noreste de México es de 37.5%, siendo la más frecuente la α-lactoalbúmina

Cultivation and selection of cyanobacteria in a closed photobioreactor used for secondary effluent and digestate treatment

“The final publication is available at Springer via http://dx.doi.org/10.1016/j.scitotenv.2017.02.097"The main objective of this study was to select and grow wastewater-borne cyanobacteria in a closed photobioreactor (PBR) inoculated with a mixed consortium of microalgae. The 30 L PBR was fed with a mixture of urban secondary effluent and digestate, and operated in semi-continuous mode. Based on the nutrients variation of the influent, three different periods were distinguished during one year of operation. Results showed that total inorganic nitrogen (TIN), inorganic phosphorus concentration (PO43 -), phosphorus volumetric load (LV-P) and carbon limited/non-limited conditions leaded to different species composition, nutrients removal and biomass production in the culture. High TIN/PO43 - concentrations in the influent (36 mg N L- 1/3 mg P L- 1), carbon limitation and an average LV-P of 0.35 mg P L- 1d- 1 were negatively related to cyanobacteria dominance and nutrients removal. On the contrary, cyanobacteria predominance over green algae and the highest microbial biomass production (averaging 0.084 g Volatile Suspended Solids (VSS) L- 1d- 1) were reached under TIN/PO43 - concentrations of 21 mg N L- 1/2 mg P L- 1, no carbon limitation and an average LV-P of 0.23 mg P-PO43 - L- 1d- 1. However, although cyanobacteria predominance was also favored with a LV-P 0.15 mg L- 1d- 1, biomass production was negatively affected due to a P limitation in the culture, resulting in a biomass production of 0.0.39 g VSS L- 1d- 1. This study shows that the dominance of cyanobacteria in a microalgal cyanobacterial community in an agitated PBR using wastewater as nutrient source can be obtained and maintained for 234 days. These data can also be applied in future biotechnology applications to optimize and enhance the production of added value products by cyanobacteria in wastewater treatment systems.Peer ReviewedPostprint (author's final draft

Nutrients and biomass dynamics in photo-sequencing batch reactors treating wastewater with high nutrients loadings

The present study investigates different strategies for the treatment of a mixture of digestate from an anaerobic digester diluted and secondary effluent from a high rate algal pond. To this aim, the performance of two photo-sequencing batch reactors (PSBRs) operated at high nutrients loading rates and different solids retention times (SRTs) were compared with a semi-continuous photobioreactor (SC). Performances were evaluated in terms of wastewater treatment, biomass composition and biopolymers accumulation during 30¿days of operation. PSBRs were operated at a hydraulic retention time (HRT) of 2¿days and SRTs of 10 and 5¿days (PSBR2-10 and PSBR2-5, respectively), whereas the semi-continuous reactor was operated at a coupled HRT/SRT of 10¿days (SC10-10). Results showed that PSBR2-5 achieved the highest removal rates in terms of TN (6.7¿mg¿L-1¿d-1), TP (0.31¿mg¿L-1¿d-1), TOC (29.32¿mg¿L-1¿d-1) and TIC (3.91¿mg¿L-1¿d-1). These results were in general 3–6 times higher than the removal rates obtained in the SC10-10 (TN 29.74¿mg¿L-1¿d-1, TP 0.96¿mg¿L-1¿d-1, TOC 29.32¿mg¿L-1¿d-1 and TIC 3.91¿mg¿L-1¿d-1). Furthermore, both PSBRs were able to produce biomass up to 0.09¿g¿L-1¿d-1, more than twofold the biomass produced by the semi-continuous reactor (0.04¿g¿L-1¿d-1), and achieved a biomass settleability of 86–92%. This study also demonstrated that the microbial composition could be controlled by the nutrients loads, since the three reactors were dominated by different species depending on the nutritional conditions. Concerning biopolymers accumulation, carbohydrates concentration achieved similar values in the three reactors (11%), whereas¿<¿0.5% of polyhydrohybutyrates (PHB) was produced. These low values in biopolymers production could be related to the lack of microorganisms as cyanobacteria that are able to accumulate carbohydrates/PHB.Peer ReviewedPostprint (published version

Production of polyhydroxybutyrates and carbohydrates in a mixed cyanobacterial culture : effect of nutrients limitation and photoperiods

In the present study, different photoperiods and nutritional conditions were applied to a mixed wastewater-borne cyanobacterial culture in order to enhance the intracellular accumulation of polyhydroxybutyrates (PHBs) and carbohydrates. Two different experimental set-ups were used. In the first, the culture was permanently exposed to illumination, while in the second, it was submitted to light/dark alternation (12h cycles). In both cases, two different nutritional regimes were also evaluated, N-limitation and P-limitation. Results showed that the highest PHB concentration (104 mg L-1) was achieved under P limited conditions and permanent illumination, whereas the highest carbohydrate concentration (838 mg L-1) was obtained under N limited condition and light/dark alternation. With regard to bioplastics and biofuel generation, this study demonstrates that the accumulation of PHBs (bioplastics) and carbohydrates (potential biofuel substrate) is favored in wastewater-borne cyanobacteria under conditions where nutrients are limited.Peer ReviewedPostprint (published version

Remoción de sólidos en aguas residuales de la industria harinera de pescado empleando biopolímeros

La industria productora de harina de pescado Maz Industrial S.A. de C.V, ubicada en Mazatlán, Sinaloa, México, vierte sus aguas residuales hacia el estero de Urías con una alta carga de materia orgánica, que contiene proteínas, grasas y aceites, lo cual, además del impacto ambiental que ocasiona, representa una pérdida económica por no recuperarla, llegando a desperdiciar hasta 11.44 t d-1, que puede retornarse a la producción. A fin de evaluar la remoción de materia orgánica en la fase de pretratamiento de dichas aguas residuales, se hicieron pruebas de coagulación, floculación y sedimentación, utilizando polímeros orgánicos naturales e inocuos; quitosán como coagulante primario, y alginato de sodio y ácido tánico como ayudantes de coagulación aniónicos. Con la mezcla de 300 mgl-1 de quitosán con 20 mgl-1 de alginato de sodio se logró una remoción de 91.84% de sólidos suspendidos totales (SST) y 90.83% de sólidos suspendidos volátiles (SSV) y con la mezcla 200 mgl -1 de quitosán con 20 mgl-1 de ácido tánico se obtuvieron remociones del 97.78% de SST y 97.79% de SSV. Con las eficiencias de remoción conseguidas en esta investigación y tomando en cuenta que el precipitado sedimentado con el empleo de estos biopolímeros no es tóxico, es posible escalar la recuperación de la materia orgánica en el ámbito industrial, para retornarla hacia el tren de elaboración de harina de pescado, facilitar el tratamiento biológico convencional del remanente de materia orgánica en el agua residual pretratada y reducir el impacto ambiental que ocasiona la descarga con alta carga orgánica

Polymer accumulation in mixed cyanobacterial cultures selected under the feast and famine strategy

In this study, a sequencing batch reactor (SBR), operated with transient carbon availability (feast and famine) and different nutrients loads, was used to select cyanobacteria accumulating poly (3-hydroxyalkanoate) (PHB) and carbohydrates from a mixed wastewater-borne microbial culture. The SBR was operated with 12 h aerobic light and 12 h anaerobic dark phases, evaluating the effect of three different operational conditions consisting on; 1) carbon limitation, 2) carbon and phosphorus limitation and 3) phosphorus limitation. Once a steady state was reached in each operational period of the SBR, part of the biomass was collected and submitted to separate batch tests in order to investigate the maximum PHB and carbohydrates accumulation levels. Batch tests were performed during 24 h of illuminated aerobic condition and 24 h of dark anaerobic condition, while inorganic carbon was constantly present. During the SBR operation, inorganic carbon was mostly used for biomass and carbohydrate production, showing very low PHB accumulation levels (<1%). Notwithstanding, in subsequent batch tests, PHB was accumulated after a complete depletion of nitrogen, reaching almost 4%. Concerning carbohydrates, it was found that phosphorus limitation (with and without carbon limitation) led to a culture mostly dominated by cyanobacteria and higher levels of carbohydrate content (43%–48%) than the culture with carbon limitation and high loads of nitrogen and phosphorus (29%). Such contents were obtained in only 24 h of incubation under aerobic illuminated conditions. Hence, these encouraging results indicate that carbon uptake and the consequent polymers production from cyanobacteria can be enhanced through carbon and nutrient feeding strategiesPeer ReviewedPostprint (author's final draft

Selection of cyanobacteria over green algae in a photo-sequencing batch bioreactor fed with wastewater

In this work, a strategy based on photo-sequencing batch operationwas used to select cyanobacteria over unsettled green algae in awastewater treatment system, evaluating for the first time the effect of hydraulic regimes on nutritional dynamics and microorganisms' competition. During 30 days of operation, an initial microalgae mixed consortia dominated by the green microalgae Scenedesmus sp. was cultivated in two different photo-sequencing batch reactors operated at hydraulic retention time (HRT) of 6 days (PSBR6) and 4 days (PSBR4) at a theoretical solids retention time (SRT) of 10 d. Both reactorswere compared with a semi-continuous reactor (SC10) operated at 10 d of HRT and 10 days of SRT (used as a control). The results indicated that PSBR6 and PSBR4 decreased Scenedesmus sp. population by 88% and 48%, respectively. However, only PSBR6 provided suitable conditions to select cyanobacteria from an initial green algae dominated culture. These conditions included volumetric loads of 11.72 mg TN L-1 d-1, 2.04mg TP L-1 d-1 and 53.31 mg TOC L-1 d-1. The remaining nutrients in the culture led also to a phosphorus limiting N:P ratio (34:1) that improved the increase of cyanobacteria from an initial 2% until 70% of the total population. In addition, PSBR6 reached a biomass production of 0.12 g L-1 d-1,while removing TN, TP and TOC by 58%, 83% and 85%, respectively. Conversely, the application of higher nutrients loads caused by lowerHRT (PSBR4) led to an increase of only 13% of cyanobacteriawhile SC10 remainedwith the same biomass composition during all the experimental time. Thus, this study showed that the dominance of cyanobacteria in microalgal-based wastewater treatment systems can be controlled by the operational and nutritional conditionsPeer ReviewedPostprint (author's final draft