A quick and effective estimation of algal density by turbidimetry developed with Chlorella vulgaris cultures

El uso de Chlorella vulgaris Beijerinck como alimento para el zooplancton implica la necesidad de optimizar el cultivo de algas para mantener su crecimiento en el tiempo. En este trabajo se desarrolló un método que relaciona la densidad del cultivo con la turbidez para estimar la biomasa algal. Esta técnica se ha mejorado mediante la aplicación del análisis digital para el recuento de las algas que promueve la exactitud y reduce el disturbio en el cultivo, con obtención rápida y fácil de resultados repetibles. Se realizaron dos cultivos de C. vulgaris en recipientes de 3 L con aireación e iluminación continua (50 µmol fotones m–2 ·s–1 a 660 nm), alcanzando 214 y 280 NTU, respectivamente. El recuento de las muestras se realizó por medio de imágenes digitales tomadas con un microscopio invertido. Se aplicaron dos técnicas para el recuento de las alícuotas: la sedimentación directa y la sedimentación con homogeneización previa. Con el fin de comparar el ajuste de ambos métodos de sedimentación, las fotografías fueron tomadas en los sectores central, medio y periférico de la cámara de sedimentación. Para ambas técnicas se contaron un mínimo de 17 individuos imagen–1 y un máximo de 404 individuos imagen–1, con un tiempo promedio de un minuto por imagen. A niveles bajos de turbidez (< 40 NTU) la dispersión de los datos fue similar entre ambas técnicas (rango error: 16-60 %). Para niveles superiores de turbidez, en la técnica de sedimentación directa se observó un mayor rango de error (31-50 %) mientras que en la técnica con homogenización previa osciló entre 5 y 13 %. El análisis de regresión evidenció un bajo ajuste de los datos (67 %), que en la sedimentación sin homogeneización responde a un patrón reiterado de aumento de densidad algal desde la periferia hacia el centro de la cámara de sedimentación. La inclusión de una homogeneización previa promueve un mejor ajuste del modelo (99 %) y determina un incremento en la consistencia del método. Con los resultados obtenidos se demuestra que la técnica turbidimétrica desarrollada puede ser utilizada con éxito en cultivos de especies de algas cuyas formas geométricas sean reconocidas por el procesador de imágenes.The use of Chlorella vulgaris Beijerinck as a food source for zooplankton requires the optimization of algal-culture conditions for prolonged growth maintenance. In this study, we developed a method that relates algal density to culture turbidity to estimate culture biomass. This method was improved by applying digital analysis for algal counting, which promotes accuracy, low culture disturbance, easy repetition and the rapid acquisition of results. Two 3-L cultures of C. vulgaris, maintained for two weeks with continuous lighting (eight light-emitting diodes at 50 µmol photons m–2 ·s–1, at 660 nm) and aerators to prevent algal sedimentation, reached turbidities of 214 and 280 NTUs, respectively. Sample counting was performed using digital images obtained with an inverted microscope. Aliquot sedimentation was compared with or without previous homogenization through photographs taken in the central, middle, and peripheral sectors of the Utermöhl settling chambers. For each procedure, we counted between 17 and 404 individuals image–1, requiring, on average, one minute image–1. At low turbidity (< 40 NTU), the data dispersion was similar between the two protocols (error range, 16 to 60 %); at higher turbidity, the direct sedimentation alone gave a larger error (31-50 %) than with prior homogenization (5-13 %). Regression analysis at low data fit (67 %) suggested that the sedimentation heterogeneity of non-homogenized samples corresponded to a pattern of settled algae having increasing density from the periphery to the centre of the chamber, but with homogenization, a better model fitting (99 %) resulted, contributing to greater consistency with that procedure. We consider that this turbidometric protocol could be used successfully with cultures of algae that have geometrical shapes recognizable by the image software.Fil: Ferrando, Noelia Soledad. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Limnología "Dr. Raúl A. Ringuelet". Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. Instituto de Limnología; ArgentinaFil: Benitez, Hernan Hugo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Limnología "Dr. Raúl A. Ringuelet". Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. Instituto de Limnología; ArgentinaFil: Gabellone, Nestor Adrian. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Limnología "Dr. Raúl A. Ringuelet". Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. Instituto de Limnología; ArgentinaFil: Claps, Maria Cristina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Limnología "Dr. Raúl A. Ringuelet". Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. Instituto de Limnología; ArgentinaFil: Altamirano, Pablo Rodrigo. Universidad Nacional de La Plata. Facultad de Ciencias Agrarias y Forestales; Argentin

Efficacy of Microalgae on the Removal of Pollutants from Wastewater

Expansion of urban populations, increased coverage of domestic water supply and sewerage give rise to greater quantities of municipal wastewater. With the current emphasis on environmental health and water pollution issues, there is an increasing discharge of waste water in developing countries. Present technologies in developing countries for treating waste water are not sufficient and cost effective. Chlorella vulgaris is a form of green microalgae efficient for pond-based wastewater treatment, rather than bacterial strains for their ability to flocculate Chlorella vulgaris in a culture suspension. A microbial flocculent would be significantly cheaper than traditional flocculants and is believed to be less potentially toxic than synthetic polymers which are currently available. Chlorella vulgaris absorbed more pollutant compared to Chlamydomonas sp., which reveals that Chlorella vulgaris is efficient than Chlamydomonas sp., for treating waste water.

Optimization of cell disruption in Raphidocelis subcapitata and Chlorella vulgaris for biomarker evaluation

Raphidocelis subcapitata and Chlorella vulgaris are bioassay microalgae with rigid cellulosic cell wall which can hinder the release of intracellular proteins often studied as toxicity biomarkers. Since cell disruption is necessary for recovering intracellular biomolecules in these organisms, this study investigated the efficiency of ultrasonication bath; ultrasonication probe; vortexer; and bead mill in disintegrating the microalgae for anti-oxidative enzyme extraction. The extent of cell disruption was evaluated and quantified using bright field microscopy. Disrupted algae appeared as ghosts. The greatest disintegration of the microalgae (83-99.6 %) was achieved using bead mill with 0.42-0.6 mm glass beads while the other methods induced little or no disruption. The degree of cell disruption using bead mill increased with exposure time, beads-solution ratio and agitation speed while larger beads caused less disruption. Findings revealed that bead milling, with specific parameters optimized, is one of the most effective methods of disintegrating the robust algal cells

The impacts of replacing air bubbles with microspheres for the clarification of algae from low cell-density culture

Dissolved Air Flotation (DAF) is a well-known coagulation–flotation system applied at large scale for microalgae harvesting. Compared to conventional harvesting technologies DAF allows high cell recovery at lower energy demand. By replacing microbubbles with microspheres, the innovative Ballasted Dissolved Air Flotation (BDAF) technique has been reported to achieve the same algae cell removal efficiency, while saving up to 80% of the energy required for the conventional DAF unit. Using three different algae cultures (Scenedesmus obliquus, Chlorella vulgaris and Arthrospira maxima), the present work investigated the practical, economic and environmental advantages of the BDAF system compared to the DAF system. 99% cells separation was achieved with both systems, nevertheless, the BDAF technology allowed up to 95% coagulant reduction depending on the algae species and the pH conditions adopted. In terms of floc structure and strength, the inclusion of microspheres in the algae floc generated a looser aggregate, showing a more compact structure within single cell alga, than large and filamentous cells. Overall, BDAF appeared to be a more reliable and sustainable harvesting system than DAF, as it allowed equal cells recovery reducing energy inputs, coagulant demand and carbon emissions

Influence of organic matter and CO2 supply on bioremediation of heavy metals by Chlorella vulgaris and Scenedesmus almeriensis in a multimetallic matrix

Producción CientíficaThis research evaluated the influence of organic matter (OM) and CO2 addition on the bioremediation potential of two microalgae typically used for wastewater treatment: Chlorella vulgaris (CV) and Scenedesmus almeriensis (SA). The heavy metal (HM) removal efficiencies and biosorption capacities of both microalgae were determined in multimetallic solutions (As, B, Cu, Mn, and Zn) mimicking the highest pollutant conditions found in the Loa river (Northern Chile). The presence of OM decreased the total biosorption capacity, specially in As (from 2.2 to 0.0 mg/g for CV and from 2.3 to 1.7 mg/g for SA) and Cu (from 3.2 to 2.3 mg/g for CV and from 2.1 to 1.6 mg/g for SA), but its influence declined over time. CO2 addition decreased the total HM biosorption capacity for both microalgae species and inhibited CV growth. Finally, metal recovery using different eluents (HCl, NaOH, and CaCl2) was evaluated at two different concentrations. HCl 0.1 M provided the highest recovery efficiencies, which supported values over 85% of As, 92% of Cu, and ≈100% of Mn and Zn from SA. The presence of OM during the loaded stage resulted in a complete recovery of As, Cu, Mn, and Zn when using HCl 0.1 M as eluent.Gobierno regional de Castilla y León (UIC 071, CLU 2017-09 and VA080G18)Ministerio de Ciencia, Innovación y Universidades (project CTQ2017-84006-C3-1-R)Unión Europea - FEDER (CLU 2017-09 and CTQ2017-84006-C3-1-R

Microalgae cultivation for lipids and carbohydrates production

Microalgae are photoautotrophic microorganisms that can produce energy both by using sunlight, water and CO2 (phototrophic metabolism) and by using organic sources such as glucose (heterotrophic metabolism). Heterotrophic growth is a key factor in microalgae research, due to its increased productivity and the lower capital and operative costs compared to photoautotrophic growth in photobioreactors. Carbohydrate production from microalgae is usually investigated for the production of biofuels (e.g. bioethanol) by successive fermentation, but also other applications can be envisaged in biopolymers. In this work an increment in carbohydrate purity after lipid extraction was found. Protein hydrolysis for different microalgae strains (Scenedesmus sp. and Chlorella sp.) was investigated. Microalgae were cultivated under photoautotrophic or heterotrophic conditions, collecting biomass at the end of the growth. Biomass samples were dried or freeze dried and used for carbohydrate and lipid extraction tests. Lipid extraction was achieved using different organic solvents (methanol-chloroform and hexane-2propanol). Basic protein hydrolysis has been carried out testing different temperatures and NaOH concentrations values. Lipids were spectrophotometrically quantified, while residual biomass was saccharificated and the total amount of sugars was measured. Significant differences about the purity of extracted carbohydrates were found comparing dried with freeze dried biomass. However, not a very promising purification of carbohydrates was achieved after protein hydrolysis, asking for further analysis. © Copyright 2017, AIDIC Servizi S.r.l

Utilization of Palm Oil Mill Effluent for Chlorella vulgaris Cultivation Medium under Mixotrophic Condition as Feedstock of Biofuel

Indonesia is largest palm oil producer in the world. Increasing of palm oil influence palm oil mill effluent (POME) production. Several researcher reported that POME is a potential medium for microalgae to grow. Microalgae cultivated in mixotrophic condition has received attention as according to higher biomass and lipid productivity to provide biofuel feedstock. The aim of this research is to study growth of Chlorella vulgaris cultured in POME medium using different organic carbon source under mixotrophic condition. Carbon source (glucose, glycerol, and acetic acid) was added in 0-1.2gr/l concentration in 40% and 100% POME. Biomass was harvested using autoflocculation method, and dry biomass was extracted using ultrasound method to obtain lipid content. Our result revealed that C. vulgaris could grow on mixotrophic condition in POME medium and produce higher biomass and lipid content rather than autotrophic condition. Concentration of organic source also influenced in growth rate and biomass production. This provides a promising process to utilize POME and produce biomass as feedstock of biofuel from microalgae. Keywords: biofuel feedstock; Chlorella vulgaris; Mixotrophic cultivation; POM

Kinetic Modeling and Numerical Simulation as Tools to Scale Microalgae Cell Membrane Permeabilization by Means of Pulsed Electric Fields (PEF) From Lab to Pilot Plants

Pulsed Electric Fields (PEF) is a promising technology for the gentle and energy efficient disruption of microalgae cells such as Chlorella vulgaris. The technology is based on the exposure of cells to a high voltage electric field, which causes the permeabilization of the cell membrane. Due to the dependency of the effective treatment conditions on the specific design of the treatment chamber, it is difficult to compare data obtained in different chambers or at different scales, e.g., lab or pilot scale. This problem can be overcome by the help of numerical simulation since it enables the accessibility to the local treatment conditions (electric field strength, temperature, flow field) inside a treatment chamber. To date, no kinetic models for the cell membrane permeabilization of microalgae are available what makes it difficult to decide if and in what extent local treatment conditions have an impact on the permeabilization. Therefore, a kinetic model for the perforation of microalgae cells of the species Chlorella vulgaris was developed in the present work. The model describes the fraction of perforated cells as a function of the electric field strength, the temperature and the treatment time by using data which were obtained in a milliliter scale batchwise treatment chamber. Thereafter, the model was implemented in a CFD simulation of a pilot-scale continuous treatment chamber with colinear electrode arrangement. The numerical results were compared to experimental measurements of cell permeabilization in a similar continuous treatment chamber. The predicted values and the experimental data agree reasonably well what demonstrates the validity of the proposed model. Therefore, it can be applied to any possible treatment chamber geometry and can be used as a tool for scaling cell permeabilization of microalgae by means of PEF from lab to pilot scale. The present work provides the first contribution showing the applicability of kinetic modeling and numerical simulation for designing PEF processes for the purpose of biorefining microalgae biomass. This can help to develop new processes and to reduce the costs for the development of new treatment chamber designs.DFG, 414044773, Open Access Publizieren 2019 - 2020 / Technische Universität Berli