Microalgal System Research Articles

Comparative study on treatment of kitchen wastewater using a mixed microalgal culture and an aerobic bacterial culture: kinetic evaluation and FAME analysis.

Microalgae-based treatment systems have been successfully used for the polishing of domestic wastewater. Research is underway in studying the suitability of using these systems as main treatment units. This study focuses on comparing the performances of a mixed microalgal culture and an aerobic bacterial culture, based on the kinetic evaluation, in removing organic carbon from a kitchen wastewater. The two systems were operated at six different solid retention times (SRTs)-2, 4, 6, 8, 10, and 12days in continuous mode. The influent and effluent samples were analyzed for chemical oxygen demand (COD), total organic carbon (TOC), total nitrogen (TN), phosphates, and surfactants. Steady-state kinetics (k, Ks, Y, and kd) for organic carbon removal were obtained by fitting experimental data in linearized Michaelis-Menten and Monod equations. The mixed microalgal system showed similar or better performance in COD and TN removal (88 and 85%, respectively) when compared with the COD and TN removal by the aerobic bacterial system (89 and 48%). A maximum lipid yield of 40% (w/w of dry biomass) was observed in the microalgal system. Saturated fatty acids accounted for 50% of the total observed FAME species. The study indicates that the mixed microalgal culture is capable of treating kitchen wastewater and has the potential to replace aerobic bacteria in biological treatment systems in certain cases.

Managing anaerobic digestate from food waste in the urban environment: Evaluating the feasibility from an interdisciplinary perspective

Abstract Anaerobic digestion of food waste within urban areas can generate decentralised renewable energy and support community enterprise activities, thereby contributing to closing the waste-energy-food loop. However, widespread uptake of small-scale, urban anaerobic digestion networks is limited by economic costs and the safe disposal of surplus digestate. This paper uses an interdisciplinary approach to assess the feasibility of anaerobic digestate management through the installation of hydroponics or algae cultivation systems, based on a case study of a micro anaerobic digestion system in London, England. Results show that installing a dewatering sifter together with a hydroponics system is a technically and economically feasible option for digestate enhancement in the urban environment. Its installation is, however, not currently justified for the system under consideration due to cost, regulatory, spatial, and contextual constraints identified using actor-network analysis. Nevertheless, if regulatory and wider contextual issues are accommodated, and more than 30 L of digestate are produced daily, a dewatering and vertical hydroponic system could result in a profit of approximately £100,000 over 10 years. While the microalgal system was also able to upgrade digestate, at present productivity is too low and the capital cost of photobioreactor technology is prohibitively expensive. This underlines the need for technical improvements and low-cost enhancement options to achieve justifiable paybacks until regulatory reforms and the wider economic situation are more favourable to anaerobic digestion treatment within cities.

Nutrient Removal by Suspended and Biofilm Microalgae for Treating the Wastewater of Agro-Industrial Pig Farm

In this study, laboratory-scale suspended and biofilm microalgal systems were constructed under outdoor climatic conditions in Northern Thailand to compare their performances on nutrient nitrogen (N) and phosphorus (P) removal and biomass production from anaerobically digested piggery wastewater. At a cultivation time of 14 days, the results showed that removal efficiencies of nitrogen and phosphorus from digested piggery wastewater in biofilm microalgal system were higher than suspended microalgal system. Biofilm system removed on average of 96 % of TKN-N and 92 % of PO43--P, whereas suspended system removed on average of 84 % of TKN-N and 87 % of PO43--P. Average biomass production achieved 1.17 g dry weight/day for suspended system, while a lower production of 0.78 g dry weight/day was found for biofilm system in which possibly due to a long harvesting frequency of every 2-weeks. Meanwhile, biofilm system has an advantage over suspended system with respect to simple biomass harvesting. This combination of findings demonstrates that biofilm microalgal system is more suitable for removing N and P from digested piggery wastewater than suspended microalgal system. Besides, biomass production in biofilm microalgal system could be further optimized by shorter harvesting frequency and partially harvesting of the biofilm biomass. This study indicates that microalgae offer the potential to recover valuable nutrient resources from piggery wastewater and use biomass for sustainable energy production or other high-value products, which will improve sustainability of agro-industrial wastewater management in the future.

Growing Fresh Water Microalgae in High Ammonium Landfill Leachate

Municipal landfills are being employed for the disposal of communities solid waste. The compacted waste in landfills naturally generate leachate (liquid) which contain high concentrations of ammonium-nitrogen NH4+-N along with other toxic compounds. NH4+-N can be used as a cheap nitrogen source for microalgae biomass production, thereby facilitating tertiary treatment of landfill leachate. Two sets of studies, laboratory scale and pilot scale open raceway pond cultivation, were conducted to evaluate the potential of indigenous fresh water microalgal species to grow in ultra-membrane treated landfill leachate TL and simultaneously remove nutrients (NH4+-N-NO3- etc.). Microalgae growth was better in 50% diluted TL (1.5 gL-1 dry biomass) with 66.27% NH4+-N removal in the lab study. Onsite raceway pond cultivation had reduced biomass growth and nutrient removal. Nitrate-nitrogen NO3-N removal was minimum from both the setups. Microalgal assimilation and nitrification was the main cause of NH4+-N removal from both the setups. When lab study duration was extended, NH4+-N was found to be released back into the leachate medium. Batch cultures (when prolonged) were observed to be not an effective nutrient removal strategy in terms of NH4+-N removal via microalgal system. Further research is needed to optimize microalgal growth and nutrient removal from landfill leachate.

From hybridomas to a robust microalgal-based production platform: molecular design of a diatom secreting monoclonal antibodies directed against the Marburg virus nucleoprotein

BackgroundThe ideal protein expression system should provide recombinant proteins in high quality and quantity involving low production costs only. However, especially for complex therapeutic proteins like monoclonal antibodies many challenges remain to meet this goal and up to now production of monoclonal antibodies is very costly and delicate. Particularly, emerging disease outbreaks like Ebola virus in Western Africa in 2014–2016 make it necessary to reevaluate existing production platforms and develop robust and cheap alternatives that are easy to handle.ResultsIn this study, we engineered the microalga Phaeodactylum tricornutum to produce monoclonal IgG antibodies against the nucleoprotein of Marburg virus, a close relative of Ebola virus causing severe hemorrhagic fever with high fatality rates in humans. Sequences for both chains of a mouse IgG antibody were retrieved from a murine hybridoma cell line and implemented in the microalgal system. Fully assembled antibodies were shown to be secreted by the alga and antibodies were proven to be functional in western blot, ELISA as well as IFA studies just like the original hybridoma produced IgG. Furthermore, synthetic variants with constant regions of a rabbit IgG and human IgG with optimized codon usage were produced and characterized.ConclusionsThis study highlights the potential of microalgae as robust and low cost expression platform for monoclonal antibodies secreting IgG antibodies directly into the culture medium. Microalgae possess rapid growth rates, need basically only water, air and sunlight for cultivation and are very easy to handle.

Carbon dioxide capture strategies from flue gas using microalgae: a review.

Global warming and pollution are the twin crises experienced globally. Biological offset of these crises are gaining importance because of its zero waste production and the ability of the organisms to thrive under extreme or polluted condition. In this context, this review highlights the recent developments in carbon dioxide (CO2) capture from flue gas using microalgae and finding the best microalgal remediation strategy through contrast and comparison of different strategies. Different flue gas microalgal remediation strategies discussed are as follows: (i) Flue gas to CO2 gas segregation using adsorbents for microalgal mitigation, (ii) CO2 separation from flue gas using absorbents and later regeneration for microalgal mitigation, (iii) Flue gas to liquid conversion for direct microalgal mitigation, and (iv) direct flue gas mitigation using microalgae. This work also studies the economic feasibility of microalgal production. The study discloses that the direct convening of flue gas with high carbon dioxide content, into microalgal system is cost-effective.

Evaluation of Agrobacterium-mediated Transformation of Chlamydomonas reinhardtii using a Synthetic amorpha-4, 11-diene Synthase Gene

Amorpha-4,11-diene synthase (ADS) is a key enzyme in biochemical pathway of the antimalarial agent artemisinin. An Agrobacterium-mediated transformation was carried out to express a synthetic ADS gene in green microalga Chlamydomonas reinhardtii strain 125C with bacterial strains GV3101 and LBA4404. The foreign gene was optimized based on codon usage bias of the microalga. Integration of the ADS in nuclear genome of C. reinhardtii was confirmed by polymerase chain reaction assay. The transgenic colonies cultured on selective medium turned yellow after three days and gradually died. Transformation procedure, growth habit of the transgenic microalgae together with probable causes of transformants loss is discussed. The present study is the first investigation for production of ADS enzyme in a microalgal system.

Cloning and characterization of a GPAT-like gene from the microalga Lobosphaera incisa (Trebouxiophyceae): overexpression in Chlamydomonas reinhardtii enhances TAG production

The oleaginous green microalga Lobosphaera (formerly Parietochloris) incisa accumulates high amounts of arachidonic-acid-rich triacylglycerols (TAG), in particular under conditions of nitrogen starvation. This photosynthetic organism is of great interest for studying the mechanisms responsible for storage lipid biosynthesis and the deposition of long-chain polyunsaturated fatty acids (LC-PUFA) in TAG. In this work, we report on cloning a complementary DNA (cDNA) for the putative L. incisa glycerol-3-phosphate acyltransferase (GPAT), whose deduced amino acid sequence features distinctive motives found in those mammalian and Arabidopsis GPAT isoforms that have been implicated in TAG biosynthesis. Temporal analysis of LiGPAT expression in the course of nitrogen starvation showed a positive relationship between changes in the transcript level and patterns of fatty acid production. When expressed in Arabidopsis leaf mesophyll protoplasts, the green fluorescent protein (GFP) fused to the C-terminus of LiGPAT localized outside the chloroplasts in agreement with its predicted extraplastidial localization. Based on an in silico analysis of a deduced amino acid sequence and on similarity to other GPATs participating in TAG biosynthesis, LiGPAT was expressed in the green model microalga Chlamydomonas reinhardtii in order to confirm the predicted function in a heterologous microalgal system. Overexpression of LiGPAT resulted in an up to 50 % increase in the content of TAG on a cell dry weight basis as compared to the control in the stationary phase culture without negative impact on growth parameters. Total fatty acids and TAG of the transformant lines featured an elevated level of oleic acid (18:1 n-9) and a concurrent decrease in C18 PUFA. Additional studies on the acyl substrate preference of LiGPAT are required.

Biological Synthesis of Silver Nanoparticles by Cell-Free Extract ofSpirulina platensis

The present study explores biological synthesis of silver nanoparticles (AgNPs) using the cell-free extract ofSpirulina platensis. Biosynthesised AgNPs were characterised by UV-Vis spectroscopy, SEM, TEM, and FTIR analysis and finally evaluated for antibacterial activity. Extracellular synthesis using aqueous extract ofS. platensisshowed the formation of well scattered, highly stable, spherical AgNPs with an average size of 30–50 nm. The size and morphology of the nanoparticles were confirmed by SEM and TEM analysis. FTIR and UV-Vis spectra showed that biomolecules, proteins and peptides, are mainly responsible for the formation and stabilisation of AgNPs. Furthermore, the synthesised nanoparticles exhibited high antibacterial activity against pathogenic Gram-negative, that is,Escherichia coli, MTCC-9721;Proteus vulgaris, MTCC-7299;Klebsiella pneumoniae, MTCC-9751, and Gram-positive, that is,Staphylococcus aureus, MTCC-9542;S. epidermidis, MTCC-2639;Bacillus cereus, MTCC-9017, bacteria. The AgNPs had shown maximum zone of inhibition (ZOI) that is31.3±1.11inP. vulgaris. Use of such a microalgal system provides a simple, cost-effective alternative template for the biosynthesis of nanomaterials of silver in a large scale that could be of great use in biomedical applications.

English

Various studies have been conducted recently using microalgal system for the production of algal lipid for biodiesel production. This study aimed at increasing the extraction efficiency of algal lipid from Chlorella sp. by the application of Chlorella viruses. The calorific value of lipid from Chlorella sp. has been reported to be higher than that of fresh water microalgae, making it a potential candidate to be used as biofuel. This is the first report on novel application of microalgal viruses for improving the extraction efficiency of algal lipid for biodiesel production through viral lysis of Chlorella vulgaris. The algal lipid extraction efficiency, increased by 11.68% in the case of Chlorella virus treated C. vulgaris when compared with Chlorella virus untreated C. vulgaris. The application of Chlorella virus and the viral encoded lytic enzymes for increasing the extraction efficiency of algal lipid will be helpful in optimizing algal biofuel industry in the future.   Key words: Micro-algal system, biodiesel, algal lipid, Chlorella viruses, viral lysis.

Microalga Scenedesmus sp.: A Potential Low-Cost Green Machine for Silver Nanoparticle Synthesis

Bionanotechnology has revolutionized nanomaterial synthesis by providing a green synthetic platform using biological systems. Among such biological systems, microalgae have tremendous potential to take up metal ions and produce nanoparticles by a detoxification process. The present study explores the intracellular and extracellular biogenic syntheses of silver nanoparticles (SNPs) using the unicellular green microalga Scenedesmus sp. Biosynthesized SNPs were characterized by AAS, UV-Vis spectroscopy, TEM, XRD, FTIR, DLS, and TGA studies and finally checked for antibacterial activity. Intracellular nanoparticle biosynthesis was initiated by a high rate of Ag(+) ion accumulation in the microalgal biomass and subsequent formation of spherical crystalline SNPs (average size, 15-20 nm) due to the biochemical reduction of Ag(+) ions. The synthesized nanoparticles were intracellular, as confirmed by the UV-Vis spectra of the outside medium. Furthermore, extracellular synthesis using boiled extract showed the formation of well scattered, highly stable, spherical SNPs with an average size of 5-10 nm. The size and morphology of the nanoparticles were confirmed by TEM. The crystalline nature of the SNPs was evident from the diffraction peaks of XRD and bright circular ring pattern of SAED. FTIR and UV-Vis spectra showed that biomolecules, proteins and peptides, are mainly responsible for the formation and stabilization of SNPs. Furthermore, the synthesized nanoparticles exhibited high antimicrobial activity against pathogenic gram-negative and gram-positive bacteria. Use of such a microalgal system provides a simple, cost-effective alternative template for the biosynthesis of nanomaterials in a large-scale system that could be of great use in biomedical applications.

Improving the Energy Balance of an Integrated Microalgal Wastewater Treatment Process

The inclusion of a microalgal system in a wastewater treatment flowsheet for residual nutrient uptake can be justified by processing the waste biomass for energy recovery. Low energy harvesting technologies and pre-treatment of the algal biomass are required to improve the overall energy balance of this integrated system. Scenedesmus obliquus and Chlorella sp., achieving nitrogen and phosphorus removal rates higher than 90 %, were used to compare cells recovery efficiency and energy requirements of two energy efficient harvesting systems: dissolved air flotation (DAF) and ballasted dissolved air flotation (BDAF). In addition, thermal hydrolysis was used as a pre-treatment to improve biogas production during anaerobic digestion. The energy required for both systems was then considered to estimate the daily energy demand and efficiency of two microalgae wastewater treatment plants with a capacity of 25,000 and 230,000 p.e., respectively. Overall, a high algal cells recovery efficiency (99 %) was achieved using low energy demand (0.04 kWh m−3 for BDAF) and a coagulant dose reduction between 42 and 50 % depending on the algal strain. Anaerobic digestion of pre-treated S. obliquus showed a threefold increase in methane yield. Compared to a traditional activated sludge process, the additional tertiary microalgal treatment generates an integrated process potentially able to achieve up to 76 % energy efficiency.

Microalgae as bioreactors for bioplastic production

BackgroundPoly-3-hydroxybutyrate (PHB) is a polyester with thermoplastic properties that is naturally occurring and produced by such bacteria as Ralstonia eutropha H16 and Bacillus megaterium. In contrast to currently utilized plastics and most synthetic polymers, PHB is biodegradable, and its production is not dependent on fossil resources making this bioplastic interesting for various industrial applications.ResultsIn this study, we report on introducing the bacterial PHB pathway of R. eutropha H16 into the diatom Phaeodactylum tricornutum, thereby demonstrating for the first time that PHB production is feasible in a microalgal system. Expression of the bacterial enzymes was sufficient to result in PHB levels of up to 10.6% of algal dry weight. The bioplastic accumulated in granule-like structures in the cytosol of the cells, as shown by light and electron microscopy.ConclusionsOur studies demonstrate the great potential of microalgae like the diatom P. tricornutum to serve as solar-powered expression factories and reveal great advantages compared to plant based production systems.

Bio-mitigation of CO 2, calcite formation and simultaneous biodiesel precursors production using Chlorella sp.

In this study, an attempt was made to use micro-algal system for the production of biodiesel precursors and simultaneous CO 2 mitigation. Chlorella sp. was found to have a higher growth rate as compared to the other algal species tested namely Chlamydomonas sp. and Synnecococcus sp. At different CO 2 concentrations (0.03%, 3%, 10% and 15%), the lipid productivity was 23.0, 20.0 and 27.3 mg/L/d respectively. Calcite produced was characterized using FT-IR, SEM and XRD. The FAME in crude biofuel was analyzed by GC-FID that found to contain palmitic acid (C16:0), docosapentaenoic acid (C22:5) and docosahexaenoic acid (C22:6). The calorific value of Chlorella sp. was found to be 29 kJ/g which is higher than values reported for fresh water microalgae making it a potential candidate to be used as an alternate fuel.

The influence of ferrous-complexed EDTA as a solubilization agent and its auto-regeneration on the removal of nitric oxide gas through the culture of green alga Scenedesmus sp

The influence of iron-complexed ehylenediaminetetraacetic acid (EDTA) was studied on nitric oxide (NO) removal using photoautotropic cultivation of green alga Scenedesmus. Fe(II)EDTA is an active solubilization agent of NO in water, while the oxidized Fe(III)EDTA is not. When a gas mixture containing 300 ppm NO was treated through the Scenedesmus culture containing 5 mM Fe(II)EDTA, a constant level of 80–85% NO removal was achieved for a prolonged period. A certain fraction of Fe(II)EDTA remained without being oxidized to Fe(III)EDTA because of the existence of reversible oxidation–reduction balance between Fe(II)EDTA and Fe(III)EDTA. When Fe(III)EDTA was added to the culture instead of Fe(II)EDTA, Fe(II) was generated via reduction of Fe(III), resulting in the increase of NO removal and cell density. This was possible because of the generated Fe(II)EDTA which contributed to the dissolution of NO. Therefore, a long-term NO removal was possible with Fe(III)EDTA, as well as with Fe(II)EDTA, in the present microalgal system. The supplementation of free EDTA was necessary to extend the period of NO removal because EDTA is consumed by biodegradation while the decrease of total iron content was not significant.

Effect of basicity on coagulation performance of polyferric chloride applied in eutrophicated raw water

Effects of the basicity of polyferric chloride (PFC) on the removal efficiencies of algal cell, turbidity and humic acid (HA) contained in eutrophicated raw water were investigated and the mechanisms were explored. The removal efficiency of both algae cells and clay particles increased gently at three different PFC dosages as the PFC basicity increased from 0 to 2.4. Adsorption of PFC species on algae and clay was the major mechanism contributing to the removal of algae and clay. PFC with a higher basicity underwent a lessened further hydrolysis when contacted with the water and resulted in less residual iron. The basicity of PFC influenced the characteristics of flocs, such as density, stability and color, when PFC was applied to remove algae. The presence of algae species with either small size or special shape made the removal of algae more difficult compared to the removal of single algae species. PFC with basicity no less than 2.0 was necessary for removing algae from micro-algal system to achieve a high removal efficiency. The optimum removal of HA was achieved at PFC basicity of 0.8 and HA removal kept almost stable with further increase in PFC basicity. The distribution of iron species in PFC solution as a function of basicity was determined in this study to better understand the mechanism of pollutants removal by PFC.

Novel technology in pollutant removal at source and bioremediation

Sewage disposal is a major environmental issue in both developed and developing countries and removal of pollutants such as organic matter, nutrients, heavy metals and persistent organic compounds is required to protect the environment. Novel biological systems using constructed mangrove wetland and immobilized microalgal beads have been developed as alternative systems for treating different types of sewage and pollution at source. The feasibility and efficiency of constructed mangrove wetland to remove organic matter and nutrients from primary settled municipal sewage were demonstrated through a series of greenhouse experiments and a pilot-scale field trial. The treatment efficiency of constructed mangrove wetland was comparable to, or higher than, the conventional constructed wetland. An immobilized microalgal system was developed to remove toxic persistent pollutants from industrial wastewater. Pollutant-resistant microalgal species were selected for culture in domestic wastewater. The harvested biomass was immobilized in alginate beads. Bench-scale experiments showed the algal beads were effective in removing industrial pollutants such as heavy metals (e.g. Cu, Zn, Ni, Cr, etc.), organometallic compounds (e.g. tributyltin, TBT), and persistent organic compounds (e.g. polycyclic aromatic hydrocarbons, PAHs) through biosorption and biodegradation. The adsorbed metals could be recovered by desorption process, and the beads could be used repeatedly for many adsorption–desorption cycles.

Astaxanthin biosynthesis from simultaneous N and P uptake by the green alga Haematococcus pluvialis in primary-treated wastewater

An alternative microalgal system for biological wastewater treatment is proposed for both the removal of nitrogen and phosphorus from wastewater and the production of a valuable carotenoid, astaxanthin. The system consists of sequential photoautotrophic cultivation and induction processes using the green alga Haematococcus pluvialis. The Haematococcus process was applied to primary-treated sewage (PTS) and primary-treated piggery wastewater (PTP) with serial dilution. H. pluvialis grew well on PTS and PTP diluted four-fold, resulting in the successful removal of nitrogen and phosphorus from both wastewaters. At that time, cell growth rates were comparable to those in the algal-defined NIES-C medium. Following the cultivation stage, N-deprived vegetative cells were transformed under photoautotrophic induction by continuous feeding of both CO 2-mixed gas and intense light to red aplanospores with substantial astaxanthin contents. The resulting astaxanthin contents accounted for about 5.1 and 5.9% of the total biomass of the PTS and PTP cultures, respectively. Our results indicate the potential of the proposed Haematococcus process as a subsidiary wastewater treatment technology with the capability of biosynthesizing the high-value antioxidant astaxanthin.

A novel micro-algal system for energy production with nitrogen recycling

A novel micro-algal system for energy production with nitrogen recycling

A novel microalgal system for energy production with nitrogen cycling

A microalga, Chlorella vulgaris, could grow in the recovered solution from the low temperature catalytic gasification of itself, by which methane rich fuel gas was obtained. All nitrogen in the microalga was converted to ammonia during the gasification, and the recovered solution, in which ammonia was dissolved, could be used as nitrogen nutrient. The result of the energy evaluation indicated that the novel microalgal system for energy production with nitrogen cycling could be created.