Screening and comparative metabolic profiling of high lipid content microalgae strains for application in wastewater treatment

Feasibility and efficiency of microalgae cultivation for nutrient recycling and energy recovery from food waste filtrate

With the continuous growth of economic and population, the generation of food waste has significantly increased in recent years. The disposition of food waste, typically through incineration or landfill, can lead to severe health and environmental problems, accompanied by high additional costs. However, the leachate produced from food waste during collection, transportation and landfill operations predominantly contains high levels of nutrients necessary for microalgae growth. The integration of microalgae cultivation into waste treatment for nutrient recycling presents a potential route for energy recovery from food waste. Therefore, this study was conducted to evaluate the feasibility of microalgae cultivation for food waste filtrate treatment. In addition, the optimal cultivation conditions and nutrient removal efficiency for microalgae in food waste filtrate treatment were investigated. The results indicated that Cyanobacterium aponinum exhibited the highest growth rate (0.530 cells d-1) and maximum cell density (9.6 × 106 cells mL-1) among eight potential microalgal species in 10% food waste filtrate treatment under 10,000 lux and 32°C. It was also observed that C. aponinum had significantly higher biomass productivity and nutrient removal efficiency under a 5% CO2 concentration. The successful cultivation of C. aponinum demonstrated that food waste filtrate could be a promising growth medium, reducing the high cost of cultivation with synthetic medium. However, further efforts should be made to utilize microalgae in food waster filtrate treatment, transitioning from laboratory condition to a pilot scale.

Molecular genetic and morphological characteristics of Micractinium thermotolerans and M. inermum (Trebouxiophyceae, Chlorophyta) from pyroclastic deposits of the Kamchatka Peninsula (Russia)

During the study of algal diversity in pyroclastic deposits of the Kamchatka Peninsula, Chlorella-like green algae strains VCA-72 and VCA-93 were isolated from samples collected from along the Baydarnaya river bed on the Shiveluch volcano in 2018 and at the outlet of thermal vapors along the edge of the caldera on the southern slope of the Gorely volcano in 2020. Identification of the strains was carried out within the framework of an integrative approach using microscopic and molecular genetic methods, including preliminary taxon identification, obtaining nucleotide sequences of the small subunit and the internal transcribed spacer rRNA, reconstruction of phylogenetic trees and secondary structures of the ITS1 and ITS2 rRNA regions. On the phylogenetic tree, strain VCA-93 was clustered in the Micractinium thermotolerans species clade. No differences were found when comparing the helical domain models of ITS1 and ITS2 in M. thermotolerans. Strain VCA-72 occupied a basal position in the M. inermum clade. The secondary structure patterns of the helices of strain VCA-72 were generally similar to those of M. inermum, but intraspecific variability was noted, mainly due to substitutions in the apical and lateral loops. Five hCBC substitutions were found in the helical regions of the studied M. inermum strains, while no CBC substitutions were found. A detailed analysis of morphology and life cycle allowed us to identify the characteristics of the cells in aging cultures: their size was significantly higher than in vegetative ones and they were pear-shaped, oval, and ellipsoidal with a shallow, wide constriction in the center. In addition, cells with colorless lipid droplets were detected in aging cultures of both species. The ability to synthesize and accumulate lipids indicates the great potential of the strains for the production of biodiesel fuel. A review of the habitats of previous and new findings allowed us to note the ecological plasticity of the studied species. The results obtained complement the information on the biogeography of the species: this is the first record of M. inermum for the territory of Russia, and that of M. thermotolerans, for the Kamchatka Peninsula.

Perspectives on cultivation and harvesting technologies of microalgae, towards environmental sustainability and life cycle analysis

The development of algae is seen as a potential and ecologically sound approach to address the increasing demands in multiple sectors. However, successful implementation of processes is highly dependent on effective growing and harvesting methods. The present study provides a complete examination of contemporary techniques employed in the production and harvesting of algae, with a particular emphasis on their sustainability. The review begins by examining several culture strategies, encompassing open ponds, closed photobioreactors, and raceway ponds. The analysis of each method is conducted in a systematic manner, with a particular focus on highlighting their advantages, limitations, and potential for expansion. This approach ensures that the conversation is in line with the objectives of sustainability. Moreover, this study explores essential elements of algae harvesting, including the processes of cell separation, dewatering, and biomass extraction. Traditional methods such as centrifugation, filtration, and sedimentation are examined in conjunction with novel, environmentally concerned strategies including flocculation, electro-coagulation, and membrane filtration. It evaluates the impacts on the environment that are caused by the cultivation process, including the usage of water and land, the use of energy, the production of carbon dioxide, and the runoff of nutrients. Furthermore, this study presents a thorough examination of the current body of research pertaining to Life Cycle Analysis (LCA) studies, presenting a perspective that emphasizes sustainability in the context of algae harvesting systems. In conclusion, the analysis ends up with an examination ahead at potential areas for future study in the cultivation and harvesting of algae. This review is an essential guide for scientists, policymakers, and industry experts associated with the advancement and implementation of algae-based technologies.

Plants, Cells, Algae, and Cyanobacteria In Vitro and Cryobank Collections at the Institute of Plant Physiology, Russian Academy of Sciences-A Platform for Research and Production Center

Ex situ collections of algae, cyanobacteria, and plant materials (cell cultures, hairy and adventitious root cultures, shoots, etc.) maintained in vitro or in liquid nitrogen (-196 °C, LN) are valuable sources of strains with unique ecological and biotechnological traits. Such collections play a vital role in bioresource conservation, science, and industry development but are rarely covered in publications. Here, we provide an overview of five genetic collections maintained at the Institute of Plant Physiology of the Russian Academy of Sciences (IPPRAS) since the 1950-1970s using in vitro and cryopreservation approaches. These collections represent different levels of plant organization, from individual cells (cell culture collection) to organs (hairy and adventitious root cultures, shoot apices) to in vitro plants. The total collection holdings comprise more than 430 strains of algae and cyanobacteria, over 200 potato clones, 117 cell cultures, and 50 strains of hairy and adventitious root cultures of medicinal and model plant species. The IPPRAS plant cryobank preserves in LN over 1000 specimens of in vitro cultures and seeds of wild and cultivated plants belonging to 457 species and 74 families. Several algae and plant cell culture strains have been adapted for cultivation in bioreactors from laboratory (5-20-L) to pilot (75-L) to semi-industrial (150-630-L) scale for the production of biomass with high nutritive or pharmacological value. Some of the strains with proven biological activities are currently used to produce cosmetics and food supplements. Here, we provide an overview of the current collections' composition and major activities, their use in research, biotechnology, and commercial application. We also highlight the most interesting studies performed with collection strains and discuss strategies for the collections' future development and exploitation in view of current trends in biotechnology and genetic resources conservation.

Geobacter sulfurreducens' Unique Metabolism Results in Cells with a High Iron and Lipid Content

Geobacter sulfurreducens is a ubiquitous iron-reducing bacterium in soils, and in engineered systems, it can respire an electrode to produce measurable electric current. Its unique metabolism, heavily dependent on an extensive network of cytochromes, requires a unique cell composition. In this work, we used metallomics, cell fraction and elemental analyses, and transcriptomics to study and analyze the cell composition of G. sulfurreducens. Elemental composition studies (C, H, O, N, and ash content) showed high C:O and H:O ratios of approximately 1.7:1 and 0.25:1, indicative of more reduced cell composition that is consistent with high lipid content. Our study shows that G. sulfurreducens cells have a large amount of iron (2 ± 0.2 μg/g dry weight) and lipids (32 ± 0.5% dry weight/dry weight) and that this composition does not change whether the cells are grown with a soluble or an insoluble electron acceptor. The high iron concentration, higher than similar microorganisms, is attributed to the production of cytochromes that are abundant in transcriptomic analyses in both solid and soluble electron acceptor growth. The unique cell composition of G. sulfurreducens must be considered when growing this microorganism for lab studies and commercial applications. IMPORTANCE Geobacter sulfurreducens is an electroactive microorganism. In nature, it grows on metallic minerals by transferring electrons to them, effectively "breathing" metals. In a manmade system, it respires an electrode to produce an electric current. It has become a model organism for the study of electroactive organisms. There are potential biotechnological applications of an organism that can bridge the gap between biology and electrical signal and, as a ubiquitous iron reducer in soils around the world, G. sulfurreducens has an impact on the global iron cycle. We measured the concentrations of metals, macromolecules, and basic elements in G. sulfurreducens to define this organism's composition. We also used gene expression data to discuss which proteins those metals could be associated with. We found that G. sulfurreducens has a large amount of lipid and iron compared to other bacteria-these observations are important for future microbiologists and biotechnologists working with the organism.

Removal of Antibiotic Resistance Genes, Class 1 Integrase Gene and Escherichia coli Indicator Gene in a Microalgae-Based Wastewater Treatment System

Microalgae-based wastewater treatment systems (AWWTS) have recently shown promise in the mitigation of antibiotic resistance genes (ARGs) from municipal wastewater (MWW). However, due to the large number of ARGs that exist in MWW, the use of indirect conventional water quality parameters to monitor ARGs reduction in wastewater would make the process less burdensome and economically affordable. In order to establish a robust relationship between the ARGs and water quality parameters, the current study employed different microalgae strains in monoculture (CM2, KL10) and multi-species combinations (CK and WW) for the MWW treatment under outdoor environmental conditions. The studied genes were quantified in the MWW influents and effluents using real-time PCR. All the cultures substantially improved the physicochemical qualities of the MWW. Out of the 14 genes analyzed in this study, tetO, tetW, tetX and ermB were decreased beyond detection within the first 4 days of treatment in all the cultures. Other genes, including blaCTX, sul1, cmlA, aadA, int1 and uidA were also decreased beyond a 2 log reduction value (LRV). The mobile genetic element, int1, correlated positively with most of the ARGs, especially sul1 (r ≤ 0.99, p < 0.01) and aadA (r ≤ 0.97, p < 0.01). Similarly, the Escherichia coli indicator gene, uidA, correlated positively with the studied genes, especially with aadA, blaCTX, blaTEM and cmlA (r ≤ 0.99 for each, p < 0.01). Some of the studied genes also correlated positively with total dissolved solids (TDS) (r ≤ 0.98, p < 0.01), and/or negatively with total suspended solids (TSS) (r ≤ −0.98, p < 0.01) and pH (r ≤ −0.98, p < 0.01). Among the tested cultures, both monocultures, i.e., KL10 and CM2 were found to be more consistent in gene suppression than their multi-species counterparts. The findings revealed water quality parameters such as TDS, TSS and E. coli as reliable proxies for ARGs mitigation in AWWTS and further highlight the superiority of monocultures over multi-species cultures in terms of gene suppression from the MWW stream.

Novel microalgae strains from selected lower Himalayan aquatic habitats as potential sources of green products

Microalgal biomass provides a renewable source of biofuels and other green products. However, in order to realize economically viable microalgal biorefinery, strategic identification and utilization of suitable microalgal feedstock is fundamental. Here, a multi-step suboptimal screening strategy was used to target promising microalgae strains from selected freshwaters of the study area. The resulting strains were found to be affiliated to seven closely-related genera of the family Scenedesmaceae, as revealed by both morphologic and molecular characterization. Following initial screening under upper psychrophilic to optimum mesophilic (irregular temperature of 14.1 to 35.9°C) cultivation conditions, superior strains were chosen for further studies. Further cultivation of the selected strains under moderate to extreme mesophilic cultivation conditions (irregular temperature of 25.7 to 42.2°C), yielded up to 74.12 mgL^-1day^-1, 19.96 mgL^-1day^-1, 48.56%, 3.34 μg/mL and 1.20 μg/mL, for biomass productivity, lipid productivity, carbohydrate content, pigments content and carotenoids content respectively. These performances were deemed promising compared with some previous, optimum conditions-based reports. Interestingly, the fatty acids profile and the high carotenoids content of the studied strains revealed possible tolerance to the stress caused by the changing suboptimal cultivation conditions. Overall, strains AY1, CM6, LY2 and KL10 were exceptional and may present sustainable, promising feedstock for utilization in large-scale generation of green products, including biodiesel, bioethanol, pigments and dietary supplements. The findings of this study, which exposed promising, eurythermal strains, would expand the current knowledge on the search for promising microalgae strains capable of performing under the largely uncontrolled large-scale cultivation settings.

Evaluation of the effects of input variables on the growth of two microalgae classes during wastewater treatment

Wastewater treatment carried out by microalgae is usually affected by the type of algal strain and the combination of cultivation parameters provided during the process. Every microalga strain has a different tolerance level towards cultivation parameters, including temperature, pH, light intensity, CO2 content, initial inoculum level, pretreatment method, reactor type and nutrient concentration in wastewater. Therefore, it is vital to supply the right combination of cultivation parameters to increase the wastewater treatment efficiency and biomass productivity of different microalgae classes. In the current investigation, the decision tree was used to analyse the dataset of class Trebouxiophyceae and Chlorophyceae. Various combinations of cultivation parameters were determined to enhance their performance in wastewater treatment. Nine combinations of cultivation parameters leading to high biomass production and eleven combinations each for high nitrogen removal efficiency and high phosphorus removal efficiency for class Trebouxiophyceae were detected by decision tree models. Similarly, eleven combinations for high biomass production, nine for high nitrogen removal efficiency, and eight for high phosphorus removal efficiency were detected for class Chlorophyceae. The results obtained through decision tree analysis can provide the optimum conditions of cultivation parameters, saving time in designing new experiments for treating wastewater at a large scale.

Co-culture of microalga Chlorella sorokiniana with syntrophic Streptomyces thermocarboxydus in cassava wastewater for wastewater treatment and biodiesel production

This study aimed to conduct a co-culture of a microalga and syntrophic actinomycetes to treat cassava a biogas effluent wastewater and enhance biodiesel production. Streptomyces thermocarboxydus strain BMI 10 produced the greatest effect on biomass production by Chlorella sorokiniana strain P21. Maximal algal biomass production and total lipid yield were increased when strain BMI 10 was co-cultured (by 21 and 25 %, respectively). Furthermore, the nutrient removal efficiency of P21 was not significantly different under sterilized and unsterilized conditions. Harvestability of the strain was also increased under both conditions. Analysis of the amount and composition of fatty acids from this co-culture biomass revealed that it was quite satisfactory for biodiesel production (54.11-61.52% saturated fatty acids with a 0.59-0.82 degree of unsaturation). Overall, the results showed the co-culture of the alga and bacterium is a holistic enhancement that couples wastewater treatment with biodiesel production.

Metabolomics-based engineering for biofuel and bio-based chemical production in microalgae and cyanobacteria: A review

Metabolomics, an essential tool in modern synthetic biology based on the design-build-test-learn platform, is useful for obtaining a detailed understanding of cellular metabolic mechanisms through comprehensive analyses of the metabolite pool size and its dynamic changes. Metabolomics is critical to the design of a rational metabolic engineering strategy by determining the rate-limiting reaction and assimilated carbon distribution in a biosynthetic pathway of interest. Microalgae and cyanobacteria are promising photosynthetic producers of biofuels and bio-based chemicals, with high potential for developing a bioeconomic society through bio-based carbon neutral manufacturing. Metabolomics technologies optimized for photosynthetic organisms have been developed and utilized in various microalgal and cyanobacterial species. This review provides a concise overview of recent achievements in photosynthetic metabolomics, emphasizing the importance of microalgal and cyanobacterial cell factories that satisfy industrial requirements.

A High-Throughput Assay for Quantifying Phenotypic Traits of Microalgae

High-throughput methods for phenotyping microalgae are in demand across a variety of research and commercial purposes. Many microalgae can be readily cultivated in multi-well plates for experimental studies which can reduce overall costs, while measuring traits from low volume samples can reduce handling. Here we develop a high-throughput quantitative phenotypic assay (QPA) that can be used to phenotype microalgae grown in multi-well plates. The QPA integrates 10 low-volume, relatively high-throughput trait measurements (growth rate, cell size, granularity, chlorophyll a, neutral lipid content, silicification, reactive oxygen species accumulation, and photophysiology parameters: ETRmax, Ik, and alpha) into one workflow. We demonstrate the utility of the QPA on Thalassiosira spp., a cosmopolitan marine diatom, phenotyping six strains in a standard nutrient rich environment (f/2 media) using the full 10-trait assay. The multivariate phenotypes of strains can be simplified into two dimensions using principal component analysis, generating a trait-scape. We determine that traits show a consistent pattern when grown in small volume compared to more typical large volumes. The QPA can thus be used for quantifying traits across different growth environments without requiring exhaustive large-scale culturing experiments, which facilitates experiments on trait plasticity. We confirm that this assay can be used to phenotype newly isolated diatom strains within 4 weeks of isolation. The QPA described here is highly amenable to customisation for other traits or unicellular taxa and provides a framework for designing high-throughput experiments. This method will have applications in experimental evolution, modelling, and for commercial applications where screening of phytoplankton traits is of high importance.

Exotic Hydrogel Matrix as an Efficient Platform for Sustainable Production of Biomass and Lipid from Chlorella sorokiniana

Concerning the climate crisis, energy disaster, and greenhouse effects, microalgae have paved the way for consideration as a biofuel feed material. The advent of polymeric materials with unique architecture at nanoscale, in combination with microalgae, has given direction for the bioeconomic yield of highly valued compounds, essentially lipid. Herein, we discuss the paramount significance of exotic hydrogel matrix (HM) with efficient violet light absorption, far-red emission, CO₂-adsorbing capability and catalyst-free condition that could increase the photosynthesis activity, alleviating the microalgal growth for the effective augmentation of lipid, protein, and chlorophyll. The intrinsic morphological and structural features of HM were revealed by a suite of characterizations that confirm its hollow tubular architecture. Fluorescence intensity measurement confirmed the electron transfer from HM to Chlorella sorokiniana, accelerating the photosynthetic rate for the improved production of lipids (98%), proteins (60%), and chlorophyll a (121%), compared to untreated C. sorokiniana control cells. Moreover, by visualizing the Nile red (NR) fluorescence response from C. sorokiniana/HM cells, a high lipid content was observed with a larger cell size (14.6 μm) compared to control cells (8.7 μm). Fatty acid methyl esters (FAMEs), obtained from C. sorokiniana/HM, were noted with a large-scale volume of C16:C18 fatty acids (>80%). We, therefore, envisage that HM plays a significant role in enhancing the generation of lipids and proteins from C. sorokiniana. These outcomes assure a qualitative transit in the bioenergy domain.

Waste biorefinery towards a sustainable circular bioeconomy: a solution to global issues

Global issues such as environmental problems and food security are currently of concern to all of us. Circular bioeconomy is a promising approach towards resolving these global issues. The production of bioenergy and biomaterials can sustain the energy-environment nexus as well as substitute the devoid of petroleum as the production feedstock, thereby contributing to a cleaner and low carbon environment. In addition, assimilation of waste into bioprocesses for the production of useful products and metabolites lead towards a sustainable circular bioeconomy. This review aims to highlight the waste biorefinery as a sustainable bio-based circular economy, and, therefore, promoting a greener environment. Several case studies on the bioprocesses utilising waste for biopolymers and bio-lipids production as well as bioprocesses incorporated with wastewater treatment are well discussed. The strategy of waste biorefinery integrated with circular bioeconomy in the perspectives of unravelling the global issues can help to tackle carbon management and greenhouse gas emissions. A waste biorefinery-circular bioeconomy strategy represents a low carbon economy by reducing greenhouse gases footprint, and holds great prospects for a sustainable and greener world.

High-throughput proteomics and metabolomic studies guide re-engineering of metabolic pathways in eukaryotic microalgae: A review

Eukaryotic microalgae are a rich source of commercially important metabolites including lipids, pigments, sugars, amino acids and enzymes. However, their inherent genetic potential is usually not enough to support high level production of metabolites of interest. In order to move on from the traditional approach of improving product yields by modification of the cultivation conditions, understanding the metabolic pathways leading to the synthesis of the bioproducts of interest is crucial. Identification of new targets for strain engineering has been greatly facilitated by the rapid development of high-throughput sequencing and spectroscopic techniques discussed in this review. Despite the availability of high throughput analytical tools, examples of gathering and application of proteomic and metabolomic data for metabolic engineering of microalgae are few and mainly limited to lipid production. The present review highlights the application of contemporary proteomic and metabolomic techniques in eukaryotic microalgae for redesigning pathways for enhanced production of algal metabolites.

Phyco-remediation of swine wastewater as a sustainable model based on circular economy

Pork production has expanded in the world in recent years. This growth has caused a significant increase in waste from this industry, especially of wastewater. Although there has been an increase in wastewater treatment, there is a lack of useful technologies for the treatment of wastewater from the pork industry. Swine farms generate high amounts of organic pollution, with large amounts of nitrogen and phosphorus with final destination into water bodies. Sadly, little attention has been devoted to animal wastes, which are currently treated in simple systems, such as stabilization ponds or just discharged to the environment without previous treatment. This uncontrolled release of swine wastewater is a major cause of eutrophication processes. Among the possible treatments, phyco-remediation seems to be a sustainable and environmentally friendly option of removing compounds from wastewater such as nitrogen, phosphorus, and some metal ions. Several studies have demonstrated the feasibility of treating swine wastewater using different microalgae species. Nevertheless, the practicability of applying this procedure at pilot-scale has not been explored before as an integrated process. This work presents an overview of the technological applications of microalgae for the treatment of wastewater from swine farms and the by-products (pigments, polysaccharides, lipids, proteins) and services of commercial interest (biodiesel, biohydrogen, bioelectricity, biogas) generated during this process. Furthermore, the environmental benefits while applying microalgae technologies are discussed.

Production of biodiesel and succinic acid from the biomass of the microalga Micractinium sp. IC-44

In this study, a combined approach to produce fatty acid methyl esters (FAMEs) and succinic acid from the biomass of the microalga Micractinium sp. IC-44 using ionic liquids (ILs) was presented. After 22 days of cultivation, the biomass productivity was 0.034 ± 0.001 g L^-1day^-1, and the lipid content was 11.5 ± 0.5%. Direct biomass transesterification using H₂SO₄ in the presence of IL [BMIM][HSO₄] resulted in a FAME yield of 42.0 ± 4.3%, which exceeded the yields obtained after transesterification of extracted lipids (20.5 ± 3.5% using ILs and 27.1 ± 2.4% using methanol/chloroform) and direct biomass transesterification without using ILs (31.6 ± 1.7%). The residual biomass obtained after direct transesterification using ILs was subjected to acid hydrolysis (sugar yield was 81.1 ± 2.4%). The purified hydrolysate was fermented using Actinobacillus succinogenes 130Z to obtain a succinic acid yield of 0.67 g g^-1 of fermentable sugars. Therefore, this study demonstrated the successful conversion of the Micractinium sp. IC-44 biomass into biodiesel and succinic acid.

Assessment of biomass potentials of microalgal communities in open pond raceways using mass cultivation

Metagenome studies have provided us with insights into the complex interactions of microorganisms with their environments and hosts. Few studies have focused on microalgae-associated metagenomes, and no study has addressed aquatic microalgae and their bacterial communities in open pond raceways (OPRs). This study explored the possibility of using microalgal biomasses from OPRs for biodiesel and biofertilizer production. The fatty acid profiles of the biomasses and the physical and chemical properties of derived fuels were evaluated. In addition, the phenotype-based environmental adaptation ability of soybean plants was assessed. The growth rate, biomass, and lipid productivity of microalgae were also examined during mass cultivation from April to November 2017. Metagenomics analysis using MiSeq identified ∼127 eukaryotic phylotypes following mass cultivation with (OPR 1) or without (OPR 3) a semitransparent film. Of these, ∼80 phylotypes were found in both OPRs, while 23 and 24 phylotypes were identified in OPRs 1 and 3, respectively. The phylotypes belonged to various genera, such as Desmodesmus, Pseudopediastrum, Tetradesmus, and Chlorella, of which, the dominant microalgal species was Desmodesmus sp. On average, OPRs 1 and 3 produced ∼8.6 and 9.9 g m⁻² d⁻¹ (0.307 and 0.309 DW L⁻¹) of total biomass, respectively, of which 14.0 and 13.3 wt% respectively, was lipid content. Fatty acid profiling revealed that total saturated fatty acids (mainly C16:0) of biodiesel obtained from the microalgal biomasses in OPRs 1 and 3 were 34.93% and 32.85%, respectively; total monounsaturated fatty acids (C16:1 and C18:1) were 32.40% and 31.64%, respectively; and polyunsaturated fatty acids (including C18:3) were 32.68% and 35.50%, respectively. Fuel properties determined by empirical equations were within the limits of biodiesel standards ASTM D6751 and EN 14214. Culture solutions with or without microalgal biomasses enhanced the environmental adaptation ability of soybean plants, increasing their seed production. Therefore, microalgal biomass produced through mass cultivation is excellent feedstock for producing high-quality biodiesel and biofertilizer.

Auto-flocculation microalgae species Tribonema sp. and Synechocystis sp. with T-IPL pretreatment to improve swine wastewater nutrient removal

It is recognized coupling microalgae, which is rich in lipids or protein with wastewater treatment offers extra economic benefits that can potentially make microalgal production feasible by reducing production costs and providing environmental benefits. However, the pretreatment of high concentration nutrients such as ammonia nitrogen (NH₃-N), total phosphorus (TP) and chemical oxygen demand (COD) in swine wastewater is the premise of application for microalgae in wastewater treatment. This study two auto-flocculation microalgae Tribonema sp. and Synechocystis sp. were selected for evaluation; they were cultivated in diluted swine wastewater together after it was pretreated with titanium dioxide (TiO₂) plus intense pulsed light (T-IPL). The results showed that the growth of the two strains in the wastewater pretreated with T-IPL grew better than when grown without the pretreatment. The content of lipid in the two algae, cultured in the pretreated wastewater, was also higher than the lipid content from the un-pretreated wastewater; but protein content was lower. Overall, the removal efficiencies of pollutants NH₃-N, TP, and COD by the two microalgae in anaerobic digestion of swine wastewater (ADSW) with T-IPL pretreatment, were higher than the removal efficiencies without pretreatment. This research also indicates that these two auto-flocculation microalgae have the potential to reduce harvesting costs. And, using T-IPL to pretreat wastewater could provide a promising method for the pretreatment of wastewater.

Effect of two lignocellulose related sugar alcohols on the growth and metabolites biosynthesis of Euglena gracilis

It is an effective solution to overcome the bottlenecks of commercial production of microalgal biomass by providing cost-effective and environment-friendly organic carbon sources for microalgal mixotrophic growth. In this study, effects of lignocellulose-related mannitol and xylitol on the growth, photosynthetic pigment content, cell morphology, and metabolites biosynthesis of freshwater microalga Euglena gracilis were investigated. The results revealed that both mannitol and xylitol effectively promoted the growth of E. gracilis, and at the optimal dosage of 4 g·L^-1, the biomass yield was increased by 4.64-fold and 3.18-fold, respectively. Increase of cell aspect ratio was only observed in mannitol treatment groups, indicating that E. gracilis had different physiological responses to mannitol and xylitol. Fourier transform infrared spectroscopy combined with multivariate analysis was applied to analyze the cellular components. The lipid content of E. gracilis was significantly promoted by these two sugar alcohols, which would increase its potential in biofuel production.

Finding of phytase: Understanding growth promotion mechanism of phytic acid to freshwater microalga Euglena gracilis

To better understand the promotion effect of phytic acid and its uptake mechanism in freshwater microalga Euglena gracilis, cell growth, photosynthetic pigment content and cell morphology of E. gracilis were evaluated under four conditions: phosphorus deficient group (CMP-), single phosphate treatment group (CMP+), single phytic acid treatment group (CMPA-), and phosphate-phytic acid mixed treatment group (CMPA+). The results showed that phytic acid could serve as the sole phosphorus source for the growth of E. gracilis, and phytase which catalyzes the hydrolysis of phytic acid was discovered for the first time in E. gracilis. Fourier transform infrared spectroscopy combined with multivariate analysis showed the good recognition of metabolites from different culture conditions especially focusing on relative carbohydrate or lipid contents. Phytic acid derived from agro-wastes is a cheap growth promoter for E. gracilis, and this E. gracilis with high nutritional value is applicable to animal feed while minimizing environmental impact.

Using a mixture of wastewater and seawater as the growth medium for wastewater treatment and lipid production by the marine diatom Phaeodactylum tricornutum

This study was conducted to evaluate the potential of the marine diatom Phaeodactylum tricornutum in nutrient removal coupled with biodiesel production using different ratios of mixed municipal wastewater (MW) and seawater (SW) as the growth medium. The results indicated that P. tricornutum exhibited high nutrient removal efficiency with the ratios of MW: SW = 1:1 and MW: SW = 2:1, e.g. 87.7-89.9% for chemical oxygen demand (COD), 82.2-86.7% for total nitrogen (TN), 96.0-97.0% for total phosphorus, and 76.9-84.2% for ammonium (NH₃-N). Significantly higher biomass and lipid productivity were obtained with aeration. The highest lipid productivity of P. tricornutum was 54.76 mg/L/day, which was obtained with a two-step cultivation using the ratio of MW: SW = 1:1 by diluting half of the mixture and bubbling with 5% CO₂ during the second step. These results suggested that the marine diatom P. tricornutum exhibited great potential for using mixed wastewater for wastewater treatment and biodiesel production.

Comprehensive characterization of microalgal isolates and lipid-extracted biomass as zero-waste bioenergy feedstock: An integrated bioremediation and biorefinery approach

The present study investigated the feasibility of domestic sewage wastewater (DSW) as an alternate to fresh-water microalgae growth media towards high-value bioenergy feedstock production. Eight native microalgal strains were screened from DSW and the effect of raw DSW (RDSW), and autoclaved DSW (ADSW) on growth and bioremediation potential were evaluated and compared with control BG11 medium. The study confirmed RDSW as a potential growth medium while Monoraphidium sp. KMC4 showed superior biomass (1.47 ± 0.08 g L^-1) and lipid yield (436.01 ± 0.06 mg L^-1). The corresponding values for bioremediation of ammonia, nitrate, phosphate, as well as COD remained within 88-100%. CHNS, biochemical, TGA, FTIR, FAME analysis of KMC4 confirmed it's potential as bioenergy feedstock. Additionally, a comprehensive characterization of lipid-extracted microalgae biomass (LEMB) was carried out which suggested that LEMB can be used as a growth promoter as well as feedstock for biogas, bioethanol, and bio-oil production.

Two-step process: Enhanced strategy for wastewater treatment using microalgae

Microalgae possess many advantages, but the lack of a suitable strategy to simultaneously facilitate their low cost cultivation and high value productions limits their commercial applications. In this study, two microalgae strains (RT_C and RT_F) isolated from a municipal wastewater treatment plant were used to establish a two-step wastewater treatment process. During step-1, RT_C was cultivated in composite wastewater due to its high tolerance of sludge centrate; followed by step-2, in which the supernatant generated from RT_C culture was used to cultivate RT_F. The NH₄⁺-N, PO₄^3--P, and COD in the wastewater were removed almost completely using this strategy. Moreover, the majority of the metal ions in the wastewater were absorbed by RT_C during step-1, and thus the powdered RT_F only contained low levels of toxic metals. Our results demonstrate that this two-step process is effective for removing pollutants and while generating a powder sufficiently clean for extracting valuable compounds.

Recent developments and key barriers to advanced biofuels: A short review

Biofuels are regarded as one of the most viable options for reduction of CO₂ emissions in the transport sector. However, conventional plant-based biofuels (e.g., biodiesel, bioethanol)'s share of total transportation-fuel consumption in 2016 was very low, about 4%, due to several major limitations including shortage of raw materials, low CO₂ mitigation effect, blending wall, and poor cost competitiveness. Advanced biofuels such as drop-in, microalgal, and electro biofuels, especially from inedible biomass, are considered to be a promising solution to the problem of how to cope with the growing biofuel demand. In this paper, recent developments in oxy-free hydrocarbon conversion via catalytic deoxygenation reactions, the selection of and lipid-content enhancement of oleaginous microalgae, electrochemical biofuel conversion, and the diversification of valuable products from biomass and intermediates are reviewed. The challenges and prospects for future development of eco-friendly and economically advanced biofuel production processes also are outlined herein.

Preparation of Stable Cross-Linked Enzyme Aggregates (CLEAs) of a Ureibacillus thermosphaericus Esterase for Application in Malathion Removal from Wastewater

In this study, the active and stable cross-linked enzyme aggregates (CLEAs) of the thermostable esterase estUT1 of the bacterium Ureibacillus thermosphaericus were prepared for application in malathion removal from municipal wastewater. Co-expression of esterase with an E. coli chaperone team (KJE, ClpB, and ELS) increased the activity of the soluble enzyme fraction up to 200.7 ± 15.5 U mg−1. Response surface methodology (RSM) was used to optimize the preparation of the CLEA-estUT1 biocatalyst to maximize its activity and minimize enzyme loss. CLEA-estUT1 with the highest activity of 29.4 ± 0.5 U mg−1 (90.6 ± 2.7% of the recovered activity) was prepared with 65.1% (w/v) ammonium sulfate, 120.6 mM glutaraldehyde, and 0.2 mM bovine serum albumin at 5.1 h of cross-linking. The biocatalyst has maximal activity at 80 °С and pH 8.0. Analysis of the properties of CLEA-estUT1 and free enzyme at 50–80 °C and pH 5.0–10.0 showed higher stability of the biocatalyst. CLEA-estUT1 showed marked tolerance against a number of chemicals and high operational stability and activity in the reaction of malathion hydrolysis in wastewater (up to 99.5 ± 1.4%). After 25 cycles of malathion hydrolysis at 37 °С, it retained 55.2 ± 1.1% of the initial activity. The high stability and reusability of CLEA-estUT1 make it applicable for the degradation of insecticides.