Enhanced biomass production through optimization of carbon source and utilization of wastewater as a nutrient source

Phycoremediation of 1,4 dioxane-laden wastewater: A Techno-economic and sustainable development approach

Microalgal tolerance to emerging contaminants (ECs) such as 1,4 dioxane (DXN) and its impact on phycoremediation performance, algal growth, biomolecules generated, and recycling the produced biomass for biochar production has been rarely reported. Hence, Chlorella vulgaris was cultivated in DXN-free wastewater (WW1) and 100 mg L-1 DXN-laden wastewater (WW2) in 1-liter photobioreactors with an operating volume of 800 ml under controlled conditions: temperature (25 ± 1 °C), light intensity (351 μmol m-2s-1), and photoperiod (12 h light:12 h dark). Interestingly, this microalgal-based system achieved up to 32.79% removal efficiency of DXN in WW2. In addition, there was no significant difference in the removal of COD (90.6% and 86.8%) and NH4-N (74.5% and 76.8%) between WW1 and WW2, respectively. Moreover, the variation in C. vulgaris growth, pigments, lipid, and carbohydrate contents between the two applied wastewaters was negligible. However, there was a significant increase in the protein yield upon exposure to DXN, suggesting the ability of C. vulgaris to secrete various antioxidant and degrading enzymes to detoxify the contaminant. These results were validated by FTIR, SEM, and EDX analysis of C. vulgaris biomass with and without DXN exposure. The harvested biomass was thermally treated at 350 °C for 60 min in an oxygen-free environment. The biochars generated from both algal systems were characterized by comparable morphologies and elemental profiles with sufficient C and N contents, indicating their applicability to enhance the soil properties. The economic evaluation of the combined phycoremediation/pyrolysis system demonstrated a net profit of 596 USD⋅y-1 with a payback period of 6.2 years and fulfilled the objectives of several sustainable development goals (SDGs). This is the first study to point to C. vulgaris as a robust microalgal strain in remediating DXN-laden wastewater accompanied by the potential recyclability of the biomass produced for biochar production.

High-throughput optimization of organic carbon provision strategies enables enhanced arachidonic acid production in novel microalgae

BACKGROUND

Microalgae are potential sustainable resources for the production of value-added chemicals that can be used as biofuels, pharmaceuticals, and nutritional supplements. Arachidonic acid (ARA), a omega-6 fatty acid, plays a crucial role in infant development and immune response, and can be used in cosmetics and pharmaceuticals. Demand for industrial-scale ARA production is continuously increasing because of its broad applicability. To address this demand, there has been a significant shift towards microorganism-based ARA production. To accelerate large-scale ARA production, it is crucial to select suitable strains and establish optimal culture conditions.

RESULTS

Here, we isolated a novel microalga Lobosphaera incisa CFRC-1, a valuable strain that holds promise as a feedstock for ARA production. Optimal cultivation conditions were investigated using a high-throughput screening method to enhance ARA production in this novel strain. Out of 71 candidates, four organic carbon substrates were identified that could be utilized by L. incisa CFRC-1. Through flask-scale verification, fructose was confirmed as the optimal organic carbon substrate for promoting microalgal growth, total lipid accumulation, and ARA production. Subsequently, we investigated appropriate substrate concentration and cultivation temperature, confirming that the optimal conditions were 30 g L- 1 of fructose and 27 ℃ of temperature. Under these optimized conditions, biomass and ARA production reached 13.05 ± 0.40 g L- 1 and 97.98 ± 7.33 mg L- 1, respectively, representing 9.6-fold and 5.3-fold increases compared to the conditions before optimization conditions. These results achieved the highest biomass and ARA production in flask-scale cultivation, indicating that our approach effectively improved both production titer and productivity.

CONCLUSIONS

This study presents a novel microalgae and optimized conditions for enhancing biomass and ARA production, suggesting that this approach is a practical way to accelerate the production of valuable microalgae-based chemicals. These findings provide a basis for large-scale production of ARA-utilizing microalgae for industrial applications.

Performance evaluation of typical flocculants for efficient harvesting of Chlorella sorokiniana under different carbon application modes

In this study, the growth characteristics of microalgae cultured with different carbon sources were analyzed, and the flocculation characteristics under the influence of carbon sources were evaluated using three typical flocculants. The results showed that the organic carbon sources could significantly increase the content of extracellular proteins in microalgae. Specifically, the extracellular protein concentrations of microalgae cultured with pure BG-11, ethanol, sodium acetate and glucose were 18.2 29.2, 97.3, and 34.7 mg/g, respectively. During the flocculation process, microalgae cultured with sodium acetate exhibited a weak response to the flocculant because of excessive extracellular proteins inhibited flocculation. In addition, the flocculation efficiency was also less than 50.0% cultured with sodium acetate in all pH test ranges when alum and chitosan were used as flocculants. It could be inferred that the flocculant initially happened to charge neutralization with the negatively charged proteins in the solution and then bridged the charges with the microalgae. These findings provide insights into the effects of different carbon sources on microalgal flocculation, promising organic integration of microalgae wastewater treatment and harvesting.

Optimization of High-Density Fermentation Conditions for Saccharomycopsis fibuligera Y1402 through Response Surface Analysis

Saccharomycopsis fibuligera, which produces enzymes like amylase and protease as well as flavor substances like β-phenyl ethanol and phenyl acetate, plays a crucial role in traditional fermented foods. However, this strain still lacks a high-density fermentation culture, which has had an impact on the strain's industrial application process. Therefore, this study investigated the optimization of medium ingredients and fermentation conditions for high-density fermentation of S. fibuligera Y1402 through single-factor design, Plackett-Burman design, steepest ascent test, and response surface analysis. The study found that glucose at 360.61 g/L, peptone at 50 g/L, yeast extract at 14.65 g/L, KH2PO4 at 5.49 g/L, MgSO4 at 0.40 g/L, and CuSO4 at 0.01 g/L were the best medium ingredients for S. fibuligera Y1402. Under these conditions, after three days of fermentation, the total colony count reached 1.79 × 108 CFU/mL. The optimal fermentation conditions were determined to be an initial pH of 6.0, an inoculum size of 1.10%, a liquid volume of 12.5 mL/250 mL, a rotation speed of 120 r/min, a fermentation temperature of 21 °C and a fermentation time of 53.50 h. When fermentation was conducted using the optimized medium and conditions, the total colony count achieved a remarkable value of 5.50 × 109 CFU/mL, exhibiting a substantial increase of nearly 31 times the original value in the optimal culture medium. This significant advancement offers valuable insights and a reference for the industrial-scale production of S. fibuligera.

Temporal assembly patterns of microbial communities in three parallel bioreactors treating low-concentration coking wastewater with differing carbon source concentrations

Carbon source is an important factor of biological treatment systems, the effects of which on their temporal community assembly patterns are not sufficiently understood currently. In this study, the temporal dynamics and driving mechanisms of the communities in three parallel bioreactors for low-concentration coking wastewater (CWW) treatment with differing carbon source concentrations (S0 with no glucose addition, S1 with 200 mg/L glucose addition and S2 with 400 mg/L glucose addition) were comprehensively studied. High-throughput sequencing and bioinformatics analyses including network analysis and Infer Community Assembly Mechanisms by Phylogenetic bin-based null model (iCAMP) were used. The communities of three systems showed turnover rates of 0.0029∼0.0034 every 15 days. Network analysis results showed that the S0 network showed higher positive correlation proportion (71.43%) and clustering coefficient (0.33), suggesting that carbon source shortage in S0 promoted interactions and cooperation of microbes. The neutral community model analysis showed that the immigration rate increased from 0.5247 in S0 to 0.6478 in S2. The iCAMP analysis results showed that drift (45.89%) and homogeneous selection (31.68%) dominated in driving the assembly of all the investigated microbial communities. The contribution of homogeneous selection increased with the increase of carbon source concentrations, from 27.92% in S0 to 36.08% in S2. The OTUs participating in aerobic respiration and tricarboxylic acid (TCA) cycle were abundant among the bins mainly affected by deterministic processes, while those related to the metabolism of refractory organic pollutants in CWW such as alkanes, benzenes and phenols were abundant in the bins dominated by stochastic processes.

Carbon metabolism characteristics of quorum quenching bacteria Rhodococcus sp. BH4 determine the bioaugmentation efficiency under different carbon source conditions

Carbon sources are critical factors influencing bacterial bioaugmentation, however, the underlying mechanisms, particularly the metabolic characteristics of bioaugmented bacteria remain poorly understood. The bioaugmented bacterium Rhodococcus sp. BH4 secretes the quorum quenching (QQ) enzyme QsdA to disrupt the quorum sensing (QS) in the activated sludge (AS) process, reducing AS yield in-situ. This study investigated the carbon metabolic characteristics of BH4 and explored the effects on bioaugmentation with different influent carbon sources. Because of the absence of glucose-specific phosphoenol phosphotransferase system (PTS), BH4 prefers sodium acetate to glucose. However, the lactones produced during extracellular glucose metabolism enhance BH4 qsdA expression. Moreover, BH4 possess carbon catabolite repression (CCR), acetate inhibits glucose utilization. BH4 microbeads were added to reactors with different carbon sources (R1: sodium acetate; R2: glucose; R3: a mixture of sodium acetate and glucose) for in-situ AS yield reduction. During operation, AS reduction efficiency decreased in the following order: R1 > R3 > R2. R2 and R3 microbeads exhibited similar QQ activity to R1, with less BH4 biomass at 5 d. 13C labeling and Michaelis-Menten equation showed that, due to differences in the competitiveness of carbon sources, R1 BH4 obtained the most carbon, whereas R2 BH4 obtained the least carbon. Moreover, acetate inhibited glucose utilization of R3 BH4. Transcriptome analysis showed that R1 BH4 qsdA expression was the lowest, R2 BH4 was the most serious form of programmed cell death, and the R3 BH4 PTS pathway was inhibited. At 10 d, R1 BH4 biomass and microbead QQ activity were higher than that in R3, and the R2 BH4 lost viability and QQ activity. This study provides new insights into bioaugmentation from the perspectives of carbon source competitiveness, carbon metabolism pathways, and CCR.

Wastewater treatment by using microalgae: Insights into fate, transport, and associated challenges

The remediation of wastewater with microalgae is a new topic that concentrates on devising a cost-effective and environmentally beneficial method. Multiple microalgae and bacterial consortiums have recently been evaluated to determine if they can purify effluent from various sources. Critical to a system's efficacy is its ability to remove nutrients such as nitrogen (N) and phosphorus (P) and heavy metals such as arsenic (As), lead (Pb), and copper (Cu). This study compared traditional wastewater treatment systems to microalgae-based systems for treating different types of wastewater. The research investigates the potential for microalgae to cleanse wastewater. The research also evaluates wastewater parameters, methods, and scientific techniques for extracting nutrients and heavy metals from polluted water. According to the literature, Microalgae can remove between 98.7% and 100% of nitrogen (N), phosphorous (P), and heavy metals from various effluents. The paper concludes by discussing the difficulties of using microalgae to remediate wastewater. The elimination of nutrients from the effluent is influenced by biomass production, osmotic capacity, temperature, pH, and O2 concentration. Therefore, a "pilot" study is recommended to investigate contaminants.

Growth Efficiency of Chlorella sorokiniana in Synthetic Media and Unsterilized Domestic Wastewater

Incorporating a variety of microalgae into wastewater treatment is considered an economically viable and environmentally sound strategy. The present work assessed the growth characteristics of Chlorella sorokiniana during cultivation in balanced synthetic media and domestic wastewater. Increasing the NH4+-N concentration to 360 mg L-1 and adding extra PO43--P and SO42--S (up to 80 and 36 mg L-1, respectively) contributed to an increase in the total biomass levels (5.7-5.9 g L-1) during the cultivation of C. sorokiniana in synthetic media. Under these conditions, the maximum concentrations of chlorophylls and carotenoids were 180 ± 7.5 and 26 ± 1.4 mg L-1, respectively. Furthermore, when studying three types of domestic wastewaters, it was noted that only one wastewater contributed to the productive growth of C. sorokiniana, but all wastewaters stimulated an increased accumulation of protein. Finally, the alga, when growing in optimal unsterilized wastewater, showed a maximum specific growth rate of 0.73 day-1, a biomass productivity of 0.21 g L-1 day-1, and 100% NH4+-N removal. These results demonstrate that the tested alga actively adapts to changes in the composition of the growth medium and accumulates high levels of protein in systems with poor-quality water.

Lipid production characteristics of a newly isolated microalga Asterarcys quadricellulare R-56 as biodiesel feedstock

In this study, a new microalgal strain, Asterarcys quadricellulare R-56, was isolated for biomass and lipid production. The effects of carbon and nitrogen sources and initial pH on the cell growth and lipid accumulation of strain R-56 were investigated. At 10 g L^-1 glucose, 0.6 g L^-1 sodium nitrate, and pH 7, the highest biomass of 4.18 g L^-1 and lipid content of 43.66% were obtained. Microalgae had a broad pH tolerance in the range of 5-11, and the pH of the culture medium was close to neutral at the end of cultivation. The maximum contents of chlorophyll, carbohydrate, and protein under the recommended culture conditions were 19.47 mg mL^-1, 21.80%, and 29.94%, respectively. Palmitic and palmitoleic acid contents in strain R-56 accounted for as high as 83.73% of total fatty acids. This study suggested that strain R-56 was a promising lipid producer for high-quality biodiesel production.

A techno-economic assessment of nutrient recovery from wastewater using microalgae: scenario in India collected from published literature

The true potential of the microalgae-based wastewater treatment (MWT) process is determined based on whether the process will provide a positive energy output and whether it is economically viable. The objectives of this study are dynamic modelling of microalgae growth based on initial wastewater concentration, temperature, solar radiation and a techno-economic assessment for an MWT scheme for application in a hot, dry climate. Through reference to relevant literature data on MWT in the Indian subcontinent, a selection of appropriate microalgal species Chlorella and Scenedesmus was made. The dynamic model developed was successfully calibrated and validated using independent experimental data collected from the published literature. Cost of production of bio-crude from microalgae grown in a hybrid photobioreactor and pond system in kitchen wastewater of Indian Institute of Technology, Hyderabad was calculated. A break-even selling price (BESP) of US$0.549/kg was obtained for the microalgae biomass. The cost of production of 1 L bio-crude was US$0.96 (Rs 69-74), which is comparable with crude oil cost. The model developed can be used by practising engineers to predict biomass growth and nutrient removal, thereby achieving a break-even point for cost efficiency.

Nutritional influences on biomass behaviour and metabolic products by Chlamydomonas reinhardtii

The recent works have shown the unicellular green alga Chlamydomonas reinhardtii is a relevant model for investigations of algal bioprocesses. In the current work, several media were evaluated in batch mode for a better understanding of C. reinhardtii metabolism. Nutrient-suppression using heterotrophic and mixotrophic conditions were performed. The findings showed C. reinhardtii metabolized lactose (from milk whey permeate) resulting in high biomass density (2.08 g/L) and total chlorophyll content (86.74 mg/m³). It was observed a specific growth rate of 0.023 h and 29 h for the doubling time. In sulfur-suppression, the algal growth (1.17 g/L) was reduced even though a carbon source (glucose) has been supplemented. Also, the specific growth rate (0.022 h) and the doubling time (31 h) was verified. The production of ethanol was slight and the acetic acid-suppression affected the C. reinhardtii performance providing slow cell growth (0.004 h) and high doubling time (154 h).

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.

Insights into the microalgae-bacteria consortia treating swine wastewater: Symbiotic mechanism and resistance genes analysis

This study investigated the effects of microalgae-bacteria consortia (MBC) (Chlorella pyrenoidosa-activated sludge (AS)) treating swine wastewater with low C/N ratios. After co-culture, the removal rates of NH₄⁺-N and PO₄^3--P increased by 53.84% and 43.52%. Furthermore, the sulfamethoxazole (SMX) degradation rates in MBC were slightly higher than in the activated sludge process. Interestingly, the absolute abundance of antibiotic resistance genes (ARGs) in effluent from MBC is relatively less than in the AS process. C. pyrenoidosa has a negative zeta potential that allows bacteria to adhere to its surface. The concentrations of carbohydrates and proteins in extracellular polymeric substance (EPS) of MBC dramatically increased compared with the AS process. At the phylum level, Proteobacteria, Bacteroidota, and Cyanobacteria were the main bacteria, while Ascomycota and Basidiomycota were the primary fungi in MBC. Overall, those findings lead to a better understanding of the swine wastewater containing antibiotic treatment by MBC.

Regulation of carbon source metabolism in mixotrophic microalgae cultivation in response to light intensity variation

Microalgae are one of the promising sources for renewable energy production, and the light intensity variation can affect the biofuel generation and carbon assimilation of mixotrophic microalgae. To reveal the response of carbon assimilation to light intensity, the effect of light intensity on the carbon source metabolism of Chlorella vulgaris under mixotrophic cultivation was investigated in this study. Moreover, the optimal carbon source composition for mixotrophic microalgae cultivation was evaluated using bicarbonate (HCO₃^-) and carbonate (CO₃^2-) as inorganic carbon sources, and glucose and acetate as organic carbon sources. The optimal light intensity for Chlorella vulgaris growth was at the range of 8000-12000 lux. For the accumulation of biochemical components, low light intensity was beneficial to protein accumulation, and high light intensity was advantageous for carbohydrate and lipid accumulation. With HCO₃^- and glucose, the maximum lipid content reached 37.0% at a light intensity of 12000 lux. The citrate synthase activity was negatively correlated with light intensity, showing an opposite trend to biomass production. High light intensity had a positive impact on Rubisco expression, which promoted the microalgae growth and carbon fixing. The energy produced by heterotrophic metabolic activities increased at low light intensity, and the enhancement of biomass production with high light intensity was mainly caused by the improved photoreaction efficiency during the mixotrophic cultivation.

Progress and challenges of contaminate removal from wastewater using microalgae biomass

The utilization of microalgae in treating wastewater has been an emerging topic focussed on finding an economically sustainable and environmentally friendly approach to treating wastewater. Over the last several years, different types of con microalgae and bacteria consortia have been experimented with to explore their potential in effectively treating wastewater from different sources. The basic features considered while determining efficiency is their capacity to remove nutrients including nitrogen (N) and phosphorus (P) and heavy metals like arsenic (As), lead (Pb), and copper (Cu). This paper reviews the efficiency of microalgae as an approach to treating wastewater from different sources and compares conventional and microalgae-based treatment systems. The paper also discusses the characteristics of wastewater, conventional methods of wastewater treatment that have been used so far, and the technological mechanisms for removing nutrients and heavy metals from contaminated water. Microalgae can successfully eliminate the suspended nutrients and have been reported to successfully remove N, P, and heavy metals by up to 99.6 %, 100 %, and 13%-100 % from different types of wastewater. However, although a microalgae-based wastewater treatment system offers some benefits, it also presents some challenges as outlined in the last section of this paper. Performance in eliminating nutrients from wastewater is affected by different parameters such as temperature, biomass productivity, osmotic ability, pH, O₂ concentration. Therefore, the conducting of pilot-scale studies and exploration of the complexities of contaminants under complex environmental conditions is recommended.

Biomass generation and biodiesel production from macroalgae grown in the irrigation canal wastewater

The wastewater concentration is commonly acceptable for macroalgae growth; this process consumes water and is applicable for bioremediation. This study evaluated biodiesel's potential production from freshwater macroalga, Nitella sp., using batch experiment. Algae were collected from wastewater saturated from irrigation canals. Water quality and algae growth environment characteristics were monitored and analyzed. COD and BOD values were 18.67 ± 4.62 mg/L and 5.40 ± 0.30 mg/L, respectively. The chemical composition contents were high, demonstrating that water quality and sufficient nutrients could support algae growth. Oil extraction was estimated by the room temperature and heat extraction methods. The biodiesel in room temperature treatment was 0.0383 ± 0.014%, and in heat, extraction treatment was 0.0723 ± 0.029%. Results confirmed that the heat extraction treatment gave a high amount of oil and biodiesel yield. Gas chromatography/mass spectrometry (GC/MS) was used to analyze fatty acid methyl esters (FAME). Results revealed that 9-octadecane was a major portion of the substance. The obtained results confirmed that the wastewater contains many elements that can be utilized for dual-mode, like bioremediation and enhanced macroalgae growth for biodiesel production. Therefore, macroalgae grown in canal wastewater were highly feasible for use in sustainable biodiesel production.

Microbial contamination control mechanism in lipid production using distillery wastewater and oleaginous yeast - Antimicrobial compounds in wastewater as a double-edged sword

Microbial contamination and the high expense of sterilization are the key factors limiting the application of resource recovery in processes such as producing lipids (can be converted to biodiesel via transesterification) from wastewater. This study was conducted to study the succession of contaminating and indigenous microorganisms, analyze the mechanism and propose a control strategy for undesirable microorganisms in the non-sterile lipid production process using distillery wastewater and oleaginous yeast. In the early stage, indigenous microorganisms (Pichia, Saccharomyces, Acetobacter and Gluconobacter) were the main competitors. Based on antimicrobial experiment and analyses of liquid chromatography-tandem mass spectrometry (LC-MS/MS) and gas chromatography mass spectrometry (GC-MS), the antimicrobial compounds (such as lactic acid 10,011-17,498 mg/L, succinic acid 210-325 mg/L and furfural 0.63-1.23 mg/L) combined with the low pH (3.2-3.8) in distillery wastewater played the primary role in the prevention of contaminating bacteria in this stage rather than the potential antimicrobial compounds from oleaginous yeast. Cinnamic acid (56-143 mg/L) was the main inhibitor against oleaginous yeast among the major antimicrobial compounds in wastewater. Its inhibition decreased when pH increased from 3.2 to 5.5. In the later stage, as the pH increased to over 7 during the culture, heterotrophic bacteria (Chryseobacterium and Sphingobacterium) with a relatively low tolerance for acidic conditions became the dominant undesirable microorganisms. Utilizing the antimicrobial activity of distillery wastewater combined with a high inoculum size and proper pH control could be effective for achieving dominant oleaginous yeast growth and improving lipid production in non-sterile conditions.

Domestic wastewater treatment in a coupled sequential batch reactor-electrochemical reactor process

The effectiveness of a sequenced biological-physicochemical reactor system for treating sewage was studied. The biological degradation was conducted in a Sequential Batch Reactor, which had innovative features for simplifying the operation and maintenance of the reactor. The reactor was operated at 4, 6, 8, and 12 hr cycle. Up to 82% removal of Chemical Oxygen Demand (COD), 50% removal of Dissolved Organic Carbon (DOC), 45% removal of Total Nitrogen (TN), and 45% removal of Total Phosphorus (TP) were achieved. The treated effluent was further polished in a continuous-flow bipolar-mode electrochemical reactor to remove additional recalcitrant organic matter from the wastewater. The process parameters were optimized using Response Surface Methodology. At the optimum condition (pH = 8.7; Current = 1.0; reaction time = 9.0), up to 90% removal of COD, 67% removal of DOC, 61% removal of TN, and 99.9% removal of TP were achieved in the coupled system. Micropollutants belonging to Pharmaceutically Active Compounds, pesticides, etc., were significantly removed. The coupled system completely removed Salmonella, Pseudomonas, and Staphylococcus. However, coliforms were detected at the outlet samples. A UV or ozone disinfection treatment is recommended for the safe reuse of the treated water for nonpotable purposes. PRACTIONER POINTS: Sequential sequential batch reactor-electrochemical reactor process (SBR-ECR) technology is effective for micropollutant removal from sewage. The coupled SBR-ECR system requires less footprint compared to conventional biological systems for wastewater treatment. Carbon material balance study revealed that more than 60% of carbon escapes from wastewater in the form of CO₂.

Effects of light intensity and nutrients on the lipid content of marine microalga (diatom) Amphiprora sp. for promising biodiesel production

In this research investigation, three microalgal species were screened (Pleurosigma sp., Amphora sp., and Amphiprora sp.) for lipid content before choosing the potential microalgae for biodiesel production. It was found that the lipid content of Amphiprora sp. was 41.48 ± 0.18%, which was higher than the Pleurosigma sp. (27.3 ± 0.8%) and Amphora sp. (22.49 ± 0.21%). The diatom microalga, Amphiprora sp. was isolated and exposed to a controlled environment. Two different media were prepared, and the main research was on the SiO₂-NP medium as the cell wall of diatom was made up of silica. Essential growth parameters were studied such as dry cell weight and chlorophyll a content. The results revealed that Amphiprora sp. cultured in the modified medium showed a higher biomass yield and growth rate in all the analyses. In Soxhlet extraction method, biodiesel yield of Amphiprora sp. in modified medium under 24 μmol m^-2 s^-1 of light intensity was 81.47 ± 1.59% when using 2% of catalyst amount with 1.5:1 volume ratio of methanol/oil in 3 h reaction time at 65 °C. Results reveled that Amphiprora sp. diatom has a higher yield of oil 52.94 ± 0.42% and can be efficiently optimized with further studies with modified nanomaterial culture medium. The present research revealed the series of experiments on microalgal lipid transesterification and in future investigation different types of nanomaterials should be used in culture medium to identify the lipid production in microalgal cells.

Municipal Wastewater: A Sustainable Source for the Green Microalgae Chlorella vulgaris Biomass Production

The need to reduce the costs associated with microalgae cultivation encouraged scientific research into coupling this process with wastewater treatment. Thus, the aim of this work was to assess the growth of Chlorella vulgaris (Chlorophyta) in different effluents from a municipal wastewater treatment plant (WWTP), namely secondary effluent (SE) and sludge run-off (SR). Assays were performed, under the same conditions, in triplicate with 4 dilution ratios of the wastewaters (25%, 50%, 75% and 100%) with the standard culture medium bold basal medium double nitrated (BBM2N) as a control. The capability of C. vulgaris for biomass production, chlorophyll synthesis and nutrients removal in the SE and SR was evaluated. The 25% SE and 25% SR showed increased specific growth rates (0.47 and 0.55 day−1, respectively) and higher biomass yields (8.64 × 107 and 1.95 × 107 cells/mL, respectively). Regarding the chlorophyll content, the 100% SR promoted the highest concentration of this pigment (2378 µg/L). This green microalga was also able to remove 94.8% of total phosphorus of SE, while in 50% SR, 31.2% was removed. Removal of 73.9% and 65.9% of total nitrogen in 50% and 100% SR, respectively, was also observed. C. vulgaris growth can, therefore, be maximized with the addition of municipal effluents, to optimize biomass production, while cleansing the effluents.

Enhanced Production of Photosynthetic Pigments and Various Metabolites and Lipids in the Cyanobacteria Synechocystis sp. PCC 7338 Culture in the Presence of Exogenous Glucose

Synechocystis strains are cyanobacteria that can produce useful biomaterials for biofuel and pharmaceutical resources. In this study, the effects of exogenous glucose (5-mM) on cell growth, photosynthetic pigments, metabolites, and lipids in Synechocystis sp. PCC 7338 (referred to as Synechocystis 7338) were investigated. Exogenous glucose increased cell growth on days 9 and 18. The highest production (mg/L) of chlorophyll a (34.66), phycocyanin (84.94), allophycocyanin (34.28), and phycoerythrin (6.90) was observed on day 18 in Synechocystis 7338 culture under 5-mM glucose. Alterations in metabolic and lipidomic profiles under 5-mM glucose were investigated using gas chromatography-mass spectrometry (MS) and nanoelectrospray ionization-MS. The highest production (relative intensity/L) of aspartic acid, glutamic acid, glycerol-3-phosphate, linolenic acid, monogalactosyldiacylglycerol (MGDG) 16:0/18:1, MGDG 16:0/20:2, MGDG 18:1/18:2, neophytadiene, oleic acid, phosphatidylglycerol (PG) 16:0/16:0, and PG 16:0/17:2 was achieved on day 9. The highest production of pyroglutamic acid and sucrose was observed on day 18. We suggest that the addition of exogenous glucose to Synechocystis 7338 culture could be an efficient strategy for improving growth of cells and production of photosynthetic pigments, metabolites, and intact lipid species for industrial applications.

Integrating micro-algae into wastewater treatment: A review

Improving the ecological status of water sources is a growing focus for many developed and developing nations, in particular with reducing nitrogen and phosphorus in wastewater effluent. In recent years, mixotrophic micro-algae have received increased interest in implementing them as part of wastewater treatment. This is based on their ability to utilise organic and inorganic carbon, as well as inorganic nitrogen (N) and phosphorous (P) in wastewater for their growth, with the desired results of a reduction in the concentration of these substances in the water. The aim of this review is to provide a critical account of micro-algae as an important step in wastewater treatment for enhancing the reduction of N, P and the chemical oxygen demand (COD) in wastewater, whilst utilising a fraction of the energy demand of conventional biological treatment systems. Here, we begin with an overview of the various steps in the treatment process, followed by a review of the cellular and metabolic mechanisms that micro-algae use to reduce N, P and COD of wastewater with identification of when the process may potentially be most effective. We also describe the various abiotic and biotic factors influencing micro-algae wastewater treatment, together with a review of bioreactor configuration and design. Furthermore, a detailed overview is provided of the current state-of-the-art in the use of micro-algae in wastewater treatment.

The Prospects of Agricultural and Food Residue Hydrolysates for Sustainable Production of Algal Products

The growing demand of microalgal biomass for biofuels, nutraceuticals, cosmetics, animal feed, and other bioproducts has created a strong interest in developing low-cost sustainable cultivation media and methods. Agricultural and food residues represent low-cost abundant and renewable sources of organic carbon that can be valorized for the cultivation of microalgae, while converting them from an environmental liability to an industrial asset. Biochemical treatment of such residues results in the release of various sugars, primarily glucose, sucrose, fructose, arabinose, and xylose along with other nutrients, such as trace elements. These sugars and nutrients can be metabolized in the absence of light (heterotrophic) or the presence of light (mixotrophic) by a variety of microalgae species for biomass and bioproduct production. The present review provides an up-to-date critical assessment of the prospects of various types of agricultural and food residues to serve as algae feedstocks and the microalgae species that can be grown on such residues under a range of cultivation conditions. Utilization of these feedstocks can create potential industrial applications for sustainable production of microalgal biomass and bioproducts.

Agricultural biowaste, rice bran, as carbon source to enhance biomass and lipid production: analysis with various growth rate models

As a byproduct of agriculture, rice bran can be a good alternative carbon source to mass-produce microalgae and increase lipid content. The purpose of this study was to investigate the effects of rice bran extract (RBE) on the mass culture and oil content of microalgae. Various parameters were applied to the growth rate model to explain the dynamics of substrate inhibition and growth of microalgae. The rice bran contains 46.1% of carbohydrates, in which is 38.3% glucose, and is very suitable as a carbon source for microalgae growth. The culture with RBE had a four times higher biomass production than microalgae cultured on Jaworski's medium (JM) with a small amount of 1 g/L. In addition, for RBE, the lipid content was three times higher and saturated fatty acid was 3% lower than were those of JM. According to the above results, when Chlorella vulgaris is cultured using RBE, a high amount of biomass and high lipid content can be obtained with a small amount of RBE. RBE is a discarded waste and has a high content of glucose, so it can be replaced by an organic carbon source to increase microbial biomass growth and lipid content at low cost.

Different interaction performance between microplastics and microalgae: The bio-elimination potential of Chlorella sp. L38 and Phaeodactylum tricornutum MASCC-0025

Microplastics have recently been identified as an important emerging global problem which affects marine organisms and even humans. As a green and cost-effective environmental purification alternative, microalgae have attracted more and more attention. In this work, the interaction between microplastics (PP, PE, PET and PVC) and microalgae (Chlorella sp. L38 and Phaeodactylum tricornutum MASCC-0025) has been investigated. In addition, SEM and TEM characterization were also carried out to observe interactions between microplastics and microalgae. Experimental results indicated that there was an obvious inhibition effect of microplastics on Phaeodactylum tricornutum MASCC-0025 growth with inhibition ratio up to 21.1%. By contrast, Chlorella sp. L38 presented strong adaptive capacity to microplastics. The key active enzymes concentration variation and characterization (SEM and TEM) images also verified the toxic effect of tested microplastics on Chlorella sp. L38 and Phaeodactylum tricornutum MASCC-0025. The toxic effect might be explained by the possible leaching of additives of four tested microplastics. It could also be observed that microalgae have a potential to be used as an alternative bio-solution for microplastics treatment.

How inoculation affects the development and the performances of microalgal-bacterial consortia treating real municipal wastewater

To date, little is known about the start-up of photobioreactors and the progressive development of stable microalgal-bacterial consortia with a view to the full-scale treatment of real wastewater. Two photo-sequencing bioreactors, one inoculated with Chlorella vulgaris (RC) and one with the absence of inoculum (RW), were fed with real municipal wastewater and run in parallel for 101 days. The influence of the inoculation was evaluated in terms of pollutant removal efficiency, excess sludge production, solids settleability and microbial community characteristics. No significant differences were observed in the removal of COD (89 ± 4%; 88 ± 3%) and ammonium (99 ± 1%; 99 ± 1%), mainly associated with bacteria activity. During the first weeks of acclimation, Chlorella vulgaris in RC promoted better P removal and very high variations of DO and pH. Conversely, under steady-state conditions, no significant differences were observed between the performances of RC and RW, showing good settleability and low effluent solids, 7 ± 8 and 13 ± 10 mg TSS/L respectively. Microbiome analysis via 16S rRNA gene sequencing showed that, despite a different evolution, the microbial community was quite similar in both reactors under steady state conditions. Overall, the results suggested that the inoculation of microalgae is not essential to engender a photobioreactor aimed at treating real municipal wastewater.

Lipids production and nutrients recycling by microalgae mixotrophic culture in anaerobic digestate of sludge using wasted organics as carbon source

Insufficient organics in anaerobic digestate of sludge limited algal mixotrophic culture and caused low lipids production. In this study, enhancing lipids production and pollutants removal by adding acidified starch wastewater was tested for Chlorella pyrenoidosa mixotrophic culture. The results showed that an optimal addition of acidified starch wastewater into anaerobic digestate of sludge (1:1, v/v) improved biomass and lipids production by 0.5-fold (to 2.59 g·L^-1) and 3.2-fold (87.3 mg·L^-1·d^-1), respectively. The acidified starch wastewater addition also improved the quality of algal biodiesel with higher saturation (typically in C16:0 and C18:0). In addition, 62% of total organic carbon, 99% of ammonium and 95% of orthophosphate in mixed wastewater were effectively removed by microalgae. This study provides a promising way to improve biodiesel production and nutrients recovery from anaerobic digestate of sludge using waste carbon source.

Biodegradation and metabolic fate of thiamphenicol via Chlorella sp. UTEX1602 and L38

Thiamphenicol (TAP) is a typical medicament in animal husbandry and aquaculture for treating diverse infections. In this work, thiamphenicol biodegradation performance via microalgae was tested. The cultivation results showed that TAP could be biodegraded via the target algae. Chlorella sp. L38 presented strong adaptive ability to high concentration TAP. Biodegradation, biosorption and bioaccumulation were the dominant metabolic fates. Biodegradation contributed around 97% of the total removal efficiency at the TAP concentration of 46.2 mg·L^-1. The removal of TAP by Chlorella L38 and UTEX1602 agreed with the kinetic range of zero-order reaction, and the shortest half-lives were 3.2 d and 5.0 d. Based on the identification of metabolites, the metabolic pathway of TAP by microalgae was proposed, including chlorination, chlorine substitution, dehydration and hydroxylation. Therefore, biological treatment via microalgae has the potential for TAP purification.

Characteristics of external carbon uptake by microalgae growth and associated effects on algal biomass composition

Water eutrophication may be affected not only by nutrients but also the coexisting organic carbon. In order to reveal the effect of external carbon on algal growth, an experimental study was conducted using Chlorella vulgaris as the representative microalgae to investigate their growth under varied N and P levels with/without added glucose at TOC = 18 mg/L. The TOC consumption by microalgae growth depended much on N and P concentrations and N/P ratio especially when P was sufficient. This ultimately increased the specific growth rate and resulted in higher N and P accumulations but lower carbon fixation in algal biomass in contrast to non-TOC addition. The biomass dry weight became much lower with TOC addition, along with an apparent change of algal composition shown by the much lower chlorophyll contents in the microalgae cells, which might associate the extent of two carbon fixation pathways - anabolism vs catabolism.

Impact of Cultivation Condition and Media Content onChlorella vulgaris Composition

Microalgae are a source material in food, pharmacy, and cosmetics industries for producing various products including high-protein nutritional supplements, synthetic pharmaceuticals, and natural colors. A promising algal source for such productions is Chlorella vulgaris which contains a considerable protein content. Similar to other microalgae, its desirability is minimal nutrient requirements since they are unicellular, photosynthetic, and fast-growing microorganisms. Another propitious option to be produced by C. vulgaris is biodiesel, since it is rich in oil too. Besides, algal well thriving in presence of increased amount of carbon dioxide makes them a practicable alternative biofuel resource without some problems of the traditional ones. At the same time, C. vulgaris is also a promising source for nutraceuticals such as amino acids, vitamins, and antioxidants. This review aims to discuss the conditions need to be observed for achieving a favorable growth efficiency of the C. vulgaris, as well as targeted productions such as biomass, antioxidant, and biofuel. Additionally, different approaches to induce any specific production are also considered comprehensively.

Light intensity affects the mixotrophic carbon exploitation in Chlorella protothecoides: consequences on microalgae-bacteria based wastewater treatment

Microalgal-bacteria consortia application on wastewater treatment has been widely studied, but a deeper comprehension of consortium interactions is still lacking. In particular, mixotrophic exploitation of organic compounds by microalgae affects gas (CO₂ and O₂) exchange between microalgae and bacteria, but it is not clear how environmental conditions may regulate algal metabolism. Using a respirometric-based protocol, we evaluated the combined effect of organic carbon and light intensity on oxygen production and consumption by C. protothecoides, and found that the chemical oxygen demand (COD) was not consumed when incident light increased. Batch experiments under different incident lights, with C. protothecoides alone and in consortium with activated sludge bacteria, confirmed the results obtained by respirometry. Continuous system experiments testing the combined effects of light intensity and residence time confirmed that, under limiting light, mixotrophy is preferred by C. protothecoides, and the nutrient (COD, N, P) removal capability of the consortium is enhanced.

The metabolic activity of denitrifying microorganisms accumulating polyphosphate in response to addition of fusel oil

The effect of distillery waste product (fusel oil) as an alternative external organic carbon source (EOCS) was investigated in terms of the metabolic properties of denitrifying polyphosphate accumulating organisms (DPAOs). Samples of the non-acclimated biomass were collected from a local full-scale wastewater treatment plant employing A²/O type bioreactors. The acclimated biomass was obtained after cultivation (with fusel oil added) in a bench-scale reactor with a process configuration similar to the full-scale bioreactor. Changes in the functional properties of the biomass were investigated by measuring the phosphate release/uptake rates (PRRs and PURs), and nitrate utilization rates (NURs) with fusel oil in anaerobic-anoxic batch tests. Furthermore, a validated extended Activated Sludge Model no 2d (ASM2d) was used as a supporting tool to analyze the experimental results and estimate the contribution of DPAOs to the overall denitrification. In the non-acclimated biomass with fusel oil, the PRRs, PURs and NURs were low and close to the rates obtained in a reference test without adding EOCS. With the acclimated biomass, the PUR and NUR increased significantly, i.e., 3.5 and 2.7 times, respectively. In the non-acclimated biomass, approximately 60.0 ± 3.6% and 20.0 ± 2.2% of the total NUR was attributed to the utilization of endogenous carbon and examined EOCS, respectively. The remaining portion (20% of the total NUR) was attributed to PHA utilization (linked to PO₄-P uptake) by DPAOs. With the acclimated biomass, the contribution of the EOCS to the NUR increased to approximately 60%, while the contribution of the endogenous carbon source decreased accordingly. Very accurate predictions of PURs and NURs (R² = 0.97–1.00) were obtained with the extended ASM2d. Based on model simulations, it was estimated that the activity of DPAOs and denitrifying ordinary heterotrophic organisms corresponded to approximately 20% and 80% of the total NUR, respectively.

Microalgae-bacteria gas exchange in wastewater: how mixotrophy may reduce the oxygen supply for bacteria

Microalgae-bacteria consortia application to wastewater treatment is considered as a potential and cheap strategy towards a self-sustaining oxygen-carbon dioxide gas exchange. However, microalgae can also carry out mixotrophy, thus reducing the net oxygen production, due to consumption of organic substrates. In this work, respirometric tests were used to quantify the oxygen reduction in the presence of biodegradable COD (chemical oxygen demand), which resulted up to 70%, depending on the biodegradability of the carbon substrate. The implication of mixotrophic metabolism on nutrient removal in urban wastewater was also measured by co-cultivating C. protothecoides with bacteria from activated sludge. To better understand the contribution of different populations, ad hoc experiments under controlled conditions were designed to quantify the nutrient consumption of bacteria and microalgae. Microalgae and bacteria were cultivated together and separately, with and without external bubbling, so to better ascertain the specific role of gas production and nutrient removal. Results showed that microalgae can remove up to 100 and 85% of P and N respectively, but the contribution on COD consumption may affect the net O₂ supply to heterotrophic bacteria. However, a mutual COD consumption by microalgae and bacteria was proved by both experimental growth curves and mass balance application, based on stoichiometry experimentally adjusted.

An approach for phycoremediation of different wastewaters and biodiesel production using microalgae

Four microalgal strains, namely, Tetraselmis indica (T. indica), Scenedesmus abundans (S. abundans), Spirulina sp., and Nostoc muscorum (N. muscorum) were cultivated on four different wastewaters in 1000 ml photobioreactors with 750 ml working volume under 94.5 μmol m^-2 s^-1 light intensity for 14 days for phycoremediation of wastewaters and sustainable biodiesel production. These microalgal strains attained maximum biomass growth in the secondary treated sewage (STS). Maximum biomass yield (0.6533 g L^-1) and lipid productivity (25.44 mg L^-1 d^-1) for T. indica were achieved in STS. T. indica removed (63.6-78.24%) of nitrate, (60.90-65.97%) of phosphate, (61.01-80.01%) of ammonical nitrogen, and (71.16-85.70%) of total organic carbon (TOC) in all four wastewaters. The fatty acid methyl ester (FAME) profile of T. indica shows the presence of myristic acid (1.2%) pentadecylic acid (0.28%), palmitic acid (10.32%), oleic acid (34.59%), linoleic acid (12.38%), and eicosanoic acid (14.88%) in STS. This study demonstrates that T. indica is the most suitable microalgal species among the four microalgal strains selected for phycoremediation of wastewaters and higher biomass production for sustainable biodiesel production.

Effect of cultivation mode on the production of docosahexaenoic acid by Tisochrysis lutea

In this study, Tisochrysis lutea was cultivated in mixotrophic and heterotrophic cultures with glycerol as a carbon source and with glucose and acetate for comparison; autotrophic cultivation was the control group without a carbon source. It was found that T. lutea used glycerol and did not use glucose and acetate under mixotrophy. Mixotrophy slightly elevated the docosahexaenoic acid (DHA) and total fatty acids (TFA) content in the dry-weight and enhanced the DHA and TFA production in medium (41.3 and 31.9% respectively) at the end of a 16-day cultivation, while heterotrophy reduced the DHA content and TFA production. Under the mixotrophy, the glycerol contribution to the DHA production (16.19 mg/L) and the TFA production (97.8 mg/L) was not very high and the DHA yield [2.63% chemical oxygen demand (COD)] and TFA yield (13.1% COD) were also very low. Furthermore, T. lutea using glycerol had a period of adaptation, indicating that T. lutea was not an ideal microalga for organic carbon utilization.

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

New strains of green microalgae were isolated and screened for growth and the production of lipids from municipal wastewater. It was shown that the strain Micractinium sp. IC-76 has a biomass productivity of 37.18 ± 4.12 mg L^-1 d^-1 and a lipid content of 36.29 ± 0.11%, with a total content of saturated and monounsaturated fatty acids of 71.9%. The efficiency of nitrogen (N-NH₄) and phosphorus (P-PO₄) removal was 96.4 ± 0.7 and 77.8 ± 5.6%, respectively. The metabolic differences at the exponential and stationary phases of growth between the closely related strains with different patterns of lipid accumulation were revealed via gas chromatography mass spectrometry metabolic profiling. The strain Micractinium sp. IC-76 in the stationary phase of growth shows a significant difference in carbohydrate metabolism, especially sucrose concentration. High lipid induction during cultivation in wastewater was also driven by changes in the biosynthesis of amino acids, fatty acids and the tricarboxylic acid cycle.

Enhanced lipid and biomass production using alcohol wastewater as carbon source for Chlorella pyrenoidosa cultivation in anaerobically digested starch wastewater in outdoors

Alcohol wastewater (AW) as carbon source for enhancing Chlorella pyrenoidosa growth and lipid accumulation in anaerobically digested starch wastewater (ADSW) was performed in outdoor cultivation. The biomass and lipid production significantly increased while adding optimal amount of AW (AW/ADSW=1:15) during exponential phase. In comparison with blank ADSW culture, the optimal AW addition increased the biomass production, lipid content and productivity by 35.29%, 102.68% and 227.91%, respectively. However, AW addition caused severe bacterial contamination and the total bacterial increased by 4.62-fold. Simultaneously, the optimal consortia of microalgae/bacteria effectively removed nutrients from the wastewater, including 405.18±36.47mgCOD_Cr/L/day, 49.15±5.54mgN/L/day and 6.72±1.24mgP/L/day.

Valorization of Spent Escherichia coli Media Using Green Microalgae Chlamydomonas reinhardtii and Feedstock Production

The coupling of Chlamydomonas reinhardtii biomass production for nutrients removal of Escherichia coli anaerobic broth (EAB) is thought to be an economically feasible option for the cultivation of microalgae. The feasibility of growing microalgae in using EAB high in nutrients for the production of more biomass was examined. EAB comprised of nutrient-abundant effluents, which can be used to produce microalgae biomass and remove environment pollutant simultaneously. In this study, C. reinhardtii 21gr (cc1690) was cultivated in different diluted E. coli anaerobic broth supplemented with trace elements under mixotrophic and heterotrophic conditions. The results showed that C. reinhardtii grown in 1×, 1/2×, 1/5× and 1/10×E. coli anaerobic broth under mixotrophic conditions exhibited specific growth rates of 2.71, 2.68, 1.45, and 1.13 day^-1, and biomass production of 201.9, 184.2, 175.5, and 163.8 mg L^-1, respectively. Under heterotrophic conditions, the specific growth rates were 1.80, 1.86, 1.75, and 1.02 day^-1, and biomass production were 45.6, 29.4, 15.8, and 12.1 mg L^-1, respectively. The removal efficiency of chemical oxygen demand, total-nitrogen and total-phosphorus from 1×E. coli anaerobic broth was 21.51, 22.41, and 15.53%. Moreover, the dry biomass had relatively high carbohydrate (44.3%) and lipid content (18.7%). Therefore, this study provides an environmentally sustainable as well economical method for biomass production in promising model microalgae and subsequently paves the way for industrial use.