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The amino acids from microalgae could be used as a substitute for food and feed supplements in the future. This study investigates the production of amino acids from microalgae Nannochloropsis sp. biomass using subcritical water technology approaches. The yield and composition of amino acids produced from subcritical water of microalgae Nannochloropsis sp. were evaluated at different temperatures (160-350 °C), time (3-30 min), and biomass loadings (1- 15% w/v). Overall results showed that the highest yield of total amino acids (1531.98 mg/100 g algae) was obtained at subcritical water operating conditions of 280 °C, 15 min reaction time, and 1% biomass loading. The studied operating conditions produced a higher yield of non-essential amino acids compared to essential amino acids. The study demonstrated that each of the individual amino acids investigated produced the highest at different ranges of subcritical water conditions. Thus, the obtained profile of the individual amino acid showed that careful management of operating parameters (temperature, time, and biomass loading) is crucial for identifying the amino acids of interest via subcritical water technology.

Lipids and eicosapentaenoic acid (EPA) compounds from Nannochloropsis oceanica biomass were extracted using a combination of ionic liquids (ILs) and microwave-assisted extraction (MAE). When compared to conventional Soxhlet extraction, the proposed novel approach in this paper successfully improved both the yield of total extracted lipids and the EPA content. The effect of selected extraction parameters including the weight of applied IL (tetramethyl ammonium chloride: [TMAm][Cl]) (0.5–2.5 g), reaction temperature (60–100 °C), and process time (5–30 min) on final products was evaluated using response surface methodology (RSM). The optimal values of parameters were determined and three-dimensional response surfaces were plotted from the mathematical models and discussed. The yield of total extracted lipids and the content of EPA were found 19.58 wt% (g g−1 of total biomass) and 37.919 mg g−1 of total FAME respectively, when the extraction process was accomplished in 24.69 min at 88.18 °C and with 1.65 g of ILs. Analysis of variance (ANOVA) was applied in the analysis of experimental data and the R2 of 0.9506 and 0.9517 for total lipid and EPA models, respectively, show that the experimental findings were well aligned with the predicted values. Furthermore, at similar condition, the extraction process was replicated using two other types of ILs namely [EMIM][Cl] and [EMPyrro][Br] to extract the total lipid and EPA. The results showed that [TMAm][Cl] performed better in extracting compounds from microalgae. Based on the findings, this study shows that the combination of ILs mediated in water-based MAE is an environmentally friendly, reliable, and efficacious approach to enhance the extraction of lipids and EPA from N. oceanica with considerable potential to be up-scaled for commercial applications.

The production of high-value bioproducts from microalgae biomass has been widely investigated. However, their production is hindered by the expensive harvesting process. To date, flocculation followed by DAF process has been accepted as one of the affordable harvesting approaches. In this study, the use of DAF technique was attempted to harvest marine microalgae Nannochloropsis sp. Batch DAF harvesting was carried out using fabricated DAF unit equipped with several compartments including separation column, product collecting vessel and rotary skimmer. Tannin-based biopolymer flocculant, AFlok-BP1 at pH 5 with a concentration of 160 mg/L was used to facilitate the flocculation of particles. The effects of different saturator pressure at 1.8, 2, and 2.2 bar were then evaluated at a constant volume of 6 L microalgae culture. The effects of different microalgae culture volumes (6, 8 and 10 L) were also evaluated at a fixed saturator pressure of 2.2 bar. The highest pressure at 2.2 bar yielded the best result with the highest total solid of 3.19 ± 0.01% and a maximum yield of 1.70 ± 0.05 g/g (wet basis). The microalgae concentration was the lowest (0.027 g/L) when 6 L of culture volume was used. However, the values were significantly higher when the culture volume was increased to 8 and 10 L to approximately 0.035 and 0.050 g/L, respectively. As a conclusion, the study provided evidence for the feasibility of DAF technique in harvesting marine microalgae Nannochloropsis sp.

Chlorella sp. are among the highest cultivated species of microalgae. They are considered as an important functional food due to their abundance and valuable health benefits. It would be useful to develop an effective method for phenolic compound extraction from Chlorella sp. using safe technology and green solvents for the applications in food and pharmaceutical fields. Pressurized hot water extraction (PHWE) is an alternative for this purpose. PHWE was employed to extract phenolic compounds from Chlorella sp. microalgae at temperatures between 100 and 250 °C. The data collected is used to create the kinetics of the extraction process. The kinetics studies revealed that the extraction from Chlorella sp. microalgae using pressurized hot water treatment follows first-order kinetics and is strongly dependent on temperature. An increasing trend in the calculated values of mass transfer coefficient, k, was noticed, with increasing temperature. The activation energy, Ea, was calculated as 11.146 kJ/mol for the extraction treatment.

Palm oil mill effluent (POME) has high chemical oxygen demand (COD), thus requires effective treatments to environmentally benign levels before discharge. In this study, immobilized microalgae cell...

Microalgae are an alternative source of renewable energy and high-value products for pharmaceutical, nutraceutical, etc., due to rich in carbohydrates, proteins, lipids, and high-density lipoproteins. Existing methods for cell disruption and extraction are costly and suffered from low proficiencies. Ionic liquids are proven to be an environmentally friendly substitute to conventional volatile organic solvents. They have been used in extracting different types of biomass, including microalgae. This article reviews the potential of ILs in extracting biomolecules, lipid, and omega-3, from microalgae biomass. The physicochemical properties of ILs, including viscosity, density, and melting point, their advantages and limitation, as well as toxicity and recyclability of ILs in lipid processing, are discussed.

Considerable evidence supports the enhanced utilization of high-quality protein to obtain optimal health subsequences. Microalgae are a valorous source of proteins that can be employed as functional, nutritional, and remedial supplies. An effective microwave-assisted extraction method based on ionic liquids has been utilized in this study to extract proteins from microalgae Nannochloropsis oceanica biomass. The study of microwave-assisted extraction was carried out under varying conditions of temperature (30–80 °C), extraction time (5–35 min), and IL concentration (0–4.67% w/v). Among the six types of examined IL, choline acetate was an effective one for extracting total protein from microalgae biomass. The highest protein yield was obtained at 0.5 g microalgae, 2% w/v [Ch][Ac], and 40 °C for 30 min, representing 26.35% of protein yield and 65.06% of total protein extracted from the Nannochloropsis oceanica biomass. Meanwhile, conventional method of Soxhlet resulted in the protein yield of 0.63%. Only 1.56% of total Nannochloropsis oceanica protein was extracted by extraction method of Soxhlet which uses the hazardous solvent. The outcomes illustrated the superiority of [Ch][Ac]-based microwave-assisted extraction to conventional methods. This innovative procedure is recommended to have significant usage for the separation of proteins. The outcomes from this study would be beneficial in recognizing and harnessing significant microalgae biochemical from IL-based microwave-assisted extraction process to develop new and improved bioproduct technologies.

Microalgae contain a significant amount of carbohydrates that can be converted further to produce valuable compounds. To extract carbohydrates from microalgae, sub-critical water extraction (SWE) is a viable and novel method. Compared to other existing chemical and biological extraction methods, SWE is more economical, effective, and efficient in terms of process conditions. This process uses high temperature and pressure of water at just below supercritical conditions to keep water at a liquid state. This study aims to investigate the factors that affect the extraction yield of carbohydrates from microalgae Nannochloropsis sp. using the SWE process. The extraction was carried out at a temperature of 160 – 320 oC, a duration of 5 – 25 min, and microalgal biomass loading of 5 - 25% w/v. The kinetics study was conducted in an extraction time of 5 – 25 min at 200 oC and 5% (w/v) biomass loading. A simplified kinetic model based on a consecutive reaction was used to describe carbohydrate production and decomposition via SWE. It was found that the maximum yield of total carbohydrate was 18.04 g/100 g which was obtained at 200 oC, 10 min, and 5% (w/v) microalgal biomass loading. The carbohydrate concentration was decreased as the temperature, extraction time and microalgal biomass loading increased. This result indicated that the SWE is a promising extraction method for carbohydrate recovery from microalgae, and the factors investigated here had a significant effect on the extraction process. The proposed kinetic model was also able to capture the experimental data well within the range of operating conditions studied in this work.

Emerging applications of amino acids in the development of biopharmaceuticals, functional foods and feeds, and biostimulants in sustainable agriculture have led to increasing interests in the development of commercially-viable technologies for amino acid production. Amongst the many technologies currently used, subcritical water reaction has the potential to offer a scalable and environmentally benign approach to amino acids synthesis. The present work investigates the kinetic and thermodynamic behaviour of amino acids synthesis from Nannochloropsis sp. biomass using subcritical water. Experiments were conducted in a batch reactor at temperatures between 250-280°C for a duration of 5-20 min using 1% (w/v) microalgal loading. The aqueous phase obtained from the reaction was directly analyzed for amino acid concentration. The highest amino acids yield of 0.0196 g AA / g biomass was obtained at 260°C for 20 min, representing 44% of amino acids extracted from the biomass. A single consecutive reaction model used for data validation showed a good agreement between the experimental and theoretical data generated. The results obtained from the kinetic study demonstrated that amino acids could be produced and decomposed rapidly from the subcritical water process. Thermodynamic analysis by transition-state theory showed that the subcritical water process as endothermic, while the Gibbs free energy showed the reaction as non-spontaneous, requiring constant external energy to support it.

The use of freely suspended cells of microalgae culture to treat wastewater is of current global interest because of their effective photosynthetic uptake of pollutants, carbon dioxide sequestration, and biomass production for desirable high value-products. Biomass immobilization is a promising option to overcome the harvesting problem that is encountered when using free-cells upon completion of the wastewater treatment process. In this study, Nannochloropsis sp. cells were immobilized in sodium alginate beads to eliminate the harvesting limitation. The microalgal beads were further cultivated in treated palm oil mill effluent (TPOME) for removal of chemical oxygen demand (COD). The effect of POME concentration on COD removal and microalgal cells growth was investigated, respectively. It was found that the maximum biomass concentration of 1.23 g/L and COD removal of 55% from 10% POME were achieved after 9 days. An increment of POME concentration did not cause any improvement to the treatment efficiency due to the inhibitory effect of high initial COD of POME on the biomass concentration and was further responsible for low COD removal. The immobilized cells showed a systematic growth, demonstrating that the beads are biocompatible as immobilization carrier. In conclusion, the immobilized microalgal cells could be a viable alternative technology system for POME treatment as well as biomass production.

This research aimed to improve the stability of Chlorella-Alginate Beads (CABs) by zeolite molecular sieves 13X. Dissolution time of synthesized Zeolite-Algal-Alginate Beads (ZABs) in a chelating agent revealed a significant improvement on the beads stability (78.5 ± 0.5 min) compared to the control beads (51.5 ± 0.5 min) under the optimum conditions of zeolite/alginate (1.5:1), pH 5 and 2% of beads. Monitoring cell growth during 5 days of incubation showed good biocompatibility of zeolite 13X. Scanning electron microscopy (SEM) indicated rough surface and spherical shapes of ZABs. Energy dispersive X-ray spectroscopy (EDX) and Fourier transform infrared spectroscopy (FTIR) of ZABs confirmed the presence of zeolite 13X within the matrix. The zeta potential value of ZABs indicated that the beads were relatively stable. The findings of this research showed that zeolite molecular sieves 13X have the potential to improve the stability of algal-alginate beads compared to common beads.

Microalgal gasification produces synthesis gas (syngas), liquid products (e.g., tar), and solid carbon (e.g., char). However, at the current state, the viability of the process is yet to be established. One of the ways to achieve that is by understanding the fundamental of microalgal gasification. This could be done by optimizing the process conditions via modeling. Therefore, this study models the microalgal gasification process and further optimizes its process conditions. The modeling work was carried out using Aspen Plus V8.8 software, where thermodynamics equilibrium and kinetics approaches were used in the calculations of Chlorella vulgaris gasification. The study was done by modeling the gasifier in three stages: drying, pyrolysis, and gasification. The model was developed using proximate and ultimate analysis data of Chlorella vulgaris. The parameters were temperature (600–1000 °C), equivalence ratio (ER) 0.1–0.4, and mass flow rate of biomass (10–100 kg/h). The syngas yields of H2, CO, CO2, and CH4 were determined and the findings were compared with the literature and some deviations of the predicted syngas compositions were presented. It was found that consistent results of syngas composition and yield were obtained between the model and the experiments. The root mean square error (RMSE) values for the effect of temperature were 0.242, 0.294, 0.228, and 0.062 for H2, CO, CO2, and CH4, respectively. Meanwhile, for the effect of loading, the values were 0.083, 0.064, 0.362, and 0.479 for H2, CO, CO2, and CH4, respectively. The optimization of the gasification from sensitivity analysis results showed that the increment of temperature favored the H2 and CO production, and the increased in biomass loading favored H2 and CH4 production. Meanwhile, the increment of ER value resulted in increasing the CO2 yield. Based on the findings, a slight deviation in the simulation results was observed compared with the experimental work. This might be resulted from the limitation of the Aspen Plus V8.8 software where some parameters need to be set as a constant value, which in this study was the heating rate.

In this work, we propose a one-step subcritical methanol extraction (SCM) process for biodiesel production from Chlorella pyrenoidosa. Therefore, the present study attempts to establish and determine the optimum operating conditions for maximum biodiesel yield from SCM of C. pyrenoidosa. A statistical approach, i.e. response surface methodology is employed in this study. The effects of three operational factors: reaction temperature (140–220 °C), reaction time (1–15 min) and methanol to algae ratio (1–9 wt.%) were investigated using a central composite design. A maximum yield of crude biodiesel of 7.1 wt.% was obtained at 160 °C, 3 min reaction time and 7 wt.% methanol to algae ratio. The analysis of variance revealed that methanol to algae ratio is the most significant factor for maximizing biodiesel yield. Regression analysis showed a good fit of the experimental data to the second-order polynomial model. With no requirement of catalyst nor any pretreatment step, SCM process is economically feasible to scale up the commercial biodiesel production from algae.

A thermal behavior study of lipid-extracted Nannochloropsis gaditana (LEA) was performed in a thermogravimetric analyzer. The study was performed by heating the sample under different heating rates (5, 10, and 15 °C/min) from room temperature to 1000 °C using N2 gas as the medium. This is crucial for thermal stability studies in a kinetic control regime. The following three stages of chemical decompositions were found: (1) moisture removal (2) devolatilization (3) fixed carbon decomposition; maximum decomposition was observed at the second stage. Activation energies of the LEA were studied using the Flynn–Wall–Ozawa model and Kissinger–Akahira–Sunose model. Main sample decomposition was observed from 100–700 °C during volatile matter evaporation. The thermal behavior study findings were used for the gasification of the sample with air to study the effect of varying reaction parameters on the compositions of the synthesis gas yield. Maximum H2 yield was found at 700 °C and 0.7 g, which were 51.2 mol% and 50.6 mol%, respectively. From the study, it was found that LEA is suitable to be used as feedstock in gasification for synthesis gas production.

The interest in utilizing algae for wastewater treatment has been increased due to many advantages. Algae-wastewater treatment system offers a cost-efficient and environmentally friendly alternative to conventional treatment processes such as electrocoagulation and flocculation. In this biosystem, algae can assimilate nutrients in the wastewater for their growth and simultaneously capture the carbon dioxide from the atmosphere during photosynthesis resulting in a decrease in the greenhouse gaseousness. Furthermore, the algal biomass obtained from the treatment process could be further converted to produce high value-added products. However, the recovery of free suspended algae from the treated effluent is one of the most important challenges during the treatment process as the current methods such as centrifugation and filtration are faced with the high cost. Immobilization of algae is a suitable approach to overcome the harvesting issue. However, there are some drawbacks with the common immobilization carriers such as alginate and polyacrylamide related to low stability and toxicity, respectively. Hence, it is necessary to apply a new carrier without the mentioned problems. One of the carriers that can be a suitable candidate for the immobilization is zeolite. To date, various types of zeolite have been used for the immobilization of cells of bacteria and yeast. If there is any possibility to apply them for the immobilization of algae, it needs to be considered in further studies. This article reviews cell immobilization technique, biomass immobilization onto zeolites, and algal immobilization with their applications. Furthermore, the potential application of zeolite as an ideal carrier for algal immobilization has been discussed.

Cross-flow ultrafiltration (UF) membrane with two different configurations, single (10 kDa and 5 kDa) and two-stage (10/5 kDa) in fractionating microalgae protein hydrolysate (MPH) were studied to obtain a low molecular weight of peptide. The effect of flow rate, trans-membrane pressure (TMP), and pH in fractionating MPH were evaluated based on permeate flux and peptide transmission. The results showed that, for single UF membrane, optimum operating parameters were at a flow rate of 23 mL/min, TMP of 1.5 bar, and pH of 9, with permeate flux of 43.65 L/m2 h (10 kDa) and 55.42 L/m2 h (5 kDa) and peptide transmission of 58.20% (10 kDa) and 67.34% (5 kDa). Meanwhile, for two-stage (10/5 kDa) UF membrane, the best parameters were observed at a flow rate of 23 mL/min, TMP of 1.5 bar, and pH of 2, with permeate flux of 69.85 L/m2 h and peptide transmission of 79.13%. Fractionation of MPH with two-stage UF membrane was observed to be better at producing a low molecular weight of peptide compared to single UF membrane. In conclusion, it was possible to produce permeate flux with a high amount of low molecular weight of peptide by controlling the operating parameters with the suitable configuration membrane.

Global warming has become a serious issue nowadays as the trend of CO2 emission is increasing by years. In Malaysia, the electricity and energy sector contributed a significant amount to the nation’s CO2 emission due to fossil fuel use. Many research works have been carried out to mitigate this issue, including carbon capture and utilization (CCUS) technology and biological carbon fixation by microalgae. This study makes a preliminary effort to screen native microalgae species in the Malaysian coal-fired power plant’s surrounding towards carbon fixation ability. Three dominant species, including Nannochloropsis sp., Tetraselmis sp., and Isochrysis sp. were identified and tested in the laboratory under ambient and pure CO2 condition to assess their growth and CO2 fixation ability. The results indicate Isochrysis sp. as the superior carbon fixer against other species. In continuation, the optimization study using Response Surface Methodology (RSM) was carried out to optimize the operating conditions of Isochrysis sp. using a customized lab-scale photobioreactor under simulated flue gas exposure. This species was further acclimatized and tested under actual flue gas generated by the power plant. Isochrysis sp. had shown its capability as a carbon fixer with CO2 fixation rate of 0.35 gCO2/L day under actual coal-fired flue gas exposure after cycles of acclimatization phase. This work is the first to demonstrate indigenous microalgae species' ability as a carbon fixer under Malaysian coal-fired flue gas exposure. Thus, the findings shall be useful in exploring the microalgae potential as a biological agent for carbon emission mitigation from power plants more sustainably.

Gasification is one of the thermochemical pathways of biomass conversion that produces synthesis gas, tar, and char. This study aims to convert algal residues via gasification at different operating conditions; temperature, equivalence ratio, and biomass loading. The study was carried out in 3 steps; (1) testing the outcomes of temperature and loading effects on synthesis gas yield, (2) experimental optimization of gasification via Design Expert, and (3) theoretical optimization of gasification via Aspen Plus simulation. Temperature and equivalence ratio highly influenced synthesis gas composition, while loading demonstrated less effect on the synthesis gas composition. The experimental and simulated gasification outcomes were compared to obtain optimized conditions that produce high H2 and CO yields. The data were validated using root mean square error. The optimized temperature, loading, and equivalence ratio were found for both algal residues that produced 36.38 and 13.28mol% of H2 and CO, respectively for lipid extracted algae (LEA) and 47.99 and 26.05mol% of H2 and CO, respectively for fucoidan extracted seaweeds (FEA). There was a considerable variation between experimental and simulated data due to the simulation and experimental limitations. The average Carbon Conversion Efficiency values were 66.36 and 80.42% for LEA and FES, respectively, denoting that LEA produced less carbon-containing products, while FES produced more carbon-containing products. In conclusion, LEA gasification yielded more H2 while FEA produced more CO.

This study performs a screening of potential Ionic Liquids (ILs) for the extraction of Docosahexaenoic Acid (DHA) compounds by the calculation of capacity values. For this purpose, a Conductor-Like Screening Model for Real Solvents (COSMO-RS) was employed to study the molecular structures of the ILs, and therefore, predict their extraction potential. The capacity values of 22 anions combined with 16 cations based ILs, were investigated to evaluate the effectiveness of ILs in the extraction of DHA. It was found that among the investigated ILs, a combination of tetramethyl ammonium with SO4 or Cl was the best fit for DHA extraction, followed by pyrrolidinium, imidazolium, pyridinium and piperidinium. Furthermore, it was observed that the extraction capacity and the selectivity of ILs decreased with an increase in alkyl chain length, therefore, ethyl chain-ILs, with the shortest chain lengths, were found to be most suitable for DHA extraction. The predicted results were validated through the experimentally calculated extraction yield of a DHA compound from Nannochloropsis sp. Microalgae. Five selected ILs, namely [EMIM][Cl], [BMIM][Cl], [TMAm][Cl], [EMPyr][Br] and [EMPyrro][Br], were selected from COSMO-RS for empirical extraction purposes, and the validation results pinpointed the good prediction capabilities of COSMO-RS. The findings in this study can simplify the process of selecting suitable ILs for DHA extraction and reduce the number of required empirical evaluations.

Subcritical water extraction (SCW) was used to extract oil from Chlorella pyrenoidosa. The operational factors such as reaction temperature, reaction time, and biomass loading influence the oil yield during the extraction process. In this study, response surface methodology was employed to identify the desired extraction conditions for maximum oil yield. Experiments were carried out in batch reactors as per central composite design with three independent factors including reaction temperature (170, 220, 270, 320, and 370°C), reaction time (1, 5, 10, 15, and 20 min), and biomass loading (1, 3, 5, 10, and 15%). A maximum oil yield of 12.89 wt.% was obtained at 320°C and 15 min, with 3% biomass loading. Sequential model tests showed the good fit of experimental data to the second-order quadratic model. This study opens the great potential of SCW to extract algal oil for use in algal biofuel production.

The marine species microalgae are an attractive source of feedstock for biofuel production and other bio-products such as omega-3 fatty acids and aquaculture feeds. The prevailing main nutrients in seawater environment for their growth are believed to be more economical than freshwater in terms of their cultivation system which may lead to low cost for upstream processing. Hence, marine microalgae provide attractive potential to be further explored. However, harvesting process of microalgae is known to be too costly because of their dilute nature that accounts for 20–30% of the overall production costs rendering using microalgae as the raw material not economically feasible. Currently the various harvesting methods including centrifugation, flocculation, flotation, filtration and magnetic separation had been applied to harvest marine species. For instance, harvesting by electrolytic means that require less energy to harvest marine species compared to the freshwater species. This can potentially help to reduce the challenges related to the exploitation of microalgae biomass. However, different techniques have their own advantages and drawbacks, whereas their cost and energy requirement vary accordingly depending on the selection of marine microalgal strains, equipment used and/or the choice of harvesting aid (flocculants, surfactant). Thus far, no single technique may still be proposed. Therefore, this paper aims to provide further details of each method used focusing only for marine species of microalgae with their respective advantages and disadvantages.

The issues involved with conventional lipid extraction methods, such as the usage of toxic solvents and accumulation of chemical waste, has motivated researchers to find an alternative approach to the extraction technology. One of the alternatives is via the Supercritical Carbon Dioxide (SC-CO2) method. This extraction method is considered as green as it provides a clean, selective and efficient process. Although the SC-CO2 method has been successfully used to extract lipids from microalgae, there are still some issues related to sample preparation and process parameters that need to be resolved. Therefore, this study investigates the effect of adding a modifier (ethanol) and using different types of holders (cotton and steam bun cloth) has on the yield of lipid from Nannochloropsis salina. The usage of a holder is required during the process due to the fine particles of the microalgae which have the potential to clog the instrument used. The SC-CO2 extraction without the modifier was conducted for 4 hours at 60°C, 30 MPa and CO2 flow rate of 4 ml/min, while the extraction with the modifier was conducted using 3.8 ml/min CO2 and 0.2 ml/min ethanol. It was found that the highest lipid yield of 0.16 g lipid / g dried microalgae was achieved using cotton cloth as a holder with the addition of the modifier. Lower amount of lipids were obtained when using the Soxhlet method (0.08 g lipid / g dried microalgae) and SC-CO2 without modification (0.02 g lipid / g dried microalgae). These preliminary findings show that the SC-CO2 process requires modifications to enhance the lipids yield from microalgae.

Harvesting, a challenging step of microalgae processing appears to be promising using flocculation method by the addition of tannin based natural biopolymer, AFlok-BP1. In this study, marine microalgae Nannochloropsis sp. was flocculated using AFlok-BP1 to evaluate its effectiveness in terms of flocculation efficiency, pH and dosages used, zeta potential, floc morphology characterization with comparison to the uses of aluminium sulphate and alkaline-induced pH. Oleaginous marine microalgae Nannochloropsis sp. was found to work effectively using AFlok-BP1 at an acidic pH 5 with more than 90% efficiency obtained at 160 mg/L. The finding was further supported with great instability of microalgae surface charge of -0.33 ± 0.27 mV, hence maximum destabilization of microalgae was believed to occur. The use of alum also effective to harvest Nannochloropsis sp. at neutral pH 7 with comparable efficiency as AFlok-BP1, but high dosage needed for more than 300 mg/L was at major concerns. Similarly, improved efficiency was observed for alkaline-induced pH for almost 100% efficiency. This would provide a better alternative for marine microalgae flocculation however, high concentration of minerals in the harvested biomass due to pH increase in need of further evaluation. To summarize, AFlok-BP1 would be a viable option to harvest marine microalgae Nannochloropsis sp. for the production of valuable compounds as it is an environmental friendly flocculant and provide no potential toxicity to the harvested biomass.

Subcritical water extraction (SWE) of essential oil (EO) from Citrus hystrix DC. leaves was optimized using response surface methodology (RSM), involving factors of particle size (0.5–1) mm, sample-to-solvent ratio (0.025–0.175) g/mL, extraction temperature (140−180) °C, and extraction time (20−40) minutes. Thus, an optimal EO yield of (2.14 ± 0.03) % (w/w) was obtained at 0.75 mm, 0.025 g/mL, 174 °C, and 29 min. SWE was found to yield significantly higher EO than the conventional hydrodistillation, within a shorter time. The regression model was established, presenting a significant quadratic correlation (R2 = 0.97) and adequate for predictions. SWE at 160 °C and 180 °C yielded 36 compounds, with isopulegol-dominant, exceeding SWE at 140 °C (21 compounds) and hydrodistillation (25 compounds). SWE with tunable temperatures not only improved the quantity of EO but was also capable of enhancing the quality because more EO compounds were extracted, offering diverse functionalities to nutraceutical sectors.