A review on pretreatment methods for lipid extraction from microalgae biomass.

Microalgal lipids are promising and sustainable sources for the production of third-generation biofuels, foods, and medicines. A high lipid yield during the extraction process in microalgae could be influenced by the suitable pretreatment and lipid extraction methods. The extraction method itself could be attributed to the economic and environmental impacts on the industry. This review summarizes the pretreatment methods including mechanical and non-mechanical techniques for cell lysis strategy before lipid extraction in microalgae biomass. The multiple strategies to achieve high lipid yields via cell disruption techniques are discussed. These strategies include mechanical (shear forces, pulse electric forces, waves, and temperature shock) and non-mechanical (chemicals, osmotic pressure, and biological) methods. At present, two techniques of the pretreatment method can be combined to increase lipid extraction from microalgae. Therefore, the extraction strategy for a large-scale application could be further strengthened to optimize lipid recovery by microalgae.

Impact of light spectra on photo-fermentative biohydrogen production by Rhodobacter sphaeroides KKU-PS1.

Purple non-sulphur bacteria can only capture up to 10 % light spectra and only 1-5 % of light is converted efficiently for biohydrogen production. To enhance light capture and conversion efficiencies, it is necessary to understand the impact of various light spectra on light harvesting pigments. During photo-fermentation, Rhodobacter sphaeroides KKU-PS1 cultivated at 30 °C and 150 rpm under different light spectra has been investigated. Results revealed that red light is more beneficial for biomass accumulation, whereas green light showed the greatest impact on photo-fermentative biohydrogen production. Light conversion efficiency by green light is 2-folds of that under control white light, hence photo-hydrogen productivity is ranked as green > red > orange > violet > blue > yellow. These experimental data demonstrated that green and red lights are essential for photo-hydrogen and biomass productions of R. sphaeroides and a clearer understanding that possibly pave the way for further photosynthetic enhancement research.

Enhancing biohydrogen gas production in anaerobic system via comparative chemical pre-treatment on palm oil mill effluent (POME).

Biological hydrogen production using palm oil mill effluent (POME) as a carbon source through dark fermentation process has been suggested to be a promising bioenergy potential and enacts as alternative renewable energy source. Results have indicated that among various 1.5% (w/v) chemical pre-treatments (sodium hydroxide, NaOH; hydrochloric acid, HCl; sulphuric acid, H2SO4; phosphoric acid, H3PO4 and nitric acid, HNO3) on POME, using H3PO4 would generate maximum biohydrogen production of 0.193 mmol/L/h, which corresponded to a yield of 1.51 mol H2/mol TCconsumed with an initial total soluble carbohydrate concentration of 23.52 g/L. Among H3PO4 concentrations (1%-10%), the soluble carbohydrate content and the biohydrogen produced was highest and increased by 1.70-fold and 2.35-fold respectively at 2.5% (w/v), as compared to untreated POME. The batch fermentation maximum hydrogen production rate and yield of 0.208 mmol/L/h and 1.69 mol H2/mol TCconsumed were achieved at optimum pre-treatment conditions of pH 5.5 and thermophilic temperature (60 °C). This study suggests that chemical pre-treatment approaches manage to produce and improve the carbohydrate utilisation process further. Continuous fermentation in CSTR at the optimum conditions produce heightened 1.5-fold biohydrogen yield for 2.5% H3PO4 at 6 h HRT as compared to batch scale. Bacterial community via next-generation sequencing analysis at optimum HRT (6 h) revealed that Thermoanaerobacterium thermosaccharolyticum registered the highest relative frequency of 20.24%. At the class level, Clostridia, Bacilli, Bacteroidia, Thermoanaerobacteria, and Gammaproteobacteria were identified as the biohydrogen-producing bacteria in the continuous system. Insightful findings from this study suggest the substantial practical utility of dilute chemical pre-treatment in improving biohydrogen production.

Unveiling antimicrobial activity of microalgae Chlorella sorokiniana (UKM2), Chlorella sp. (UKM8) and Scenedesmus sp. (UKM9).

Microalgae represent promising sources of bioactive compounds for pharmaceutical and industrial applications. The emergence of antibiotic resistant bacteria leads to the need to explore new cost-effective, safe, and potent bioactive compounds from the microalgae. This study aimed to investigate the potential of local microalgae for their antimicrobial properties and bioactive compounds. Three local microalgae namely Chlorella sorokiniana (UKM2), Chlorella sp. UKM8, and Scenedesmus sp. UKM9 biomass methanol extracts (ME) were prepared and tested against Gram-positive and Gram-negative bacteria. Chlorella sp. UKM8-ME showed the highest antibacterial activity. UKM8-ME minimum inhibitory concentrations were in the range of 0.312 to 6.25 mg/mL. Cytotoxicity evaluation using MTT assay showed that the microalgae methanolic extracts did not exhibit cytotoxicity against Vero-cells. The UKM8-ME was mainly containing 28 compounds from the Gas Chromatography-Mass Spectrometry (GC-MS) analysis. Major compounds of UKM8-ME included phenol (18.5%), hexadecanoic acid (18.25%), phytol (14.43%), 9,12-octadecadienoic acid (13.69%), and bicyclo[3.1.1]heptane (7.23%), which have been previously described to possess antimicrobial activity. Hence, Chlorella sp. (UKM8) methanol extracts showed promising antibacterial activity. More comprehensive studies are required to purify these antimicrobial compounds and develop our understanding on their mechanism in UKM8-ME to unleash their specific potential.

Dose-response analysis of toxic effect from palm oil mill effluent (POME) by-products on biohydrogen producing bacteria - A preliminary study on microbial density and determination of EC50.

The stimulant and toxicity effects of reported organic (acetic acid, propionic acid, butyric acid, formic acid, oil & grease) and inorganic (copper) by-products presented in palm oil mill effluent on anaerobic bacterial population were examined in this paper. The toxicity test had shown that acetic, propionic and butyric acids tend to stimulate the bacterial density level (survival rate more than 50%), while formic acid, copper, oil and grease were shown to have suppressed the density level (survival rate less than 50%). The highest biomass recorded was 1.66 mg/L for the concentration of acetic acid at 216 mg/L and lowest biomass concentration, 0.90 mg/L for copper at 1.40 mg/L. Biohydrogen-producing bacteria have a favourable growth rate around pH 5.5. The comparison of half maximal effective concentration (EC50) values between two test duration on the effects of organic and inorganic by-products postulate that bacteria had a higher tolerance towards volatile fatty acids. While acetic, butyric and propionic acids had exhibited higher tolerance EC50 values for bacteria, but the opposite trend was observed for formic acid, copper and oil & grease.

Potential Utilisation of Dark-Fermented Palm Oil Mill Effluent in Continuous Production of Biomethane by Self-Granulated Mixed Culture.

Two-stage anaerobic digestion of palm oil mill effluent (POME) is a promising method for converting the waste from the largest agricultural industry in Southeast Asia into a clean and sustainable energy. This study investigates the degradation of acid-rich effluent from the dark fermentation stage for the production of biomethane (BioCH4) in a 30-L continuous stirred-tank reactor (CSTR). The continuous methanogenic process was operated with varied HRTs (10 - 1 day) and OLRs (4.6-40.6 gCOD/L.d-1) under thermophilic conditions. Methanothermobacter sp. was the dominant thermophilic archaea that was responsible for the production rate of 4.3 LCH4/LPOME.d-1 and methane yield of 256.77 LCH4kgCOD at HRT of 2 d, which is the lowest HRT reported in the literature. The process was able to digest 85% and 64% of the initial POME's COD and TSS, respectively. The formation of methane producing granules (MPG) played a pivotal role in sustaining the efficient and productive anaerobic system. We report herein that the anaerobic digestion was not only beneficial in reducing the contaminants in the liquid effluent, but generating BioCH4 gas with a positive net energy gain of 7.6 kJ/gCOD.

Growth improvement and metabolic profiling of native and commercial Chlorella sorokiniana strains acclimatized in recycled agricultural wastewater.

This study investigated acclimation ability of native Chlorella sorokiniana (CS-N) and commercial Chlorella sorokiniana (CS-C) in palm oil mill effluent (POME), their metabolic profile and feasibility of effluent recycling for dilution purpose. Maximum specific growth rate, µmax and lag time, λ of the microalgae were evaluated. Result shows both strains produced comparable growth in POME, with µmax of 0.31 day-1 and 0.30 day-1 respectively, albeit longer λ by the CS-C. However, three cycles of acclimation was able to reduce λ from eight days to two days for CS-C. Metabolic profiling using principal component analysis (PCA) shows clear cluster of acclimatized strains to suggest better stress tolerance of CS-N. Finally, a remarkable µmax of 0.57 day-1 without lag phase was achieved using acclimatized CS-N in 40% POME concentration. Acclimation has successfully shortened the λ and dilution with final effluent was proved to be feasible for further improvement of the microalgae growth.

Palm oil mill effluent treatment and CO2 sequestration by using microalgae-sustainable strategies for environmental protection.

In this era of globalization, various products and technologies are being developed by the industries. While resources and energy are utilized from processes, wastes are being excreted through water streams, air, and ground. Without realizing it, environmental pollutions increase as the country develops. Effective technology is desired to create green factories that are able to overcome these issues. Wastewater is classified as the water coming from domestic or industrial sources. Wastewater treatment includes physical, chemical, and biological treatment processes. Aerobic and anaerobic processes are utilized in biological treatment approach. However, the current biological approaches emit greenhouse gases (GHGs), methane, and carbon dioxide that contribute to global warming. Microalgae can be the alternative to treating wastewater as it is able to consume nutrients from wastewater loading and fix CO2 as it undergoes photosynthesis. The utilization of microalgae in the system will directly reduce GHG emissions with low operating cost within a short period of time. The aim of this review is to discuss the uses of native microalgae species in palm oil mill effluent (POME) and flue gas remediation. In addition, the discussion on the optimal microalgae cultivation parameter selection is included as this is significant for effective microalgae-based treatment operations.

An overview: biomolecules from microalgae for animal feed and aquaculture.

Despite being more popular for biofuel, microalgae have gained a lot of attention as a source of biomolecules and biomass for feed purposes. Algae farming can be established using land as well as sea and strategies can be designed in order to gain the products of specific interest in the optimal way. A general overview of the contributions of Algae to meet the requirements of nutrients in animal/aquaculture feed is presented in this study. In addition to its applications in animal/aquaculture feed, algae can produce a number of biomolecules including astaxanthin, lutein, beta-carotene, chlorophyll, phycobiliprotein, Polyunsaturated Fatty Acids (PUFAs), beta-1,3-glucan, and pharmaceutical and nutraceutical compounds which have been reviewed with respect to their commercial importance and current status. The review is further extended to highlight the adequate utilization of value added products in the feeds for livestock, poultry and aquaculture (with emphasis in shrimp farming).

Performance of AFEX™ pretreated rice straw as source of fermentable sugars: the influence of particle size.

BACKGROUND: It is widely believed that reducing the lignocellulosic biomass particle size would improve the biomass digestibility by increasing the total surface area and eliminating mass and heat transfer limitation during hydrolysis reactions. However, past studies demonstrate that particle size influences biomass digestibility to a limited extent. Thus, this paper studies the effect of particle size (milled: 2 mm, 5 mm, cut: 2 cm and 5 cm) on rice straw conversion. Two different Ammonia Fiber Expansion (AFEX) pretreament conditions, AFEX C1 (low severity) and AFEX C2 (high severity) are used to pretreat the rice straw (named as AC1RS and AC2RS substrates respectively) at different particle size. RESULTS: Hydrolysis of AC1RS substrates showed declining sugar conversion trends as the size of milled and cut substrates increased. Hydrolysis of AC2RS substrates demonstrated opposite conversion trends between milled and cut substrates. Increasing the glucan loading to 6% during hydrolysis reduced the sugar conversions significantly in most of AC1RS and AC2RS except for AC1RS-2 mm and AC2RS-5 cm. Both AC1RS-2 mm and AC2RS-5 cm indicated gradual decreasing trends in sugar conversion at high glucan loading. Analysis of SEM imaging for URS and AFEX pretreated rice straw also indicated qualitative agreement with the experimental data of hydrolysis. The largest particle size, AC2RS-5 cm produced the highest sugar yield of 486.12 g/kg of rice straw during hydrolysis at 6% glucan loading equivalent to 76.0% of total theoretical maximum sugar yield, with an average conversion of 85.9% from total glucan and xylan. In contrast, AC1RS-5 cm gave the lowest sugar yield with only 107.6 g/kg of rice straw, about 16.8% of total theoretical maximum sugar yield, and equivalent to one-quarter of AC2RS-5 cm sugar yield. CONCLUSIONS: The larger cut rice straw particles (5 cm) significantly demonstrated higher sugar conversion when compared to small particles during enzymatic hydrolysis when treated using high severity AFEX conditions. Analysis of SEM imaging positively supported the interpretation of the experimental hydrolysis trend and kinetic data.