Search

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. [ABSTRACT FROM AUTHOR]

A current Microbial Desalination Cell (MDC) system often uses chemicals or air cathodes that are toxic and impractical for scalable applications. This work presents the MDC performance that utilized microalgae species Chlamydomonas sp. (UKM6) and Scenedesmus sp. (UKM9). These species supported the role of the terminal electron acceptor in the cathode chamber of photosynthetic MDCs (PhMDC). The results showed that PhMDC-UKM9 and UKM6 produced 1942 mW/m3 and 1714 mW/m3 power densities with 44% and 32% desalination rates, respectively. The desalination of salt concentration (35 g/L) was approaching the practical application of seawater. Both UKM6 and UKM9 achieved chemical oxygen demand (COD) removal in the anode chamber by 49% and 53%, respectively. 16S microbial community analysis in anolyte revealed phylum Firmicutes as the dominion community. This study demonstrated that the local microalgae species integrate power production, wastewater treatment, and water purification through PhMDC operation, comparable with other studies using commercial microalgae. [Display omitted] • Microalgae as biocatalysts support catalytic performance of PhMDC. • Maximum power achieved was 1942 mW/m3 from Scenedesmus sp. UKM9. • PhMDC with microalgae produced three folds more power density than control. • 97% Firmicutes dominated the microbial community of anolyte. • PhMDC-UKM9 showed the highest COD removal (53%) and desalination efficiencies (44.8%). [ABSTRACT FROM AUTHOR]

The dissolved CO 2 that causes ocean acidification has great potential for bioenergy production. In this study, we demonstrate that activated methanogens in waste sewage sludge (WSS) are useful for converting bicarbonate in seawater into methane. These activated methanogens were adapted in different seawater sources for methane production through repeated batch experiments that resulted in an increase of 300–400 fold in the methane yield. During these repeated batch experiments, the microbial communities in WSS adapted to the high salinity of seawater to generate more methane. Microbial community analysis showed the dominance of Achromobacter xylosoxidans, Serrati sp. and methanogens including Methanobacterium sp., Methanosarcina sp., and Methanosaeta concillii . Using a 13 C-labeled isotope, we demonstrate that 81% of the methane is derived from microbial conversion of NaH 13 CO 2 in artificial seawater. Therefore, this study shows that oceans, with the largest surface area on Earth, have a potential as a substrate for methane energy production via an acclimated consortium approach. [ABSTRACT FROM AUTHOR]

Carbon dioxide (CO 2 ) is the main greenhouse gas; hence, processes are needed to remove it from the environment. Here, CO 2 was used as the substrate to generate methane (CH 4 ) by using enriched methanogens after anaerobic enrichment of waste activated sludge (WAS); therefore, we demonstrate that methanogens from WAS have significant potential for converting the greenhouse gas CO 2 into the fuel methane. Methane production was found to increase 70 fold by active methanogens in the enriched methanogens culture after 3 days in the presence of H 2 and CO 2 . Throughout the process, CO 2 was completely consumed after 4 days of incubation in the vials after sparging with a mixture of H 2 and CO 2 , resulting in significant biological CO 2 sequestration by methanogens. Using a mixture of H 2 and 13 CO 2 , we also demonstrated that the methane produced is due to the utilization of CO 2 . Microbial community studies via by quantitative real time PCR (qRT-PCR) indicate the dominance of archaea in the enriched methanogens culture of WAS. Archaeal community studies of the enriched methanogens via high-throughput 16S rRNA sequencing also showed that the archaea consist mainly of hydrogenotrophic and aceticlastic methanogens such as Methanobacteriaceae , Methanospirillaceae and Methanosarcinaceae spp. which are actively grown in H 2 and CO 2 . We envision that CO 2 gas from power plants can be directed to enriched methanogens of WAS to prevent release of this greenhouse gas while generating a useful biofuel (methane) or other valuable products using this single carbon atom. [ABSTRACT FROM AUTHOR]

Appropriate control of waste activated sludge (WAS) is required to solve the annual increment of WAS volume. The low bacterial activity at low temperatures poses a difficulty in reducing or utilizing WAS in cold weather regions and/or during the winter season. This study reveals a practical method to enhance sludge reduction at a low temperature using isolated strains of Pseudomonas and Aeromonas species. The effect of inoculating each strain into WAS was examined at different temperatures (4 °C, 10 °C, 12 °C, 15 °C, 20 °C, and 30 °C) and under an aerobic condition. Sludge reduction showed 2- to 8-fold improvement at the temperature range from 4 °C to 15 °C. Both strains are psychrophilic and can produce protease and lipase for sludge degradation even at low temperatures. Thus, biological WAS treatment at a psychrophilic temperature can be enhanced by inoculating these promising strains. [ABSTRACT FROM AUTHOR]

The management of waste activated sludge (WAS) recycling is a concern that affects the development of the future low-carbon society, particularly sludge reduction and biomass utilization. In this study, we investigated the effect of removing extracellular polymeric substances (EPS), which play important roles in the adhesion and flocculation of WAS, on increased sludge disintegration, thereby enhancing sludge reduction and methane production by anaerobic digestion. EPS removal from WAS by ethylenediaminetetraacetic acid (EDTA) significantly enhanced sludge reduction, i.e., 49 ± 5% compared with 27 ± 1% of the control at the end the digestion process. Methane production was also improved in WAS without EPS by 8881 ± 109 CH 4 μmol g −1 dry-weight of sludge. Microbial activity was determined by denaturing gradient gel electrophoresis and real-time polymerase chain reaction, which showed that the hydrolysis and acetogenesis stages were enhanced by pretreatment with 2% EDTA, with a larger methanogenic community and better methane production. [ABSTRACT FROM AUTHOR]

Abstract: Biohydrogen is considered a promising and environmentally friendly energy source. Escherichia coli BW25113 hyaB hybC hycA fdoG frdc ldhA aceE has been previously engineered for elevated biohydrogen production from glucose. In this study, we show that this strain can also use biomass from oil palm frond (OPF) juice and sewage sludge as substrates. Substrate improvement was accomplished when hydrogen productivity increased 8-fold after enzymatic treatment of the sludge with a mixture of amylase and cellulase. The OPF juice with sewage sludge provided an optimum carbon/nitrogen ratio since the yield of biohydrogen increased to 1.5 from 1.3 mol H2/mol glucose compared to our previous study. In this study, we also reveal that our engineered strain improved 200-fold biohydrogen productivity from biomass sources compared to the unmodified host. In conclusion, we determined that our engineered strain can use biomass as an alternative substrate for enhanced biohydrogen production. [Copyright &y& Elsevier]

Abstract: An anaerobic fermentation of food waste was conducted in a 0.5 L bioreactor incubated at a thermophilic temperature of 55 °C to evaluate the effects of different controlled pH values (5.0, 5.5 and 6.0) on biohydrogen production. Effective biohydrogen production was found at controlled pH 5.5 and 6.0 corresponding to lower lactic acid production compared to pH 5.0. It was demonstrated that biohydrogen production from food waste was pH-dependent with hydrogen yields of 79, 76 and 23 mmol H2/L-media/d for pH 5.5, 6.0 and 5.0, respectively. Specific microbial determination for Clostridium sp. and total bacteria quantification were carried out by the fluorescent in-situ hybridization (FISH) technique. The number of Clostridium sp. for acclimatized sludge, fermentation broth at pH 5.0, 5.5 and 6.0 were 2.9 × 108, 3.6 × 108, 7.8 × 108 and 5.4 × 108 cells/ml, respectively. The quantification analysis showed that 92% of the total bacteria belonged to Clostridium sp. from clusters I and XI from the sample at controlled pH 5.5. The denaturing gradient gel electrophoresis (DGGE) bands of the sample after heat-treatment, acclimatization and during fermentation indicated the presence of Bacteroidetes, Caloromator australicus sp. and Clostridium sp. [Copyright &y& Elsevier]

Optimization of microalgal biomass harvesting is essential to produce effective and optimum outcomes that can contribute towards a feasible and economical harvesting technique. Two Chlorella species were used, namely, C. vulgaris and C. sorokiniana UKM3. Two essential factors affecting microalgal biomass harvesting via flocculation, namely, the initial pH of the microalgal broth and flocculant (chitosan) concentration were studied. The optimization process was conducted by using a response surface methodology (RSM) based on the model of face-centered-central composite design (FC-CCD). The potential for biofuel application of the harvested biomass was evaluated based on the production of fatty acid methyl esters (FAMEs) by transesterification. The quadratic models obtained from the RSM significantly fitted the experiment data as the p-values were less than 0.05. The initial pH of the microalgal suspension was found to have a more significant effect on the flocculation process than flocculant concentration. For C. vulgaris, the highest flocculant efficiency of 98.7% was obtained at a chitosan concentration of 0.2 g L−1 and an initial pH of 12.0, whereas for C. sorokiniana UKM3, at 0.15 g L−1 of chitosan and initial pH of 12.0 produced the highest efficiency of 97.1%. The harvested biomass of both species exhibited a high content of palmitic acid (C16:0) with 29.74 wt% and 11.81 wt% of dry biomass for C. vulgaris and C. sorokiniana UKM3, respectively. This study showed that Chlorella species can be harvested efficiently using the flocculation process and manifested an excellent potential for biodiesel production where palmitic acid (C16:0) is one of the main compounds for high-acid oil-biodiesel. [ABSTRACT FROM AUTHOR]

Culture scaffolds allow microalgae cultivation with minimum water requirement using the air-liquid interface approach. However, the stability of cellulose-based scaffolds in microalgae cultivation remains questionable. In this study, the stability of regenerated cellulose culture scaffolds was enhanced by adjusting TiO 2 loading and casting gap. The membrane scaffolds were synthesized using cellulose dissolved in NaOH/urea aqueous solution with various loading of TiO 2 nanoparticles. The TiO 2 nanoparticles were embedded into the porous membrane scaffolds as proven by Fourier transform infrared spectra, scanning electron microscopic images, and energy-dispersive X-ray spectra. Although surface hydrophilicity and porosity were enhanced by increasing TiO 2 and casting gap, the scaffold pore size was reduced. Cellulose membrane scaffold with 0.05 wt% of TiO 2 concentration and thickness of 100 μm attained the highest percentage of Navicula incerta growth rate, up to 37.4%. The membrane scaffolds remained stable in terms of weight, porosity and pore size even they were immersed in acidic solution, hydrogen peroxide or autoclaved at 121 °C for 15 min. The optimal cellulose membrane scaffold is with TiO 2 loading of 0.5 wt% and thickness of 100 μm, resulting in supporting the highest N. incerta growth rate and and exhibits good membrane stability. [Display omitted] • The hydrophilicity of scaffolds enhanced with the increasing of TiO 2 nanoparticles. • The contact angle of scaffolds reduced to 38.5 ± 0.9° when 0.2 wt% TiO 2 added. • Scaffolds with 0.05 wt% TiO 2 and 100 μm showed the highest microalgae growth rate of 37.4%. • The membrane scaffolds remained stable even undergone sterilization. [ABSTRACT FROM AUTHOR]

Microalgae cultivation using open cultivation systems requires large area and it is susceptible to contamination as well as weather changes. Meanwhile, the closed systems require large capital investment, and they are susceptible to the build-up of dissolved oxygen. Air-liquid interface culture systems with low water-footprint, but high packing density can be used for microalgae cultivation if low-cost culture scaffolds are available. In this study, cellulose-based scaffolds were synthesized using NaOH/urea aqueous solution as the solvent. Titanium dioxide (TiO 2), silica gel and polyethylene glycol 1000 (PEG 1000) nanoparticles were added into the membrane scaffolds to increase the hydrophilicity of nutrient absorbing to support the growth of microalgae. The membrane scaffolds were characterized by FTIR, SEM, contact angle, porosity and porometry. All three nanoparticles additives showed their ability in reducing the contact angle of membrane scaffolds from 63.4 ± 2.3° to a range of 52.6 ± 1.2° to 38.8 ± 1.5° due to the hydrophilic properties of the nanoparticles. The decreasing in pore size when nanoparticles were added did not affect the porosity of membrane scaffolds. Cellulose membrane scaffold with TiO 2 showed the highest percentage of microalgae Navicula incerta growth rate of 22.1% because of the antibacterial properties of TiO 2 in lowering the risk of cell contamination and enhancing the growth of N. incerta. The results exhibited that cellulose-based scaffold with TiO 2 added could be an effective support in plant cell culture field. [Display omitted] • Cellulose-based scaffolds were synthesized using cellulose dispersed in NaOH/urea solvent. • Nanoparticles were added to enhance scaffold properties. • The contact angle of membrane scaffolds reduced to 38.8 ± 1.5° due to hydrophilicity. • Scaffold with TiO 2 nanoparticles showed the highest microalgae growth rate of 21.7%. • Nutrient adsorption of microalgae was enhanced by air-liquid interface cultivation. [ABSTRACT FROM AUTHOR]

[Display omitted] • Cellulose nanofibers (CNF) were extracted from Chlorella vulgaris. • Extraction involved alkaline treatment, bleaching, and acid hydrolysis in a blender. • Maximum yield (58.5%) was achieved using sulphuric acid with a concentration of 60%. • Nanocellulose was incorporated into carboxymethyl cellulose/sodium alginate beads. • Methylene blue adsorption capacity raised from 28.46 mg/g to 109.03 mg/g. Water pollution requires sustainable materials to develop green treatment solutions. Nanocellulose with outstanding properties is a sustainable building block of adsorbent for wastewater treatment. However, nanocellulose extraction from plants remains an energy and chemical-intensive process. This study aims to produce nanocellulose from microalgae via facile extraction for the synthesis of hydrogel adsorbents. Without TEMPO-mediated oxidation, nanocellulose was successfully extracted from Chlorella vulgaris through alkaline treatment, bleaching, and hydrolysis only in a high-speed blender in this study. The effects of acid concentration on nanocellulose properties were studied. The maximum yield (58.5%) was achieved using sulphuric acid with a concentration of 60%(v/v). Scanning electron microscopy and transmission electron microscopy images showed the fibrillated structure at the nanoscale. Fourier-transform infrared spectroscopy results confirmed the elimination of lignin and hemicellulose through alkaline treatment, while X-ray diffraction patterns proved that microalgae nanocellulose were typical cellulose I. The microalgae nanocellulose was further incorporated into carboxymethyl cellulose/sodium alginate beads. Methylene blue adsorption capacity raised from 28.46 mg/g to 109.03 mg/g. Dye removal percentage as high as 93.7% could be achieved due to the hydrogen bonding and electrostatic interaction with carboxylate groups. [ABSTRACT FROM AUTHOR]

Summary: The low cost, low over‐potential loss, good catalytic properties for hydrogen evolution reaction (HER), high corrosion stability, commercially available, and could be applied in pH‐neutral solution and ambient temperature are important properties for the cathode materials when it is applied in microbial electrolysis cell (MEC) technology. This study has two‐pronged objectives: the first is to investigate the feasibility of titanium (Ti) and graphite felt (GF) coated with nickel (Ni), and the second is to generate hydrogen from the fermentation effluent (FE). The electrodeposition (ED) method was used to deposit Ni catalyst onto Ti (Ni/Ti) and GF (Ni/GF) surfaces. The scanning electron microscopy (SEM) and energy dispersive X‐ray (EDX) spectroscopy were used to characterize the cathode morphology and element composition. The catalytic properties of Ni/Ti and Ni/GF could be evaluated using the linear sweep voltammetry tests. The maximum volumetric H2 production rates of MEC using Ni/Ti and Ni/GF cathodes were obtained at 0.39 ± 0.01 and 0.33 ± 0.03 m3 H2 m−3 d−1 respectively. The Ni/Ti and Ni/GF cathodes could be used as alternative cathodes while producing hydrogen from FE. [ABSTRACT FROM AUTHOR]

Palm oil mill effluent (POME) is a highly polluted agro-industrial wastewater. The CO2 in industrial flue gas requires treatment before it can be discharged into the environment. Utilizing microalgae as the agent to treat wastewater and industrial flue gas is a waste-to-wealth approach. The resulting biomass can be commercialized in the form of valuable products. Chlorella sp. is a microalgal species that can tolerate the pollutant load and has been proven to be a suitable species for CO2 fixation. In this study, Chlorella sp. was cultivated in POME with the aim of reducing the pollutants in the POME and simultaneously capturing CO2. The optimization of the operational conditions of this microalgae-based treatment system was carried out using the response surface methodology (RSM) face centered-central composite design (FC-CCD). Operational factors include the air concentration of CO2 (10-25% v/v), the inlet gas flow rate of 500-2000 mL min−1, and initial inoculum concentration (10-30% v/v) of Chlorella sp. cultivated in POME. The target deliverables include the maximum amount of CO2 fixed by Chlorella sp. and the total nitrogen (TN) reduction as indicators of pollutant reduction by this treatment system. We found that a limited supply of CO2 caused growth limitation, while excess CO2 resulted in acid production that triggered microalgae growth inhibition. The optimum operational conditions were 10% v/v CO2, 1670 mL min−1 aeration rate, and 24.8% v/v inoculum concentration, predicted to simultaneously fix CO2 at 0.12 g of CO2 L−1 day−1 and reduce 80.9% TN, respectively. [ABSTRACT FROM AUTHOR]

Microalgae cultivation in open ponds requires a large footprint, while most photobioreactors need improvement in the ratio of surface to volume and energy consumption. In this study, polyethersulfone (PES) and poly(vinylidene fluoride) (PVDF) hollow fiber membranes with a large surface area were rearranged into open-ended and dead-ended configurations to improve the air-liquid interface cultivation of Navicula incerta. N. incerta were successfully grown on the porous membrane surface with the nutrients circulating inside the lumen. Fourier-transform infrared spectra showed the accumulation of polysaccharides, proteins and humic acids. Hydrophilic polysaccharides reduced water contact angles on PES and PVDF membranes to 37.2 ± 2.6° and 55.7 ± 3.3°, respectively. However, the porosity of PES (80.1 ± 1.1%) and PVDF (61.3 ± 4.5%) membranes were not significantly affected even after cultivation and harvesting of N. incerta. Scanning electron images further confirmed that N. incerta , cell debris and extracellular organic matter accumulated on the membrane. With large pores and a hydrophobic surface, PVDF hollow fiber membranes offered a greater improvement in N. incerta cell growth rate compared to PES hollow fiber membranes despite using different configurations. In the dead-ended configuration, they even attained the greatest improvement in N. incerta growth rate, up to 54.0%. However, PES hollow fiber membranes only achieved improvement in harvesting efficiency within the range of 18.7–38.0% due to weak cell adhesion. PVDF hollow fiber membranes significantly promoted the growth of microalgae N. incerta through the air-liquid interface system, leading to potential applications in wastewater treatment. [Display omitted] • PES and PVDF hollow fiber membranes were rearranged for the air-liquid interface cultivation. • Microalgae grew on the membrane surface with the nutrients circulating inside the lumen. • Membrane porosity remained after cultivation and harvesting through air purge. • PVDF membrane with large pores and a hydrophobic surface promoted cell growth rate. • The dead-ended configuration attained an improvement of 54.0% in cell growth rate. [ABSTRACT FROM AUTHOR]

Palm oil mill effluent (POME) contains nutrients such as carbon, nitrogen and phosphorus, and poses a threat to the environment especially if released untreated into water bodies. The phylum Chlorophyta contains microalgae from the genus Scenedesmus which are utilised as bioremediation agents. This study was conducted to evaluate the performance of Scenedesmus sp. UKM9 to remove chemical oxygen demand (COD) and nutrients (NH 4 + and PO 4 3−) from anaerobic POME by considering photoperiods and pollutant loading rates as environmental parameters. The results showed that the removal of COD (57% removal) and NH 4 + (100% removal) was the highest in a 12h:12h (light:dark) photoperiod and a pollutant loading rate of 61.67 mg L−1 day−1 COD. Removal of PO 4 3− (91% removal) was highest in a 16h:8h (light:dark) photoperiod and a pollutant loading rate of 11.67 mg L−1 day−1 COD. The removal of COD, nitrogen and phosphate occurred via the actions of microalgae through assimilation, bacteria through oxidation and precipitation through the formation of calcium phosphate complexes. These findings suggest that Scenedesmus sp. strain UKM9 is a potential bioremediation agent for treating POME. [Display omitted] • Cultivation of Scenedesmus sp. strain UKM9 in palm oil mill effluent (POME). • Effect of photoperiods and pollutant loading rates were investigated. • High removal of COD and NH 4 + in 12 h compared to 24 h photoperiod. • High removal of PO 4 3− 16 h photoperiod. • Scenedesmus sp. strain UKM9 is a potential bioremediation agent for treating POME. [ABSTRACT FROM AUTHOR]

• Catalytic properties of Ni-Fe and GF/Pt were characterized using LSV tests. • Tafel slope was determined based on the data points in the onset potential. • EGF can be used as substrate for hydrogen production. • Ni-Fe shows comparable performance with GF/Pt cathode in BES application. The high cost of Pt-based cathode, and its possibility of being poisoned by the presence of buffer in the electrolyte are two paramount issues in the BES system. The Ni-Fe has become one of the good alternatives because it has excellent catalytic properties, inexpensive, commercially available and low toxicity to microorganisms. In this study, Ni-Fe foam applied as a cathode in dual-chamber BES, while effluent of glucose fermentation as a substrate in the anode side. The characteristic of Ni-Fe surface was analyzed by using field emission scanning electron microscopy. Whereas, the catalytic property of Ni-Fe was evaluated by using linear sweep voltammetry test. The maximum hydrogen production rate and yield obtained were 500 ± 80 m3/m3/d and 470.2 ± 11.2 mL/g COD, respectively. The results show that the Ni-Fe has comparable performance to GF/Pt. Hence it could be used as an alternative cathode in BES application. [ABSTRACT FROM AUTHOR]