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Microalgae demonstrate significant potential as a source of liquid-based biofuels. However, increasing biomass productivity in existing cultivation systems is a critical prerequisite for their successful integration into large-scale operations. Thus, the current work aimed to accelerate the growth of C. vulgaris via exogenous supplementation of biostimulant derived from onion peel waste. Under the optimal growth conditions, which entailed a biostimulant dosage of 37.5% v/v, a pH of 3, an air flow rate of 0.4 L/min, and a 2% v/v inoculum harvested during the mid-log phase, yielded a maximum biomass concentration of 1.865 g/L. Under the arbitrarily optimized parameters, a comparable growth pattern was evident in the upscaled cultivation of C. vulgaris, underscoring the potential commercial viability of the biostimulant. The biostimulant, characterized through gas chromatography-mass spectrometry (GC-MS) analysis, revealed a composition rich in polyphenolic and organo-sulphur compounds, notably including allyl trisulfide (28.13%), methyl allyl trisulfide (23.04%), and allyl disulfide (20.78%), showcasing potent antioxidant properties. Additionally, microalgae treated with the biostimulant consistently retained their lipid content at 18.44% without any significant reduction. Furthermore, a significant rise in saturated fatty acid (SFA) content was observed, with C16:0 and C18:1 dominating both bench-scale (44.08% and 14.01%) and upscaled (51.12% and 13.07%) microalgae cultures, in contrast to the control group where C18:2 was prevalent. Consequently, SFA contents reached 54.35% and 65.43% in bench-scale and upscaled samples respectively, compared to 33.73% in the control culture. These compositional characteristics align well with the requirements for producing high-quality crude biodiesel., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Ltd. All rights reserved.)

The article titled "A Review on Insights for Green Production of Unconventional Protein and Energy Sources Derived from the Larval Biomass of Black Soldier Fly" has been retracted by the Processes Editorial Office due to major scientific errors and concerns about the validity of the findings. An investigation confirmed the presence of a major scientific error, leading to the decision to retract the publication. The retraction was approved by the Editor-in-Chief of the journal, although the authors did not agree with the retraction. [Extracted from the article]

The article titled "In-Situ Yeast Fermentation Medium in Fortifying Protein and Lipid Accumulations in the Harvested Larval Biomass of Black Soldier Fly" has been retracted by the Processes Editorial Office due to concerns regarding major scientific errors and the overall validity of the findings. An investigation conducted by the Editorial Office and Editorial Board found that the integrity of the central findings of the study could not be satisfactorily verified based on the presented material. The retraction was approved by the Editor-in-Chief of the journal, although the authors did not agree with the retraction. [Extracted from the article]

Conventional microalgal cultivation method relied on suspended growth or attached growth that uses inert solid surfaces, requiring the addition of external carbon sources to promote microalgal growth. The inert solid substrates for attached microalgae pose constraints on the maximal capabilities of these microorganisms as it does not possess the ability to provide the necessary nutritional support required for optimal microalgal growth. As a result, microalgae are obliged to only rely on the solid substrate as a means of attachment, without any further nutritional provisions. Slower growth rates, larger resource requirements, and exorbitant operating expenses had prompted the exploration of an alternative strategy, i.e; the innovative use of solid organic waste as nutritional source cum attachment platform. The findings of this review unveil key insights into microalgae cultivation system, offering a solution to economic challenges in the production phase. This innovation not only promotes economic feasibility and sustainability, but also contributes to economically viable and environmentally sustainable biofuel production. [Display omitted] • New breakthroughs for conventional attached microalgal cultivation system. • Intrinsic environmental and nutrient factors to spur attached microalgal growth. • Organic solid wastes exude nutrients for populating attached microalgal cells. [ABSTRACT FROM AUTHOR]

Abstract In order to retain a high concentration of activated sludge in the wastewater treatment plant, the dense activated sludge is entrapped into the polyvinyl alcohol (PVA) cryogel beads. For protecting the entrapped activated sludge biomass from the inhibitory effect exerted by recalcitrant pollutant, i.e., 4-chlorophenol (4-CP), the novel PVA cryogel beads with external surface covered by the powdered activated carbon (PAC) were successfully synthesized in this study. The synthesis was achieved by extruding the biomass-PVA polymeric matrix into the gelatin solution containing PAC. The maximum PAC density on the external surface of cryogel beads was calculated to be in the range of 938–978 mg/m2. The PAC distributed on the external surface of cryogel beads was found to possess a higher 4-CP adsorption capacity than the beads with homogenized PAC. These cryogel beads were also capable of shielding the activated sludge biomass entrapped within beads from being directly exposed to the inhibitory effect of 4-CP via adsorption by PAC distributed on the external surface. Thus, only low concentration of 4-CP was diffused into the beads and biodegraded to achieve a total removal of 4-CP. This beneficial effect was later confirmed could last for more than 20 cycles of uses in removing 4-CP via the simultaneous adsorption and biodegradation processes. Highlights • Immobilized biomass cryogel beads synthesis with PAC attached on external surface. • Biomass shielding from inhibitory effect of 4-chlorophenol via adsorption by PAC. • Removal of 4-cholrophenol via the simultaneous adsorption and biodegradation. • Recyclability of cryogel beads in treating wastewater containing 4-chlorophenol. [ABSTRACT FROM AUTHOR]

The symbiotic relationships between activated sludge and microalgae were explored for bio-remediating nitrogen-rich wastewater and producing lipid-based biofuel simultaneously. Various inoculation ratios of activated sludge to microalgae (AS:MA) biomasses were employed to unveil the mechanism of NH 4 + -N removal in relation to lipid production from algal-bacterial biomass. The presence of nitrifiers in converting NH 4 + -N into oxidized nitrogen (NO 2 − -N and NO 3 − -N) had greatly enhanced the total nitrogen removal in the co-cultivation bioreactors as compared with the individual culture of either activated sludge or microalgae. Accordingly, achieving near complete nitrogen removal (97–98%) when the bioreactors were inoculated with AS:MA ratios of 1:0.75 and beyond. The kinetic growths of co-cultivated activated sludge and microalgae biomasses were also investigated using Verhulst model; demonstrating a significant increase of specific biomass growth rate with increasing of initial microalgae inoculation ratio. The AS:MA ratio of 1:0.75 was considered optimum for the symbiotic algal-bacterial interactions, attaining the highest lipid yield of 130 mg/L and flocculation efficiency of 42% which would aid the biomass harvesting process. [ABSTRACT FROM AUTHOR]

• Mechanisms of biohydrogen production from various microalgal metabolic activities. • Genetic engineering on microalgal strains in enhancing biohydrogen production. • Environmental factors that influence the biohydrogen production from microalgae. • Problems associated to microalgal biohydrogen production and overcoming strategies. The global depletion of fossil fuel reserves and associated environmental crisis have led researchers to explore microalgal biomass which has been proven could be a promising potential as a renewable energy feedstock. Biofuels such as biodiesel, bioethanol and hydrogen can be produced from microalgae. Indeed, microalgae are best employed for hydrogen generation because the microalgal cells have high growth rate, can grow in diverse habitats and non-arable lands, can solve the fuel versus food conflicts as well as can capture and assimilate the atmospheric carbon dioxide. Hydrogen that is produced from microalgae is a clean and sustainable option to replace or complement the fossil fuel demands. The combustion of hydrogen produces only water and no greenhouse gases emission which will assuage the untoward effect on the environment. Moreover, it can also be used directly to generate electricity in fuel cells and engines. Another sector that is looking into hydrogen as a replacement for fossil fuels, is transportation inclusive of the aviation industry. The use of hydrogen as an energy carrier in airplanes offers several advantages, the burning of hydrogen in the jet engines would produce water vapour which will eliminate carbon-related emissions. However, this also comes with limitations such as new designs and larger tanks for hydrogen storage. Besides, the mechanisms of hydrogen production from microalgae are also sporadic and not well documented systematically, pre-empting researchers from exploring this new energy source inclusively. The factors affecting the microalgal hydrogen production are as well essential, but still poorly conceived, leading to the low outputs in terms of hydrogen yields from microalgae. Accordingly, this article reviews various mechanisms and methods employed for producing hydrogen from microalgae as well as the pre-treatment procedures for enhancing the rates of hydrogen production from microalgae. Furthermore, the enhancement of hydrogen yields through state-of-the-art techniques and genetic engineering the microalgal strains are also unveiled to materialize the hydrogen production at an industrial scale. This review intents to shift the paradigm from typical hydrocarbon biofuels to green hydrogen adoption, hastening the carbon neutrality target that benefits the natural environment the most. [ABSTRACT FROM AUTHOR]

The feasibility of using dried attached-growth biomass from the polyurethane (PU) foam cubes as a solid carbon source to enhance the denitrification process in the intermittently aerated moving bed sequencing batch reactor (IA-MBSBR) during the treatment of low COD/N containing wastewater was investigated. By packing the IA-MBSBR with 8 % ( v/ v) of 8-mL PU foam cubes saturated with dried attached-growth biomass, total nitrogen removal efficiency of 80 % could be achieved for 10 consecutive cycles of operation when the intermittent aeration strategy of consecutive 1 h of aeration followed by 2 h of non-aeration period during the REACT period of the IA-MBSBR was adopted. Negligible release of ammonium nitrogen (NH-N) and slow-release of COD from the dried biomass would ensure that the use of this solid carbon source would not further burden the treatment system. The slow-releasing COD was found to have no effect in promoting the assimilation process and would also allow the carbon source to be used for many cycles of operation. The 'carbon-spent' PU foam cubes could be reused by merely drying at 60 °C at the end of the operational mode. Thus, the dried attached-growth biomass formed on the PU foam cubes could be exploited as an alternative solid carbon source for the enhancement of denitrification process in the IA-MBSBR. [ABSTRACT FROM AUTHOR]

Abstract: The performance of moving bed sequencing batch reactors (MBSBRs) added with 8 % (v/v) of polyurethane (PU) foam cubes as carrier media in nitrogen removal was investigated in treating low COD/N wastewater. The results indicate that MBSBR with 8-mL cubes achieved the highest total nitrogen (TN) removal efficiency of 37% during the aeration period, followed by 31%, 24% and 19 % for MBSBRs with 27-, 64- and 125-mL cubes, respectively. The increased TN removal in MBSBRs was mainly due to simultaneous nitrification and denitrification (SND) process which was verified by batch studies. The relatively lower TN removal in MBSBR with larger PU foam cubes was attributed to the observation that larger PU foam cubes were not fully attached by biomass. Higher concentrations of 8-mL PU foam cubes in batch reactors yielded higher TN removal. [Copyright &y& Elsevier]

Over the past decade, there has been a surge of interest in using char (hydrochar or biochar) derived from biomass as persulfate (PS, either peroxymonosulfate or peroxydisulfate) activator for anthropogenic pollutants removal. While extensive investigation showed that char could be used as a PS activator, its sustainability over prolonged application is equivocal. This review provides an assessment of the knowledge gap related to the sustainability of char as a PS activator. The desirable char properties for PS activation are identified, include the high specific surface area and favorable surface chemistry. Various synthesis strategies to obtain the desirable properties during biomass pre-treatment, hydrochar and biochar synthesis, and char post-treatment are discussed. Thereafter, factors related to the sustainability of employing char as a PS activator for anthropogenic pollutants removal are critically evaluated. Among the critical factors include performance uncertainty, competing adsorption process, char stability during PS activation, biomass precursor variation, scalability, and toxic components in char. Finally, some potential research directions are provided. Fulfilling the sustainability factors will provide opportunity to employ char as an economical and efficient catalyst for sustainable environmental remediation. [Display omitted] • The desirable char properties as persulfate activator for pollutant removal are identified. • Various strategies to obtain the desirable properties are discussed. • Factors affecting sustainability of char as persulfate activator are critically evaluated. • Prospects of developing sustainable char as persulfate activation are proposed. [ABSTRACT FROM AUTHOR]

A novel sequential flow baffled microalgal-bacterial (SFB-AlgalBac) photobioreactor was designed to cater for the synergistic interactions between microalgal and bacterial consortia to enhance nitrogen assimilation into microalgal biomass from nutrient-rich wastewater medium. The performance of the SFB-AlgalBac photobioreactor was found to be optimum at the influent flow rate of 5.0 L/d, equivalent to 20 days of hydraulic retention time (HRT). The highest microalgal nitrogen assimilation rate (0.0271 /d) and biomass productivity (1350 mg/d) were recorded amidst this flow rate. Further increase to the 10.0 L/d flow rate reduced the photobioreactor performance, as evidenced by a reduction in microalgal biomass productivity (>10%). The microalgal biomass per unit of nitrogen assimilated values were attained at 16.69 mg/mg for the 5.0 L/d flow rate as opposed to 7.73 mg/mg for the 10.0 L/d flow rate, despite both having comparable specific growth rates. Also, the prior influent treatment by activated sludge was found to exude extracellular polymeric substances which significantly improved the microalgal biomass settleability up to 37%. The employment of SFB-AlgalBac photobioreactor is anticipated could exploit the low-cost nitrogen sources from nutrient-rich wastewaters via bioconversion into valuable microalgal biomass while fulfilling the requirements of sustainable wastewater treatment technologies. ga1 • New photobioreactor design to enhance microalgal biomass growth. • Rederived kinetic growth model to predict optimum flow rate for photobioreactor. • Prior bacterial nitrification promoting nitrogen assimilation by microalgae. • Extracellular polymeric substances from bacteria flocculating microalgal cells. • Potential low-cost nitrogen exploitation from nutrient-rich wastewater. [ABSTRACT FROM AUTHOR]

The potentiality of a microalgal-bacterial culture system was explored in bioremediating wastewater while generating biomass for biodiesel production. A pre-determined optimal activated sludge and microalgal ratio was adopted and cultivation performance was evaluated in both synthetic and municipal wastewater media for nitrogen removal along with biomass and lipid generation for biodiesel production. The microalgal-bacterial consortium grown in the municipal wastewater medium produced higher biomass and lipid yields than those in the synthetic wastewater medium. The presence of trace elements in the municipal wastewater medium, e.g., iron and copper, contributed to the upsurge of biomass, thereby leading to higher lipid productivity. Both the microbial cultures in the synthetic and municipal wastewater media demonstrated similar total nitrogen removal efficiencies above 97%. However, the nitrification and assimilation rates were relatively higher for the microbial culture in the municipal wastewater medium, corresponding to the higher microbial biomass growth. Accordingly, the feasibility of the microalgal-bacterial consortium for bioremediating real municipal wastewaters was attested in this study by virtue of higher biomass and lipid production. The assessment of fatty acid methyl esters (FAME) composition showed the mixed microbial biomasses comprised 80–93% C16 to C18 FAME species, signifying efficient fuel combustion properties for quality biodiesel requirements. [ABSTRACT FROM AUTHOR]

The purpose of this review is to reveal the lipid and protein contents in black soldier fly larvae (BSFL) for the sustainable production of protein and energy sources. It has been observed from studies in the literature that the larval lipid and protein contents vary with the rearing conditions as well as the downstream processing employed. The homogenous, heterogenous and microbial-treated substrates via fermentation are used to rear BSFL and are compared in this review for the simultaneous production of larval protein and biodiesel. Moreover, the best moisture content and the aeration rate of larval feeding substrates are also reported in this review to enhance the growth of BSFL. As the downstream process after harvesting starts with larval inactivation, various related methods have also been reviewed in relation to its impact on the quality/quantity of larval protein and lipids. Subsequently, the other downstream processes, namely, extraction and transesterification to biodiesel, are finally epitomized from the literature to provide a comprehensive review for the production of unconventional protein and lipid sources from BSFL feedstock. Incontrovertibly, the review accentuates the great potential use of BSFL biomass as a green source of protein and lipids for energy production in the form of biodiesel. The traditional protein and energy sources, preponderantly fishmeal, are unsustainable naturally, pressingly calling for immediate substitutions to cater for the rising demands. Accordingly, this review stresses the benefits of using BSFL biomass in detailing its production from upstream all the way to downstream processes which are green and economical at the same time. [ABSTRACT FROM AUTHOR]

Recently, worldwide researchers have been focusing on exploiting of black soldier fly larval (BSFL) biomass to serve as the feed mediums for farmed animals, including aquaculture farming, in order to assuage the rising demands for protein sources. In this study, yeast was introduced into coconut endosperm waste (CEW) whilst serving as the feeding medium to rear BSFL in simultaneously performed in situ fermentation. It was found that at a 2.5 wt% yeast concentration, the total biomass gained, growth rate and rearing time were improved to 1.145 g, 0.085 g/day and 13.5 days, respectively. In terms of solid waste reduction, the inoculation of yeast over 0.5 wt% in CEW was able to achieve more than 50% overall degradation, with the waste reduction indexes (WRIs) ranging from 0.038 to 0.040 g/day. Disregarding the concentration of yeast introduced, the protein productivity from 20 BSFL was enhanced from only 0.018 g/day (the control) to 0.025 g/day with the presence of yeast at arbitrary concentrations. On the other hand, the larval protein yield was fortified from the control (28%) to a highest value of 35% with the presence of a mere 0.02 wt% yeast concentration. To summarize, the inclusion of a minimal amount of yeast into CEW for in situ fermentation ultimately enhanced the growth of BSFL, as well as its protein yield and productivity. [ABSTRACT FROM AUTHOR]

Microalgae showcase an extraordinary capacity for synthesizing high-value phytochemicals (HVPCs), offering substantial potential for diverse applications across various industries. Emerging research suggests that subjecting microalgae to abiotic stress during cultivation and the harvesting stages can further enhance the accumulation of valuable metabolites within their cells, including carotenoids, antioxidants, and vitamins. This study delves into the pivotal impacts of manipulating abiotic stress on microalgae yields, with a particular focus on biomass and selected HVPCs that have received limited attention in the existing literature. Moreover, approaches to utilising abiotic stress to increase HVPCs production while minimising adverse effects on biomass productivity were discussed. The present study also encompasses a techno-economic assessment (TEA) aimed at pinpointing significant bottlenecks in the conversion of microalgae biomass into high-value products and evaluating the desirability of various conversion pathways. The TEA methodology serves as a valuable tool for both researchers and practitioners in the quest to identify sustainable strategies for transforming microalgae biomass into high-value products and goods. Overall, this comprehensive review sheds light on the pivotal role of abiotic stress in microalgae cultivation, promising insights that could lead to more efficient and sustainable approaches for HVPCs production. • Abiotic stresses are crucial for phytochemicals secretion in microalgae. • Impacts of various stresses on HVPCs production are examined. • Possibilities for one-pot production of biomass and HVPCs are discussed. • Techno-economic constraints were gauged and addressed. • Future directions to improve microalgae industry are elucidated. [ABSTRACT FROM AUTHOR]

The prime objective of this study was to simultaneously enhance the lipid and protein yields from black soldier fly larvae (BSFL) fed with waste coconut endosperm. The waste coconut endosperm impoverished with nutrient content lost during milk extraction was nutritively fortified via self-fermentation process with time period ranging from 2 to 8 weeks before administering to BSFL. The results showed peak nutrient content was attained from week-4 self-fermented waste coconut endosperm. Using this feed medium, the BSFL prepupae could accumulate 58% of its biomass weight with lipid. The low polyunsaturated fatty acid (6%) and high C18:1 (50%) also guaranteed high biodiesel quality derived from BSFL. Nevertheless, the longer BSFL rearing duration when fed with week-6 self-fermented waste coconut endosperm had triggered a slight increase in protein yield (18%) in comparison with week-4 medium (15%). In considering of organic waste treatment advantage of week-4 self-fermented waste coconut endosperm, a total waste reduction of 0.019 g/d was successfully measured using only 20 BSFL. Therefore, week-4 self-fermented period was concluded as an optimum to produce ideal waste coconut endosperm feed medium for BSFL in enhancing the simultaneous lipid and protein yields. [ABSTRACT FROM AUTHOR]

In the present study, cultivation of Chlorella vulgaris was extensively explored under semi-continuous approach to enhance its growth. The microalgae were cultivated in a photobioreactor supplemented with compost derived from chicken waste as an alternative nutrients source in both batch and semi-continuous cultivations. It was found that Chlorella vulgaris grew well up to 17 cycles of semi-continuous cultivation based on the following conditions for each cycle (3 days per cycle): 30% (v/v) removal of cultivation medium and 0.04 L/L of chicken compost in cultivation medium of pH 3. The average biomass productivity attained through these conditions was 0.0736 g/L/day, which was higher than batch cultivation (0.0568 g/L/day). Besides, the average total lipid content from each cycle under semi-continuous cultivation was maintained in the range of 25–35 wt%. The success of lipid extraction from the microalgae biomass was evidenced by the result of Fourier Transform Infrared Red (FT-IR) analysis that revealed lower peak intensity of carbon, especially in the range 2809–3012 cm −1 after lipid extraction. It was also worthwhile to mention that the fatty acid methyl ester (FAME) compositions of Chlorella vulgaris consisted mainly of C16:0 and C18:3 that were not significantly altered during the semi-continuous cultivation. Both saturated and unsaturated fatty acids in the harvested biomass accounted for approximately 26.3% and 73.3%, respectively, within 5 cycles of the cultivation. [ABSTRACT FROM AUTHOR]

[Display omitted] • Biological methods to produce sustainable biohydrogen from microalgae are reviewed. • Hydrogenase and nitrogenase enzymes involve in microalgal biohydrogen production. • Key parameters that influence the biohydrogen production from microalgae. • Challenges, resolutions, and prospects of biohydrogen derived from microalgae. Hydrogen is the most promising alternative energy recently that is renewable and clean due to its sustainability, great potential as energy source and efficiency during the conversion. In fact, microalgal biohydrogen has attracted significant attentions as a clean and sustainable fuel to achieve the carbon neutrality and sustainability in environment. In this review, the mechanisms of biological methods and electrochemical methods, and the enzymes involved in the biohydrogen generation from microalgae have been inclusively and rudimentary detailed. The review also summarizes the benefits and drawbacks of each technique, and compares the biohydrogen yields from each method based on the results reported by the recent studies. Furthermore, the key factors that influence the biohydrogen yields including pH, light intensity, cell density, temperature and substrate introduced have been addressed as well in this review. Moreover, the review also highlights the primary shortcomings encountered which are oxygen sensitivity of enzymes and low biohydrogen yield. Lastly, the resolutions to enhance the biohydrogen production together with the future prospects for sustainable biohydrogen production from microalgae are opined systematically. [ABSTRACT FROM AUTHOR]

[Display omitted] • Microalgae biomass is identified as a feasible feedstock for biodiesel production. • Process parameters of in-situ transesterification from microalgae was reviewed. • In-situ transesterification from wet paste microalgae shows promising results. • Reaction conditions of in-situ transesterification affect the biodiesel composition. • Reaction kinetics and thermodynamic of in-situ transesterification was reviewed. One-step in-situ transesterification has been recognized as an alternative approach to produce biodiesel from microalgae biomass. Based on technoeconomic perspective, in-situ transesterification of microalgae is more energy efficient than the conventional two-step process and thus economically competitive for biodiesel production. However, a comprehensive review on the effect of processing parameters towards conversion efficiency of microalgae biomass to biodiesel via in-situ transesterification is still lacking in the literature. Therefore, this review was intended to deliberate on fundamental understanding of this technology, including the effect of different reaction parameters towards biodiesel yield, technoeconomic impact of using wet paste microalgae, biodiesel composition profiles, and the state-of-the-art of the process. Besides, reaction kinetic and thermodynamics aspect of in-situ transesterification from microalgae were also discussed in detail. This review also provided in-depth information for process design and intensification under dedicated in-situ transesterification reaction condition for sustainable biodiesel production. Concurrently, research gaps in in-situ transesterification process was addressed for future study. [ABSTRACT FROM AUTHOR]

• C. vulgaris grown mixotrophically via photoperiod regime in municipal wastewater. • Prolonged light period in mixotrophy had promoted microalgal biomass growth. • Prolonged dark period in mixotrophy had induced cellular lipid accumulation. • Optimum 16:8h light/dark cycle photoperiod for biomass and lipid productivities. • High fraction of unsaturated FAME content in microalgal biodiesel from mixotrophy. The performances of autotrophic and heterotrophic metabolisms in Chlorella vulgaris were assessed from various photoperiod regimes for the sustainable microalgal biodiesel production. Accordingly, the cellular biomass growth and lipid content in relation to the organic nutrient removals from municipal wastewater medium were evaluated from the various light/dark photoperiod cycles amidst mixotrophic metabolism. The mixotrophic treatment had been proven effective in producing high microalgal biomass and lipid while alternating its autotrophic and heterotrophic metabolisms. Thus, exploiting the optimum cellular biosynthesis pathways in inducing both biomass growth and lipid accumulation. Amidst mixotrophy, prolonging light condition would favour biomass growth, whilst extending dark condition had elevated cell lipid content. Accordingly, the 16:8 (light:dark) hours/cycle photoperiod was found adequate in yielding high biomass and lipid productions (0.89 and 0.16 g/L, respectively), while achieving near complete removal (>94%) of chemical oxygen demand and ammonium-nitrogen from municipal wastewater. The dominant FAME constituents of C16 and C18 comprised of 90.65%-100% of total FAME with the high unsaturation degree could proffer an excellent quality of microalgal biodiesel with low pour point, suitable for application in cold climate regions. [ABSTRACT FROM AUTHOR]

[Display omitted] • Steam reforming (SR) is promising for high H 2 production and economical profit. • The feedstocks for SR process are mostly non-renewable hydrocarbon. • H 2 can also be produced from SR of alternative feedstocks, liquid biomass waste. • Liquid biomass feedstocks for SR: industrial effluents, biomass-derived solvents and lipids. • SR of industrial effluents is less practical due to the presence of high water. Alternative energy sources have been the main interest since past decades due to inclining energy demand and growing environmental consciousness. Hydrogen (H 2) which is known as a clean fuel and most viable energy carrier for the future, is highly potential due to its high mass-based energy density. Among the diverse thermochemical techniques introduced to generate H 2 in an economical way, steam reforming (SR) emerged as a promising option due to high H 2 production ability and economical profit. Presently, the feedstocks for mature SR technology are mostly non-renewable resources such as fossil fuel (coal, diesel, gasoline, and natural gas). H 2 can also be produced from SR from alternative feedstocks such as liquid biomass waste and biomass derived oxygenates. This approach will not only solve disposal problem, but also open new breakthrough for renewable resources utilization. In this review, the concept, advantages, prospects and challenges of bio-H 2 production via SR process over industrial effluents, solvents, biomass-derived solvents, and lipids are reviewed. These organic-rich feedstocks are mostly waste that caused pollution issues or produced in glut, thus proper utilization of these materials is an urgent need. SR of these alternative feedstocks are viable due to the high H 2 yields obtained upon the transformation of their high-water volume content. [ABSTRACT FROM AUTHOR]

The suspended microalgal cultivation systems targeting the production of lipid for biodiesel is still unable to meet the commercial and economic feasibility due to high energy and cost inputs during the harvesting process. Currently, the attached microalgal cultivation systems are known as an innovative technology to resolve the problematic aspects of suspended cultivation as the biomass can be easily separated from the culture medium with negligible energy input and no chemical need. Accordingly, this paper is focusing on reviewing various support materials utilized by researchers in growing the attached microalgal biomass in either fixed bed or fluidized bed bioreactor to ensure sustainable biomass production prior for biodiesel. An extensive review of the cultivation conditions impacting the growth of attached microalgal biomass is conducted in determining the optimized condition to enhance biomass productivity. The novelty of this paper is presented through in-depth analyses and discussions concerning the kinetic models and mechanisms study in selecting the suitable support materials for attached microalgal growth system. The incorporation of the cultivation condition parameter in predicting the growth of attached microalgae biomass via kinetic study is crucial in proffering new directions for technological developments and microalgal industry application. The ability of attached microalgal biomass in efficiently assimilate the nutrients available in the nutrient-rich wastewater for the microalgae growth is considered as an economical feasible approached. The suitable photobioreactor designs for growing the attached microalgal biomass are also discussed in detail in ensuring the sustainability of attached microalgal biomass production. Image 1 • Attached cultivation to ease microalgal biomass harvest for biodiesel production. • Microalgae cells attachment mechanism onto the support material. • Kinetic model to predict the growth of attached microalgal biomass. • Nutrient-rich wastewater treatment via assimilation by attached microalgal biomass. • Type of photobioreactors to promote the growth of attached microalgal biomass. [ABSTRACT FROM AUTHOR]

The microalgal-bacterial co-cultivation was adopted as an alternative in making microbial-based biofuel production to be more feasible in considering the economic and environmental prospects. Accordingly, the microalgal-bacterial symbiotic relationship was exploited to enhance the microbial biomass yield, while bioremediating the nitrogen-rich municipal wastewater. An optimized inoculation ratio of microalgae and activated sludge (AS:MA) was predetermined and further optimization was performed in terms of different increment ratios to enhance the bioremediation process. The nitrogen removal was found accelerating with the increase of the increment ratios of inoculated AS:MA, though all the increment ratios had recorded a near complete total nitrogen removal (94–95%). In light of treatment efficiency and lipid production, the increment ratio of 0.5 was hailed as the best microbial population size in accounting the total nitrogen removal efficiency of 94.45%, while not compromising the lipid production of 0.241 g/L. Moreover, the cultures in municipal wastewater had attained higher biomass and lipid productions of 1.42 g/L and 0.242 g/L, respectively, as compared with the synthetic wastewater which were only 1.12 g/L (biomass yield) and 0.175 g/L (lipid yield). This was possibly due to the presence of trace elements which had contributed to the increase of biomass yield; thus, higher lipid attainability from the microalgal-bacterial culture. This synergistic microalgal-bacterial approach had been proven to be effective in treating wastewater, while also producing useful biomass for eventual lipid production with comparable net energy ratio (NER) value of 0.27, obtained from the life-cycle analysis (LCA) studies. Thereby, contributing towards long-term sustainability and possible commercialization of microbial-based biofuel production. • Wastewater treatment and lipid production by microalgal-bacterial populations. • Presence of trace elements contributing to high biomass and lipid attainability. • Microalgal-bacterial-based biofuel achieved comparable energy balance feasibility. [ABSTRACT FROM AUTHOR]