Extraction of bio-flocculant from okra using hydrothermal and microwave extraction methods combined with a techno-economic assessment

Since the usage of chemical flocculants especially polyacrylamides is closely related with environmental pollution and health hazards, synthesis of environmental friendly and economic viable bio-flocculants that exhibit high flocculating efficiency is highly desirable. The production of natural bio-flocculants extracted from plant is urgently needed as an alternative to chemical flocculants due to their inherent low toxicity, biodegradability and low environmental footprint. In this study, a plant-based bio-flocculant was extracted from Hibiscus/Abelmoschus esculentus (okra) with conventional hydrothermal extraction (CHE) and microwave assisted extraction (MAE) processes by using water as solvent. The aims of this work were to produce the bio-flocculant through environmentally friendly and economically feasible process, optimise its extraction yield, optimise its flocculating and sludge dewatering properties, and also minimise its production cost in order to be comparable to chemical flocculants (polyacrylamides) from perspectives of quality and cost. The extraction efficiencies of bio-flocculants were justified by the optimised yields, the flocculating abilities were evaluated by the removal of suspended solids (SS) and turbidity after flocculation process and sludge volume index (SVI) whereas the sludge dewatering abilities were assessed by SS removal after filtration and water recovery. Single factor experimental design was employed to study the effects of extraction temperature, time, solvent loading, and agitation speed and particle size on yield, flocculating and dewatering properties of bio-flocculants. The influence of extraction parameters to yield and the reliability of the experimental data were verified by analysing the single factor experimental results with response surface methodology. Results showed that extraction yields were significantly affected by extraction temperature and time and solvent loading. Prolonged extraction (few hours) at high temperature (60-90 ˚C) decreased the yields of bio-flocculants extracted with CHE method. Conversely, extraction at high temperature was favourable for MAE method to raise the yield due to short extraction time in minutes. Flocculating abilities of bio-flocculants were not significantly affected by the extraction conditions whilst the sludge dewatering abilities were mainly influenced by the temperature and particle size. High extraction temperature at ≥ 70 ˚C and the smallest okra particle size at 1mm were the crucial conditions for extraction of bio-flocculants with high dewatering abilities which showed >95% of SS removal after filtration and ≥75% of water recovery. The optimised yield of CHE at 25.9% was obtained at 50 ˚C, 2 hours, solvent loading of 2.5 w/w and agitation at 200 rpm. On the other hand, microwave-extracted bio-flocculants were best extracted at 90 ˚C, 10 minutes, and solvent loading of 3.5 w/w and okra particle size at 1mm to get the optimised yield at 48.7%. These results revealed that the extraction yield has been enhanced by 87.8% by using MAE method and the extraction time was markedly reduced from hours to minutes. This study uses a combination of empirical observations and an analysis of mass transfer behaviour to yield new insights into the mechanism of MAE. Enhancements in extraction rate and yield achieved by microwave extraction were observed experimentally compared with hydrothermal extraction at temperatures in excess of 50 ˚C, however at lower temperatures there was no observable difference between the two processes. A step-change in extraction yield between microwave and hydrothermal processes was shown to be caused by selective heating. A temperature gradient of the order of 1 ˚C is sufficient to reduce the water chemical potential within the plant cell structure, which causes diffusion of water solvent into plant cell such that internal plant cell pressures can increase to the point where disruption occurs. These findings demonstrate the need to operate microwave extraction processes at a temperature that enables selective heating, and a newly-proposed mass transfer phenomenon that could have wider positive implications for extraction and leaching processes. The bio-flocculants extracted with both methods were applied in flocculation and sludge dewatering without pH alteration and addition of coagulant. Efficient flocculating abilities were attained with >99% of SS and turbidity removal and 95% SS removal after filtration and 75% water recovery during sludge dewatering at dosage of 30 mg/L, and was shown to be comparable to or even better than polyacrylamides due to achievement of higher water recovery at the same dosage. Dried bio-flocculants were found to have higher dewatering abilities than aqueous bio-flocculants, probably because drying at low temperature (40 ˚C) has minimised the moisture content and extended the shelf life of bio-flocculants. Biopolymer bridging was preliminary predicted as the plausible bio-flocculation mechanism. The economic feasibility of production of industrial scale bio-flocculant was investigated and the production process was modelled by using SuperPro Designer v9.0 simulation software. The MAE process in continuous mode was verified to be more economically viable than CHE process either in batch or continuous mode if the production scale was beyond 15 tonne/year. Sensitivity analysis for continuous microwave process was conducted and the results indicated the strong influences of annual production and extraction yield followed by raw material okra price on the unit production cost. Continuous microwave process with extraction conditions at 90 ˚C, 10 minutes and solvent loading of 3.5 w/w was identified as the optimised scheme for production of industrial scale bio-flocculant at the lowest production cost. The estimated selling price of aqueous and dried bio-flocculants for an annual production of 220 tonne/year were 41 and 52 $/kg respectively, and was shown to be lower than food grade bio-flocculants but higher than polyacrylamides. This work has clearly showed that okra bio-flocculant could offer a feasible and sustainable alternative to synthetic flocculants for water treatment and sludge dewatering applications due to its high efficiency in flocculating and dewatering, and can be extracted using only water as a solvent, minimising the environmental footprint of the extraction process

Extraction of bio-flocculant from okra using hydrothermal and microwave extraction methods combined with a techno-economic assessment

Since the usage of chemical flocculants especially polyacrylamides is closely related with environmental pollution and health hazards, synthesis of environmental friendly and economic viable bio-flocculants that exhibit high flocculating efficiency is highly desirable. The production of natural bio-flocculants extracted from plant is urgently needed as an alternative to chemical flocculants due to their inherent low toxicity, biodegradability and low environmental footprint. In this study, a plant-based bio-flocculant was extracted from Hibiscus/Abelmoschus esculentus (okra) with conventional hydrothermal extraction (CHE) and microwave assisted extraction (MAE) processes by using water as solvent. The aims of this work were to produce the bio-flocculant through environmentally friendly and economically feasible process, optimise its extraction yield, optimise its flocculating and sludge dewatering properties, and also minimise its production cost in order to be comparable to chemical flocculants (polyacrylamides) from perspectives of quality and cost. The extraction efficiencies of bio-flocculants were justified by the optimised yields, the flocculating abilities were evaluated by the removal of suspended solids (SS) and turbidity after flocculation process and sludge volume index (SVI) whereas the sludge dewatering abilities were assessed by SS removal after filtration and water recovery. Single factor experimental design was employed to study the effects of extraction temperature, time, solvent loading, and agitation speed and particle size on yield, flocculating and dewatering properties of bio-flocculants. The influence of extraction parameters to yield and the reliability of the experimental data were verified by analysing the single factor experimental results with response surface methodology. Results showed that extraction yields were significantly affected by extraction temperature and time and solvent loading. Prolonged extraction (few hours) at high temperature (60-90 ˚C) decreased the yields of bio-flocculants extracted with CHE method. Conversely, extraction at high temperature was favourable for MAE method to raise the yield due to short extraction time in minutes. Flocculating abilities of bio-flocculants were not significantly affected by the extraction conditions whilst the sludge dewatering abilities were mainly influenced by the temperature and particle size. High extraction temperature at ≥ 70 ˚C and the smallest okra particle size at 1mm were the crucial conditions for extraction of bio-flocculants with high dewatering abilities which showed >95% of SS removal after filtration and ≥75% of water recovery. The optimised yield of CHE at 25.9% was obtained at 50 ˚C, 2 hours, solvent loading of 2.5 w/w and agitation at 200 rpm. On the other hand, microwave-extracted bio-flocculants were best extracted at 90 ˚C, 10 minutes, and solvent loading of 3.5 w/w and okra particle size at 1mm to get the optimised yield at 48.7%. These results revealed that the extraction yield has been enhanced by 87.8% by using MAE method and the extraction time was markedly reduced from hours to minutes. This study uses a combination of empirical observations and an analysis of mass transfer behaviour to yield new insights into the mechanism of MAE. Enhancements in extraction rate and yield achieved by microwave extraction were observed experimentally compared with hydrothermal extraction at temperatures in excess of 50 ˚C, however at lower temperatures there was no observable difference between the two processes. A step-change in extraction yield between microwave and hydrothermal processes was shown to be caused by selective heating. A temperature gradient of the order of 1 ˚C is sufficient to reduce the water chemical potential within the plant cell structure, which causes diffusion of water solvent into plant cell such that internal plant cell pressures can increase to the point where disruption occurs. These findings demonstrate the need to operate microwave extraction processes at a temperature that enables selective heating, and a newly-proposed mass transfer phenomenon that could have wider positive implications for extraction and leaching processes. The bio-flocculants extracted with both methods were applied in flocculation and sludge dewatering without pH alteration and addition of coagulant. Efficient flocculating abilities were attained with >99% of SS and turbidity removal and 95% SS removal after filtration and 75% water recovery during sludge dewatering at dosage of 30 mg/L, and was shown to be comparable to or even better than polyacrylamides due to achievement of higher water recovery at the same dosage. Dried bio-flocculants were found to have higher dewatering abilities than aqueous bio-flocculants, probably because drying at low temperature (40 ˚C) has minimised the moisture content and extended the shelf life of bio-flocculants. Biopolymer bridging was preliminary predicted as the plausible bio-flocculation mechanism. The economic feasibility of production of industrial scale bio-flocculant was investigated and the production process was modelled by using SuperPro Designer v9.0 simulation software. The MAE process in continuous mode was verified to be more economically viable than CHE process either in batch or continuous mode if the production scale was beyond 15 tonne/year. Sensitivity analysis for continuous microwave process was conducted and the results indicated the strong influences of annual production and extraction yield followed by raw material okra price on the unit production cost. Continuous microwave process with extraction conditions at 90 ˚C, 10 minutes and solvent loading of 3.5 w/w was identified as the optimised scheme for production of industrial scale bio-flocculant at the lowest production cost. The estimated selling price of aqueous and dried bio-flocculants for an annual production of 220 tonne/year were 41 and 52 $/kg respectively, and was shown to be lower than food grade bio-flocculants but higher than polyacrylamides. This work has clearly showed that okra bio-flocculant could offer a feasible and sustainable alternative to synthetic flocculants for water treatment and sludge dewatering applications due to its high efficiency in flocculating and dewatering, and can be extracted using only water as a solvent, minimising the environmental footprint of the extraction process

Review of supercritical water gasification with lignocellulosic real biomass as the feedstocks: Process parameters, biomass composition, catalyst development, reactor design and its challenges

Supercritical water gasification (SCWG) is a combined thermal decomposition and hydrolysis process for converting wet biomass feedstock with high water content potentially (80 wt%) to syngas. The process bypasses the need for an energy intensive pre-drying step and also needs relatively shorter residence times (of the order of seconds to minutes) when compared to conventional gasification. The main target of SCWG is to obtain syngas rich in hydrogen whilst minimising char formation. In recent years, SCWG studies have advanced from using model compounds (e.g. glucose and cellulose) towards the use of real biomass and its waste (e.g. sugarcane trash). The use of biomass as a feedstock creates real opportunities for the technology since it is available in some form, regardless of location. This review discusses the findings from SCWG studies that have used real biomass as a feedstock. The effects of reaction temperature, pressure, residence time and feedstock concentration to the hydrogen yields are presented. The relationship between the main components in biomass (cellulose, hemicellulose and lignin) and hydrogen yields are also discussed. Homogeneous and heterogeneous catalysts have been used to enhance SCWG with real biomass feedstock and the benefits of these approaches are also considered. The economic benefits of running the catalytic SCWG at 400 °C compared to non-catalytic operation at 600 °C is evaluated. Reactor configuration and process conditions vary across the literature, and various authors describe the associated challenges (char formation and plugging, corrosion) as well as promising solutions to tackle these key challenges

Unsaturated Fatty Acids Repress the Expression of ATP-Binding Cassette Transporter A1 in HepG2 and FHs 74 Int Cells

Adenosine triphosphate–binding cassette transporter A1 (ABCA1) plays a critical role in the formation and metabolism of high-density lipoproteins (HDLs). Adenosine triphosphate–binding cassette transporter A1 in the liver and small intestine, in particular, accounts for approximately 90% of plasma HDL cholesterol. Therefore, any alterations in the hepatic and intestinal expression of ABCA1 could have a large impact on HDL biogenesis. We tested the hypothesis that ABCA1 expression is regulated differentially by different types of fatty acids in the liver and small intestine. Human hepatoma HepG2 and human small intestine epithelial FHs 74 Int cells were used as an in vitro model. Cells were incubated with saturated and unsaturated fatty acids in the presence or absence of T0901317, a synthetic agonist of liver X receptor. Unsaturated fatty acids decreased ABCA1 protein levels at 100 μmol/L of concentration regardless of the agonist with a minimal effect on messenger RNA abundance. Incubation of HepG2 and FHs 74 Int cells with rottlerin, a protein kinase C δ (PKCδ) inhibitor, increased ABCA1 protein but did not abolish linoleic acid–induced decrease in ABCA1 protein levels. Depletion of PKCδ using small interfering RNA showed decreased ABCA1 protein levels in control, palmitic acid–, and linoleic acid–treated cells, but the repressive effect of linoleic acid was sustained. In conclusion, our results indicate that unsaturated fatty acids regulate ABCA1 expression in HepG2 and FHs 74 Int cells at the posttranscriptional level, and PKCδ is likely to be involved in maintaining ABCA1 protein levels

Techno-economic assessment of scale-up of bio-flocculant extraction and production by using okra as biomass feedstock

This paper reports a techno-economic assessment for industrial scale bio-flocculant production with okra as biomass feedstock. The sludge dewatering ability of the bio-flocculant was evaluated prior to economic analysis. Several optimisation strategies were investigated in order to lower the bio-flocculant production cost. The results showed that continuous mode microwave extraction was more economically beneficial than conventional extraction in batch and continuous modes. Sensitivity analysis revealed that the production cost was significantly affected by annual production and extract yield, and moderately influenced by raw material price. The optimised scheme for bio-flocculant production was continuous mode microwave extraction at 90° C, a residence time of 10 minutes, a water loading of 3.5 w/w and production rate of 220 tonnes per year. The economic assessment showed that the gross margin was positive, return on investment was in the expected range of 20 to 30% and payback time was within 5 years

Incidence of acute cerebrovascular events in patients with rheumatic or calcific mitral stenosis: a systematic review and meta-analysis

Background Patients with mitral stenosis (MS) may be predisposed to acute cerebrovascular events (ACE) and peripheral thromboembolic events (TEE). Concomitant atrial fibrillation (AF), mitral annular calcification (MAC) and rheumatic heart disease (RHD) are independent risk factors. Our aim was to evaluate the incidence of ACEs in MS patients and the implications of AF, MAC, and RHD on thromboembolic risks. Methods This systematic review was registered on PROSPERO (CRD42021291316). Six databases were searched from inception to 19th December 2021. The clinical outcomes were composite ACE, ischaemic stroke/transient ischaemic attack (TIA), and peripheral TEE. Results We included 16 and 9 papers, respectively, in our qualitative and quantitative analyses. The MS cohort with AF had the highest incidence of composite ACE (31.55%; 95%CI 3.60-85.03; I 2 =99%), followed by the MAC (14.85%; 95%CI 7.21-28.11; I 2 =98%), overall MS (8.30%; 95%CI 3.45-18.63; I 2 =96%) and rheumatic MS population (4.92%; 95%CI 3.53-6.83; I 2 =38%). Stroke/TIA were reported in 29.62% of the concomitant AF subgroup (95%CI 2.91-85.51; I 2 =99%) and in 7.11% of the overall MS patients (95%CI 1.91-23.16; I 2 =97%). However, the heterogeneity of the pooled incidence of clinical outcomes in all groups, except the rheumatic MS group, were substantial and significant. The logit-transformed proportion of composite ACE increased by 0.0141 (95% CI 0.0111-0.0171; p<0.01) per year of follow-up. Conclusion In the MS population, MAC and concomitant AF are risk factors for the development of ACE. The scarcity of data in our systematic review reflects the need for further studies to explore thromboembolic risks in all MS subtypes

Sustainability of bioenergy – mapping the risks and benefits to inform future bioenergy systems

Bioenergy is widely included in energy strategies for its GHG mitigation potential. Bioenergy technologies will likely have to be deployed at scale to meet decarbonisation targets, and consequently biomass will have to be increasingly grown/mobilised. Sustainability risks associated with bioenergy may intensify with increasing deployment and where feedstocks are sourced through international trade. This research applies the Bioeconomy Sustainability Indicator Model (BSIM) to map and analyse the performance of bioenergy across 126 sustainability issues, evaluating 16 bioenergy case studies that reflect the breadth of biomass resources, technologies, energy vectors and bio-products. The research finds common trends in sustainability performance across projects that can inform bioenergy policy and decision making. Potential sustainability benefits are identified for People (jobs, skills, income, energy access); for Development (economy, energy, land utilisation); for Natural Systems (soil, heavy metals), and; for Climate Change (emissions, fuels). Also, consistent trends of sustainability risks where focus is required to ensure the viability of bioenergy projects, including for infrastructure, feedstock mobilisation, techno-economics and carbon stocks. Emission mitigation may be a primary objective for bioenergy, this research finds bioenergy projects can provide potential benefits far beyond emissions - there is an argument for supporting projects based on the ecosystem services and/or economic stimulation they may deliver. Also given the broad dynamics and characteristics of bioenergy projects, a rigid approach of assessing sustainability may be incompatible. Awarding ‘credit’ across a broader range of sustainability indicators in addition to requiring minimum performances in key areas, may be more effective at ensuring bioenergy sustainability

The N-Terminal Amphipathic Helix of the Topological Specificity Factor MinE Is Associated with Shaping Membrane Curvature

Pole-to-pole oscillations of the Min proteins in Escherichia coli are required for the proper placement of the division septum. Direct interaction of MinE with the cell membrane is critical for the dynamic behavior of the Min system. In vitro, this MinE-membrane interaction led to membrane deformation; however, the underlying mechanism remained unclear. Here we report that MinE-induced membrane deformation involves the formation of an amphipathic helix of MinE2–9, which, together with the adjacent basic residues, function as membrane anchors. Biochemical evidence suggested that the membrane association induces formation of the helix, with the helical face, consisting of A2, L3, and F6, inserted into the membrane. Insertion of this helix into the cell membrane can influence local membrane curvature and lead to drastic changes in membrane topology. Accordingly, MinE showed characteristic features of protein-induced membrane tubulation and lipid clustering in in vitro reconstituted systems. In conclusion, MinE shares common protein signatures with a group of membrane trafficking proteins in eukaryotic cells. These MinE signatures appear to affect membrane curvature

A review on development and application of plant-based bioflocculants and grafted bioflocculants

Flocculation is extensively employed for clarification through sedimentation. Application of eco-friendly plant-based bioflocculants in wastewater treatment has attracted significant attention lately with high removal capability in terms of solids, turbidity, color, and dye. However, moderate flocculating property and short shelf life restrict their development. To enhance the flocculating ability, natural polysaccharides derived from plants are chemically modified by inclusion of synthetic, nonbiodegradable monomers (e.g., acrylamide) onto their backbone to produce grafted bioflocculants. This review is aimed to provide an overview of the development and flocculating efficiencies of plant-based bioflocculants and grafted bioflocculants for the first time. Furthermore, the processing methods, flocculation mechanism, and the current challenges are discussed. All the reported studies about plant-derived bioflocculants are conducted under lab-scale conditions in wastewater treatment. Hence, the possibility to apply natural bioflocculants in food and beverage, mineral, paper and pulp, and oleo-chemical and biodiesel industries is discussed and evaluated