A synergistic use of microalgae and macroalgae for heavy metal bioremediation and bioenergy production through hydrothermal liquefaction

In this investigation a novel synergistic approach for the bioremediation of metal-contaminated water and bioenergy production was developed. Two microalgae, Chlorella vulgaris and Arthrospira platensis (Spirulina), and two macroalgae, Ulva lactuca and Sargassum muticum, were used as passive bioremediation agents for the metals Ni(II), Zn(II), Cd(II) and Cu(II). The metals were added singularly and in combination between 10–150 mM. The metal contaminated biomass was then processed through hydrothermal liquefaction to yield four phases: a bio-crude oil, an aqueous phase, solid residue and gas. Both C. vulgaris and A. platensis gave high bio-crude yields of 39 and 31 wt% respectively, while U. lactuca and S. muticum gave 14% and 9% respectively. Initial studies demonstrated that the addition of up to 150 mM of the target metal sulfates to the biomass feedstock did not significantly affect bio-crude production, and, for microalgae, over 99% of the target metals were partitioned to the solid phase products predominantly as phosphates or oxides. Subsequently, bioremediation of waste water and HTL were successfully coupled, with over 80% of a 10 mM solution of the metals biosorbed, though efficacy depended heavily on the algal species. Upon HTL of the remediating biomass, the yield and composition of the bio-crude were not changed significantly. For the microalgae, the aqueous phase contained significant nitrogen, potassium and phosphate levels, and the majority of the target metals deposited in the solid phase, with over 99.5% metal recovery for Spirulina when all four metals were used. The macroalgal species were not as effective in this process, with limited phosphate recovery in the aqueous phase (albeit with extensive potassium recovery) and with less than 50% of the target metals depositing in the solid residue for the Ulva species examined, presumably due to the affinity of the metals to proteinous species rather than polysaccharide in this species. Combining microalgal bioremediation with hydrothermal liquefaction is therefore a potentially highly effective method of remediating contaminated waste waters, whilst a macroalgae based process may offer a cheaper alternative, albeit with substantially reduced efficacy. The recovery of the target metals and multiple product formation improves the economic viability of the process, thereby valorising the bioremediation process and subsidising environmental clean-up

The storage stability of biocrude obtained by the hydrothermal liquefaction of microalgae

Hydrothermal liquefaction (HTL) is a promising technology that can produce biocrude oil from wet biomass. The biocrudes, while generally acknowledged to be more stable than pyrolysis oils, are still thought to degrade relatively quickly, which limits their applicability. In this investigation, the storage stability of biocrude produced from hydrothermal liquefaction of microalgae was systematically studied over 60 days, and the effect of the storage material, feedstock species, liquefaction temperature and storage temperature were assessed. Biocrudes obtained at 300 °C and 350 °C from the microalgae Spirulina and Chlorella vulgaris were stored at three temperatures: cold (4 °C), ambient (20 °C) and elevated temperatures (35 °C), over the two-month period. The dynamic viscosity, higher heating value, thermogravimetric analysis and elemental and chemical composition were assessed. The viscosity of the biocrudes only increased considerably at 35 °C. The reaction temperature and biomass type were also strong determining factors of the impact on biocrude stability. Biocrudes produced from C. vulgaris were more stable than the Spirulina, and the crudes formed at 350 °C were considerably less reactive than those produced at 300 °C. This demonstrates that biocrudes can be stored without substantial degradation, allowing a more flexible approach to upgrading to value products.</p

Saltwater based fractionation and valorisation of macroalgae

BACKGROUND: Macroalgae are gaining increasing interest as an important biomass feedstock. Yet when valorising marine bio�mass, the presence of salt can pose a substantial obstacle to the effectiveness of downstream biological and chemical processes, as well as the engineering infrastructure required. Accordingly, dewatering, washing and drying are often considered the first and crucial primary steps in processing marine biomass such macroalgae. The high costs of these processes can make further marine biorefinery commercialisation prohibitive. This investigation assesses simple pre-treatments for macroalgal biomass in saltwater, thereby reducing the freshwater footprint, and removing the need for an energy-intensive washing and drying stage. RESULTS: Using acid and basic catalysts, the carbohydrate and soluble protein components were fractionated into a soluble aqueous phase, for further fermentation and a solid phase suitable for hydrothermal liquefaction. The presence of saltwater was found to aid the fractionation process, solubilising more of the biomass. The use of H2SO4 produced more monosaccha�rides, whereas NaOH solubilised higher levels of biomass at lower temperatures. The aqueous phase was demonstrated to be suitable for biological processing with the salt tolerant yeast Metschnikowia pulcherrima, and the residual solids suitable for processing via hydrothermal liquefaction. CONCLUSION: By contrast with existing pre-treatment strategies, we demonstrate that an entirely salt-based biochemical con�version route is a potentially viable option. For the first time this work demonstrates that, rather than a hindrance, the presence of saltwater can be advantageous, and could provide an alternative, more cost-effective pathway to achieving a successful macroalgal-based biorefinery. © 2020 Society of Chemical Industr

A synergistic use of microalgae and macroalgae for heavy metal bioremediation and bioenergy production through hydrothermal liquefaction

In this investigation a novel synergistic approach for the bioremediation of metal-contaminated water and bioenergy production was developed. Two microalgae, Chlorella vulgaris and Arthrospira platensis (Spirulina), and two macroalgae, Ulva lactuca and Sargassum muticum, were used as passive bioremediation agents for the metals Ni(II), Zn(II), Cd(II) and Cu(II). The metals were added singularly and in combination between 10–150 mM. The metal contaminated biomass was then processed through hydrothermal liquefaction to yield four phases: a bio-crude oil, an aqueous phase, solid residue and gas. Both C. vulgaris and A. platensis gave high bio-crude yields of 39 and 31 wt% respectively, while U. lactuca and S. muticum gave 14% and 9% respectively. Initial studies demonstrated that the addition of up to 150 mM of the target metal sulfates to the biomass feedstock did not significantly affect bio-crude production, and, for microalgae, over 99% of the target metals were partitioned to the solid phase products predominantly as phosphates or oxides. Subsequently, bioremediation of waste water and HTL were successfully coupled, with over 80% of a 10 mM solution of the metals biosorbed, though efficacy depended heavily on the algal species. Upon HTL of the remediating biomass, the yield and composition of the bio-crude were not changed significantly. For the microalgae, the aqueous phase contained significant nitrogen, potassium and phosphate levels, and the majority of the target metals deposited in the solid phase, with over 99.5% metal recovery for Spirulina when all four metals were used. The macroalgal species were not as effective in this process, with limited phosphate recovery in the aqueous phase (albeit with extensive potassium recovery) and with less than 50% of the target metals depositing in the solid residue for the Ulva species examined, presumably due to the affinity of the metals to proteinous species rather than polysaccharide in this species. Combining microalgal bioremediation with hydrothermal liquefaction is therefore a potentially highly effective method of remediating contaminated waste waters, whilst a macroalgae based process may offer a cheaper alternative, albeit with substantially reduced efficacy. The recovery of the target metals and multiple product formation improves the economic viability of the process, thereby valorising the bioremediation process and subsidising environmental clean-up

Effects of geographical location on potentially valuable components in Ulva intestinalis sampled along the Swedish coast

Macroalgal biomass has the potential to become an important source of chemicals and commodities in a future biorefinery. Currently, production of macroalgal biomass is expensive and the content of high-value compounds is often low. Therefore, in this study the biochemical composition of\ua0Ulva intestinalis\ua0along the Swedish west coast and the east coast up to Stockholm was assessed with the aim of determining how the content of potentially valuable compounds, such as rhamnose, iduronic acid and PUFAs, could be maximized by utilizing natural variation in the choice of marine cultivation site. Along the investigated coastline, the salinity dropped from 19.4‰ at high latitudes along the west coast to 5.4‰ at Stockholm. Nitrogen and phosphorus availability varied, while temperature was similar at all locations. The two major components of biomass, carbohydrates and ash, varied inversely with the highest content of ash in the west and carbohydrates in the east. In addition, total fatty acids were significantly higher in west coast samples at 3.2\ua0g 100\ua0g–1\ua0dw, with a higher proportion of mono- and polyunsaturated fatty acids. Some health-beneficial fatty acids were found, including EPA and DPA, at 10–50\ua0mg 100\ua0g–1\ua0dw, respectively. The metal content and elemental composition varied widely, probably due to the influence of specific local conditions. The P content was correlated with the phosphorus concentration in waters at the locations. In PCA analysis, the monosaccharides constituting the cell wall polysaccharide ulvan were found to vary by geographical location, with higher levels possibly associated with lower salinities. However, only glucuronic acid differed significantly between sites. These results show the considerable geographical variability in the composition of Swedish\ua0U. intestinalis\ua0and suggest that different salinities could be used to create a lipid- or carbohydrate-rich biomass

Effect of Geographical Location on the Variation in Products Formed from the Hydrothermal Liquefaction of Ulva intestinalis

Hydrothermal liquefaction (HTL) of macroalgae offers a promising route to advanced biofuel production, although the distinct biochemical compositions of different macroalgae species can lead to widely different product yields and compositions. On the basis of this, there is an implicit assumption that there exists a universal optimal feedstock species for a bioenergy-based biorefinery, which could be exploited across a wide region. However, no studies to date have examined the effect of this large geographical variation on a single macroalgae species for biofuel production. In this study, 24 samples of Ulva intestinalis were collected along 1200 km of Swedish coastline and assessed as a feedstock for HTL. Significant variation in composition was observed between samples from Baltic and Atlantic regions, but substantial variation also existed between sites within close proximity. This was reflected in the HTL biocrude oil yields, which varied between 9 and 20% (14-28% dry and ash-free basis) across the sample set. In a number of cases, greater variation was seen for adjacent sites than for sites at opposite ends of the sampling spectrum. Biocrude oil yields in this study also differed substantially from those previously obtained for U. intestinalis from the United Kingdom and Vietnam. Localized environmental conditions affected the HTL product composition significantly, in particular, the elemental distribution within the sample set. The variability observed in this study suggests that no single species will be dominant within a macroalgal biorefinery concept, but rather a species would need to be selected to match the needs of the exact local environment

Exploring a range of UK seaweed species for the production of fuels and fertiliser

Displacing crude oil in the fuel industry is vital for ensuring global energy security. Hydrothermal liquefaction (HTL) of macroalgae has been shown to generate bio-crude oils that can potentially be co-refined with mineral crude, or upgraded to hydrocarbon biofuels. HTL utilises water as one of the reactants, and produces four clear product phases which all have economic value and could potentially be used as a basis for a future biorefinery. Alongside the bio-crude oil, these comprise a gas phase (predominantly CO2), a solid residue containing carbon and most of the inorganic material, and a water phase. This contains a range of dissolved elements, including K, Mg, N and P, which are all classed as vital macronutrients for plant growth. The distribution of elements in each of the four phases is highly susceptible to the HTL operating conditions.This project aims to examine a range UK-based macroalgae species to identify a suitable feedstock for a UK HTL biorefinery. HTL reaction conditions were optimised to give maximised bio-crude yields using the brown macroalga Ascophyllum nodosum. Aqueous phase macronutrient content was also considered, with a view to utilise the aqueous phase as an industrial fertiliser. A range of South West UK macroalgae species (belonging to all three major macroalgae classes: green, brown and red) were subsequently screened, with energy and nutrient balances carried out.Ultimately, a biorefinery design incorporating macroalgae cultivation, harvesting and processing will be finalised, and a Life Cycle Assessment (LCA) carried out to quantify the system’s overall environmental impact

Analysis of seaweeds from South West England as a biorefinery feedstock

Seaweeds contain many varied and commercially valuable components, from individual pigments and metabolites through to whole biomass, and yet they remain an under cultivated and underutilised commodity. Currently, commercial exploitation of seaweeds is predominantly limited to whole biomass consumption or single product extracts for the food industry. The development of a seaweed biorefinery, based around multiple products and services, could provide an important opportunity to exploit new and currently underexplored markets. Here, we assessed the native and invasive seaweeds on the South West coast of the UK to determine their characteristics and potential for exploitation through a biorefinery pipeline, looking at multiple components including pigments, carbohydrates, lipids, proteins and other metabolites.</p