Biodiversity Improves Life Cycle Sustainability Metrics in Algal Biofuel Production.

Algal biofuel has yet to realize its potential as a commercial and sustainable bioenergy source, largely due to the challenge of maximizing and sustaining biomass production with respect to energetic and material inputs in large-scale cultivation. Experimental studies have shown that multispecies algal polycultures can be designed to enhance biomass production, stability, and nutrient recycling compared to monocultures. Yet, it remains unclear whether these impacts of biodiversity make polycultures more sustainable than monocultures. Here, we present results of a comparative life cycle assessment (LCA) for algal biorefineries to compare the sustainability metrics of monocultures and polycultures of six fresh-water algal species. Our results showed that when algae were grown in outdoor experimental ponds, certain bicultures improved the energy return on investment (EROI) and greenhouse gas emissions (GHGs) by 20% and 16%, respectively, compared to the best monoculture. Bicultures outperformed monocultures by performing multiple functions simultaneously (e.g., improved stability, nutrient efficiency, biocrude characteristics), which outweighed the higher productivity attainable by a monoculture. Our results demonstrate that algal polycultures with optimized multifunctionality lead to enhanced life cycle metrics, highlighting the significant potential of ecological engineering for enabling future environmentally sustainable algal biorefineries.

Ecological Engineering Helps Maximize Function in Algal Oil Production.

Algal biofuels have the potential to curb the emissions of greenhouse gases from fossil fuels, but current growing methods fail to produce fuels that meet the multiple standards necessary for economical industrial use. For example, algae grown as monocultures for biofuel production have not simultaneously and economically achieved high yields of the high-quality lipid-rich biomass desired for the industrial-scale production of bio-oil. Decades of study in the field of ecology have demonstrated that simultaneous increases in multiple functions, such as the quantity and quality of biomass, can occur in natural ecosystems by increasing biological diversity. Here, we show that species consortia of algae can improve the production of bio-oil, which benefits from both a high biomass yield and a high quality of biomass rich in fatty acids. We explain the underlying causes of increased quantity and quality of algal biomass among species consortia by showing that, relative to monocultures, species consortia can differentially regulate lipid metabolism genes while growing to higher levels of biomass, in part due to a greater utilization of nutrient resources. We identify multiple genes involved in lipid biosynthesis that are frequently upregulated in bicultures and further show that these elevated levels of gene expression are highly predictive of the elevated levels in biculture relative to that in monoculture of multiple quality metrics of algal biomass. These results show that interactions between species can alter the expression of lipid metabolism genes and further demonstrate that our understanding of diversity-function relationships from natural ecosystems can be harnessed to improve the production of bio-oil.IMPORTANCE Algal biofuels are one of the more promising forms of renewable energy. In our study, we investigate whether ecological interactions between species of microalgae regulate two important factors in cultivation-the biomass of the crop produced and the quality of the biomass that is produced. We found that species interactions often improved production yields, especially the fatty acid content of the algal biomass, and that differentially expressed genes involved in fatty acid metabolism are predictive of improved quality metrics of bio-oil. Other studies have found that diversity often improves productivity and stability in agricultural and natural ecosystems. Our results provide further evidence that growing multispecies crops of microalgae may improve the production of high-quality biomass for bio-oil.

Ecological Stoichiometry Meets Ecological Engineering: Using Polycultures to Enhance the Multifunctionality of Algal Biocrude Systems.

For algal biofuels to be economically sustainable and avoid exacerbating nutrient pollution, algal cultivation and processing must maximize rates of biofuel production while simultaneously minimizing the consumption of nitrogen (N) and phosphorus (P) fertilizers. We experimentally tested whether algal polycultures could be engineered to improve N and P nutrient-use efficiency compared to monocultures by balancing trade-offs in nutrient-use efficiency and biocrude production. We analyzed the flows of N and P through the processes of cultivation, biocrude production through hydrothermal liquefaction, and nutrient recycling in a laboratory-scale system. None of the six species we examined exhibited high N efficiency, P efficiency, and biocrude production simultaneously; each had poor performance in at least one function (i.e., <25th percentile). Polycultures of two to six species did not outperform the best species in any single function, but some polycultures exhibited more balanced performance and maintained all three functions at higher levels simultaneously than any of the monocultures (i.e., >67th percentile). Moreover, certain polycultures came closer to optimizing all three functions than any of the monocultures. By balancing trade-offs between N and P efficiency and biocrude production, polycultures could be used to simultaneously reduce the demand for both N and P fertilizers by up to 85%.

Power of Plankton: Effects of Algal Biodiversity on Biocrude Production and Stability.

Algae-derived biocrude oil is a possible renewable energy alternative to fossil fuel based crude oil. Outdoor cultivation in raceway ponds is estimated to provide a better return on energy invested than closed photobioreactor systems. However, in these open systems, algal crops are subjected to environmental variation in temperature and irradiance, as well as biotic invasions which can cause costly crop instabilities. In this paper, we used an experimental approach to investigate the ability of species richness to maximize and stabilize biocrude production in the face of weekly temperature fluctuations between 17 and 27 °C, relative to a constant-temperature control. We hypothesized that species richness would lead to higher mean biocrude production and greater stability of biocrude production over time in the variable temperature environment. Counter to our hypothesis, species richness tended to cause a decline in mean biocrude production, regardless of environmental temperature variation. However, biodiversity did have stabilizing effects on biocrude production over time in the variable temperature environment and not in the constant temperature environment. Altogether, our results suggest that when the most productive and stable monoculture is unknown, inoculating raceway ponds with a diverse mixture of algae will tend to ensure stable harvests over time.

Trash to Treasure: From Harmful Algal Blooms to High-Performance Electrodes for Sodium-Ion Batteries.

Harmful algal blooms (HABs) are frequently reported around the globe. HABs are typically caused by the so-called blue-green algae in eutrophic waters. These fast-growing HABs could be a good source for biomass. Unlike terrestrial plants, they need no land or soil. If HABs could be harvested on a large scale, it could not only possible to mitigate the issue of HABs but also provide a source of biomass. Herein, we demonstrate a facile procedure for converting the HABs into a promising high-performance negative-electrode material for sodium-ion batteries (SIBs). The carbon material derived from blue-green algae demonstrated promising electrochemical performance in reversible sodium storage. The algae used in this work was collected directly from Lake Erie during the algal blooms that affected 500 000 residents in Toledo in 2014. The carbon, derived from the freshly collected HABs by calcination in argon without any additional purification process, delivered a highly stable reversible specific capacity (∼230 mAh/g at a testing current of 20 mA/g) with nearly 100% Columbic efficiency in sodium storage. Impressive rate performance was achieved with a capacity of ∼135 mAh/g even after the testing current was increased fivefold. This proof of concept provides a promising route for mitigating the issue of HABs as "trash" and for generating high-capacity, low-cost electrodes for SIBs as "treasure".

Anisole hydrolysis in high temperature water.

We investigated the hydrolysis of anisole to phenol in high-temperature water with and without water-tolerant Lewis acid catalysis. With no catalyst present, anisole hydrolyzes to phenol in 97% yield after 24 hours at 365 °C, our experimentally determined optimal temperature and time. Experiments with varied water density and analysis of comparable literature data suggest that anisole hydrolysis is almost third order in water, when the S(N)2 mechanism dominates. Of the water-tolerant Lewis acid catalysts studied, In(OTf)(3) offered the best phenol yield. Anisole hydrolysis was first order in catalyst and first order in substrate. Introducing In(OTf)(3) catalysis lowered the activation energy for anisole hydrolysis to 31 ± 1 kcal mol(-1). Anisole hydrolysis in high-temperature water with In(OTf)(3) catalysis is competitive with other techniques in the literature based on rate and yield. In the presence of 5 mol% In(OTf)(3) catalyst, anisole hydrolyzes to phenol in 97% yield after 90 minutes at 300 °C.

Intermediates and kinetics for phenol gasification in supercritical water.

We processed phenol with supercritical water in a series of experiments, which systematically varied the temperature, water density, reactant concentration, and reaction time. Both the gas and liquid phases were analyzed post-reaction using gas chromatographic techniques, which identified and quantified the reaction intermediates and products, including H(2), CO, CH(4), and CO(2) in the gas phase and twenty different compounds--mainly polycyclic aromatic hydrocarbons--in the liquid phase. Many of these liquid phase compounds were identified for the first time and could pose environmental risks. Higher temperatures promoted gasification and resulted in a product gas rich in H(2) and CH(4) (33% and 29%, respectively, at 700 °C), but char yields increased as well. We implicated dibenzofuran and other identified phenolic dimers as precursor molecules for char formation pathways, which can be driven by free radical polymerization at high temperatures. Examination of the trends in conversion as a function of initial water and phenol concentrations revealed competing effects, and these informed the kinetic modeling of phenol disappearance. Two different reaction pathways emerged from the kinetic modeling: one in which rate ∝ [phenol](1.73)[water](-16.60) and the other in which rate ∝ [phenol](0.92)[water](1.39). These pathways may correspond to pyrolysis, which dominates when there is abundant phenol and little water, and hydrothermal reactions, which dominate in excess water. This result confirms that supercritical water gasification of phenol does not simply follow first-order kinetics, as previous efforts to model phenol disappearance had assumed.

Kinetic model for supercritical water gasification of algae.

The article reports the first quantitative kinetics model for supercritical water gasification (SCWG) of real biomass (algae) that describes the formation of the individual gaseous products. The phenomenological model is based on a set of reaction pathways that includes two types of compounds being intermediate between the algal biomass and the final gaseous products. To best correlate the experimental gas yields obtained at 450, 500 and 550 °C, the model allowed one type of intermediate to react to gases more quickly than the other type of intermediate. The model parameters indicate that gas yields increase with temperature because higher temperatures favor production of the more easily gasified intermediate and the production of gas at the expense of char. The model can accurately predict the qualitative influence of the biomass loading and water density on the gas yields. Sensitivity analysis and reaction rate analysis indicate that steam reforming of intermediates is an important source of H(2), whereas direct decomposition of the intermediate species is the main source of CO, CO(2) and CH(4).

Protocol to develop component additivity models that predict oil yield from hydrothermal liquefaction.

Here, we describe steps for performing hydrothermal liquefaction (HTL) experiments and developing component additivity models that predict oil yields from HTL of mixtures with biomass and plastics. Such models could be developed for predicting outcomes from any thermochemical valorization process (e.g., pyrolysis) for any feedstock. The HTL protocol explains experiments with both a single component and mixture. The model is constrained to the specific plastic feedstocks and solvents for product recovery used in the experiments. For complete details on the use and execution of this protocol, please refer to Seshasayee et al. (2021).

Hydrothermal liquefaction of polysaccharide feedstocks with heterogeneous catalysts.

Hydrothermal liquefaction (HTL) of starch, cellulose, pectin, and chitin with Pd/C, Co-Mo/γ-Al2O3, and zeolite was investigated at 320 °C for 30 min. Using Co-Mo/γ-Al2O3 at 5 wt% loading led to the highest biocrude yields from starch (25 wt%) and cellulose (23 wt%). The yields from cellulose are more than twice those from noncatalytic HTL (11 wt%). Co-Mo/γ-Al2O3 was also the only catalyst (25 wt% loading) to increase biocrude yields (by 1.6 - 2.6 wt%) from HTL of chitin and pectin. The biocrudes were characterized by elemental analysis, TGA, FT-IR and GC-MS. Catalytic HTL with Co-Mo/γ-Al2O3 had little effect on the elemental composition of the biocrudes. The presence of Co-Mo/γ-Al2O3 increased the low-boiling portion of biocrude from<30% to over 50% for HTL of starch. Finally, a component additivity model that accurately predicts biocrude yields from catalytic HTL of a mixture is presented.

Component additivity model for plastics-biomass mixtures during hydrothermal liquefaction in sub-, near-, and supercritical water.

We produced oils via hydrothermal liquefaction (HTL) of binary mixtures of biomass components (e.g., lignin, cellulose, starch) with different plastics and binary mixtures of plastics themselves. Cellulose, starch, and lignin demonstrated synergistic interactions (i.e., enhanced oil yields) with the plastics tested (polypropylene, polycarbonate, polystyrene, and polyethylene terephthalate). Polystyrene exhibited synergy during HTL with the three other plastics as did polypropylene during HTL with PET or PC. We used the experimental results to develop the first component-additivity model that predicts the oil yields from HTL of biomass-plastic and plastic-plastic mixtures. The model accounts for interactions among and between biomass components and plastic components in sub-, near-, and supercritical water. The model predicts 88% of 48 published oil yields from HTL experiments with mixtures containing plastics to within 10 wt%.

Hydrothermal carbonization of simulated food waste for recovery of fatty acids and nutrients.

We conducted Hydrothermal carbonization (HTC) of simulated food waste under different reaction conditions (180 to 220 °C, 15 and 30 min), with the aim of recovering both fatty acids from the hydrochar and nutrients from the aqueous-phase products. HTC of the simulated food waste produced hydrochar that retained up to 78% of the original fatty acids. These retained fatty acids were extracted from the hydrochar using ethanol, a food-grade solvent, and gave a net recovery of fatty acid of âˆ¼ 50%. The HTC process partitioned more than 50 wt% of the phosphorus and around 38 wt% of the nitrogen into the aqueous-phase products. A reaction path consistent with decarboxylation predominated during HTC under all of the reaction conditions investigated. A path consistent with dehydration was also observed, but only for the more severe reaction conditions. This work illustrates the potential that HTC has for valorization of food waste.

Supercritical water gasification of phenol over Ni-Ru bimetallic catalysts.

Incorporating Ru in a Ni catalyst for gasification of phenol in supercritical water at 450 °C and 30 min promoted formation of cyclohexanol via hydrogenation, which is a key step toward gasification. Both Ni and Ni-Ru catalysts were effective to reduce the formation of cyclohexanone and oligomerization products, compared with the case with no catalyst. H2 and CH4 yields increased as the Ru/Ni ratio increased, as did the carbon and hydrogen yields in the gas phase products. The Ni80Ru20/Al2O3 catalyst provided good gasification performance and it exhibits Ru (101), Ru (100) and Ni (111) facets and evidence of overlaid bimetallic particles. DFT calculations show that the presence of Ru (either as pure Ru or as a Ni-Ru alloy) reduces the energy barrier for phenol hydrogenation by close to 0.2 eV relative to pure Ni, and that the energy barrier is not as largely affected by the amount of Ru present, provided it is non-zero.

Modeling the effects of microalga biochemical content on the kinetics and biocrude yields from hydrothermal liquefaction.

A kinetic model for the hydrothermal liquefaction (HTL) of microalgae was developed and its performance in predicting biocrude yields was tested. Kinetic interactions between algal proteins, carbohydrates, and lipids were also included for the first time. These interactions provided a better fit of the data used to determine model parameters, but the kinetics model lacking interactions provided a better prediction of published biocrude yields. This model predicted 70 published biocrude yields to within ±5wt% given the biochemical composition of the alga and the HTL temperature and time as model inputs. Forty-two other published biocrude yields were predicted to within ±10wt%. The model accurately predicts that feedstocks richer in proteins or lipids give higher biocrude yields than those abundant in carbohydrates. This updated model better predicts the combined influences of HTL reaction conditions and algae biochemical composition on HTL biocrude yields than any other model currently available.

Effect of temperature, water loading, and Ru/C catalyst on water-insoluble and water-soluble biocrude fractions from hydrothermal liquefaction of algae.

Hydrothermal liquefaction (HTL) converts algal biomass into a crude bio-oil (biocrude) and aqueous-phase products. The effect of temperature, water loading, and added H2 and/or Ru/C catalyst on the properties of the biocrude that spontaneously separates from the aqueous phase post reaction and also the biocrude that is extractable from the aqueous phase by dichloromethane is explored herein. This report is the first to elucidate how the yields, compositions, heating values, and energy recoveries of the two biocrudes vary with the processing conditions above. Increasing temperature from 350 to 400°C increased the yield of water-insoluble biocrude (38.1-42.5wt%) and its hexane-soluble subfraction (63.7-85.6wt%) while decreasing the yield of extractable, water-soluble biocrude (6.6-2.5wt%). The Ru/C catalyst had the same effect. Reaction temperature and catalysts could be used to manipulate the proportions of water-soluble and water-insoluble biocrude from algae HTL and thereby manipulate biocrude quantity and quality.

Hydrothermal liquefaction of sewage sludge under isothermal and fast conditions.

We investigated the effects of water loading, sludge moisture content, recovery solvent, and additives on the product yields and compositions from isothermal (673K, 60min) and fast (773K, 1min) hydrothermal liquefaction (HTL) of sewage sludge. The water loading (which affects pressure within the reactor) plays a small role in product yields. The sludge moisture content had a larger effect with the highest biocrude yields (26.8wt% from isothermal HTL and 27.5wt% from fast HTL) being produced from sludge that was 85wt% moisture. The HTL biocrude from sludge mainly contains long-chain aliphatic hydrocarbon moieties and aliphatic acids. Dichloromethane recovered more biocrude and energy content (∼50%) than did the other solvents tested. Added K2CO3, Na2CO3, HCOOH, CH3COOH, MoO3-CoO/γ-Al2O3 and Ru/C significantly decrease the biocrude yield when their loadings are 50wt% of the dried sludge. The additives, excepting carbonates, enhance gasification of sludge.

Algal polycultures enhance coproduct recycling from hydrothermal liquefaction.

The aim of this study was to determine if polycultures of algae could enhance tolerance to aqueous-phase coproduct (ACP) from hydrothermal liquefaction (HTL) of algal biomass to produce biocrude. The growth of algal monocultures and polycultures was characterized across a range ACP concentrations and sources. All of the monocultures were either killed or inhibited by 2% ACP, but polycultures of the same species were viable at up to 10%. The addition of ACP increased the growth rate (up to 25%) and biomass production (53%) of polycultures, several of which were more productive in ACP than any monoculture was in the presence or absence of ACP. These results suggest that a cultivation process that applies biodiversity to nutrient recycling could produce more algae with less fertilizer consumption.

Effects of processing conditions on biocrude yields from fast hydrothermal liquefaction of microalgae.

This study investigated the effects of algae species, reaction time, and reactor loading on the biocrude yield from fast hydrothermal liquefaction (HTL) of microalgae. Fast HTL reaction times were always less than 2 min and employed rapid heating and nonisothermal conditions. The highest biocrude yield obtained was 67±5 wt.% (dry basis). With all other process variables fixed, increasing the reaction time in a 600 °C sand bath by 15 s increments led to a rapid increase in biocrude yield between 15 and 45 s. At longer times, the biocrude yield decreased. Low reactor loadings generally gave higher biocrude yields than did higher loadings. The low reactor loadings may facilitate biocrude production by facilitating cell rupture and/or increasing the effective concentration of algal cells in the hot, compressed water in the reactor.