Thermochemical Conversion of Duckweed Biomass to Gasoline, Diesel, and Jet Fuel: Process Synthesis and Global Optimization

Progress in thermochemical conversion of aquatic weeds in shellfish aquaculture for biofuel generation: Technical and economic perspectives

Rapid growth of aquatic weeds in treatment pond poses undesirable challenge to shellfish aquaculture, requiring the farmers to dispose these weeds on a regular basis. This article reviews the potential and application of various aquatic weeds for generation of biofuels using recent thermochemical technologies (torrefaction, hydrothermal carbonization/liquefaction, pyrolysis, gasification). The influence of key operational parameters for optimising the aquatic weed conversion efficiency was discussed, including the advantages, drawbacks and techno-economic aspects of the thermochemical technologies, and their viability for large-scale application. Via extensive study in small and large scale operation, and the economic benefits derived, pyrolysis is identified as a promising thermochemical technology for aquatic weed conversion. The perspectives, challenges and future directions in thermochemical conversion of aquatic weeds to biofuels were also reviewed. This review provides useful information to promote circular economy by integrating shellfish aquaculture with thermochemical biorefinery of aquatic weeds rather than disposing them in landfills.

Kinetic Study of Product Distribution Using Various Data-Driven and Statistical Models for Fischer-Tropsch Synthesis

Three modeling techniques, namely, a radial basis function neural network (RBFNN), a comprehensive kinetic with genetic algorithm (CKGA), and a response surface methodology (RSM), were used to study the kinetics of Fischer-Tropsch (FT) synthesis. Using a 29 × 37 (4 independent process parameters as inputs and corresponding 36 responses as outputs) matrix with total 1073 data sets for data training through RBFNN, the established model is capable of predicting hydrocarbon product distribution i.e., the paraffin formation rate (C₂-C₁₅) and the olefin to paraffin ratio (OPR) within acceptable uncertainties. With additional validation data sets (15 × 36 matrix with total 540 data sets), the uncertainties of using three different models were compared and the outcomes were: RBFNN (±5% uncertainties), RSM (±10% uncertainties), and CKGA (±30% uncertainties), respectively. A new effective strategy for kinetic study of the complex FT synthesis is proposed: RBFNN is used for data matrix generation with a limited number of experimental data sets (due to its fast converge and less computation time), CKGA is used for mechanism selections by the Langmuir-Hinshelwood-Hougen-Watson (LHHW) approach using a genetic algorithm to find out potential reaction pathways, and RSM is used for statistical analysis of the investigated data matrix (generated from RBFNN through central composite design) upon responses and subsequent singular/multiple optimizations. The proposed strategy is a very useful and practical tool in process engineering design and practice for the product distribution during FT synthesis.

Progress in thermochemical conversion of duckweed and upgrading of the bio-oil: A critical review

The processing of duckweed has been included in the list of promising pathways for biofuels production. This property is attributed to its simple manual harvesting method and its ability for high protein or starch content, depending on its species and growing environment. The biofuels production from duckweed, is not only a solution to energy and environmental problems, but also a reliable way to realize the utilization of duckweed. This critical review focuses on the bio-oil production from duckweed via pyrolysis and hydrothermal liquefaction processes. First, characteristics and eco-environmental benefits of duckweed are reviewed. Next, the impacts of different parameters on the properties and distribution of bio-oil from pyrolysis and hydrothermal liquefaction are discussed in detail. Subsequently, the effect of hydrogen donor solvents (as reaction media for upgrading) and catalysts on the upgrading of duckweed bio-oil are extensively discussed. This paper ends with the prospects for further development in thermochemical valorization of duckweed.

The role and effectiveness of monoculture and polyculture phytoremediation systems in fish farm wastewater

Phytoremediation offers a sustainable solution to aquaculture pollution, but studies with critical evaluations of the treatment performances of macrophyte systems are limited. This study intended to evaluate the roles and treatment profiles of Spirodela polyrhiza (L.) Schleid. and Lemna sp. systems in terms of ammonia, nitrate, nitrite, phosphate (NH3-N, NO3 --N, NO2 --N, PO4 3-), chemical oxygen demand (COD), turbidity, and total suspended solids (TSS) on fish farm wastewater and to elucidate the rationale behind the removal of the pollutants and the changes in a raceway pond rig. The nitrogen and phosphorus removal in the Spirodela polyrhiza monoculture system outperformed the other configured systems. An 81% reduction in ammonia (to 3.90 mg of NH3-N/L), and sharp declines of up to 75%, 88%, and 71% in TSS, turbidity, and COD levels were recorded within two days, while significant decreases in nitrate, nitrite, and phosphate levels were observed. This indicated that the system could inhibit nitrate and nitrite spikes in waters (nitrification) via reducing the available ammonia and limiting subsequent nitrite and nitrate conversion, while reducing TSS in algal-bloom wastewater via shading. High biomass productivity and superior protein content were observed in the macrophyte systems (S. polyrhiza + Lemna sp. polyculture system), with up to 112% and 12% increases, respectively. This study demonstrated that the S. polyrhiza monoculture system is effective at treating fish farm wastewater, lowering the levels of relevant inorganic and organic pollutants, and it could be used as a biofilter for natural waters, preserving the existing ecology.

A framework to predict the price of energy for the end-users with applications to monetary and energy policies

Energy affects every single individual and entity in the world. Therefore, it is crucial to precisely quantify the “price of energy” and study how it evolves through time, through major political and social events, and through changes in energy and monetary policies. Here, we develop a predictive framework, an index to calculate the average price of energy in the United States. The complex energy landscape is thoroughly analysed to accurately determine the two key factors of this framework: the total demand of the energy products directed to the end-use sectors, and the corresponding price of each product. A rolling horizon predictive methodology is introduced to estimate future energy demands, with excellent predictive capability, shown over a period of 174 months. The effectiveness of the framework is demonstrated by addressing two policy questions of significant public interest.

Global energy transformation requires quantifying the "price of energy" and studying its evolution. Here the authors present a predictive framework that calculates the average US price of energy, estimating future energy demands for up to four years with excellent accuracy, designing and optimizing energy and monetary policies.

Potential of invasive watermilfoil (Myriophyllum spp.) to remediate eutrophic waterbodies with organic and inorganic pollutants

Watermilfoil (Myriophyllum) is one of the world's most troublesome invasive aquatic weeds. Although current management practices may inhibit its expansion, it also impacts not only the quality of water but habitat deterioration. Therefore, the need for developing highly efficient and low-cost biotechnologies with resource recovery into the agriculture field as a complementary management strategy cannot be overstated. Here, we reviewe the scientific/grey literature to offer readers a precise and panoramic view of the invasive watermilfoil ecology, regional problems, impacts, ecosystem services, and management. In this regard, an in-depth review aimed to assess the potential for reducing non-point source inorganic and organic pollutants using invasive watermilfoil, with the sustainable approaches, while offering other services and mitigating ecological trade-offs is presented. Global distributions, growth, and current progress on the management and utilization of invasive watermilfoil biomass are summarized to develop the aim, which is to convey challenges during the implementation of large-scale weed use. In short, pollutant assimilation in plant and bacterial communities linked to this weed considerably contribute to the reduction and degradation of pollutants from both natural and artificial systems. Although several considerations in recycling and reusing biomass need to be considered, the potential reuse of the harvested material for livestock feed, compost and direct use in farming systems offer an additional strategy to achieve sustainable ecosystem restoration. Further research and development may focus on a more detailed economic modeling approach that integrates the costs (worker's wage, harvesting, transportation, and energy consumption), legal and regulatory barriers, health risks and ecosystem service benefits (biodiversity improvement, and pollutant removal) to holistically evaluate the economic, environmental, and societal value of reusing and recycling this waste material.

Comparison of nutrient removal and biomass production between macrophytes and microalgae for treating artificial citrus nursery wastewater

Macrophyte (Lemna minor) and microalgae (Chlorella vulgaris and Scenesdesmus quadricauda) were used for treating artificial wastewater mimicking recirculating soilless citrus nursery system discharge in the laboratory environment. L. minor gave a better dry biomass yield (0.059 ± 0.003 g/L/day) than C. vulgaris (0.033 ± 0.002 g/L/day) and S. quadricauda (0.039 ± 0.001 g/L/day). Furthermore, L. minor had a higher nutrient (total N and P) and soluble minerals (S, K, Ca, Mg, Zn, Cu, and Mn) removal capabilities than microalgae due to a more natural high growth rate in non-optimized culture conditions.

Anaerobic bioprocessing of wastewater-derived duckweed: Maximizing product yields in a biorefinery value cascade

This study integrated the sugar and carboxylate platforms to enhance duckweed processing in biorefineries. Two or three bioprocesses (ethanol fermentation, acidogenic digestion, and methanogenic digestion) were sequentially integrated to maximize the carbon-to-carbon conversion of wastewater-derived duckweed into bioproducts, through a series of laboratory-scale experiments. Reactors were fed either raw (dried), liquid-hot-water-pretreated, or enzymatically-saccharified duckweed. Subsequently, the target bioproduct was separated from the reactor liquor and the residues further processed. The total bioproduct carbon yield of 0.69 ± 0.07 g per gram of duckweed-C was obtained by sequential acidogenic and methanogenic digestion. Three sequential bioprocesses revealed nearly as high yields (0.66 ± 0.08 g of bioproduct-C per duckweed-C), but caused more gaseous carbon (dioxide) loss. For this three-stage value cascade, yields of each process in conventional units were: 0.186 ± 0.001 g ethanol/g duckweed; 611 ± 64 mg volatile fatty acids as acetic acid/g VS; and 434 ± 0.2 ml methane/g VS.

Effect of pH and temperature on microbial community structure and carboxylic acid yield during the acidogenic digestion of duckweed

BACKGROUND

Duckweeds (Lemnaceae) are efficient aquatic plants for wastewater treatment due to their high nutrient-uptake capabilities and resilience to severe environmental conditions. Combined with their rapid growth rates, high starch, and low lignin contents, duckweeds have also gained popularity as a biofuel feedstock for thermochemical conversion and alcohol fermentation. However, studies on the acidogenic anaerobic digestion of duckweed into carboxylic acids, another group of chemicals which are precursors of higher-value chemicals and biofuels, are lacking. In this study, a series of laboratory batch experiments were performed to determine the favorable operating conditions (i.e., temperature and pH) to maximize carboxylic acid production from wastewater-derived duckweed during acidogenic digestion. Batch reactors with 25 g/l solid loading were operated anaerobically for 21 days under mesophilic (35 °C) or thermophilic (55 °C) conditions at an acidic (5.3) or basic (9.2) pH. At the conclusion of the experiment, the dominant microbial communities under various operating conditions were assessed using high-throughput sequencing.

RESULTS

The highest duckweed-carboxylic acid conversion of 388 ± 28 mg acetic acid equivalent per gram volatile solids was observed under mesophilic and basic conditions, with an average production rate of 0.59 g/l/day. This result is comparable to those reported for acidogenic digestion of other organics such as food waste. The superior performance observed under these conditions was attributed to both chemical treatment and microbial bioconversion. Hydrogen recovery was only observed under acidic thermophilic conditions, as 23.5 ± 0.5 ml/g of duckweed volatile solids added. More than temperature, pH controlled the overall structure of the microbial communities. For instance, differentially abundant enrichments of Veillonellaceae acidaminococcus were observed in acidic samples, whereas enrichments of Clostridiaceae alkaliphilus were found in the basic samples. Acidic mesophilic conditions were found to enrich acetoclastic methanogenic populations over processing times longer than 10 days.

CONCLUSIONS

Operating conditions have a significant effect on the yield and composition of the end products resulting from acidogenic digestion of duckweed. Wastewater-derived duckweed is a technically feasible alternative feedstock for the production of advanced biofuel precursors; however, techno-economic analysis is needed to determine integrated full-scale system feasibility and economic viability.

Effect of Exogenous General Plant Growth Regulators on the Growth of the Duckweed Lemna minor

Gibberellic acid (GA₃), indole-3-acetic acid (IAA), salicylic acid (SA), abscidic acid (ABA), jasmonic acid (JA) 1-amino cyclopropane-1-carboxylic acid (ACC) and aminoethoxyvinylglycine (AVG) are popular growth regulators of plants. However, the effects of their exogenous addition on the biomass production of aquatic plants, including Lemnoideae plants, "duckweeds," are largely unknown. In this study, the growth of Lemna minor was tested for 10 d in Hoagland medium containing each compound at different concentrations of 0-50 μM. GA₃, IAA, and SA were found to have no apparent positive effect on the growth at all concentrations tested. Conversely, ACC and JA moderately and AVG and ABA severely inhibited the growth of L. minor. Among the tested compounds, ascorbic acid had an apparent growth-promoting effect.

Purification and reuse of non-point source wastewater via Myriophyllum-based integrative biotechnology: A review

In this review, the applications of Myriophyllum-based integrative biotechnology to remove common non-point source (NPS) pollutants, such as nitrogen, phosphorus, heavy metals, and organic pollutants (e.g., pesticides and antibiotics) are summarized. The removal of these pollutants via various mechanisms, including uptake by plant and microbial communities in macrophyte-based treatment systems are discussed. This review highlights the potential use of Myriophyllum biomass to produce animal feed, fertilizer, and other valuable by-products, which can yield cost-effective returns and attract more attention to the regulation and recycling of NPS pollutants. In addition, it demonstrates that utilization of Myriophyllum species is a promising and reliable strategy for wastewater treatment. The future development of sustainable Myriophyllum-based treatment systems is discussed from various perspectives.

Enhanced biomass production of duckweeds by inoculating a plant growth-promoting bacterium, Acinetobacter calcoaceticus P23, in sterile medium and non-sterile environmental waters

Duckweed offers the promise of a co-benefit culture combining water purification with biomass production. Acinetobacter calcoaceticus P23 is a plant growth-promoting bacterium isolated from a duckweed, Lemna aequinoctialis. This study quantified its growth-promoting effect on three duckweeds (L. aoukikusa, L. minor, and Spirodela polyrhiza) in sterile Hoagland solution and evaluated its usefulness in duckweed culture under non-sterile conditions. P23 promoted growth of three duckweeds in sterile Hoagland solution at low to high nutrient concentrations (1.25-10 mg NO₃-N/L and 0.25-2.0 mg PO₄-P/L). It increased the biomass production of L. aequinoctialis 3.8-4.3-fold, of L. minor 2.3-3.3-fold, and of S. polyrhiza 1.4-1.5-fold after 7 days compared with noninoculated controls. P23 also increased the biomass production of L. minor 2.4-fold in pond water and 1.7-fold in secondary effluent of a sewage treatment plant under non-sterile conditions at laboratory-scale experiments. P23 rescued L. minor from growth inhibition caused by microorganisms indigenous to the pond water. The results demonstrate that the use of P23 in duckweed culture can improve the efficiency of duckweed biomass production, and a positive effect of P23 on duckweed-based wastewater treatment can be assumed.

Effects of high ammonium level on biomass accumulation of common duckweed Lemna minor L

Growing common duckweed Lemna minor L. in diluted livestock wastewater is an alternative option for pollutants removal and consequently the accumulated duckweed biomass can be used for bioenergy production. However, the biomass accumulation can be inhibited by high level of ammonium (NH4 (+)) in non-diluted livestock wastewater and the mechanism of ammonium inhibition is not fully understood. In this study, the effect of high concentration of NH4 (+) on L. minor biomass accumulation was investigated using NH4 (+) as sole source of nitrogen (N). NH4 (+)-induced toxicity symptoms were observed when L. minor was exposed to high concentrations of ammonium nitrogen (NH4 (+)-N) after a 7-day cultivation. L. minor exposed to the NH4 (+)-N concentration of 840 mg l(-1) exhibited reduced relative growth rate, contents of carbon (C) and photosynthetic pigments, and C/N ratio. Ammonium irons were inhibitory to the synthesis of photosynthetic pigments and caused C/N imbalance in L. minor. These symptoms could further cause premature senescence of the fronds, and restrain their reproduction, growth and biomass accumulation. L. minor could grow at NH4 (+)-N concentrations of 7-84 mg l(-1) and the optimal NH4 (+)-N concentration was 28 mg l(-1).

Energy Supply Chain Optimization of Hybrid Feedstock Processes: A Review

The economic, environmental, and social performances of energy systems depend on their geographical locations and the surrounding market infrastructure for feedstocks and energy products. Strategic decisions to locate energy conversion facilities must take all upstream and downstream operations into account, prompting the development of supply chain modeling and optimization methods. This article reviews the contributions of energy supply chain studies that include heat, power, and liquid fuels production. Studies are categorized based on specific features of the mathematical model, highlighting those that address energy supply chain models with and without considerations of multiperiod decisions. Studies that incorporate uncertainties are discussed, and opportunities for future research developments are outlined.