The effect of functional unit and co-product handling methods on life cycle assessment of an algal biorefinery

Evidencing the importance of the functional unit in comparative life cycle assessment of organic berry crops

LCA methodology provides the best framework to evaluate environmental impacts in agriculture systems. However, the interpretation of LCA results, in particular when the objective was to compare different production systems, could be affected by the selection of the functional unit (FU). That is why an accurate definition of the FU, in agreement with the function considered for the systems analysed, is essential. In this work, the organic production at small scale of blueberry, raspberry, blackberry and cape gooseberry in North Spain has been analysed following LCA methodology. Although a different distribution of environmental loads was obtained for each crop, in all cases, the main contributions to most of the considered environmental categories were electric and fertiliser consumptions. The different production systems have been compared on the basis of the environmental impacts associated considering different FUs, i.e. based on fruit mass, cultivated area, farm-gate price and nutritional quality of fruits. Carbon footprints (CF) have been also calculated. It was observed that the order of the crops with respect to their environmental performances was the same for the blueberry and raspberry crops (with the lowest and the highest CF, respectively), independently of the selected FU, whereas the order of the blackberry and cape gooseberry crops was interchanged, depending on the FU used. This work supports the need of being aware of the final objective of the orchards when choosing the FU (i.e. producing fruits, cultivating an area, economic benefits or nourishing people), so that valid conclusions can be achieved from the environmental comparison, even for different agricultural products.

Assessing sustainability of microalgae-based wastewater treatment: Environmental considerations and impacts on human health

An integrated life cycle assessment (LCA) and quantitative microbial risk assessment (QMRA) were conducted to assess microalgae-mediated wastewater disinfection (M-WWD). M-WWD was achieved by replacing ultraviolet disinfection with a microalgal open raceway pond in an existing sewage treatment plant (STP) in India. Regarding impacts on human health, both M-WWD and STP yielded comparable life cycle impacts, around 0.01 disability-adjusted life years (DALYs) per person per year. However, QMRA impacts for M-WWD (0.053 DALYs per person per year) were slightly lower than that for STP while considering exposure to E. coli O157:H7 and adenovirus. Additionally, a comparative LCA resolved the dilemma about the appropriate utilization of microalgal biomass. Among biodiesel, biocrude, and biogas production, the lowest impacts of 0.015 DALYs per person per year were obtained for biocrude for 1 m3 water treated by M-WWD. Electricity consumption in microalgae cultivation was a major environmental hotspot. Overall, M-WWD, followed by production of microalgal biocrude, emerged as a sustainable alternative from environmental and public health perspectives. These findings set the foundation for pilot-scale M-WWD system development, testing, and economic evaluation. Such comprehensive investigations, encompassing LCA, QMRA, and resource recovery scenarios, offer crucial insights for stakeholders and decision-makers in wastewater treatment and environmental management.

Strategies and challenges to enhance commercial viability of algal biorefineries for biofuel production

The rise in energy consumption would quadruple in the coming century and the, existing energy resources might be insufficient to meet the demand of the growing population. An alternative and sustainable energy resource is therefore needed to address the fossil fuel deficiency. The utility of microalgae strains in the aspect of biorefinery has been in research for quite some time. Algal biorefinery is an alternate way of renewable energy however even after decades of research it still suffers from commercialization bottlenecks. The current manuscript reviews the scenarios where the innovation needs an ignition for its commercialization. This review discusses the prospects of up-scale cultivation, and harvesting algal biomass for biorefineries. It narrates algal biorefinery hurdles that can be solved using integrated technology approach, life cycle assessment and applications of nanotechnology. The review also sheds light upon the ties of algal biorefineries with its economic viability.

Global Life Cycle and Techno-Economic Assessment of Algal-Based Biofuels

Techno-economic analyses (TEAs) and life cycle assessments (LCAs) of algal biofuels often focus on locations in suboptimal latitudes for algal cultivation, which can under-represent the sustainability potential of the technology. This study identifies the optimal global productivity potential, environmental impacts, and economic viability of algal biofuels by using validated biophysical and sustainability modeling. The biophysical model simulates growth rates of Scenedesmus obliquusbased on temperature, photoinhibition, and respiration effects at 6685 global locations. Region-specific labor costs, construction factors, and tax rates allow for spatially resolved TEA, while the LCA includes regional impacts of electricity, hydrogen, and nutrient markets across ten environmental categories. The analysis identifies optimal locations for algal biofuel production in terms of environmental impacts and economic viability which are shown to follow biomass yields. Modeling results highlight the global variability of productivity with maximum yields ranging between 24.8 and 27.5 g m-2 d-1 in equatorial regions. Environmental impact results show favorable locations tracked with low-carbon electricity grids, with the well-to-wheels global warming potential (GWP) ranging from 31 to 45 g CO2eq MJ-1 in South America and Central Africa. When including direct land use change impacts, the GWP ranged between 44 and 55 g CO2eq MJ-1 in these high-productivity regions. Low-carbon electricity also favors air quality and eutrophication impacts. The TEA shows that minimum algal fuel prices of $1.89-$2.15 per liter of gasoline-equivalent are possible in southeast Asia and Venezuela. This discussion focuses on the challenges and opportunities to reduce fuel prices and the environmental impacts of algal biofuels in various global regions.

Vineyard Pruning Extracts as Natural Antioxidants for Biodiesel Stability: Experimental Tests and Preliminary Life Cycle Assessment

The control of the oxidative stability of biodiesel and blends of biodiesel with diesel is one of the major concerns of the biofuel industry. The oxidative degradation of biodiesel can be accelerated by several factors, and this is most critical in the so-called second generation biodiesel, which is produced from low-cost raw materials with lower environmental impacts. The addition of antioxidants is imperative to ensure the oxidative stability of biodiesel, and these are considered products of high commercial value. The antioxidants currently available on the market are from synthetic origin, so the existence/availability of alternative antioxidants of natural origin (less dependent on fossil sources) at a competitive price presents itself as a strong business opportunity. This work describes and characterizes a sustainable alternative to synthetic antioxidants used in the biodiesel market developed from extracts of vineyard pruning waste (VPW), which are naturally rich in phenolic compounds with antioxidant properties. A hydrothermal extraction process was applied as a more efficient and sustainable technology than the conventional one with the potential of the extracts as antioxidant additives in biodiesel evaluated in Rancitech equipment. The VPW extract showed comparable antioxidant activity as the commercial antioxidant butylated hydroxytoluene (BHT) typically used in biodiesel. The stability of the biodiesel is dependent from the amount of the extract added. Further, for the first time, the assessment of the environmental impacts of using natural extracts to control the oxidative stability of biodiesel in the production process is also discussed as a key factor of the process environmental sustainability.

Life cycle assessment of microalgal biorefinery: A state-of-the-art review

Microalgal biorefineries represent an opportunity to economically and environmentally justify the production of bioproducts. The generation of bioproducts within a biorefinery system must quantitatively demonstrate its viability in displacing traditional fossil-based refineries. To this end, several works have conducted life cycle analyses on microalgal biorefineries and have shown technological bottlenecks due to energy-intensive processes. This state-of-the-art review covers different studies that examined microalgal biorefineries through life cycle assessments and has identified strategic technologies for the sustainable production of microalgal biofuels through biorefineries. Different metrics were introduced to supplement life cycle assessment studies for the sustainable production of microalgal biofuel. Challenges in the comparison of various life cycle assessment studies were identified, and the future design choices for microalgal biorefineries were established.

Could microalgae offer promising options for climate action via their agri-food applications?

In 2021 the Intergovernmental Panel on Climate Change (IPCC) issued the first volume of its latest authoritative report on climate change. Underlining the seriousness of the situation, the United Nations Secretary-General branded its findings a “code red for humanity.” The need for climate action is now evident, but finding viable pathways forward can be elusive. Microalgae have been attracting attention as a category of “future food,” with species like Arthrospira platensis (spirulina) and Chlorella vulgaris (chlorella) seeing growing uptake by consumers while research interest continues to expand. One timely but neglected question is whether microalgae might offer options for promising climate actions via their agri-food applications. Specifically, might they offer scope to help secure food supplies, while also providing climate resilient livelihood pathways for vulnerable farmers already grappling with food insecurity and environmental degradation? This paper reports on a review of the academic literature on microalgae as an agri-food technology, notably their uses as a food, feed, biofertilizer, biostimulant, and biochar. This family of applications was found to offer promising climate actions vis-à-vis both mitigating and adapting to climate change. Aspects pertinent to adaptation include growing rapidly under controlled conditions, reusing water, providing potent nutrition for humans and animals, and supporting resilient crop production. Agri-food applications of microalgae also provide opportunities to mitigate climate change that could be explored. The paper concludes by flagging possible risks and obstacles as well as research and policy priorities to elaborate and harness this potential.

Research trends and market opportunities of microalgal biorefinery technologies from circular bioeconomy perspectives

Microalgae as an alternative feedstock for sustainable bio-products have gained significant interest over years. Even though scientific productivity related to microalgae-based research has increased in recent decades, translation to industrial scale is still lacking. Therefore, it is essential to understand the current state-of-art and, identify research gaps and hotspots driving industrial scale up. The present review through scientometric analysis attempted to delineate the research evolution contributing to this emerging field. The research trends were analysed over the last decade globally highlighting the collaborative network between the countries. The comprehensive knowledge map generated confirmed microalgal biorefinery as a scientifically active field, where the present research interest is focussed on synergistically integrating the unit processes involved to make it enviro-economically feasible. Market opportunities and regulatory policy requirements along with the consensus need to adopt circular bio-economy perspectives were highlighted to facilitate real-time implementation of microalgal biorefinery.

Safflower-based biorefinery producing a broad spectrum of biofuels and biochemicals: A life cycle assessment perspective

Global environmental awareness has encouraged further research towards biofuel production and consumption. Despite the favorable properties of biofuels, the sustainability of their conventional production pathways from agricultural feedstocks has been questioned. Therefore, the use of non-food feedstocks as a promising approach to ensure sustainable biofuel production is encouraged. However, the use of synthetic solvents/chemicals and energy carriers during biofuel production and the consequent adverse environmental effects are still challenging. On the other hand, biofuel production is also associated with generating large volumes of waste and wastewater. Accordingly, the circular bioeconomy as an innovative approach to ensure complete valorization of feedstocks and generated waste streams under the biorefinery scheme is proposed. In line with that, the current study aims to assess the environmental sustainability of bioethanol production in a safflower-based biorefinery using the life cycle assessment framework. Based on the obtained results, safflower production and its processing into 1 MJ bioethanol under the safflower-based biorefinery led to damage of 2.23E-07 disability-adjusted life years (DALY), 2.35E-02 potentially disappeared fraction (PDF)*m²*yr, 4.76E-01 kg CO₂ eq., and 3.82 MJ primary on the human health, ecosystem quality, climate change, and resources, respectively. Moreover, it was revealed that despite adverse environmental effects associated with safflower production and processing, the substitution of conventional products, i.e., products that are the typical products in the market without having environmental criteria, with their bio-counterparts, i.e., products produced in the biorefinery based on environmental criteria could overshadow the unfavorable effects and substantially enhance the overall sustainability of the biorefinery system. The developed safflower-based biorefinery led to seven- and two-time reduction in damage to the ecosystem quality and resources damage categories, respectively. The reductions in damage to human health and climate change were also found to be 52% and 24%, respectively. The weighted environmental impacts of the safflower-based biorefinery decreased by 64% due to the production of bioproducts, mainly biodiesel and biogas, replacing their fossil-based counterparts, i.e., diesel and natural gas, respectively. Finally, although the main focus of the developed safflower-based biorefinery was biofuel production, waste valorization and mainly animal feed played a significant role in improving the associated environmental impacts.

Innovative microalgae biomass harvesting methods: Technical feasibility and life cycle analysis

In order to ease one of the main challenges of biomass production in wastewater, the harvest stage, this study proposes as main innovations: the comparison of technical and environmental performance of different methods of harvesting biomass which have not been addressed in the literature and the projection of an optimal environmental scenario for biomass harvesting. For this, three harvesting methods were evaluated and compared, namely the gravitational sedimentation (GS) via settling tank, coagulation with tannin followed by gravitational sedimentation (TC/GS), and a biofilm reactor operated in parallel with a settling tank (BR/GS). TC/GS required less time to concentrate the biomass (121.13 g/day); however, the biomass had a higher moisture content (99.02%), which may compromise its direct application for production of most bioproducts and bioenergy, only a dewatering step is recommended. The harvesting methods interfered in biomass characterisation, mainly in carbohydrate content, which was higher in biomass concentrated over time (28-37%) than biomass concentrated in a single day by coagulation (13.8%). The results of the life cycle assessment revealed that in scenarios which included TC/GS methods and the BR/GS presented less environmental impact in relation to only GS. Additionally, the combination of these two methods comprises the best scenario and promises to optimise the harvest of biomass grown in wastewater.

Life Cycle Assessment of the Mesophilic, Thermophilic, and Temperature-Phased Anaerobic Digestion of Sewage Sludge

In this study the environmental impact of the anaerobic digestion (AD) of sewage sludge within an activated sludge wastewater treatment plant (WWTP) was investigated. Three alternative AD systems (mesophilic, thermophilic, and temperature-phased anaerobic digestion (TPAD)) were compared to determine which system may have the best environmental performance. Two life cycle assessments (LCA) were performed considering: (i) the whole WWTP (for a functional unit (FU) of 1 m3 of treated wastewater), and (ii) the sludge line (SL) alone (for FU of 1 m3 of produced methane). The data for the LCA were obtained from previous laboratory experimental work in combination with full-scale WWTP and literature. According to the results, the WWTP with TPAD outperforms those with mesophilic and thermophilic AD in most analyzed impact categories (i.e., Human toxicity, Ionizing radiation, Metal and Fossil depletion, Agricultural land occupation, Terrestrial acidification, Freshwater eutrophication, and Ozone depletion), except for Climate change where the WWTP with mesophilic AD performed better than with TPAD by 7%. In the case of the SL alone, the production of heat and electricity (here accounted for as avoided environmental impacts) led to credits in most of the analyzed impact categories except for Human toxicity where credits did not balance out the impacts caused by the wastewater treatment system. The best AD alternative was thermophilic concerning all environmental impact categories, besides Climate change and Human toxicity. Differences between both LCA results may be attributed to the FU.