Pretreatment and fermentation of salt-water grown algal biomass as a feedstock for biofuels and high-value biochemicals

De-risking Pretreatment of Microalgae To Produce Fuels and Chemical Co-products

Conversion of microalgae to renewable fuels and chemical co-products by pretreating and fractionation holds promise as an algal biorefinery concept, but a better understanding of the pretreatment performance as a function of algae strain and composition is necessary to de-risk algae conversion operations. Similarly, there are few examples of algae pretreatment at scales larger than the bench scale. This work aims to de-risk algal biorefinery operations by evaluating the pretreatment performance across nine different microalgae samples and five different pretreatment methods at small (5 mL) scale and further de-risk the operation by scaling pretreatment for one species to the 80 L scale. The pretreatment performance was evaluated by solubilization of feedstock carbon and nitrogen [as total organic carbon (TOC) and total nitrogen (TN)] into the aqueous hydrolysate and extractability of lipids [as fatty acid methyl esters (FAMEs)] from the pretreated solids. A range of responses was noted among the algae samples across pretreatments, with the current dilute Brønsted acid pretreatment using H2SO4 being the most consistent and robust. This pretreatment produced TOC yields to the hydrolysate ranging from 27.7 to 51.1%, TN yields ranging from 12.3 to 76.2%, and FAME yields ranging from 57.9 to 89.9%. In contrast, the other explored pretreatments (other dilute acid pretreatments, dilute alkali pretreatment with NaOH, enzymatic pretreatment, and flash hydrolysis) produced lower or more variable yields across the three metrics. In light of the greater consistency across samples for dilute acid pretreatment, this method was scaled to 80 L to demonstrate scalability with microalgae feedstocks.

Influence of light intensity and photoperiod on the pigment and, lipid production of Dunaliella tertiolecta and Nannochloropsis oculata under three different culture medium

Microalgal biomass has the ability to store huge amount of triacylglycerides as fatty ester methyl esters (FAME) and carotenoids which has made algae as potential candidate for biorefinery approach. Essential fatty acid such as palmitic acid, stearic acid, arachidonic acid and eicospentanoic acid have been produced which are known for their various applications. The present study was aimed to evaluate the influence of different light intensities (120 and 250 μE/m²/s) and photoperiod (16:8h and 13:11h light/dark cycle) on the production of lipid, biomass and lutein. Dunaliella tertiolecta and Nannochloropsis oculata was grown for 23 days in F/2, sea salt media (SSM, Distilled water (DW) and SSM (natural seawater media,NSW) under two different light intensities and photoperiod regimes at 25 ᵒC. SSM (NSW) showed maximum accumulation of lipid in D.tertiolecta (34.56 mg/L/d). SSM (DW)- biomass showed 1.5 times higher lutein productivity of 0.253 mg/L/d under 13:11h light/dark cycle at 250 μE/m²/s compared to same medium under 16:8h light/dark cycles at 120 μE/m²/s. Where as in N.oculata, F/2 biomass showed higher lipid and lutein productivity of 15.69 and 0.279 mg/L/d, respectively The laboratory scale cultivation parameters and related media cost showed the suitability of different culture media adaptation to large scale production.

Advances in algal biomass pretreatment and its valorisation into biochemical and bioenergy by the microbial processes

Urbanization and pollution are the major issues of the current time own to the exhaustive consumption of fossil fuels which have a detrimental effect on the nation's economies and air quality due to greenhouse gas (GHG) emissions and shortage of energy reserves. Algae, an autotrophic organism provides a green substitute for energy as well as commercial products. Algal extracts become an efficient source for bioactive compounds having anti-microbial, anti-oxidative, anti-inflammatory, and anti-cancerous potential. Besides the conventional approach, residual biomass from any algal-based process might act as a renewable substrate for fermentation. Likewise, lignocellulosic biomass, algal biomass can also be processed for sugar recovery by different pre-treatment strategies like acid and alkali hydrolysis, microwave, ionic liquid, and ammonia fiber explosion, etc. Residual algal biomass hydrolysate can be used as a feedstock to produce bioenergy (biohydrogen, biogas, methane) and biochemicals (organic acids, polyhydroxyalkanoates) via microbial fermentation.

Enabling Production of Algal Biofuels by Techno-Economic Optimization of Co-Product Suites

Recent techno-economic analysis (TEA) has underscored that for algal biofuels to be cost competitive with petroleum fuels, co-products are necessary to offset the cost of fuel production. The co-product suite must scale with fuel production while also maximizing value from the non-fuel precursor components. The co-product suite also depends on algal biomass composition, which is highly dynamic and depends on environmental conditions during cultivation. Intentional shifts in composition during cultivation are often associated with reduced biomass productivity, which can increase feedstock production costs for the algae-based biorefinery. The optimal algae-based biorefinery configuration is thus a function of many factors. We have found that comprehensive TEA, which requires the construction of process models with detailed mass and energy balances, along with a complete accounting of capital and operating expenditures for a commercial-scale production facility, provides invaluable insight into the viability of a proposed biorefinery configuration. This insight is reflected in improved viability for one biorefining approach that we have developed over the last 10 years, namely, the Combined Algal Processing (CAP) approach. This approach fractionates algal biomass into carbohydrate-, lipid-, and protein-rich fractions, and tailors upgrading chemistry to the composition of each fraction. In particular, transitioning from valorization of only the lipids to a co-product suite from multiple components of high-carbohydrate algal biomass can reduce the minimum fuel selling price (MFSP) from more than $8/gallon of gasoline equivalent (GGE) to $2.50/GGE. This paper summarizes that progress and discusses several surprising implications in this optimization approach.

Algal biomass valorisation to high-value chemicals and bioproducts: Recent advances, opportunities and challenges

Algae are considered promising biomass resources for biofuel production. However, some arguments doubt the economical and energetical feasibility of algal cultivation, harvesting, and conversion processes. Beyond biofuel, value-added bioproducts can be generated via algae conversion, which would enhance the economic feasibility of algal biorefineries. This review primarily focuses on valuable chemical and bioproduct production from algae. The methods for effective recovery of valuable algae components, and their applications are summarized. The potential routes for the conversion of lipids, carbohydrates, and proteins to valuable chemicals and bioproducts are assessed from recent studies. In addition, this review proposes the following challenges for future algal biorefineries: (1) utilization of naturally grown algae instead of cultivated algae; (2) fractionation of algae to individual components towards high-selectivity products; (3) avoidance of humin formation from algal carbohydrate conversion; (4) development of strategies for algal protein utilisation; and (5) development of efficient processes for commercialization and industrialization.

Bioethanol production from defatted biomass of Nannochloropsis oculata microalgae grown under mixotrophic conditions

In order to improve the economic feasibility and environmental sustainability of microalgal bioethanol production, a nontoxic, copious agricultural waste, sugarcane bagasse aqueous extract (SBAE) was used for cultivating Nannochloropsis oculata microalga (NNO-1 UTEX Culture LB 2164) as potential sources of substitutes for traditional nutrition to reduce the costs in cultivation through acid digestion and enzymatic treatment before being fermented by Saccharomyces cerevisiae (NRRLY-2034). The primary target of this research was to find out the ethanol from hydrolysate of the defatted biomass of N. oculata grown mixotrophically on SBAE and CO₂ as carbon sources. For acid hydrolysis (AH), the highest carbohydrate yield 252.84 mg/g DW has been obtained with 5.0% (v/v) H₂SO₄ at 121 °C for 15 min for defatted biomass cultivated mixotrophically on sugarcane bagasse aqueous extract (SBAE) regarding 207.41 mg/g DW for defatted biomass cultivated autotrophically (control treatment). Whereas, the highest levels of reducing sugars has been obtained with 4.0% (v/v) H₂SO₄ 157.47±1.60 mg/g DW for defatted biomass cultivated mixotrophically compared with 135.30 mg/g DW for the defatted control treatment. The combination of acid hydrolysis 2.0% (v/v) H₂SO₄ followed by enzymatic treatment (AEH) increased the carbohydrate yields to 268.53 mg/g DW for defatted biomass cultivated mixotrophically on SBAE regarding 177.73 mg/g DW for the defatted control treatment. However, the highest levels of reducing sugars have been obtained with 3.0% (v/v) H₂SO₄ followed by enzyme treatment that gave 232.39±1.77 for defatted biomass cultivated mixotrophically on SBAE and 150.75 mg/g DW for the defatted control treatment. The sugar composition of the polysaccharides showed that glucose was the principal polysaccharide sugar (60.7-62.49%) of N. oculata defatted biomass. Fermentation of the hydrolysates by Saccharomyces cerevisiae for the acid pretreated defatted biomass samples gave ethanol yield of 0.86 g/L (0.062 g/g sugar consumed) for control and 1.17 g/L (0.069 g/g sugar consumed) for SBAE mixotrophic. Whereas, the maximum ethanol yield of 6.17±0.47 g/L (0.26±0.11 g/g sugar consumed) has been obtained with samples from defatted biomass grown mixotrophically (SBAE mixotrophic) pretreated with acid coupled enzyme hydrolysis.

Novel application of microalgae platform for biodesalination process: A review

Freshwater demand is rising worldwide due to largely increasing population and industrialization. Latest focus is to explore the Ocean and saline effluent from industries to produce freshwater in a sustainable way via algal desalination. Current physicochemical desalination technology is not only an energy-intensive and expensive process but also gives severe environmental impact from brine and GHGs emissions. Therefore, it is neither environmentally-friendly nor feasible to countries with limited resources. Biodesalination could be an attractive technology with recent breakthroughs in algal bioprocess with fast growth rate under highly saline conditions to effectively remove salts optimally 50-67% from saline water. Algal desalination mainly occurs through biosorption and bioaccumulation which governs by biotic and abiotic factors e.g., strain, temperature, pH, light and nutrients etc. This review provides a current scenario of this novel technology by an in-depth assessment of technological advancement, social impact, possible risks and scope for policy implications.

A Recommendation for a Pre-Standardized Marine Microalgal Dry Weight Determination Protocol for Laboratory Scale Culture Using Ammonium Formate as a Washing Agent

Simple Summary

Microalgae are increasingly recognized as a source of valuable biomass with numerous health benefits. Cleaning of marine microalgal biomass is very crucial for microalgal studies as the salt on the microalgae cells will lead to overestimation of biomass determination. Incomplete washing of salt from microalgae could also interfere with the nutritional analyses. The biomass, especially dry weight, has been utilized for nutritional or compositional evaluation. Although standard methods of marine microalgal dry weight determination are available, these methods did not provide comprehensive details, and the parameters vary among themselves. Without a standard method, a comparison of results among previous studies can be misleading and unreliable. Therefore, the current study aimed to investigate and determine the ideal setting of several parameters in the marine microalgal dry weight determination for laboratory-scale culture. The present findings could assist in developing a standardized protocol to ensure a high quality of biomass for microalgal studies.

Abstract

Microalgal biomass is one of the crucial criteria in microalgal studies. Many reported methods, even the well-established protocol on microalgal dry weight (DW) determination, vary greatly, and reliable comparative assessment amongst published results could be problematic. This study aimed to determine the best condition of critical parameters in marine microalgal DW determination for laboratory-scale culture using four different marine microalgal species. These parameters included the washing process, grades of glass microfiber filter (GMF), GMF pretreatment conditions, washing agent (ammonium formate) concentrations, culture: washing agent ratios (v:v) and washing cycles. GMF grade GF/A with precombustion at 450 °C provided the most satisfactory DW and the highest ash-free dry weight (AFDW)/DW ratio. Furthermore, 0.05 M ammonium formate with 1:2 culture: washing agent ratio and a minimum of two washing cycles appeared to be the best settings of microalgal DW determination. The present treatment increased the AFDW/DW ratio of the four respective microalgae by a minimum of 19%. The findings of this study could serve as a pivotal reference in developing a standardized protocol of marine microalgal DW determination to obtain veracious and reliable marine microalgal DW.

A critical look into different salt removal treatments for the production of high value pigments and fatty acids from marine microalgae Chlorella vulgaris (NIOT-74)

The prime challenge in seawater culture of microalgae for high value biomolecules production is presence of salt. Hence, twelve different salt removal treatments were evaluated for their impact on the lutein, total carotenoid, chlorophyll yields and fatty acid profile of marine microalgae Chlorella vulgaris (NIOT-74). The effectiveness of different treatments on salt removal was also visualized with the aid of Scanning Electron Microscope (SEM). Among the tested treatments, washing the algal biomass with 0.5 % HCl augmented the lutein (11.56 mg/g) and total carotenoid yield (60.88 mg/g) 1.82 and 1.86 fold respectively, in comparison to untreated control. Highest chlorophyll content (30.64 mg/g) was noticed in the distilled water wash treatment. Different salt removal treatments also impacted the fatty acid profile and degree of unsaturation of the fatty acids significantly. This study thus, signified the importance of salt removal treatments for the commercial production of biomolecules from marine microalgae cultured in natural seawater.

Draft Genome Sequence of the Biofuel-Relevant Microalga Desmodesmus armatus

A draft genome of 906 scaffolds of 115.8 Mb was assembled for Desmodesmus armatus, a diploid, lipid- and storage carbohydrate-accumulating microalga proven relevant for large-scale, outdoor cultivation, and serves as a model alga platform for improving photosynthetic efficiency and carbon assimilation for next-generation bioenergy production.

A draft genome of 906 scaffolds of 115.8 Mb was assembled for Desmodesmus armatus, a diploid, lipid- and storage carbohydrate-accumulating microalga proven relevant for large-scale, outdoor cultivation, and serves as a model alga platform for improving photosynthetic efficiency and carbon assimilation for next-generation bioenergy production.

Algal biorefinery models with self-sustainable closed loop approach: Trends and prospective for blue-bioeconomy

Microalgae due to its metabolic versatility have received a focal attention in the biorefinery and bioeconomy context. Microalgae products have broad and promising application potential in the domain of renewable fuels/energy, nutraceutical, pharmaceuticals and cosmetics. Biorefining of microalgal biomass in a circular loop with an aim to maximize resource recovery is being considered as one of the sustainable option that will have both economical and environmental viability. The expansive scope of microalgae cultivation with self-sustainability approach was discussed in this communication in the framework of blue-bioeconomy. Microalgae based primary products, cultivation strategies, valorization of microalgae biomass for secondary products and integrated biorefinery models for the production of multi-based products were discussed. The need and prospect of self-sustainable models in closed loop format was also elaborated.