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Graphical abstract Currently, the enormous generation of contaminated disposed face masks raises many environmental concerns. The present study provides a novel route for efficient crude bio-oil production from disposed masks through co-hydrothermal liquefaction (Co-HTL) with Spirulina platensis grown in wastewater. Ultimate and proximate analysis confirmed that S. platensis contains relatively high nitrogen content (9.13%dw), which decreased by increasing the mask blend ratio. However, carbon and hydrogen contents were higher in masks (83.84 and 13.77%dw, respectively). In addition, masks showed 29.6% higher volatiles than S. platensis, which resulted in 94.2% lower ash content. Thermal decomposition of masks started at a higher temperature (≈330 °C) comparing to S. platensis (≈208 °C). The highest bio-oil yield was recorded by HTL of S. platensis and Co-HTL with 25% (w/w) masks at 300 °C, which showed insignificant differences with each other. GC/MS analysis of the bio-oil produced from HTL of algal biomass showed a high proportion of nitrogen- and oxygen-containing compounds (3.6% and 11.9%, respectively), with relatively low hydrocarbons (17.4%). Mask blend ratio at 25% reduced the nitrogen-containing compounds by 55.6% and enhanced the hydrocarbons by 43.7%. Moreover, blending of masks with S. platensis enhanced the compounds within the diesel range in favor of gasoline and heavy oil. Overall, the present study provides an innovative route for enhanced bio-oil production through mask recycling coupled with wastewater treatment. Supplementary Information The online version contains supplementary material available at 10.1007/s13399-021-01891-2.

Heavy metal contamination in aquatic environments has been a hot topic in the past decades. The current study aims to analyze levels of heavy metals and human health risk implications associated with fish consumption from the Yangtze River. Muscles of 60 fish samples which comprised six different fish species: Hypophthalmichthys molitrix , Ctenopharyngodon idellus , Blicca bjoerkna , Mylopharyngodon piceus , Carassius carassius, and Pelteobagrus fulvidraco ; were analyzed for total lead (Pb), cadmium (Cd), zinc (Zn), aluminium (Al) cobalt (Co), magnesium (Mg), chromium (Cr), and copper (Cu). The health risk indicators associated with consumers’ health were estimated for both children and adults. The finding of the study revealed that of the analyzed metals, Zn recorded the highest mean concentration of 9.87 µg/g in Carassius carassius followed by Mn (7.97 µg/g) in Pelteobagrus fulvidraco , Cu (2.07 µg/g) in Mylopharyngodon piceus , Pb (1.04 µg/g) in Hypophthalmichthys molitrix , Cr (0.63 µg/g) in Hypophthalmichthys molitrix , Cd (0.19 µg/g) in Blicca bjoerkna and Ni (0.16 µg/g) in Pelteobagrus fulvidraco all measured in wet weight ( w/w ). In addition, the health risk assessments revealed that children are at heightened non-carcinogenic risk for Pb, Cd, and Co upon consuming the examined fish species. The principal component analysis revealed that the pollution of metals in the Yangtze River originates mainly from anthropogenic activities and could deteriorate the quality of fish in the Yangtze River. Therefore, this study could contribute scientific information to help in proper monitoring and regulations to protect the natural resources and human health along the Yangtze River.

The dilute sulfuric acid hydrolysis was employed to optimize saccharification of the green seaweed Valoniopsis pachynema by response surface methodology (RSM) and the retrieved hydrolysates were characterized. The RSM quantitative evaluation of total sugar recovery on acid hydrolysates indicated that 3% dilute sulfuric acid was sufficient to retrieve optimum level of saccharification with 2.15 h incubation time at 60 °C. Fourier-transform infrared spectroscopy (FTIR) and Scanning Electron Microscopy (SEM) with Energy Dispersive X-Ray Analysis (EDAX) images of seaweed evidenced that seaweed surface polysaccharides were hydrolyzed by 3% dilute sulfuric acid, further this treatment showed improved polymer dissolution when compared to other concentrations. The acid treated seaweed pellets indicated effective colonization and encouraged growth in adhesion analysis of microalgae C. vulgaris MSU-AGM 14. By combining with algae culture medium and at different concentrations of acid hydrolysate showed higher biomass (0.111 ± 0.001 g L−1 d−1) and lipid productivity (18.18 ± 0.19 mg L−1 d−1) and improved elemental contents in mixotrophic condition. These results evidenced that mixotrophic cultivation enhances microalgae growth and lipid productivity by presence of extracellular polysaccharide and leads to initial colonization and prolonged period of growth. The overall results expressed that dilute 3% sulfuric acid hydrolysis retrieved high amount of total sugar content (38.5 ± 0.2 mg g−1) from green seaweed V. pachynema and promotes microalgae biomass and lipid productivity significantly.

In the present study, biomass and lipid production of the biodiesel promising green microalga Tetradesmus obliquus BPL16 were studied by application of p-coumaric acid as a suggested novel growth regulator found predominantly in phenolics-rich streams. It was used in its pure form along with two phytohormones (jasmonic acid and salicylic acid). Using 100 μM jasmonic acid, 10 μM salicylic acid and 1 mM p-coumaric acid improved biomass production by 85.4%, 54.9% and 34.1%, respectively, over the control. In addition, significant increments in lipid content by 22%, 105.6%, and 145.4%, respectively, over the control were obtained at the aformentioned concentrations. Neutral lipids were significantly improved under elicitor-supplemented conditions. Moreover, fatty acid methyl esters (FAMEs) profile was also vitally influenced with drastic increase in oleic acid (C18:1) proportion by 81.7% and 73.6% over the control at 10 μM of jasmonic acid and 1 mM of p-coumaric acid, respectively. Application of p-coumaric acid resulted in estimated biodiesel energy output of 10.8 MJ kg−1 which represented 141% and 9.4% higher than the control and jasmonic acid, respectively. In conclusion, the present study suggested p-coumaric acid as a novel growth regulator for instant synchronized growth and lipid accumulation in microalgae for enhanced biodiesel production.

Catalytic co-pyrolysis of seaweed Enteromorpha clathrata (EN) and cellulose (CEL) with catalysts ZSM-5 and MCM-41 was investigated by TG, Py–GC/MS and fixed-bed experiments. The effects of temperature, catalysts, seaweed and cellulose ratio were examined on product yields distribution and bio-oil compositions by catalytic co-pyrolysis. The maximum bio-oil yield was recorded at the ratio of 1:1 (EN and CEL) with ZSM-5/MCM-41 at 500 °C on co-pyrolytic process. The interaction of radicals and faster heat transfer rate of EN/CEL induces the synergistic effects with catalysts. The advantage of mesoporous molecular sieve along with acidic microporous zeolite of ZSM-5/MCM-41 improved the cracking, dehydration, decarbonylation, decarboxylation, dealkylation, aromatization, oligomerization and deamination reactions. The overall study revealed that the amount of N-containing compounds were decreased and significantly elevated bio-oil production with increased furans and aromatics.

Geopolymer concrete (GPC) has drawn widespread attention as a universally accepted ideal green material to improve environmental conditions in recent years. The present study systematically quantifies and compares the environmental impact of fly ash GPC and ordinary Portland cement (OPC) concrete under different strength grades by conducting life cycle assessment (LCA). The alkali activator solution to fly ash ratio (S/F), sodium hydroxide concentration (CNaOH), and sodium silicate to sodium hydroxide ratio (SS/SH) were further used as three key parameters to consider their sensitivity to strength and CO2 emissions. The correlation and influence rules were analyzed by Multivariate Analysis of Variance (MANOVA) and Gray Relational Analysis (GRA). The results indicated that the CO2 emission of GPC can be reduced by 62.73%, and the correlation between CO2 emission and compressive strength is not significant for GPC. The degree of influence of the three factors on the compressive strength is CNaOH (66.5%) > SS/SH (20.7%) > S/F (9%) and on CO2 emissions is S/F (87.2%) > SS/SH (10.3%) > CNaOH (2.4%). Fly ash GPC effectively controls the environmental deterioration without compromising its compressive strength; in fact, it even in favor.

Microalgae has been known as one of the efficient biological carbon dioxide (CO2) sequesters. In recent years, they have been applied to improve the air quality by reducing CO2 concentration and boosting oxygen (O2) level, and have the ability to tolerate diverse toxic elements in the air. The current study investigates the effect of tobacco smoke on the growth, biochemical, and biodiesel characteristics of two Chlamydomonas strains. For this purpose, strains were exposed to seven days of tobacco smoke by burning one cigarette per hour in a closed box containing the air supply. CHL-2220 continued its proliferation without demonstrating any inhibition, while the growth of the other strain (CHL-2221) was inhibited severely. Tobacco smoke significantly altered the biochemical composition of CHL-2221, and caused the accumulation of more carotenoids and carbohydrates as part of the stress response. The analyzed biodiesel parameters presented poor quality from the extracted lipid of both strains. However, the fatty acid profile of the studied strain demonstrated their promising application as nutrient food supplements and feed for animals.

The present study designed an innovative route for two-step biodiesel recovery from lipidic food waste followed by microalgae cultivation. Optimization of oil conversion showed the highest fatty acid methyl esters (FAMEs) recovery of 92.6% (lipid basis). Microalgal lipid accumulation enhanced by the increased lipid-free waste hydrolysate ratio in the medium, where the maximum lipid content of 26.2 dw% was recorded using 50% hydrolysate. Application of 30% hydrolysate ratio resulted in the maximum recorded lipid productivity, which was 99.4% higher than that of the control and insignificant with 40% hydrolysate. Waste oil-derived FAMEs showed 69.0% higher saturated fatty acids (SFAs) proportion than that of algal lipids. In contrast, the highest polyunsaturated fatty acids (PUFAs) proportion (48.8% of total fatty acids) was recorded in microalgal lipids. The study concluded that mixing microalgal lipids with waste oil (1:1, w/w) provides a desirable practical route for enhanced biodiesel production complying with the international standards.

Application of antimicrobial botanical extracts and other natural products is receiving increasing attention. The present study aimed to evaluate the antifungal activities of some macroalgae collected from Alexandria beach, Egypt for treatment of fungal urinary tract infections (UTIs). Methanol extracts of Ulva lactuca showed the highest recorded antifungal activity against Aspergillus flavus and Aspergillus niger, while Enteromorpha linza showed the highest antifungal activity against Candida tropicalis. In addition, methanol extracts of both macroalgae showed a significant urease inhibition of the corresponding fungi. Lineweaver–Burk plots indicated a reversible non-competitive mechanism for U. lactuca extract, whereas E. linza extract showed a reversible competitive inhibition. Fatty acids profile of methanol extracts of U. lactuca and E. linza showed predominance of octadecanoic acid and hexadecanoic acid (48.4% and 62.9% of total fatty acids, respectively). In addition, GC/MS results showed significant proportions of the biologically active compounds; benzodioxoles such as piperonylbutoxide, organochlorines such as p,p’-dichlorodiphenyltrichloroethane (DDT) in U. lactuca and phytosterols such as stigmastan derivatives in E. linza. The present study represents an advancement in the knowledge of the chemistry and antifungal potential of macroalgae against UTIs and offers promising trend for drug discovery from marine macroalgae.

The present study aimed to optimize the culture conditions for algal growth and lipid production of Desmodesmus intermedius. Different environmental factors including nitrogen content, salinity, ki...

In the present study, the effect of trace metal nutrients on biomass and lipid productivity of Scenedesmus obliquus cultured in municipal wastewater was evaluated. Lipid productivity of S. obliquus significantly increased by 18.63%, 19.21%, and 27.95% by adding trace metals of Mo, Mn, and Fe, respectively, with the highest lipid productivity of 24.69 mg/(L·d) in case of Fe (3.00 mg/L FeSO4·7H2O). GC analysis of the lipids showed that the control (WW) and ferrous sulfate–treated cultures had very similar compositions, and both of them contained considerable proportions C16-18, showing their suitability for biodiesel production. Moreover, using FeSO4·7H2O enhanced the removal rates of total phosphorus, ammonia nitrogen, and total nitrogen in municipal wastewater, which attained 94.7%, 99.2%, and 95.8%, respectively.

The present work investigated the potential of acidogenesis digestate rich in volatile fatty acids (Bio-DAcid) and methanogenesis digestate rich in ammonia (Bio-DMeth) as a green method for the pretreatment of rice straw and biomethane production. After pretreatment with Bio-DMeth for 48 h, a maximum hemicellulose reduction of 22.4% was recorded, while 48 h of Bio-DAcid showed the lowest reduction of 15.7%. In addition, pretreatment for 48 h with Bio-DMeth and Bio-DAcid showed significant removal of lignin by 16.6 and 11.0%, respectively. SEM and FTIR confirmed major increase in straw porosity and degradation after all applied pretreatments. The highest significant biomethane content of 71.2% was recorded in 24 h Bio-DAcid-pretreated straw. However, the highest significant yield of 249.1 L kg−1 VS was recorded from the 48 h Bio-DMeth-pretreated straw, which was 9.8, 19.6, and 27.0% higher than 24 h Bio-DMeth-, 24 h Bio-DAcid and 48 h Bio-DMeth-treated straw, respectively. Importantly, pretreatment with Bio-DMeth for 24 h showed the highest estimated net bioenergy output of 7.37 GJ ton−1 dry straw, which represented 28.6 and 0.13% increase over that of the control and 48 h Bio-DMeth-pretreated straw, respectively. The present study suggested application of Bio-DMeth for 24 h as an efficient eco-friendly pretreatment method for efficient AD of rice straw.

The strategic microalgal lipid production without growth reduction is the desideratum for sustainable microalgal biodiesel production. The present study investigated the effect of polysorbates (polysorbate 20, polysorbate 40, polysorbate 60 & polysorbate 80) supplementation on growth, biomass and lipid production of microalga Tetradesmus obliquus BPL16. T. obliquus BPL16 at controlled condition showed 12.5% dry cell weight (DCW) of lipid content and 0.8 g L−1 of biomass production. Each of the four tested polysorbates at various concentrations magnificently influenced the green microalga with a maximum lipid production of 47.1% DCW and 46.5% DCW achieved at 0.15% of polysorbate 80 and 0.1% of polysorbate 60 supplementations respectively. The maximum biomass (2.6 g L−1) production was achieved at 0.15% of polysorbate 40 and polysorbate 60 supplementation respectively. In addition, neutral lipids and vital fatty acids proportion increased at high lipid productive conditions enabled by polysorbate supplementation.

Nowadays, macroalgae are widely discussed as advantageous alternative feedstock for crude bio-oil production using pyrolysis. In the present work, pyrolysis products of Enteromorpha clathrata washed with 7% phosphoric acid, hydrochloric acid and sulfuric acid were studied. In general, washing with diluted acids resulted in significant increase in the yields of bio-oil and non-condensable gas over the control in favor of the bio-char. In addition, HCl pretreatment enhanced the relative contents of aliphatic hydrocarbons in the bio-oil by 1.5 times over the control. Furthermore, HCl pretreatment showed 37% and 52.6% reduction in acids and oxygen-containing compounds, respectively, with respect to the control. FTIR analysis showed that acid-washing led to reduction in O H stretching vibration, confirming that it can disrupt hydroxyl bonds reducing phenols, carboxylic acids and water impurities in the bio-oil. In conclusion, washing of biomass using diluted acids could play a key role to enhance the bio-oil yield and significantly influence products characteristics; particularly, HCl enhanced bio-oil yield with higher aliphatic hydrocarbons proportion.

Torrefaction is a promising pretreatment technology for biomass and its pyrolysis products upgrading. The aim of this study was to investigate the effect of torrefaction on the pyrolysis of seaweed biomass. TG, Py-GC/MS and fixed-bed experiments were used at a series of typical torrefaction temperatures (225 °C, 250 °C, 275 °C and 300 °C) and pyrolysis temperatures (450 °C, 500 °C, and 550 °C). The results showed that increasing of torrefaction temperature led to gradual reduction in moisture content and volatile content due to the precipitation of water and volatile functional groups (OH, NH, CO, C=O, etc.), which resulted in increase of solid products of torrefied seaweed. In addition, the liquid yield showed a promotion at first and then decreased. It also indicated that thermal stability of seaweed became stronger after the pretreatment leading to the initial pyrolysis temperature shifting toward the high temperature section. Meanwhile, the maximum pyrolysis weight loss rate and the total weight loss got a reduction. Moreover, the optimal conditions for maximum bio-oil production were obtained when the temperature of torrefaction was 250 °C at the pyrolysis temperature of 500 °C. Furthermore, the bio-oil under such conditions gave the highest relative content of aromatic hydrocarbons.

The present study aimed to investigate synergistic effects on properties of bio-oil/bio-char and transferring regularity of chlorine during co-pyrolysis of macroalgae Enteromorpha clathrata (EN) mixed with different mass percentage of polyvinyl chloride (PVC) (5 wt%, 10 wt%, 15 wt%, 20 wt%, and 25 wt%) in a fixed bed reactor at 550 °C. The results showed that the experimental values of bio-oils were 0.43–2.57 wt% lower than the calculated values, while the bio-chars were 1.28–4.93 wt% higher. From the GC–MS analysis of bio-oils, the relative contents of oxygenated and nitrogenated compounds were reduced significantly while those of phenols, aromatic and aliphatic compounds were increased dramatically during co-pyrolysis of EN and PVC. Interaction during co-pyrolysis of EN and PVC decreased the H/C atomic ratio of bio-chars, enhancing the aromatic degree. In addition, the chlorine distribution in bio-chars increased whereas decreased in bio-oils and non-condensable gas with the addition content of PVC increasing. The results showed that a majority of chlorine from EN-PVC blends was trapped in bio-char products, which was favorable to the utilization of bio-oils and friendly to pyrolysis equipment and environment.

Co-pyrolysis of Enteromorpha prolifera (EP) (seaweeds) with waste plastics (high density polyethylene (HDPE)) for maximum yield of enhanced biofuels has been investigated. Main and interaction effe...

The present work aimed to explore the optimized conditions of hydrothermal co-liquefaction (co-HTL) of the green seaweed “Enteromorpha clathrata (EN)” and the lignocellulosic agricultural waste “rice husk (RH)”. Separate hydrothermal liquefaction (HTL) of EN and RH showed bio-oil yields of 26.0% and 45.6%, respectively. However, co-HTL under optimized conditions showed significant increase in the bio-oil yield by 71.7% over that of EN, and insignificant difference with that of RH. Nevertheless, the conversion ratio of co-HTL showed 10.6% significant increase over that of RH. GC-MS results showed that main compounds of EN and RH bio-oil lump into the C15–C20 and C5–C12 regions, mainly representing carbon range of diesel and gasoline, respectively. Short-chain (C5–C12) and long-chain (C14–C20) compounds in the bio-oil obtained by co-HTL represented 72% and 28%, respectively. In addition, the ratio of aromatic compounds in the bio-oil of RH was reduced by 9.3% as a result of co-HTL. In conclusion, results suggested 50% ethanol as a co-solvent, 300 °C and 45 min as optimum conditions for co-HTL of EN:RH (1:1 w/w). The present study demonstrated an efficient route for co-HTL of 3rd generation feedstocks with 2nd generation feedstocks which will have a significant impact on large-scale applications.

Lipid extraction is a key step of biodiesel production from microalgae, however, the application of traditional extraction methods was limited due to the difficulties of cell disruption as well as solvent toxicity. In this work, pretreatment method using pulsed electric field (PEF), was primarily applied to lipid extraction process from microalgae Chlorella pyrenoidosa grown in wastewater. After the pretreatment with PEF, the yields of fatty acid methyl esters from C.pyrenoidosa was 12.0% higher than traditional pretreatment with ultrasonic. The results indicated that PEF was an effective method for cell disruption. Fluorescence staining and scanning electron microscopy showed that the integrity of the cell membrane of microalgae was damaged under pulsed electric field, which enhanced the penetration of solvents and lipid extraction.

This study investigates the characteristics of pyrolysis char/coke and elemental morphological changes on surface of char/coke produced, during co-pyrolysis of seaweed (EN) and rice husk (HU) at various temperatures through XPS, FTIR and SEM analysis methods. Analysis of pyrolysis products including by-products will help to partly explore co-pyrolysis synergistic mechanisms of the seaweed and rice husk. Thus, fast pyrolysis of EN and HU was conducted in a fixed bed reactor. Coke/char from the individual pyrolysis of EN and HU respectively at different temperatures, and those from co-pyrolysis of EN and HU (1:1) at 550 °C, were analyzed. Results revealed that the co-pyrolysis process has synergistic effects. Moreover, the release of nitrogenous substances was found to be inhibited by addition of HU at low temperature ( O functional groups at the middle temperature range, but also contributes to the cleavage of ether bonds of some water-soluble polysaccharides at high temperature (320–550 °C) level, hence generating aromatic compounds. Besides, the analysis of pore structures, pore size distributions and fractal dimensions of pyrolysis char/coke also show that the co-pyrolysis process has a synergistic effect.

Screening of native microalgal species for different biotechnological applications is a key step to achieve a strong algal database with successful commercial applications. In the present study, a new strain namely Nannochloropsis oceanica NIOF15/001 was isolated and identified phylogenetically using rbcL and the newly designed Cyt-c as an alternative molecular marker. The late exponential phase of the isolate was recorded at the 10th day of growth in f/2 medium, with a maximum cellular dry weight (CDW) of 0.722 g L−1 and relatively high lipid content of 37.7% of CDW. The isolate showed biomass and lipid productivities of 75.6 and 28.6 mg L−1 day−1, respectively. The recorded biomass productivity in the current study was 1.4, 3.0, 3.6 and 2.0 times higher than that recorded in the previous studies for N. oceanica IMET, N. oceanica CASACC201, N. oceanica DUT01 and N. oceanica CCNM 1081, respectively. In general, values of cetane number (52.3), iodine value (94.7 g I2/100 g oil), cold filter plugging point (4.7 °C) and kinematic viscosity (3.97 mm2 s−1) of the produced fatty acid methyl esters complied with those recommended by international standards. Furthermore, application of 0.1 g L−1 of lipid-free dry biomass enhanced Artemia survival by 500% and growth by 40%. The present study suggested the new isolate N. oceanica NIOF15/001 as a promising marine microalga for dual use in aquaculture and biodiesel production.

Nowadays, microalgae are widely discussed as a promising feedstock for biodiesel production due to the legitimate concerns about the consequences of using edible oils. Selection of the most suitable microalgal species relies on several key parameters such as growth rate, lipid productivity and fatty acid profile. In the present study, different species of Scenedesmus were isolated and compared for their efficiency as biodiesel feedstocks. S. obliquus showed the highest biomass productivity of 0.102 g CDW L−1 d−1 at stationary phase. However, S. intermedius showed the highest significant lipid content of 400.9 mg g−1 CDW. Regarding lipid productivity, S. obliquus was the most lipid productive strain at stationary phase with up to 24.94 mg L−1 d−1, representing 23.9% significant increase over that of S. intermedius. In addition, cetane number and iodine value of S. obliquus FAMEs were 54.12 and 110.37 g I2/100 g, respectively. Moreover, FAMEs of S. obliquus showed kinematic viscosity and specific gravity of 1.9–6.0 mm2 s−1 and 0.88 g cm−3, respectively, which are in accordance with the international standards. Among the different studied species of Scenedesmus, the present study nominated S. obliquus as a promising renewable feedstock for biodiesel production.