Progress in biohythane production from microalgae-wastewater sludge co-digestion: An integrated biorefinery approach.

Recent advances in microalgae to biohythane (bio-H2 and bio-CH4) conversion have achieved growing attention due to their eco-friendly and energy-efficient nature. Although microalgae are considered a potential 3rd - 4th generation biomass, their low C/N ratio and cell-wall biopolymers are challenging for biohythane production. This study emphasizes the solutions to mitigate the adverse effects of microalgae-based biohythane production using co-digestion with wastewater sludge. Wastewater sludge, an emerging environmental concern, is reviewed to be an effective co-substrate with microalgae to establish a biorefinery approach. The future trends and prospects of this biorefinery approach is critically reviewed to attain a profitable process. This study also reviewed the advantages of microalgae-wastewater co-cultivation and the application of activated sludge for bio-flocculation as a cost-effective solution for microalgae cultivation and harvesting. Microalgae-wastewater co-cultivation is also recommended to be effective for biohythane purification. The liquid digestate is suggested to be used as a culture media to enhance microalgal growth; whereas, the solid digestate could be transformed into resources through hydrothermal processes as a solution of digestate management. A practical biorefinery approach combining the synergistic benefits of microalgae-wastewater sludge and its biological conversion to biohythane would be an adjoining link to the beginning of a sustainable future.

Enhanced methane production coupled with livestock wastewater treatment using anaerobic membrane bioreactor: Performance and membrane filtration properties.

The present study introduced a new method for enhanced biomethane production and pollution control of swine wastewater (SW) using anaerobic membrane bioreactor (AnMBR). Results confirmed 35 °C as the optimum temperature for enhanced anaerobic digestion which resulted in relatively higher methane production rate and potential. In AnMBR system, robust pollutants removal and conversion rate were achieved under various hydraulic retention time (HRT) ranging from 20 to 10 days, while the highest methane yield (0.24 L/g-CODremoved) and microbial activity (6.65 mg-COD/g-VSS·h) were recorded at HRT of 15 days. Reduction of HRT to 10 days resulted in serious membrane fouling due to accumulation of extracellularpolymericsubstances(EPS) and cake layer on the membrane. However, cake layer as the dominant membrane foulant could be effectively removed through periodic physical backwash to recover the membrane permeability. Overall, the suggested AnMBR is a promising technology to enhance SW treatment and energy recovery.

Commercial Seaweed Liquid Extract as Strawberry Biostimulants and Bioethanol Production.

Seaweeds are increasingly intriguing as a sustainable source of bioactive compounds. They have applications in agriculture, fuels, feed, and food products. To become a cost-competitive product with zero waste, a biorefinery approach is applied, where several products are valorized at the same time. True-Algae-Max (TAM®) has been investigated for its ability to improve the yield and nutritional facts of a strawberry plant. Three concentrations of TAM (0, 50, and 100%) were examined by foliar spray in 2017 with 50% NPK chemical fertilizer. Results indicated that growth, yield, chlorophyll, and potassium content were significantly improved by TAM treatments. TAM50 % resulted in maximum root length, leaf area, plant fresh weight, fruit weight, and yield with an increase ranging from 10 to 110% compared to control. Compared to the NPK control, strawberries grown with TAM50% improved total soluble solids (TSS) from 7.58 to 10.12% and anthocyanin from 23.08 to 29.42 mg CGE 100 g-1. Noteworthily, this reduced total sugar, and total phenolics were boosted by TAM applications, while non-reducing sugar was reduced compared to control. On the other hand, whole seaweed biomass and TAM residuals were used for bioethanol production by acid scarification. The maximum bioethanol yield was observed in residual biomass (0.34 g g-1 dw), while the whole seaweed biomass showed only 0.20 g g-1 dw. These results proved the biorefinery concept of using seaweed extract as a biostimulator and bioethanol production.

Life Cycle Assessment and Impact Correlation Analysis of Fly Ash Geopolymer Concrete.

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.

Integrated approach for enhanced bio-oil recovery from disposed face masks through co-hydrothermal liquefaction with Spirulina platensis grown in wastewater.

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.

Valorization of lipidic food waste for enhanced biodiesel recovery through two-step conversion: A novel microalgae-integrated approach.

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.

Potential Applications of Arthrospira platensis Lipid-Free Biomass in Bioremediation of Organic Dye from Industrial Textile Effluents and Its Influence on Marine Rotifer (Brachionus plicatilis).

Arthrospira platensis is one of the most important cultured microalgal species in the world. Arthrospira complete dry biomass (ACDB) has been reported as an interesting feedstock for many industries, including biodiesel production. The A. platensis by-product of biodiesel production (lipid-free biomass; LFB) is a source of proteins, functional molecules, and carbohydrates, and can also be reused in several applications. The current study investigated the efficiency of ACDB and LFB in bioremediation of dye (Ismate violet 2R, IV2R) from textile effluents. In addition, the potential of ACDB and LFB loaded by IV2R as a feed for Rotifer, Brachionus plicatilis, was examined. The surface of the adsorbents was characterized by SEM, FTIR, and Raman analysis to understand the adsorption mechanism. The batch sorption method was examined as a function of adsorbent dose (0.02-0.01 g L-1), solution initial concentration (10-100 mg L-1), pH (2-10), and contact time (15-180 min). The kinetic studies and adsorption isotherm models (Freundlich, Langmuir, Tempkin, and Halsey) were used to describe the interaction between dye and adsorbents. The results concluded that the adsorption process increased with increasing ACDB and LFB dose, contact time (120 min), initial IV2R concentration (10 mg L-1), and acidity pH (2 and 6, respectively). For the elimination of industrial textile wastewater, the ACDB and LFB sorbents have good elimination ability of a dye solution by 75.7% and 61.11%, respectively. The kinetic interaction between dye and adsorbents fitted well to Langmuir, Freundlish, and Halsey models for LFB, and Langmuir for ACDB at optimum conditions with R2 > 0.9. In addition, based on the bioassay study, the ACDB and LFB loaded by IV2R up to 0.02 g L-1 may be used as feed for the marine Rotifer B. plicatilis.

Enhancement of biodiesel yield and characteristics through in-situ solvo-thermal co-transesterification of wet microalgae with spent coffee grounds.

This study evaluated in-situ co-transesterification of wet spent coffee ground (SCG)/microalgae mixture for enhanced biodiesel production. SCG and microalgae showed lipid contents of 16.0 and 23.6 wt%, respectively. A total of 27 transesterification runs were performed using wet SCG:algae (1:1, w/w) at different temperatures, times, and solvent ratios. Box-Behnken quadratic model suggested 198 °C, 6 mL solvent g-1 biomass, and reaction time of 132 min as the optimum conditions for maximum biodiesel yield. At different SCG/microalgae blend ratios, pure microalgae showed the highest biodiesel yield of 20.15 wt%. Increase of SCG ratio resulted in significant reduction in the biodiesel yield, reaching the lowest value of 11.2 wt% using pure SCG. On the other hand, SCG showed better biodiesel characteristics than microalgae regarding iodine value, cetane number, and oxidation stability. The present results confirmed that SCG-algae blend results in dual effect of enhancing biodiesel yield and quality, comparing to the individual transesterification.

A novel bifunctional aldehyde/alcohol dehydrogenase catalyzing reduction of acetyl-CoA to ethanol at temperatures up to 95 °C.

Hyperthermophilic Thermotoga spp. are excellent candidates for the biosynthesis of cellulosic ethanol producing strains because they can grow optimally at 80 °C with ability to degrade and utilize cellulosic biomass. In T. neapolitana (Tne), a putative iron-containing alcohol dehydrogenase was, for the first time, revealed to be a bifunctional aldehyde/alcohol dehydrogenase (Fe-AAdh) that catalyzed both reactions from acetyl-coenzyme A (ac-CoA) to acetaldehyde (ac-ald), and from ac-ald to ethanol, while the putative aldehyde dehydrogenase (Aldh) exhibited only CoA-independent activity that oxidizes ac-ald to acetic acid. The biochemical properties of Fe-AAdh were characterized, and bioinformatics were analyzed. Fe-AAdh exhibited the highest activities for the reductions of ac-CoA and acetaldehyde at 80-85 °C, pH 7.54, and had a 1-h half-life at about 92 °C. The Fe-AAdh gene is highly conserved in Thermotoga spp., Pyrococcus furiosus and Thermococcus kodakarensis, indicating the existence of a fermentation pathway from ac-CoA to ethanol via acetaldehyde as the intermediate in hyperthermophiles.

A close-loop integrated approach for microalgae cultivation and efficient utilization of agar-free seaweed residues for enhanced biofuel recovery.

The aim of this work was to evaluate a novel integrated biorefinery route for enhanced energy recovery from seaweeds and microalgae. Agar extraction prior to anaerobic digestion recorded the highest biogas productivity of 32.57 L kg-1 VS d-1. Supplementation of the microalgal growth medium with anaerobic digestate from agar-extracted biomass enhanced the microalgal growth, recording the highest dry weight of 4.57 g L-1 at 20% digestate ratio. In addition, lipid content showed the highest value of 25.8 %dw. Due to enhancement of growth and lipid content, 20% digestate ratio showed the highest lipid productivity and FAMEs recovery (65.2 mg L-1 d-1 and 123.3 mg g-1dw, respectively), with enhanced biodiesel characteristics. The present study estimated annual revenue of 1252.7 US$ ton-1 from the whole Gracilaria multipartita biomass conversion into biogas, while that through agar extraction deserved 36087.0 US$ ton-1, with enhanced annual biodiesel yield by 69.7% over the control medium.

Screening of seaweeds for sustainable biofuel recovery through sequential biodiesel and bioethanol production.

The present study evaluated the sequential biodiesel-bioethanol production from seaweeds. A total of 22 macroalgal species were collected at different seasons and screened based on lipid and carbohydrate contents as well as biomass production. The promising species was selected, based on the relative increase in energy compounds (REEC, %), for further energy conversion. Seasonal and annual biomass yields of the studied species showed significant variations. The rhodophyte Amphiroa compressa and the chlorophyte Ulva intestinalis showed the highest annual biomass yield of 75.2 and 61.5 g m-2 year-1, respectively. However, the highest annual carbohydrate productivity (ACP) and annual lipid productivity (ALP) were recorded for Ulva fasciata and Ulva intestinalis (17.0 and 3.0 g m-2 year-1, respectively). The later was selected for further studies because it showed 14.8% higher REEC value than Ulva fasciata. Saturated fatty acids (SAFs) showed 73.4%, with palmitic acid as a dominant fatty acid (43.8%). Therefore, biodiesel showed high saturation degree, with average degree of unsaturation (ADU) of 0.508. All the measured biodiesel characteristics complied the international standards. The first route of biodiesel production (R1) from Ulva intestinalis showed biodiesel recovery of 32.3 mg g-1 dw. The hydrolysate obtained after saccharification of the whole biomass (R2) and lipid-free biomass (R3) contained 1.22 and 1.15 g L-1, respectively, reducing sugars. However, bioethanol yield from R3 was 0.081 g g-1 dw, which represented 14.1% higher than that of R2. Therefore, application of sequential biofuel production using R3 resulted in gross energy output of 3.44 GJ ton-1 dw, which was 170.9% and 82.0% higher than R1 and R2, respectively. The present study recommended the naturally-grown Ulva intestinalis as a potential feedstock for enhanced energy recovery through sequential biodiesel-bioethanol production.

Tibet plateau probiotic mitigates chromate toxicity in mice by alleviating oxidative stress in gut microbiota.

Heavy metal contamination in food endangers human health. Probiotics can protect animals and human against heavy metals, but the detoxification mechanism has not been fully clarified. Here, mice were supplemented with Pediococcus acidilactici strain BT36 isolated from Tibetan plateau yogurt, with strong antioxidant activity but no chromate reduction ability for 20 days to ensure gut colonization. Strain BT36 decreased chromate accumulation, reduced oxidative stress, and attenuated histological damage in the liver of mice. 16S rRNA and metatranscriptome sequencing analysis of fecal microbiota showed that BT36 reversed Cr(VI)-induced changes in gut microbial composition and metabolic activity. Specifically, BT36 recovered the expressions of 788 genes, including 34 inherent Cr remediation-relevant genes. Functional analysis of 10 unannotated genes regulated by BT36 suggested the existence of a new Cr(VI)-reduction gene in the gut microbiota. Thus, BT36 can modulate the gut microbiota in response to Cr(VI) induced oxidative stress and protect against Cr toxicity.

Enhancement of biodiesel yield from a halophilic green microalga isolated under extreme hypersaline conditions through stepwise salinity adaptation strategy.

In the present study, a halophilic microalgal species was isolated from a hypersaline lagoon with salinity average of 45.3‰ and identified as Dunaliella salina KSA-HS022. It was further cultivated at a salinity range of 50-250‰, applied directly to batch cultures or through stepwise increase in a semi-continuous culture. The later showed the highest biomass productivity of 0.191 g L-1 d-1 at 125‰, which represented 45.8% higher than the corresponding batch culture (control). Oxidative markers in the control cultures were significantly higher than those of the adapted culture, confirming reduction of oxidative stress by adaptation. In addition, stepwise adaptation showed the highest lipid productivity of 56.5 mg L-1 d-1 at 150‰ (39.9% higher than the corresponding control), which resulted in the highest fatty acid methyl esters productivity. Moreover, stepwise increase of salinity up to 150‰ enhanced the biodiesel characteristics, offering a new route for enhanced biodiesel production at extraordinary salinity levels.

Evaluation of animal- and plant-based lipidic waste in anaerobic digestion: kinetics of long-chain fatty acids degradation.

Recently, lipidic wastes have been reported to enhance biomethane production through anaerobic co-digestion (ACD). These lipidic wastes were of animal and plant origins. The comparison of animal and plant lipidic wastes with the microbial communities involved in lipid degradation have not been given adequate attention in pervious reviews. However, there is need to demonstrate the differences between these wastes in terms of their long-chain fatty acids (LCFAs) composition, nature, and availability. This review discusses the characterization and comparison of animal and plant lipidic wastes as co-substrates, while summarizing the potential of biomethane production in the laboratory, as well as pilot and full-scale operations. The degradation kinetics of LCFAs existing in animal and plant lipidic wastes were also highlighted during the operation process, along with the challenges (such as inhibition by LCFAs, sludge washout, sludge flotation, and foaming). Discussion on the use of the next gene sequencing (NGS) for the microbial community in the ACD of lipidic wastes was considered to understand the interspecies interactions among various microbes. The economic feasibility of lipidic wastes in the ACD along with biogas yield has also been evaluated. The use of lipids (animal and plant based) in anaerobic digestion with the application of combined pretreatment or an acclimatized microbial consortium could be a potential approach for maximum energy recovery from the waste in terms of biomethane production.

Enhancement of biogas production from rape straw using different co-pretreatment techniques and anaerobic co-digestion with cattle manure.

The present study investigated the possibility of valorizing rape straw through anaerobic digestion and the possibility of improving biomethane yield by pretreatment with H2SO4, combined H2SO4 with steam explosion (SE) and SE combined with superfine grinding (SFG). To evaluate the pretreatment method efficiency, several analytical techniques were applied. Additionally, the performance of co-digesting of cattle manure (CM) with pretreated rape straw (PRS) at different ratios was evaluated. The results showed that combined pretreatment could dissolve the lignocellulosic fiber structure, which positively stimulated methane yield. The highest cumulative CH4 yield (CMY) of 305.7 mLg-1VS was achieved by combined SE at 180 °C for 5 min with SFG, which was 77.84% higher than the untreated. The CMY was further improved by 11.4-59% higher than the control (CM) using co-digestion. This study confirmed that, under optimal parameters of AD, pretreatment with SEG180 could significantly boost the CMY from co-digestion of CM and PRS.

Reducing residual antibiotic levels in animal feces using intestinal Escherichia coli with surface-displayed erythromycin esterase.

Antibiotics are widely used in livestock and poultry industries, which results in large quantities of antibiotic residues in manure that influences subsequent treatments. In this study, an Escherichia coli strain was engineered to display erythromycin esterase on its cell surface. The engineered strain (E. coli ereA) efficiently degraded erythromycin by opening the macrocyclic 14-membered lactone ring in solution. Erythromycin (50 mg/L) was completely degraded in a solution by E. coli ereA (1 × 109 CFU/mL) within 24 h. E. coli ereA retained over 86.7 % of the initial enzyme activity after 40 days of storage at 25 °C, and 78.5 % of the initial activity after seven repeated batch reactions in solution at 25 °C. Mice were fed with E. coli ereA and real-time quantitative PCR data showed that E. coli ereA colonized in the mice large intestine. The mice group fed E. coli ereA exhibited 83.13 % decrease in erythromycin levels in their feces compared with the mice group not fed E. coli ereA. E. coli ereA eliminated antibiotics from the source preventing its release into the environment. The surface-engineered strain therefore is an effective alternative agent for treating recalcitrant antibiotics, and has the potential to be applied in livestock and poultry industries.

Influence of nutrient supplementation and starvation conditions on the biomass and lipid productivities of Micractinium reisseri grown in wastewater for biodiesel production.

Generation of biodiesel from microalgae grown in wastewater can offer a cost-effective approach, whilst wastewaters usually do not contain the optimum concentrations of the essential nutrients and carbon sources that result in lowering the productivities of biomass and lipid. This study aimed to overcome this limitation by manipulating wastewater with various concentrations of nutrients (NO3-, PO43-, Cl- and SO42-) and three carbon sources either individually or in combination to cultivate Micractinium reisseri for biodiesel production. Initially, various dilutions of wastewater were tested and a concentration up to 75% of wastewater showed the highest biomass productivity (0.076 g L-1 d-1) and lipid productivity (0.014 g L-1 d-1). The optimum manipulating conditions for maximum lipid production and the highest productivity required 50% decrease in phosphorous from the concentration of the control medium and supplementation with 1.0 g L-1 of glucose. Under this condition, biomass and lipid productivities increased by 1.7 and 4-folds, respectively, compared to those observed in the control. Furthermore, phosphorous starvation condition in the presence of glucose significantly improved fatty acid profile in the biomass and biodiesel quality related parameters.

Sonochemical assisted fabrication of 3D hierarchical porous carbon for high-performance symmetric supercapacitor.

A scalable fabrication of 3D hierarchical porous carbon structure (3D-HPC) has been achieved via a simple sonochemical route at different pyrolysis temperatures. It is worth noting that all the 3D-HPC samples possess oxygen-functional groups after activation by KOH and self-doped by nitrogen, which are beneficial to improving their surface wettability as well as increasing the electro-active surface area between the electrode and the surrounding electrolyte, consequently enhancing their electrochemical performance. Remarkably, the resulting carbon sample pyrolyzed at 850 °C (AC-850) possesses a maximum doping level of 2.75 at% and a high surface area of 1376.19 m2 g-1, which exhibits high electrochemical performance with high capacitance up to 269.19 F g-1 at a current density of 2 A g-1. Moreover remarkably, the AC-850-based symmetric supercapacitor delivers a high energy density of 21.4 Wh kg-1 at a power density of 531.2 W kg-1 with excellent rate performance and superior cycling stability (94.7% retention over 5000 cycles). The present approach is very suitable for large scale production of high-quality porous carbon materials at low cost, which can be used in different aspects, such as energy storage, gas storage, environmental remediation, and so on.

Biomass briquetting reduces the energy loss during long-term ensiling and enhances anaerobic digestion: A case study on rice straw.

The present study evaluated the impact of briquetting prior to ensiling on rice straw characteristics and anaerobic digestion performance. Ensiling for 10 months significantly reduced cellulose, hemicellulose and lignin of the uncompressed straw by 50.3%, 61.6% and 34.6%, respectively. However, increase of briquetting ratio enhanced the cellulose and hemicellulose contents at different ensiling times. In addition, increasing of ensiling time significantly reduced the biogas yield, while the highest cumulative biogas yield of 313.8 L kg-1 VS was obtained from rice straw ensiled for 7 days at 1:6 briquetting ratio. Interestingly, the maximum biogas productivity of 1:6 briquetted straw after 10 months ensiling was 17.7% higher than that of the uncompressed straw ensiled for 7 days. Thus, briquetting prior to ensiling is a favorable approach to reduce the mass loss for enhanced biogas yield and energy recovery.