Evolution of membrane fouling and cleaning strategy development in municipal wastewater reclamation by nanofiltration.

Membrane fouling is a serious concern in municipal wastewater treatment using nanofiltration (NF). The variation of NF membrane fouling at different operational durations were monitored and evaluated to understand the evolution of fouling mechanism in the present study. Six representative cleaning methods were picked for tests to deconstruct the structure and composition of the fouling layers on membrane surface. Characteristics of membrane surface morphology and foulants were analysed using advanced methods to investigate the evolution of membrane fouling. Both the composition and concentration of foulants on membrane surface showed significant variations with time during the whole operational duration, indicating the necessity of clear and precise understanding for the evolution of membrane fouling to expound its mechanism in depth. The fouling layers were mainly composed of hydrophobic organics while most inorganic salts were deposited on the surface or embedded into the upper layer of the cake in a short duration. However, after a long duration, the cake layer became thinner with much higher proportion of hydrophilic organics. Meanwhile, more inorganic foulants penetrated deep into the cake layer or even directly absorbed on the membrane surface, which resulted in more complicated fouling scenarios. Moreover, more efficient and effective targeted cleaning strategies could be further established based on the fouling mechanism identified.

Interaction of Chlorella vulgaris and bacteria when co-cultivated in anaerobically digested swine manure.

Mono-culture and co-culture of algae (Chlorella vulgaris) and bacteria (activated sludge) on anaerobically digested swine manure (ADSM) were investigated in this research. The results showed that during the co-cultivation biomass growth was promoted (2.43 ± 0.11 g/L) compared with the algae-only culture (1.09 ± 0.03 g/L), and the aerobic bacteria growth was initially promoted, then inhibited. The SEM (Scanning Electron Microscope) observation indicated that the amount of the C. vulgaris increased while bacteria 'disappeared' over time. After 30 min settlement, 95.5% of the biomass in co-cultivation group precipitated, while only 40.4% of the biomass settled for the algae-only group was. It is believed that the presence of bacteria enhanced the settling rate through the formation of algal consortium flocs. Bacterial community diversity and composition were measured and the results indicated that the bacterial diversity dropped and the bacterial active classes changed in the co-cultivation group.

The immune-enhancing potential of peptide fractions from fermented Spirulina platensis by mixed probiotics.

Mixed fermentation with different microorganisms can facilitate fermentation metabolism and increase the low molecular metabolites accumulation, thereby enhancing the bioactive activity. In this study, we evaluated the immune-stimulating activities of Spirulina platensis and different extracts from fermented S. platensis (FS) by mixed probiotics in vitro, by measuring the proliferation and Th1/Th2 immunomodulatory potential on murine primary splenic lymphocytes. The results showed that mixed fermentation enhanced the immunomodulatory activity of S. platensis with higher lymphocyte proliferation compared with non-fermented S. platensis (NFS). Notably, the low molecular weight (<3 kDa) peptide fraction from fermented S. platensis (L-PFS), especially at 40 µg/ml, presented the strongest activity in promoting lymphocytes proliferation and modulating cytokines (IL-2 and IL-10) secretion. Meanwhile, L-PFS enhanced the relative mRNA expression of Th1 cytokine (IFN-γ) and Th2 cytokine (IL-4), along with inhibiting the relative mRNA expression of Th1 cytokines (IL-2 and TNF-α) and Th2 cytokine (IL-10) compared with Concanavalin A-treated lymphocytes. PRACTICAL APPLICATIONS: Fermentation with mixed probiotics could effectively improve the bioactive activity of S. platensis. In particular, L-PFS screened from the FS could significantly contribute to the immune-enhancing activity of lymphocytes, promote the Th1/Th2 balance, and provide insights for the investigation of FS as the potential immunomodulatory food products.

Characterization, bioavailability and protective effects of phenolic-rich extracts from almond hulls against pro-oxidant induced toxicity in Caco-2 cells.

Almond hulls, the main by-product of almond production, are considered a valuable source of bioactive phenolic compounds. This study aimed to characterize the phenolic composition, bioavailability of the phenolic-rich extracts from almond hulls (PEAH), and their protective effect on oxidative stressed Caco-2 cells induced by tert-butylhydroperoxide (t-BOOH). The ultra-performance liquid chromatography-tandem mass spectrometry (UPLC-MS) analysis detected 11 phenolic compounds in the PEAH with high total phenolic content and antioxidant activity. Oxidative Caco-2 cell damage was reduced by PEAH, especially at 5 µg/mL, through scavenging reactive oxygen species (ROS), modulating the cellular endogenous antioxidant system and cell redox at a predictable status. Also, in vitro digestion influenced the phenolic compounds' composition and antioxidant power of PEAH. These results suggested that almond hulls, rich in phenolic compounds, can meliorate the oxidative stressed Caco-2 cells and restore its impaired redox balance, and ultimately improve health benefits.

Tribonema sp. and Chlorella zofingiensis co-culture to treat swine wastewater diluted with fishery wastewater to facilitate harvest.

Cultivating microalgae on wastewaters is an effective way to produce algal biomass whereas harvesting microalgae is a costly operation. This study we examined the feasibility of co-culturing a high-value microalga with an auto-flocculating strain to enable efficient recovery of biomass. Experiments were conducted to co-cultivate Chlorella zofingiensis with Tribonema sp. on swine wastewater diluted by fishery wastewater under different conditions. The result showed the optimal inoculum ratio of Tribonema sp. to Chlorella zofingiensis was 1:1. The removal efficiencies of pollutants (NH4+-N, TN, TP, and COD) and lipid content were high when the co-culture ratios of Tribonema sp. were high. Also, some larger chain fatty acids, specifically C20:5 and C22:6 were present when the two strains co-culture. The recovery efficiency increased with the increasing proportion of auto-flocculating Tribonema sp.. Algae co-culture has the potential to address limitations in substrate utilization by individual strains, also improve the recovery of biomass.

Cobalt enrichment enhances the tolerance of Botryococcus braunii to high concentration of CO2.

This work mainly studied B. braunii adapted to different CO2 concentrations with cobalt enrichment, and developed a process for CO2 capture, hydrocarbon production and cobalt removal. The results showed that B. braunii favored rapid growth at 5.0% (v/v) CO2, and the highest biomass was 1.89 g.L-1 with 4.5 mg.L-1 of cobalt. Hydrocarbon productivity in high concentration CO2 (5.0% and 10.0%) with cobalt enrichment was higher than that in Chu 13 medium. The change in cobalt removal efficiency mainly corresponded to the growth of B. braunii. The LCE of B. braunii in cobalt-rich with high CO2 concentration (5.0% and 10.0%) was 15.7%, and 14.9%, respectively, which was higher than that in normal medium. CO2 fixation rates were also higher in cobalt enrichment coupled with high CO2 concentration. This study not only provides ideas for the removal of toxic metal cobalt, but also has great potential for CO2 biofixation.

A novel algal biofilm photobioreactor for efficient hog manure wastewater utilization and treatment.

This study developed a high-efficiency algal biofilm photobioreactor for microalgae by designing a special array of curtain membrane components. This paper also discusses the growth and nutrient composition of Chlorella vulgaris, and hog manure wastewater utilization and purification. It was found that after about 5 days of culture, the biomass of C. vulgaris on the membrane could reach as high as 7.37 g/m2 and the algae were easily harvested by mechanical scraping. The lipid content of C. vulgaris on the membrane structure was 10.17% while the lipid content of the algae in suspension was 14.29%. The light intensity showed a significant effect on the fatty acid composition. The C. vulgaris grew very well, and achieved deep purification of the hog manure wastewater; the COD, TP, TN, and NH4+-N removal rates reached 95.67%, 64.40%, 69.55%, and 91.24%, respectively.

Microalgae-based wastewater treatment for nutrients recovery: A review.

The water resource crisis and concerns with environmental pollution are pushing for upgrading of conventional wastewater treatment process. Microalgae-based wastewater treatment process has shown many advantages that can meet the new demand for improved wastewater treatment. However, considering the issues related to the complexity of wastewater characteristics and adaptability of microalgae species, and the challenges to the design and optimization of treatment processes in order to achieve higher removal efficiencies with lower costs, further exploration and research are still needed. This review provides an overview of microalgae strains commonly used for wastewater treatment, physical and chemical properties of various wastewaters and their suitability for algae cultivation, factors affecting algae growth, nutrient assimilation/removal and biomass productivity. The design and operation of microalgae-based wastewater treatment processes are also discussed. Moreover, the issues and limitations of microalgae-based wastewater treatment are also discussed and suggestions are proposed for the further research and development.

High-value chemicals from Botryococcus braunii and their current applications - A review.

Botryococcus braunii is known for its high yield of extracellular hydrocarbons and polysaccharides. Hydrocarbons, especially botryococcenes and squalene can be used as not only fuels but also alternative feedstock for other fossil-based products. Exopolysaccharides excreted from B. braunii can be used as scaffolds for polyesters production, and have a notable potential for synthesis of nanoparticles. B. braunii is also a rich source of carotenoids, especially the unique secondary carotenoids such as botryoxanthins that have never been found in other microalgae. The morphology, physiology, and outer cell walls of B. braunii are complex. Understanding the colony structure shall provide insights into the mechanism of cell growth and chemicals secretion. It is possible to improve the production economics of the alga with advanced culture systems. Moreover, investigation of metabolic pathways for B. braunii may help us understand their regulation and provide valuable information for strain selection and optimal production of high-value chemicals.

Exogenic glucose as an electron donor for algal hydrogenases to promote hydrogen photoproduction by Chlorella pyrenoidosa.

In this work, glucose addition (0.7 g l-1) almost doubled hydrogen yield of Chlorella pyrenoidosa (121.1 ml l-1 vs 65.5 ml l-1), with a positive correlation between hydrogen production and glucose consumption (-0.977, P < 0.01). When the electrons transport from water photolysis to algal hydrogenase was inhibited, the hydrogen productivity declined by 21.1%; whereas it dramatically decreased by 70.9% when the algal nicotinamide adeninedinucleotide dehydrogenase (NADH) was inhibited. Therefore, in the presence of glucose, the electrons for algae based hydrogen production would be mainly from glucose glycolysis rather than water photolysis. Further deuterated-glucose trial indicated that the glucose might serve as an electron donor for algal hydrogenases. Finally, a tentative electron transport route from glucose to algal hydrogenase was proposed, hoping to provide more scientific direction for further algae-based hydrogen production improvement.

Sustainable Non-Thermal Plasma-Assisted Nitrogen Fixation-Synergistic Catalysis.

In this Minireview, the multiple chemical synergies present in catalytic non-thermal plasma-assisted nitrogen fixation (NTPNF) are uncovered through a critical exploration of the underlying mechanisms, during which the catalyst, plasma, and reactants play different roles. For the gas-phase NTPNF, the synergies consist of different aspects of the catalytic pathways such as electron-impact dissociation; Zeldovich mechanism in the PNO interactions; and Eley-Rideal, Langmuir-Hinshelwood, surface adsorption, and diffusion mechanisms for the plasma-catalyst interactions. The synergies within the gas-liquid NTPNF involve contributions of plasma and UV excitation to the gas-phase reactions and the UV excitation of molecules at the liquid-surface interface, which improves synthesis of aqueous nitrate, nitrite, and ammonium products. Based on the various synergistic mechanisms during NTPNF, future potential applications are proposed for how NTPNF could benefit the sustainable nitrogen fixation industry.

Cultivation of Chlorella vulgaris in sludge extracts: Nutrient removal and algal utilization.

In order to utilize the excess sludge and reduce the cost of algal cultivation, Chlorella vulgaris was cultivated in increasing proportions of sludge extracts for simultaneous nutrients removal and algal utilization. Results showed that C. vulgaris cultivated in the 100% sludge extract gained the highest total biomass (33.98 ±â€¯0.30 × 106 cells/mL) and showed good results in TOC (absolute value 175 mg/L) and nutrients (TN: 77.1%; TP: 95.0%) removals. According to the Excitation-emission matrix spectra (EEMs) analysis, the 8th day was suggested as the optimal time for biomass harvesting. Although the lipid contents showed a negative correlation with the proportion of sludge extract, the FAME analysis showed that the saturated fatty acids (SFA) contents decreased and the unsaturated fatty acids (UFA) content increased as the concentration of sludge extract increased. The 100% sludge extract could be a desirable alternative medium for the algae cultivation.

Intermittent-vacuum assisted thermophilic co-digestion of corn stover and liquid swine manure: Salinity inhibition.

In this study, the effects of Intermittent-Vacuum Stripping (IVS) on activities of methanogenesis in co-digestion of corn stover with liquid swine manure (LSM + CS) under thermophilic anaerobic digestion (TAD) conditions were evaluated. A 65% methanogenesis activity inhibition was observed in pretreated LSM plus corn stover (pLSM + CS), while 60 and 165 mL/L/day CH4 productions were achieved in pLSM + CS and LSM + CS, respectively. The high salinity condition (5.28%) after IVS pretreatment was considered the primary inhibitor in pLSM + CS, while the ammonia (≤600 mg/L), C:N ratio (15.52) and volatile solid loading rate (3 g/kg-1·day-1) didn't show a negative effect on CH4 production. When salinities were increased from 2% to 4% and 8%, 50% and 100% inhibition were observed respectively. The butyrate accumulation was a potential indicator of the non-salinity-inhibition status for methanogenesis in TAD.

Integrated process for anaerobically digested swine manure treatment.

An integrated three-step process was proposed for the treatment of the anaerobically digested swine manure (ADSM). The flocculation and struvite precipitation were used as the pre-treatment to remove the particles and reduce phosphorus to balance the condition for the algae growth. In the biological step, the 40% group (2.5× dilution) represented the optimal cultivation condition for the A + B co-cultivation, with the highest biomass concentration of 2.325 ±â€¯0.16 g/L and performed well with nutrients removal (COD: 9770 ±â€¯184 mg/L; TN: 235 ±â€¯5.4 mg/L; TP: 25.3 ±â€¯0.8 mg/L). 94.8% of the biomass from the 40% group could naturally settle down in 30 min which is good for harvest. The activated carbon adsorption was applied as the advanced treatment to resolve the issues with the dark color and residual compounds. After these processes, the removal efficiencies of COD, TN, TP and NH4-N reached 97.2%, 94.0%, 99.7% and 99.9%, respectively.

Correction: In situ plasma-assisted atmospheric nitrogen fixation using water and spray-type jet plasma.

Correction for 'In situ plasma-assisted atmospheric nitrogen fixation using water and spray-type jet plasma' by Peng Peng et al., Chem. Commun., 2018, 54, 2886-2889.

Cultivation of Chlorella vulgaris on anaerobically digested swine manure with daily recycling of the post-harvest culture broth.

In this work, a cultivation system with daily recycling of the post-harvest culture broth was set up and performed in order to reuse the water and nutrients in pretreated anaerobically digested swine manure, which was used as media to cultivate Chlorella vulgaris (UTEX 2714) at different recycling ratios. Results showed that the alga grew well in the system with an accumulative algal biomass and productivity of 1.68-3.47g/L and 234.1-532.2mg/L/d, respectively, at the end of the cultivation. Additionally, chemical compositions in this alga varied with the change of recycling ratios, and the highest productivities of carbohydrate, protein and lipids (76.4, 257.2 and 183.7mg/L/d, respectively) were obtained in the system with a recycling ratio of 1/4 or 1/6. Fatty acid profiles indicated that this alga could be used as a good-quality biodiesel feedstock with a biodiesel productivity of 9.65-40.1mg/L/d.

In-situ and ex-situ catalytic upgrading of vapors from microwave-assisted pyrolysis of lignin.

In-situ and ex-situ catalytic upgrading with HZSM-5 of vapors from microwave-assisted pyrolysis of lignin were studied. The in-situ process produced higher bio-oil and less char than ex-situ process. The gas yield was similar for both processes. The ex-situ process had higher selectivity to aromatics and produced more syngas and less CO2 than the in-situ process. Additional experiments on ex-situ process found that the bio-oil yield and coke deposition decreased while the gas yield increased at higher catalyst-to-lignin ratios and catalytic upgrading temperatures. The increased catalyst-to-lignin ratio from 0 to 0.3 reduced the selectivity of methoxy phenols from 73.7% to 22.6% while increased that of aromatics from 1.1% to 41.4%. The highest selectivity of alkyl phenols (31.9%) was obtained at 0.2 of catalyst-to-lignin ratio. Higher catalytic temperatures favored greater conversion of methoxy phenols to alkyl phenols and aromatics. Appropriate catalyst-to-lignin ratio (0.3) together with higher catalytic temperatures favored syngas formation.

Microwave-assisted co-pyrolysis of brown coal and corn stover for oil production.

The controversial synergistic effect between brown coal and biomass during co-pyrolysis deserves further investigation. This study detailed the oil production from microwave-assisted co-pyrolysis of brown coal (BC) and corn stover (CS) at different CS/BC ratios (0, 0.33, 0.50, 0.67, and 1) and pyrolysis temperatures (500, 550, and 600 °C). The results showed that a higher CS/BC ratio resulted in higher oil yield, and a higher pyrolysis temperature increased oil yield for brown coal and coal/corn mixtures. Corn stover and brown coal showed different pyrolysis characteristics, and positive synergistic effect on oil yield was observed only at CS/BC ratio of 0.33 and pyrolysis temperature of 600 °C. Oils from brown coal mainly included hydrocarbons and phenols whereas oils from corn stover and coal/corn mixtures were dominated by ketones, phenols, and aldehydes. Positive synergistic effects were observed for ketones, aldehydes, acids, and esters whereas negative synergistic effects for hydrocarbons, phenols and alcohols.

In situ plasma-assisted atmospheric nitrogen fixation using water and spray-type jet plasma.

In this study, a sustainable nitrogen fixation process was presented under atmospheric conditions and without introducing hydrogen or any catalyst. The novel in situ synthesis in this study used an advanced spray-type jet plasma, which significantly improved the fixation rate of nitrite, nitrate, and ammonium. Furthermore, the mechanism focusing on the co-synthesis of the abovementioned three nitrogen compounds was proposed based on the synergistic interactions between the gas-phase plasma and liquid surface dissociation.

A comparative study between fungal pellet- and spore-assisted microalgae harvesting methods for algae bioflocculation.

Fungi assisted microalgae bioflocculation is an emerging, efficient and cost-effective microalgal harvesting method, but no study has systematically evaluated and compared fungal spore-assisted (FSA) and fungal pellet-assisted (FPA) microalgal harvesting methods. In this study, harvesting Chlorella sp. cells by co-culture with Penicillium sp. spores or pellets was compared. Temperature, glucose concentration, pH and fungi:algae ratio were the critical parameters for harvesting efficiency. The highest flocculation efficiency (99%) of FSA method was achieved in 28 h at 40 °C, 160 rpm, 5 g glucose/L and 1.1 × 104 cells/mL (spore). FPA method can harvest 98.26% algae cells in 2.5 h at 34 °C, 160 rpm, pH 4.0 with the fungi:algae ratio of 1:2. The carbon input for FPA is only half of that for FSA. FPA takes less time and needs less glucose input compared with FSA and may be more promising to be further developed as an effective microalgae bioflocculation method.