Role of nitrogen transport for efficient energy conversion potential in low carbon and high nitrogen/phosphorus wastewater by microalgal-bacterial system.

Microalgal-bacterial system (MBS) is potential biotechnology in wastewater treatment because it can remedy defects of conventional processes (e.g., insufficient carbon source and imbalanced elements ratio). However, the mechanisms of nitrogen (N) transport and removal in MBS are still unclear. In this study, it was discovered that MBS was conducive to adsorb NH4+-N and NO3--N through electrical neutralization, while extracellular polymeric substances (EPS) could provide binding sites (e.g., -OH and -CH3) for enhancing N transport and removal. The microalgae-bacteria interaction could accelerate N transport and removal from aqueous solution to cell. More importantly, the microalgal starch biosynthetic metabolism exhibited demonstrating the energy production potential could be boosted via MBS. Overall, the NO3--N and NH4+-N removal efficiencies, and energy yield were 82.28%, 94.15%, and 86.81 kJ/L, respectively, which are better than other relevant studies. Altogether, it is meaningful for revealing the applicability of MBS for treating wastewater and producing energy.

Exploring the potential of a newly constructed manganese peroxidase-producing yeast consortium for tolerating lignin degradation inhibitors while simultaneously decolorizing and detoxifying textile azo dye wastewater.

MnP-YC4, a newly constructed manganese peroxidase-producing yeast consortium, has been developed to withstand lignin degradation inhibitors while degrading and detoxifying azo dye. MnP-YC4 tolerance to major biomass-derived inhibitors was promising. MnP induced by lignin was found to be highly related to dye decolorization by MnP-YC4. Simulated azo dye-containing wastewater supplemented with a lignin co-substrate (3,5-Dimethoxy-4-hydroxybenzaldehyde) decolorized up to 100, 91, and 76% at final concentrations of 20, 40, and 60%, respectively. MnP-YC4 effectively decolorized the real textile wastewater sample, reaching up to 91.4%, and the COD value decreased significantly during the decolorization, reaching 7160 mg/l within 7 days. A possible dye biodegradation pathway was proposed based on the degradation products identified by UV-vis, FTIR, GC/MS, and HPLC techniques, beginning with azo bond cleavage and eventually mineralized to CO2 and H2O. When compared to the phytotoxic original dye, the phytotoxicity of MnP-YC4 treated dye-containing wastewater samples confirmed the nontoxic nature.

Improving reverse osmosis concentrate treatment and nutrients conversion to Chlorella vulgaris bioenergy assisted with granular activated carbon.

Landfill leachate (LL), especially the reverse osmosis concentrate (ROC), is a societal burden due to high toxicity but may have intrinsic values attributing to copious nutrients and organics. ROC bioremediation by microalgae has attracted much attentions benefiting from its extra advantage of bioenergy production. However, efficient microalgae cultivation with ROC is still a challenging task attributing to notorious ROC characteristics, like high chromaticity and toxicity. To alleviate these negative influences, a technique integrating granular activated carbon (GAC) pretreatment and microalgae bioremediation was proposed, with which nitrogen and phosphorus removal efficiencies achieved 100% along with an optimized microalgal biomass concentration of 1.44 g/L and lipid yield of 482.4 mg/L. Furthermore, a total volumetric energy yield of 33.6 kJ/L was acquired, which was conducive to realize energy valorization. The visualization evidence of three-dimensional fluorescence spectroscopy revealed chromaticity degradation mechanism of ROC as humic acids reduction and transfer to family of soluble microbial by-products. Meanwhile, contributions of GAC adsorption and microalgae assimilation on nutrients removal were analyzed. Together, this work provides a promising method and valuable information for ROC bioremediation with microalgae.

Converting nitrogen and phosphorus wastewater into bioenergy using microalgae-bacteria consortia: A critical review.

Conventional wastewater treatment using activated sludge cannot efficiently eliminate nitrogen and phosphorus, thus engendering the risk of water eutrophication and ecosystem disruption. Fortunately, a new wastewater treatment process applying microalgae-bacteria consortia has attracted considerable interests due to its excellent performance of nutrients removal. Moreover, some bacteria facilitate the harvest of microalgal biomass through bio-flocculation. Additionally, while stimulating the functional bacteria, the improved biomass and enriched components also brighten bioenergy production from the perspective of practical applications. Thus, this review first summarizes the current development of nutrients removal and mutualistic interaction using microalgae-bacteria consortia. Then, advancements in bio-flocculation are completely described and the corresponding mechanisms are thoroughly revealed. Eventually, the recent advances of bioenergy production (i.e., biodiesel, biohydrogen, bioethanol, and bioelectricity) using microalgae-bacteria consortia are comprehensively discussed. Together, this review will provide the ongoing challenges and future developmental directions for better converting nitrogen and phosphorus wastewater into bioenergy using microalgae-bacteria consortia.

A review on microalgae cultivation and harvesting, and their biomass extraction processing using ionic liquids.

The richness of high-value bio-compounds derived from microalgae has made microalgae a promising and sustainable source of useful product. The present work starts with a review on the usage of open pond and photobioreactor in culturing various microalgae strains, followed by an in-depth evaluation on the common harvesting techniques used to collect microalgae from culture medium. The harvesting methods discussed include filtration, centrifugation, flocculation, and flotation. Additionally, the advanced extraction technologies using ionic liquids as extractive solvents applied to extract high-value bio-compounds such as lipids, carbohydrates, proteins, and other bioactive compounds from microalgae biomass are summarized and discussed. However, more work needs to be done to fully utilize the potential of microalgae biomass for the application in large-scale production of biofuels, food additives, and nutritive supplements.

Biorefining and the Functional Properties of Proteins from Lipid and Pigment Extract Residue of Chlorella pyrenoidosa.

Microalgae are considered as excellent candidates for bioactive compounds, yet microalgal residues remaining after the extraction of one or two compounds are usually discarded, which is not economical. This study demonstrates the alkaline extraction of proteins from Chlorella pyrenoidosa residue after lipid and pigment extractions, and their functional properties. Single-factor experiments and response surface methodology were used to obtain the optimal conditions for protein extraction. Based on our results, a maximum protein yield of 722.70 mg/g, was obtained under the following extraction conditions: sodium hydroxide concentration 7.90%, extraction temperature 70.00 °C, extraction time 34.80 min, and microalgal residue concentration 8.20 mg/mL. The molecular weight of microalgal residue protein isolate (MRPI) was mainly distributed at the regions of 0.18-0.50 kDa, 0.50-1.50 kDa, and 1.50-5.00 kDa. The essential amino acid content was greater than the values recommended by FAO/WHO standards; a high essential amino acid index value (1.49) was another good indication that MRPI is suitable for human consumption. Moreover, MRPI exhibited excellent emulsifying properties and antioxidant activity, which suggests it may be useful as an emulsifying agent and antioxidant. These findings could improve the extraction methods of functional protein from microalgal residue and add value to microalgae-based bioactive compound production processes.

Using a trait-based approach to optimize mixotrophic growth of the red microalga Porphyridium purpureum towards fatty acid production.

BACKGROUND: Organic carbon sources have been reported to simultaneously increase the growth and lipid accumulation in microalgae. However, there have been no studies of the mixotrophic growth of Porphyridium purpureum in organic carbon media. In this study, three organic carbon sources, glucose, sodium acetate, and glycerol were used as substrates for the mixotrophic growth of P. purpureum. Moreover, a novel trait-based approach combined with Generalized Additive Modeling was conducted to determine the dosage of each organic carbon source that optimized the concentration of cell biomass or fatty acid. RESULTS: A 0.50% (w/v) dosage of glucose was optimum for the enhancement of the cell growth of P. purpureum, whereas sodium acetate performed well in enhancing cell growth, arachidonic acid (ARA) and eicosapentaenoic acid (EPA) content, and glycerol was characterized by its best performance in promoting both cell growth and ARA/EPA ratio. The optimum dosages of sodium acetate and glycerol for the ARA concentration were 0.25% (w/v) and 0.38% (v/v), respectively. An ARA concentration of 211.47 mg L-1 was obtained at the optimum dosage of glycerol, which is the highest ever reported. CONCLUSIONS: The results suggested that a comprehensive consider of several traits offers an effective strategy to select an optimum dosage for economic and safe microalgae cultivation. This study represents the first attempt of mixotrophic growth of P. purpureum and proved that both biomass and ARA accumulation could be enhanced under supplements of organic carbon sources, which brightens the commercial cultivation of microalgae for ARA production.

Effect of plant species compositions on performance of lab-scale constructed wetland through investigating photosynthesis and microbial communities.

This study focused on the effects of plant compositions on removal rates of pollutants in microcosms through investigating rhizosphere microbial populations, photosynthetic efficiency and growth characteristics. Mixed-culture groups improved the removal efficiency of TN and TP significantly but exhibited lower COD removal rates. Total plant biomasses were improved as the species richness increased, but the N/P content in the plants was mainly affected by the type of species. The mixed-culture groups showed lower photosynthesis rates and oxygen supply generated from roots under high irradiation. Microbial communities of the cultured groups in the rhizosphere exhibited significant differences. According to principal component analysis (PCA), the fungi were the typical microbes of SPA, SPAB, and SPABC, resulted in improvement in nutrient accumulation. These results demonstrated that a mixed culture strategy can represent the overyielding of biomass, promote the photo-protection mechanism, and will further increase the removal rates of pollutants in a constructed wetland.

Microalgae-based biorefinery--from biofuels to natural products.

The potential for biodiesel production from microalgal lipids and for CO2 mitigation due to photoautotrophic growth of microalgae have recently been recognized. Microalgae biomass also has other valuable components, including carbohydrates, long chain fatty acids, pigments and proteins. The microalgae-based carbohydrates consist mainly of cellulose and starch without lignin; thus they can be ready carbon source for the fermentation industry. Some microalgae can produce long chain fatty acids (such as DHA and EPA) as valuable health food supplements. In addition, microalgal pigments and proteins have considerable potential for many medical applications. This review article presents comprehensive information on the current state of these commercial applications, as well as the utilization and characteristics of the microalgal components, in addition to the key factors and challenges that should be addressed during the production of these materials, and thus provides a useful report that can aid the development of an efficient microalgae-based biorefinery process.