Photocatalytic Optical Hollow Fiber with Enhanced Visible-light-driven CO2 Reduction.

A visible-light-driven CO2 reduction optical fiber is fabricated using graphene-like nitrogen-doped composites and hollow quartz optical fibers to achieve enhanced activity, selectivity, and light utilization for CO2 photoreduction. The composites are synthesized from a lead-based metal-organic framework (TMOF-10-NH2 ) and g-C3 N4 nanosheet (CNNS) via electrostatic self-assembly. The TMOF-10-NH2 /g-C3 N4 (TMOF/CNNS) photocatalyst with an S-type heterojunction is coated on optical fiber. The TMOF/CNNS coating, which has a bandgap energy of 2.15 eV, has good photoinduced capability at the coating interfaces, high photogenerated electron-hole pair yield, and high charge transfer rate. The conduction band potential of the TMOF/CNNS coating is more negative than that for CO2 reduction. Moreover, TMOF facilitates the CO desorption on its surface, thereby improving the selectivity for CO production. High CO2 photoreduction and selectivity for CO production is demonstrated by the TMOF/CNNS-coated optical fiber with the cladding/core diameter of 2000/1000 µm, 10 wt% TMOF in CNNS, coating thickness of 25 µm, initial CO2 concentration of 90 vol%, and relative humidity of 88% RH under the excitation wavelength of 380-780 nm. Overall, the photocatalytic hollow optical fiber developed herein provides an effective and efficient approach for the enhancement of light utilization efficiency of photocatalysts and selective CO2 reduction.

Production of sustainable biofuels from microalgae with CO2 bio-sequestration and life cycle assessment.

Due to anthropogenic emissions, there is an increase in the concentration of carbon dioxide (CO2) in the atmosphere. Microalgae are versatile, universal, and photosynthetic microorganisms present in nature. Biological CO2 sequestration using microalgae is a novel concept in CO2 mitigation strategies. In the current review, the difference between carbon capture and storage (CCS), carbon capture utilization and storage (CCUS), and carbon capture and utilization (CCU) is clarified. The current status of CO2 sequestration techniques is discussed, including various methods and a comparative analysis of abiotic and biotic sequestration. Particular focus is given to sequestration methods associated with microalgae, including advantages of CO2 bio-sequestration using microalgae, a summary of microalgae species that tolerate high CO2 concentrations, biochemistry of microalgal CO2 biofixation, and elements influencing the microalgal CO2 sequestration. In addition, this review highlights and summarizes the research efforts made on the production of various biofuels using microalgae. Notably, Chlorella sp. is found to be the most beneficial microalgae, with a sizeable hydrogen (H2) generation capability ranging from 6.1 to 31.2 mL H2/g microalgae, as well as the species of C. salina, C. fusca, Parachlorella kessleri, C. homosphaera, C. vacuolate, C. pyrenoidosa, C. sorokiniana, C. lewinii, and C. protothecoides. Lastly, the technical feasibility and life cycle analysis are analyzed. This comprehensive review will pave the way for promoting more aggressive research on microalgae-based CO2 sequestration.

Plastic optical fiber sensor for temperature-independent high-sensitivity detection of humidity.

A simple U-shaped plastic optical fiber evanescent-wave sensor was fabricated for temperature-independent highly sensitive detection of humidity. The sensing region of the sensor was subjected to five cycles of heating-cooling to improve temperature independence. The effects of the polyimide (PI) coating thickness, number of graphene oxide (GO) coating layers, and alternate PI-GO coating sequence were investigated to optimize sensitivity. The fabricated sensor exhibited high-temperature independence and good sensitivity of 0.17×10-2 (% relative humidity)-1 in the temperature range of 10°C to 70°C.

Monitoring Biohydrogen Production and Metabolic Heat in Biofilms by Fiber Bragg Grating Sensors.

A fiber Bragg grating (FBG) was created to accurately and simultaneously monitor the biohydrogen and metabolic heat production in biofilms containing Rhodopseudomonas palustris CQK-01 photosynthetic bacteria (PSB). The proposed hydrogen sensor was made from an FBG unit separated into two regions by a wet etching process; a thin region with a diameter of 15 µm was employed to monitor the temperature. A smaller region of the etched FBG with a diameter of 8.0 µm was coated with a 50 nm-thick Pd film by sputtering to determine the responses to the temperature and hydrogen concentration. To monitor the biohydrogen production and metabolic heat within the biofilms, three FBGs were evenly distributed in a polydimethylsiloxane channel (biofilm carrier) with vertical distances of 80 µm. In addition, the thickness, surface morphology, active biomass, and porosity of the biofilms were investigated. The FBG sensor can rapidly and accurately determine the difference in Bragg wavelength shifts caused by changes in the hydrogen concentration and temperature. The measured biohydrogen concentration is highly correlated with the real biohydrogen production with a correlation of 0.9765. The biohydrogen production capacity of PSB in the surface layer is much higher than that internally because of sharp decreases in the active biomass and porosity from the surface to within the biofilm. The highest biohydrogen concentration is obtained at 1.218 × 104 ppm for a biofilm thickness of 165 µm, and the temperature difference from metabolic heat production is ∼1.1 °C in the biofilm culture.

Monitoring Microalgal Biofilm Growth and Phenol Degradation with Fiber-Optic Sensors.

Simple D-type plastic optical fiber (POF) probes (i.e., sensor, reference, and photochemical probes) were created to accurately monitor the progression and phenol degradation of a Chlorella vulgaris biofilm. The sensor and reference probes were used to monitor the biofilm growth (thickness). The sensor probe, which consisted of a D-shaped POF and Canada balsam doped with GeO2 (CBG) coating, was developed to monitor the biofilm growth and change in the liquid-phase composition and its concentration inside the biofilm. The reference probe, which comprised a D-shaped POF, CBG coating, and glass fiber membrane (to separate the liquids from Chlorella vulgaris), was used to measure the response to changes in the liquid phase. A model was developed to demonstrate the accurate measurement of the biofilm thickness. The photochemical POF probe was coupled with a high-permselectivity phenol polymer membrane to monitor the phenol concentration and analyze the degradation time of 50 mg/L phenol with microalgal biofilms. A fixed relationship was obtained between the biofilm sensor output information and biofilm thickness for a biofilm thickness range of 0-290 µm with a periodic supply of 50 mg/L phenol solution. The highest phenol degradation rate occurred at a biofilm thickness of 191-222 µm. The proposed system can be used to investigate microalgal biomass and can provide a promising avenue for research on renewable resources and pollutant degradation.

Photochemical reflective optical fiber sensor for selective detection of phenol in aqueous solutions.

A photochemical fiber-optic sensor was developed by integrating a plastic optical fiber (POF), polymer membrane, gold mirror, and TiO2-based composite, and was shown to sensitively and selectively detect phenol in aqueous solution. The sensing element consisted of a thinned POF and visible-light-driven SiO2/N-doped TiO2 coating. The gold mirror was used to develop a reflective POF probe. The polymer membrane with high phenol permselectivity was employed to form a micro-channel between the membrane and probe. Our findings highlight the sensor's capability of phenol detection in aqueous solutions with high sensitivity of 0.294×10-3 (mg·L-1)-1, pH immunity ranging from 2.0 to 14.0, and high selectivity with a limit of detection of 30 µg·L-1.

Chitosan derived N-doped carbon anchored Co3O4-doped MoS2 nanosheets as an efficient peroxymonosulfate activator for degradation of dyes.

Peroxymonosulfate (PMS), which is dominated by non-free radical pathway, has a good removal effect on organic pollutants in complex water matrices. In this article, a biodegradable cobalt-based catalyst (Co3O4/MoS2@NCS) was synthesized by a simple hydrothermal method with chitosan (CS) as nitrogen­carbon precursor and doped with Cobaltic­cobaltous oxide (Co3O4) and Molybdenum disulfide (MoS2), and was used to activate PMS to degrade dye wastewater. Electrochemical tests showed that Co3O4/MoS2@NCS exhibited higher current density and cycling area than MoS2@NCS and MoS2. In the Co3O4/MoS2@NCS/PMS system, the degradation rate of 30 mg·L-1 rhodamine B (RhB) reached 97.75 % within 5 min, and kept as high as 94.34 % after 5 cycles. Its rate constant was 1.91 and 8.37 times that of MoS2@NCS/PMS and MoS2/PMS, respectively. It had good complex background matrices and acid-base anti-interference ability, and had good universality and reusability. The degradation rate of methyl orange (MO) and methylene blue (MB) were more than 91 % within 5 min at pH 4.8. The experimental results demonstrated that MoS2-modified CS as a carrier exposed a large number of active sites, which not only dispersed Co3O4 nanoparticles and improved the stability of the catalyst, but also provided abundant electron rich groups, and promoted the activation of PMS and the production of reactive oxygen species (ROS). PMS was effectively activated by catalytic sites (Co3+/Co2+, Mo4+/Mo5+/Mo6+, CO, pyridine N, pyrrole N, hydroxyl group and unsaturated sulfur), producing a large number of radicals that attack RhB molecules, causing chromophore cleavage, ring opening, and mineralization. Among them, non-free radical 1O2 was the main ROS for RhB degradation. This work is expected to provide a new idea for the design and synthesis of environmentally friendly and efficient MoS2-modified cobalt-based catalysts.

Advanced wastewater treatment with microalgae-indigenous bacterial interactions.

Microalgal-indigenous bacterial wastewater treatment (MBWT) emerges as a promising approach for the concurrent removal of nitrogen (N) and phosphorus (P). Despite its potential, the prevalent use of MBWT in batch systems limits its broader application. Furthermore, the success of MBWT critically depends on the stable self-adaptation and synergistic interactions between microalgae and indigenous bacteria, yet the underlying biological mechanisms are not fully understood. Here we explore the viability and microbial dynamics of a continuous flow microalgae-indigenous bacteria advanced wastewater treatment system (CFMBAWTS) in processing actual secondary effluent, with a focus on varying hydraulic retention times (HRTs). The research highlights a stable, mutually beneficial relationship between indigenous bacteria and microalgae. Microalgae and indigenous bacteria can create an optimal environment for each other by providing essential cofactors (like iron, vitamins, and indole-3-acetic acid), oxygen, dissolved organic matter, and tryptophan. This collaboration leads to effective microbial growth, enhanced N and P removal, and energy generation. The study also uncovers crucial metabolic pathways, functional genes, and patterns of microbial succession. Significantly, the effluent NH4+-N and P levels complied with the Chinese national Class-II, Class-V, Class-IA, and Class-IB wastewater discharge standards when the HRT was reduced from 15 to 6 h. Optimal results, including the highest rates of CO2 fixation (1.23 g L-1), total energy yield (32.35 kJ L-1), and the maximal lipid (33.91%) and carbohydrate (41.91%) content, were observed at an HRT of 15 h. Overall, this study not only confirms the feasibility of CFMBAWTS but also lays a crucial foundation for enhancing our understanding of this technology and propelling its practical application in wastewater treatment plants.

Adsorption performance of Ni(II) by KOH-modified biochar derived from different microalgae species.

Microalgae biochar is potential adsorbents to remove heavy metals from wastewater due to abundant functional groups, high porosity and wide sources, but performance is not fully developed since it depends on microalgae species attributing to distinct morphology and biomass compositions. Here, two microalgae species Chlorella Pyrenoidosa and Scenedesmus Obliquus were used for biochar preparation via KOH-modification, biochar properties and their influences on Ni(II) adsorption were investigated. Ni(II) adsorption performances responding to biochar properties and operating conditions were upgraded via progressive optimization and response surface methodology. Together, adsorption isotherms and kinetics were analyzed to obtain significant factors for Ni(II) removal. As results, 100 % of Ni(II) removal was achieved under 100 mg/L initial Ni(II) concentration as pH was higher than the biochar zero-charge point of 6.87 with low biochar dosage (0.5 g/L), which provides an efficient approach for heavy metal removal from wastewater with microalgae biochar.

Simultaneously enhancement in the assimilation of microalgal nitrogen and the accumulation of carbohydrate by Debaryomyces hansenii.

Microalgae-based techniques are considered an alternative to traditional activated sludge processes for removing nitrogen from wastewater. Bacteria consortia have been broadly conducted as one of the most important partners. However, fungal effects on the removal of nutrients and changes in physiological properties of microalgae, and their impact mechanisms remain unclear. The current work demonstrates that, adding fungi increased the nitrogen assimilation of microalgae and the generation of carbohydrates compared to pure microalgal cultivation. The NH4+-N removal efficiency was 95.0% within 48 h using the microalgae-fungi system. At 48 h, total sugars (glucose, xylose, and arabinose) accounted for 24.2 ± 4.2% per dry weight in the microalgae-fungi group. Gene ontology (GO) enrichment analysis revealed that, among various processes, phosphorylation and carbohydrate metabolic processes were more prominent. Gene encoding the key enzymes of glycolysis, pyruvate kinase, and phosphofructokinase were significantly up-regulated. Overall, for the first time, this study provides new insights into the art of microalgae-fungi consortia for producing value-added metabolites.

Polyacrylate stabilized ZVI/Cu bimetallic nanoparticles for removal of hexavalent chromium from wastewater.

In this work, a magnetic core-shell composite zero-valent iron/copper-polyacrylate (ZVI/Cu-PAA) was synthesized by a simple liquid-phase reduction process and used for hexavalent chromium Cr(VI) removal from wastewater. The optimization experiments show that the optimal dosages of polyacrylate and Cu are 7.00 wt% and 8.25 wt%, respectively. The maximum adsorption capacity and removal rate of Cr(VI) by ZVI/Cu-PAA reached 106.12 mg g-1 and 99.05% at pH 5.5, respectively. Furthermore, the presence of coexisting ions such as Ca2+, Mg2+, Na+, and NO3- had no significant effect on its Cr(VI) removal performance. The excellent performance of ZVI/Cu-PAA is attributed to that the modification of polyacrylate can not only give more active sites but also inhibit agglomeration of nano-metallic particles, while Cu doping promotes the electron generation and transformation of Fe(III)/Fe(II) and Cu(II)/Cu(I) redox cycles. This makes ZVI/Cu-PAA has rich active sites and excellent stability, and has broad application prospects in the remediation of Cr (VI) polluted wastewater. The magnetic core-shell composite ZVI/Cu-PAA has excellent Cr (VI) removal performance because of its rich active sites and high electron transformation efficiency.

Comprehensive insights into antibiotic resistance gene migration in microalgal-bacterial consortia: Mechanisms, factors, and perspectives.

With the overuse of antibiotics, antibiotic resistance gene (ARG) prevalence is gradually increasing. ARGs are considered emerging contaminants that are broadly concentrated and dispersed in most aquatic environments. Recently, interest in microalgal-bacterial biotreatment of antibiotics has increased, as eukaryotes are not the primary target of antimicrobial drugs. Moreover, research has shown that microalgal-bacterial consortia can minimize the transmission of antibiotic resistance in the environment. Unfortunately, reviews surrounding the ARG migration mechanism in microalgal-bacterial consortia have not yet been performed. This review briefly introduces the migration of ARGs in aquatic environments. Additionally, an in-depth summary of horizontal gene transfer (HGT) between cyanobacteria and bacteria and from bacteria to eukaryotic microalgae is presented. Factors influencing gene transfer in microalgal-bacterial consortia are discussed systematically, including bacteriophage abundance, environmental conditions (temperature, pH, and nutrient availability), and other selective pressure conditions including nanomaterials, heavy metals, and pharmaceuticals and personal care products. Furthermore, considering that quorum sensing could be involved in DNA transformation by affecting secondary metabolites, current knowledge surrounding quorum sensing regulation of HGT of ARGs is summarized. In summary, this review gives valuable information to promote the development of practical and innovative techniques for ARG removal by microalgal-bacterial consortia.

Revealing the role of microalgae-bacteria niche for boosting wastewater treatment and energy reclamation in response to temperature.

Conventional biological treatment usually cannot achieve the same high water quality as advanced treatment when conducted under varied temperatures. Here, satisfactory wastewater treatment efficiency was observed in a microalgae-bacteria consortia (MBC) over a wide temperature range because of the predominance of microalgae. Microalgae contributed more toward wastewater treatment at low temperature because of the unsatisfactory performance of the accompanying bacteria, which experienced cold stress (e.g., bacterial abundance below 3000 sequences) and executed defensive strategies (e.g., enrichment of cold-shock proteins). A low abundance of amoA-C and hao indicated that conventional nitrogen removal was replaced through the involvement of microalgae. Diverse heterotrophic bacteria for nitrogen removal were identified at medium and high temperatures, implying this microbial niche treatment contained diverse flexible consortia with temperature variation. Additionally, pathogenic bacteria were eliminated through microalgal photosynthesis. After fitting the neutral community model and calculating the ecological niche, microalgae achieved a maximum niche breadth of 5.21 and the lowest niche overlap of 0.38, while the accompanying bacterial community in the consortia were shaped through deterministic processes. Finally, the maximum energy yield of 87.4 kJ L-1 and lipid production of 1.9 g L-1 were achieved at medium temperature. Altogether, this study demonstrates that advanced treatment and energy reclamation can be achieved through microalgae-bacteria niche strategies.

Polyaniline/g-C3N4/Bi2O3/Ti photoanode for visible light responsive photocatalytic fuel cell degradation of rhodamine B and electricity generation.

In order to develop efficient photoanode to improve the performance of visible light responsive photocatalytic fuel cell (PFC), in this work, polyaniline/g-C3N4/Bi2O3/Ti photoanode was successfully prepared using silica-sol drop coating method, and assembled with Cu cathode to construct PFC to decompose rhodamine B and generate electricity simultaneously. The degradation rate, maximum photocurrent density and maximum power density of this PFC were 91.23%, 0.086 mA cm-2 and 4.78 µW cm-2, respectively, which were 1.4 and 1.8 times, 2.4 and 4.5 times, and 1.9 and 7.3 times those of the corresponding values of the PFCs with g-C3N4/Bi2O3/Ti and Bi2O3/Ti photoanodes, respectively. This is attributed to the type II heterojunction structure formed among polyaniline, g-C3N4 and Bi2O3 in the polyaniline/g-C3N4/Bi2O3/Ti photoanode. Among them, polyaniline has π-π conjugated structure, which can rapidly transfer the electronic charge between g-C3N4 and Bi2O3, thus enhancing the separation efficiency of photo-generated e--h+ pairs spatially and reducing their recombination, extending the visible light response wavelength of the photocatalyst, and finally improving its photocatalytic properties. This study can provide significant reference for the research of Bi2O3-based visible light responsive PFC.

Zr4+ and glutaraldehyde cross-linked polyethyleneimine functionalized chitosan composite: Synthesis, characterization, Cr(VI) adsorption performance, mechanism and regeneration.

In order to improve the stability, electrostatic interaction and ion exchange ability of chitosan for Cr (VI) removal, it is an effective strategy to introduce polyvalent metal ions and polymers into chitosan molecular chain through crosslinking. In this paper, Zr4+ and glutaraldehyde crosslinked polyethyleneimine functionalized chitosan (CGPZ) composite was successfully synthesized and characterized by XRD, SEM, FTIR, BET, and XPS. The results showed that polyethyleneimine was successfully grafted onto chitosan by Schiff base reaction, while the appearance of ZrO and ZrN bonds verified the successful preparation of CGPZ. The monolayer maximum adsorption capacity of Cr(VI) by CGPZ was 593.72 mg g-1 at 298 K and t = 210 min. The removal efficiency of 100 mg L-1 Cr(VI) reached 95.7 %. The thermodynamic, isotherm and kinetic results show that the adsorption process of Cr (VI) by CGPZ is a spontaneous endothermic process controlled by entropy, which accords with Freundlich model and pseudo-second-order kinetic model. The regeneration experiments show that both HCl and NaOH can effectively desorb Cr(III) and Cr(VI) from the adsorbent surface, and the adsorbent has good acid-base resistance and regeneration performance. The removal of Cr(VI) mainly involves electrostatic attraction, ion exchange, reduction and complexation. CGPZ can synergistically adsorb Cr(VI) by electrostatic interaction of -NH2/-C=N and ion exchange of Cl- ion in the center of Zr, then reduce Cr(VI) to Cr(III) (45.4 % at pH = 2.0) by the -OH group on its surface, and chelate Cr(III) through COO- and -NH- groups.

Enhanced energy recovery from landfill leachate by linking light and dark bio-reactions: Underlying synergistic effects of dual microalgal interaction.

Bioconversion of nutrients and energy from landfill leachate (LL) to biohydrogen and volatile fatty acids (VFAs) using dark fermentation (DF) is a promising technique for developing a sustainable ecosystem. However, poor performance of DF caused by vulnerable fermentative bacteria vitality and strong LL toxicity significantly hinder its commercialization. Herein, an integrated technique linking microalgae photosynthesis and DF was proposed, in which mixed microalgae were applied to robustly reclaim nutrients and chemical oxygen demand (COD) from LL. Then, microalgae biomass was fermented into biohydrogen and VFAs using the DF process. Underlying synergistic mechanisms of the interaction of Scenedesmus obliquus and Chlorella vulgaris resulting from the functioning of extracellular polymeric substances (EPS) were discussed in detail. For better absorption of nutrients from LL, the mixed microalgae secreted obviously more EPS than pure microalgae, which played vital roles in the assimilation of cellular nutrients by forming more negative zeta potential and secreting more tyrosine-/tryptophan-family proteins in EPS. Besides, mixed microalgae produced more intracellular proteins and carbohydrates than the pure microalgae, thereby providing more feedstock for DF and achieving higher energy yield of 10.80 kJ/L than 6.64 kJ/L that was obtained when pure microalgae were used. Moreover, the energy conversion efficiency of 7.75% was higher for mixed microalgae than 4.77% that was obtained for pure microalgae. This work may inspire efficient disposal of LL and production of bioenergy, together with filling the knowledge gaps of synergistic mechanisms of dual microalgal interactions.

Photocatalytic synergistic biofilms enhance tetracycline degradation and conversion.

Tetracyclines are refractory pollutants that cause persistent harm to the environment and human health. Therefore, it is urgently necessary to develop methods to promote the efficient degradation and conversion of tetracyclines in wastewater. This report proposes a photobiocatalytic synergistic system involving the coupling of GeO2/Zn-doped phosphotungstic acid hydrate/TiO2 (GeO2/Zn-HPW/TiO2)-loaded photocatalytic optical hollow fibers (POHFs) and an algal-bacterial biofilm. The GeO2/Zn-HPW/TiO2 photocatalyst exhibits a broad absorption edge extending to 1000 nm, as well as high-efficiency photoelectric conversion and electron transfer, which allow the GeO2/Zn-HPW/TiO2-coated POHFs to provide high light intensity to promote biofilm growth. The resulting high photocatalytic activity rapidly and stably reduces the toxicity and increases the biodegradability of tetracycline-containing wastewater. The biofilm enriched with Salinarimonas, Coelastrella sp., and Rhizobium, maintains its activity for the rapid photocatalytic degradation and biotransformation of intermediates to generate the O2 required for photocatalysis. Overall, the synergistic photocatalytic biofilm system developed herein provides an effective and efficient approach for the rapid degradation and conversion of water containing high concentrations of tetracycline.

Emerging biological wastewater treatment using microalgal-bacterial granules: A review.

Aiming at deepening the understanding of the formation and evolution of emerging microalgal-bacterial granule (MBG)-based wastewater treatment systems, the recent advances regarding the formation processes, transfer phenomena, innovative bioreactors development and wastewater treatment performance of MBG-based systems are comprehensively reviewed in this work. Particularly, the successful establishments of MBG-based systems with various inocula are summarized. Besides, as the indispensable factors for biochemical reactions in MBGs, the light and substrates (organic matters, inorganic nutrients, etc) need to undergo complicated and multi-scale transfer processes before being assimilated by microorganisms within MBGs. Therefore, the involved transfer phenomena and mechanisms in MBG-based bioreactors are critically discussed. Subsequently, some recent advances of MBG-based bioreactors, the application of MBG-based systems in treating various synthetic and real wastewater, and the future development directions are discussed. In short, this review helps in promoting the development of MBG-based systems by presenting current research status and future perspectives.

Recent progress on converting CO2 into microalgal biomass using suspended photobioreactors.

Inhomogeneous light distribution and poor CO2 transfer capacity are two critical concerns impeding microalgal photosynthesis in practical suspended photobioreactors (PBRs). To provide valuable guidance on designing high-performance PBRs, recent progress on enhancing light and CO2 availabilities is systematically summarized in this review. Particularly, for the first time, the strategies on elevating light availability are classified and discussed from the perspectives of increasing incident light intensity, introducing internal illumination, optimizing flow field, regulating biomass concentrations, and enlarging illumination surface areas. Meanwhile, the strategies on enhancing CO2 light availability are outlined from the aspects of generating smaller bubbles, extending bubbles residence time, and facilitating CO2 dissolution using extra additives. Given the microalgal biomass production using current PBRs are still suffering from low productivity and economic feasibility, the possible future directions for PBRs implementation and development are presented. Altogether, this review is beneficial to furthering development of PBRs as a practical technology.

Microalgae-driven swine wastewater biotreatment: Nutrient recovery, key microbial community and current challenges.

As a promising technology, the microalgae-driven strategy can achieve environmentally sustainable and economically viable swine wastewater treatment. Currently, most microalgae-based research focuses on remediation improvement and biomass accumulation, while information on the removal mechanisms and dominant microorganisms is emerging but still limited. In this review, the major removal mechanisms of pollutants and pathogenic bacteria are systematically discussed. In addition, the bacterial and microalgal community during the swine wastewater treatment process are summarized. In general, Blastomonas, Flavobacterium, Skermanella, Calothrix and Sedimentibacter exhibit a high relative abundance. In contrast to the bacterial community, the microalgal community does not change much during swine wastewater treatment. Additionally, the effects of various parameters (characteristics of swine wastewater and cultivation conditions) on microalgal growth and current challenges in the microalgae-driven biotreatment process are comprehensively introduced. This review stresses the need to integrate bacterial and microalgal ecology information into the conventional design of full-scale swine wastewater treatment systems and operations. Herein, future research needs are also proposed, which will facilitate the development and operation of a more efficient microalgae-based swine wastewater treatment process.