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The use of heterogeneous catalysts in the transesterification reaction is an eco-friendly and cost-effective approach for biodiesel production as compared to the homogeneous catalyst-based processes. In this study, a heterogeneous cobalt doping Zn/Al complex oxide was prepared by a simple birch-templating method, and successfully applied to the transesterification of jatropha oil with methanol. The catalyst had strong diffraction peaks of ZnAl2O4 spinel crystal with substitutional doping of amorphous cobalt atom. It had a tendency to achieve a high base strength whilst increasing the specific surface area in the presence of cobalt. By contrast to the impregnation and coprecipitation methods, the crystalline particles from templating method were uniformly distributed on the catalyst surface, thus forming a well-defined tiled network with large amounts of grain-free pores. The exposure of available activity sites resulted in a biodiesel yield of 91.4%. After used several times and recycled, the regenerated catalyst also exhibited good catalytic potency without obvious deactivation. The transesterification kinetics satisfied the Pseudo first order model that controlled by the reaction temperature and catalyst dosage. The thermodynamic parameters of ΔH of 16.7 kJ/mol, ΔS of −284.6 J/mol/K, and ΔG of 140.0 kJ/mol suggested an endothermic, endergonic, and non-spontaneous nature of the reaction.

Acid mine drainage is an extraordinarily acidic and highly heavy metal ion-contaminated leachate, seriously threatening the environment. In this work, an industrial solid waste of steel slag is the adsorbent to remediate the simulated acid mine drainage containing a large amount of Fe(II) ions. Due to the excellent physicochemical properties and structures, steel slag exhibited remarkable Fe(II) removal performance. Its maximum removal efficiency was up to 100%. The initial pH, the dosage and particle size of steel slag, and initial concentration of heavy metal ions on Fe(II) removal efficiency were determined. The pseudo-second-order model and Freundlich isotherm model well described the adsorption behavior of steel slag, implying that the adsorption of Fe(II) by steel slag was mainly multilayer chemisorption. The thermodynamic study demonstrated that the adsorption process was endothermic and spontaneous; the enthalpy change was calculated to equal 91.21 kJ/mol. Mechanism study showed that the entire removal process of Fe(II) by steel slag was completed by electrostatic adsorption, chemical precipitation, and surface complexation in cooperation, and the chemical precipitation was the dominant mechanism. Meaningfully, this study provides a valuable strategy and path for engineering applications of AMD remediation by steel slag, which is prospective as an ideal candidate for Fe(II) ions elimination, inspiring the future development of "Treating the wastes with wastes."

Phenolic pollution from wastewater induces harmful effects on aquatic ecosystems and human health, calling for advanced remediation methods. Common methods have a single purpose, e.g., contaminant degradation, whereas there is few knowledge on methods combining degradation and algal production. We coupled N-doped TiO2-coated photocatalysis with optical fibers and a microalgal biofilm to both remove 4-chlorophenol and produce biomass. We also monitored bacterial population and biomass production in microalgal biofilms. Results show that the biofilm maintained rapid removal of 4-chlorophenol while maintaining the growth of the microalgal biomass, with values of about 78 µM/h for 4-chlorophenol removal, 41 µM/h for dechlorination and 1.8 g/h/m2 for the rate of biofilm growth. The biofilm became enriched in Salinarimonas and Pseudomonas. Our findings thus reveal a synergy between an optical catalyst and a bioreactor for potential wastewater remediation and microalgal biomass production.

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

Inhomogeneous light distribution and poor CO

Harmful algal blooms (HABs) are growing threats that cause tens of billion dollars economic loss annually. Aiming at efficient disposal of HABs, a cheap and eco-friendly cationic straw was developed by etherification of wheat straw, which replaced hydroxyl groups on cellulose by quaternary ammonium groups. It endowed the cationic straw with high positive charge and achieved 93.92% of harvesting efficiency by enhancing HABs cells aggregation via charge neutralization. Different from inorganic salts-based flocculants, HABs harvesting by the cationic straw is a spontaneous and exothermic process with negative ΔG° and ΔH° under all adsorption conditions. Thermodynamics and kinetics analysis elucidated that HABs adsorption process by cationic straw were mainly driven by physical forces. Together, cationic straw preparation and HABs harvesting processes were comprehensively optimized with orthogonal experiments. The work may inspire cost-effective HABs disposal and fill knowledge gaps of process nature for HABs harvesting.

Globally eruptive harmful algal blooms (HABs) have caused numerous negative effects on aquatic ecosystem and human health. Conversion of HABs into biohythane via dark fermentation (DF) is a promising approach to simultaneously cope with environmental and energy issues, but low HABs harvesting efficiency and biohythane productivity severely hinder its application. Here we designed a gradient electro-processing strategy for efficient HABs harvesting and disruption, which had intrinsic advantages of no secondary pollution and high economic feasibility. Firstly, low current density (0.888-4.444 mA/cm

Wastewater remediation using microbial fuel cells (MFC) is an advanced method to produce energy and reduce environmental pollution, yet actual energy yields are low and mineral matter is hardly removed. Here we constructed a dual-membrane cylinder photo-microbial fuel cell (DCP-MFC), equipped with cation and anion exchange membranes, to produce electricity and microalgae, and to remove both organics and minerals. Results show that this cell displayed higher electric generation capacity, of 671.6 mV and 0.39 W/m2, during 1000 h of stable running, than the control cell, of 601.2 mV and 0.31 W/m2. Microalgal biomass increased from 2.90 to 3.80 g/L owing to dissolved oxygen scavenging. Nitrogen recovery increased from 0 to 92.6%. Energy yield increased from 2.33 kJ for the control MFC to 118.28 kJ for microalgal cultivation, and to 155.21 kJ for the DCP-MFC. Microbial community analysis revealed that nitrate was mostly converted into nitrite by denitrifying bacteria in the anode chamber, then used by microalgae in the cathode chamber of the DCP-MFC.

Reverse osmosis concentrate (ROC) disposal with microalgae has attracted increasing interest because of its intrinsic advantages, like simultaneous wastewater remediation and bioenergy production. ...

Aiming at elevating Scenedesmus obliquus biofilm growth from the perspectives of CO2 transfer enhancement and light delivery optimization, a membrane-based photobioreactor with built-in optical fib...

Antibiotics abuse has triggered a growing environmental problem, posing a major threat to both ecosystem and human health. Unfortunately, there are still several shortcomings to current antibiotics removal technologies. Microalgae-bacteria consortia have been shown to be a promising antibiotics treatment technology owing to advantages of high antibiotics removal efficiency, low operational cost, and carbon emission reduction. This review aims to introduce the removal mechanisms, influencing factors, and future research perspectives for using microalgae-bacteria consortia to remove antibiotics. The interaction mechanisms between microalgae and bacteria are comprehensively revealed, and their exclusive advantages have been summarized in a "Trilogy" strategy, including "reinforced physical contact", "upgraded substance utilization along with antibiotics degradation", and "robust biological regulation". What's more, the relationship between different interaction mechanisms is emphatically analyzed. The important influencing factors, including concentration and classes of antibiotics, environmental conditions, and operational parameters, of antibiotics removal were also assessed. Three innovative treatment systems (microalgae-bacteria fuel cells (MBFCs), microalgae-bacteria membrane photobioreactors (MB-MPBRs), and microalgae-bacteria granular sludge (MBGS)) along with three advanced techniques (metabolic engineering, machine learning, and molecular docking and dynamics) are then introduced. In addition, concrete implementing schemes of the above advanced techniques are also provided. Finally, the current challenges and future research directions in using microalgae-bacteria consortia to remove antibiotics have been summarized. Overall, this review addresses the current state of microalgae-bacteria consortia for antibiotics treatment and provides corresponding recommendations for enhancing antibiotics removal efficiency.

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

The effective strategy to solve the problems of low mechanical strength, low adsorption efficiency and poor stability of chitosan is to modify it. In this work, Zr

Technologies for conversion of microbial energy have recently attracted interest to transform waste into bioenergy, thus addressing simultaneously environmental and energy issues. Nonetheless, actual microbial systems for energy conversion have limitations such as low rate of mass transfer, uneven energy distribution and strong inhibition of products and by-products. These technical bottlenecks can be alleviated by using membranes, which regulate the transfer of mass, heat and energy. Here we review applications of membranes for microbial energy conversion. We discuss mechanisms, functions and development of membranes for feedstock preparation, bioenergy production and bioproduct post-treatment. We present key membrane factors that control the efficiency of microbial fuel cells. We address membrane biofouling problems and anti-fouling approaches, in order to improve future commercialization.

This study investigated the effects of microalgae-bacteria consortia (MBC) (Chlorella pyrenoidosa-activated sludge (AS)) treating swine wastewater with low C/N ratios. After co-culture, the removal rates of NH

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.

Biochar (BC) adsorption has been widely acknowledged as an efficient approach for the removal of antibiotics. Despite the importance of oxygen-containing functional groups for the antibiotics removal, most of these may be obtained in BC only relying on the addition of oxidants. Herein, an environmentally friendly and oxygen-enriched functional groups adsorbent, namely Chlamydomonas BC (CBC), was fabricated via simple pyrolysis process. Then, the H-bonding, electron donor-acceptor and electrostatic attraction were identified as the main mechanisms regarding sulfathiazole (STZ) adsorption (506.38 mg/g). The carbon-oxygen functional groups on the surface of CBC (61%), especially -COOH and -OH, acted as a pivotal component. Additionally, further theoretical calculation led to the observation that STZ exhibited the highest chemical reactivity (η = 0.04), strong electron exchange capacity (μ = -0.16), remarkable electron accepting capacity (ω = 0.28) and excellent electron transfer efficiency (E

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.

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.

The aim of this work was to realize high-efficiency nutrients recovery from landfill leachate (LL) for microalgal lipids production. Negative effects of LL on microalgal lipid synthesis was revealed and a scalable membrane-based tubular photobioreactor (SM-PBR) was proposed to offset these negative effects. Microalgal biomass concentration was improved from 0 g/L in the traditional PBR to 2.13 g/L in the SM-PBR. Major operating conditions were optimized to enhance nutrients recovery and lipid productivity. The maximum N recovery efficiency of 74.31% and the maximum daily lipid production of 404.98 mg/d were obtained under the volume ratio of 5:3 (microalgae culture/LL stream) and phosphate feeding concentration of 50 mg/L. The obtained lipid was convinced to have a good combustion and anti-degradation property, with high cetane number (52%) and low linolenic acid content (12%). The SM-PBR provided a feasible approach for large-scale microalgal lipid production with LL.

We present a highly sensitive photocatalytic plastic optic-fiber (POF) sensor for the selective detection of phenol in aqueous solutions. To obtain high sensitivity and low limit of detection (LOD) of the sensor, part of the POF cladding was removed and replaced by a Canada balsam doped with GeO2 (CBG); a UV–vis-light-driven photocatalytic material, that is a CdS-sensitized Er3+YAlO3/SiO2/TiO2 (EYST) composite, was coated on the CBG film. To realize highly selective detection of phenol in water, a high phenol permselectivity and pH independence polymer membrane was fixed on the CdS-sensitized EYST-CBG-coated POF. Furthermore, a model was developed to show that the phenol concentration can be determined by measuring the change in transmitted light intensity of the POF sensor and the sensitivity of the sensors can be improved by employing the CdS-sensitized EYST film. The results showed that the proposed photocatalytic POF sensor has a high sensitivity of -0.39 (mg·mL−1)−1 and low LOD of 15 μg·L−1 for the selective detection of phenol in aqueous solutions with pH ranging from 2.0 to 14.0.