Effect of Processing Parameters on Flocculation of Picochlorum oklahomensis

The flocculation process is commonly used to separate suspended solids from water. The microalgae strain, Picochlorum oklahomensis (PO), was investigated for its flocculation characteristics. Efficiencies of biopolymer addition, pH adjustment and electroflocculation for biomass recovery from the culture medium were examined. Flocculation efficiency of PO increased sharply above pH 11 and reached 97 % at pH 13. Chitosan was more effective in flocculating PO cells than sodium alginate and cationic starch. A generalized linear mixed model using a beta distribution for response was utilized for optimization of the chitosan flocculation process variables. Biomass: chitosan ratio, pH and settling time (ST) were the independent variables. There were significant 3-way interactions among the variables. The highest PO flocculation efficiency, 98.4 %, was obtained at biomass: chitosan ratio of 2.78, pH 9 and ST of 12 h. The electroflocculation efficiency improved with increasing current, operation time (OT) and ST. The highest electroflocculation efficiency, 99.74 %, was obtained under the following conditions; 0.8 A (ampere) and 15 min and 12 h, OT and ST, respectively. This study demonstrated that pH adjustment, chitosan addition and electroflocculation were all technically viable methods to flocculate PO cells. However, selection of the most suitable technique and the optimum treatment conditions needs to be based not only on the application of algal biomass, but also on an economic feasibility study.     

Clarification of suspensions by colloidal gas aphrons

Colloidal gas aphrons (CGAs), generated from dilute solutions of four surfactants, were used to clarify palm oil mill effluent (POME), suspensions of microalgae and suspensions of three inorganic minerals. In POME and the algal suspensions, each CGA was most effective at a pH value close to the pK value of the surfactant concerned. This effect was not tested in the inorganic suspensions. The efficiency of air utilization was directly related to the concentration of solids in the suspensions, the size, density and nature of the solids having secondary effects. Comparison with data in the literature led to a general correlation embracing a variety of suspensions and flotation systems. Shedding of collected material from the foam layer was also a direct function of solids concentration. CGAs offer advantages over other systems of air-assisted flotation in relation to the requirements for equipment and to the management of process operations.     

Simultaneous Removal of Algae and Their Secondary Algal Metabolites from Water by Hybrid System of DAF and PAC Adsorption

Abstract

The feasibility of a hybrid system consisting of powdered activated carbon (PAC) adsorption and dissolved air flotation (DAF) processes was examined for the simultaneous removal of algae (anabaena and mycrocystis) and their secondary algal metabolites (2‐methylisoboneol and geosmin). Before studying the hybrid system, adsorption equilibrium and kinetics of organics (2‐methylisoboneol and geosmin) produced from algae on three powdered activated carbons (wood‐based, coal‐based, coconut‐based) were studied. The flotation efficiency of algae and PAC in DAF process was evaluated with zeta potential measurements. Interestingly, we found that the agglomerate of bubble and PAC particle can be successfully floated by DAF. In addition, the simultaneous removal of algae and organics (i.e., secondary algal metabolites) dissolved in water can be achieved by using the hybrid system of adsorption/DAF processes.     

Operating and scale‐up factors for the electrolytic removal of algae from eutrophied lakewater

Electrolytic removal of algae was conducted in batch and continuous reactors to investigate operating factors affecting removal efficiency and to explore engineering relationships which could be useful for operation and scale‐up. The system integrated both electro‐flocculation and electro‐flotation mechanisms by using polyvalent metal anodes and inert metal cathodes. Batch reactor studies confirmed that high electrical input power or higher electrical current achieved higher and faster removal efficiencies. Natural liquid circulation was observed during electrolytic operation and increased with higher electrical power. However, a small degree of external mixing may be useful at lower electrical power input. Electro‐flotation alone could not achieve complete algae removal (maximum efficiency 40–50%), and showed the importance of algal floc formation for the complete removal of algae. In continuous electrolysis experiments, the ratio of the volumetric current intensity (amperes dm^?3) and the chlorophyll a loading (mg dm^?3 h^?1) was found to be a useful operating and scale‐up factor to balance high algal removal efficiency with minimum release of excess aluminum. This ratio was eventually found to be just the charge dose or the amount of coulombs required to remove a unit mass of chlorophyll a. The optimum charge dose was determined and used to relate the operating current and electrolysis time of a continuous process. © 2002 Society of Chemical Industry     

能源微藻无泡采收新方法及其性能

采用低密度浮珠颗粒代替气泡的无泡采收方法,高效低成本采收能源微藻. 以常见能源微藻小球藻为例,以硅硼酸钠为浮珠,比较了浮珠浮选工艺与传统气浮法的区别,通过响应面法优化了浮珠浮选工艺. 结果表明,以硅硼酸钠为浮珠的无泡采收效果较理想,浮珠颗粒粒径、浓度和搅拌速率对采收率影响显著,颗粒直径56 ?m、浓度0.546 g/L、搅拌速率133 r/min的条件下采收率最好,达83.7%.     

微藻采收技术的进展与展望

从微藻培养液的特性出发,总结了目前微藻采收工艺中预处理和富集分离阶段的各种方法,包括预氧化、化学絮凝、物理预处理、沉降、过滤、离心、泡载和气浮等. 已有研究结果表明,经预氧化处理后,细胞分泌胞外产物,有利于絮凝沉降,但药剂过量会引起细胞损伤甚至消亡;化学絮凝和物理处理可以大大提高后续富集分离的效率. 由于微藻培养液浓度低、粒度小,传统的沉降、过滤、离心等方法用于微藻的采收都存在效率低、成本高的限制,而气浮法适用于低浓度悬浮体系的富集分离,是微藻采收可行的技术途径之一.     

能源微藻采收技术研究进展

能源微藻由于生长周期短、油脂含量高、可再生、低污染等优点,被认为是未来最有潜力替代化石能源的生物质能源。但是,目前能源微藻生产成本（尤其是在采收环节）过高,阻碍了其产业化进程。本文综述了国内、外能源微藻的采收方法,对絮凝、离心、过滤、气浮等传统方法的作用机理和采收效率进行了比较：絮凝法适用广,离心法效率高;过滤法处理个体大的藻类较为经济;气浮法工艺简单、能耗低。同时,阐述了能源微藻采收的新方法——磁选法、正向渗透技术、真空气举、微生物共生法等,其中,磁选法回收率高,正向渗透技术低污染,真空气举能耗低,微生物共生法可与传统方法相结合,减少化学絮凝药剂的使用。最后,指出了能源微藻采收过程中存在的问题以及今后的发展方向：可通过多种方法相结合来降低采收成本,以期为能源微藻早日实现产业化提供参考。     

Removal of Resin from Mechanical Pulps by Selective Flotation: Mechanisms of Resin Flotation and Yield Loss of Fibers

Abstract

The amount of wood resin in mechanical pulp suspensions could be decreased using a selective flotation process. In selective flotation air‐bubbles are dispersed into low consistency pulp suspensions mechanically by an impeller or by injectors. Resin particles attach to the air‐bubbles and are lifted to the top of the pulp suspension from where they are removed, along with the flotation froth. The very small size of the resin particles (average diameter <1.0 micron) suggests that they are driven toward the air‐bubbles mainly by Brownian diffusion and that attachment of the resin particles to the air‐bubbles takes place through colloidal interactions. The resin flotation followed approximate first‐order kinetics. The mechanism of yield loss of fibers was entrainment, whereby they were hydraulically transported into the froth along with the water.     

Preparation and characterization of poly(vinyl alcohol) biocomposites with microalgae ash

Gasification of microalgae feedstock generates mineral ash. In this work, raw ash is produced from lipid‐extracted algal biomass of the Nannochloropsis salina strain. Prior to using it as filler for composite fabrication with poly(vinyl alcohol), raw ash (RASH) is activated with NaOH and surface modified with (3‐aminopropyl)triethoxysilane. Surface modification of activated ash (PASH) significantly improves interfacial interaction between surface‐modified ash (GASH) and polymer matrix. Higher ultimate tensile strength of PVA/GASH composites is recorded, compared with PVA/RASH and PVA/PASH. Young's modulus of biocomposites appears to increase proportionally to loading of the fillers. Thermal properties of polymeric materials of PVA with these ashes are stable. This is the first report to demonstrate the utilization of microalgal ash, the leftover after completed gasification of algal biomass, as an efficient filler for production of value‐added polymeric materials. It is proposed that microalgal ash is capable of improving the economic feasibility of microalgae‐based biorefinery. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43599.     

Efficient separation of (R)‐(‐)‐mandelic acid biosynthesized from (R,S)‐mandelonitrile by nitrilase using ion‐exchange process

BACKGROUND: (R)‐(‐)‐Mandelic acid (R‐MA) is an important intermediate and chiral regent with broad uses. An efficient method for the separation of R‐MA from the bioreaction mixture with high yield is of great importance, thus, the main objective of this work is to investigate the recovery of R‐MA using an ion‐exchange process. RESULTS: The equilibrium isotherms for the separation of R‐MA by resin HZ202 were obtained in the pH range 5.0–9.0 and temperature range 25–35 °C. The equilibrium data are well fitted by the Langmuir isotherm. Batch kinetic experiments showed that the mobility of R‐MA^? in solution was rapid and the R‐MA^?/OH^? ion‐exchange process reached equilibrium after about 60 min. Adsorption kinetics were analyzed by a linear driving force mass‐transfer model, yielding good prediction of the kinetic behavior. In fixed bed column experiments, the breakthrough curves of R‐MA from the solution on resin HZ202 were determined at different flow rates and R‐MA was eluted with different concentrations of HCl. A favorable breakthrough curve and optimal eluant concentration were obtained. The results were used for the separation of R‐MA biosynthesized from (R,S)‐mandelonitrile with nitrilase, and separation was successfully achieved with above 90% recovery yield. CONCLUSION: Resin HZ202 presents favorable behavior for the recovery of R‐MA, in terms of capacity, kinetics, affinity, and susceptibility to regeneration. The results of this study provide an efficient method for R‐MA recovery from bioreaction mixture and could potentially be used in industry. Copyright © 2010 Society of Chemical Industry     

Lipid and Biomass Distribution and Recovery from Two Microalgae by Aqueous and Alcohol Processing

The objective of this study was to determine lipid and biomass distribution during aqueous and alcohol processing of oleaginous microalgae, with the intention of fully extracting lipid from the dewatered cell paste. Two species, Nannochloropsis and Schizochytrium, were used. It is shown that most of the total lipid, 73% for Nannochloropsis and 87% for Schizochytrium, was held by the cell solids obtained by centrifugation during the aqueous process, justifying the need to develop a more effective lipid-extraction method. Use of ethanol at elevated temperature enabled efficient extraction of lipid from the cell mass and at the same time improved biomass precipitation and recovery in the solid or cake fraction. More than 68 and 95% of total lipid was recovered on a 50-g scale (as-is paste basis) from Nannochloropsis and Schizochytrium, respectively. Approximately 65% of the biomass was recovered in the solid fraction for both algae from the alcohol process, compared with the much lower biomass recovery, 38 and 16% for Nannochloropsis and Schizochytrium by the aqueous process. Therefore, oil and biomass fractionation by use of pure water is far less effective than fractionation by use of alcohol, and the alcohol process has great promise in algal oil recovery.     

Optimization of hollow fiber membrane cleaning process for microalgae harvest

Biodiesel made from microalgae could be a possible replacement for fossil fuel. The separation of microalgae from their culture medium is a critical process in biotechnology. Membrane techniques seem to be effective, reliable, and safe, despite some limitations such as the progressive fouling and the associated decline in flux. Microalgae harvested from membranes have less chemical contamination and therefore membrane systems are more environmentally friendly than other harvesting techniques. We used a microfiltration (MF) system to concentrate the microalgae Tetraselmis sp. KCTC12236BP. Two cleaning processes, forward flushing and backwashing, were assessed to minimize the fouling required to concentrate the microalgae Tetraselmis sp. KCTC12236BP. It was concluded that backwashing was a more effective method than forward flushing. Furthermore, higher frequencies of backwashing greatly improved the membrane flux. However, even though the optimum cleaning frequency for maintaining high flux was every 5 min, from the perspective of microalgae concentrate and energy consumption, better results were obtained when backwashing was applied every 10 min. Under these conditions the microalgae culture reached 90% concentration in 60 min.     

Formation and Microstructures of Whipped Oils Composed of Vegetable Oils and High-Melting Fat Crystals

This paper reports the experimental results of processes used for the formation of whipped oils composed of vegetable oils (salad oil) and high‐melting fat crystals [fully hydrogenated rapeseed oil rich in behenic acid (FHR‐B)]. No emulsifier was added to form this whipped oil. Microprobe FT‐IR spectroscopy, synchrotron radiation microbeam X‐ray diffraction (SR‐μ‐XRD), polarized optical microscopy, and differential scanning calorimetry (DSC) were employed to observe fine fat crystal particles of the most stable polymorph of β (β‐fat crystal), FHR‐B, and their adsorption at the air–oil surface before, during, and after the formation of the whipped oil. The results obtained revealed the following: (1) The preparation of an organogel composed of salad oil and small fibrous β‐fat crystals using a special tempering procedure was a prerequisite for forming whipped oil. (2) The β‐fat crystals were adsorbed at the air–oil surface to encapsulate the air bubbles during the formation process of whipped oil. (3) The values of overrun of the whipped oil reached >200 % after an aeration time of 30 min at 20 °C. (4) The SR‐μ‐XRD experiments demonstrated that the lamellar planes of the β‐fat crystals near the air–oil surface were arranged almost parallel to the air–oil surface plane. The present study provides the first evidence that tiny fat crystal particles may cause aeration in liquid oils without the addition of other whip‐assisting substances such as emulsifier crystals.     

Subcritical co‐solvents extraction of lipid from wet microalgae pastes of Nannochloropsis sp.

In this paper subcritical co‐solvents extraction (SCE) of algal lipid from wet pastes of Nannochloropsis sp. is examined. The influences of five operating parameters including the ratio between ethanol to hexane, the ratio of mixed solvents to algal biomass (dry weight), extraction temperature, pressure, and time were investigated. The determined optimum extraction conditions were 3:1 (hexane to ethanol ratio), 10:1 ratio (co‐solvents to microalgae (dry weight) ratio), 90°C, 1.4 MPa, and 50 min, which could produce 88% recovery rate of the total lipids. In addition, electron micrographs of transmission electron microscopy (TEM) and scanning electron microscopy (SEM) were conducted to show that the algal cell presented shrunken, collapsed with some wrinkles and microholes after SCE extraction. The main composition of total lipids extracted under the optimum conditions was TAG which represented more than 80%. And the fatty acid profile of triglycerides revealed that C16:0 (35.67 ± 0.2%), C18:1 (26.84 ± 0.044%) and C16:1 (25.96 ± 0.011%) were dominant. Practical applications: The reported method could save energy consumption significantly through avoiding deep dewatering (for example drying). The composition of the extracted lipid is suitable for the production of high quality biodiesel.     

Evaluating Cell Disruption Strategies for Aqueous Lipid Extraction from Oleaginous Scenedesmus obliquus at High Solid Loadings

Among various renewable energy sources, the production of biofuels derived from algal lipids holds bright prospects. One of the major roadblocks in the successful commercialization of microalgal biofuels is the existing energy‐intensive lipid extraction. In the present investigation, an attempt is made to assess aqueous lipid extraction strategies from oleaginous Scenedesmus obliquus at a high solid loading of 15% (w/v). In this study, four surfactants and five enzymes are evaluated for cell disruption of S. obliquus. It is the first report citing cetyl pyridinium bromide as the most suitable cationic detergent for surfactant‐assisted extraction, with a lipid recovery as high as 31.4%. However, during the evaluation of enzyme‐based cell disruption, neutral protease emerges as the best biocatalyst resulting in a lipid recovery of ≈75%. Total lipid extraction is accomplished using a two solvent system comprising of water‐immiscible ethyl acetate, followed by chloroform addition. The study revalidates the fact that the biochemical composition of Scenedesmus sp. plays a vital role while identifying and formulating an efficient and green process for microalgal cell disruption for enhanced lipid extraction under aqueous conditions. Practical Applications: The results of the present study demonstrate that if the biochemical composition of any oleaginous algal cell wall is known, aqueous enzymatic lipid extraction can be employed rather than taking up the conventional route of drying followed by Soxhlet extraction. The combination of using the cheap sources of enzymes and water‐immiscible green solvents like ethyl acetate can be lucrative downstream procedures for the lipid recovery from wet algal biomass when compared to traditional procedures.     

Removal of nutrients from hydroponic greenhouse effluent by alkali precipitation and algae cultivation method

BACKGROUND: Hydroponic greenhouse effluent has high concentrations of total phosphorus (30–100 mg PO₄‐P L^?1) and nitrates (200–300 mg NO₃‐N L^?1). Current technologies for effluent treatment have limitations of performance and high maintenance costs. The goals of this study were to investigate strategies which combine alkali treatment and microalgae cultivation for removal of nutrients from hydroponic greenhouse effluent. RESULTS: Treatment with strong alkali was found to effectively remove 97% of total phophorous especially in the form of phosphate, without affecting the nitrate ion concentration in the greenhouse effluent. After alkali treatment, marine algae Dunaliella salina (UTEX 1644) cultivation on treated hydroponic effluent (pH 7.5) showed > 80% decrease in nitrate content in the effluent within 4 days of cultivation. In the same period, the carotene content of the micro‐algal system was in the range 0.5 ± 0.02 µg mg^?1 (dry cell weight) which was 1.5 times higher than in the control. CONCLUSION: This study demonstrated that combination of a conventional alkali precipitation method with a microalgae treatment system is a highly efficient approach for the removal of excess nutrients from hydroponic greenhouse effluent in a short treatment time. The microalgae can provide a source of value in the form of carotene. © 2012 Society of Chemical Industry     

Stable ‘Floating' Air Diffusion Biocathode Based on Direct Electron Transfer Reactions Between Carbon Particles and High Redox Potential Laccase

We report on the assembly and characterisation of a high potential, stable, mediator‐less and cofactor free biocathode based on a fungal laccase (Lc), adsorbed on highly dispersed carbonaceous materials. First, the stability and activity of Trametes hirsuta Lc immobilised on different carbon particles were studied and compared to the solubilised enzyme. Based on the experimental results and a literature analysis, the carbonaceous material BM‐4 was chosen to design efficient and stable biocatalysts for the production of a ‘floating' air diffusion Lc‐based biocathode. Voltammetric characteristics and operational stability of the biocathode were investigated. The current density of oxygen reduction at the motionless biocathode in a quiet, air saturated citrate buffer (100 mM, pH 4.5, 23 °C) reached values as high as 0.3 mA cm^–2 already at 0.7 V versus NHE. The operational stability of the biocathode depended on the current density of the device. For example, at low current density (20 μA cm^–2), the biocathode lost only 5× of its initial power after 1 month of continuous operation. However, when the device was polarised at 150 mV it lost more than 32× of its initial power in just 10 min. We also found that co‐immobilisation of Lc and peroxidase on highly dispersed carbon materials could protect the biocatalyst from rapid inactivation by hydrogen peroxide produced during electrocatalytic reactions at high‐current densities.     

A New Hybrid Flotation—Microfiltration Cell

Abstract

The investigated hybrid cell combines the advantages of both flotation and membrane separation, while overcoming their limitations and having as an outcome clean water from a industrial wastewater. Hence, metals recovery from dilute aqueous solutions was a promising application of this innovative process, further to solid/liquid separation. The specific objective was to apply the process for the efficient separation of effluents containing metals (here, zinc). The main examined parameters were the following: the metal initial concentration, flotation surfactant applied, and air flowrate. The successful contribution of precipitate flotation was highlighted, while the observed metal removals were of the order of ～100%.     

Removal of Organophosphorus Pesticides from Aqueous Solution by Using Adsorptive Bubble Separation Techniques

Abstract

Two organophosphorus pesticides, ddvp (phosphoric acid 2,2-dichlorovinyl dimethyl ester) and phorate (phosphorodithioic acid o,o-diethyl s-[(ethylthio)methyl] ester) were removed from aqueous solution by three adsorptive bubble separation techniques: air stripping, solvent sublation, and adsorbing colloid flotation. The effects of pH, flow rate, surfactant, ethanol, ionic strength, and coprecipitant concentration on the efficiency of pesticide removal were studied. Over 97% of phorate was removed in 30 min by solvent sublation, and 90% of phorate was removed in 10 min by adsorbing colloid flotation with Fe(OH)₃, floc. The separations of ddvp by these techniques were not effective.     

The influence of frother types and concentrations on fine particles’ entrainment using column flotation

Entrainment which is the characteristic feature of fine particles is closely related to water recovery. It is based on the changes depending on the establishment of linear relationship between water recovery and solid recovery. This paper deals with the investigation of the effect of frother types and concentrations on fine particles’ entrainment using column flotation. Entrainment of fine particle using a mixture of artificial ore (celestite:calcite; 1:1) was investigated in column flotation. In a two-phase system (water/air), the variation of bubble diameters and gas hold-up with a superficial air rates using different frother types and concentrations were tested. The results showed that the frother types and concentrations had significant effect on the grade and recovery, superficial air rate, gas hold-up and fine gangue entrainment. Entrainment factors for frother types and concentrations were compared in flotation column. Kirjaveinen^[11] model was used for describing the specific entrained factor (P_i) of hydrophilic particles. It has been found that Kirjaveinen model supports the results of this study.