Highest Flocculation Efficiency Research Articles

A step towards more eco-friendly and efficient microalgal harvesting: Inducing flocculation in the non-naturally flocculating strain Chlorella vulgaris (13-1) without chemical additives

Flocculation is often regarded as a cost-effective and reliable method for microalgal harvesting. However, the traditional method often requires the addition of chemical agents to induce flocculation. This carries certain disadvantages including the chemical contamination of the biomass and the subsequent need to remove the flocculants from the medium. To address these issues, this study aimed to induce flocculation in a naturally non-flocculating strain (Chlorella vulgaris 13-1) without resorting to chemical additives, with the ultimate goal of increasing harvesting efficiency. Scanning electron microscopy showed that Scotelliopsis reticulata UFA-2, a naturally flocculating strain, produces extracellular polymeric substances (EPS) whereas 13-1 does not. As a result, two methods were used to induce flocculation in 13-1: co-cultivation of UFA-2 and 13-1, and insertion of EPS produced by UFA-2 into the growth medium of 13-1. The co-cultivation of 13-1 with UFA-2 significantly increased the flocculation efficiency compared to that of 13-1 alone (30 % higher flocculation efficiency after one hour of settling and 52 % higher after three hours of settling). Alternatively, the insertion of dry tightly-bound (TB) UFA-2 EPS into 13-1 cultures also improved flocculation efficiency (by 19 % compared to the control), while addition of soluble or loosely-bound (LB) EPS was less efficient (less than 1 % and 10 %, respectively). FTIR results showed that the composition of TB-EPS was different to that of LB and soluble EPS. TB-EPS contained higher proportions of proteins and different types of carbohydrates, potentially contributing to its increased efficacy in inducing flocculation in microalgae.

Synthesizing cationic polymers and tuning their properties for microalgae harvesting

This study reports a facile technique to synthesize and tune the cationic polymer, poly(3-acrylamidopropyl)trimethylammonium chloride (PAPTAC), in terms of molecular weight and surface change for harvesting three microalgae species (Scenedesmus sp., P.purpureum, and C. vulgaris). The PAPTAC polymer was synthesised by UV-induced free-radical polymerisation. Polymer tuning was demonstrated by regulating the monomer concentration (60 to 360 mg/mL) and UV power (36 and 60 W) for polymerisation. The obtained PAPTAC polymer was evaluated for harvesting three different microalgae species and compared to a commercially available polymer. The highest flocculation efficiency for Scenedesmus sp. and P. purpureum was observed at a dosage of 25 mg-polymer/g of dry biomass by using PAPTAC-90, resulting in higher flocculation efficiency than the commercial polymer. Results in this study show evidence of effective neutralisation of the negative charge surface of microalgae cells by the produced cationic PAPTAC polymer and polymer bridging for effective flocculation. The obtained PAPTAC polymer was less effective for harvesting C. vulgaris, possibly due to other factors such as cell morphology and composition of extracellular polymeric substances of at the cell membrane that may also influence harvesting performance.

Usage of Moringa oleifera residual seeds promotes efficient flocculation of Tetradesmus dimorphus biomass.

Bio-flocculation is a sustainable low-cost harvesting technique for microalgae biomass production; however, it is generally less efficient than chemical flocculants. This study aims to investigate the efficiency of Moringa oleifera seeds as a bio-flocculant for harvesting Tetradesmus dimorphus biomass. Four extracts from integral and residual (seeds without lipids) biomass of M. oleifera seeds using salt or aqueous solutions were used at four concentrations (100, 200, 300, and 400 ppm). Flocculation efficiency (FE) increased as the pH decreased. The addition of the extracts reduced the pH of the cultures, dispensing pH adjustment after dosing the flocculating agent. Salt extracts exhibited higher flocculation efficiency than aqueous extracts. The highest flocculation efficiency (~ 98%) was obtained using a salt extract of residual biomass of seeds in any concentration varying from 100 to 400 ppm. The predicted values obtained from a data modeling using response surface methodology approached the real values (r2 = 0.9382), resulting in an adequate optimization of the flocculant concentration of ~ 335 ppm and pH 5.6 for a predicted FE of ~ 106%. The findings of the present study confirmed that the salt extract from residual biomass of M. oleifera seeds is an effective bio-flocculant for T. dimorphus biomass harvesting.

Carbon-induced effective lipid accumulation and self-flocculation for biofuel production of Tetradesmus obliquus FACHB-12

Utilizing rich organic matter in wastewater for microalgae cultivation is an attractive strategy to solve the high-cost issue in microalgae biodiesel production. In this study, common carbon sources in wastewater were used as nutrients to explore their effects on biomass accumulation and lipid production of Tetradesmus obliquus FACHB-12. The highest carbon fixation (1.2 g C·L−1) and biomass accumulation (1.99 g L−1) was achieved using glucose as the only carbon source for the microalgae cultivation in the designed system. In comparison, the high flocculation efficiency (89.63%) with the addition of glycerol achieved the recovery of lipids and starch at 0.36 g L−1 and 0.023 g L−1, respectively. In addition, results revealed that microalgae cells cultured with glycerol had the highest extracellular polymers fluorescence intensity of 2.84*104 R.U.·g−1. This study provides insights of common carbon sources in wastewater for culturing microalgae, which leads to the potential reduction in microalgae cultivation cost and primary dewatering cost in practice.

Outdoor phycoremediation and biomass harvesting optimization of microalgae Botryococcus sp. cultivated in food processing wastewater using an enclosed photobioreactor

Microalgae cultivation is well known as a sustainable method for eco-friendly wastewater phycoremediation and valuable biomass production. This study investigates the feasibility and kinetic removal of organic compounds and nutrients from food processing wastewater (FPW) using Botryococcus sp. in an enclosed photobioreactor. Simultaneously, response surface methodology (RSM) via face-centered central composite design (FCCCD) was applied to optimize the effects of alum and chitosan dosage and pH sensitivity on flocculation efficiency. The maximum growth rate of Botryococcus sp. cultivated in FPW was 1.83 mg day−1with the highest removal of chemical oxygen demand (COD), total organic carbon (TOC), and total phosphorus (TP) after 12 days of phycoremediation of 96.1%, 87.2%, and 35.4%, respectively. A second-order polynomial function fits well with the experimental results. Both coagulant dosage and pH significantly (p < 0.05) affect the flocculation efficiency of Botryococcus sp. biomass cultivated in FPW. The highest flocculation efficiency (92.4%) was obtained at a dosage of 166 mg L−1and pH 12 for alum coagulant, while 94.9% flocculation efficiency was achieved with optimum chitosan dosage and pH of 30 mg L−1and 5.54, respectively. In general, Botryococcus sp. shows a great removal efficiency of FPW contamination, whereas RSM provides excellent analysis for biomass harvesting optimization using a flocculation technique.

Preparation of carboxymethylated lignin-based multifunctional flocculant and its application for copper-containing wastewater

High efficiency lignin-grafted cationic polyacrylamide multifunctional flocculant (CL-CPAs) was synthesized via “grafting to” strategy using carboxymethylated lignin (CL), acrylamide (AM) and methylacryloyloxyethyltrimethyl ammonium chloride (DMC) as raw materials. The synthesized CL-CPAs showed high flocculation efficiency. Only a small dosage between 3.6 and 4.2 mg‧L−1 of CL-CPAs and a short flocculation time of 1–2 min were needed for sedimentation of kaolin suspension. Meanwhile, the carboxyl groups on the modified lignin endowed CL-CPAs with good copper ion capture function through complexation and electrostatic interaction. In addition, simultaneous flocculation of kaolin suspension and removal of copper ion was achieved for CL-CPAs attributing to the charge neutralization, bridging, and electrostatic complexation. The synthesized carboxymethylated lignin-based flocculants are cheap, environmentally friendly and technically feasible, showing broad prospects in wastewater treatment.

Autoflocculation of microalgae, via magnesium hydroxide precipitation, in a high rate algal pond treating municipal wastewater in the South Australian Riverland

High rate algal ponds (HRAP) are considered a promising system for coupling wastewater treatment with the growth of microalgae biomass. However, the absence of a cost-effective harvesting method limits this application. In this study, in situ autoflocculation, via magnesium hydroxide precipitation, was assessed in a HRAP containing 33 m3 of HRAP treated municipal wastewater which had a total suspended solids concentration of 115.00 mg L−1. Autoflocculation was induced using MgCl2.6H2O to increase the magnesium concentration of the wastewater to 82.63 ± 0.09 mg L−1, followed by the addition of 182 mg L−1 of slaked lime to increase the pH to 11. A high flocculation efficiency, determined by the reduction in turbidity, of 91.52 ± 0.57% was achieved with good removal of total suspended solids, 84.93 ± 1.00%. Excellent nutrient removal, 91.10 ± 0.14% of total phosphorus, and pathogen removal, a 3 log10 reduction in E. coli MPN 100 mL−1, was also observed. Hydrochemical modelling (PHREECQC-2) identified improvements in operational conditions to reduce cost. Autoflocculation, via magnesium hydroxide precipitation, was shown to be a promising method for harvesting microalgae and nutrients.

Enhancement of Lipid Productivity and Self-flocculation by Cocultivating Monoraphidium sp. FXY-10 and Heveochlorella sp. Yu Under Mixotrophic Mode.

To maintain high microalgae lipid productivity and flocculation efficiency simultaneously and reduce the production cost of microalgae lipids, Monoraphidium sp. FXY-10 with high lipid-producing capacity and Heveochlorella sp. Yu with strong self-flocculation ability were cocultivated and studied. Cocultivated microalgae lipid productivity and flocculation efficiency were increased to 203.8 mg L-1 day-1 and 70.55%, respectively, which is potentially related to the excessive competitive depletion of nitrogen sources and the upregulation of correlative key genes in lipid anabolic metabolism. Under cocultivation conditions, microalgae cells could enter the stationary phase 2 days earlier than that under monocultivation conditions, thus reducing the culture time. Relative expression of the accD, ME, and rbcL genes was upregulated to varying degrees, and the enzyme activities of ACCase, ME, and RuBisCO were also significantly increased compared with those in monocultivation. Moreover, fatty acid composition showed that microalgae lipids in cocultivation exhibited potential as a feedstock for biodiesel.

Assessing the effects of operating parameters on flocculation of Chlorella vulgaris using bioflocculants extracted from miscellaneous waste biomass

Harvesting of microalgae is one of the main challenges in the production of biodiesel due to the small cell size of microalgae cells. Chemical flocculants have been generally used in the harvesting of microalgae, but they are harmful to the environment and relatively costly. Therefore, the utilization of waste biomass in producing bioflocculants is the current research niche to introduce environmental-friendly harvesting method and to minimize the cost of biodiesel production. Thus, in the current work, flocculation Chlorella vulgaris using mild acid-extracted bioflocculants from miscellaneous waste biomass (cockle shell, peanut shell and banana peel) were conducted by varying the pH values, the dosage of bioflocculants and temperatures. Cockle shell bioflocculant demonstrated the best flocculation performance, with highest flocculation efficiency of 85.2% compared to the peanut shell bioflocculant with flocculation efficiency of 37% and banana peel bioflocculant with flocculation efficiency of 16.3%. The optimum flocculation conditions for cockle shell bioflocculant were determined as follow: pH 9, bioflocculant dosage of 140mg/L and temperature of 30oC. The findings herein presented practical applicability of bioflocculants extracted from cockle shell for safe, rapid and inexpensive microalgae harvesting.

Harvesting Nannochloropsis oculata by Chitosan and AlCl3-Induced Flocculation: Effects of Microalgal Condition on Flocculation Performance

Flocculation showed the potential for harvesting microalgae at a low cost. The inorganic flocculant (AlCl3) and organic flocculant (chitosan) are two representative and common flocculants, which were suited for different conditions (pH, salinity, and cell density). To investigate the effects of the three factors on the flocculation performance of the two flocculants, especially for the interaction effects among these factors, single-factor experiments and response surface methodology (RSM) were conducted. The results indicated that AlCl3 performed better under alkaline conditions, whereas chitosan showed better performance at acidic pH. Salinity had little influence on the flocculation efficiency (FE) of AlCl3. By contrast, increasing salinity reduced the FE of chitosan, especially above 8.4 g/L. As cell density increased, the optimal dosage of AlCl3 increased to a constant ~ 26 g/L. In contrast, the optimal dosage of chitosan continuously increased within the studied range. Also, RSM revealed significant interaction effects of [salinity][cell density] for AlCl3, due to which AlCl3 showed a good flocculation performance under either high cell density or high salinity conditions but poor with both high together. Significant interaction effects of [salinity][cell density] for chitosan was observed, and one of the two factors hence alleviated the negative influence from the other. Considering their performance under the different condition and the interaction effects, dual flocculation with AlCl3 + chitosan on multiplex conditions was evaluated, and the results indicated that higher FE with wider applicability could be achieved with lower dosages of the dual flocculant compared with utilization of the two flocculants individually under most of the conditions.

A comprehensive analysis of an effective flocculation method for high quality microalgal biomass harvesting

Flocculation is a low-cost harvesting technique for microalgae biomass production, but flocculation efficiency is species dependent. In this study, we investigated the efficacy of two synthetic (polyacrylamide) and one natural (chitosan) flocculants against three algal species: the cyanobacterium Synechocystis sp., the freshwater Chlorella vulgaris, and the marine Phaeodactylum tricornutum at laboratory and pilot scales to evaluate harvesting efficiency, biomass integrity and media recycling. Growth phase affected the harvesting efficiency of the eukaryotic microalgae. The flocculation was optimal at stationary phase with high flocculation efficiency achieved using polyacrylamides at 24–36 mg/g dry weight. The effect of the flocculants on the harvested biomass was investigated. The flocculated Synechocystis sp. showed a higher proportion of compromised cells compared to C. vulgaris and P. tricornutum likely due to differences in cell walls composition. Compromised cells could lead to the release of valuable products into the surrounding growth media during flocculation. The residual culture media was recycled once with no impact on cell growth for all treatments and algal species. The flocculation technique was demonstrated at pilot-scale using 350 L microalgal suspension, showing an efficiency of 82–90% at a polyacrylamide dosage of 6.5–10 mg/L. This efficiency and the biomass quality are comparable to the laboratory-scale results. Overall, results indicate that polyacrylamide flocculants work on a wide range of species without the need for pre-treatment. The information generated in this study can contribute to making the microalgae industry more competitive.

A Novel Bioflocculant from Raoultella planticola Enhances Removal of Copper Ions from Water

Copper is one of the most toxic heavy metals. In this work, a sampling survey of copper ions in the water of Songhua River flowing through the chemical and living areas of Jilin City was studied. A new bioflocculant from Raoultella planticola was obtained. The investigation of Songhua River flowing through Jilin City shows that the copper concentration is between 0.07 ppb and 0.16 ppb. The bioflocculant supporting graphite oxide (GO) as a bioflocculant inducer used in this study has been utilized in treatment of copper ions in water. GO and bioflocculant infrared radiation (IR) spectrum and zeta potential were studied. Flocculational conditions of copper ion (0.2 ppm) were modeled and optimized using RSM (response surface methodology). Our data showed that flocculation efficiency was over 80%. Significant influencing factors and variables were pH, flocculation time, bioflocculant dosage, and GO inducer which had major impact effects on flocculation efficiency. The highest flocculation efficiency which is 86.01% was achieved at pH=5, at 1.62 h and 13.11 mg bioflocculant with 13.11 mg GO as an inducer. However, temperature (A) and GO inducer were significant impact factors on the flocculation efficiency.

Bioflocculation technique for microalgal harvesting and wastewater nutrient recovery

Fungal assist microalgal cultivation is getting substantial considerations due to the highly efficiency of bioflocculation process without requirements of added chemicals and little bit energy input. So, Fungi pelletization-assisted microalgal cultivation were applied for improving algal harvesting process and nutrient recovery as step wise for wastewater treatment. Two strains of microalgae (Nannochloropsis salina and Chlorella salina) and three species of fungi (Penicillium chrysogenum, Aspergillus niger and Aspergillus fumigatus) were used to evaluate the effect of fungi–algae pelletization process on wastewater recovery. After 48 hour of cultivation, the highest flocculation efficiency (98.9%) was recorded by A. fumigatus assist C. salina, while the lowest percentage (85.9%) recorded by A. niger assist N. Salina. The highest nutrient removal percentage was for nitrite by A. niger assist C. salina /tap water (98.4%) followed by phosphate A. fumigates assist N. salina/sea and tap water (90.9%), then ammonia by A. fumigates assist N. salina /seawater (89.5%).. This study concluded that the bioflocculation technique is a highly promising compared to traditional algal harvesting techniques and other biological wastewater treatment methods.

Using a novel polysaccharide BM2 produced by Bacillus megaterium strain PL8 as an efficient bioflocculant for wastewater treatment

In this study, the purification and characterization of a novel polysaccharide-based bioflocculant BM2 produced by a bacterium Bacillus megaterium strain PL8 with self-flocculating property were investigated. The results showed that BM2 was an acidic polysaccharide composed of Gal, GalUA, Glc, GlcUA and Man at a molar ratio of 45.1: 33.8:9.3:9.2:2.4, respectively. The molecular weight of BM2 was 4.55 × 106 Da. BM2 had high flocculation efficiencies across a wide pH ranged from 4 to 11 and a wide temperature ranged from 20 to 100 °C towards kaolin clay. BM2 was a cation-independent bioflocculant which could achieve high flocculation activity without the addition of other cations. Adsorption bridging was the main mechanism in the flocculation process of BM2 towards kaolin clay. The BM2 also displayed a high removal efficiency in terms of Congo red (88.14%) and Pb2+ ions (82.64%). These results suggested that BM2 had a great potential as an efficient bioflocculant candidate in wastewater treatment.

Simultaneous nitriles degradation and bioflocculant production by immobilized K. oxytoca strain in a continuous flow reactor

High cost is one of the limiting factors in the industrial production of bioflocculant. Simultaneous preparation of bioflocculant from the contaminants in wastewater was considered as a potential approach to reduce the production cost. In this study, butyronitrile and succinonitrile were verified as sole nitrogen sources for the growth of strain K. oxytoca GS-4-08 in batch experiments. Moreover, more than 90 % of the mixed nitriles could be degraded in a continuous flow reactor, and the bioflocculant could be prepared simultaneously in the effluent. All the as-prepared bioflocculants exhibited high flocculation efficiencies of over 90 % toward Kaolin solution. FTIR and XPS results further unveiled that, the bioflocculant samples with abundance of carboxyl, amine and hydroxyl groups may play an important role on adsorption of Pd2+. The adsorption process could be well simulated by Freundlich model, and the Kf values were as high as 452.8 mg1−1/n l1/n g-1. The results obtained in this study not only confirm the technical feasibility for preparation of bioflocculant from various single nitrile and/or mixed nitriles, but also promise its economic feasibility.

Valorization of glycerol/ethanol-rich wastewater to bioflocculants: recovery, properties, and performance.

Microbial extracellular polymeric substances (EPS) were produced in two membrane bioreactors, each separately treating fresh and saline synthetic wastewater (consisting of glycerol and ethanol), with the purpose of applying them as sustainable bioflocculants. The reactors were operated under nitrogen-rich (COD/N ratios of 5 and 20) and limited (COD/N ratios of 60 and 100) conditions. Under both conditions, high COD removal efficiencies of 87-96% were achieved. However, nitrogen limitation enhanced EPS production, particularly the polysaccharide fraction. The maximum EPS recovery (g EPS-COD/g CODinfluent) from the fresh wastewater was 54% and 36% recovery was obtained from the saline (30 g NaCl/L) wastewater. The biopolymers had molecular weights up to 2.1 MDa and anionic charge densities of 2.3-4.7 meq/g at pH 7. Using kaolin clay suspensions, high flocculation efficiencies of 85-92% turbidity removal were achieved at EPS dosages below 0.5 mg/g clay. Interestingly, EPS produced under saline conditions proved to be better flocculants in a saline environment than the corresponding freshwater EPS in the same environment. The results demonstrate the potential of glycerol/ethanol-rich wastewater, namely biodiesel/ethanol industrial wastewater, as suitable substrates to produce EPS as effective bioflocculants.

Amino-Acid-Modified-Cashew Gum Flocculant: Synthesis, Characterization, and Application

Amphoteric poly(O-methacryloyl-l-serine)-grafted cashew gum (CG-g-P(SerMA)) flocculant was obtained with highly efficient in separation and sequential recovery of kaolin particles from aqueous suspension. The highest flocculation efficiency was achieved with a flocculant synthesized using an O-methacryloyl-l-serine:cashew gum molar ratio of 3:1. The CG-g-P(SerMA) at a dosage of 3.0 mg L−1 resulted in a flocculation efficiency of more than 90% within 20 min for kaolin suspension. The efficiency, in standard experiments, the flocculant CG-g-P(SerMA) was superior to cashew gum and polyacrylamide-based commercial flocculants. The flocculation mechanism involves electrostatic interactions between the negatively charged surface of the kaolin and the protonated amino groups of the flocculant under acidic conditions. These results provide new opportunities and challenges for understanding and improving the removal of impurities present in water and wastewater.

Potential use of flocculating oleaginous yeasts for bioconversion of industrial wastes into biodiesel feedstocks

Factors affecting flocculating properties of two oleaginous yeasts, Candida tropicalis X37 and Yarrowia lipolytica TISTR 5151 were evaluated in order to simplify harvesting process and increase process productivity. Among these two yeasts, Y. lipolytica TISTR 5151 showed high flocculation efficiency (>95%) at acidic pH while C. tropicalis X37 gradually flocculated independently to pH. Both yeasts and their mixed culture grew well and accumulated high lipid content (>30%) in palm oil mill effluent added with crude glycerol at 1–2%. Interestingly, the mixed culture enhanced lipid productivity and COD removal possibly due to stabilization of pH and efficient organic carbon consumption. Y. lipolytica TISTR 5151 with appropriate inoculum size could also be used as bioflocculent for other yeasts. The fatty acid composition of yeast lipids and their prospect fuel properties indicate their potential use as biodiesel feedstocks.

Bioflocculation Activity in Harvesting System: A Biotechnology Approach for Microalgae Biomass

A study on Ankistrodesmus sp.—a freshwater green microalgae species—as a bioflocculant based on its physicochemical properties and flocculation rate has been carried out. The molecular identification via 16S rDNA showed 99% resemblance of this green microalga to the Ankistrodesmus fumigatus strain. The optimum batch culture condition for the bioflocculant production was initiated by 10% inoculum (v/v). The low-concentrated bioflocculant of 10% (v/v) is considered as thermostable with a high flocculation rate to harvest the biomass of Chlorella sp. at a pH range of 5 to 9. The source of molasses, the mixture of yeast extract were used as the optimum sources of carbon and Ammonium sulfate were used as the optimum sources of nitrogen in the growth medium. Ankistrodesmus sp. bioflocculant has a high flocculation efficiency over a wide range of pH (5–9) with a low dose requirement of 10% v/v at 25°C. Hence, it is immensely competitive to promote the economic viability of the production process. Accordingly, Ankistrodesmus sp. bioflocculant has a high potential to be applied on an industrial scale in tropical regions as it does not require additional production cost.

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.