Bio-based Flocculants Research Articles

Recent progress and perspectives of typical renewable bio-based flocculants: characteristics and application in wastewater treatment.

The research on bio-based flocculants for waste resource utilization and environmental protection has garnered significant attention. Bio-based flocculants encompass plant-based, animal-based, and microbial variants that are prepared and modified through biological, chemical, and physical methods. These flocculants possess abundant functional groups, unique structures, and distinctive characteristics. This review comprehensively discussed the removal rates of conventional pollutants and emerging pollutants by bio-based flocculants, the interaction between these flocculants and pollutants, their impact on flocculation performance in wastewater treatment, as well as their application cost. Furthermore, it described the common challenges faced by bio-based flocculants in practical applications along with various improvement strategies to address them. With their safety profile, environmental friendliness, efficiency, renewability, and wide availability from diverse sources, bio-based flocculants hold great potential for widespread use in wastewater treatment.

Nanofibrillated cationic cellulose derivatives as flocculants for domestic wastewater treatment

Natural-based coagulants have emerged as a reliable option to implement more sustainable operations and management of wastewater treatment plants. This work aims at evaluating the use of cationic nanofibrillated celluloses (cNFC) as novel bio-based flocculants to treat domestic wastewaters by the most widely employed treatment process – coagulation/flocculation. Two cNFC samples were prepared with different charge densities and tested as coagulant/flocculants using different water characteristics. The effect of cNFCs was studied by measuring the residual turbidity and dissolved organic carbon. The aggregation mechanism and kinetics of flocculation were also evaluated. Results show that cNFC can be used as an efficient flocculant to treat medium and high DOC waters since they considerably reduce turbidity (turbidity removals varied between 66.0 % and 85.7 % for the waters and cNFCs tested) without increasing dissolved organic carbon. Instead, cNFC removed dissolved organic carbon from domestic wastewaters (between 22.1 % and 65.5 % of DOC removals for the waters and cNFCs tested), which is a novel remarkable finding and a step forward in this knowledge area. High density charged cNFC revealed superior removal capacity at lower doses than the commercial coagulant FeCl3.

The preparation of gallic acid-grafted cationic chitosan as effective salt-tolerant flocculants.

In this work, gallic acid was successfully grafted onto quaternary aminated chitosan to prepare a high efficiency cationic flocculant. The mechanism of flocculation and different influencing factors were studied in detail. The prepared flocculant only needs 60 mg L-1 to achieve a 98.7% and 94.5% removal rate on methyl blue (MB) and Congo red (CR), respectively. The high removal rate (93.2%) of a CR-MB mixed dye also confirms the universality of flocculation. In addition, kaolin as a simulated suspended solid was removed at a rate of 97% in the experiment at a dosage of 3 mg L-1. A zeta potential test showed that it worked best when the potential of the flocculation system was zero; this was because an electrostatic balance was reached between the flocculant and pollutant. Importantly, the three-functional molecules can provide more possibilities to form hydrogen bonds with water molecules, which is conducive to the stretching of flocculant molecular chains in salt water. The flocculant maintained a high stability in four different salt environments and has a positive industrial application significance. Furthermore, the flocculation experiment of the actual wastewater of the printing and dyeing plant found that the dye wastewater changed obviously from turbidity to clarification, which proved the practical application potential of the flocculant. This work provides a feasible idea for the preparation of bio-based flocculants.

A rapid removal of Phaeocystis globosa from seawater by peroxymonosulfate enhanced cellulose nanocrystals coagulation

Cellulose nanocrystals (CNC) are recognized as promising bio-based flocculants for controlling harmful algal blooms (HABs). Due to the charge shielding effect in seawater and the strong mobility of algae cells, CNC can’t effectively remove Phaeocystis globosa from seawater. To solve this problem, peroxymonosulfate (PMS) was used to enhance the coagulation of CNC for rapidly removal of P. globosa. The results showed that 91.7% of Chl-a, 95.2% of OD680, and 97.2% of turbidity of P. globosa were reduced within 3 h with the use of 200 mg L−1 of CNC and 20 mg L−1 of PMS. The removal of P. globosa was consisted of inactivation and flocculation. Notably, electron paramagnetic resonance (EPR) spectrums and quenching experiments revealed that the inactivation of P. globosa was dominated by PMS oxidation and 1O2. Subsequently, CNC entrained inactivated algal cells to settle to the bottom to achieve efficient removal of P. globosa. The content of total organic carbon (TOC) and chemical oxygen demand (COD) decreased significantly, indicating that a low emission risk of algal cell effluent was produced in the CNC-PMS system. In view of the excellent performance on P. globosa removal, we believe that the CNC-PMS system has great potential for HABs treatments.

Production of Cationic Starch-Based Flocculants and Their Application in Thickening and Dewatering of the Municipal Sewage Sludge

Polymer flocculants are used to promote solid-liquid separation processes in wastewater treatment technologies, and bio-based flocculants possess many advantages over conventional synthetic polymers. Potato starch microgranules were chemically modified and mechanically sheared to produce modified starch flocculants. The effectiveness of produced cationic starch (CS) and cross-linked cationic starch (CCS) flocculants in the thickening and dewatering of surplus activated sewage sludge was evaluated and compared with that of synthetic cationic flocculants (SCFs) The flocculation efficiency of SCF, CS, and CCS in sludge thickening was determined by measuring the filtration rate of treated surplus activated sludge. Comparing the optimal dose of SCFs and CCS flocculants needed for thickening, the CCS dose was more than 10 times higher, but a wide flocculation window was determined. The impact of used flocculants on the dewatering performance of surplus activated sludge at optimal dose conditions was investigated by measuring capillary suction time. The filtration efficiencies (dewaterability) of surplus activated sludge using SCF, CS, and CCS were 69, 67, and 72%, respectively. The study results imply that mechanically processed cross-linked cationic starch has a great potential to be used as an alternative green flocculant in surplus activated sludge thickening and dewatering operations in municipal sewage sludge treatment processes.

Behavior of Sludge Dewaterability and Nutrient Contents after Treatment with Cellulose-Based Flocculants with Combined PTS and Catalytic Behavior of Sludge towards Tetracycline Degradation

Wastewater treatment plants are increasingly interested in adopting inorganic coagulants and organic flocculants in their sludge treatment process since sludge disposal costs more than half of the overall operational costs. This study synthesized poly titanium sulfate (PTS) by different molar ratios and used the best one with cellulose-based flocculants for sludge conditioning. PTS synthesized with a 1:2 molar ratio showed the lowest capillary suction time (CST) of sludge and was selected for further studies with cellulose-based flocculants. As bio-based flocculants have gained popularity due to current environmental problems, cationized cellulose-based flocculants (Ce-CTA) were used in this work with or without PTS for sludge treatment. After coagulation–flocculation, dewaterability of sludge enhanced, and the Lowry and Anthrone method was used to assess proteins and polysaccharides. Next, metal content and nutrients such as total phosphorus, phosphate, and nitrate were measured by ICP-OES and IC, and we found promising results of phosphate especially at pH 3. Higher total phosphorus content was found at pH 3 and 9, and even at pH 6 after PTS or PTS+Ce-CTA treatment. In addition, PTS-treated sludge materials also showed catalytic behavior, suggesting a new research avenue for future development. Based on this study, the PTS+Ce-CTA combination is promising for sludge treatment and nutrient recovery, along with the possibility for the further valorization of the sludge materials.

The transition away from chemical flocculants: Commercially viable harvesting of Phaeodactylum tricornutum

Harvesting can contribute up to 15% of the total production cost for microalgal biomanufacturing. Using flocculants is potentially a cost-effective approach but there has been considerable debate on the efficacy, cost, toxicity to the cell and environment, and the effect on the biomass further downstream. In this study, a range of biobased flocculants (chitosan from crab shells, Moringa oleifera seed extract, pectin from bananas, tannic acid-based derivatives from Acacia tree bark and egg shell powder) were compared with traditional chemical flocculants (aluminium sulphate, iron chloride and sodium hydroxide) for harvesting the diatom Phaeodactylum tricornutum. It was concluded that Tanac’s tannin based Tanfloc 8025 (SL range) was the most promising, requiring a low concentration (10.4 kg ton−1 biomass), at low cost ($27.04 ton−1 microalgal biomass). The flocculant was effective over a wide pH (7.5–10.0) and temperature (15–28 °C) range and harvesting (>85% efficiency) occurred in 10 mins, which resulted in a biomass concentration factor of ≥ 5.69.

Recent Achievements in Polymer Bio-Based Flocculants for Water Treatment.

Polymer flocculants are used to promote solid–liquid separation processes in potable water and wastewater treatment. Recently, bio-based flocculants have received a lot of attention due to their superior advantages over conventional synthetic polymers or inorganic agents. Among natural polymers, polysaccharides show many benefits such as biodegradability, non-toxicity, ability to undergo different chemical modifications, and wide accessibility from renewable sources. The following article provides an overview of bio-based flocculants and their potential application in water treatment, which may be an indication to look for safer alternatives compared to synthetic polymers. Based on the recent literature, a new approach in searching for biopolymer flocculants sources, flocculation mechanisms, test methods, and factors affecting this process are presented. Particular attention is paid to flocculants based on starch, cellulose, chitosan, and their derivatives because they are low-cost and ecological materials, accepted in industrial practice. New trends in water treatment technology, including biosynthetic polymers, nanobioflocculants, and stimulant-responsive flocculants are also considered.

Harvesting of marine microalgae using cationic cellulose nanocrystals

Flocculation of marine microalgae is challenging because of the high ionic strength of the culture medium. We investigated cationic cellulose nanocrystals (CNCs) as biobased flocculants for the marine microalgae Nannochloropsis oculata, and compared its performance to chitosan. Cationic CNCs induced flocculation at a low dose of 11 mg L-1, while chitosan required a dose of 35 mg L-1. Our cationic CNCs possess a permanent positive charge, allowing flocculation over a wide pH-range (4 to 10). The CNC maximum flocculation efficiency was 90 %, while chitosan achieved > 95 %, attributed to small flocs remaining in suspension for CNCs. However, centrifugation for 1 min at 180 g or gravity filtration using a 30 μm nylon filter after CNC flocculation resulted in the removal of these small, stable flocs (∼150 μm diam) and > 95% harvesting efficiency. Cationic CNCs can thus serve as a sustainable alternative natural flocculant for harvesting both freshwater and marine microalgae.

Green wastewater treatment flocculants and fixatives prepared from cellulose using high-consistency processing and deep eutectic solvents

Cellulose offers a large renewable raw material base and can be chemically modified in a variety of ways to introduce new functionalities such as cationic charge, that are required in effective waste water treatment for any polymers. Cationic cellulose derivatives were synthesized using both conventional and novel methods from several commercially available cellulose pulps. The cationic derivatives were used as biobased flocculants to treat real-life wastewater samples in a head-to-head comparison with cationic polyacrylamides. A novel high-consistency, high shear mixing heterogeneous mixing method enables the preparation of cellulose derivatives without the use of solvent or high cost solubilization methods. When higher cationic charge is required, deep eutectic solvents can be used to modify cellulose. Both the molecular weight and charge of the cationic cellulose derivatives have a drastic influence on performance in water treatment applications. Flocculation experiments with real-life waste water samples revealed that cationic cellulose derivatives are able to effectively function as flocculants and fixatives, and even outperform commercial polyacrylamides. The highest achieved level of turbidity removal was 93.2%. Cationic cellulose derivatives provided good efficacy in sludge dewatering, Focused Beam Reflectance Measurement flocculation tests and anionic trash fixing, which are crucial properties for the pulp and paper industry.

Removal of lignin from straw spent pulping liquor using synthetic cationic and biobased flocculants

Abstract The spent pulping liquor (SPL) obtained from straw processed by soda (alkaline) pulping contains dissolved non-sulfonated lignin. The lignin can be separated from SPL using acid or cationic flocculants which are potentially hazardous to the environment. In this study, the performance of the biobased protein flocculant hemoglobin (HEM) with and without added calcium chloride was compared with that of a high charge density synthetic cationic flocculant, poly (diallyldimethylammonium chlorides) (pDADMAC). Turbidity measurements gave overly broad concentration ranges for optimal lignin removal which may be related to the mechanism of flocculation which requires several major steps: Conversion of dissolved lignin to particulate lignin, formation of particulate lignin flocs, and subsequent sedimentation of these flocs. An optimal flocculant concentration or concentration range was estimated using the three methods: average Zeta potential corresponding to the lowest turbidity range; a novel method using the maximum percent pellet mass calculated using the dried masses of the pellet and supernatant after centrifugation; measurement of supernatant lignin using spectroscopy. HEM light absorption interfered with spectroscopic lignin determination, and a method for correcting the measurements was devised. This study shows that HEM is an effective flocculant for nonsulfonated lignin in SPL. The HEM-lignin complex is a potential high protein component of animal feed.

Solubilization of meat & bone meal protein by dilute acid hydrolysis for the production of bio-based flocculant

Flocculants are substances that cause suspended particles to aggregate, therefore accelerating sedimentation to produce a clarified solution. They find use in a huge variety of applications including wastewater treatment, erosion control, and paper manufacture. Meat and bone meal (MBM) is a high protein by-product of meat processing. Protein extracted from MBM has been shown to have good flocculation activity, but this protein has poor solubility. Previous attempts to improve solubility through alkaline or enzymatic hydrolysis have produced small protein fragments with low flocculation activity. The objective of this project was to produce large, soluble MBM protein fragments by applying reaction conditions that are known to hydrolyze peptide bonds only at aspartic acid and asparagine residues. In this project, milled MBM was suspended in 0.03N hydrogen chloride solution, under vacuum, and incubated at 108°C. Samples were removed after 1, 2, and 4h, and the soluble and insoluble material was separated. The molar mass distribution of soluble material was examined by size exclusion chromatography (SEC), progressive solubilization of protein was measured by using a test for organic nitrogen, and flocculation activity was tested by measuring kaolin clarification effectiveness (KCE). Results showed that at all hydrolysis times, concentration of solubilized material was increased approximately 3-fold compared to the acid-free controls. Results also showed that as reaction duration increased, more MBM protein was solubilized, but average molecular weight (MW) of solute was reduced, and flocculation activity was dependent on reaction duration. The dilute acid hydrolysis (DAH) employed in this project could be a simple and inexpensive treatment that has potential to add value to MBM and provide a new source for bio-based flocculants.

Methylation of hemoglobin to enhance flocculant performance

AbstractBACKGROUNDSynthetic organic polymer flocculants can be highly effective at clarifying suspensions, but these substances may also have negative environmental and health effects. Relatively few studies have been done using biobased flocculants, which are more environment friendly. Hemoglobin (Hb) has previously been demonstrated to be a promising flocculant of kaolin and lignin suspensions. This study examines the methylation of Hb side chain carboxyl groups for the purpose of improving its flocculation performance at near‐neutral pH.RESULTSPotentiometric titration of methylated Hb (MeHb) showed an approximately 28% degree of methylation when the Hb was suspended in methanol with 0.8 mol L−1 HCl for 48 h. Under some conditions, MeHb clarified suspensions of kaolin at one‐quarter the dose that was required for Hb. Furthermore, MeHb exhibited flocculant activity over a wide pH range, compared with Hb. The percentage of original turbidity removed was 37% for Hb while 60% of the original turbidity was removed for MeHb at near‐neutral pH (pH = 6.8).CONCLUSIONSVery small doses of methylated hemoglobin (MeHb) rapidly clarify suspensions of kaolin. The potential of MeHb as a biobased flocculant for the clarification of water for industrial or municipal use was demonstrated. Published 2017. This article is a U.S. Government work and is in the public domain in the USA.

Poultry Blood Preservation and the Impactof Preservation on Flocculant Activity

<abstract><title><italic>Abstract.</italic></title> Chicken blood is an attractive but problematic raw material for the production of biobased flocculants. Blood begins to degrade as soon as it is collected – it rapidly coagulates, and at longer time scales, the red blood cells lyse and microbial growth results in hydrogen sulfide production. This study investigated the extent to which these types of degradation can be limited by inexpensive chemical treatments, under non-sterile, non-refrigerated conditions. It is shown that while the anticoagulants potassium citrate and potassium oxalate are effective under refrigerated conditions, at ambient temperatures they can only prevent coagulation for about one day. The effectiveness of potassium EDTA, on the other hand, is not as temperature dependent and can prevent coagulation for at least four days at ambient temperature. Similarly, blood treated with oxalate or citrate produces dangerous amounts of hydrogen sulfide, but blood treated with EDTA produces significantly less of the toxic gas. Anticoagulated blood does undergo some red blood cell lysis under the conditions investigated, and a method for limiting this lysis is proposed. Finally, it is shown that chicken blood preserved with EDTA can be held in non-refrigerated, non-sterile conditions for at least four days without sacrificing the effectiveness of the flocculant made from the blood.

Properties and flocculation efficiency of cationized biopolymers and their applicability in papermaking and in conditioning of pulp and paper sludge

Safe biodegradable “green” alternatives with minimal environmental and health risks have received widespread research interest. Thirty different kinds of bio-based flocculants (modified starches, modified celluloses, native chitosan, and lignin-based flocculant) were pre-tested using a simple jar test for the examination of the applicability of new organic flocculants in papermaking and in conditioning of waste activated sludge from the pulp and paper industry. Three starch-based and two cellulose-based polymers were chosen for further flocculation and filtrations tests. Key optimization parameters for the polymer were identified as the increasing of molecular weight and nitrogen content. The starch-based polymer had the best performance in both applications, but in neither of the cases did it function as well as the commercial polyacrylamide-based polymers. The importance of the molecular weight came up in the experiments. The developed starch-based polymer was cationic and had the charge density used in industry. On the other hand, although cationic flocculants are the most used in sludge conditioning, also anionic and non-ionic polymers are needed, depending on the characteristics of the sludge to be flocculated. Overall action of the tailored polymers was also studied in order to predict their potential as papermaking retention and dewatering aids.