Flocculation Effect Research Articles

Combined effect of flocculation and ammonia stripping on different biogas slurries

The combined use of flocculation and ammonia stripping could be an efficient method for treating biogas slurry (BS). In this study, the operating parameters of ammonia stripping after flocculation were optimized. Swine manure biogas slurry (SMBS) and chicken manure biogas slurry (CMBS) were used as raw materials, and the flocculation efficiency and ammonia nitrogen removal rate (ANRR) were the main indices to evaluate the process performance. The bioflocculant (BF), polyaluminium chloride (PAC), ferric chloride (FC), and calcium oxide (CaO) were used as flocculants for the different biogas slurry flocculation. The results showed that CaO was more suitable for SMBS; the flocculation efficiency reached 56.63 % at the additive concentration of 5 g/L. Moreover, the ANRR was significantly improved by over 80 % after flocculation. However, the best flocculation potential on CMBS was achieved at an additive concentration of 0.3 g/L, and the flocculation efficiency reached 44.44 %. The ANRR reached 94.42 % at 45 ℃. This study provides a scientific basis and feasible scheme for treating different BS.

Harvesting Optimization, Biomass, and Lipid Content Analysis of Euglena sp. Culture with Ettlia texensis Bioflocculant and Commercial Chitosan

Graphical Abstract Highlight Research Bioflocculation technique can improve the harvesting effectiveness of semimass culture of Euglena The addition of E. texensis can significantly increase the flocculation efficiency of Euglena The addition of commercial chitosan was able to increase the flocculation efficiency of Euglena sp. The biomass and lipid content produced by Euglena with E. texensis flocculant agent showed higher results than the biomass and lipid content produced by Euglena sp. with commercial chitosan flocculant agent. Abstract Euglena sp. has a high potential to be developed as biofuel. However, the high cost and energy required for the harvesting process are hindering the production. Flocculation using natural substances, such as microorganisms and biopolymers, offers a promising solution to minimize energy and production costs, so it is applicable on a mass scale. Ettlia texensis is one of the autoflocculating microalgae that can excrete extracellular polymeric substances (EPS). Chitosan is a linear copolymer of D-glucosamine and N-acetyl-D-glucosamine produced by the deacetylation of chitin, which is usually exploited by marine crustaceans, shrimp, and crabs. Chitosan has a very high cation load, so it is often used for coagulation or flocculation. This study explores the potential of E. texensis and chitosan as flocculant agents to harvest the mass culture of Euglena sp. by giving different doses E. texensis with 1:0.25 (E3), 1:0.5 (E4), 1:1 (E5), and 1:2 (E6), and chitosan with 1.25 mg (C1), 2.5 mg (C2), 3.75 mg (C3), and 5 mg (C4). This research began with the cultivation of Euglena sp. and E. texensis on a 50 L scale for 12 days. The effectiveness of flocculation was measured by the spectrophotometric method. Based on this research, the best treatment for harvesting Euglena sp. culture by bioflocculation was shown by the addition of chitosan (5 mg) with the recovery of 84.83%, 0.2213 mg/mL biomass, and 0.2117 mg/mL lipid content. Meanwhile, with E. texensis, the best was shown by the ratio of 1:2 with recovery 84.71%, 0.2053 mg/mL biomass, and 0.1753 mg/mL

Preparation of grafted starch‐based cationic flocculants and its removal of reactive and disperse dyes

AbstractIn this paper, a starch‐based flocculant (ADSt) with medium and low temperature solubility and enhanced flocculation effect was synthesized using corn starch, acrylamide, and dimethyldiallyl ammonium chloride as main materials by the ethanol‐alkali method and grafting method. The main mechanism of ADSt's flocculation was electrical neutralization and bridging. The flocculation performance of ADSt was verified by using it along with polymeric aluminum chloride (PAC) as coagulant/flocculant, dispersible dye (dispersible yellow RGFL), and reactive dye (active trimeric blue KN‐G) to simulate dye wastewater. For the dispersed yellow water sample and active emerald blue water sample, the dosage of PAC was 40 and 35 mg/L respectively. When the dosage of ADSt was 10 mg/L with a dye content of 100 mg/L, the decolorization rates for both dyes reached up to 96.2% and 94.4% respectively. The properties of the flocs such as size and two‐dimensional fractal structure were described. The prepared ADSt maintained a good flocculation effect in the pH range of 5–9 due to its excellent water solubility achieved through the ethanol‐alkali preparation process, where its solubility reached 86.7% at 30°C. Overall, the preparation process for ADSt is simple, cost‐effective, while providing an effective solution for treating printing and dyeing wastewater.

Purification Processes for Generating Cationic Lignin-Acrylamide Polymers.

Purification is an essential step in many polymerization processes for fabricating highly pure polymers. This study considered various purification methods for purifying the product of lignin, acrylamide (AM), and diallyl dimethylammonium chloride (DADMAC) copolymerization reactions at a laboratory scale. The charge density, yield, molecular weight, and solubility analyses confirmed that ethanol extraction and membrane filtration were the most effective processes for producing lignin-p(AM)-p(DADMAC). The 1H NMR analysis revealed that the membrane dialysis effectively removed unreacted AM and DADMAC monomers from the reaction medium. The produced samples of the ethanol-extraction and dialysis processes had higher solubility and yield compared to the product of the acidification process. Thermogravimetric studies confirmed that the ethanol-extracted and dialyzed samples had a degradation temperature (220 °C) higher than that of the acidified samples (160 °C). The rheological studies confirmed that the viscosities of the polymer solutions were influenced more by the solubility than by the molecular weight of the generated polymers within the molecular weight range examined in this study. The flocculation studies confirmed that the ethanol-extracted and dialyzed polymers were more effective flocculants than the acidified samples for the particles of a kaolinite suspension. Based on the above results, membrane filtration with a larger pore size could be an environmentally friendly method for effectively purifying lignin-p(AM)-p(DADMAC).

Enhanced degradation of crude oil by immobilized bacterial consortium through eliminating microbial flocculation towards crude oil

Microbial degradation is considered an effective and sustainable technique for the remediation of oily sludge; thus, the acquisition of crude oil-degrading bacteria is crucial for effective bioremediation. This study introduces a novel domestication-enrichment-isolation (DEI) strategy to isolate crude oil-degrading bacteria from oily sludge. Two strains, Rhodococcus rhodochrous JS-24 (R.rh) and Gordonia cholesterolivorans JS-13 (G.ch), demonstrated the highest degradation rates of 53.7% and 34.6%, respectively, within 7 days. While no synergistic effect was observed with their combined use in free bacterial consortia, and the overall degradation rate decreased to 51.9 %, which was weaker than that of R. rh treatment alone. The decrease in degradation rate is attributed to microbial flocculation towards crude oil: most droplets of crude oil were encapsulated into spherical aggregations by G. ch, thereby hindering the contact and degradation of droplets by R. rh. In contrast, immobilization technology significantly enhanced crude oil degradation by eliminating this flocculation effect. The immobilized bacterial consortium achieved a 95.5% degradation rate, representing the highest degradation rate reported for bacterial consortia. This study reveals for the first time that the side effects of bioflocculation on crude oil degradation and provides guidance for the construction of bacterial consortium.

Carbon-ash separation of coal gasification fine slag by flocculation-flotation process

ABSTRACT Coal gasification slag (CGFS), which was a bulk solid waste in coal chemical industry, shows great application potential in the preparation of silica microspheres, zeolites ceramic materials, etc. However, its high residual carbon characteristics hinder to its development. Decarburization is a necessary precondition for the effective utilization of CGFS. The efficient separation of carbon or ash from CGFS remains a challenge due to its ultra-fine particle size. This work provides a novel flocculation-flotation process to achieve the complete carbon-ash separation of CGFS. The addition of anionic polyacrylamide (APAM) or polyethylene oxide (PEO) had positive effect on the flotation of CGFS, especially for APAM. With APAM dosage of 50 g/t, the ash content of carbon slag and ash slag were 59.04% and 97.11%, respectively. In this process, the zeta potential of carbon slag and ash slag decreased from −17.43 and −11.77 mV to −23.45 and −29.80 mV, respectively. The greater change of zeta potential of ash slag indicates its stronger adsorption of APAM, leading to the higher flocculation trend of ash particles than that of carbon slag. APAM has selective flocculation effect on ash slag, which contributed to reduce the mechanical entrainment during flotation, thereby achieving complete carbon-ash separation of CGFS.

COPOLYMER BASED ON [(3-METHACRYLOYLAMINO)PROPYL] TRIMETHYLAMMONIUM CHLORIDE AS A FLOCCULANT FOR INDUSTRIAL WATER TREATMENT

The using of polymeric flocculants in the development of the oil industry in Kazakhstan is one of the innovative tasks. Therefore, the creation of new effective flocculants based on available industrial monomers with structure-forming is an urgent task. The mechanism of action of flocculants is based on the phenomenon of adsorption of flocculant molecules on the surface of colloidal particles, the formation of a network structure of flocculant molecules, and the adhesion of colloidal particles due to van der Waals and other forces. New polymeric flocculant with different molar composition was synthesized by radical copolymerization [(3-methacryloylamino)propyl]trimethylammonium chloride (TMAPMACh) with N,N-dimethyl-acrylamide (DMAA) at 333 K in the presence of ammonium persulfate, (NH4)2S2O8 as an initiator. The molar composition of the synthesized TMAPMACh-DMAA copolymer was determined by FTIR and NMR spectroscopy and conductometric titration with AgNO3 solution. The flocculation properties of the copolymers were studied by measuring the sedimentation of dispersed particles of bentonite suspension in the presence of the flocculant. Sedimentation degree was determined by measuring the optical density of the suspension. It was found that TMAPMACh-DMAA copolymers had a flocculating effect and could be used for industrial wastewater treatment. Thermogravimetric analysis showed that this copolymer was thermally stable up to 270°C. Therefore, it can be used in deep well drilling to regulate the properties of drilling fluids.

Development and evaluation of amine-functionalized β-cyclodextrin grafted starch as a natural flocculant for turbidity removal in water treatment

Recently, biopolymers have been used as coagulants/flocculants due to their biodegradability, low cost, and renewability. In this study, an environmentally friendly amine-functionalized starch-based flocculant was successfully prepared. Initially, β-cyclodextrin was grafted onto the starch backbone to increase the number of hydroxyl groups, and this composite was named CD-starch. Subsequently, in order to introduce cationic properties and enhance effective flocculation, CD-starch was modified using amine functional groups. The surface functional groups were engineered by introducing different amine to CD-starch ratios (0.5:1, 1:1, 2:1 w/w), named A-CD-starch 0.5, 1 and 2, respectively. Following the characterization of the synthesized substrate, its performance in the flocculation process of a kaolin suspension was investigated. The effects of different parameters, including pH, flocculant dosage, and initial turbidity on wastewater turbidity removal, was investigated. The results showed that a higher ratio of amine to CD-starch leads to a better amination reaction due to the greater availability of nitrogen for alkylation. Jar experiments showed that for initial turbidities of 50, 150 and 300 NTU, the appropriate doses of flocculant were 0.070, 0.085 and 0.130 mg/mL, respectively. For these initial turbidities, the maximum turbidity removal was achieved 80.1 %, 92 %, and 97.8 %, respectively. This work provides an innovative natural flocculant based on starch which can effectively treat turbid wastewaters.

A Review of Chitosan as a Coagulant of Health-Related Microorganisms in Water and Wastewater

The coagulation and flocculation properties of chitosan, an organic biopolymer derived from chitin, have been researched as an alternative to synthetic polymers and inorganic metal salt coagulants currently used in water and wastewater treatment. In an effort to encourage further research into the practical uses of chitosan as green chemistry in water and wastewater treatment and to promote the efficacious removal of microbial contaminants in drinking and wastewater, we have summarized the current state of research pertaining to the treatment of microorganisms in water and wastewater. A search of PubMed revealed 720 possible titles and abstracts, of which 44 full-text articles were identified as matching the eligibility criteria for inclusion in this systematic review. Results are presented based on the type of water matrix treated (i.e., drinking water, wastewater, and recreational waters) and a summary table providing details on the types and forms of chitosan utilized and the treatment mechanisms and processes described in the study. We find chitosan to be an effective coagulant, flocculant, and adsorbent for removing microbes from water and wastewater; some modified forms of chitosan can inactivate microbes and achieve disinfection, such as those containing metals like silver and antimicrobial chemicals like quaternary ammonium compounds or other strong oxidants, and use with filtration or electrochemical processes can achieve extensive reductions in microbes to meet performance targets of the World Health Organization.

Implementation of selective flocculation process in drilling operations to optimize per-flex fluid volume consumption and reduce the carbon footprint

One of the significant challenges faced by the oil and gas industry is the reduction of the carbon footprint associated with drilling operations. This paper presents a case study on the implementation of a selective flocculation process to optimize the consumption of PER-FLEX fluid, a high-performance water-based mud (WBM), during drilling operations. Conducted in a Colombian oil field, this study demonstrates how the adjustment of polymer concentration and injection rates in the flocculation process can reduce the need for fluid dilution, thereby decreasing water and chemical consumption, waste production, and CO2 equivalent (CO2 eq.) emissions. The findings highlight the effectiveness of selective flocculation in enhancing drilling fluid performance and contributing to sustainability goals.

Interface dynamics in dewatering processes of high-water-content slurry flocculated with PAC

This study addresses the challenge of the reverse effect observed in the dewatering process of waste slurry as poly-aluminum chloride (PAC) dosages increase. It investigates the flocculation mechanism of PAC at varying dosages in a high-water-content slurry using molecular dynamics simulation methods. The results indicate that PAC molecules primarily adsorb montmorillonite particles while exerting negligible influence on quartz. Dewatering efficiency is influenced by the adsorption-repulsion interaction at the PAC-montmorillonite interface. Efficiency increases with PAC dosage up to an optimum level due to enhanced adsorption but decreases thereafter due to increasing repulsion. Within this optimal range, montmorillonite interfaces exhibit a higher negative charge, facilitating stable PAC adsorption and leading to increased aggregation of montmorillonite particles, thereby forming flocs. The adsorption capacity of PAC on montmorillonite particles escalates with dosage until achieving the optimal flocculation effect. However, surpassing this optimal dosage prompts repulsion among outer PAC molecules, gradually causing montmorillonite particles to separate due to repulsion, thereby weakening the flocculation effect. This research provides theoretical support for the flocculation and dewatering of PAC in high-water-content waste slurry, emphasizing the rational and cost-effective addition of PAC in practical applications.

Development of a limestone-based ballasted material for enhanced co-removal of turbidity and fluoride from coal mine water: An efficacy study

The rapid progression of coal mining technology in recent years has resulted to the discharge of mine water with excessively high levels of turbidity and fluoride, presenting a complex contamination issue. This study develop an innovative limestone-based ballasted material, integrating it with ballasted flocculation technology. The synergistic effects of surface flocculation and adsorption have enabled the simultaneous and efficient removal of high concentrations of turbidity and fluoride. The influence of various parameters, including the dosage of the coagulant, flocculant, ballasted material, and the stability under long-term continuous operation, on the performance of this new technology was investigated. Findings indicate that an increase in the dosage of the coagulant, polyaluminum chloride (PAC), positively affects the removal of turbidity and fluoride ions, with an optimal dosage of 60 mg/L. The addition of polyacrylamide (PAM) showed that both conventional and ballasted coagulation techniques exhibit an initial increase followed by a decrease in turbidity removal efficiency, and an ascending trend in fluoride removal efficiency, with an optimal PAM dosage of 1.0 mg/L. The dosage of the new ballasted material was determined based on the initial water turbidity and fluoride concentrations, an increase in its dosage led to a progressive reduction in effluent turbidity and a corresponding increase in fluoride removal. A 30-day continuous operation confirmed the stability of the new process, with a treatment cost of approximately 2.67 $/t. The pseudo-first-order kinetic model and the Langmuir adsorption isotherm equation provided satisfactory fits to the treatment data, suggesting that both conventional and ballasted coagulation involve a combination of surface adsorption and intraparticle diffusion mechanisms for the removal of turbidity and fluoride.

A laboratory investigation for assessing the effectiveness of wastewater treatment using flocculation process in building stone processing industry on stone surface quality and abrasive tool wear

In this study, the effect of presence and concentration of two synthetic polymeric flocculants with different charging mechanisms (anionic and cationic) on surface quality and abrasive tool wear in polishing process of building stones was investigated. The polishing tests were performed in laboratory scale on two stone samples (granite and marble). An index, entitled improvement index (I) was defined for evaluating the effectiveness of flocculants on surface quality and abrasive tool wear. The results revealed that flocculation process had a noticeable effect on enhancement of surface quality and reduction of abrasive tool wear for both stone samples. The cationic flocculant was more effective for granite sample and anionic flocculant was more effective for marble sample. The granite particles mainly exhibit negative surface charge while the marble particles have positive surface charge in the pH range of wastewater used for polishing tests. Therefore, charge neutralization mechanism plays a major role in flocculation process of granite and marble samples. It was found that the use of flocculation process for treatment of wastewater in stone processing plants leads to increase of abrasive tool lifespan and more high-quality products.

Study on the effect and mechanism of polyethylene oxide and alum in flotation separation of fine smithsonite/calcite

The flotation separation of fine smithsonite and calcite has always been a challenging issue in the mineral processing industry. Both minerals are microfine particle distribution in nature, requiring ultra-fine grinding to maximize their liberation, which makes their flotation separation difficult. This study investigated the effects of PEO (Polyethylene oxide) and alum as combination agent on the flotation separation of fine smithsonite and calcite. The research results showed that using PEO and alum as combination agent can effectively separate fine smithsonite and calcite. PEO has a flocculation effects on both minerals, and Alum has better selective adsorption and flocculation effects on calcite, thereby effectively reducing the recovery of calcite. After treatment with PEO and alum, soluble starch tends to adsorb on the surface of calcite more than smithsonite, selectively depressing calcite in flotation separation, thus allowing for the effective flotation separation of fine smithsonite and calcite.

Enhancing microplastic removal from natural water using coagulant aids

Microplastic (MP) pollution poses a significant environmental challenge, underscoring the need for improved water treatment methods. This study investigates the effectiveness of coagulation, flocculation, and sedimentation processes for removing microbeads, focusing on key factors that influence removal efficiency. Among the coagulants tested, polyaluminium chloride (PAC) demonstrated superior performance by enhancing the aggregation of microplastics with flocs. Optimal treatment conditions were determined to be 0.4 mmol/L PAC and 3 mg/L polyacrylamide (PAM) at pH 8 (before adding PAC), with rapid stirring at 240 rpm for 1 min, followed by slow stirring at 35 rpm for 13 min, and a sedimentation period of 25 min. Under these conditions, removal efficiencies exceeded 95 % for a range of microbeads (10–1000 μm: Polystyrene (PS), Polypropylene (PP), Polyvinyl chloride (PVC), Polyamide (PA), Polyethylene (PE), and Polyurethane (PU)) from natural water samples. Without PAM, PAC alone achieved a 97 % removal rate for PS microbeads. The addition of PAM maintained high removal efficiency, while aluminium sulphate and ferric chloride were less effective, with removal rates of 67 % and 48 % for PS microbeads, respectively. PAM enhanced MP removal across various coagulants and microbead types, with maximum efficiency observed at PAM concentrations of ≥3 mg/L. The treatment also demonstrated that organic matter in Regent's Park pond water could further improve MP removal. Size significantly impacts removal efficiency: larger microbeads (1 mm to >250 μm) were removed more effectively (95 %) compared to smaller ones (10 to <250 μm), which had a lower removal rate of 49 %. Denser microbeads like PVC (density 1.38 g/cm³) settled more efficiently than lighter microbeads such as PE (density 0.97 g/cm³). These findings suggest a need for advanced technologies to better remove lighter, smaller MPs from water.

Study on Demulsification Pre-Treatment of Emulsified Wastewater

In this paper, the flocculation effect of single flocculants and compound flocculants on emulsified wastewater under different conditions was studied. The effect of flocculant type, dose, settling time and composite ratio of flocculant on the treatment of emulsified wastewater were investigated through single-factor condition tests, and then the optimal conditions of flocculants for treating emulsified wastewater were obtained. The results showed that the single inorganic flocculant could break the stable state of the emulsion when the pH was adjusted to 7 and formed tiny flocs, but it took a long time to settle down. The single organic flocculant had no flocculation effect. The inorganic–organic composite flocculants could effectively solve the problem of emulsion breaking and flocculation, and could form large flocs and alum flower formations at the same time, with mud and water effectively separated. The best conditions for the composite flocculants were as follows: under the condition of room temperature and pH 7, the dose of PFC was 2250 mg/L and APAM was 5 mg, the homogeneous stirring time was 10 min, and the settling time was 0.5 h. The removal rate of COD and turbidity reached 84.75% and 99.86%. The study could provide a new treatment idea and method for the pretreatment of stabilized high-turbidity wastewater.

Selective aggregation of hematite from quartz using charged polyacrylamides: In-situ sizing

Recovering fine valuable material has been a significant challenge in minerals processing. This primarily stems from insufficient collision opportunities between fine particles and bubbles, specifically when utilising traditional recovery methods such as froth flotation. This research endeavours to address this challenge by exploring the use of various commercially available, high molecular weight polymers- specifically polyacrylamide (PAM)- to selectively aggregate hematite from quartz. Investigation of the conditions in which selective aggregation of hematite over quartz occurs, with the goal to achieve aggregate sizes of between 20 and 150 μm, were undertaken. Targeting this size range ensure that conditions are optimised for future use in conventional mechanical flotation cells as an efficient mineral recovery method. The study investigates the selectivity of charged PAM towards hematite and quartz at pH 10, using adsorption studies. Anionic PAM demonstrates a preference for hematite, with a range of charge density studies, highlighting stronger adsorption capacity with lower charge density polymers. Using BlazeMetrics probe technology for in-situ sizing and imaging, it was observed that conditioning 50–300 g APAM per t of hematite resulted in aggregates in the range of 30–230 μm after 5 min. Interestingly, the charge density of APAM does not markedly affect the size of the hematite aggregates, although altering the charge density of the polymer impacts the selectivity towards quartz. Additionally, cationic PAM results in the simultaneous aggregation of both hematite and quartz, not demonstrating selectivity. To mitigate heterocoagulation between minerals, a common dispersant, sodium hexametaphosphate (SHMP), was employed, which notably prevents quartz aggregation. Separation of aggregated hematite from quartz by sedimentation was only slightly effective with the majority of quartz settling with the hematite. Adding up to 1000 g of dispersant per t of hematite reduced the amount of quartz in the sediment bed by 23 %. The dispersant increased the magnitude of the negative zeta potential of the two minerals, particularly hematite, lowering heterocoagulation and improving effectiveness of hematite flocculation.

Optimization of calcined eggshell as an effective coagulant for treating colloidal particles in complex effluents in the CPCP industry: mechanistic insights, scale-up design, and comparative analysis with alum

Highly turbid industrial effluent poses significant challenges to environmental sustainability. In this study, we investigated the optimal aggregation kinetics for the removal of colloidal and turbid particles in Cosmetics and Personal Care Products (CPCP) industrial effluent using calcined eggshell (CES) and industrial-grade aluminum sulfate as flocculants. The effluent characteristics were determined following ASTM specifications, and process optimization was carried out using a response surface design approach. The optimal operating conditions at a settling time of 3 min were found to be pH 8, 0.2 g/L dosage of CES, pH 10, and 0.3 g/L of alum dosage. The flocculation efficiencies of CES and alum were found to be 80% and 78%, respectively, demonstrating the effectiveness of both flocculants in removing colloidal particles and reducing turbidity in CPCP effluent. Mechanistic studies revealed that CES achieved particle removal through enmeshment and inter-particle bridging with a significant aggregation rate (1.3 × 10−7) and a lower floc breakup tendency (2.8 × 10−14) compared to alum-sweep flocculation. The hydrodynamics at a velocity gradient of 269s−1 ≤ G ≤ 29s−1 indicated spontaneous agglomeration within a flocculation period of ≤10 min, indicating rapid and efficient particle removal. The findings of this study justify the use of CES as a sustainable and effective option for the removal of colloid/turbid particles from CPCP effluent. The optimized operating conditions and mechanistic insights into the flocculation process contribute to establishing an optimized sedimentation geometry, with specified aspect ratio, detention time, hypothetical settling, and sludge depth for CES, ensuring the favorable stability of the finished CPCP effluent before discharge.

Flotation of ultra-low ash coal combined with ultrasonic pretreatment

ABSTRACT Ultra-low ash coal is an essential clean energy and material. The preparation of ultra-low ash coal by flotation is facing challenges due to the inherent drawbacks. This work aims to enhance the flotation efficiency of ultra-low ash coal by ultrasonic pretreatment. Timed-release flotation experiments were conducted with ultrasonic pretreatment before and after collector addition. The results showed that the recovery and combustible recovery and flotation perfect index of clean coal increased after ultrasonic pretreatment. Additionally, the flotation circuits can reduce from three to two times to obtain clean coal with ash content around 5%. The particle size distribution of coal varied from unimodal to bimodal after ultrasonic pretreatment no matter whether collector was added, indicating that ultrasonic had both dispersing and flocculation effects. Scanning electron microscope (SEM) analysis illustrated that the surface of coal was cleaned due to the ultra-fine gangue particles coated on coal surface was dispersed, and the flocculation of low-ash coal particles was promoted after ultrasonic pretreatment. Consequently, the ultra-low ash coal with higher recovery and quality could be obtained with simplified circuits.

Ecotoxicological risk assessment on coagulation-flocculation in water/wastewater treatment: a systematic review.

It is undeniable that removal efficiency is the main factor in coagulation-flocculation (C-F) process for wastewater treatment. However, as far as environmental safety is concerned, the ecotoxicological aspect of the C-F process needs to be examined further. In this study, a systematic review was performed based on publications related to the toxicity research in C-F technology for wastewater treatment. Through a series of screening steps, available toxicity studies were categorized into four themes, namely acute toxicity, phytotoxicity, cytotoxicity, and genotoxicity, which comprised 48 articles. A compilation of the methodologies executed for each theme was also outlined. The findings show that conventional metallic coagulants (e.g., alum, iron chloride, and iron sulfate) were less toxic when tested on test species such as Daphnia magna (water flea), Lattuca sativa (lettuce), and animal cells compared to synthetic polymers. Natural coagulants such as chitosan or Moringa oleifera were less toxic compared to metallic coagulants; however, inconsistent results were observed. Moreover, an advanced C-F (electrocoagulation) as well as integration between C-F and Fenton, adsorption, and photocatalytic does not significantly change the toxicological profile of the system. It was found that diverse coagulants and flocculants, species sensitivity, complexity in toxicity testing, and dynamic environmental conditions were some key challenges faced in this field. Finally, it was expected that advances in technology, interdisciplinary collaboration, and a growing awareness of environmental sustainability will drive efforts to develop more effective and eco-friendly coagulants and flocculants, improve toxicity testing methodologies, and enhance the overall efficiency and safety of water and wastewater treatment processes.