Floc Characteristics Research Articles

Research on benthic plume sedimentation characteristics and temperature effect in deep-sea nodule mining operation

The benthic plume generated by nodule mining operations has garnered significant attention due to its intricate environmental impact and the limitations of existing plume control techniques. Prior research has suggested that temperature effects can facilitate the aggregation of suspended sediments; however, a more detailed understanding is needed. In this study, a series of experiments were conducted to examine the sedimentation behavior of the benthic plume and the influence of temperature on its sedimentation process. Suspension concentrations of the plume were monitored over an hour, while flocs characteristics were investigated at 30 and 60-min intervals. A novel function describing the relationship between temperature effects and concentration changes was developed. Results indicate that higher temperatures can accelerate the deposition process by approximately 3–6 times, emphasizing the necessity to consider low water temperatures in laboratory studies of benthic plumes. Moreover, the integration of temperature effects and micro-eddies in plume aggregation research may offer new opportunities for developing advanced plume control and separation methods.

Characteristics of mud flocs in the subseabed methane hydrate reservoir and behaviours in flowing water

Recently, it was found that mud flocculates, or flocs, coexist with methane hydrate within turbidite layers off the Japanese coast. There is a concern that mud flocs may be broken down by the flow of pure water generated from the dissociation of methane hydrate, causing sand troubles in the production wells. To clarify the characteristics of the flocs, in this study, the samples of mud flocs collected from natural cores having contained methane hydrate were observed before and after sonication in a pure-water ultrasonic bath. Then, these flocs were placed in distilled water flow to investigate their mechanical stability. As a result, it was confirmed that the flocs mainly consist of silt together with a little clay and fine sand. In addition, these flocs were found to be stable for flow rates on the order of magnitude of 10−3 m/s, which is expected inside the strata during gas production from methane hydrate. However, it was also found that, after the distilled water flow experiments, the flocs were decomposed into silt and clay particles when pressed with a handheld needle in the air, suggesting that the floc might be a source of the fine particles as underground stress conditions change, although not many flocs are likely to be immersed in pure water alone.

A strategy to alleviate membrane fouling by optimizing the structure of the cake layer formed by flocs deposited directly on the membrane in the ultrafiltration process through coagulation and nanoscale Fe3O4/Fe3O4@SiO2 load

Membrane fouling has always been a problem hindering the practicability of ultrafiltration. Direct regulation of the structure of the cake layer formed by rapid deposition of flocs as a “secondary barrier” in the in-line coagulation ultrafiltration (C-UF) process has acquired importance as a research topic in comparison to membrane modification and standard coagulation ultrafiltration. In this study, membrane fouling was controlled in the C-UF process via coagulation/nano-scale Fe3O4 load (C/FL-UF) and coagulation/nano-scale Fe3O4@SiO2 load (C/FSL-UF). The promotion effects of these two processes (C/FL-UF and C/FSL-UF) on the reduction of membrane fouling and improvement of water quality were systematically studied employing simulated surface water. Floc characteristics, XDLVO theory, and the Hermia model, etc were employed to explain the optimization of cake layer. For coagulation/Fe3O4 load, the floc size was large and loose, whereas, for coagulation/Fe3O4@SiO2 load with high recoverability., the floc size was slightly loose. The newly constructed cake layer had improved porosity, structural stability and capacity of water transport. Meanwhile, decrease of unit adhesion free energy and secondary minimum depth along with the substantial increase of energy barrier between the reconstructed cake layers and membranes or colloids explained the mechanism of reduced membrane fouling from the surface energetics. The gradual decrease of water contact angle and the optical images proved that the affinity of the cake layer was significantly reduced. Hermia model further validated the accuracy of this study in controlling membrane fouling by regulating the formation of the cake layer. Finally, the study concluded by analyzing the practicability and efficacy of the procedure to further elucidate the applicability of this research.

Integrated ultra scale-down and multivariate analysis of flocculation and centrifugation for enhanced primary recovery

A linked ultra scale-down (USD) flocculation and centrifugation system facilitates rapid bioprocess development and evaluation. These techniques allow studies to be undertaken at high throughput using as little as 50 mL of feed material. They enable the investigation of multiple conditions, thus generating a relatively large amount of data.This study establishes USD flocculation and centrifugation and joins a sequential multivariate data analysis (MVDA) to evaluate the multiparameter effects on primary recovery performance. MVDA techniques such as Principal Component Analysis (PCA) and Partial Least Squares (PLS) were used to handle the complex data sets and investigate the relationships between process parameters and responses. A strategy to assess floc characteristics using PCA was proposed to eliminate the visual inspection, and aid in the analysis, of particle size distribution (PSD) datasets. The PSD of non-sheared and sheared flocs provide good indicators of floc centrifuge performance.The findings show that this USD system can be used to forecast pilot scale performance. The sequential analysis demonstrated that the produced flocs are shear-sensitive in which feed preparation and process shear significantly impact the centrifugation of those flocs. Strong flocs may not necessarily result from high Camp number values (≥ 105) where optimisation of the flocculation chemical parameters is required.The novel integration of the USD systems with MVDA is a powerful platform to optimise and expand process know-how.

Effective Chlorella vulgaris Biomass Harvesting through Sulfate and Chloride Flocculants

Efficient microalgae harvesting is a great challenge hindering diverse industrial applications of microalgae. Flocculation is regarded as an effective and promising technology for microalgae harvesting. In this study, sulfate (Al2(SO4)3 and Fe2(SO4)3) and chloride flocculants (AlCl3 and FeCl3) were used to harvest Chlorella vulgaris. Flocculation conditions, including flocculant dose, flocculation time, stirring speed, stirring time, and flocculation pH, were optimized, and flocculant effects on microalgal cell status, floc characteristics, biomass composition, algal cell re-culture, and media recycling were investigated. All flocculants exhibited efficient flocculation efficiency (93.5–98.8%) with lower doses of sulfate salts (60 mg/L algal culture) and higher doses of chloride salts (100 mg/L algal culture). The tested flocculants had no obvious influence on biomass composition (including lipids, carbohydrates, proteins, and carotenoids), and microalgal cells in flocs could efficiently regrow. The spent medium of all treatments was successfully recycled for subsequent cell growth, thus reducing dependency on fresh medium.

Uncovering the optimal structural characteristics of flocs for microalgae flotation using Python-OpenCV

Coagulation-based dissolved air flotation is generally recognized as an efficient and economical method for removal of algae from eutrophicated water, whose efficiency is directly affected by the structural characteristics of flocs. However, it is not clear which floc structures are suitable for microalgal floatation, whether large and compact flocs or small and loose flocs have good rising performance. In this study, a novel technology for dynamically tracking the growth and rising behaviors of flocs was developed based on Python-OpenCV to visually uncover the optimal structural characteristics of flocs for Microcysts aeruginosa coagulation-flotation. Different coagulation flow fields (velocity gradient, G) were adopted to artificially create flocs with various structural characteristics and floatation kinetics. Results showed that G value had significant effects on the growth and rising behaviors of flocs, thus achieving intuitively different flotation kinetics. An idea rising velocity of 91.5 m h−1 was achieved by flocs with optimal structural characteristics generated at a suitable G of 34.1 s−1, which was 29–75% higher than that of flocs at other G. The rising velocity of floc was synergistically determined by the size and fractal dimension of floc. The structural characteristics (size and fractal dimension) of flocs were introduced into the calculation model of rising velocity, which guided the principle of optimal floc structure characteristics (large and compact) suitable for Microcysts aeruginosa removal using DAF. These may provide new technology for the studies of the growth and settling/rising behaviors of flocs, and lay a theoretical foundation for the design of DAF system with high load rate and the selection of optimal operating conditions applied to cyanobacteria blooms prevention and control.

Simultaneous In Situ Characterization of Turbulent Flocculation and Reactor Mixing Using Image Analysis and Particle Image Velocimetry in Unison

Floc characteristics, including their size distribution, mean size, and fractal dimension, are impacted by mixing intensity and duration, coagulant dosing method, dose, type, and pH. Herein, we directly employ flocs inherently generated during treatment to determine instantaneous velocity fields, which were further utilized to estimate local velocity gradients and turbulent kinetic energy dissipation (TKED) rates. This novel non-intrusive methodology, which combines particle image velocimetry (PIV) and an imagery-based sizing scheme, was examined through the characteristics of reactor mixing and flocculation from in situ measurements for conventional FeCl3 chemical coagulation and iron electrocoagulation (EC). Our first-of-its-kind procedure avoids the need to externally add artificial seeding particles for PIV analysis, automatically reducing the number of experiments, and simultaneously improves both accuracy and precision by linking fluid dynamics and particle characteristics with only a single experiment. The TKED rates estimated using flocs were largely similar with conventional artificial seeding at the early stage of flocculation when flocs were smaller. However, the new method is expected to estimate turbulence more accurately in the flocs’ microenvironment during the later stages of tapered flocculation when particle sizes are similar to dissipation eddy dimensions, especially at high particle concentrations (i.e., highly turbid waters). Measured size distributions, mean sizes, and fractal dimensions confirm the robustness of the present imagery-based sizing scheme and showed that EC produced numerous and more compact flocs than conventional coagulation.

Using the Flocculation Index to optimise coagulant dosing during drinking water treatment

Flocs produced during drinking water treatment play a key role in particle separation and removal. Floc characteristics affect both sedimentation and filtration efficiency, however, the methods used to optimise the coagulant dose during treatment do not usually take these into account. This study investigated the feasibility of using the Flocculation Index (FI), obtained from a photometric dispersion analyser (PDA) during flocculation, as a control parameter to optimise turbidity removal. Five waters, natural and synthetic, with different turbidity levels (from 6 to ⁓120 NTU) and low DOC (i.e., <5 mg/L) were used to study the effects of various alum doses on floc characteristics [i.e., initial floc aggregation (IFA), plateau (P) and variance (VAR)]. No correlation was found between the IFA and VAR values and the alum dose achieving the greatest turbidity removal and relative settling factor (RSF). However, P followed a similar pattern to the RSF, and was negatively correlated with the residual turbidity. An optimisation model was developed using response surface methodology and the effects of two independent variables (i.e., raw turbidity and alum dose) on P values were investigated. The model achieved a high correlation (R2 of ⁓98 %, p-value <0.05) and was validated using waters with different turbidity levels. It predicted the alum dose within 8 % error. The results indicate that the FI can be used as an alternative parameter for optimising the coagulation process.

Enhanced iron recovery from magnetic separation of ultrafine specularite through polymer-bridging flocculation: A study of flocculation performance and mechanism

The refractory low-grade iron ores are generally ground to fine particles in beneficiation, and the conventional magnetic separation process has difficulties in sufficiently recovering ultrafine Fe-bearing minerals, resulting in the loss of Fe to the tailings. In this study, the polymer-bridging flocculation performance of cross-linked starch (CLS), carboxymethyl starch (CMS), and sodium alginate (SA) on ultrafine specularite were explored by flocculation-magnetic separation and flocculation-sedimentation tests. The characteristics of specularite flocs and flocculation mechanism of three polymeric agents on specularite were researched with microscopic observation, laser particle measurement, zeta potential test, and FTIR analysis. The results showed that the flocculation of ultrafine specularite with CLS, CMS and SA increased the iron concentrate yield by 12.50%, 6.40% and 18.74% under optimal conditions. The CLS and CMS performed excellent selectivity for specularite, while SA exhibited poor selectivity due to its flocculation behavior on quartz. After the addition of CLS, CMS and SA, the ultrafine specularite was flocculated significantly, with the content of particles smaller than 20 μm reduced from 82.68% to 67.72%, 68.92% and 45.23%, correspondingly. The flocculation mechanism confirmed that the interactions of three flocculants with specularite included hydrogen bonding, chemisorption of carboxyl and hydroxyl groups, while neither CLS nor CMS interacted with quartz except for the hydrogen bonding adsorption of SA on the quartz surface.

The response and anti-stress mechanisms of nitrifying sludge under long-term exposure to CdSe quantum dots

The wide application of CdSe quantum dots (QDs) increases its stress risk to sewage treatment systems. This study evaluated the response of nitrification performance, floc characteristics and microbial community of nitrifying sludge under long-term exposure to CdSe QDs. Results showed CdSe QDs (≥1 mg/L) would decrease the activity of ammonia monooxygenase (AMO). Under the stress of 30 mg/L CdSe QDs, the activity of AMO was reduced by 66%, while the activities of hydroxylamine oxidase and nitrite oxidoreductase were enhanced by 19.1% and 26%, respectively. Thus, the final nitrification effects were not adversely affected, and the production rates of NO2−-N and NO3−-N were accelerated. Additionally, CdSe QDs improved biomass concentration in sludge and maintained the stability of sludge settleability. High throughput sequencing analysis showed that CdSe QDs evidently reduced the abundance and diversity of microbial community in nitrifying sludge. The abundances of amino acid metabolism and lipid metabolism were enriched. Moreover, CdSe QDs decreased the fluorescence intensity of tryptophan-like protein from 2,326 to 1,179 a.u. in loosely bound extracellular polymeric substances (EPSs) and from 3,792 to 3,117 a.u. in tightly bound EPSs. To relieve CdSe QD stress, the polysaccharide content increased from 0.31 to 0.61 mg/g MLSS and intracellular antioxidant defense was activated. With CdSe QD level increasing to 30 mg/L, the total antioxygenic capacity and the activities of catalase were enhanced up to 411% and 143.2%, respectively. Thereby, CdSe QDs had little adverse effects on cell membrane integrity, microbial metabolism and the abundance of Nitrospirae.

Comparative analysis of floc characteristics and microbial communities in anoxic and aerobic suspended growth processes.

A fully anoxic suspended growth process is an appealing alternative to conventional activated sludge (AS) due to considerable aeration reduction and improved carbon processing efficiency for biological nutrient removal (BNR). With development of the hybrid membrane aerated biofilm reactor (MABR) technology, implementation of a fully anoxic suspended growth community in BNR facilities became practical. To better understand potential limitations with the elimination of aeration, we carried out microscopic examination and 16S rRNA gene-based microbial community profiling to determine how an anoxic suspended growth would differ from the conventional aerobic process in floc characteristics, microbial diversity, microbial temporal dynamics, and community assembly pattern. Fewer filamentous populations were found in the anoxic mixed liquor, suggesting easily sheared flocs. The anoxic microbial community had distinct composition and structure, but its diversity and temporal dynamics were similar to the conventional aerobic community. A variety of well-studied functional guilds were also identified in the anoxic community. The anoxic microbial community assembly was more stochastic than the conventional aerobic community, but deterministic assembly was still significant with a large core microbiome adapted to the anoxic condition. PRACTITIONER POINTS: Flocs developed under the anoxic conditions had less filamentous backbones, implying reduced flocculation capacity and easily sheared flocs. Knowledge about the ecophysiology of Thauera, Thiothrix, and Trichococcus can help achieve good properties of the anoxic flocs. A diverse microbial community sustainably adapted to the fully anoxic condition, containing a variety of filaments, denitrifiers, and PAOs. The anoxic microbial community displayed a similar degree of diversity and temporal dynamics compared to the aerobic counterpart. The anoxic community's assembly was more stochastic, so it may be less subject to changes in environmental variables.

Characteristic Analysis on Temporal Evolution of Granulation in a Modified Anaerobic Digestion System

In the present study, the surface morphology, particle size distribution, sedimentation performance, and fractal characteristics of sludge flocs in a modified anaerobic baffled reactor (mABR) during start-up were analyzed by digital image analysis technology. The results showed that the special structure of mABR enabled successful start-up and granular sludge formation in a relatively short time. After the granular sludge was mature, the COD removal rate could quickly recover to the level before the change in organic loading rates (OLRs) within just six days, increasing from the lowest value of 76.8% to 80.2%, which indicated that the granular sludge could maintain a relatively stable micro-environment and make the metabolic process continue when the influent conditions changed suddenly. It was expected that this paper would be helpful for researchers to further develop a unified theory for anaerobic granulation and technology for expediting the formation of mABR granules.

Study on the characteristics and mechanism of the flocculation behaviour in a novel fluidized bed flocculator

Fluidized bed flocculator is a novel and efficient flocculation reactor. It has an efficiency that directly affected by flow field parameters. However, the structural characteristics of flocs and their influence on subsequent settling performance in fluidized bed flocculators are not clear. In this study, a multi-stage velocity gradient fluidized bed flocculator (MGF) was constructed for the continuous flocculation-sedimentation of kaolinite to investigate the growth and sedimentation behaviour of flocs. Additionally, MGF was compared with traditional mechanical stirring flocculation (MSF). Results showed that MGF achieved a higher removal efficiency (97.6 ± 0.7 %) with less coagulant and flocculant than MSF. Moreover, flocs generated in the MGF yielded a faster settling performance, which can reduce the sedimentation time by 60 times. Comparative analysis of floc structural characteristics, as well as their relationship with the settling velocity, demonstrated that flocs in MGF were more compacted than those in MSFs and thus achieved higher settling velocity. The settling velocity was collaboratively dominated by the size and fractal dimension of flocs. A modified Stokes’ settling velocity equation introducing the structural characteristics of flocs was derived, and verified by actual data to accurately and quantitatively describe the settling velocity of irregular flocs. These results indicated that MGFs have a better flocculation and sedimentation performance than MSFs for solid–liquid separation, and may lay a theoretical foundation for the design of efficient fluidized bed flocculators and popularize their application in practical engineering.

The Synergistic Effects of Al3+ and Chitosan on the Solid-Liquid Separation of Coal Wastewater and Their Mechanism of Action.

It is important to identify an environmentally friendly and efficient flocculant that can replace polyacrylamide for the solid–liquid separation of coal wastewater. In this study, to explore whether chitosan can be used as an environmentally friendly and efficient flocculant for the solid–liquid separation of coal wastewater, AlCl3–chitosan was used to conduct flocculation–sedimentation and dewatering tests under different chitosan dosages and shear-strength conditions for the prepared coal wastewater. Focused beam reflectance was measured to dynamically monitor the number of refractory fine particles, and the settled flocs were photographed and analyzed with microscopy to explore the effect of AlCl3–chitosan on the flocculation settlement effect and floc characteristics. The synergistic mechanisms of AlCl3 and chitosan were investigated using quartz crystal dissipative microbalance and zeta potential measurement. The results showed that the addition of chitosan can significantly improve the flocculation–sedimentation and dewatering effects of coal wastewater. A reasonable dosage under a certain shear strength is conducive to the reduction of fine slime particles, which results in a compact floc structure, increases the floc size, and improves the settling effect. The synergistic effect of AlCl3–chitosan improved the electric neutralization and adsorption bridging abilities of the chitosan, and the mixed solution of AlCl3 and chitosan had stronger adsorption on the carbon surface. This study provides a new approach to the selection of flocculants for coal wastewater treatment.

Comparison of polyferric chloride and polytitanium chloride in removal of organic and inorganic pollutants from young and old municipal solid waste leachate

The present study compared the polytitanium chloride (PTC) and polyferric chloride (PFC) in removal of Pollutants from young and old solid waste leachate. Moreover, synthesis of PTC and PFC coagulants, field emission scanning electron microscopy (FESEM) images, energy-dispersive X-ray spectroscopy (EDX) analysis, Fourier transform infrared spectroscopy (FTIR) analysis of PTC and PFC coagulants and flocs characteristics were examined. At optimal coagulant doses (250 mg/L for PTC and 400 mg/L for PFC), PTC removal efficiencies in old leachate for COD, readily biodegradable COD (rbCOD), color, TSS, turbidity, and total Kjeldahl nitrogen (TKN) were 91.30%, 92.94%, 99.80%, 98.06%, 99.76%, and 98%, respectively and for PFC were 81.15%, 81.17%, 94.23%, 90.32%, 96.09%, and 94.28%, respectively. PTC removal efficiencies in young leachate for COD, rbCOD, color, TSS, turbidity, and TKN, were 71.08%, 80.30%, 70.45%, 83.07%, 88%, and 88.57%, respectively, and for PFC were 65.06%, 71.21%, 61.36%, 80.76%, 84%, and 83%, respectively. According to FESEM-EDX analysis, flocs resulting from PTC coagulant were larger in size and more compacted in structure compared to PFC flocs. The results of this study indicated that PTC had a higher efficiency than PFC; therefore, it can be used as a suitable option for solid waste leachate treatment, especially old leachate.

Aggregation and settling characteristics of particulate matter and DOM in a southern China reservoir: Influence of hydraulic conditions and dosing methods

For the in-situ treatment process of landscape waters, ponds, reservoirs and other water bodies, there is a significant deviation between the experiment results and the actual treatment effect due to volume amplification effect. Therefore, this study systematically explored the influence of hydraulic conditions, dosing frequency, dosing intervals of coagulant, and coagulant dilution multiples on the removal efficiency of particulate and organic matter on a large scale to precisely simulate the practical treatment situation. Results showed that dosing intervals and dosing frequency played an important role in the aggregation and settling process of particulate matter by influencing the energy barrier between particles, while hydraulic conditions affected the structure and settling characteristics of flocs. The overall trend of the total organic matter was consistent with that of particulate matter. However, only the freshly formed aluminum hydroxide precipitates had adsorption activity to humic substances. The adsorption could be completed rapidly so that hydraulic conditions had no influence on the aggregation process of humic substances. While during stirring and aging process, humic substances was found to be released due to the polymerization and crystallization of aluminum precipitates. From the results of pilot tests, a treatment strategy was implemented for a reservoir in southern China and the ideal treatment effect was achieved. This study provided theoretical foundation and design guidance for the in-situ coagulation treatment of landscape waters, ponds and reservoirs.

Investigation of polyaluminum chloride (PACl) coagulation to remove cyanobacteria from maintenance to decay stage: Performance and mechanism

Cyanobacterial bloom is a global issue affecting drinking water supply, and coagulation process is important to remove cyanobacteria. Cyanobacteria can get into decay stage after a long-term maintenance stage during a successive bloom. Some studies compared cyanobacterial coagulation at both stages, but their removal performance is still an argument. To well address this debate, the performance and mechanism of PACl coagulation to remove cyanobacterial cells at both stages, was compared with or without extracellular organic matters (EOMs) in this study. Results showed that cyanobacterial coagulation performed better at decay stage than that at maintenance stage without EOMs, treated by equal dosages of PACl. However, an opposite result was observed with EOMs, since EOMs at maintenance stage exhibited lower inhibitory effects on the coagulation due to fewer contents and negative charge. Meanwhile, inter-particle bridging for cyanobacterial coagulation at maintenance stage became stronger via elevated high-MW EOMs than that at decay stage. Analyses of Zeta potential and flocs characteristics revealed that electrical neutralization was the main coagulation mechanism at both stages without EOMs, and electrostatic patch was responsible for cyanobacterial coagulation with EOMs. Moreover, inter-particle bridging and sweeping flocculation were involved in cyanobacterial coagulation with EOMs, leading to loosely flocs with a decrease of fractal dimension (Df, 0.6–0.7), intensity factor (If, 0.2–0.7), and recovery factor (Rf, 0.3–0.9). Overall, EOMs could differ the performance and mechanism of cyanobacterial coagulation at both stages, and thus, managing varied EOMs would be vitally necessary to optimize cyanobacterial coagulation from maintenance to decay stage of a successive bloom.

A hindered settling velocity model related to the fractal dimension and activated sludge flocs characteristics: Application to a sludge with a previous fragmentation and flocculation process

The modelling of the activated sludge hindered settling velocity as a function of the flocs characteristics and the incorporation of these models to the secondary settling tanks simulation is a hardly studied subject. Commonly used empirical models cannot describe the changes in the settling velocity caused by changes in the flocs characteristics. In this paper, a model for the hindered settling velocity as a function of the fractal dimension and other flocs characteristics is proposed. The model was used to describe the settling velocity after a flocculation process originated by activated sludge fragmentation. The model reproduces the observed abrupt decrease of hindered settling velocity in a small range of suspended solids concentration. It also enables to relate the flocs characteristics and the settling velocity to the fragmentation and sludge aggregation mechanisms.

Coagulation performance and floc properties for synchronous removal of reactive dye and polyethylene terephthalate microplastics

As a new type of pollutant, microplastics are widely distributed in printing and dyeing wastewater. Coagulation performance, floc characteristics and mechanisms for synchronous removal of reactive orange and polyethylene terephthalate (PET) microplastics using magnesium hydroxide and polyacrylamide (PAM) were investigated in this paper. The floc properties were evaluated by laser particle size analysis and on line intelligent photometric dispersion analysis. Coagulation mechanism was investigated by scanning electron microscope (SEM), Fourier transform infrared spectroscope (FTIR) and Zeta analyzer. The results showed that the removal efficiencies for reactive orange and PET were 98 % and 93 % under the optimal conditions of magnesium ion 100 mg/L, PAM 4 mg/L with pH value 11.75. The increase of pH, coagulant and PAM dosage would significantly enhance the removal efficiency. The average floc size reached 61.90 µm and these flocs aggregated together for fast sedimentation. Meanwhile, electrical neutralization and adsorption for reactive orange by magnesium hydroxide, PAM bridging for PET were the main mechanisms. The removal behavior of reactive orange and PET microplastics during coagulation has potential applications for the removal of printing and dyeing wastewater.

Quantification of 3-dimensional structure and properties of flocculated natural suspended sediment

Natural sediment flocs are fragile and highly heterogeneous aggregates of biogenic and minerogenic material typically with high porosity and low density. In aquatic environments dominated by fine, cohesive or mixed sediments they can dominate suspended sediment flux. Consequently, monitoring and modelling the behaviour, transport and distribution of flocs is very important for many aquatic industries, maintenance of waterways and conservation and management of aquatic waterbodies. Mathematical models that predict the behaviour of flocs rely on the accurate assessments of the size, shape, density, porosity and fractal dimension of flocs. These inherently 3-dimensional (3D) characteristics are typically derived from 2-dimensional (2D) data, largely due to the challenges associated with sampling, capturing, imaging and quantifying these fragile aggregates. We have developed new volumetric microscopy techniques which can quantify 3D internal and external structures and characteristics of sediment flocs. Here, these techniques were applied to quantify the 3D size (volume), shape and fractal dimension of natural and artificial sediment flocs and compare them to standard 2D approaches. Our study demonstrates that 2D approaches are under-estimating shape complexity and over-estimating the size and mass settling flux of flocs by up to two orders of magnitude, and the discrepancy between 2D and 3D is most marked for natural, organic rich macroflocs. Our study has significant implications for estimations of sediment flux at local to global scales within in aquatic environments. These new data and approaches offer the potential to improve the current parameterisation of sediment transport models and to improve the accuracy of current field-monitoring techniques.