Fine Solids Research Articles

Evaluation of Surface and Subsurface Processes in Permeable Pavement Infiltration Trenches

The hydrologic performance of permeable pavement systems can be affected by clogging at the pavement surface and/or clogging at the interface where the subsurface storage layer meets the underlying soil. The objective of this paper was to evaluate changes in infiltration and exfiltration using three pressure transducers installed in piezometers along the length of two, 2.47-m wide, permeable pavement strips. Each system was retrofitted in the parking lane of a curb-and-gutter system in Louisville, Kentucky. The strips received run-on from a drainage area about 20–25 times larger than the paver area. Below each permeable pavement strip (16.8-m and 36.6-m long) was a deep (3.0 m) and narrow (0.6 m) infiltration trench. Piezometers were installed at the bottom of the trench about 1 m from the uphill edge, and at roughly one-third and two-thirds along the permeable paver strips, to measure the rise and fall of water for 13 months. Initially, infiltrating run-on was localized near the uphill edge. During periods with intense runoff, the localized inflow accumulated in the trench faster than it could move laterally creating a measureable subsurface gradient between piezometers. Runoff transported solids to the uphill edge where a portion was filtered and accumulated between the paver blocks. With time, surface clogging progressed along the paver strip past the next piezometer. The localized infiltration caused the subsurface water level gradient between piezometers to reverse. After each event, the exfiltration rate per wetted surface area was calculated for fixed 0.15-m intervals. The exfiltration rate decreased drastically after the first few events. The primary cause of the initial exfiltration rate decline was attributed to infiltrating water rinsing the fine solids attached to the washed aggregate and depositing them at the bottom of the trench. Silt and clay-sized particles (particle size smaller than 75 μm) accounted for about 1.7–1.8% of the washed aggregate mass. This large source of fine-grained particles from construction materials can be eliminated if cleaner aggregate is available and used. A continued and significant decrease in exfiltration rate with age was measured during year 1 of use. To optimize the design of these systems, a lifecycle analysis incorporating exfiltration rate decline with age should be included. Another item to consider during the design process is the variability of urban soils. Although these sites are across the street from one another, exfiltration rates were markedly different. Installation should be targeted in soils with larger hydraulic conductivities to improve hydrologic performance, so more preconstruction soil borings and soil tests are necessary to characterize the in situ soils.

Migration of Fine Solids into Product Bitumen from Solvent Extraction of Alberta Oilsands

The extraction of bitumen from the oilsands using solvents has the potential to avoid the environmental problems with wet tailings associated with water-based extraction technology. One of the key performance parameters for this technology is the concentration of fine solids in the recovered bitumen. In this study, the concentration and properties of the fine solids in cyclohexane-extracted bitumen were examined as a function of the water content of the ore. Total water contents from 3.4–13.4 wt % gave the lowest concentrations of fine solids in the bitumen, ca. 0.2 wt % of the initial mass of a low-fines content ore. Higher fine solids contents in the bitumen were observed with water concentrations outside this range and with higher concentrations of fine solids in the initial oilsands ore. The fine solids exhibited a distribution of surface properties, and the most hydrophobic, carbon rich solids were carried into the bitumen even under the most favorable conditions. When the bitumen was more contaminat...

Pseudomonas putida Biofilm Facilitates Fine Solids, Water and Oil Separation from Oil Sands Tailings

Aims: The generation of the tailings, poor settling slurry contaminated with emulsified bitumen, significantly increases the negative impact of oil sands operations on the environment and human health (contamination of surface and ground water with hydrocarbons and naphthenic acids, methane emission), as well as operation cost. Poor effectiveness of conventional tailings settling and clean-up technologies contributes to the daily increase of the quantity of tailings deposited in ponds covering now more than 130 km. There is an urgent need for development of novel tailings settling technologies. The aim of the present study is a comparative analysis of the impact of Pseudomonas putida planktonic and biofilm populations on oil, solids and water separation in tailings, and the investigation of the mechanisms involved in bioseparation. Methodology: Mature fine tailings (MFT) were exposed to Pseudomonas putida planktonic populations and biofilms at agitation followed by static conditions for settling. Oil-solids-water separation was determined by water and oil release from MFT in comparison with untreated tailings. Interaction of tailings with microbial populations was Research Article Kostenko et al.; JSRR, Article no. JSRR.2014.004 111 investigated with scanning electron microscopy (SEM), confocal scanning laser microscopy (CSLM) and energy-dispersive X-ray (EDAX) spectroscopy. Results: The exposure of mature fine tailings to microbial cultures, and especially to biofilms, significantly increase tailings densification, dewatering and bitumen release. The separation efficiency is associated with fine clay aggregation due to the interaction with the microbial cells, biofilm colonies and extracellular polymeric substances (EPS). Conclusion: The mechanism driving the observed biodensification is the aggregation of fine solids via flocculation by biofilm-produced EPS and bacterial cells. Microorganisms were also observed to destabilize emulsions and enhanced residual bitumen release from tailings.

Pilot 규모의 경사판 침전지 시험을 통한 국내 석탄광산배수내 부유물질의 지구화학적 반응특성 및 조정영향

Fine suspended solids from coal mine drainage were treated in the treating plant, using two different pilot-scale inclined clarifiers: radial and lamella types. Suspended solids in the mine drainage were monitored along with other geochemical factors, and metal contents. Fe and Mn are the main chemical components in the drainage, which exist predominantly as total metal forms, whereas dissolved portion is negligible. The raw mine drainage is subject to physical and chemical treatment using <TEX>$CaCO_3$</TEX> and NaOH, therefore the suspended solids are thought to be composed of Fe and Mn precipitates, possibly <TEX>$Fe(OH)_3$</TEX>, along with carbonate precipitates. The elemental composition of precipitates are confirmed by SEM-EDS analysis. As nearly all the dissolved ions were precipitated in the primary process by <TEX>$CaCO_3$</TEX>, no further aeration or prolonged oxygenation are of necessity in this plant. Adoption of inclined clarifier proved to be effective in treating fine suspended solids in the current plant. Successful application of the inclined clarifier will also be beneficial to improve the current treating process by excluding the current application of chemical agent in the first stage. The final effluents from the pilot plant meet the national standards and the low dissolved Fe and Mn contents are expected not to cause secondary precipitation after discharge.

침전 및 여과를 통한 H 광산배수 내 미세부유물질 및 용해성 중금속의 제거 : 현장실험을 중심으로

Fine suspended solids and soluble heavy metals generated from mine drainage could destroy environment as the aesthetic landscapes, and depreciate water quality. Therefore, this research is focused on process development applied the actual field for controlling fine suspended solids and heavy metals, and so that bench-scale tests were performed for field application based on advanced researches. The field of mine drainage in this research was in H mine located Taebaek-si, Gangwon-do. The inclination plates were mounted 2 kinds of arrangement (octagon and radial types) in circle type settling basin. The inclination plates could be helped to settle of suspended solids; decreased 34% of suspended solids and 50% of turbidity in effluent. Radial type of inclination plates showed the results that is more efficient to settle of suspended solids (average to 3.45 mg/L) compared to octagon type. In the experiments to decrease retention time of mine drainage in settling basin from 6 hrs to 1.5 hrs, suspended solid concentration was exceeded to 30 mg/L as the standard for suspended solid at 10 days after the operation under tha retention time of 3hrs and 1.5hrs. In the tests for filtration, granular activated carbons were indicated the better effective to filtering and absorption of fine suspended solid and soluble heavy metals than anthracite.

Use of carbon dioxide stripping for struvite crystallization to save caustic dosage: performance at pilotscale operation

The feasibility of stripping CO2 from anaerobic digester centrate (generated in a sludge dewatering process) to raise pH, and therefore reduce the cost of caustic chemical(s) dosage for similar operation in a struvite-recovery system, was investigated. A cascade CO2 stripper was installed in a pilot-scale, struvite-recovery reactor system at the Lulu Island Wastewater Treatment Plant, Richmond, British Columbia, Canada, as a replacement of part of (about 1/3) the reactor downpipe. Centrate was used as the process feed. Both the influent and the effluent from the struvite reactor were analyzed for pH, temperature (°C), and concentrations of Mg, NH4-N, and PO4-P. Results indicated that, by adding the CO2 stripper, caustic chemical savings was as much as 46% – 65%. Moreover, because of the capability of the stripper in providing a more gradual pH increase, fewer fine solids were produced in the reactor than when caustic solution was used to raise the pH of the reactor.

Intensive rearing of cod larvae (Gadus morhua) in recirculating aquaculture systems (RAS) implementing a membrane bioreactor (MBR) for enhanced colloidal particle and fine suspended solids removal

Intensive rearing of Atlantic cod larvae (Gadus morhua) was investigated in a conventional recirculating aquaculture system (cRAS) and a membrane modified RAS (mRAS). Cod larvae are sensitive to water quality, and beneficial effects on growth and survival from enhanced removal of colloidal particles, fine suspended solids and nutrient reduction were expected. Membrane bioreactors (MBR) are a potential technology for advanced water treatment in aquaculture. The aim of this project was to assess the effect of an MBR system for enhanced treatment in RAS. A cRAS and mRAS treatment train were operated in parallel. In the mRAS Scheme 8.5% of the recycle stream was filtered through the membrane at any time. The mRAS scheme demonstrated a significantly lower turbidity and number of colloidal particles as compared to the cRAS scheme, as well as significantly lower bacteria concentrations and more stability. Overall a 13% higher cod larvae growth (weight, %) at 40dph and 3.5% higher survival rate at 50dph was measured in the mRAS scheme. Results show there is a great potential of implementing a membrane filtration system in aquaculture recycling systems.

Membrane performance and fouling behavior of membrane bioreactors installed in marine recirculating aquaculture systems

Accumulation of fine suspended solids and colloids in a recirculating aquaculture system (RAS) can be avoided by integrating a membrane filtration unit into the system, where the inclusion of a membrane bioreactor (MBR) may be an alternative. The main purpose of the study was to identify how the feeding regime affected membrane performance and fouling phenomena caused by dissolved and submicron colloidal particles in the system, and how the membrane impacted general water quality and particle characterization. To be able to evaluate membrane performance and fouling behavior, transmembrane pressure (TMP) was monitored and assessed in relation to changes in rearing conditions and different water quality parameters observed. From this study the positive influence on the chosen water quality parameters was apparent, where an improved water quality was observed when including a membrane filtration in RAS. Selected water quality parameters and TMP changed during the experimental period in response to the feeding regime, where algae paste, decaying rotifers and dry feed seemed to contribute the most to membrane fouling. Analysis of the concentration of submicron particles and particle size distribution (PSD) (particles<1μm) showed both a higher concentration and a more spread distribution in the rotifer/algae paste and dry feed period compared to the Artemia period, which might explain the observed increase in fouling. This study also showed that adapted procedures for concentrate removal are important to prevent hydrolysis of retained particles in the concentrate and leakage of nutrients and organic matter back to the system.

Integrated Membrane Bioreactor for Water Quality Control in Marine Recirculating Aquaculture Systems

The aquaculture live feed organisms Acartia tonsa (a calanoid copepod, experiment 1) and Brachionus “Cayman” (a rotifer, experiment 2) were cultivated in marine recirculating aquaculture systems (RAS), respectively. The pilot plant was built as a combination of conventional RAS (cRAS) and as a modified RAS which implemented an ultrafiltration membrane bioreactor (MBR) for the removal of fine suspended solids and colloidal particles as part of the treatment system (mRAS). The two treatment schemes were connected to the same biofilter (a moving bed bioreactor). In the first experiment, the membrane was operated with no extraction of concentrate, and hydraulic retention time (HRT) of 6 hours (i.e., water exchange in the cultivation tanks of 4 times per day). In the second experiment, the membrane was operated with daily extraction of concentrate, and HRT of 12 hours. Results show that the MBR option is more efficient in removing particles from the recycle stream than conventional RAS. However, the impact this has on the number of particles in the live feed cultivation tanks is not readily apparent based on particle analysis. The amount of suspended solids added during feeding exceeds the amount removed in the recycle system. This requires a higher recirculation rate and different membrane operating conditions.

Correlation of thermal conductivity of suspension plasma sprayed yttria stabilized zirconia coatings with some microstructural effects

Yttria-stabilized zirconia (3YSZ) coatings were successfully obtained by suspension plasma spraying. The coatings present generally two-zones-microstructure comprising nanostructured zones contributed by unmolten, partially sintered nanoparticles surrounded by lamellar splats formed from molten and agglomerated in-flight fine solids. In addition, different types of cracks inside the coating microstructure were classified and quantified by image analysis such as e.g. inner microcracks and segmentation cracks associated with quenching process as well as horizontal interlamellar cracks. Thermophysical properties of sprayed coatings were tested with a thermal diffusivity set up basing onto light flash principle. Subsequently, the thermal conductivity was determined with the use of literature data of density and specific heat. The calculations showed very low thermal conductivities values. The values did not correlate with coatings porosity data. Consequently, the analysis of variance (ANOVA) test allowed evaluating the possible impact of the various types of cracks on thermal conductivity. By this analysis, a good correlation between vertical cracks, which include microcracks and segmentation cracks, and thermal conductivity was found. The findings also confirmed the increase of thermal conductivity associated with this type of cracks.

Characterisation of atmospheric deposited particles during a dust storm in urban areas of Eastern Australia

The characteristics of dust particles deposited during the 2009 dust storm in the Gold Coast and Brisbane regions of Australia are discussed in this paper. The study outcomes provide important knowledge in relation to the potential impacts of dust storm related pollution on ecosystem health in the context that the frequency of dust storms is predicted to increase due to anthropogenic desert surface modifications and climate change impacts. The investigated dust storm contributed a large fraction of fine particles to the environment with an increased amount of total suspended solids, compared to dry deposition under ambient conditions. Although the dust storm passed over forested areas, the organic carbon content in the dust was relatively low. The primary metals present in the dust storm deposition were aluminium, iron and manganese, which are common soil minerals in Australia. The dust storm deposition did not contain significant loads of nickel, cadmium, copper and lead, which are commonly present in the urban environment. Furthermore, the comparison between the ambient and dust storm chromium and zinc loads suggested that these metals were contributed to the dust storm by local anthropogenic sources. The potential ecosystem health impacts of the 2009 dust storm include, increased fine solids deposition on ground surfaces resulting in an enhanced capacity to adsorb toxic pollutants as well as increased aluminium, iron and manganese loads. In contrast, the ecosystem health impacts related to organic carbon and other metals from dust storm atmospheric deposition are not considered to be significant.

The crud formation during the long-term operation of the V(V) and Cr(VI) extraction

The roles of the emulsifiers in the crud formation during the long-term operation during the vanadium and chromium extraction were studied. The crud produced in the long-term operation of extraction was determined by GC–MS for organic phase and XPS for solid particles. The results indicate that the redox reaction occurs between Cr(VI) and organic compounds, and the reduction products of Cr(VI) induce more stable emulsion. Additionally, the roles of other types of solid particles and organic compounds confirmed before were carried out by thermodynamic calculation and experiments combined with discussion. Three-dimensional network structure of silica and precipitation of various cations act as the major incentives to stimulate the emulsion. Whereafter, crystallization of sodium sulfate and the reduction of Cr(VI) take place at the surface of emulsion droplet, and the organic compounds are prone to be adsorbed by these fine solids which subsequently consolidate the newly formed surface of droplet. The interactions between emulsion droplets were calculated according to the extended DLVO theory. The comprehensive stabilization mechanisms were also proposed, including the composite interfacial film mechanism, the steric hindrance mechanism and the double electric layer mechanism.

광산배수 부유물질 저감을 위한 다양한 여과 매질의 특성 및 적용성 평가 - H 석탄광산 배수

Fine suspended solids from mine drainage draw attentions due to their potential adverse influences on the water quality, such as increasing turbidity and degrading aesthetic landscape. Currently, sand filter beds are adapted in some mine drainage treating systems. However, more efficient system is in demand, as the existing sand beds reveal some problems, such as frequent maintenance intervals. Various filtering mediums including fly ash, mine tailing aggregates and the sand were tested for improving the current system, using column experimental set-up. Mine drainage samples were collected from the current treating systems in the abandoned H coal mine. The experiment was run for 7 days. Suspended solids recorded as 100.9 mg/L and the value exceeds the current standard, 30 mg/L. Sand was proved to still be the optimum medium for the fine suspended solids, compared to fly ash and fly ash + sand. Mine tailing aggregates were placed at the exit of the columns, substituting gravels. The tailing aggregates is made by mine tailings and clay. Sand bed filters can also be improved by mixing granular activated carbon, which was found to be economical and efficient in the batch experiment, conducted at the same time.

H 광산배수 내 미세부유물질 및 용해성 중금속의 제거를 위한 침전 및 여과 공법에 관한 연구

Fine suspended solids generated effluence from treatment process of mine drainage could destroy environment as the aesthetic landscapes, and depreciate water quality. Therefore, the purpose of this research is focused on process development applied the actual field for controlling fine suspended solids and heavy metals, and so lab-scale test was performed for inducement of basic data. The mine drainage used in this research was sampled in H mine located Jeongseon-gun, Gangwon-do. Concentration of suspended solid, arsenic, iron and manganese was exceeded the standard of contaminant limitation for the clean water, and particle size of suspended solid was less than 10 m as fine particle. Although hydraulic retention time of mine drainage for effective settling was required more than 6 hours, hydraulic retention time would be increased in winter season when the settling efficiency could be reduced because of viscosity decreasing. Moreover, installed inclination plate helped to increase settling efficiency of suspended solid about 48 %. Filtering media that was the most effective removal of suspended solids and heavy metal was decided granular activated carbon of 1~2 mm was the optimal size.

Assessment of Existing Roadside Swales with Engineered Filter Soil: II. Treatment Efficiency and in situ Mobilization in Soil Columns

Use of roadside infiltration systems using engineered filter soil for optimized treatment has been common practice in Germany for decades, but little documentation is available regarding their long-term treatment performance. Here we present the results of laboratory leaching experiments with intact soil columns (15 cm i.d., 25-30 cm length) collected from two German roadside infiltration swales constructed in 1997. The columns were irrigated with synthetic solutions of unpolluted or polluted (dissolved heavy metals and fine suspended solids) road runoff, as well as a soluble nonreactive tracer (bromide) and a dye (brilliant blue). The experiments were performed at two irrigation rates corresponding to catchment rainfall intensities of approximately 5.1 and 34 mm/h. The bromide curves indicated that preferential flow was more pronounced at high irrigation rates, which was supported by the flow patterns revealed in the dye tracing experiment. Nonetheless, the soils seemed to be capable of retaining most of the dissolved heavy metals from the polluted road runoff at both low and high irrigation rates, except for Cr, which appears to pass through the soil as chromate. Fluorescent microspheres (diameter = 5 μm) used as surrogates for fine suspended solids were efficiently retained by the soils (>99%). However, despite promising treatment abilities, internal mobilization of heavy metals and P from the soil was observed, resulting in potentially critical effluent concentrations of Cu, Zn, and Pb. This is mainly ascribed to high concentrations of in situ mobilized dissolved organic carbon (DOC). Suggestions are provided for possible improvements and further research to minimize DOC mobilization in engineered filter soils.

Solvent screening for non‐aqueous extraction of Alberta oil sands

AbstractNon‐aqueous extraction of bitumen from oil sands has the potential to reduce fresh water demand of the extraction process and eliminate tailings ponds. In this study, different light hydrocarbon solvents, including aromatics, cycloalkanes, biologically derived solvents and mixtures of solvents were compared for extraction of bitumen from Alberta oil sands at room temperature and ambient pressure. The solvents are compared based on bitumen recovery, the amount of residual solvent in the extracted oil sands tailings and the content of fine solids in the extracted bitumen. The extraction experiments were carried out in a multistage process with agitation in rotary mixers and vibration sieving. The oil sands tailings were dried under ambient conditions, and their residual solvent contents were measured by a purge and trap system followed by gas chromatography. The elemental compositions of the extraction tailings were measured to calculate bitumen recovery. Supernatants from the extraction tests were centrifuged to separate and measure the contents of fine solid particles. Except for limonene and isoprene, the tested solvents showed good bitumen recoveries of around 95%. The solvent drying rates and residual solvent contents in the extracted oil sands tailings correlated to solvent vapour pressure. The contents of fine solids in the extracted bitumen (supernatant) were below 2.9% for all solvents except n‐heptane‐rich ones. Based on these findings, cyclohexane is the best candidate solvent for bitumen extraction, with 94.4% bitumen recovery, 5 mg of residual solvent per kilogram of extraction tailings and 1.4 wt% fine solids in the recovered bitumen. © 2012 Canadian Society for Chemical Engineering

Influence of water and ethanol on transport properties of the jets used in suspension plasma spraying

The suspensions of fine solids in such liquids as water, ethanol or their mixtures are increasingly used as a feedstock in thermal spraying using plasma jets. The liquids are evaporated during processing what modifies thermodynamic and transport properties of the jets. The transport properties, such as viscosity and thermal conductivity were calculated for of argon with hydrogen plasma working gases mixed with evaporated entirely suspension liquids. The suspension liquids were water, ethanol and their mixtures having the composition increasing from water with 25wt.% of ethanol to water with 75wt.% ethanol. Finally, the factor, known as ability of melting factor, describing the capacity of plasma to melt solid particles was calculated. The calculation showed that the presence of vapors of water, ethanol or their mixtures increases considerably the heat transfer of the plasma working gases to the particles.

Comparing the effects of feeding a grain- or a fish meal-based diet on water quality, waste production, and rainbow trout Oncorhynchus mykiss performance within low exchange water recirculating aquaculture systems

Feeding a fish meal-free grain-based diet (GB) was compared to feeding a fish meal-based diet (FM) relative to water quality criteria, waste production, water treatment process performance, and rainbow trout Oncorhynchus mykiss performance within six replicated water recirculating aquaculture systems (WRAS) operated at low exchange (0.26% of the total recycle flow; system hydraulic retention time=6.7 days). Rainbow trout (214±3g to begin) were fed the GB diet within three WRAS and the FM diet within the other three WRAS for 3 months. Feeding the GB diet resulted in significantly greater total ammonia nitrogen (TAN) throughout the study, as well as significantly greater total suspended solids (TSS) and carbonaceous biochemical oxygen demand (BOD) over the greater part of the study. Greater counts of fine solids (2–30μm) were associated with the GB diet. Water clarity was improved for the GB diet as reflected by significantly reduced true color and increased ultraviolet transmittance. Total and dissolved phosphorous, as well as the daily mass captured per kg feed of total phosphorous were significantly lower within the effluent associated with the GB diet. The daily mass of total nitrogen and TSS captured per kg feed and discharged from each WRAS was equal between diets, but waste load among three discharge flows varied. Waste removal efficiency across unit processes was similar between diets, with the exception of solids removal efficiency across the microscreen drum filter and the radial flow settler, which was generally lower for the GB diet. Rainbow trout growth, feed conversion, condition factor, and survival were similar between diets. Survival was 99.5±0.2% for both diet treatments. Skin-on fillet yield and whole-body protein levels were significantly greater at the end of the study for trout fed the GB diet. Overall, the GB diet evaluated during the present study proved to be a viable feed option for use within a low exchange WRAS. However, further refinements to grain-based diet formulations and/or use of ozone to improve water quality when feeding GB diets within low exchange WRAS could be beneficial.

Discrete phase modeling study for particle motion in storm water retention

This study compares three different types of multiple phase models to determine the most appropriate one for predicting the behavior of various types of storm water solids in a rectangular retention chamber. Two Lagrangian frame of coupled and uncoupled particle tracking models based on the interaction between the discrete phase and the continuous phase were tested. The third model was a sediment transport model using the Eulerian frame. This study tested five different storm water solids classified by particle size and settling characteristics. Particle retention efficiency and computational time were considered in determining the most appropriate multiphase model. For the gross solids, the Lagrangian coupled model provided the best agreement with the physical model measurements. The Eulerian frame model matched retention efficiency well for the high density coarse and finer solids. Although the Eulerian frame shows reliable retention prediction for most of the solid types, the Lagrangian coupled model can be an effective alternative requiring significantly reduced computational time.

Suspended solid abatement in a conical fluidized bed flocculator

With the random movement of silica gel beads in a conical fluidized bed, micro-vortices resulting from the fluidization promoted the collision and aggregation of suspended fine kaolin powders. The abatement efficiencies of the suspended fine solids under several hydrodynamic conditions were studied, and a suitable control strategy for operating the conical fluidized bed flocculators was identified. The suspended solids abatement efficiency was found to increase with increasing Camp Number and flocculation time (T), but decreased with the increase of velocity gradient (G) within the range studied in this research (165.1–189.6 s−1). The abatement efficiencies were all more than 60% at the range of G = 165−180 s−1 and T = 15−33 s at an initial kaolin solid concentration of 150 mg·L−1, polymer aluminum chloride dosage of 60 mg·L−1 and sedimentation time of 20 min. However, the formation of flocs was influenced by the liquid backmixing. Excessive backmixing caused the breakup of flocs and resulted in difficulty for the fine powders to aggregate and sediment to the reactor bottom. The results of the calculated fractal dimension and measured free sedimentation velocity of flocs obtained at different runs showed similar flocs properties, and indicated an easy control strategy for sedimentation of the flocs.