Flocculation Time Research Articles

Influência do tamanho de flocos e da concentração de ar dissolvido na eficiência da flotação

RESUMO O presente artigo apresenta resultados de pesquisa que teve por objetivo a investigação da influência do tamanho de partículas floculadas na eficiência da clarificação de águas para abastecimento por flotação por ar dissolvido (FAD) com o emprego de método e equipamento para a aquisição e análise de imagens especialmente desenvolvidos para a caracterização da distribuição de tamanho de flocos e microbolhas de ar presentes no processo de flotação. Os ensaios foram realizados com água sintética (temperatura de 26,0±0,5oC; turbidez de 7,5±0,2 NTU; cor aparente de 38±1 uC; alcalinidade de 29,8±0,6 mgCaCO3.L-1; condutividade de 59,3±0,8 µS.cm-1; UV254nm de 0,128±0,004cm-1), a qual foi coagulada com a aplicação de 1,9 mg.L-1 de Al3+ (pH de 6,6±0,05; 22,5 mg.L-1alum). Os resultados alcançados demonstraram que: i) a distribuição de tamanho de partículas floculadas influenciou diretamente a clarificação por flotação da água em estudo, sendo que as melhores condições de floculação foram aquelas que conduziram à formação, em sua maioria, de partículas floculadas com diâmetro médio de Feret acima de 300 µm; ii) os menores valores residuais dos parâmetros analisados na água em estudo foram alcançados com o emprego da Condição 2 de floculação (T=17 min/G=60 s-1) associada a uma concentração em massa de ar (Cb) de 4,8 mg.L-1, entretanto, a FAD foi capaz de operar também com boa eficiência com a utilização de tempo de floculação (T) de 10 minutos; iii) o método e o equipamento desenvolvidos nesta pesquisa para aquisição e análise de imagens demonstraram constituir importantes ferramentas para a obtenção das distribuições de tamanho de flocos e microbolhas de ar.

Effects of the fractal structure and size distribution of flocs on the removal of particulate matter

This study sought to evaluate the effect of form and particle size distribution of formed flocs during flocculation on the removal of particulate matter (PM) by settling. The understanding of the intrinsic processes of water treatment is fundamental for the improvement of these processes, and this understanding is often limited by the use of indirect measurements. For this reason, this study evaluated the relationships among the morphology, particle size distribution (PSD), and particle volume distribution of flocs formed with mean flocculation velocity gradients (Gf) from 20 to 60 s−1 and settling velocities from 0.5 to 5.0 cm s−1 at flocculation times (Tf) from 10 to 60 min. A correlation analysis of all of the parameters was performed to identify the most significant direct measurement for characterizing the removal of PM. Strong correlations among parameters were observed when considering the variation with Gf for a given Tf, and moderate correlations were observed when considering the variation with Tf for a given Gf. The strong correlations that resulted from the alteration of Gf were a consequence of the significant changes in the morphological characteristics, PSD, and PVD of the flocs. The lower strengths of the correlations with the variation in Tf can be explained by the rapid attainment of the equilibrium steady-state between aggregation and disaggregation forces.

Optimization of flocculation efficiency of lipid-rich marine Chlorella sp. biomass and evaluation of its composition in different cultivation modes

This study aimed to optimize flocculation efficiency of lipid-rich marine Chlorella sp. biomass and evaluate its composition in different cultivation modes. Among three flocculants including Al3+, Mg2+ and Ca2+ tested, Al3+ was most effective for harvesting microalgal biomass. Four important parameters for flocculation were optimized through response surface methodology. The maximum flocculation efficiency in photoautotrophic culture was achieved at pH 10, flocculation time of 15min, Al3+ concentration of 2.22mM and microalgal cells of 0.47g/L. The flocculation in mixotrophic culture required lower amount of Al3+ (0.74mM) than that in photoautotrophic and heterotrophic cultures (2.22mM). The biomass harvested from mixotrophic culture contained lipid at the highest content of 42.08±0.58% followed by photoautotrophic (32.08±3.88%) and heterotrophic (30.42±1.13%) cultures. The lipid-extracted microalgal biomass residues (LMBRs) contained protein as high as 38–44% and several minerals showing their potential use as animal feed and their carbohydrate content were 16–29%.

Cells Harvesting of Tropic Ocean Oleaginous Microalga Strain Desmodesmus Sp. WC08

For biomass recovery of tropic ocean oleaginous microalgae strain Desmodesmus sp. WC08, eight flocculation methods (pH adjustment, Al2 (SO4)3, polyacrylamide, AlCl3, Ca (OH) 2, FeCl3, alum and chitosan) were evaluated and optimized. The results indicated that ferric chloride, aluminum sulfate, aluminum chloride and chitosan exhibited high flocculation ability and their flocculation efficiency were all beyond 94% at the optimal dosage (0.15, 0.4 and 0.03 gL-1, respectively). Chitosan displayed the most tremendous potential for biomass recovery from culture broth based on its feasibility and safety. Acetic acid and hydrous chloride, used to dissolving chitosan, had no significant difference in the flocculation efficiency. And when the pH of culture broth was set 5 or 6, the flocculation efficiency of chitosan was higher and the required flocculation time was less. More dose chitosan was needed to harvest the biomass following the cell growth stage. Overall, the optimal flocculation reagent for harvesting biomass of Desmodesmus sp. WC08 is chitosan, and its optimal flocculation conditions are: just when the pH of the culture broth was set to 6 and the dosage of chitosan was 0.03 g/L at the end of microalgae cultivation, more than 110g of algal biomass can be recovered just by per 1 g of chitosan. Meanwhile, there is little residual chitosan found in the final flocculation supernatant which can be reused to some extent.

Removal of Bentonite from Raw water by Novel Coagulant Based on Chitosan and Tannin

Polymer based on chitosan and tannin have been prepared and characterized using FTIR, UV, GC-Mass, X-ray spectra DSC and TG. All characterization techniques confirm the existence of chitosan and tannin. The effectiveness of chitosan-tannin polymer as a coagulant flocculant in treatment of surface water has been studied. Tests were carried out in laboratory on two kinds of water. The first one is synthesis water mixed with high and low concentrations of bentonite, simulating thus turbid water. The second one is raw water from the treatment station of Shatt Al-Arab River. The performance of coagulation flocculation process has been assessed by measuring the supernatant turbidity for different pH, doses and flocculation time of chitosan-tannin polymer. The obtained results show that chitosan-tannin polymer effectiveness was strongly dependent on pH and the doses of chitosan-tannin polymer, on the initial turbidity and on the water quality.

Optimization of multi-stage velocity gradients in a cylindrical fluidized bed flocculator

Flocculation time is conventionally believed to be proportional to the flocculation efficiency of a cylindrical fluidized bed flocculator. However, in a single-stage velocity gradient situation, the flocculation efficiency decreases when the optimal flocculation time is exceeded. A multi-stage velocity gradient was established in a cylindrical fluidized bed flocculator, based on the hydraulic classification theory. This multi-stage velocity gradient fluidized bed flocculator (MGF) created a more suitable environment for floc growth and protection, which was confirmed by the size distribution of flocs along the bed height. Correspondingly, the abatement efficiencies for Kaolin slurry and dyed wastewater treatment in the MGF were enhanced by 5–10%, and by 7–20%, respectively, compared with those in the single-stage velocity gradient fluidized bed flocculators (SGFs). The initial bed height distribution ratio along the velocity gradients was an important factor for MGF optimization.

Coprecipitation of vanadium with iron(III) in drinking water: a pilot-scale study

Vanadium concentrations higher than the Maximum Contaminant Level (MCL) of 50 μg/L set by the Italian Regulation were found in the groundwater of Mount Etna (Italy). Vanadium removal from this natural water by coprecipitation with iron(III) has been investigated in this study. Preliminary experiments were carried out at bench scale, while a large part of the study was conducted using a continuous flow pilot plant, operated in both in-line filtration (in-line iron(III) dosage followed by sand filtration with two sand filters in series) and direct filtration (iron(III) dosage in a flash mixed reactor, flocculation, sand filtration with two sand filters in series). Vanadium was effectively removed below the MCL by coprecipitation with iron (hydr)oxides produced by dosing ferric chloride. The pre-oxidation with chlorine has improved the vanadium removal by more than 25%, possibly due to the change in vanadium speciation. The breakthrough of iron micro-precipitates, with coprecipitated vanadium, has limited the duration of the process cycle because it resulted in iron concentration in the effluent higher than its MCL (0.2 mg/L). The addition of a cationic polyelectrolyte as flocculant aid has improved the flocs removal and therefore both iron and vanadium were removed well below their respective MCLs. The operating conditions were also optimized at pilot scale to minimize the sludge production while achieving the target vanadium effectiveness. Overall, the optimal condition to remove vanadium below its MCL (removal effectiveness >85%) requires a direct filtration scheme, a pre-oxidation with NaOCl = 0.3 mg/L, a FeCl3 dose of 5 mg/L, a flocculation time of 20 min, and the addition of 0.3 mg/L of a cationic polyelectrolyte as flocculant aid.

Effect of Natural Clarifying Agents ZTC1+1 II on Purification of <i>Angelica</i> Polysaccharides

Apply the univariate and orthogonal experiments, the purity of polysaccharide as index, to optimize the best purification conditions of natural clarifying agents ZTC1+1IIon Angelica polysaccharides. To determine the optimal temperature, the amount of clarifying agent, the concentration of the extracting solution ofAngelica, flocculation time, to select stable and feasible polysaccharide purification process.

Experimental Study on Sewage Treatment by Vortex-Grid Flocculation Technology

The aim of this test is to study the effect of treating CODCr, NH3-N, TP and turbidity of sewage with addition of coagulant PAC by using technology of combining vortex-grid flocculation tank with inclined tube sedimentation tank. The results show that the removal rate of devices treating CODCr, NH3-N, TP and turbidity are 68.36%, 22.22%, 82.60% and 80.90% respectively after the stability of the device operation on the condition that the dosage is 25 mg/L and the optimum flocculation time is 17 min.

Experimental Study on Sewage Treatment by Grid Flocculation Technology

Using grid flocculation technology inspected the effect of treatment of sewage by the addition of coagulant PAC. After the device is stable, under the 40 mg/L of dosage and 17.1 min of flocculation time conditions, the removal of turbidity, COD, NH3-N and TP is 72%, 48%, 13.8% and 77%.

저탁도 해수원수 특성에 적합한 응집 - 여과 공정의 최적화

This research is focused on coagulation and sand filtration process as a pretreatment of RO seawater desalination. RO systems require sufficient and reliable pretreatment process to produce superior quality of RO feedwater that can mitigate RO membrane fouling. This experiment was conducted to investigate the effectiveness of coagulation and filtration process under various experimental conditions including different coagulant dose, flocculation mixing intensity and time, turbidity, and filtration rate. The experimental results showed that the optimum pretreatment conditions resulting in lower SDI value suitable for RO feedwater were coagulation pH 6.5, raw water turbidity greater than 4 NTU, and media bed depth greater than 550 mm. However, flocculation mixing intensity, coagulant dose, and filtration rate relatively affected little on the filtration efficiency.

Seasonality of floc strength in the southern North Sea

The suspended particulate matter (SPM) concentration in the high turbidity zones of the southern North Sea is inversely correlated with chlorophyll (Chl) concentration. During winter, SPM concentration is high and Chl concentration is low and vice versa during summer. This seasonality has often been associated with the seasonal pattern in wind forcing. However, the decrease in SPM concentration corresponds well with the spring algal bloom. Does the decrease of SPM concentration caused by changing wind conditions cause the start of algae bloom, or does the algae bloom decrease SPM concentrations through enhanced flocculation and deposition? To answer the question, measurements from 2011 of particle size distribution (PSD), SPM, and Chl concentrations from the southern North Sea have been analyzed. The results indicate that the frequency of occurrence of macroflocs has a seasonal signal, while seasonality has little impact upon floc size. The data from a highly turbid coastal zone suggest that the maximum size of the macroflocs is controlled by turbulence and the available flocculation time during a tidal cycle, but the strength of the macroflocs is controlled by the availability of sticky organic substances associated with enhanced primary production during spring and summer. The results highlight the shift from mainly microflocs and flocculi in winter toward more muddy marine snow with larger amounts of macroflocs in spring and summer. The macroflocs will reduce the SPM concentrations in the turbidity maximum area as they settle faster. Consequently, the SPM concentration decreases and the light condition increases in the surface layer enhancing algae growth further.

Flocculation and floc break-up related to tidally induced turbulent shear in a low-turbidity, microtidal estuary

Flocculation and floc break-up dynamics were studied in two field campaigns with calm winds in the northernmost part of the Danish Wadden Sea. The studies were carried out using a LISST-100C together with CTD-instruments and a current meter. A quasi-Lagrangian profiling method was used to assess the dynamics on a short temporal scale (<tidal cycle) in the frame of the entire water column in the first campaign. In the second campaign the instruments were moored (Eulerian deployment) to get information on a longer temporal scale (>tidal cycle). The quasi-Lagrangian measurements showed strong flocculation and floc break-up dynamics in the lower part of the water column in the period around slack water. These dynamics were confirmed in the Eulerian deployments and were reoccurring in every tidal cycle. The dynamics were mostly governed by changes in turbulent shear. Strong microflocs with a lower mean threshold diameter of 50–60μm present at high turbulent shear flocculated to form fragile macroflocs with sizes of several hundred microns and mean diameters above 80μm around slack water periods. A hysteresis in floc break-up and flocculation was found at high water slack (HWS), as flocs formed at a root mean square velocity gradient (G) around 1s−1 were not broken up until the shear reached G>4s−1. As an effect, the flocculation time (time for flocculation from constituent microflocs to fragile macroflocs) was roughly 100min while the equivalent floc break-up time was roughly 200min. The asymmetrical, flood-dominated tidal wave showed how longer periods of low turbulent shear enhanced the hysteresis. The study demonstrates how the combination of the two deployment types will give a more adequate description of the flocculation dynamics over tidal cycles. Moreover, it shows the importance of incorporating specific flocculation aspects in numerical models, as a failure to incorporate the flocculation hysteresis results in an underestimation of the net import of sediment by about 30%.

Appraisal of Cassava Starch as Coagulant Aid in the Alum Coagulation of Congo Red from Aqua System

Cassava starch (CS) was evaluated as coagulant aid in the alum coagulation of an acid dye, Congo red (CR), from aqua system. The use of CS, as coagulant aid reduced the value of the optimum alum dose, required for coagulation of CR, by 50%. The abilities of alum and CS were assessed, separately, on the coagulation of varying concentrations of CR contaminated water by method of continuous variation of the alum and CS dosages. Alum coagulated the CR while the CS performed poorly. Varying dosages of the CS were combined with half the optimum alum dose, for each concentration, and reduction in the aqua CR concentration was observed. The percentage of CR removed was appreciable at all the pH studied and the amount of CR removed increased with increase in the flocculation time. The kinetics of the flocculation process was studied by fitting the data obtained to a kinetic model and the flocculation rate constant increased with increase in the initial CR concentration.

Exploration on bioflocculation of Nannochloropsis oculata using response surface methodology for biodiesel production.

Harvesting of algal biomass in biodiesel production involves high energy input and cost incurred process. In order to overcome these problems, bioflocculation process was employed and the efficiency of this process was further improved by the addition of a cationic inducer. In this work marine Bacillus subtilis was used for bioflocculation of Nannochloropsis oculata and ZnCl2 as cationic inducer. This study worked under the principle of divalent cationic bridging (DCB) theory. Under temperature stress and high pH, the bacterium produced exopolysaccharide that bound with microalga Nannochloropsis oculata and flocculated them. A maximum efficiency of 95.43% was observed with the optimised RSM parameters—temperature 30.78°C, pH 10.8, flocculation time 6.7 h, bioflocculant size 0.38 mL, and cationic inducer concentration 0.035 mM. The present investigation focused on the cost effective harvesting of microalga on a larger scale for biodiesel production than using toxic, ecofriendly chemical flocculants.

Comparison of naturally prepared coagulants for removal of COD and color from textile wastewater

&lt;p&gt;The wastewater generated by the textile industry is rated as the most polluting among all industrial sectors considering both volumes discharged and effluent composition. Present investigation intended for COD and color removal from textile wastewater using naturally prepared coagulants i.e. Surjana Seed Powder (SSP), Maize Seed Powder (MSP) and Chitosan. Effect of coagulant dose, flocculation time and temperature has been studied. The Sludge Volume Index (SVI) and turbidity were examined for various effects. SSP was more effective than Chitosan and MSP for the removal of COD and color and also, Chitosan was more efficient than SSP and MSP considering SVI and turbidity. Maximum percentage reduction corresponds to 75.6 and 62.8 was obtained for removal of COD and color respectively using SSP.&lt;/p&gt;

Thixotropic behavior of self compacting concrete with different mineral admixtures

Experimental investigations are carried out on Self Compacting Concrete (SCC) in the presence of mineral admixtures silica fume, limestone powder and fly ash for a target slump of 700±20mm and minimum static segregation. SCC is a thixotropic material whose steady state is governed by Bingham constitutive model and it flocculates with resting time. The characteristic flocculation time is obtained for the different mixes, together with the flocculation rate Athix based on ICAR rheometer measurements. Results indicate that addition of silica fume (2.5% replacement), limestone powder (15% replacement) and fly ash (10% replacement) increases flocculation rate Athix significantly.

Optimization of phosphorus removal in secondary effluent using immersed ultrafiltration membranes with in-line coagulant pretreatment — implications for advanced water treatment and reuse applications

In-line addition of alum and ferric chloride was conducted at a hollow-fibre immersed ultrafiltration (UF) membrane pilot plant, using secondary effluent from a municipal wastewater treatment plant (WWTP) as the feed. The objective of such pretreatment was to remove phosphorus from the feed from an initial concentration of approximately 5 mg/L to below 0·3 mg/L. The simplified in-line coagulant addition process involved hydraulic mixing of the coagulant into the feed and subsequent flocculation, and a greatly reduced (12 – 14 min) flocculation time relative to conventional coagulation-flocculation-settling treatment. Both alum and ferric chloride effectively removed phosphorus to below the 0·3 mg/L threshold when applied as a pretreatment at optimized doses, both of which were below the WWTP’s current coagulant dose (as ferrous chloride). This simplified pre-treatment scheme provided consistent enhanced removal of phosphorus and organic compounds. These results suggest that simplified in-line coagulant addition in advance of immersed UF membranes enhances the ability to produce treated effluent suitable for water-reuse applications.

Organics removal and protein recovery from wastewater discharged during the production of chondroitin sulfate

Bentonite, chitosan and polyaluminum chloride (PAC) were applied to treat wastewater discharged during the production of chondroitin sulfate and recover protein dissolved in the wastewater. The results showed that the combination of pH 9.00, 3-4 mL chitosan solution, 2 g of bentonite and 5 mL of 8% PAC solution per 100 mL of wastewater with a 4.0 h flocculation time were the optimal conditions for the recovery of protein and removal of total organic carbon (TOC) from wastewater. A pilot-scale test also was conducted, and 130 kg (dry weight) of sediment was obtained from 1.1 m(3) of discharged wastewater. This sediment contained abundant amino acids (proteins comprised 61% of the total sediment), after the recovery of protein, the dissolved TOC concentration in wastewater was decreased by approximately 80% and the residual wastewater could be readily disposed using a traditional activated sludge process.

Experimental Study on Micro-Polluted Raw Water of Kongmu Lake Treatment by Vortex Clarifier

Through pilot scale test, inspection the effect of treatment of micro-polluted raw water of Kongmu Lake with vortex clarifier accomplished by the addition of coagulant PAC. After the stable operation of the vortex clarifier, in the 30 mg/L of dosage and 6.8 min of flocculation time conditions, the removal of turbidity, NH3-N, TP, UV254 and COD is 94.2%, 22.9%, 84.8%, 45.2% and 78.5%.