Flocculation Sedimentation Research Articles

Harvesting microalgae by flocculation–sedimentation

Slurries of five marine and freshwater microalgae (Chlorella vulgaris, Choricystis minor, Cylindrotheca fusiformis, Neochloris sp., Nannochloropsis salina) were effectively flocculated using aluminum sulfate and ferric chloride as flocculants. The flocculant dose for 95% removal of the algal biomass by sedimentation in a standardized 62min treatment depended on the following factors: the type of the flocculant; the algal species and cell diameter; the concentration of the biomass in the algal slurry; and the ionic strength of the suspending fluid. For all algae, the flocculant dose for 95% removal of the cells increased linearly with the concentration of the biomass in the slurry. Aluminum sulfate was a generally better flocculant than ferric chloride. Less flocculant was required for flocculation from a high ionic strength medium for the one alga (C. vulgaris) that could be grown both in freshwater- and seawater-based media. Quantitative relationships are reported for the flocculant dose dependence on the biomass concentration in suspensions of the five algae.

Flocculated sediments can reduce the size of sediment basin at construction sites

Due to stringent water quality regulations on stormwater discharges, there is increasing interest in chemically-assisted settling of suspended sediments at construction sites. This study investigated settling characteristics of flocculated sediment by polyacrylamide (PAM) in a top-loading settling tube. Studied sediment materials were obtained from construction sites in North Carolina, USA: Coastal Plain loamy sand (CPLS), Piedmont sandy clay loam (PSCL), Piedmont silt loam (PSL), and Mountain clay loam (MCL). The four different sediment suspensions mixed with and without dissolved PAM were introduced to the top of the column individually. During a 1-h settling period, samples were taken at 1-m depth from surface at various times and analyzed for total suspended solids (TSS). Flocculated sediment by PAM greatly increased its settled TSS fraction up to 95–97% only in 1-min settling period compared to those of unflocculated sediment (16–72%). The settling improvement by PAM was profound in the finer-textured soils (PSL and MCL) by increasing their median particle settling velocity (>2 cm s−1) compared to unflocculated counterparts (<1.1 cm s−1). Estimated surface area requirement of sediment basin suggested that the basins receiving flocculated sediment could be reduced in size (surface area) by 2- to 4-times compared to those receiving unflocculated sediment. Our results suggests that current sediment basin design could be modified when chemically-assisted settling is implemented, taking up less space and cost in construction sites.

Influence of flocculation on sediment deposition process at the Three Gorges Reservoir.

By comparing the original particle gradation of sediment from the Three Gorges Reservoir with the single particle gradation, the differences in these two particle gradations showed that there is sediment flocculation in the Three Gorges Reservoir, which can accelerate the sediment deposition rate in the reservoir. In order to determine the influence of flocculation on the sediment settling velocity, sediment was collected at the Three Gorges Reservoir, and the indoor quiescent settling experiment was performed to study the mechanism of sediment flocculation. The experimental results showed that sediments aggregated from single particles into floccules in the settling processes. The single particles smaller than 0.022 mm will participate in the formation of floccules, which accounts for 83% of the total amount of sediment in the Three Gorges Reservoir. Moreover, the degree of sediment flocculation and the increase in sediment settling velocity were directly proportional to the sediment concentration. Taking the average particle size and the median particle size as the representative particle size, respectively, the maximum flocculation factors were calculated to be 3.4 and 5.0. Due to the sediment flocculation, the volume of sediment deposition will increase by 66% when the mass settling flux factor of total sediment had a maximum value of 1.66, suggesting that flocculation has a significant influence on the sediment deposition rate in the Three Gorges Reservoir.

Outcomes of submerged macrophyte restoration in a shallow impounded, eutrophic river

Restoration of submerged macrophytes in eutrophic shallow freshwater ecosystems is rarely undertaken without additional measures to improve water clarity. Increasing water clarity is extremely difficult to achieve in some eutrophic waters, so this study trialled the establishment of macrophytes directly into a turbid, phytoplankton-dominated system. The submerged macrophyte Vallisneria australis grew successfully in five 48-m2 protective exclosures, from transplants attached to steel mesh for anchorage in flocculent sediments. Plant growth, water quality, and zooplankton and macroinvertebrate richness and abundance were measured and compared with open water control plots throughout the growing season. V. australis grew well despite poor water quality (total phosphorus 44–1400 µg l−1; total nitrogen 650–14,000 µg l−1; chlorophyll a 1.6–770 µg l−1; turbidity 3–207 NTU), attaining 85–100% cover after 6 months. Water quality was not improved within macrophyte meadows and zooplankton grazing was not enhanced. Richness and abundance of macroinvertebrates increased and additional native macrophyte species colonised the exclosures. Co-dominance of phytoplankton and macrophytes was achieved in exclosures, with beneficial outcomes for biodiversity. Rapid destruction of macrophyte meadows by waterbirds on removal of protective cages indicated the need for continued protection for long-term establishment of submerged macrophytes.

Urban wastewater treatment by seven species of microalgae and an algal bloom: Biomass production, N and P removal kinetics and harvestability

This study evaluates the capacity of seven species and a Bloom of microalgae to grow in urban wastewater. Nutrient removal kinetics and biomass harvesting by means of centrifugation and coagulation–flocculation-sedimentation have been also tested. Results show that the best biomass productivities ranged from between 118 and 108 mgSS L−1 d−1 for the Bloom (Bl) and Scenedesmus obliquus (Sco). Regarding nutrient removal, microalgae were able to remove the total dissolved phosphorus and nitrogen concentrations by more than 80% and 87% respectively, depending on the species tested. The final total dissolved concentration of nitrogen and phosphorus in the culture media complies with the European Commission Directive 98/15/CE on urban wastewater treatment. Regarding harvesting, the results of coagulation–flocculation sedimentation using a 60 mg L−1 dose of Ferric chloride were similar between species, exceeding the biomass removal efficiency by more than 90%. The results of centrifugation (time required to remove 90% of solids at 1000 rpm) were not similar between species, with the shortest time being 2.9 min for Sco, followed by the bloom (7.25 min). An overall analysis suggested that the natural bloom and Scenedesmus obliquus seem to be the best candidates to grow in pre-treated wastewater, according to their biomass production, nutrient removal capability and harvestability.

The turbidity maximum zone in a shallow, well-flushed Sabaki estuary in Kenya

The spatial–temporal variability and the behaviour of the Estuarine Turbidity Maximum (ETM) zone in the shallow, ephemeral, well-flushed Sabaki estuary located in the northern region of the Kenya coast, were studied during a period of moderate river discharge. The estuary is one of the most turbid estuaries along the coast of East Africa, characterised by high sediment input and high suspended matter (SPM) concentrations. The estuary is completely flushed after every tidal cycle and it experiences high salinity and SPM concentration gradients at high water (HW). The ETM was present at HW during periods when the river runoff was near the long-term average of 73m3s−1 and also when the river runoff was relatively low (35m3s−1). The SPM concentrations in the ETM zone varied significantly depending on the river sediment input and phase of the semi-diurnal tide. The SPM concentrations in the ETM were on average 50% greater than those associated with river runoff. The ETM was located up-estuary during periods when river runoff was around the average and further down-estuary during periods of low river runoff, due to different sediment settling rates. There was a tendency for the accumulation of fine sediments and clay mud in a zone of low current velocities located in the lower middle region of the estuary below the freshwater–saltwater interface, causing formation of an ETM zone. The ETM was separated from the salt-limit due to the lag in time in the tidally-driven resuspension of bottom mud and subsequent tidally-driven advection of turbid water up-estuary during the flood period. The relatively low current velocities combined with high horizontal and vertical gradient in eddy diffusivity in the central region of the estuary, tended to favour rapid settling of flocculated sediments, leading to the formation of the ETM. The study concludes that rapid settling through non-turbulent pycnocline is the dominant mechanism responsible for the formation of the Sabaki estuary ETM. The study also shows that the formation of inter-tidal mudflats is related to the ETM dynamics.

Aquatic humic substances, iron, and manganese removal by ultrafiltration and nanofiltration membranes combined with coagulation–flocculation–sedimentation

Iron and manganese removal is made conventionally by oxidation methods; however, when aquatic humic substances (HS) are present, they can affect the removal, with another treatment process being necessary. This study focused on performance of ultrafiltration (UF) and nanofiltration (NF), preceded by coagulation, flocculation, and sedimentation stages for iron, manganese, and HS removal, with two water sources that present superior levels of humic compounds, and measured by dissolved organic carbon (DOC) and UV absorbance at 254 nm. Coagulation, flocculation, and sedimentation combined with UF/NF efficiently removed dissolved iron, HS, apparent color, and turbidity. Almost total iron removal was already attained in the prior steps of coagulation, flocculation, and sedimentation, obtaining final values of dissolved iron of less than 0.001 mg L−1 for the two types of water studied. However, the complete system did not appear effective (less than 50% efficiency) in dissolved manganese removal, although a significant reduction in the HS was achieved (approximately 80% after UF and 90% after NF measured as DOC, for two types of water). Pretreatment was shown to be effective in reducing the loss of filtration flow because of the removal of high-molecular-weight HS, thus minimizing the formation of fouling on the membrane.

A method to refine crude cottonseed oil using non-toxic polyamine-based cationic polymers

The traditional method to refine crude cottonseed oil is time-consuming and expensive. This study evaluates the effectiveness of coagulation–flocculation–sedimentation process using quaternary polyamine-based polymers in refining crude cottonseed oil. Flocculated by four commercial polyamine-based cationic polymers (SL2700, SL3000, SL4500 and SL5000) with varied molecular weight (MW) and charge density (CD) and followed by coagulation with sodium hydroxide, crude cottonseed oil can be effectively purified. Free fatty acids, gossypol, pigments and trace elements are all effectively and sufficiently removed by the four polymers in a MW- and CD-dependent manner. Our results suggest that the use of polyamine-based cationic polymers may offer an effective and feasible alternative to the traditional method for crude cottonseed oil refining.

Determining the Existence of the Fine Sediment Flocculation in the Three Gorges Reservoir

Several proofs for the existence of flocculation in the Three Gorges Reservoir (TGR) are found through field measurements and laboratory experiments. The suspended particles and bed sediments are fine, and the particle diameters stay the same along the water depth, indicating that flocculation may occur. Both the vertical distributions of sediment concentrations (at low flow velocities) and measured settling velocities suggest that the effective settling velocities are larger than those of the primary particles, providing strong evidence for flocculation. The flow velocity zones of deposition and transportation are found, and the demarcation velocity of the two zones is approximately 0.5–0.6 m/s. It is thought that flocculation occurs when the flow velocity is smaller than the demarcation velocity; otherwise, the flocs will be disrupted by turbulent shear. Laboratory experiments are conducted by using the sampled bed sediments, and floc structures are also observed, confirming the existence of flocculation in the TGR.

Fermentation brines from Spanish style green table olives processing: treatment alternatives before recycling or recovery operations

AbstractBACKGROUNDFermentation brine from Spanish style green table olives processing (FTOP) is characterized by very high conductivity (around 88 mS cm‐1), high values of suspended solids (near 1300 mg L‐1), chemical oxygen demand (around 17 900 mg L‐1) and total phenols (1000 mg L‐1). In this work, fermentation brines have been exhaustively characterized and pH adjustment–sedimentation, coagulation–flocculation–sedimentation and adsorption with activated carbon have been evaluated.RESULTS AND CONCLUSIONSThe pretreatment selection will depend on the final FTOP management. If no polyphenols elimination is required in view of a further recovery, the best pretreatment is pH adjustment to 9 plus sedimentation. The removal efficiencies achieved were 33.1% suspended solids, 82.5% turbidity and only 10.4% of polyphenols. However, if the final FTOP treatment was biological, the best pretreatment is adsorption with powder active carbon, because this pretreatment implies the maximum reduction of phenols in FTOP, which inhibit microorganism activity in the biological process. The maximum total phenols removal efficiency was 96% with 8 g L‐1 of BM8 powder activated carbon (21% soluble COD). © 2014 Society of Chemical Industry

Determination of Settling Velocity of Suspended Sediment in Estuary

The settling velocity of sediment is a hot issue and a basic problem in study of sediment transport and estuarine engineering. According to field hydrodynamics and sediment data around the South Passage of the Changjiang River in China, this paper detected the characteristics of sediment particle size and vertical distribution pattern of suspended sediment concentration, and further estimated the settling velocity of suspended sediment in three methods. The results show that the sediments including suspended and bed load can be categorized into cohesive sediments and the sediment concentration profile agree well with logarithmic distribution. Furthermore, by comparison, it is found that the Rouse formula is more reasonable for estimating the settling velocity of fine sediment, but the Zhang Ruijin and Stokes formula obviously underestimate the values of settling velocity, caused by do not taking into account the flocculation of fine sediment in estuary.

Impacts of Flocculation on Sediment Basin Performance and Design

<abstract> <bold><sc>Abstract.</sc></bold> There is increasing interest in controlling turbidity in construction site runoff using chemical flocculant treatments. Since flocculated sediment is likely to behave much differently from untreated sediment, changes to current sediment basin designs may be appropriate. This study evaluated a system consisting of three fiber check dams in a lined ditch discharging to sediment basins that differed in their configuration. Three different basin configurations were tested with and without granular polyacrylamide (PAM) applied to the weir of each check dam: (1) standard basin with a 2:1 length to width (L/W) ratio, (2) horizontal basin with a 1:2 L/W ratio, and (3) standard basin with a rising floor toward the exit (spillway). All configurations included two porous baffles of jute/coir netting across the full width of the basin. For each treatment of PAM and basin configuration, sediment-laden stormwater flows (0.014 to 0.056 m³ s^-1) were introduced to the ditch for 29 min, and water samples were collected at the ditch entrance (influent), ditch exit, and basin exit. Regardless of PAM treatment, total suspended solids (TSS) concentrations were reduced by more than 55% at the ditch exit and by up to 90% at the basin exit relative to the influent (3,700 mg L^-1). The 1:2 L/W basin reduced TSS more than either of the 2:1 L/W basins without flocculation, but there was no significant difference in TSS when sediment was treated with PAM. Turbidity at the ditch exit was similar to the influent (less than 10% difference) without flocculation but was greatly reduced (>66%) with flocculation. The PAM treatment lowered turbidity further (>88%) at the basin exit and was similar among all basin configurations. The particle size distribution of flocculated sediment was shifted into coarser fractions, enhancing settling in the basin. The estimation of basin surface area requirement based on the measured particle size suggested that basins receiving flocculated sediment could be reduced in surface area and altered in configuration while improving water quality for construction site discharges.

Physicochemical analysis and adequation of olive oil mill wastewater after advanced oxidation process for reclamation by pressure-driven membrane technology

Physicochemical characterization of olive mill wastewaters (OMW) was studied after a primary and secondary treatment was implemented in an olive oil factory in Jaén (Spain), comprising natural precipitation, Fenton-like reaction, flocculation–sedimentation and olive stone filtration in series. The application of membrane technology in improving the quality of the secondary-treated OMW (OMW/ST) was examined, to reduce the hazardous electroconductivity (EC) values (2–3mScm−1). Particle size distribution on OMW/ST shows supra-micron colloids and suspended solids as well as sub-micron particles with a mean size below 1.5μm remaining in considerable concentration. The high organic pollutants percentage (31.7%) registered with an average diameter below 3kDa is sensibly relevant for membrane fouling. Mesophilic aerobic bacteria growth warns of possible membrane biofouling formation. The saturation index indicates to work upon recovery factor below 90%. Finally, operating at a pressure equal to 15bar ensured low fouling and high flux production on the selected NF membrane (69.9Lh−1m−2) and significant rejection efficiencies (55.5% and 88.5% for EC and COD). This permits obtaining an effluent with good quality according to the recommendations of the Food and Agricultural Association (FAO) with the goal of reusing the regenerated water for irrigation.

Sediment texture and nutrients of Muttukadu, sand bar built backwaters, Tamilnadu, India

Muttukadu backwater form a complex system of shallow estuarine network spread over an area of 0.87 km2 meant for fishing and boating activities. The study area is connected to the sea by a bar mouth, the width of which is variable from a few meters to 200 m in different months. Mouth closes due to sandbar formation from March to September. A combination of reduced river discharge, the build-up of an oceanic bar as a result of onshore sediment transport by long-period swell wave action during summer, cause the formation of sand bar. Sediments are the major sink for chemical components of water bodies and sediment chemical analyses afford methods for measurements of the quality of overlying water and the levels of potential pollutants. Station 1(0.5 km away from the mouth) and 9 which is in the sea is always sand dominated as they are influenced by the nearshore dynamics. The saline sea water, which enters the estuary, resuspends the flocculated sediments at the mouth and transports the fine floccules to the water column during the open condition. pH (7.7) of the sediment is high during monsoon season. The total nitrogen (4.7µg/L) of sediments is higher during summer season due to the oxidation of dead plant organic matter, which has settled on the top layer. Total Phosphate shows a positive correlation with silt. Phosphorus load is high in the stations 5, 6, 7 and 8 is 2.3, 2.1, 4 and 2.5 (µg/L) which is located in the upstream of the backwater and in Buckingham canal compared with the mouth region, indicating that the environment is substantially influenced by local sources of sewage, industrial effluent etc.

Simulation for Fine Sediment Flocculating Settlement in Flowing Water and Its Influencing Factors

The aim of this study is to simulate the growth process of fine Sediment flocculation fractal, which based on DLCA and three graphics technology. With the simulation, we analyze the effects of particle effective collision probability, initial concentration and particle diameter on sedimentation distance and distribution. The flow fractal structure was analyzed by graphic technology. Researches in this study have some theoretical and practical value on the control and treatment of Yellow River high turbidity flow.

Investigation of the variability of floc sizes on the Louisiana Shelf using acoustic estimates of cohesive sediment properties

Abstract Vertical profiles of suspended sediment concentration and floc size estimated from acoustic backscatter are used together with turbulent shear estimates to investigate cohesive sediment flocculation under different flow conditions. Concentration measurements by optical backscatter sensors at two levels are used to calibrate the acoustic backscatter intensity. A strong correlation is observed between suspended sediment concentration and turbulence intensity. Mean size of flocs increases toward the bottom except within the bottom few centimeters, where floc breakage is observed due to strong turbulence. Simultaneous shear rate and floc size profiles show that low shear promotes flocculation at low concentrations. Increasing turbulence intensity increases the amount of sediment in the water column, but decreases the floc size, indicating floc breakage. Thus, these effects are seen at cm-scale vertical resolution in the field for the first time. The results support previously published numerical, experimental and lower resolution field studies.

Theory on Orthokinetic Flocculation of Cohesive Sediment: A Review

Investigation on flocculation phenomenon of cohesive fine-grained sediment has been a important part of sediment dynamics. During all of three dynamical factors (i.e., Brownian motion, flow shear and differential settling) that have been verified to play important roles in promoting flocculation of cohesive sediment, the influence of flow shear on sediment flocculation has been paid great attention by many researchers (this flocculation pattern has been termed as “orthokinetic flocculation” in most of published literatures). Among many researches regarding orthokinetic flocculation, the dynamical equation developed by Smoluchowski in 1917 (we called it as Smoluchowski equation hereafter) has been widely adopted as an origin and basement for theoretically analyzing sediment flocculation under a shear flow. Meanwhile, many researchers have also pointed out the deficiencies of Smoluchowski equation (this is because the derivation of Smoluchowski equation was based on six different assumptions), and correspondingly have amended this equation from different aspects. In this paper, we attempt to summarize these results, hopefully providing the theoretical research of sediment orthokinetic flocculation with some references.

Criteria for Distinguishing Floc Sedimentation and Gel-Like Network Sedimentation of Cohesive Fine-Grained Sediment in a Turbulent Flow

The study on the criteria used to distinguish floc sedimentation and gel-like network sedimentation of cohesive fine-grained sediment in a turbulent flow has rarely been carried out. In this preliminary study, we derive three criteria to distinguish these two different sedimentation phases by considering the comparison of the time that a characteristic floc takes to settle through mean distance between characteristic flocs and the time that it takes to move through the same distance under the influence of a turbulent flow. These criteria incorporate physical and chemical factors that have been verified to have some influences on the sediment flocculation in some published literatures, and a simple analysis result is found to be consistent with our qualitative understandings of flocculation phenomenon of cohesive fine-grained sediment.

Experimental study on slime water flocculation sediment based on the montmorillonite hydration expansion inhibition

Through the montmorillonite settlement experiment in the clear water and electrolyte solution, the influence of slime water settling character was studied in clear water and different electrolyte solution, the montmorillonite’s hydration expansion effectively restrained was verified, the process method to wash coal with the electrolyte was put forward, and the results indicate that the solution of 10 g/L KCl is optimal inhibitor on the montmorillonite in the tested three kinds of electrolyte solution. With the contrast test in clear water and electrolyte solution, two reagent adding way can be selected in KCl solution: one way is to add PAM separately, the effectively sedimentation can be made with simply 0.1% anion; the other way is the coordination with polymeric aluminum and PAM, the anionic of PAM and polymeric aluminum are 0.02% and 0.5% respectively. However, in clear water, the polymeric aluminum must be joined together with the anionic PAM, and the amount of the PAM reaches 0.5%, which is 25 times as great as that in KCL solution. The field work with raw coal further verifies the above conclusions further.

Treatment of oil sands process-affected water with ceramic ultrafiltration membrane: Effects of operating conditions on membrane performance

This study investigated the performance of 1kDa ceramic ultrafiltration membrane for the removal of inorganic and organic compounds from oil sands process-affected water (OSPW) generated after thermal operations of heavy oil recovery in Alberta, Canada. The OSPW was pretreated with alum coagulant, and the effect of operating conditions on subsequent membrane filtration was studied. While permeate flux increased with increasing trans-membrane pressure (TMP) from 1.4bar to 3.5bar, greater permeate flux decline was observed at TMP of 3.5bar due to increased accumulation of foulants at the membrane surface. The membrane filtration performed at cross-flow velocity (CFV) of 0.2L/min was characterized by the lowest initial and steady-state permeate fluxes and by the highest normalized flux decline compared to higher CFVs. This effect was attributed to lower turbulence at the membrane surface which might have promoted the buildup of contaminants. According to the resistance-in-series model, no irreversible membrane fouling was observed when OSPW was pretreated with coagulation–flocculation–sedimentation. The pore blocking and cake layer formation dominated at the beginning of filtration, whereas cake layer formation was the primary fouling mechanism at later stages. The final membrane permeates met the requirements for the high pressure-driven membrane processes (i.e., nanofiltration and reverse osmosis) with respect to turbidity and silt density index (SDI15) values. Up to 38.6±2.7% (depending on TMP and CFV values) of chemical oxygen demand (COD) was removed, and the removal percentages of the acid extractable fraction (AEF) and naphthenic acids (NAs) were less because of the small sizes of NAs and other organic compounds contributing to the AEF as compared to the membrane pore sizes.