Solid-liquid Separation Processes Research Articles

Removal of heavy metals using a brewer’s yeast strain of Saccharomyces cerevisiae: The flocculation as a separation process

In this work, a brewer’s yeast strain was used to remove heavy metals from a synthetic effluent. The solid–liquid separation process was carried out using the flocculation ability of the strain. The yeast strain was able to sediment in the presence of Cu 2+, Ni 2+, Zn 2+, Cd 2+ and Cr 3+, which evidences that the flocculation can be used as a cheap and natural separation process for an enlarged range of industrial effluents. For a biomass concentration higher than 0.5 g/l, more than 95% of the cells were settled after 5 min; this fact shows that the auto-aggregation of yeast biomass is a rapid and efficient separation process. Cells inactivated at 45 °C maintain the sedimentation characteristics, while cells inactivated at 80 °C lose partially (40%) the flocculation. The passage of metal-loaded effluent through a series of sequential batches allowed, after the second batch, the reduction of the Ni 2+concentration in solution for values below the legal limit of discharge of wastewater in natural waters (2 mg/l); this procedure corresponds to a removal of 91%. A subsequent batch had a marginal effect on Ni 2+ removal (96%). Together, the results obtained suggest that the use of brewing flocculent biomass looks a promising alternative in the bioremediation of metal-loaded industrial effluents since the removal of the heavy metals and cell separation are simultaneously achieved.

Solid-Liquid Separation Process: Modelling for Design and Development of Gravity Deep-Bed Filters for Water Treatment

This work focuses on the conception and formulation of appropriate filtration models for use by water treatment professionals for design, development and management of deep-bed (depth) filters. Performance and optimization studies were carried out using data (turbidity, filtration rate, head loss) acquired from pilot filter test runs. The curves developed from these studies were utilized for the formulation of steady-state and hydro-dynamic models of depth filtration. An effluent quality model was developed, relating depth of flow in filter bed with effluent turbidity. This model was verified and validated. The depths obtained are in good agreement with standard values from literature.

Optimization of the wash liquor flow rate to improve washing of pre-deliquored filter cakes

Filter cake washing is a common way of improving the quality in purity of particulate products in solid–liquid separation processes. In industrial applications, this process step is usually treated as a black box where optimization is performed through trial and error. Decisive progress has been made in academia by the development of physical models to describe the washing phenomena inside a porous structure such as filter cakes. Although some models have led to a better understanding of the process, experimental efforts are still inevitable for determining optimization strategies. This contribution is an empirical approach to investigate the influence of important process parameters of washing pre-deliquored cakes with the focus on the wash liquor and filtrate flow rate. In washing a pre-deliquored cake, low moisture content at the time of wash liquor addition can be very disadvantageous for the wash efficiency due to inhomogeneous flow. This can be the result of a poor re-wetting process while washing at low wash liquor flow rates. An increase of the flow rate was observed to be very advantageous to set higher moisture content of the filter cake and therefore enforce a homogeneous distribution of the wash liquor. A homogeneous distribution of the wash liquor inside the cake is generally required for good washing.

Analysis of constant-current electro-osmotic dewatering of various solid–liquid systems by considering the creep deformation

A constant-current electro-osmotic dewatering (EOD) of various solid–liquid systems is analyzed using the Terzaghi–Voigt combined model by considering the creep deformation of the material. Electro-osmotic dewatering experiments under constant electric current density of bentonite clay, KC-flock, zinc oxide and some of their mixtures are carried out. The basic differential equation based on the model is solved analytically by assuming that both electro-osmotic pressure gradient E pg and modified consolidation coefficient C e of the material are constant. The solution can explain the time course of changes in solid compressive pressure distribution. The theory can also explain the final moisture distribution of the material. The progress of electro-osmotic dewatering can be represented by an average consolidation ratio U c as in mechanical expression. Both C e and E pg increase with an electric current density i. A larger C e leads to a higher dewatering rate; a larger E pg results in a higher solid compressive pressure distribution in the material. It is found that the amount of creep deformation depends upon the dewatering rate; the faster the dewatering rate, the larger the creep deformation, i.e., the creep deformation is more remarkable when a higher current density is applied to the material. The effectiveness of EOD can be represented by the relative difference of the initial and final void ratios. Variations of the effectiveness of dewatering with the material composition, electric current density i, preconsolidation pressure p s1 and total solid volume per unit cross-sectional area ω 0 are investigated. It is found that higher composition of charged material and higher current density show improved dewatering. For higher ω 0, slight increase in effectiveness of dewatering is observed. For significant decrease of preconsolidation pressure, a relatively small increase in the effectiveness is observed. Therefore, among these, the material composition and current density are the main EOD parameters that can be used to determine the feasibility of EOD as efficient solid–liquid separation process.

Effects to Improve the Quality of Life: Color, Performance and Protection from Ciba Specialty Chemicals

Ciba Specialty Chemicals creates effects to improve the quality of life. Building on its technical competencies, the company has developed major innovative product groups that provide color, performance and protection. Antioxidants and light stabilizers protect plastics, coatings, photographic pictures and wood from degradation induced by sunlight, air, ozone, heat, fire and mechanical stress. UV absorbers protect human skin from sunburn and photo-induced ageing. Pigments and dyes add beautiful colors to objects of everyday life, serve as recording media for optical information storage on digital versatile discs (DVDs) and are used as color filters in liquid crystal displays (LCDs). Effect pigments allow creation of color and visual effects by interference. Polymeric flocculants are essential components for solid–liquid separation processes in wastewater treatment and paper production. Photolatent catalysts are key components for light-induced polymerization reactions. New sterically hindered N-alkoxyamines are initiators for nitroxide mediated radical polymerization (NMP) reactions leading to new pigment dispersants with well-defined molecular weights and narrow molecular weight distribution. New N-acyloxyamines are proposed as peroxide substitutes for controlled degradation of high molecular weight polypropylene. A new clarifier can be used to produce polypropylene with enhanced transparency and excellent mechanical properties. Progress in enabling sciences such as nanotechnology and biotechnology together with new technologies entering the markets will offer outstanding opportunities for new developments in specialty chemicals.

In situ analysis of flocs

Research Article| February 01 2007 In situ analysis of flocs Rajat K. Chakraborti; Rajat K. Chakraborti 1CH2M HILL, Inc., 325 Hillcrest Drive, Suite 125Thousand Oaks, CA 93063, USA Tel: +1 (805) 371 7822 Fax: +1 (805) 371 7818; E-mail: rajat.chakraborti@ch2m.com Search for other works by this author on: This Site PubMed Google Scholar Kevin H. Gardner; Kevin H. Gardner 2Environmental Research Group, Department of Civil Engineering, University of New Hampshire, 336 Gregg Hall, Durham, NH 03824, USA Search for other works by this author on: This Site PubMed Google Scholar Jagjit Kaur; Jagjit Kaur 3CH2M HILL, Inc., 1000 Willshire Blvd, 21st floorLos Angeles, CA 90017, USA Search for other works by this author on: This Site PubMed Google Scholar Joseph F. Atkinson Joseph F. Atkinson 4Great Lakes Program, Department of Civil, Structural, and Environmental Engineering, State University of New York at Buffalo, 207 Jarvis HallBuffalo, NY 14260, USA Search for other works by this author on: This Site PubMed Google Scholar Journal of Water Supply: Research and Technology-Aqua (2007) 56 (1): 1–11. https://doi.org/10.2166/aqua.2007.063 Article history Received: March 15 2006 Accepted: August 02 2006 Views Icon Views Article contents Figures & tables Video Audio Supplementary Data Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Cite Icon Cite Permissions Search Site Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentAll JournalsThis Journal Search Advanced Search Citation Rajat K. Chakraborti, Kevin H. Gardner, Jagjit Kaur, Joseph F. Atkinson; In situ analysis of flocs. Journal of Water Supply: Research and Technology-Aqua 1 February 2007; 56 (1): 1–11. doi: https://doi.org/10.2166/aqua.2007.063 Download citation file: Ris (Zotero) Reference Manager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex The physical properties of suspended particles and the relationship between particle size and structure were investigated. In situ properties of the aggregates in a coagulation–flocculation process were obtained using a non-intrusive image analysis technique. Derived properties, including density, porosity and the number of primary particles in a floc, were estimated from aggregate structure using a fractal approach, which better represents the distribution of mass in an aggregate, compared with a conventional Euclidean approach which considers uniform mass distribution in an assumed spherical shape. A spherical particle assumption overlooks the highly porous nature of real aggregates and underestimates volume, which subsequently influences coagulation and settling estimates in solid–liquid separation processes. The present results illustrate a strong inverse relationship between the fractal dimension and aggregate length, consistent with the idea that larger aggregates in general are more porous. In addition, correlations between the solids content, floc density and the number of primary particles that constitute a floc of a given size were established. It is suggested that the aggregation process produces flocs of constantly changing morphology and related physical properties. Overall, these findings can provide additional information for understanding and modeling suspended particle characteristics. aggregate structure, density, floc properties, fractal geometry, number of particles, porosity This content is only available as a PDF. © IWA Publishing 2007 You do not currently have access to this content.

Recent Developments in Research and Machinery of Solid–Liquid Separation Processes

Separation of particles from liquids is an extremely widespread problem, which has to be solved under very different aspects in nearly all industrial production processes, in environmental protection, in water purification, and every day in our personal lives. The very different nature of separation problems has led to the development of a large number of mechanical separation principles. Although a lot of successful research work has been done in the past, there are still today many open questions left about process understanding and calculation. After a systematic view to the different physical principles of mechanical solid–liquid separation processes, some recent developments are discussed more in detail.

Impact of Aggregate Size and Structure on Biosolids Settleability

Settling is an important solid–liquid separation process in wastewater treatment. While solids concentration is an important factor influencing settling velocity of particles, other solids characteristics including particle size, shape, and structure also play an important role in settling rate. The “compactness” of bacterial aggregates in particular is recognized to exert a great influence on solid phase dynamic behavior since it has a substantial effect on fluid flow through the aggregate, which, in turn, affects the particles buoyancy. With the recognition that biosolids structure can be described by fractal methods, we now have a convenient means of parameterizing aggregate “compactness.” In this article, we examine the fractal nature of bacterial aggregates (which are the main component of the solids in wastewater treatment processes) using small angle light-scattering methods and assess the impact of aggregate compactness (as described by fractal dimension) on settling velocity of both single aggregates and large aggregate clusters. The results indicate that settling velocity is strongly dependent on both size and aggregate structure, with the larger and less compact flocs settling more quickly as a result of the significant extent of flow through the bacterial assemblages.

The role of interparticle forces in colloidal aggregates: local investigations and modelling of restructuring during filtration

Industrial solid-liquid separation processes, such as pressure filtration or membrane processes, involve the application of pressure to suspensions. In response, some water is extracted, the suspension volume is reduced, and the dispersed aggregates start to form a network. In recent works, we aimed to make a prediction for the response of aggregates to stress which occurs during a filtration. We chose model systems made of aggregated silica nanoparticles. Some of these systems offer a strong resistance to applied stresses, and retain their permeability; others yield and collapse. We used small angle neutron scattering by which we can locally quantify the particle distribution withi the network to determine the processes by which particles reorganise during collapse: we found that reordering processes at the scale of 1 to 10 particle diameters control the course of collapse and the loss of permeability. Finally we constructed a numerical model for describing the processes by which colloidal aggregates are compressed. This model predicts that the response of such networks to pressure follows some scaling laws, which depend only on the elastic vs. dissipative nature of interparticle bonds.

Solid–liquid separation in suspension atomization

The aim of this paper is to define the conditions controlling the fragmentation process within the atomization of a suspension. Correlations for the droplet diameter of a suspension spray generated by a twin-fluid nozzle have been derived. Two separate regimes in suspension atomization have been identified with respect to the solid particle size. The atomized droplets from suspensions containing relatively fine solid particles are suspension droplets (containing liquid and solid particles). In this case a correlation for the drop size distribution in the spray of a twin-fluid nozzle has been deduced. Droplet size measurements in the suspension spray with varying solid particle sizes showed that when the suspended solid particle size exceeds a critical value, solid particles and liquid will be more and more separated. This effect is indicated by a bimodal size distribution in the suspension spray. It is shown that complete solid–liquid separation in the suspension spray may be achieved, where the pure liquid drops are significantly smaller than the separated solid particles. The critical process conditions where the solid–liquid separation process is found will be derived. Depending on the operating conditions of the atomizer, the resulting pure liquid droplet size is equal or less than the hydraulic diameter.

Aggregate Structures and Solid-Liquid Separation Processes

Aggregate Structures and Solid-Liquid Separation Processes

Investigation of the Flocculation of Colloidal Suspensions by Controlling Adsorbed Layer Microstructure and Population Balance Modelling

The stability of colloidal suspensions is determined primarily by the interactions among suspended particles, which in turn depends on pH, electrolyte concentration, temperature and so on. In most practical systems, flocculation or stabilization is controlled by adsorbing polymers, surfactants or their mixtures. In this paper, the role of adsorbed layer microstructural properties, particularly polymer conformation at solid–liquid interface, in controlling stability and efficiency of flocculation is examined. When polymers are used, their conformation can be manipulated by changing solution conditions such as pH and/or by the addition of a secondary polymer or surfactant. A multi-pronged approach involving the use of fluorescence, ESR, Raman and NMR spectroscopic techniques along with measurements of surface charge and hydrophobicity was employed to explore the structure of the adsorbed layer. A detailed population balance model for coagulation and flocculation of colloidal suspensions by inorganic salts and polymers is then presented incorporating the modern theories of surface forces. In particular, the classical DLVO theory is modified for flocculation by polymers and integrated in a population balance framework for the kinetics of flocculation. The open and irregular structure of flocs is accounted for by embedding the mass fractal dimension of flocs in the model. For demonstration, the evolution of mean floc size with time is simulated for flocculation of hematite and polystyrene latex suspensions. The model predictions are in reasonable agreement with experimental data. As it is computationally less intensive, the proposed model can be utilized for online optimization and control of solid–liquid separation processes that are widely encountered in water treatment, mineral processing, waste management, and so on.

From colloidal dispersions to colloidal pastes through solid-liquid separation processes

Abstract Solid-liquid separation is an operation that starts with a dispersion of solid particles in a liquid and removes some of the liquid from the particles, producing a concentrated solid paste and a clean liquid phase. It is similar to thermodynamic processes where pressure is applied to a system in order to reduce its volume. In dispersions, the resistance to this osmotic compression depends on interactions between the dispersed particles. The first part of this work deals with dispersions of repelling particles, which are either silica nanoparticles or synthetic clay platelets, dispersed in aqueous solutions. In these conditions, each particle is surrounded by an ionic layer, which repels other ionic layers. This results in a structure with strong short-range order. At high particle volume fractions, the overlap of ionic layers generates large osmotic pressures; these pressures may be calculated, through the cell model, as the cost of reducing the volume of each cell. The variation of osmotic pressure with volume fraction is the equation of state of the dispersion. The second part of this work deals with dispersions of aggregated particles, which are silica nanoparticles, dispersed in water and flocculated by multivalent cations. This produces large bushy aggregates, with fractal structures that are maintained through interparticle surface-surface bonds. As the paste is submitted to osmotic pressures, small relative displacements of the aggregated particles lead to structural collapse. The final structure is made of a dense skeleton immersed in a nearly homogeneous matrix of aggregated particles. The variation of osmotic resistance with volume fraction is the compression law of the paste; it may be calculated through a numerical model that takes into account the noncentral interparticle forces. According to this model, the response of aggregated pastes to applied stress may be controlled through the manipulation of interparticle adhesion.

Pore structure analysis of particle beds for fluid transport simulation during filtration

Accurate assessment of the transport properties of porous media (in our case, filter cake) is of major importance in the development of improved filtration processes. Implications from these studies are important in the design and operation of filtration equipment in order to enhance the efficiency of this important solid–liquid separation process. The microstructure and connectivity of pore space are important features to describe detailed fluid flow phenomena in filter cake during fine particle filtration. In this regard, 3D characterization of pore structure is essential. The pore structure has to be described by parameters which are of special relevance to the interpretation of fluid transport phenomena. These parameters should be based on directly measured variables of the pore system and not inferred from indirect variables (such as those determined empirically from transport processes) valid only for a particular pore structure. In this way, fundamental relationships between pore structure and fluid transport at the microstructure level can be described. In order to achieve this level of sophistication, the three-dimensional interconnected pore structure of filter cake must be determined. Study of fluid transport phenomena in filter cake using X-ray microtomography (XMT) to characterize the complex three-dimensional pore geometry is discussed. On this basis, the lattice Boltzmann (LB) method is used to simulate fluid flow and to begin to establish a fundamental relationship between pore microstructure and effective transport coefficients. For example, can network analysis using skeletonization procedures be used to confirm fundamental relationships that might be developed? Eventually then, with this detailed model, design and operating variables could be optimized for improved filtration efficiency.

Solids removal in upflow anaerobic reactors, a review

This desk study deals with the mechanisms and parameters affecting particles separation from wastewater in mainly upflow anaerobic reactors. Despite the fact that the functioning of upflow anaerobic sludge blanket (UASB) systems depends on both physical parameters and biological processes, the physical parameters have been barely reported in the literature. The reason is that the underlying mechanisms are very complex and depend on various interrelated parameters. In addition, the lack of a serious attempt to gather the entire physical theme into one picture has resulted in just a superficial understanding of this field of science. Better understanding of the interaction and role of these parameters is essential for the development of anaerobic treatment technologies. In this study, the various parameters that might affect the solid liquid separation process by filtration through the sludge bed of a UASB have been elaborated. These parameters have been classified into (1) reactor operational conditions (temperature, organic loading rate, hydraulic retention time and upflow velocity), (2) influent characteristics (influent concentration, influent particle size and influent particle charge) and (3) sludge bed characteristics (particle size distribution, extracellular polymeric substances, and charge). The overall output of this study includes (1) a literature review, (2) structuring of this field of science, and (3) highlighting fields where research is needed.

Deformation of Individual Aggregates and Flocs

The production of flocs or aggregates is important to many solid–liquid separation processes; well‐known examples are found in water treatment and mineral processing. When sedimentation is used to remove these aggregates from suspension, a voluminous sludge results. Reduction of the liquid content of such sludges may be key to process economics, either through improved product quality or decreased disposal charges. Although consolidation of sludge blankets has been studied extensively, the deformation of individual aggregates and flocs has not. Indeed, little quantitative information is available regarding the force required to alter the physical conformation of an aggregate or floc. In this study, a technique has been developed to measure compressive force and aggregate volume simultaneously during deformation. These data show that different compression strategies can significantly affect the work requirement per unit volume of interstitial fluid expelled. The technique reported here makes it possible to quantify the force and work requirements for floc deformation, and also to identify changes in the physicochemical environment (for flocculation) that improve overall process efficiency.

Critical evaluation of treatment strategies involving adsorption and chelation for wastewater containing copper, zinc and cyanide

Industrial wastewater containing heavy metals and cyanide requires treatment for removal of both metals and cyanide before disposal. Conventional methods for treatment of such wastewater involve alkaline-chlorination for cyanide destruction, followed by pH adjustment for metal precipitation, and subsequent removal of precipitate by solid–liquid separation processes. However, excessive sludge production, slow metal precipitation kinetics, and inefficient metal removal due to poor settling and aggregation of metal precipitates, are major drawbacks of the above process. This has rekindled interest in alternative metal removal strategies involving metal adsorption and metal chelation. The objective of the study described in this paper is to critically evaluate treatment strategies involving some indigenous adsorbents and a low-cost chelating agent for treatment of a simulated wastewater containing copper and zinc, complexed with cyanide. Treatment strategies involving three adsorbents, sulfonated coal, biosorbent G. lucidum, and iron oxide coated sand (IOCS), and a chelating agent, insoluble agro-based starch xanthate (IAX), were tested. The evaluation procedure involved comparison of the performance of these treatment strategies with that of conventional treatment. Results indicate that treatment using the chelating agent IAX has the greatest potential as an alternative to the conventional treatment technique. The three adsorbents tested, although reported to be very effective in removing copper and zinc from pure systems, exhibit diminished metal removal capacity in the presence of cyanide, and hence are unsuitable.

膜利用高度排水処理における浸漬型膜ろ過部に関する研究

Cross-flow microfiltration is one of the most promising solid-liquid separation processes, which can provide thorough separation with high rate.A suspension to be filtrated is forced tangentially over a membrane surface to back-transport the filtered colloidal particles from it.By the simulation with the rheological equation of activated sludge and the equation of the filtration with submerged membrane, suitable membrane module design was decided as the clearance in the flat-type membrane module having elements inside of 8 mm.The Pilot-plant had been operated successfully for 6 months.

Bridging flocculation studied by light scattering and settling

Polymers are used increasingly in solid–liquid separation processes. Bridging flocculation is the most common particle aggregation mechanism in these processes. However, little is known about the structure of the aggregates formed. This paper presents a critical comparison of two of the techniques that can be very useful tools for the characterisation of aggregate structures, i.e. static light scattering and settling. Of particular interest was their applicability for bridging flocculated aggregates. Both techniques were tested on two model systems: salt-induced fast coagulation and polymer-induced bridging flocculation of colloidal alumina particles. For diffusion-limited cluster–cluster aggregation at a high salt concentration, aggregate mass fractal dimensions of 1.75 and 1.65 were obtained from the light scattering and settling experiments, respectively. For bridging flocculation whereby flocs were formed using dual polymers, light scattering and settling gave mass fractal dimensions of 2.12 and 1.85, respectively. It was concluded that each of these techniques has certain advantages and disadvantages, therefore, it is best to view them as complementary. The settling method may be better suited for studying aggregates in bridging flocculation where floc sizes can be quite large which may cause the light scattering technique to become inapplicable.

Optimization of slurry flocculation and dewatering based on electrokinetic and rheological phenomena

The use of chemical additives known as conditioners or flocculants is crucial in assuring the proper functioning of many solid-liquid separation processes, and dewatering in particular. The additive used is often a water soluble polymer with high molecular mass, strong adsorptive properties, and often a large amount of ionic charge. The type of polymer used, and its exact dose, may change with process or flow conditions, and these changes may lead to poor operation. However, advances in the understanding of conditioning and flocculation of slurries and sludges now make it possible to develop scientifically-based strategies for optimizing these processes. These advances have utilized new characterization methods that allow insight into fundamental aspects of the process. In several cases the analyses employed are also amenable to continuous reading, and therefore to automatic feedback control of the process. This paper describes these advances and suggests conditioning and flocculation control strategies that will allow optimization of subsequent dewatering processes. The research advances described are: (1) use of the streaming current detector for monitoring and controlling dewaterability; (2) evaluation of floc strength by streaming current and rheological and methods; (3) use of rheological characteristics of conditioned residuals for dose control; (4) application of liquid-stream viscosity for polymer dose monitoring and control; and (5) quantification and verification of mixing conditions in conditioning processes, and use for mixing similitude. These developments should aid in the proper initial selection of a conditioner product (flocculant) and its dose, and allow optimization based on continuous monitoring if the sludge conditions vary significantly over time.