Coagulation And Flocculation Mechanisms

The main challenge in removing turbidity and organics from water supplies is to cope with impurities that are negatively charged at natural pH levels, and have formed a stabilised dispersion. Initially it is a matter of destabilising the dispersion and coagulating the contaminants. This is done by adding positively charged species in appropriate quantities to neutralise the charge on the impurities. A flocculation step involving a polymer is then used to bring together the particles so that...

1

Molecular structure of microcystin LR Fig. 12. Molecular structures of the microcystin toxins a) mLA, b) mYR and c) mRR 4.3.2. Influences on the adsorption of microcystins The information available in the literature on the adsorption of mLR onto activated carbon indicates that, as with the adsorption of most microcontaminants, the removal efficiency is dependent on the type of activated carbon and the water quality conditions 28, 70-72 . Newcombe and Nicholson 72 have reported a direct...

Natural Impurities In Water

Impurities may be dissolved compounds as well as insoluble particles, and may be of organic or inorganic origin 7 , Some of the more commonly found natural components containing organic material are, in decreasing size order, zooplankton, phytoplankton, bacteria, viruses, clay-humic acid complexes, humic acids, proteins, polysaccharides, fulvic acids, and very small species such as fatty acids, carbohydrates, amino acids and hydrocarbons. They are formed by the biological degradation of organic...

Activated Carbon Characteristics

Activated Charcoal Point Zero Charge

Typically, water treatment plants employ activated carbons in powdered or granular form, and these activated carbons are manufactured from relatively heterogeneous base materials such as bituminous or sub-bituminous coal, lignite, peat, coconut shells, or wood. Activated carbons (including activated carbon fibers) can also be prepared from homogeneous polymeric base materials such as polyacrylonitrile, cellulose or phenolic resin 22 , but such activated carbons are not currently applied in...

Packed Bed Filtration

A description of packed bed filtration in water treatment is provided here, summarized from some previous publications by the author and coworkers 81, 82 . A mathematical description of the removal process in packed bed filtration was presented by Iwasaki 83 and has been developed and used extensively since that time Here C is the concentration of particles in suspension in the filter at depth L and fa is a filter coefficient that is a function of several physical properties of the system...

Info

Effect of adsorbent hydrophobicity on MTBE adsorption from (A) cyclohexane and (B) water. MTBE adsorption capacities were normalized by the pore volume in the size range of 8 to 11 A, and aqueous MTBE adsorption capacities were determined at an equilibrium liquid phase concentration of 50 pg L1. AW - acid-washed, OAW - H202 oxidized, HAW - heat-treated in hydrogen, AAW -heat-treated in ammonia (from Li et al. 19 ) 5.2.2. Aromatic industrial pollutants With respect to interactions...

The Electrical Double Layer

An aquasol does not have a net electrical charge. The particle charge arising from surface complex formation, isomorphous substitution, and other reactions is termed the primary charge of the particle. This charge must be counterbalanced in the aquasol system and this occurs in the interfacial region adjacent to the particle. Fig. 1 is a schematic representation of a negatively charged particle in water with a cloud of ions (diffuse layer) surrounding it. Because the particle in the sketch has...

References

Thurman, Organic Geochemistry of Natural Waters. Martinus Nijhoff Dr. W. Junk Publishers, 1986. 2 K.A. Hunter, Mar. Chem, 9 (1980) 49. 3 F.J. Stevenson, Humus Chemistry. Wiley Interscience Publications. John Wiley and Sons, New York (1982). 4 E.M. Thurman and R.L Malcolm, Environ. Sci. Technol. 15 (1981) 463. 5 J.A. Leenheer, J.P. Croue, M. Benjamin, G.V. Korshin, C.J. Hwang, A. Bruchet and G.R. Aiken, Comprehensive isolation of natural organic matter from water for spectral...

Manganese Associated Problems

There seems little doubt that neutral pH water drawn from a source which is well-oxygenated will contain manganese oxides as the main manganese species, while water drawn from a source of low to zero dissolved oxygen can be expected to have manganese present as soluble Mn2+(aq) 24 . Thus, where water is drawn from a summer stratified dam or lake, the epilimnic water will contain mainly oxidised manganese species, while the hypolimnic waters will contain almost exclusively the soluble Mn(II)...

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0.00 0.05 0.10 0.15 0.20 0.25 0.30 0.35 0.40 Volume Fraction,< t> Fig. 8. Diffusivity as a function of volume fraction of solids for a range of sludges using ferric chloride as the coagulant. The data is from the work of Harbour et al. 33 The data is very closely grouped indicating that these sludges have very similar properties even though they are formed under different conditions in terms of raw water quality and clarification conditions. In general, they have a lower compressibility...

Manganese removal

Diagram Specie Manganese Versus

National Research Centre for Environmental Toxicology, University of Queensland, 39 Kessels Road, Coopers Plains, Queensland, 4108 Australia A survey of end-user perception of problems associated with their reticulated water identified taste, odour and colour as being their prime concerns 1 , It is thus in this context, somewhat ironic that many taste odour complaints are often associated with the presence of chlorine, whose introduction to drinking water has been described as the greatest...

The Effect Of Biofilms On Copper And Lead Containing Materials

The choice of pipe material and the accumulation of corrosion products can dramatically impact the ability to control the effects of biofilms in drinking-water systems. Biofilms are known to significantly influence the accumulation, transport and transformation of heavy metals. In water distribution systems containing copper and lead tubing, the presence of biological deposits can lead to the increased release of Pb (II) or Cu (II) into drinking water. In addition to corrosion problems, this...

Dlvo Theory

When two similar particles and their associated electrical double layers approach each other, their diffuse ion atmospheres overlap and a coulombic repulsive force is produced. The classic DLVO theory 13, 28 considers this electrostatic repulsion together with the van der Waals attractive interaction in assessing the interaction forces 28 or the interaction energies 13 between the particles. Here an approach to determine the coulombic interaction force for a simple system will be outlined and...

Van Der Waals Interactions

Van der Waals interactions are ubiquitous, existing between atoms, molecules, colloidal particles, and macroscopic objects. They have an important role in hydrodynamic retardation or the lubrication effect between solids without them, hydrodynamic drag would prevent interparticle contacts from occurring. They have a role in many other phenomena in gases, liquids, and solids including the aggregation and deposition of aquasols in aquatic environments. For this reason an overview of their origins...

Fundamentals Of Adsorption

To clearly illustrate the effects of activated carbon surface chemistry on adsorption, fundamental interactions controlling the adsorption of aqueous pollutants need to be considered first. The adsorptive removal of industrial pollutants from aqueous solution is affected by the following three interactions 8 pollutant (ads rbate) - activated carbon (adsorbent) interactions, water (solvent) - activated carbon (adsorbent) interactions, and pollutant (ads rbate) - water (solvent) interactions....

Biofilms And Corrosion

The main constituents of biofilm are the microbial cells, their extracellular polymeric substances (EPS), and inorganic precipitates. The latter originate from the bulk aqueous phase or are formed as corrosion products of the substratum. EPS, comprising macromolecules such as polysaccharides, proteins, nucleic acids and lipids, constitute the biofilm matrix and are often referred to as glycocalix or slime 7 . Microorganisms and or their metabolites, e.g. enzymes active within the EPS matrix,...

Wit

For the Hamaker constant of two different phases interacting across a vacuum, the following geometric assumption is frequently made A,2 A A22 (9) The corresponding relationship for the van der Waals interaction force per unit area is The Hamaker constants for these systems, An and A 2, depend on the types of atoms comprising the materials and the atom density in each material. In principle, Hamaker constants can be calculated from molecular properties of the materials however, these properties...

Mass Balance

Biofilm Corrosion

The framework for the analysis of the origin and dynamics of particles is a mass balance model for a network. Within the model, the different processes dealing with particles can be quantified and analysed. The mass balance can be applied to the complete network, but can also be applied to selected parts of the networks. The model of the mass balance is used to sum up the relevant processes involved in particle input and particle generation in the network. All these processes are interconnected...

Practical Aspects Of Orthokinetics Flocculation

From the orthokinetic rate coefficient in Eq. (5), it is possible to derive the flocculation rate for equal particles in terms of the rate of decrease of total particle number concentration, as in Eq. (2) - --aNlGd' -akaN2t dt 3 T a T This expression only applies in the very early stages of the flocculation process, but is still helpful for exploring practical consequences. The presence of a d3 term in Eq. (8) implies that the volume of particles plays a significant part. The volume fraction of...

Preoxidation

The effective removal of arsenic from water usually requires the complete oxidation of As(III) to achieve the required drinking water standard. There are various means of oxidation available, but in drinking water treatment, additional aspects must be considered, such as the limited list of chemicals, residual oxidants and oxidation by-products or the oxidation of other inorganic and organic water constituents. Thus, the national drinking water and treatment regulations will therefore be...

Dewatering Models

There are a number of dewatering devices common to the potable water treatment industry and although it is beyond the scope of this chapter to provide an in-depth analysis of each of these devices, the fundamental parameters affecting performance of a number of devices in the context of the above discussion will be considered. The devices of interest are clarifiers, filters and centrifuges. Clarification is a process that occurs in any type of clarifier, thickener or settler that concentrates...

Surface Measurment Methods

The general operation of the AFM has been reviewed in detail elsewhere 28-29 and will be only briefly described here. The essential components of the AFM are a piezo-electric ceramic, force sensor (cantilever spring), laser photodiode assembly, and a feedback system. AFM measurements can be performed either in various liquids (such as water) or gases (such as air) and all measurement reported here have been made in liquids. The silicon wafer, on which the Cryptosporidium oocyst was mounted,...

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Diffuse layer charge ad -0.197 - Surface potential i 0 +287 mV Interfacial ion concentrations at x Na+ x 8.7 x 10'4 M For these conditions (high ionic stength, low pH, high surface charge), the charged Stern layer-Gouy-Chapman model predicts that about 30 of the surface charge is balanced in the charged Stern layer. The diffuse layer potential is reduced by about 18 mV compared to the diffuse layer model and the concentration of counterions calculated at the inside of the diffuse layer is...

Rise Velocity Of Flocbubble Aggregates

To calculate the rise velocity of floc-bubble aggregates requires the determination of the aggregate size and density. The aggregate equivalent diameter (dji,) produced from N bubbles of size db attached to a floe particle of size dp is estimated by The floe-bubble aggregate density pp, is estimated from the weighted average of the air bubble and floe densities Next, a modified Stokes equation is used to estimate the floc-bubble aggregate rise rate K accounts for floe shape and the drag force....

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Double Layer Theory Aquatic Chemistry

Parameters used in the calculations are given in the legend to Fig. 4. These have been selected to represent situations of interest in aquasols. The particle's radius, a, is set at 50 nm, in the lower part of the colloidal size range. The ionic strength (I) is set at 0.1, typical of estuarine waters and commonly considered to promote the coagulation of many colloids. A value of 1020 J is chosen for the Hamaker constant (A) this is in the range of many aquasols and is also appropriate for the...

Kawamura Water Treatment

Water Works Assoc., 68 (1976) 328. 2 D. Rout, R. Verma and S. K. Agarwal, Water Sci. Technol., 40(2) (1999) 137. 3 D.J. Nozaic, S.D. Freese and P. Thompson, Water Sci. Technol. Water Supply, 1(1) (2001) 43. 4 D. Faust and O.M. Aly, Chemistry of Water Treatment, Butterworths, Boston, 1983. 5 A.D. Levine, B.A. Bolto and D.R. Dixon, Reactions of Polyelectrolytes with other Water Treatment Chemicals, AwwaRF Report, AWWA Research Foundation, Denver, 2004. 6 R.-J. Leu and...

Practicalities In The Use Of Polyelectrolytes

There are a number of practical issues that need particular attention when using polyelectrolytes for water treatment. Equipment designed for storing, mixing and feeding polymers takes into account the unique physical characteristics of polymers, and has been much discussed elsewhere 68, 85, 86 Mixing is of paramount importance 87 , beginning with initial high energy mixing during the polymer wetting stage in the case of a solid polymer, especially for a polymer of very high molecular weight,...

Collisions And Attachment Of Particles With Bubbles

It is useful to distinguish between the sizes of bubbles and particles for dispersed air flotation versus dissolved air flotation processes. Dispersed air flotation processes commonly used for mineral separation from ores involve large bubbles and large particles, sizes of millimeters or fraction thereof. The adhesion or attachment of these large bubbles to particles is described as a three phase phenomena in which contact angles are measured and used to quantify adhesion. High contact angles...

A

The floe strength expressed in this way is a force per unit area or pressure and values from a few Nm'2 up to around 1000 Nm 2 have been reported, depending on the system. This means that, for typical floes of around 100 pm in size, the actual force required for breakage would lie somewhere in a range from nN - pN. The number of particle-particle bonds per unit area must depend on the density of the floe and hence on the fractal dimension. For open, low density structures low df , there will be...

I

Eq. 9 describes the efficiency of removal of particles or floes onto bubbles within the contact zone. The model is instructive in that it identifies important variables affecting contact zone performance. These include the particle-bubble attachment efficiency a'pb the single collector efficiency rjr , bubble size d , , bubble rise velocity vb , bubble volume concentration and the contact zone detention time tc . Table 3 provides a summary of these variables. The variables are categorized in...