Suspended and Colloidal Matter

Suspended matter down to bacterial size can best be removed by subsidence in settling ponds and by skimming off floating material such as grease, which may form a paste that coats heat-exchange surfaces. Filtration would, no doubt, do a better job (see later), but on a large scale it is not always cost-effective (besides, filters tend to clog). 

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The second example (Fig. 6) is different. The difference between the shape of wastewater spectra is due to the distribution of suspended and colloids matters (see Chapter 6) and to the nature of dissolved organic matter. For example, the importance of the absorption peak at 225 nm (related to benzenic surfactants) of the samples is variable. 

The production of sugar from sugarbeet requires approximately 200 kg of quicklime per tonne of sugar. The raw beet is washed and chopped and treated with hot water to extract the sugar. The sugar solution also contains dissolved, suspended and colloidal matter. 

In the absence of CRMs it is possible to estimate the accuracy by determining the spike recovery of a given parameter. During method validation, spike recovery is established by spiking the analyte into an appropriate matrix at a minimum of three levels which span the range of interest. Since this procedure introduces the analyte in the soluble form, the recovery does not account for extraction efficiency from solid matrices such as sediment and biological tissue or from suspended and colloidal matter in liquid samples. Recovery is calculated on a percentage basis as follows ... 

Typically RO systems are preceded by pretreatment units to remove suspended solids/colloidal matter and add chemicals that control biological growth and reduce scaling. Membranes are typically made of synthetic polymers coated on a backing (skin). Examples of membrane materials include polyamides, cellulose acetate and sulfonated polysulfone. 

Raw water may also contain suspended and colloidal mineral matter, plant detritus, algae, and protozoa but this should all be substantially removed by effective water treatment. 

The speciation, concentrations and residence times of dissolved substances in natural waters are dependent on many factors and processes. Important factors Include temperature, pH, redox potential, ionic strength and the concentrations of other dissolved species such as organic and Inorganic ligands as well as the presence of suspended particulate and colloidal matter. Important processes in addition to rate of input, and biochemical cycling include precipitation, complexatlon, coagulation and adsorption onto suspended particulate matter. 

UV absorption spectra of wastewater are not easy to understand in view of their featureless shapes, partly due to the effect of suspended matters. The latter are very heterogeneous and responsible for diffuse absorbance more intense in the UV region than in visible. Actually, UV responses of particulate and colloidal matter are often the result of both chemical and physical responses related to their nature (organic for a great part and able to adsorb soluble compounds such as surfactants). For example, in case of slate particles (mineral) of a few micrometers, the spectrum is flat. The absorbance is uniform and higher for smaller particles. The chemical absorbance related to the presence of suspended solids of organic nature seems to emphasise spectrum slope and to create shoulders (Fig. 6). 

With this method, carbonate removal plus partial softening (with a reduction in M alk and TH), can be associated with clarification plus coagulation (with elimination of suspended, organic and colloidal matter) in the same settler. 

The continuous pastelike deposit is not the same as the other deposits. It contains no elements larger than sodium, and may be organic. It is likely that these deposits are the result of precipitation of suspended particulate and colloidal matter that forms a sedimentary deposit over the ocean floor (79). 

MBR processes retain particulate and colloidal matter. Thus, substances, including metals and metalloids that are bound-adsorbed to particulate and colloidal substances are effectively removed by the MBR process. In the CAS process the particulate metals attached to the suspended solids that escape into the final effluent are not removed. Also colloidal substances may not settle and escspe in the effluent. Thus, it is expected that MBR processes will have higher performance concerning the removal of heavy metals from municipal wastewater compared to CAS. 

Advanced treatment processes are required to remove microorganisms, disinfection by-product (DBP) precursors, synthetic organic chemicals (SOCs), susp ded and colloidal particles, natural organic matter, and salts from drinking water supplies. Microfiltration (MF) and ultrafiltiation (UF) are low-pressure membrane processes that can be applied to remove microorganisms and suspended and colloidal particles. Classification of membrane technologies based on their pore size and the size of particles and molecules retained is illustrated in Figure 6.1. 

Water and Waste Water Treatment. PAG products are used in water treatment for removal of suspended soHds (turbidity) and other contaminants such as natural organic matter from surface waters. Microorganisms and colloidal particles of silt and clay are stabilized by surface electrostatic charges preventing the particles from coalescing. Historically, alum (aluminum sulfate hydrate) was used to neutralize these charges by surface adsorption of Al cations formed upon hydrolysis of the alum. Since 1983 PAG has been sold as an alum replacement in the treatment of natural water for U.S. municipal and industrial use. 

The humic/organic matter coatings of different solid phases (i. e., SPm /SP0M), such as soils, sediments, suspended solids, colloids, and biocolloids/biosolids, interact with organic pollutants in aqueous systems in various ways. Adsorption is an important interaction mode. The reversibility and/or irreversibility of the adsorption processes is of major importance. The question whether the bound residues of pollutants are to be considered definitely inactivated has been the focus of extensive research. This question was posed as follows. Have the adsorbed pollutants become common components incorporated into the humic polymer coating of solid phases (i. e., being absorbed), or are they only momentarily inactivated in reversibly bound forms thus representing a possible source of pollution by a time-delayed release of toxic units ... 

Multimedia filters, which consist of a top layer of coarse and low density anthracite, layers of silica, and then dense finest medium vitreous silicate, remove about 98% of particulates >20 tm. These filters are regularly back-washed to avoid buildup of particulates. Finer filters (S-lO tm) are used to remove suspended matter and colloidal materials. To prevent scaling due to water hardness, sodium ions generated from brine are exchanged with calcium and magnesium ions in the water. Activated carbon or metabisulfite is used to remove chlorine. 

Finally, it is worth mentioning the turbidity of the water, which reflects the presence of suspended solids (SS), such as dust and sand particles as well as organic matter and colloidal particles. Most water sources supplied from a well or a city main will have low levels of suspended solids, perhaps... 

Reactions of dissolved species with particulate and colloidal suspended matter include adsorption/desorption, complexation, ion-exchange, precipitation/dissolution, coprecipitation during coagulation and flocculation (Morgan, 1966 Stumm and Morgan, 1981 Parks, 1975). These processes are particularly important at the land-sea boundary in estuaries (Duinker, 1980 Martin et al., this volume). The interaction with particles > 0.45 ym is not discussed here. 

Turbidity is a drinking water quality parameter and a groundwater well stabilization indicator. The clarity of water defines a physical property of turbidity. Suspended matter, such as clay and silt particles, organic matter, microscopic organisms, and colloids, causes natural waters to be turbid. Turbidity is measured optically as a lightscattering property of water. 

Applicable to unpolluted samples with a low content of organic matter. Samples should be filtered to avoid interference from suspended particles or colloidal matter and organic compounds. Several ions (Br-, SCN-, I-, COf-, N02, Fe2+, Fe3+, and Cr(VI)) may be important interferents... 

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