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Selected other parameters

The world of chemical analyses - even that of environmental or more restricted that of wastewater analyses - is hardly to survey. For many analytes, there exist several analytical methods, and additionally wastewaters contain innumerable different kinds of constituents. The routineously measured wastewater parameters are mainly given above. But these are really the minority of possible parameters.

For the determination of metals, there exist special methods as flame emission photometry (e.g. important for the fertilizer component potassium). In this procedure the aqueous sample is transferred into a flame where the metals are electronically excited resulting in an emission of light of a particular wavelength. This emission can be detected and used for quantification of the concerning metal ion.

A similar method is also useful for the determination of some toxic heavy metals (atomic emission spectrometry/inductively coupled plasma, AES/ICP). The aqueous solution is pumped into a small plasma generated by high frequency fields where the metals are electronically excited leading to emission of light of that wavelength which is characteristic for the particular metal of concern. With this method, several metals can be determined simultaneously.

On the other hand, aqueous solutions of metal salts can also absorb distinct wavelengthes of light, when they are heated to very high temperatures (flame or graphite furnace) and converted from ions to atoms by this. The light absorbed by the atoms can be used for quantification of particular metal ions in aqueous solutions like wastewaters. The method is called atomic absorption spectrometry (AAS). Solids have to be digested prior to AAS analysis if their metal content is to be analyzed. Details for such methods can be read in the "Standard Methods" (Greenberg et al. 1985).

Sometimes, there is interest in the concentrations of particular organic compounds contained in wastewaters. For such analyses, gas chromatography is a useful tool, but very complex in execution. For many gas chromatographic methods, wastewater samples have to limits for particular trace organics. and the final concentrate is then analyzed. A very small volume of the concentrate (in the range of one µl) is transferred to the so-called injector of the gas chromatograph by a syringe. The injector is heated to temperatures in the range of 200°C and flushed by the inert carrier gas (very often helium is used). At these high temperatures the total solution evaporates at once and the analytes as well as the extractant are transported by the carrier gas to a separation device, the so-called column. The column is usually a capillary made of fused silica (a material that has substituted glass which had been used earlier for manufacturing capillaries for gas chromatography) of some 10 m length. The inner wall of the capillary is lined by thin films of particular polymers which control the separation characteristics of the column. Different analytes (as well as the extractant) show different interactions with the polymer film material and thus exhibit different velocities passing the column. The temperature of the column also affects separation of analytes and varies - depending on the separation problem - between room temperature and around 300°C. It can also be changed during the chromatographic run ("temperature program"). At the end of the column the carrier gas (and the analytes as well as the extractants arriving at different times) are detected by devices like flame ionisation or electron capture detectors giving signals which are related to the concentrations of the analytes in the extract. Very useful are mass spectrometers for detection, because the detected mass fragments of the analytes can serve as "fingerprints" resulting in identification of particular organic compounds after comparison to computerized mass spectra of known organics.

However, not every organic compound can be analyzed by gas chromatography. If the boiling point of an organic is very high (> 400°C) the analyte is not sufficiently volatile to enter the column of the gas chromatograph and it will stay in the injector being subdued to thermal decay. That is why injectors have to be cleaned from time to time. It has been shown that only a minority of organic wastewater constituents are susceptible to gas chromatography. Gulyas (1997) could only identify 1 to 2 % of the TOC of biologically treated municipal wastewater as particular organic compounds by gas chromatography/mass spectrometry. Even in an untreated oil reclaiming wastewater only 2 % of TOC corresponded to particular organics identified in a dichloromethane extract of this wastewater (Gulyas and Reich, 2000).

Microbiological parameters of wastewaters are extremely important for judging their pathogenic potential. On the other hand, there exist also microorganisms which are useful for wastewater purification. The principal microorganisms of concern in water and wastewater include bacteria, fungi, algae, protozoa, worms, rotifers, crustaceans and viruses (Tchobanoglous and Schroeder 1987). Methods for the detection of pathogenic microorganisms are available. However, indicator organisms for faecal contamination are rather used than tests for pathogens, because procedures for the isolation of certain pathogenic bacteria are tedious and complicated and are not recommended for routine use (Greenberg et al., 1985). Therefore, indicator organisms are determined with the coliform group being a principal indicator of faecal bacteria. The coliform group density in waters is looked at as a criterion of the degree of pollution and thus of sanitary quality. For microbiological analyses, culture media are used allowing the microorganisms contained in waters to grow under certain conditions resulting in an amount of cultured bacteria which can be detected by inspection and quantified by counting the grown bacteria colonies. It has to be noted that different bacterial species have different nutrient and Environment requirements. This selectivity is very useful when it is desired to enumerate one or a very few species of bacteria to the exclusion of others. Therefore, nutrient medium and environmental conditions have to be carfully selected. For the coliform group of bacteria used as an indicator for faecal contamination of waters and probable presence of pathogens there exist particular media which can be prepared and sterilized in the microbiological laboratory. For more convenient microbiological analyses, several of these media are also commercially available. Prerequisites for microbiolgical laboratories can be found in the "Standard Methods" (Greenberg et al., 1985).

For the determination of bacteria in waters with low bacterial content, in general three techniques are available: the membrane-filter technique, the solid medium technique (plate count method) and the liquid medium technique (Tchobanoglous and Schroeder, 1987). For details of execution of bacterial counts, see Greenberg et al. (1985). Applying the membrane-filter technique, a known volume of water is filtered over a membrane filter with 0.45 µm pore width. Then the filter is removed from the filtration unit and transferred to a small petri dish containing a sterile absorbent pad saturated with a suitable culture medium. The filter membrane is placed face up on the culture medium. After incubation in the inverted position, the bacterial colonies are counted and the counts are related to the volume which had been filtered (Tchobanoglous and Schroeder, 1987).

For waters with higher numbers of bacteria (e.g. the effluent of a wastewater tretament plant or river water receiving the effluent or even raw sewage) the other two methods are suitable which include dilution steps of the water containing the bacteria (see figure 9).

Figure 9: Illustration of methods to obtain bacterial counts: (b) use of a solid medium; (a) use of a liquid medium (Tchobanoglous and Schroeder 1987)

In the plate count method (see figure 9b) the first operation is preparation of 10-fold dilutions of the sample. Of each dilution as well as of the original sample 1 ml is pipetted into separate sterile petri dishes. Subsequently 12 to 20 ml of liquified culture medium is poured into each petri dish. After mixing medium and sample the mixture is allowed to solidify and subsequently the petri dishes are inverted and incubated at 35°C for 48 hours. The next operation is counting of the developped bacterial colonies. For quantification, only dishes with colony numbers between 30 and 300 are utilized. At higher numbers of colonies clumped growth of bacteria will occur resulting in too low numbers of counted colonies.

Coliforms are capable of fermenting lactose with the production of an abundance of gas. This effect is utilized in counts of coliforms given in figure 9a. Again, 10-fold dilutions of the sample are prepared. Of each dilution 1 ml is transferred to the test tubes in multiplicate. The test tubes contain the fermentation medium and an inverted gas collection tube. After a 24 hour period of incubation at 44.5°C, gas observed in the inner fermentation tube indicates the presence of coliforms in the diluted sample. For example, if a 10-fold serial dilution is made and growth, as measured by gas production, is observed in the 10-n but not in the 10-(n+1) dilution, then it can be concluded that the sample contains at least 10n cells per ml but less than 10n+1 cells per ml.

Another group of parameters useful for judging the quality of effluents of wastewater treatment plants is toxicity. Toxicity determination comprises a huge variety of tests because the test organisms can be varied (even using parts of living organisms like cell cultures) and the endpoint of toxic action can also be varied (using different metabolic events in the organism, occurrence of different diseases, damages or finally death of the investigated organism). For characterizing toxicity of waters, several tests using organisms living in water (e.g. algae, ciliated protozoa, daphnia, corals, annelids, crustaceans, aquatic insects, mollusks, fish) have been standardized (Greenberg et al. 1985). Tragically, also toxicity tests with humans are run (which of course are unintentional) in epidemiological studies which try to find associations e.g. between constituents of drinking water (chemical hazardous substances as well as pathogenic microorganisms) and excessive mortalities in terms of particular diseases in collectives consuming the drinking water of concern. However, these epidemiological studies are no routineously applied "toxicity tests" because they require huge efforts and usually exhibit high statistical uncertainties.

previousAdsorbable organic halides (AOX) Sampling and preparation techniques of wastewater