impurities in water. Transparency of water in the lake Characteristics of waters by the value of total hardness
The transparency of water depends on the amount of mechanical suspended solids and chemical impurities contained in it. Turbid water is always suspicious in epizootic and sanitary terms. There are several methods for determining the transparency of water.
comparison method. The test water is poured into one cylinder made of colorless glass, and distilled water is poured into the other. Water can be rated as clear, slightly transparent, slightly opalescent, opalescent, slightly turbid, turbid, and highly turbid.
disk method. To determine the transparency of water directly in the reservoir, a white enameled disk is used - the Secchi disk (Fig. 2). When the disk is immersed in water, the depth at which it ceases to be visible and at which it becomes visible again when removed is noted. The average of these two values shows the transparency of the water in the reservoir. In clear water, the disk remains visible at a depth of several meters: in very muddy water it disappears at a depth of 25-30 cm.
Font method (Snellen). More accurate results are achieved using a flat-bottomed glass calorimeter (Fig. 3). The calorimeter is installed at a height of 4 cm from the standard font No. 1:
The investigated water after shaking is poured into the cylinder. Then they look down through the column of water at the font, gradually releasing water from the calorimeter tap until it becomes possible to clearly see font No. 1. The height of the liquid in the cylinder, expressed in centimeters, is a measure of transparency. Water is considered transparent if the font is clearly visible through a column of water of 30 cm. Water with a transparency of 20 to 30 cm is considered slightly cloudy, from 10 to 20 cm - cloudy, up to 10 cm is unsuitable for drinking purposes. Good clear water after standing does not give a deposit.
ring method. Water transparency can be determined using a ring (Fig. 3). To do this, use a wire ring with a diameter of 1-1.5 cm and a wire cross section of 1 mm. Holding the handle, the wire ring is lowered into the cylinder with the investigated water until its contours become invisible. Then, with a ruler, measure the depth (cm) at which the ring becomes clearly visible when removed. An indicator of acceptable transparency is considered to be 40 cm. The data obtained “by the ring” can be converted into indications “by the font” (Table 1).
Table 1
Translation of water transparency values "on the ring" to the value "on the font"
Transparency of water according to the Secchi disk, according to the cross, according to the font. Turbidity of water. The smell of water. Water color.
There are suspended solids in the water, which reduce its transparency. There are several methods for determining the transparency of water.
- According to the disk of Secchi. To measure the transparency of river water, a Secchi disk with a diameter of 30 cm is used, which is lowered on a rope into the water, attaching a weight to it so that the disk goes vertically down. Instead of a Secchi disk, you can use a plate, lid, bowl, placed in a grid. The disk is lowered until it is visible. The depth to which you lowered the disk will be an indicator of the transparency of the water.
- By the cross. Find the maximum height of the water column, through which the pattern of a black cross is visible on a white background with a line thickness of 1 mm, and four black circles with a diameter of 1 mm. The height of the cylinder in which the determination is carried out must be at least 350 cm. At the bottom of it is a porcelain plate with a cross. Bottom part cylinder should be illuminated by a 300 W lamp.
- By font. A standard font is placed under a cylinder 60 cm high and 3-3.5 cm in diameter at a distance of 4 cm from the bottom, the test sample is poured into the cylinder so that the font can be read, and the maximum height of the water column is determined. The method for quantitative determination of transparency is based on determining the height of the water column, at which it is still possible to visually distinguish (read) a black font 3.5 mm high and a line width of 0.35 mm on a white background or see an adjustment mark (for example, a black cross on white paper) . The method used is unified and complies with ISO 7027.
Water has increased turbidity due to the content of coarsely dispersed inorganic and organic impurities. The turbidity of water is determined by the gravimetric method, and by a photoelectric colorimeter. The weight method is that 500-1000 ml of turbid water is filtered through a dense filter with a diameter of 9-11 cm. The filter is preliminarily dried and weighed on an analytical balance. After filtering, the filter with sediment is dried at a temperature of 105-110 degrees for 1.5-2 hours, cooled and weighed again. The amount of suspended solids in the test water is calculated from the difference between the masses of the filter before and after filtration.
In Russia, the turbidity of water is determined photometrically by comparing samples of the studied water with standard suspensions. The measurement result is expressed in mg / dm 3 using the main standard suspension of kaolin (turbidity for kaolin) or in MU/dm 3 (turbidity units per dm 3) when using formazin stock standard suspension. The last unit of measurement is also called the Turbidity Unit. according to Formazin(EMF) or in Western terminology FTU (formazine Turbidity Unit). 1FTU=1EMF=1EM/dm 3 .
AT recent times The photometric method for measuring turbidity by formazin has been established as the main one all over the world, which is reflected in the ISO 7027 standard (Water quality - Determination of turbidity). According to this standard, the unit of measure for turbidity is FNU (formazine Nephelometric Unit). Agency for Protection Environment USA (U.S. EPA) and World Organization The World Health Organization (WHO) uses the Nephelometric Turbidity Unit (NTU) for turbidity.
The relationship between the basic turbidity units is as follows:
1 FTU(EMF)=1 FNU=1 NTU
WHO does not standardize turbidity according to indications of health effects, however, from the point of view of appearance recommends that turbidity be no higher than 5 NTU (nephelometric turbidity unit) and, for decontamination purposes, no more than 1 NTU.
Odors in the water may be associated with vital activity aquatic organisms or appear when they die - these are natural smells. The smell of water in a reservoir can also be caused by sewage effluents entering it, industrial effluents are artificial odors. First, a qualitative assessment of the smell is given according to the relevant features:
- marsh,
- earthy,
- fish,
- putrefactive,
- aromatic,
- oil, etc.
The strength of the smell is evaluated on a 5-point scale. The flask with a ground stopper is filled 2/3 with water and immediately closed, shaken vigorously, opened and the intensity and nature of the odor are immediately noted.
A qualitative assessment of the color is made by comparing the sample with distilled water. To do this, separately investigated and distilled water is poured into glasses made of colorless glass, against the background white sheet in daylight, they are viewed from above and from the side, the chromaticity is evaluated as the observed color, in the absence of color, the water is considered colorless.
The temperature in water sources is determined by a scoop or conventional thermometer wrapped in several layers of gauze. The thermometer is kept in water for 15 minutes at the sampling depth, after which readings are taken.
The most favorable temperature for drinking water is 8-16°C.
Definition of transparency
The transparency of water depends on the amount of mechanical suspended solids and chemical impurities contained in it. Turbid water is always suspicious in epizootic and sanitary terms. There are several methods for determining the transparency of water.
comparison method. The test water is poured into one cylinder made of colorless glass, and distilled water is poured into the other. Water can be rated as clear, slightly transparent, slightly opalescent, opalescent, slightly turbid, turbid, and highly turbid.
Rice. 2. Secchi disk.
disk method. To determine the transparency of water directly in the reservoir, a white enameled disk is used - the Secchi disk (Fig. 2). When the disk is immersed in water, the depth at which it ceases to be visible and at which it becomes visible again when removed is noted. The average of these two values shows the transparency of the water in the reservoir. In clear water, the disk remains visible at a depth of several meters; in very turbid water, it disappears at a depth of 25-30 cm.Rice. 3. Calorimeter.
The investigated water after shaking is poured into the cylinder. Then they look down through the column of water at the font, gradually releasing water from the calorimeter tap until it becomes possible to clearly see font No. 1. The height of the liquid in the cylinder, expressed in centimeters, is a measure of transparency. Water is considered transparent if the font is clearly visible through a column of water of 30 cm. Water with a transparency of 20 to 30 cm is considered slightly cloudy, from 10 to 20 cm - cloudy, up to 10 cm is unsuitable for drinking purposes. Good clear water after standing does not precipitate.
Rice. 3. Determination of water transparency by the ring method.
ring method. Water transparency can be determined using a ring (Fig. 3). To do this, use a wire ring with a diameter of 1-1.5 cm and a wire cross section of 1 mm. Holding the handle, the wire ring is lowered into the cylinder with the investigated water until its contours become invisible. Then, with a ruler, measure the depth (cm) at which the ring becomes clearly visible when removed. An indicator of acceptable transparency is considered to be 40 cm. The data obtained “by the ring” can be converted into indications “by the font” (Table 1).Table 1
Translation of water transparency values "on the ring" to the value "on the font"
The main contaminants present in Wastewater ah city treatment facilities, grouped and presented in Scheme 1
Organic matter in wastewater physical condition can be in undissolved, colloidal and dissolved states, depending on the size of their constituent particles (Table 1). As the particle size of pollutants changes, they are sequentially removed at all stages of biological treatment (Scheme 2).
Table 1 Composition organic matter in raw wastewater by particle size
Scheme 1
Water transparency
The transparency of waste water is due to the presence of undissolved and colloidal impurities in it. The measure of transparency is the height of the water column at which you can read the font through it. certain size and type. City wastewater entering the treatment has a transparency of 1-5 cm. The effect of treatment is most quickly and simply estimated by the transparency of the treated water, which depends on the quality of the treatment, as well as the presence in the water of small flakes of activated sludge that do not settle in two hours. and dispersed bacteria. Crushing of sludge flakes can be the result of the decay of larger, older flakes, the consequence of their rupture by gases, or under the influence of toxic sewage. Small flakes can stick together again, but, having reached a certain small size, they do not grow further. Transparency is the most prompt, sensitive to violations, indicator of the quality of cleaning. Any, even minor, unfavorable changes in the composition of wastewater and in the technological mode of their treatment lead to the dispersion of sludge flakes, disruption of flocculation, and, consequently, to a drop in the transparency of treated water.
Biological wastewater treatment should provide at least 12 cm of purified water transparency. With complete, satisfactory biological treatment, the transparency is 30 centimeters or more, and with such transparency, all other sanitary indicators of pollution, as a rule, correspond high degree cleaning.
Transparency is determined in shaken (characterizes the presence of suspended and colloidal substances), and settled (the presence of colloidal substances) samples. Transparency in the settled sample characterizes the operation of aerotanks, transparency in the shaken one characterizes the operation of secondary settling tanks.
Examples. If the transparency of purified water in a shaken sample is 19 cm, and in a settled one 28 cm, we can conclude that the aerotanks (colloidal substances are well removed) and secondary sedimentation tanks work satisfactorily (it can be expected that the removal of suspended solids in purified water will not exceed 15 mg/dm3 ),
Scheme 2 Sequential removal of organic particles (depending on their size) on different steps wastewater treatment
If, according to the results of the analysis, the transparency in the shaken sample is 10 cm, and in the settled sample it is 30 cm, this means that colloidal substances are well removed from wastewater in aerotanks, but the secondary settling tanks do not work satisfactorily and provide low transparency of treated water.
A change in the transparency of the nadil water can serve as an operational signal about changes in the purification process even when other methods of physical and chemical control do not yet record deviations, since all violations are accompanied by crushing of activated sludge flakes, which is immediately fixed by the reduced transparency of the above silt water.
Transparency sea water is the ratio of the radiation flux that has passed through the water without changing direction, a path equal to unity, to the radiation flux that has entered the water in the form of a parallel beam. The transparency of sea water is closely related to the transmittance T of sea water, which is understood as the ratio of the radiation flux transmitted by a certain layer of water I z to the radiation flux incident on this layer I 0 , i.e. T \u003d \u003d e - with z. Transmittance is the opposite of light attenuation, and transmittance is a measure of how much light travels a given length of path in seawater. Then the transparency of sea water will be Θ=e - c, which means that it is related to the light attenuation index c.
Along with the indicated physical definition of transparency, the concept is used conditional (or relative) n transparency, which is understood as the depth of the cessation of visibility of a white disk with a diameter of 30 cm (disc of Secchi).
The disappearance depth of the white disc or relative transparency is related to the physical concept of transparency, since both characteristics depend on the light attenuation coefficient.
The physical nature of the disappearance of the disk at a certain depth is that when the light flux penetrates into the water column, it is weakened due to scattering and absorption. At the same time, with increasing depth, there is an increase in the flow of scattered light to the sides (due to higher-order scattering). At a certain depth, the flow scattered to the sides is equal to the flow of direct light. Consequently, if the disk is lowered below this depth, then the flow scattered to the sides will be greater than the main flow going down, and the disk will cease to be visible.
According to the calculations of academician V.V. Shuleikin, the depth at which the energies of the main stream and the stream scattered to the sides are equalized, corresponding to the depth of the disappearance of the disk, is equal to two natural lengths of light attenuation for all seas. In other words, the product of the scattering index and transparency is a constant value equal to 2, i.e. k λ × z = 2, where z - depth of disappearance of the white disk. This ratio makes it possible to link the conditional characteristic of sea water - relative transparency with a physical characteristic - the scattering index k λ . Since the scattering index is an integral part of the attenuation index, it is also possible to relate the relative transparency to the attenuation index, and, consequently, to the physical characteristics of transparency. But since there is no direct proportionality between the absorption and scattering indices, then in each sea the relationship between the attenuation index and transparency will be different.
Relative transparency depends on the height from which observations are made, the state of the sea surface, and lighting conditions.
As the height of observations increases, relative transparency increases due to the decrease in the influence of the light flux reflected from the sea surface, which interferes with observations.
During waves, there is an increase in the reflected flow and a weakening of the flow penetrating into the depths of the sea, which leads to a decrease in relative transparency. This was noticed in antiquity by pearl seekers who dived on the bottom of the sea with olive oil in his mouth. The oil released by them from their mouths floated to the surface of the sea, smoothed out small waves and improved the illumination of the bottom.
In the absence of clouds, the relative transparency decreases, as observations are difficult. sun glare. Powerful cumulus clouds significantly reduce the light flux incident on the sea surface, which also reduces relative transparency. The most favorable lighting conditions are created in the presence of cirrus clouds.
The greatest number of optical observations relates to measurements of relative transparency with a white disk.
Relative transparency varies greatly depending on the content of suspended particles in sea water. In coastal waters rich in plankton, the relative transparency does not exceed a few meters, while in the open ocean it reaches tens of meters.
The clearest waters are found in subtropical zone World Ocean. In the Sargasso Sea, relative transparency is 66.5 m, and this sea is considered the standard of transparency. Such high transparency in the subtropical belt is associated with the almost complete absence of suspended particles and the weak development of plankton. in the Weddell Sea and pacific ocean near the islands of Tonga, an even higher transparency was measured - 67 m. In temperate and high latitudes, the relative transparency reaches 10-20 m.
In the seas, transparency varies considerably. So, in the Mediterranean Sea it reaches 60 m, in the Japanese - 30 m, Black - 28 m, Baltic - 11-13 m. In the bays and especially near the mouths of the rivers, the transparency ranges from several centimeters to several tens of centimeters.
When considering the issue of the color of the sea, two concepts are distinguished: the color of the sea and the color of sea water.
Under the color of the sea refers to the apparent color of its surface. The color of the sea in a strong way depends on the optical properties of the water itself and on external factors . Therefore, it varies depending on external conditions (illumination of the sea with direct sunlight and diffused light, on the angle of view, waves, the presence of impurities in the water, and other reasons).
Own color of sea water is a consequence of selective absorption and scattering, i.e. it depends on the optical properties of water and the thickness of the considered water layer, but does not depend on external factors. Taking into account the selective attenuation of light in the sea, it can be calculated that even for clear ocean water at a depth of 25 m, sunlight will be deprived of the entire red part of the spectrum, then with increasing depth the yellow part will disappear and the color of the water will appear greenish, only the blue part will remain at a depth of 100 m and the color of the water will be blue. Therefore, it is possible to talk about the color of water when the water column is considered. In this case, depending on the water column, the color of the water will be different, although its optical properties do not change.
The color of sea water is assessed using the water color scale (Forel-Uhle scale), which consists of a set of test tubes with color solutions. Determination of the color of water consists in the visual selection of a test tube, the color of the solution of which is closest to the color of water. The color of the water is indicated by the number of the corresponding test tube on the color scale.
An observer standing on the shore or watching from a ship sees not the color of the water, but the color of the sea. In this case, the color of the sea is determined by the ratio of the magnitudes and the spectral composition of the two main light fluxes that enter the eye of the observer. The first of them is the flow of the light flux reflected by the surface of the sea, falling from the Sun and the firmament, the second is the light flux of diffuse light coming from the depths of the sea. So as the reflected stream is white, as it increases, the color of the sea becomes less saturated (whitish). When the observer looks vertically down at the surface, he sees a stream of diffuse light, and the reflected stream is small - the color of the sea is saturated. When moving the gaze to the horizon, the color of the sea becomes less saturated (whitish), approaching the color of the sky, due to the increase in the reflected flow.
In the oceans there are huge expanses of dark blue water (the color of the oceanic desert), indicating the absence of foreign impurities in the water and its exceptional transparency. As you approach the coast, there is a gradual transition to bluish-green, and in the immediate vicinity of the coast - to green and yellow-green tones (the color of biological productivity). Near the mouth of the Yellow River, which flows into the Yellow Sea, a yellow and even brown tint of water prevails, due to the removal of a huge amount of yellow loess by the river.