Coliform bacteria are always present in the digestive tract of animals and humans, as well as in their waste products. They can also be found on plants, soil and water, where contamination is a serious problem due to the possibility of disease transmission caused by various pathogens.
Harm to the body
Are coliform bacteria harmful? Most do not cause illness, however, some rare strains of E. coli can cause serious illness. In addition to people, sheep and cattle can be infected. It is worrying that contaminated water, in its external characteristics, is no different from ordinary drinking water in taste, smell and appearance. Coliform bacteria are found even in environments that are considered to be impeccable in every sense. Testing is the only reliable way to find out about the presence of pathogenic bacteria.
What happens when detected?
What to do if coliform or any other bacteria are found in drinking water? In this case, repairs or modifications to the water supply system will be necessary. When consumed, disinfection requires mandatory boiling, as well as repeated testing, which can confirm that the contamination has not been eliminated if it was thermotolerant coliform bacteria.
Indicator organisms
Common coliforms are often called indicator organisms because they indicate the potential presence of disease-causing bacteria in water, such as E. coli. Although most strains are harmless and live in the intestines of healthy people and animals, some can produce toxins, cause serious illness, and even be fatal. If pathogenic bacteria are present in the body, the most common symptoms are gastrointestinal upset, fever, abdominal pain and diarrhea. Symptoms are more pronounced in children or older family members.
Safe water
If there are no common coliform bacteria in the water, then it can be assumed with almost complete certainty that it is microbiologically safe for drinking.
If they were detected, then additional tests would be justified.
Bacteria love warmth and moisture
Temperature and weather conditions also play an important role. For example, E. coli prefers to live on the surface of the earth and likes warmth, so coliform bacteria in drinking water appear as a result of movement in underground streams during warm and humid weather conditions, while the least amount of bacteria will be found in the winter season.
Shock chlorination
To effectively kill bacteria, chlorine is used, which oxidizes all impurities. Its amount will be affected by water characteristics such as pH level and temperature. On average, the weight per liter is approximately 0.3-0.5 milligrams. It takes approximately 30 minutes to kill common coliform bacteria in drinking water. Contact time can be reduced by increasing the chlorine dose, but this may require additional filters to remove specific tastes and odors.
Harmful ultraviolet light
Ultraviolet rays are considered a popular disinfection option. This method does not involve the use of any chemical compounds. However, this remedy is not used where total coliform bacteria exceed one thousand colonies per 100 ml of water. The device itself consists of a UV lamp surrounded by a quartz glass sleeve through which a liquid flows, irradiated with ultraviolet light. The untreated water inside the apparatus must be completely clean and free from any visible contamination, blockages or turbidity to allow exposure to all harmful organisms.
Other cleaning options
There are many other treatments used to disinfect water. However, they are not recommended for long-term use for various reasons.
- Boiling. At 100 degrees Celsius for one minute, bacteria are effectively killed. This method is often used to disinfect water during emergencies or when necessary. This is a time-consuming and energy-intensive process and is typically only used in small quantities of water. This is not a long-term or permanent option for water disinfection.
- Ozonation. In recent years, this method has been used as a way to improve water quality and eliminate various problems, including bacterial contamination. Like chlorine, ozone is a strong oxidizing agent that kills bacteria. But at the same time, this gas is unstable and can only be obtained using electricity. Ozonation units are not generally recommended for disinfection because they are much more expensive than chlorination or ultraviolet systems.
- Iodization. The once popular method of disinfection has recently been recommended only for short-term or emergency water disinfection.
Thermotolerant coliform bacteria
This is a special group of living organisms that are capable of fermenting lactose at 44-45 degrees Celsius. These include the genus Escherichia and some species of Klebsiella, Enterobacter and Citrobacter. If foreign organisms are present in the water, this indicates that it has not been sufficiently purified, has been re-contaminated, or contains too many nutrients. If they are detected, it is necessary to check for the presence of coliform bacteria that are resistant to elevated temperatures.
Microbiological analysis
If coliforms were detected, this may indicate that they got into the water. Thus, various diseases begin to spread. In contaminated drinking water you can find strains of salmonella, shigella, E. coli and many other pathogens that range from mild digestive tract disorders to severe forms of dysentery, cholera, typhoid fever and many others.
Household sources of infection
The quality of drinking water is monitored and regularly checked by specialized sanitary services. What can an ordinary person do to protect themselves and protect themselves from unwanted infection? What are the sources of water pollution in domestic conditions?
- Water from the cooler. The more people touch this device, the greater the likelihood of harmful bacteria entering. Studies show that the water in every third cooler is simply teeming with living organisms.
- Rainwater. Surprisingly, moisture collected after rain is a favorable environment for the development of coliform bacteria. Advanced gardeners do not use such water even for watering plants.
- Lakes and reservoirs are also considered a risk group, since all living organisms, not just bacteria, multiply faster in stagnant water. An exception is the oceans, where the development and spread of harmful forms there is minimal.
- Pipeline condition. If the drain pipes have not been changed or cleaned for a long time, this can also lead to problems.
Bacteria of the Escherichia coli group (coliforms) are a group of bacteria from the family Enterobacteriaceae, conditionally distinguished by morphological and cultural characteristics, used by sanitary microbiology as a marker of fecal contamination; they belong to the group of so-called sanitary indicator microorganisms.
Bacteria of the E. coli group include representatives of the genera Escherichia (including E. coli), Citrobacter (a typical representative of C. coli citrovorum), Enterobacter (a typical representative of E. aerogenes), which are combined into one family Enterobacteriaceae due to the common morphological and cultural properties . They are characterized by different enzymatic properties and antigenic structure.
4. The presence of what bacteria indicates fresh fecal contamination of water?
These bacteria include thermotolerant coliform bacteria, fecal coliforms, which ferment lactose to acid and gas at a temperature of 44°C for 24 hours and do not grow on a nitrate medium.
The detection of enterococcus also indicates fresh fecal contamination.
There is a known method for determining fresh fecal contamination, which consists in isolating enterococci from the test water, and when the index of these microorganisms is over 500, the arrival of fresh fecal contamination is assumed.
5. What indicators are determined during sanitary-microbiological testing of water?
1. Determination of the number of saprophytic microorganisms.
2 . Determination of the number of lactose-positive Escherichia coli.
3 . Determination of the number of Escherichia coli.
4. Determination of the number of enterococci.
5 . Determination of the number of staphylococci.
6 . Determination of the number of PFU of E. coli phages.
7 . Determination of bacteria of the genera Salmonella and Shigella.
8 . Determination of the presence of intestinal viruses.
9 . Definition of Vibrio cholerae.
6. What is a “germ number” and how is it determined?
Microbial number is a quantitative indicator of bacterial contamination of the environment, one of the laboratory sanitary and hygienic indicators, indicating the “total number of microbes” in 1 ml of water, 1 g of solid product or soil, 1 m 3 of air, grown at MPA at 37 ° C in 48 hours
To determine the microbial number, inoculations are done in compliance with the rules of asepsis into Petri dishes with MPA using the pouring method so that from 30 to 300 colonies grow on the dishes.
7. What method is used to detect coliforms in water?
There are two methods for determining the number of coliform bacteria: fermentation and membrane filters.
The essence of the membrane filter method is to concentrate bacteria from a certain volume of test water on a membrane filter and grow them at a temperature of 37 ± 0.5 ° C in Endo medium. This temperature creates optimal conditions for growing bacteria.
8. For what purposes are the Koch and Krotov methods used?
The Koch and Krotov methods are used for sanitary and microbiological examination of air.
9. Name the sanitary indicator microorganisms, by the presence of which in the air one can assess its purity?
Sanitary indicator microorganisms for air are Staphylococcus aureus and hemolytic streptococci (Staphylococcus aureus, group Streptococcus viridans and Streptococcus haemolyticus).
10. What is the aspiration method and for what purpose is it used?
The aspiration method is based on the forced settling of microorganisms onto the surface of a dense nutrient medium or into a trapping liquid. For this purpose, the Krotov apparatus, the Rechmensky bacteria trap, the POV-1 device, etc. are used.
To determine the total number of bacteria, two samples of 100 liters each are taken. The crops are incubated in a thermostat for 24 hours and then left for 48 hours at room temperature. The number of colonies on the plates is counted, the arithmetic mean is calculated and recalculated to the number of microorganisms in 1 m 3 of air.
Air testing includes determining the total number of saprophytic bacteria, staphylococci, streptococci, which are indicators of biological contamination of the air by the microflora of the human nasopharynx.
11. On what media is coliform cultured?
On Endo medium, on simple nutrient media: meat-peptone broth (MPB), meat-peptone agar (MPA).
12. What objects and items are subject to examination in the premises of pharmacies during sanitary and microbiological control?
Objects of bacteriological research in pharmacies during sanitary and microbiological control:
1 . Distilled water.
2 . Injection solutions before sterilization.
3 . Injection solutions after sterilization.
4 . Eye drops after sterilization.
5 . Eye drops prepared under aseptic conditions on sterile bases.
6 . Dry medicinal substances used for the preparation of injection solutions.
7. Pharmaceutical glassware, stoppers, gaskets, other auxiliary materials.
8. Inventory, equipment, hands and sanitary clothing for personnel.
9 . Air environment.
The main sanitary indicator microorganisms are bacteria of the coliform group (coliforms), which unite 3 genera of microorganisms - Escherichia, Citrobacter, Enterobacter, members of the Enterobacteriaceae family. They share many common morphological, cultural and enzymatic properties.
In accordance with GOST 2874-82 and GOST 18963-73, coliforms include small, motile, gram-negative, non-spore-forming rods that do not have oxidase activity, lactose fermenting and glucose with the formation of acid and gas at a temperature of 37 ° C (within 5-24 hours) (Figure 45).
Escherichia coli (coliform bacteria) are facultative anaerobes that grow well in universal nutrient media and are resistant to many aniline dyes. They are characterized by wide adaptive variability, as a result of which various variants arise, which complicates their classification.
Of all the bacteria of the coli group, microorganisms of the genus Escherichia have the greatest sanitary and indicative importance.
Based on their ability to break down lactose at a temperature of 37°C, coliforms are divided into lactose-negative and lactose-positive Escherichia coli (LKP), or coliform, which are standardized according to international standards. From the LCP groups, fecal coliforms (FEC) are isolated, which are capable of fermenting lactose at a temperature of 44.5 °C. These include E. coli, which does not grow on citrate medium.
To differentiate coliform bacteria, Endo medium is used, on which E. coli produces characteristic growth in the form of red colonies with a metallic sheen.
Endo medium is a selective medium for enterobacteria and is available in dry form. It contains MPA, lactose, basic fuchsin, sodium sulfate and phosphate.
Preparation of the medium: dissolve 5 g of dry medium in 100 cm 3 of distilled water, boil with constant stirring
Rice. 45. Escherichia coli: a- colonies; b– cells
2-3 minutes and pour into Petri dishes. To prevent the formation of large amounts of condensate, the medium after boiling is cooled to 50 °C. The prepared medium is pink in color. Colonies of lactose-positive strains are red (the resulting lactic acid reacts with sodium sulfate, causing fuchsin to restore its color), while lactose-negative ones are colorless or slightly pink.
When coliforms grow on liquid nutrient media (LMM), significant turbidity of the medium and the formation of a grayish, easily broken sediment are observed. A film usually does not form on the surface of the broth.
On MPA, coliforms form medium-sized, round, smooth, shiny, translucent colonies.
E. coli does not liquefy gelatin and is capable of fermenting a number of carbohydrates - lactose, glucose, maltose, sucrose with the formation of acid and gas. Enzymatic properties (fermentation of carbohydrates) are variable, therefore, when differentiating coliforms, they are not taken into account independently, but in combination with other tests.
In milk, coliform bacteria multiply well, bringing its acidity to 60-80 °T and forming an uneven spongy clot in it. In the presence of lactic acid bacteria, under the influence of the antibiotic substances and acid they secrete, the growth of E. coli is inhibited. Under pasteurization regimes adopted in the dairy industry, E. coli are killed. Conventional disinfectants in generally accepted dilutions disinfect equipment from these bacteria.
The sanitary indicative significance of individual genera of bacteria from the group of coliforms varies. The detection of bacteria of the genus Escherichia in food products, water, soil, and equipment indicates fresh fecal contamination of these objects, which is of great sanitary and epidemiological significance.
It is sometimes believed that bacteria of the genera Citrobacter and Enterobacter are modified Escherichia after being in the external environment. Consequently, Citrobacter and Enterobacter are indicators of older (several weeks) fecal contamination and therefore have less sanitary value compared to bacteria of the genus Escherichia.
Differentiation of coliform bacteria is carried out taking into account differences in the physiological properties of microorganisms. On this basis, special tests have been developed that are used to recognize fecal and non-fecal Escherichia coli, the main of which is the TIMATS (TLIMAC) set of signs:
T - temperature test;
I - indole formation test;
M - reaction with methylene red;
A - reaction to acetylmethylcarbinol (Voges-Proskauer reaction);
C - citrate test;
L - lactose fermentation.
Temperature test(Eijkman test) - the ability to ferment glucose and other carbohydrates (lactose, mannitol) with the formation of gas at a temperature of 44-46 ° C (usually 44.5 ° C). For Escherichia, the temperature test is positive; representatives of the genera Citrobacter and Enterobacter do not have this ability. This test is determined on special media Eikman, Kessler, Boulizh.
Eijkman's medium (glucose-peptone medium): peptone - 10 g; sodium chloride - 5 g, glucose - 5 g; tap water 1,000 cm3. In a concentrated medium, the composition of all ingredients except water is increased 10 times. The medium is poured into test tubes or flasks with fermentation tubes (gas tubes), sterilized with flowing steam for 30 minutes for 3 days (sterilization in an autoclave at 112°C-15 minutes is allowed).
Indole formation test- the ability to break down the amino acid tryptophan, which is part of many proteins, releasing a number of products, including indole, which turns the medium red when interacting with reagents containing paradimethylamidobenzaldehyde. Indole is produced by Escherichia, bacteria from the genera Citrobacter and Enterobacter do not produce indole. The presence of indole is determined in old broth cultures (preferably in Hottinger broth containing 200-300 mg% tryptophan) using Ehrlich's reagent.
Ehrlich's reagent: paradimethylamidobenzaldehyde - 4 g; 96° ethyl alcohol - 380 cm 3; concentrated hydrochloric (hydrochloric) acid - 80 cm 3. Before adding (0.5-1 cm 3) Ehrlich's reagent to the culture, 0.5-1 cm 3 hydrochloric acid ether is added to it (to extract indole).
Studies of the biochemical properties of E. coli after development in milk with starter cultures have shown variability in the indole trait; 36% of E. coli strains may lose the ability to produce indole. Therefore, the use of this characteristic when monitoring fermented milk products may lead to incorrect results.
Reaction with methyl red(Clark reaction) is to determine the intensity of acid formation during the fermentation of glucose in a nutrient medium. Methyl red is used as an indicator, a few drops of which are added to a 3-5-day culture grown on Clark's medium. At pH 5 and below, the indicator changes from light yellow to red, which indicates intense acid formation. Representatives of the genera Escherichia and Citrobacter give a red color to the medium, and Enterobacter gives a yellow color.
At pH above 5, the medium remains light yellow.
Clark's medium: proteose (or other peptone) - 5 g; dextrose - 5 g; K 2 NPO4 - 5 g; distilled water up to 800 cm 3. The mixture is heated for 20 minutes, stirring occasionally, filtered, cooled, and the volume is adjusted to 1,000 cm 3 with distilled water. Pour into 10 cm3 tubes and sterilize at 121 °C for 15 minutes.
Indicator: methyl red - 0.1 g; ethyl alcohol 300 cm 3. After dissolving the indicator, add 200 cm 3 of distilled water.
Reaction to acetylmethylcarbinol(Voges-Proskauer, 1898) reveals the ability of microorganisms to form the aromatic substance acetylmethylcarbinol (acetoin) in a medium with glucose.
To set up the reaction, the same volume of 40% KOH solution is added to 5 cm 3 of a 4-5-day culture grown on peptone medium with glucose or Clark's medium. To speed up the reaction, 0.3 g of creatine [CMeaga reagent (Mira)] is added to 100 cm 3 of alkali. In the presence of acetylmethyl carbinol, the medium turns pink.
Acetylmethylcarbinol (acetoin) is produced by bacteria of the genus Enterobacter. Escherichia and representatives of the genus Citrobacter do not have this ability.
Citrate test- the ability of microorganisms to assimilate. citric acid or its salts as the only carbon source. The culture under study is sown on citrate synthetic Coser medium or solid Simmons medium.
Bacteria of the genera Citrobacter and Enterobacter grow on citrate media (cause turbidity and discoloration in liquid media and the formation of specific colonies on solid media) and are called citrate positive or citrate-assimilating bacteria , whereas Escherichia does not grow on these media and is called citrate negative .
Coser's citrate synthetic medium: MgSO 4 x 7H 2 O - 0.2 g; NH 4 H 2 PO4 - 1.5 g; K 2 NRO 4 - 1 g; sodium citrate x 5 H 2 O - 2.53 g; distilled water - 1,000 cm 3 To determine changes in the reaction of the medium, add 10 cm 3 of a 0.5% alcohol solution of bromothymol blue.
Simmons medium: add 2% agar to Coser medium, adjust the pH to 7.2-7.4, and sterilize in an autoclave at 112 °C for 15 minutes. The indicator is added after sterilization, before pouring into sterile tubes. The medium is olive green in color.
When determining the content of citrate-negative Escherichia in fermented milk products, inflated results can be obtained due to additional consideration of representatives of the genus Enterobacter that have lost the ability to utilize citrates.
The citrate test should be accompanied by microscopy of the specimens since Enterococcus faecalis metabolizes citrates and can be mistaken for citrate-positive Escherichia coli.
Lactose fermentation common to most species of the Enterobacteriaceae family. Representatives of the genus Escherichia (with the exception of lactose-negative variants) ferment lactose; Citrobacter and Enterobacter ferment lactose inconsistently. The ability of microorganisms to ferment lactose is studied on special lactose-containing media with various indicators (Endo medium, Hiss medium, etc.
Quite often, E. coli may have atypical signs of the TIMAC (TLIMAC) complex, which makes their differentiation difficult. This is explained by the fact that in the external environment, E. coli are exposed to various factors, resulting in a change in a number of their biological properties. For example, after being in the external environment, E. coli loses the ability to ferment lactose, ferment carbohydrates at 43 ° C and even at 37 ° C, but acquires the ability to assimilate (digest) citrates.
With long-term use of antibiotics and other medicinal drugs, lactose-negative variants of Escherichia are also found in the human intestine.
In the complex of signs of TIMAC, the main ones are temperature and citrate tests. They are the most stable, which makes it possible to differentiate coliform bacteria of fecal origin from coliforms living in the external environment.
The greatest sanitary and indicative importance are E. coli that do not grow in Coser’s medium with citrates (as the only source of carbon nutrition) and ferment carbohydrates at 43-45 ° C (E. coli). They are indicators of fresh fecal contamination.
In the dairy industry, coliform bacteria are identified as sanitary indicator microorganisms, inoculated on Kessler medium and cultivated at 37 °C for 24 hours.
Preparation of modified Kessler medium: 16 g of dry Kessler medium is placed in a flask and topped up with drinking water to 1,000 cm 3 . The mixture is boiled with stirring for 25 minutes. The volume is brought to 1,000 cm 3 with drinking water and filtered through cotton wool. Pour into test tubes with 5 cm 3 floats or cones with 40-50 cm 3 floats and sterilize at 12 °C for 10 minutes. The medium is dark purple in color.
It is possible to prepare Kessler medium from individual ingredients.
To do this, add 10 g of peptone and 50 cm 3 of sterile bile (bovine or other farm animal bile) to 1,000 cm 3 of drinking water, boil the mixture with stirring for 25 minutes and filter it through cotton wool. 2.5 g of lactose are dissolved in the resulting filtrate and the volume is adjusted to 1,000 cm 3 with drinking water, the pH is set to 7.4-7.6, after which 2 cm 3 of a crystal violet solution with a mass concentration of 10 g/dm 3 is added, poured into test tubes with floats or flasks with floats of 40-50 cm 3 and sterilized at 121 ° C for 10 minutes. The prepared medium should be dark purple in color.
The criteria for the sanitary assessment of food products and other environmental objects for the presence of sanitary indicative microorganisms are provided for by GOSTs and Sanitary Rules and Norms, which indicate that coliform bacteria should not be detected in certain quantities of the product, i.e. the number of sanitary indicative microorganisms per unit of product is standardized. So, for example, in pasteurized milk, E. coli should not be detected in 1 cm3, in liquid kefir starter, E. coli bacteria are not allowed in 3 cm3, in sour cream and cottage cheese - in 0.001 cm3 (g), etc.
ENTEROCOCCI
The taxonomy and biological properties of enterococci are presented in Chapter 10.
Enterococci, along with coliform bacteria, are permanent inhabitants of the intestines of humans and warm-blooded animals; they are released into the external environment in large quantities, and their detection in food products, water, and soil indicates fecal contamination of these objects.
The advantages of enterococci as sanitary indicator microbes lie in their greater resistance to physical and chemical influences, the presence of selective media that make it possible to detect enterococci in heavily contaminated objects, the ease of differentiating them from similar species and some differences between enterococci of human and animal origin, which has a significant significance from an epidemiological point of view.
It has been established that Ent. faecalis and its variants, Ent. faecium. Ent. predominates in the intestinal contents of cattle, pigs, sheep, and horses. faecium. Detection in the external environment Ent. faecalis and its variants have a certain sanitary and epidemiological significance as an indicator of contamination of an object with human feces; detection Ent. faecium is an indicator of contamination from animal feces.
Other advantages of enterococci as sanitary indicator microorganisms are that they do not reproduce outside the intestines of humans and animals (with the exception of food); in the external environment do not undergo such profound changes as E. coli, and persist longer in the external environment compared to them.
There are selective nutrient media that make it possible to isolate enterococci in pure culture from objects heavily contaminated with foreign microflora. To determine enterococci, milk medium with polymyxin according to Kalina is often used (see Chapter 10).
Enterococci are extremely resistant to low temperatures, heat, chlorination, high concentrations of sugar and salt, and high acidity. They can withstand heating temperatures of 60-56 °C for 30 minutes (pasteurization modes must neutralize enterococci), are able to grow in the presence of 6.5% NaCl, 40% bile, in media with a pH of 9.6-10.- In this regard for products that are not subject to storage, the indicator of sanitary condition is bacteria of the coli group, and for products that are stored for a long time at low temperatures, it is better to identify enterococci as sanitary indicator microorganisms. This is explained by the fact that E. coli die faster than enterococci and their presence or absence does not reflect the sanitary condition of such products.
The number of enterococci in food products varies within quite significant limits - from 10 3 to 10 6 per 1 g or 1 cm 3.
The presence of a large number of enterococci in products that have undergone heat treatment indicates poor pasteurization efficiency (violation of regimes), post-pasteurization contamination, or storage under conditions favorable for the development of enterococci.
In official documents - the International Standard for the Study of Drinking Water, the Standard for the Study of Drinking Water and Wastewater adopted in the USA, and the European Standard - enterococci are accepted as an additional indicator of the sanitary and hygienic quality of water, and the International Standard emphasizes that when detected in When testing water for atypical E. coli, the presence or absence of enterococci is decisive for judging fecal contamination.
In our country, enterococci, along with coliform bacteria, are used as sanitary indicator microorganisms in the sanitary assessment of water from open reservoirs, especially wells, the water of which is used in the technological process.
Enterococci are also recommended for use as sanitary indicator microorganisms when assessing the quality of chlorination of drinking water, when examining water from mineral springs, as well as food products with a high concentration of salt (meat products).
Before sterilization. The air is assessed by the content of Staphylococcus aureus entering it from the upper respiratory tract and oral cavity. It is considered an indicator of droplet air pollution. Other microbes that reflect the sanitary problems of a particular object are yeast and mold fungi, Pseudomonas aeruginosa, and salmonella.
General and thermotolerant coliform bacteria (in 3 samples of 100 ml of water)
When determining water quality, it is necessary to calculate the amount of coliform bacteria present to determine whether the water meets established standards. To count positive coliform tests (presumptive, confirmatory and fecal), a (Multiple fermentation tubes) is used. When counting, a method of statistical processing of test results carried out with serial dilution of the sample is used. Research results are presented in the form of the most probable number of coliform bacteria (MPN). For example, NP 10 means that there are 10 coliform bacteria per 100 ml of water.
In most cases, the study of the restoration of the number of bacteria was carried out on the total and fecal coliform groups of bacteria. At the same time, the question of how dangerous the restoration of the number of coliform bacteria is to health remains open, since different types of bacteria have different pathogenic properties, in addition, neither general nor fecal coliform groups of bacteria are the only pathogenic microbiological factors operating in the water environment.
The purpose of this work was to investigate the phenomenon of apparent recovery of these three major subgroups of coliform bacteria in chlorinated wastewater. Recovery of bacteria in chlorinated waters and their survival in non-chlorinated waters have been carried out. In cases where, over long periods of time after chlorination, the destruction of bacteria does not differ significantly from natural, the feasibility of chlorination is questionable, especially if the wastewater is not immediately used by humans after it is discharged.
The data presented shows how statistically significant the increase in the content of coliform bacteria is. It was found that the content of all subgroups of bacteria increases; the maximum content is observed on the fourth or fifth day (Table 13.5).
| Rice. 12.3. Diagram of a typical installation for biological wastewater treatment and tests that must be carried out to determine the degree of efficiency of its operation / - determination of flow parameters g - coarse impurities 3 - sand trap 4 - primary settling tank 5 - sediment from primary settling tanks 5 - compactor 7 - sludge water 8 compacted sediment 9 - vacuum filter / O -filtrate - conditioning chemicals t - cake 13 - biological treatment and sedimentation 14 - excess activated sludge 5 - chlorination C - flow rate 55 - suspended solids content U55 - loss on ignition of suspended solids - dry residue coliorts - content of fecal coliform bacteria |
The effectiveness of the disinfection process is determined by analysis of a group of coliform bacteria, which are indicators of water quality. The sensitivity of bacteria to chlorination is well known, while the effect of chlorination on protozoa and viruses is not entirely clear. Protozoan larvae and intestinal viruses are more resistant to chlorine than coliforms and other intestinal bacteria. However, there is very little evidence to suggest that current water treatment practices are deficient. There have been no documented outbreaks of diseases associated with the consumption of water containing viral or protozoal infections.
Almost all states now require coliform testing of treated water, with the number of tests required depending on the population served. Fecal coliform counting, although usually unnecessary from a regulatory perspective, is straightforward and can provide additional insight into the situation. Sometimes, in relation to a specific installation, limit values for certain indicators are specifically set, such as the concentration of residual chlorine, turbidity, content of dissolved solids, nitrates, and color. The concentration of residual chlorine in the distribution system is measured to determine whether chlorination is sufficient. Other laboratory tests are related to monitoring chemical treatments, identifying and correcting certain problems occurring in distribution system facilities, and consumer complaints about water quality. Chemical reagents must meet the requirements of the relevant specifications and should be subjected to traditional analysis, with a fine imposed on the supplier if they deviate from the specifications. For example, lime is typically purchased at 88-90% CaO, alum at 17% AI2O3, and activated carbon to specifications for phenol content. If the chemical supply contract specifies penalties for the supplier based on laboratory test results, this can prevent the water treatment plant from receiving substandard materials.
Restoring the content of coliform bacteria in chlorinated waters
Initial