Harmful gas detection in water supply and sewage treatment industry

The water supply and sewage treatment industry will produce many toxic and flammable gases, these gases need to be detected and removed. Due to different application methods, locations and treatment processes, the harmful gases produced are very different, but the solutions are the same-that is, the use of fixed and portable gas detection instruments.

At each stage of the process of water purification and sewage treatment, a variety of harmful gases are generated. Although for most (if not all) facilities, the harmful gases produced are the same; however, some specific sites require special treatment processes and special gas detection methods. In most cases, a combination of fixed and portable gas detection instruments is required.

The role of installing gas detection equipment is not only to monitor the process, but more importantly for safety needs, to avoid casualties. Such safety equipment must be built strong enough to withstand the stringent requirements of water supply and sewage treatment plants. The harsh environment is diverse, with unpredictable water levels and physical damage to the testing equipment, as well as acidic or alkaline environments resulting from the reaction of gases such as hydrogen sulfide and chlorine with water.

Drinking water purification facilities

For drinking water purification facilities, possible harmful gases include chlorine, sulfur dioxide, ammonia, ozone, and chlorine dioxide. These gases originate from gas storage areas, gas use areas, and ozone generators.

Most drinking water needs to undergo the physical treatment process of flocculation, filtration and ion exchange in the early stage. Only at the stage of treatment / disinfection, after the use of chemicals, will gaseous hazards be generated. Chlorine is a traditional water treatment disinfectant. In many countries, this is a legal requirement. Although other non-chemical methods (such as ultraviolet disinfection) can be used, the reason for choosing the chlorine treatment method is that it can bring residual disinfectant downstream. During the treatment with chlorine gas, from the chlorine gas storage tank to the final generation of clean water, each step must be strictly monitored, including monitoring of the valve and each room through which the chlorine gas pipe passes.

Most water plants still use chlorine gas treatment methods, but some plants have begun to switch to other alternative methods, such as ozone, chlorine dioxide or sodium hypochlorite. In addition, these factories that still use chlorine gas often use sulfur dioxide to remove the chlorine gas in the water after water treatment. All the gases mentioned above are hazardous substances and must be effectively monitored. Only a very low concentration of sulfur dioxide can cause harm to life. The chlorine gas has a high density and can be quickly absorbed by most substances, making it difficult to detect in the storage area. Recently, people are paying more and more attention to the concentration of carbon dioxide in the enclosed space of the chalk area.

Due to the different types of harmful gases and the need for people to enter in certain areas of the water treatment plant, it is often necessary to combine portable and fixed gas detection equipment. Gas storage areas, ozone generators, rooms through which gas pipes pass, and water treatment workshops should always be equipped with fixed detectors to detect specific gases (or gas mixtures). In addition, when the operator needs to enter a closed space where harmful gases are present, even if fixed detectors have been installed in these places, a portable detector should be taken with you as an additional safety precaution. In addition, as required, these portable detectors can detect either a single gas or multiple gases.

Sewage treatment facilities

Sewage treatment facilities can produce many harmful gases, such as methane (combustible gas), hydrogen sulfide, carbon monoxide and carbon dioxide. There are various sources of these gases, such as sewage tanks, pumping stations, aeration tanks, sludge digestion tanks, deodorization plants and treatment plants.

Primary and secondary treatment processes, such as aeration and sludge digestion, are usually high-risk areas for biogas production. These biogas produced from sludge contain methane, hydrogen sulfide, and carbon dioxide and other harmful substances. In addition to being extremely explosive, methane can also cause a decrease in oxygen concentration, which increases the risk of suffocation. On the other hand, hydrogen sulfide has a special odor at low concentration (0.0047ppm), which is very easy to distinguish; but when the concentration exceeds 150ppm, the human olfactory nerve will be damaged and cannot smell its odor, thus covering up In its true existence, even if the hydrogen sulfide reaches a lethal concentration of 800 pm, the workers will not smell its odor, which is fatal. Since biogas is extremely flammable, the biogas generated in the process of sludge digestion can be used for power generation. Therefore, if it leaks from the digester, it will be very dangerous and may cause an explosion.

Like drinking water treatment, wastewater is usually treated with chlorine (or chlorine substitutes) before it can be discharged into the factory. Therefore, the same strict gas monitoring is also required at each stage from storage to final processing.

Fixed gas detectors used to detect flammable gas must be installed in places such as sewage outlets and wet wells, because the liquid containing flammable gas is discharged into the sewer from these places, the combustible gas floats on the surface, and then gathers in the wet well Here, the flammable concentration is finally reached, which poses a great danger. The fixed detectors used to detect methane, carbon dioxide, oxygen and hydrogen sulfide must also be installed in all places where sludge is decomposed and processed. In addition, the deodorization workshop also needs to install fixed detectors for detecting high and low concentrations of hydrogen sulfide. Operators must bring a portable gas detector to enter enclosed spaces, such as sewage tanks, pump stations, sludge digestion tanks, and sewage treatment plants. In these cases, a composite gas detector is generally used.

case study

Recently, Southern Water in the United Kingdom purchased more than 800 Tetra series portable gas detectors from Crowcon for employees working in closed environments such as wastewater, sewage, clean water and water processing departments. , And for the conversion process of chlorine gas. At the same time, it is also available to non-frontline employees, including scientists, technicians, health and safety consultants, and employee trainers.

"We are now in the age of 'high IQ workers' and they all want to know what is happening around them," said Andy Nicholls, senior health and safety consultant at Southern Waterworks.

"Our employees are very aware of the laws and regulations related to health and safety. They want to have equipment that meets the requirements in any environment." We chose the Tetra series equipment because they are simple to operate, easy to maintain, and very durable. They can save lives in danger, and the price of instruments is insignificant in front of human lives. "

in conclusion

Each gas has its own characteristics, so in any environment where the concentration of harmful gases is most likely to accumulate (or the gas concentration is reduced, such as oxygen), fixed or portable gas detection equipment must be installed or worn. Like other industries, the water supply and wastewater treatment industries are constantly seeking ways to reduce costs; however, there must be no reduction in employee safety. Gas accidents in these industries are not as simple as causing injuries—but deaths. As part of the comprehensive safety regulations, gas detection must be prioritized and must meet industry best practice standards. However, in terms of measures to ensure the safety of employees, even in the most dangerous areas, there are still many unsatisfactory places, and there is still a long way to go.

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