Safety | Don’t be careless; there are so many safety hazards in the wastewater treatment process as well

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bg8.png Chemical companies require large amounts of water in their production processes, which results in significant wastewater generation. This wastewater often contains toxic substances as well as flammable and explosive materials, and handling it can lead to safety accidents. Any mistakes in this process can have severe consequences for the chemical companies involved. Next, let’s take a look at the various risk factors present in the wastewater treatment process. Dangers of wastewater treatment systems in chemical enterprises 1. Presence of explosive gas mixtures Wastewater discharged by chemical enterprises often contains soluble and flammable gases. Under certain conditions, these gases can easily form explosive mixtures with the liquid. This is evident in several ways: First, if there is a breach in the sealing of the equipment systems or if there is overflow due to improper operation, flammable and explosive gases can easily enter the wastewater, thereby posing risks to the safe operation of the system. Second, after high-temperature steam and wastewater enter the sewer system, it causes the temperature of the wastewater to rise, and the volatile flammable liquids that evaporate may pose a hazard. Third, during gas absorption and desorption, if flammable liquids or gases are present, they will be released as the temperature rises; at that point, the flammable liquids will continuously overflow from the outlet. 2 Can produce hazardous substances Various substances discharged into the sewer system can react with each other, which may result in the formation of flammable, explosive, or even self-igniting substances. 3 Spread of fires 　　Wastewater pipes are widespread in industrial areas, and explosions or fires that occur there often spread along the wastewater treatment systems; if not stopped in time, this can lead to cascading damage. 4. Ignition sources 　There are a variety of ignition sources in wastewater treatment processes, including mechanical expansion, friction sparks, welding sparks, lit cigarette butts, and sparks from vehicle exhaust systems. Analysis of sewage treatment accidents Over the past decade of rapid development, sewage treatment plants have experienced numerous safety accidents. 　　Hydrogen sulfide gas is commonly produced in sewage pipes; it is a gas that is soluble in water and has an odor similar to that of rotten eggs. Mild exposure can cause dizziness and fatigue; examination reveals conjunctival congestion and dry rales in the lungs ； Moderate exposure can cause dizziness, palpitations, difficulty breathing, followed by confusion, vomiting, diarrhea, convulsions, and even coma; ultimately, death may occur due to respiratory paralysis ； When exposed to extremely high concentrations of hydrogen sulfide, a \"electric shock-like\" poisoning occurs; the affected person collapses within seconds with respiratory failure. Prolonged exposure can cause a decline in the sense of smell, as well as neurasthenia syndrome and autonomic nervous system dysfunction. Wastewater enters the various sections of the wastewater treatment plant, and these sections become filled with this gas. Especially in pipes with poor ventilation, at the bottom of wells and ponds, these are places where hydrogen sulfide is rampant. Biogas, scientifically known as methane, is also produced in the sludge digester. It is colorless and odorless, insoluble in water, but it is flammable and explosive, posing equally great hazards. Various bacteria and parasite eggs also exist in sewage, and accidental contact with them can cause harm to humans as well. 　　At the Yuncheng Wastewater Treatment Plant in Shanxi Province, at around 9:20 a.m. on May 20, 2007, a worker was cleaning debris in the wastewater tank of the wastewater lifting pump room; he suffocated due to lack of oxygen. His two colleagues went down to rescue him and also faced danger. The three were rescued and taken to the hospital, but they died despite efforts to save them. 　　At the Yinjiabao Wastewater Treatment Plant in Taiyuan, at 1:00 p.m. on August 8, 2006, a worker was performing maintenance on the gate of the inlet well. He first opened the manhole cover to allow ventilation, then went down. Feeling unwell after a while, he came back up, rested for 30 minutes, and went down again without coming back up. Then three people went in to rescue them, and as a result all four died in the well. Hydrogen sulfide gas is the culprit behind the accident. 　　Property staff in the North Area of Xinhualian Home in Tongzhou, Beijing, suffered an poisoning incident while carrying out maintenance work in a sewage well. First, 3 people went down into the well; after those 3 suffered from poisoning, another 7 people went down to rescue them, and in the end, all 10 people were poisoned. Six property staff members died, and 4 were rescued from critical condition. One of them was a firefighter. He and his comrades rescued 4 people in succession, but the air respirator he was wearing was pulled off by one of the trapped individuals, causing him to be poisoned and unfortunately perish. 　　On April 7, 1986, at a wastewater treatment plant, Manager Zhang, who was just 26 years old and a graduate of Tongji University, led several technicians to a subordinate wastewater pumping station to measure the technical parameters of the machinery there and assess how well the equipment was functioning. At 9 a.m. that day, Manager Zhang and five colleagues turned off the water pumps and entered the indoor sewage tank; suddenly, a large amount of hydrogen sulfide gas rushed in, and like a flash of lightning, all of them collapsed. Other personnel at the pumping station, seeing this, quickly called for help. A nearby construction team heard the noise and rushed to the scene; more than ten people were organized to carry out rescue efforts, and 4 people were rescued from the indoor sewage tank, 3 of whom died on their way to the hospital. It was later discovered that two people were missing, so personnel were immediately organized to search the pool wearing gas masks; one body was found in the sewage. Firefighters arrived and discovered another body after entering the pool. To date, 5 out of the 6 people have died, including that young factory manager. The culprit of the accident was hydrogen sulfide. On-site tests showed that three and a half hours after the accident, the hydrogen sulfide concentration was still as high as 600 mg/m3, which is nearly 60 times above the **health standards. When the concentration reaches 1000 mg/m3, those in contact with it die instantly, as if struck by lightning. 　　Their deaths are inseparable from their own carelessness. First of all, this is a place where hydrogen sulfide is produced, yet they entered there without any protective measures. Moreover, after the accident, there were no effective emergency rescue methods; after some futile efforts, 5 people lost their lives. Safety measures for the wastewater treatment systems in chemical enterprises 1. Proper installation of wastewater pipes: It is strictly prohibited for enterprise water pipelines to pass through residential areas, tank groups, or production facilities. For wastewater from workshops, open ditches and pipes must be installed; when the wastewater is treated in these open ditches, clean water should be used to prevent secondary pollution. For outdoor sewer pipelines, they need to be sealed off and covered with soil and buried pipes. 　　For domestic sewers, it is strictly prohibited to connect them directly to other waterways. If mixing of domestic wastewater with chemical wastewater cannot be avoided, pumps can be used for transfer, but care must be taken to prevent flammable and explosive gases from entering such systems. 2. Prevent safety hazards caused by improper mixing. During actual operations, it is strictly prohibited to mix substances that can produce flammable or explosive materials together. Additionally, the floor of the workshop, as well as the pipes and water tanks used in cleaning equipment, must be cleaned with clean water to prevent flammable or explosive materials from accumulating in those pipes. When treating the wastewater generated from the cleaning of hazardous materials equipment, it is necessary to first carry out purification to remove harmful substances as well as flammable and explosive materials; the wastewater can only be discharged once it meets the specified standards. 3. Avoid the formation of explosive gas mixtures. Waste water generated by process equipment must not be discharged directly into sewer systems; before disposal, flammable gases and liquids must be completely removed from it. This can be achieved by installing local degassing and evaporation systems in the workshop, as well as a plant-wide wastewater degassing system. Furthermore, it should be noted that wastewater with a temperature exceeding 40 degrees Celsius should not be discharged directly; flanges and liquid seal devices need to be installed in the pipeline from the process equipment to the sewer system. 4. Prevent combustion and explosions from spreading along the pipes. In sewage treatment systems, it is necessary to install water seal wells in order to prevent combustion and explosions from spreading along the pipes. When setting up these water seals, the following points need to be taken into consideration: Each sewage discharge system requires an appropriate water seal. If the distance between two such water seals through the pipes exceeds 300 meters, then additional water seal wells are needed. Water seals need to be installed at the locations of furnaces, pumps, towers, and heat exchange equipment in process units. Water seals need to be added to the inlet and outlet pipes of the oil separator, and inspection wells should be designed in a sealed manner. If the production facilities require open ditches for drainage, water seal wells must be used to separate these ditches, with their length being limited to 20 meters. 5 Preventing damage to the sewage treatment system 　To prevent corrosion of wells, sewer pipes, and water chambers, it is necessary to use materials with high corrosion resistance. For large-diameter pipes, reinforced concrete pipes can be used, while for medium and small-diameter pipes, acid-resistant ceramic pipes can be employed. Buildings can be coated with asphalt. For equipment used in transporting and treating wastewater, alloy steel is the preferred material; carbon steel can also be used. 　　To prevent sediment from clogging pipelines, water pipes, and facilities, it is necessary to use grit chambers and clarifiers for purification before discharging wastewater, in order to remove the suspended particles. Additionally, to avoid the accumulation of solid particles in sewer lines, an inclined design must be employed; the specific slope can be calculated using a formula. 6 Eliminate ignition sources. In sewers filled with steam and flammable gases, work is strictly prohibited until the hazards are eliminated. Exhaust pipes are forbidden to be installed within 15 meters of areas where sparks or open flames may occur. For the buildings and equipment in sewage treatment plants, fire separation distances must be established in accordance with the \"Code for Fire Protection Design of Petrochemical Enterprises\". If combustible gases and liquids cannot be properly discharged during the production process and require repair, an accident alarm must be activated to prevent these combustible gases and liquids from igniting a fire source. Summary: Chemical enterprises are prone to hazardous accidents, with a high incidence of explosions. To reduce the frequency of such safety incidents, it is necessary to select appropriate mechanical equipment and conduct regular inspections. Additionally, comprehensive management measures must be established to enhance the safety awareness of operators. Only by adopting these multiple approaches can potential safety hazards in the wastewater treatment systems of chemical enterprises be addressed at an early stage.