Wastewater Treatment Plants
The treatment and proper disposal of wastewater is a necessary undertaking. Storm water and sewage is treated to remove impurities, so that the treated water can be safely released into rivers, oceans, landscaping networks, or recycled irrigation systems. Since the wastewater treatment workers often operate mechanical equipment, use treatment tanks, or handle water-treating chemicals, there are a few hazards to wastewater plant operators and workers.
The CDC has several guidelines for hygiene practices and Personal Protective Equipment (PPE) when working in wastewater treatment plants, but it’s also critical that the toxic and combustible gases are properly monitored to prevent worker exposure and provide a safer environment for personnel.
Gases Found in Wastewater Treatment Facilities
The processes involved in treating wastewater produce numerous toxic and/or combustible gases, exposing treatment plant operators to these hazardous chemical agents. These agents are generated during the treatment process, or excreted in the reagents and effluents used in processing.
Wastewater treatment plants should have sensors in place to monitor three primary gases:
- CH⁴ (Methane)
- O² (Oxygen)
- H²S (Hydrogen Sulfide)
Methane is a flammable gas that can cause combustion or health hazards to workers who are exposed at higher concentrations. The gas is a byproduct of the decomposition of the organic materials in the waste flows entering the plant. A high concentration of methane gas is primarily dangerous because of the risk of combustion, jeopardizing worker safety. Methane gas can also displace oxygen, making it difficult for personnel to work effectively. It can result in rapid breathing or heart rate, slurred speech, vision problems, nausea or vomiting, headaches, memory loss and more.
Oxygen is used for biological treatment at wastewater treatment plants in an aerobic activated-sludge process within the aeration system. Oxygen can also be displaced by other gases that are found in wastewater treatment facilities. Buildup is dangerous in confined spaces within the plant because it facilitates combustion and may cause an explosion if there is a spark or ignition when the oxygen interacts with methane gases. Additionally, an environment where oxygen has been displaced by other gases can cause an immediate danger to life and health.
Hydrogen Sulfide is a compound often found in wastewater and in the associated air spaces. In addition to being a health risk for wastewater and sewer treatment plant workers, hydrogen sulfide can be an environmental pollutant. H²S is produced by the septic conditions in wastewater and during the biological reduction of sulfates and decomposition of organic materials. Exposure to high concentrations of hydrogen sulfide has been known to cause brain damage, long-term neurological conditions or death. In addition to the health and safety issues, H2S is a corrosive gas that can damage building materials if allowed to build up.
While most of these gases aren’t dangerous in small amounts, high concentrations can pose serious health and safety risks for wastewater treatment plant workers. Additionally, methane and oxygen can react and cause an explosion in some conditions, where the concentration of the gases is higher and there is a spark or ignition. To prevent this from happening and reduce safety hazards, treatment plants should have monitoring for lower explosive limits (LELs). Monitoring the LEL for methane will be particularly important, since it’s lower explosive limit is just 5 percent by volume.
Most people are familiar with hazards from combustible gases such as propane, acetylene, and natural gas, but people often don’t consider the hazards of oxygen and oxygen-depleting gases in the case of a leak. If a gas such as carbon dioxide or nitrogen leaks, these gases can quickly displace the oxygen. If the concentration of oxygen by as little as 1 – 2 percent), individuals in the space will begin to feel the effects immediately.