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What's involved in wastewater treatment?

Wastewater is the combination of liquid and water waste from homes, commercial buildings, and industrial facilities. Wastewater treatment is a process of water and sewage purification, where contaminants are removed from effluent to allow the water to be returned to the water cycle with an acceptable impact on the environment. This process is commonly known as water reclamation.

A wastewater treatment system should be made up of several technologies that address the specific wastewater treatment needs. They should be designed to handle process variations in contamination and flow, variations in water chemistry needs, required chemical volume adjustment, and possible changes in water effluent requirements.

There tends to be three stages of Water Treatment.

  • The first stage being the wastewater is temporarily held in a tank to allow the heavier solids to sink while the lighter solids float to the top. These materials are held back, while the remaining liquid is discharged or pushed onto the next stage of the cycle.
  • The next stage is designed to degrade the biological content of the waste. This allows for a safer release into the local environment, with contaminants reduced to safe levels.
  • The final stage, is to improve the quality of the water to domestic and industrial standards, ensuring the water is safe for drinking purposes.

What gases are found in wastewater treatment?


Treatment of wastewater and sewage is commonly associated with hazards such as the presence of toxic and flammable gases, hazardous biosolids, volatile chemicals, as well as oxygen deficiencies. Through the process of wastewater treatment, the main emphasis on safety, is monitoring gas concentrations for chlorine dioxide (ClO₂), ozone (O₃), hydrogen peroxide (H₂O₂), sodium hypochlorite (NaClO) (used in the water disinfection process). Hydrogen sulphide (H₂S) and methane (CH₄) occurring as wastewater residues. Finally, hydrochloric acid (HCl) and sulphur dioxide (SO₂) (commonly used in dichlorination).

What risks are involved in wastewater handling?

Serious effects can occur from toxic gases, vapours, or liquids from inhalation, ingestion, or skin contact. Asphyxiation can occur due to toxic atmospheres, resulting in low oxygen levels. Additionally, there is a risk of explosions happening because of sparks, the character of some chemicals, or high temperatures. So, it is vital that risk assessments and rigid processes are put in place to mitigate these risks.

What safety measures should be in place?

Acknowledging and assessing the risks are key in developing solutions for working in confined spaces, the handling of hazardous substances, plant safety, and emergency escape. Workers who are involved in process of wastewater treatment should be provided with special protection to enable them to complete their day-to-day jobs safely. It’s unlikely the risks will be permanently stopped as there is a lot of manual work and maintenance to be carried out. So, a protection model must be in place to offer the utmost protection to employees in their job roles.

Working in a confined space in the wastewater industry

Within the wastewater treatment industry, there is a vast range of confined space work, where employees need to enter tanks, treatment units, sewers, manholes, pumping stations, storage areas, reservoirs, boreholes, and more. Within these confined spaces there is a risk to human safety due to the common presence of Hydrogen Sulphide, Methane, and a lack of Oxygen. These tasks may be routine work for experienced water treatment employees, but the risks are extremely high, and the highest level of protection must be used.

Workers must be provided with personal gas detection to perform pre-entry checks and ensure their safety while in the confined spaces. The use of a pumped gas detector to perform clearance measurements allows for the presence of hazardous gas to be monitored prior to an employee entering the space. Once this check has been carried out and established it is safe to enter, personal monitoring must be carried out continuously. The concentration of gases in a confined space can change quickly, due to leakage for example, so continuous monitoring is vital.

Handling of hazardous materials in wastewater

Chlorine and Ozone are frequently used during the chemical disinfection process and carry a risk to those working in water treatment. They can lead to explosions, poisoning, fires, and consume oxygen. Both require precise handling, adequate protection, and continual monitoring to ensure workers' safety. Workplace exposure limits for the likes of Chlorine and Ozone are very low due to the dangers they pose to workers. It is key that employers have preventative measures in place and have suitable respiratory protection, chemical protection suits, and gas monitors to protect their employees. 

Potential contact with hazardous substances can be fatal. In the event of an alarm, employees must have the equipment to be able to rescue themselves. Having suitable escape equipment within employees' reach can help workers get themselves out of a possibly fatal situation as soon as possible. If there are high levels of Chlorine, Ozone, Hydrogen Sulphide. Methane or a lack of Oxygen it can be a matter of seconds before these hazardous substances could have an adverse effect on workers. Filtered escape hoods and oxygen self-rescuers are a must in the wastewater industry, to allow employees to escape possibly life-threatening situations if they arise. 

Plant Safety in wastewater

Besides workers being equipped with personal protection. They should be able to rely on their workplace being adequately monitored, minimizing risks as much as possible. As mentioned, the main priority for employers is monitoring gas concentrations. Employers must ensure the lowest possible rate of accidents and the lowest rate of false alarms as humanly possible. Gas area monitoring is the best solution for observing a large area that could pose a risk to employees and surrounding areas. Having a robust fixed gas detection system in place is a must, to minimise the risk and keep on top of gas levels within the wastewater treatment industry. As stated above, there is a presence of multiple dangerous substances, so there may well be a need for multiple systems in different locations of the plant. 

Products for Detection

Our recommended multi-gas detectors some of which can be used for confined space pre-entry, personal protection, or area monitoring. For confined space pre-entry checks, it is recommended that a pumped monitor is used. The use of a pumped monitor allows for a sampling tube to be fed into the confined space from the outside, confirming it is safe for workers to enter.

Products for Protection

Our recommended personal protection equipment...

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