Mitigating health hazards for workers at biological wastewater treatment plants

Aug. 23, 2016

Wastewater Dan tackles the problem of worker safety: By examining wastewater plant practices, operators can decide which of these procedures are needed to keep employees safe.

800Sewage is the used water of a community and can include domestic wastewater and industrial effluent. Combined sewer systems include stormwater such as road runoff, which carries oils, salts, metals and asbestos. Many systems, especially older ones, receive infiltration, which can carry pesticides and herbicides from soil applications. For many years, work in the wastewater treatment field was regarded as the most hazardous to workers, particularly because of deaths involving confined space entry.

The wastewater treatment area is seen as slightly less hazardous today, but treatment plant workers still experience health problems and death. Specifically, these experiences involve chemicals in the sewer system and in regular work exposures throughout the facility’s operations.

Health effects

Some chemical-related health complaints are acute in nature and involve short-term exposures and complaints such as irritations of the eyes, nose or throat. Other problems are chronic and result from repeated exposures, sometimes over several years, that negatively affect internal organs or cause
allergic reactions.

Surveys indicate that wastewater treatment may generate aerosols containing microbiological and chemical factors. The primary path of exposure for aerosols is probably
inhalation. The physical layouts of many sewage treatment plants involve open tanks and drainage areas; plants typically are not designed to prevent aerial dispersion of effluent during the treatment process. Volatile organics in wastewater may be vaporized or air-stripped during treatment. Many of the compounds are carcinogens and/or mutagens, so sewage workers may be at increased risk of cancer or adverse birth defects.

Infections from exposure to waterborne disease organisms may be subclinical or may appear as actual diseases.

Treatment personnel have reported nausea, vomiting, upset stomach, diarrhea and flu-like symptoms. Written reports of antibodies in workers’ blood document disease exposures.

Many workers tend to build immunities to some organisms after several years of exposure; young workers tend to be ill more often than experienced workers.

This article examines how exposure occurs during the treatment processes; ways to reduce exposure by engineering controls, administrative controls, process control strategies, and protective equipment; and some suggested medical surveillance.


Effluent treatment plant workers may be exposed to chemicals or organisms by direct contact with sewage, water and sludges, or by inhalation of gases, particles, aerosols, vapors or droplets. These hazards may come into the plant in soluble form or bound to suspended solids. Compounds reported from sludge analyses include chlorinated organic solvents, polychlorinated biphenyls (PCBs) and pesticides, petroleum hydrocarbons, flame retardants, heavy metals, asbestos, dioxins and radioactive materials.

The concentration of organics and metals in sludge is indicative of the region’s industries. In one case, high concentrations of PCBs and sludge were caused by the fabrication of electrical equipment upstream from the treatment plant. Chemical derivatives formed by microbiological or other operations during the sewage treatment process may be more or less toxic than the original compound. Disease-causing organisms have been found in sewage sludge, so sewage workers may be at increased risk of infection or diseases.

Decreasing risks to workers

Ways to reduce chemical exposure and diseases include:

  • Administrative controls can be used for rotating personnel between the various treatment plant operations. This would reduce inhalation of air-stripped chemicals and aerosols, and may help the development of immunity to diseases by keeping exposure low, perhaps too low for a disease-causing dose to be inhaled.
  • Engineering controls manage ventilation for processes located within the building, including splash guards for dewatering equipment where appropriate, and design or operational features to reduce air-stripping and aerosols that can cause disease. Air sampling for chemicals and their airborne levels may be useful.
  • Enforce pretreatment regulations to reduce air-stripping chemicals at the source.
  • Plant trees around the aeration basin to capture the droplets and particles.
  • Reduce the amount of air-stripping and aerosol formation by using finer bubbles for aeration.
  • Reduce air-stripping and aerosols by using diffused aeration rather than mechanical aeration.
  • Consider floating covers on the mixed liquor of the aeration basin. Some plants have had success with biodegradable oils or collapsing foam detergents.
  • Consider suppressing the droplets just above the surface by using water spray to beat down the wastewater droplets.
  • Consider disinfecting the airborne particles by using ultraviolet lights.
  • Cover the primary clarification process unit weir area to shield it from wind or use submerged effluent collectors, such as pipes with orifices, rather than weirs.
  • Avoid handling screenings by hand to prevent injuries.
  • Label piping so that potable and nonpotable water are clearly
  • Processes to significantly reduce pathogens are treatment processes such as aerobic and anaerobic digestion, air drying, low temperature composting, lime stabilization or other techniques that equally reduce pathogens. If sludge treated in one of these ways is applied to land:
    • Food crops that could contact sludge cannot be grown for a period of time.
    • Animals whose products are intended for human consumption cannot be frozen for a while.
    • Public access is restricted for some months.
  • Ionizing radiation kills Salmonella and coliform bacteria.
  • Worker exposure can be reduced with the use of and proper care of protective clothing and
  • Heavy-duty rubber gloves and boots can be used to prevent skin contact with wastewater and sludges.
  • Remove contaminated clothing after job completion.
  • Shower at work and change into clean clothes and shoes.
  • Wash hands with soap and water before eating or smoking and whenever hands contact wastewater and sludge. Care for cuts and abrasions promptly.


To keep workers safe, operators can examine their plant practices and consider implementing the procedures listed.

Known in the industry as "Wastewater Dan," Dan Theobald, proprietor of Environmental Services, is a professional wastewater and safety consultant/trainer. He has more than 24 years of hands-on experience operating wastewater treatment processing units.

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