Hazards In Sewage Treatment Plants Biology Essay


Wastewater consists of a mixture of domestic sewage which includes waste from sinks, household toilets, showers, washing machines. It also consists of industrial effluent, occasional run-off of surface water and ground water which has infiltrated into the sewers.

99.99% of wastewater consists of water, and 0.01 % of it comprises of dissolved or suspended solid matter (www.fairfield-city.org/wastewater.cfm Date Accessed 14.02.13)

2.1 Wastewater Biology

Untreated sewage may contain a number of disease causing organisms including bacteria, viruses, fungus, worms and protozoa (McCunney, 1986; Weldon et al, 2000; Schlosser et al, 1999).

Airborne bacteria concentrations are usually very high where sewage is agitated, such as near incoming wastewater inlets and sludge treatment areas (Laitinen et al, 1994). Compare to other areas of a WWTP, a few airborne bacteria have also been found in "clean" areas such as control rooms (Laitinen et al, 1994).

The major route of exposure to these microorganisms is the "foecal-oral route" (McCunney, 1986). This commonly occurs during eating, drinking, smoking or by touching the face with contaminated hands or gloves (HSE, 1998). Inhalation of aerosols containing microorganisms is not so common. Nevertheless it is an essential method of entry. Skin absorption is less frequent since pathogens only enter skin damaged by cuts, burns, blisters, or puncture wounds (Laitinen et al 1994; McCunney, 1986). The mucous membranes such as in the eyes and nose may also provide a pathway of entry for certain disease causing microorganisms.

2.2 Hazards in sewage treatment plants

2.2.1 Biological Hazards in wastewater

Lady using a tablet
Lady using a tablet


Essay Writers

Lady Using Tablet

Get your grade
or your money back

using our Essay Writing Service!

Essay Writing Service

Diseases are caused by infectious agents such as bacteria, viruses, protozoa, helminths and fungi which are present in the raw domestic wastewater mainly from human origin and in agricultural wastes. Diseases are also caused by contact with the toxins released by the infectious organisms, by insects or rodents thriving in the sludge drying beds (ILO Encyclopedia of Occupational Health and Safety, 1983).

The following infectious agents can be found in raw wastewater:

Table 2.1: The biological organisms in wastewater


Signs & Symptoms



Nausea, headache, diarrhea and vomiting; almost always with a fever.

Tetanus (lockjaw)

Muscular stiffness in jaw, neck. Sweating, fever, difficulty swallowing.


Cramps, diarrhea, fever, bloody stool, nausea, vomiting.

Leptospirosis (Weil's Disease)

Intestinal problems, liver and kidney disease, jaundice.

E. coli

Diarrhea, vomiting, little or no fever, blood often seen in stool.


Chills, fever, swollen lymph nodes, stomach pain, diarrhea, vomiting.


Diarrhea, fever, abdominal pain that resembles appendicitis.


Hepatitis A

Fever, abdominal pain, nausea, jaundice, dark-colored urine.

Hepatitis B

Nausea, vomiting, loss of appetite, jaundice, joint pain.

Hepatitis C

Develops slowly, loss of appetite, stomach pain, nausea and vomiting. Jaundice is less common.


Destroys immune system, prone to opportunistic infections.


Fever, headache, nausea, muscle pain and stiffness, paralysis.


Entameoebahistolytica (amebiasis)

Mild nausea, loose stool, abdominal tenderness. In severe cases can spread throughout the body and attack other organs, especially the liver.

Giardia lamblia

Cramps, weight loss, loose/greasy stool, bloating. Fever is rare.

Sources: AFSCME; Utah Dept. of Health.

2.2.2 Virus Hepatitis A

A study was carried out to determine whether or not occupational exposure to sewage is associated with a higher seroprevalence of hepatitis A virus. In order to carry out the study about 600 sewage workers in Singapore were tested. The study showed that sewage workers had an increased occupational risk of acquiring HAV infection and should be protected by active immunisation (B. H. Heng, K. T. Goh, S. Doraisingham, and G. H. Quek, 1994).

2.2.3 Bacteria Helicobacter pylori

Several studies have shown that there was an increased risk for gastric cancer among sewage workers. During the last decade, the bacterium Helicobacter pylori has appeared as one important risk factor for gastric cancer and is now considered a class I carcinogen by the International Agency for Research on Cancer (Rajnarayan R. Tiwari, 2008). Legionella

Legionella pneumophiliais usually spread by water aerosols caused either pneumonia or a no pneumonic disease (Pontiac fever). An investigation on American sewage workers found that there was no increased risk of infection with L

Lady using a tablet
Lady using a tablet


Writing Services

Lady Using Tablet

Always on Time

Marked to Standard

Order Now

pneumophilia. But recently some cases of Pontiac fever have been reported in workers exposed to aerosols from a sewage plant in the food industry treating only organic industrial waste. L pneumophilia, similar to that present in the infected workers was cultured from the sludge (Gregersen P, Grunnet K, Uldum SA, Andersen BH, Madsen H. 1999).

2.2.4 Parasites

There has been a significant positive association between the finding of protozoa in faeces from sewage workers and the duration of exposure to sewage, (Knobloch J,Bialek R,Hagemann J. Intestinaler Protozoenbefall durchberufsbedingten Abwasserkontakt,1983). It has been reported that the prevalence of infestation with intestinal parasites was decreased by adopting good hygienic practices (Schlosser, O., et al, 1999). An increased risk for giardiasis has been reported among workers in France and Germany (Schlosser et al, 1999; Knobloch J, Bialek R, Hagemann J. Intestinalerb Protozoenbefallb durchberufsbedingtenb Abwasserkontakt,1983; Doby JM, Duval JM, Beaucournu JC.Amibiase, 1980; Clark CS, Linnemann CC, Clark JG, Gartside PS.1984; Sullivan R, LinnemannJr CC, Clark CS, Walzer PD.1987).An increased incidence of Entamoebahistiolytica has been reported in sewage exposed workers in France, but not in Germany (Bialek R, Hagemann J. Intestinaler Protozoenbefalldurchberufsbedingten Abwasserkontakt. Dtsch Med Wochenschr, 1983; Doby JM, Duval JM, Beaucournu JC.Amibiase, 1980).

2.3 Chemical Hazard

Wastewater contains a great amount of industrial contaminants which may harm those people who come into contact with sewage.

According to the Pennsylvania DEP, methane and carbon dioxide were the most common chemical byproducts of wastewater. If found in a small enclosed space with a quantity of sewage, these gases could crowd out oxygen and asphyxiate anyone trapped in the area (Nellie J.Brown, 1997).

Sewage workers were also exposed to gases such as hydrogen disulfide, methane, ammonia and carbon monoxide. Watt and his colleagues carried out a study on 26

sewer workers exposed to smell and it was found that 53.8% developed sub-acute symptoms including sore throat, cough, chest tightness, breathlessness, thirst, sweating and irritability. Severity of symptoms seemed to be dose related (Watt MM, Watt SJ, Seaton A. 1997).

2.4 Physical Hazard

Physical hazards were caused due to exposures to excessive noise levels from mechanical equipment, UV radiation and adverse weather such as low or high temperature, and rain. (ILO Encyclopedia of Occupational Health and Safety, 1998)

2.5 Ergonomic Factors

Musculoskeletal injuries were caused by over exertion during handling heavy loads, such as containers of chemicals, or by awkward working postures including frequent bending (ILO Encyclopedia of Occupational Health and Safety, 1983).

Sewage workers have reported osteoarthritic problems and intervertebral disc herniation which are the common spinal disorders (ILO Encyclopedia of Occupational Health and Safety, 1970). An investigation was carried out by Friedrich on 255 sewage workers to determine the occurrence of spinal troubles (i.e., neck, upper back and lower back pain [LBP]). He reported that the 12-month prevalence rates of neck, upper back and LBP were 52.4%, 54.8% and 72.8%, respectively." He concluded that the occurrence of spinal troubles and work disability due to LBP increased with age, weekly duration of stooping, lifting and higher abnormal illness-behavior scores (Friedrich M, Cermak T, Heiller I, 2000).

2.6 Psychosocial and organizational factors

Discomfort and psychological problems were related to prolonged wearing of protective clothing, the bad smells of the wastes, the feeling of working with "soiled"

liquids in a "dirty" and not too "respectable "occupation, and to the worries caused by awareness of the dangers of the workplace (ILO Encyclopedia of Occupational Health and Safety, 1983).

2.7 Accidental hazards

Accidental hazards which occurred in wastewater treatment plants included the followings:

Slips and falls on floors made slippery by water, aqueous solutions or solvents.

Falls into ponds, pits, clarifiers or tanks causing injuries or drowning.

Hazards related to entry into confined spaces. Suffocation can occur due to oxygen shortage, poisoning such as hydrogen sulfide.

Burns, by steam or hot vapors, by splashes of hot plating baths, solvent sand other liquids, by contact with hot surfaces (e.g., annealing ovens),

Electric shock caused by contact with faulty electrical equipment and cables.

Cuts and pricks by sharp tools sharp edges.

Injuries especially of eyes caused by flying particles, in particular from rotating brush cleaning or wheel grinding.

Lady using a tablet
Lady using a tablet

This Essay is

a Student's Work

Lady Using Tablet

This essay has been submitted by a student. This is not an example of the work written by our professional essay writers.

Examples of our work

Fire and explosions due to the formation and release of flammable gases such as methane, hydrogen during processing.

Strong chemical reactions caused by uncontrolled mixing of chemicals

For example when mixing water with concentrated sulfuric acid during the preparation of reagents for wastewater treatment.

Acute poisoning caused by various chemicals such as gaseous chlorine present in the wastes which is used as reagents, or released during the treatment.

Acute intoxication caused if mistakenly drank untreated wastewater.

Poisoning by phosgene, this may be formed if a worker smokes in the presence of chlorinated-solvent vapors, or if welding or other flames or arcs are used.

Chemical burns by corrosive liquids.

Damage to eyes by splashes of irritating or corrosive liquids (ILO Encyclopedia of Occupational Health and Safety, 1998).

At a sewage treatment plant in Homeballe in Kimberley,five men aged between thirty and fifty who were repairing the pipes had lost their lives after drowning in a bay. It was believed that they may have gone unconscious due to the toxic fumes from the sewage and the area that they were in then filled up with water and sewage causing all five men to then drown (Jonckie on November 6th, 2012).

2.8 Health problems of workers at the treatment plant

2.8.1 Effects on skin and mucous membranes among the workers

Many sewage workers have reported skin disorders (Lundholm M, Rylander R, 1983; Scarlett-Kranz JM, Babish JG, Strickland D, Lisk DJ, 1987) and inflammation of the eyes (Lundholm M, Rylander R, 1983; Mattsby I, Rylander R., 1978).After an accidental exposure to dust containing sludge, several incinerator workers at a sewage treatment plant in Toronto, Canada were affected by irritant contact dermatitis (Nethercott JR, 1981).

2.8.2 Effects on the nervous system

Studies have also revealed that central nervous system symptoms such as headache, unusual tiredness, and concentration difficulties have been found among the sewage workers. In addition, an increased risk for non-specific work related gastrointestinal symptoms was found among the sewage workers (J Thorn, L Beijer, R Rylander, 2002).

2.8.3 Respiratory symptoms

Several studies have been done to study the respiratory function of sewage workers. All of them demonstrated that respiratory symptoms such as chronic bronchitis and toxic pneumonitis were common among these workers (J Thorn, L Beijer, R Rylander, 2002). Moreover, abnormal respiratory functions which arose due to exposure to endotoxins and airborne bacteria by way of bio aerosols were also discovered in those sewage workers. Furthermore, Zuskin et al. reported that sewage workers were exposed to different occupational noxious agents, which may lead to the development of chronic lung function changes (Zuskin E, Mustajbegovic J, Schachter EN, 1993).

2.9 Health & Safety of workers

According to OSHA, the employer should give the worker:

Training and education about the hazards present at the wastewater treatment plant.

A place onsite with clean water for washing hands

A place to wash and clean up after work.

The right PPE, such as gloves, goggles, a face shield, water-resistant suit, or respirator, depending on the job type.

Clean areas for eating and smoking.

Cleaning facilities or services for clothing and equipment. (If clothing is badly soiled, change out of it. Keep equipment clean to limit your exposures to the disease-causing agents (Anon, 2004).

2.9.1 Safety of workers

In wastewater treatment plants, engineering controls and work practices are the best ways to protect workers from exposures to disease. When engineering controls are not possible, the use personal protective equipment (PPE) is encouraged (Anon, 2004). Engineering controls

Engineering controls remove or reduce the hazard either by initial engineering design specifications or by applying methods such as substitution, isolation or ventilation (Raterman, 2002). Administrative control

Administrative controls that minimise employees' exposures by scheduling reduce work times in contaminant areas, good work practices and employee training. Appropriate training which includes hazard recognition and work practices specific to the employees' job that can help reduce exposures are given (Raterman, 2002). Personal Protective Equipment (PPE)

"Personal Protective Equipment" means any equipment intended to be worn or held by an employee and which protects him against risk to his health or safety. It includes:

(a) Any addition or accessory designed to meet that objective; and

(b) Clothing affording protection against the weather;

(Occupational Safety and Health act, 2005)

Workers handling sewage are provided with proper PPE. The following PPE are recommended for workers handing sewage:

Goggles: to protect eyes from splashes of human waste or sewage.

Protective face mask or splash-proof face shield: to protect nose and mouth from splashes of human waste or sewage.

Liquid-repellent coveralls: to keep human waste or sewage off clothing.

Waterproof gloves: to prevent exposure to sewage.

Rubber boots: to prevent exposure to sewage.(Centers for Disease Control and Prevention, 2002). Training for Workers

All workers who handle sewage receive training. The training should include information on basic hygiene practices; use and disposal of personal protective equipment; proper handling of sewage; signs and symptoms of the different types of

diseases present; and ways in which diseases can be transmitted. Workers are also advised to immediately seek medical attention if displaying any signs or symptoms such as vomiting, stomach cramps and watery diarrhea (Centers for Disease Control and Prevention, 2002).

2.10 Hygiene Practices

2.10.1 Hygiene

Hygiene is the association of human sciences, professions, technologies and disciplines for the purpose of protecting the health of individuals and community from any harmful exposure (Goldner, 2009). The science of hygiene comprises of disciplines, microbiology, parasitology, immunology, toxicology, entomology, pharmacology, environmental health including geography, topography, and engineering, all with a view to limit, inhibit, or block sources and characteristics that deter from normal living.

2.10.2 Hygiene at Work

Protecting workers against disease, ill-health or impairment due to chemical, microbiological and physical health hazards, not only during, but after work, has been the traditional goal of occupational hygiene. Prevention of occupational diseases emanating from the workplace due to toxic exposures has been one of the primary roles (Pityn, 2007).

A well planned and properly executed sanitation program for the workplace is of great importance for both the workers and the employers as it helps a company to attain better productivity in a safer work place and it ensures good working conditions for the workers.

2.11 Medical surveillance

According to Occupational Safety and Health act, health surveillance should be provided to employees who are exposed to potentially hazardous substance. The medical surveillance should be free of charge and should be carried out at intervals

of not less than once every 6 months or at shorter intervals as the medical practitioner may advise. (Occupational Safety and Health act 2005).

2.12 The role of Waste Water Management Authority (WMA)

The WMA manages the public sewerage system which consists of 515 km of sewer network, 19 treatment plants and 50 pumping stations with the main treatment plants located at St-Martin, Grand-Baie, Baie-du-Tombeau, and Montagne Jacquot.

The Wastewater Management Authority (WMA) has been established as a corporate body under the Wastewater Management Authority Act to be responsible for all matters relating to the collection, treatment and disposal of wastewater. It operates as an autonomous organization under the aegis of the Ministry of Renewable Energy and Public Utilities.

The WMA thus plays an important role in the protection of the environment and in ensuring the country's sustainable development by the provision of appropriate water pollution standards, wastewater control systems and management services to the entire population of Mauritius (www.gov.mu Accessed on 16.12.12).

2.13 The purpose of this study

The general aim of the present study is to identify the general conditions of workers, the possible communicable and non-communicable disease which may affect the workers, the different types of symptoms experienced by the workers at the workplace, the personal protective equipment provided to the workers and the potential risk that can affect the workplace.

In addition, information collected from the survey shall broaden the knowledge of sewage workers in regards to the harmful effects of sewage on health.