The Important Contaminants In Waste Water Biology Essay

Published: Last Edited:

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

Wastewater is water that has been foul by the community. It includes substances such as human waste, food scraps, oils, soaps and chemicals. In homes, this includes water from sinks, showers, toilets, washing machines and dishwashers. In industries, it includes chemicals and toxic compounds.

Wastewater also includes storm runoff. Although some people assume that the rain that runs down the street during a storm is fairly clean, it isn't. Harmful substances that wash off roads, parking lots, and rooftops can harm our rivers and lakes.

1.1.2 Important contaminants in waste water

Suspended solids

It can lead to development of sludge deposits and anaerobic conditions when untreated wastewater is discharged to the aquatic environment.

Biodegradable organics.

They are generally made up of proteins, carbohydrates and fats. They are measured in terms of BOD and COD. If discharged into inland rivers, streams or lakes, their biological stabilization can deplete natural oxygen resources and cause septic conditions that are detrimental to aquatic species.



They are found in waste-water can cause infectious diseases.

Priority pollutants

This includes organic and inorganic compounds and they may be highly toxic, carcinogenic, mutagenic or teratogenic.

Refractory organics

They tend to resist conventional waste-water treatment include surfactants, phenols and agricultural pesticides.

Heavy metals

They are usually added by commercial and industrial activities and must be removed for reuse of the waste-water.

Dissolved inorganic

This includes calcium, sodium and sulfates are often initially added to domestic water supplies, and may have to be removed for waste-water reuse.

Source: Adapted from Metcalf and Eddy, Inc., Wastewater Engineering, 3rd edition.

Nitrogen and phosphorus are other contaminants of concern in wastewater. They are both macronutrients which plays an important role in the growth of plants and microorganisms. If wastewaters are release directly into the sea or river without proper treatment, it may cause disturbance in the natural aquatic ecosystems. These nutrients may lead to overgrowth of algae and aquatic plants, leading to oxygen loss in these waters, hence, leading to death of aquatic plants and animals.

Furthermore, wastewaters also contain household chemicals used for cleaning and personal hygiene. These include soaps, detergents, shampoo, toilet bowl cleaners, bleach, and drain cleaners. While moderate quantities are acceptable in wastewater, excessive amounts may have adverse effects on a wastewater treatment system.

Other hazardous chemicals, such as paints, paint thinners and antifreeze, can also be found in wastewaters. Ref: Judith Simmsims, MS, 2006 ,Onsite Wastewater Treatment System, National Association of Local Boards of Health

1.2 Wastewater Treatment methods

Wastewater treatment consists of applying known technology to enhance the quality of wastewater. However, wastewater treatment can be characterized by the nature of the treatment process operation being used; for example, physical, chemical or biological Adequate treatment is necessary to prevent contamination of receiving waters to a point which might interfere with future use, whether it will be used for water supply, recreation, irrigation or any other prerequisite purpose. access 16.01.2013

1.2.1 Physical operations include the followings:

Sedimentation (Clarification)




Flotation and Skimming


1.2.2 Physical Treatment

In the physical methods there is no gross chemical or biological changes which are carried out and only physical phenomena are used to treat the wastewater.

Examples of physical methods would be coarse screening to remove big objects and sedimentation (clarification). In the process of sedimentation, physical phenomena involving the settling of solids by gravity are allowed to operate. Typically this consists of mainly holding wastewater for a short period of time in a tank under calm conditions, allowing the heavier solids to settle, and removing the "clarified" effluent. Sedimentation for solids separation is usually employed at the beginning and end of wastewater treatment operations. Another physical treatment process use to achieve treatment is the aeration technique that is, physically adding air, basically to provide oxygen to the wastewater. Another physical phenomenon used in treatment consists of filtration. Here wastewater is passed through a filter medium to separate solids. Sand filters are used to further remove entrained solids from a treated wastewater. Certain phenomena will occur during the sedimentation process and can be strategically used to further improve the quality of water. This permits greases or oils to float to the surface and skimming or physically removing them from the wastewaters is frequently carried out to be able to achieve better treatment.

In some industrial wastewater treatment processes strong or unwanted wastes are sometimes produced over short periods of time. Since such waste may damage the biological treatment process, these wastes are sometimes held, mixed with other wastewaters, and slowly released, hence eliminating "shocks" to the treatment plant. This is known as equalization. A further type of "equalization" can be used to equalize wide variations in flow rates. For example, the wet well of a pump station can receive widely varying amounts of wastewater and, in turn, pump the wastes onward at more constant rates.

1.2.3 Chemical operation includes the followings:






Chemical treatment is the use of certain chemical reaction or reactions to upgrade the water quality. Undoubtedly the most frequently used chemical process is chlorination. Chlorine is a strong oxidizing chemical, which is used to kill bacteria and to slow down the rate of decomposition of the wastewater. Bacterial kill is achieved when vital biological processes are affected by the chlorine. Another strong oxidizing agent that can also been used as an oxidizing disinfectant is ozone.

The most common chemical process used in many industrial wastewater treatment operations is neutralization. Neutralization involves the addition of acid or base to regulate the pH levels back to neutrality. Since lime is a base it is occasionally used in the neutralization of acid wastes.

Coagulation involves the addition of a chemical that, through a chemical reaction, forms an insoluble end product that serves to eliminate substances from the wastewater. Polyvalent metals are typically used as coagulating chemicals in wastewater treatment and typical coagulants would include lime (that can also be used in neutralization), certain iron containing compounds (such as ferric chloride or ferric sulfate) and alum (aluminum sulfate).

Some processes may in fact be physical and chemical in nature. The use of activated carbon to "adsorb" or remove organics, for example, involves both chemical and physical processes.

1.2.4 Biological process includes the following:


Activated Sludge Treatment Methods

Trickling Filtration

Oxidation Ponds


Aerobic Digestion


Anaerobic Digestion

Septic Tanks


Biological treatment methods involve the use microorganisms, mainly bacteria, in the biochemical decomposition of wastewaters to stabilize the end products. More microorganisms, or sludge, are formed and some of the waste is converted to carbon dioxide, water and other end products. Normally, biological treatment methods can be divided into aerobic and anaerobic methods, based on the oxygen demand available.

The aim behind wastewater treatment is typically to remove enough solids from the wastewater to allow the remaining to be discharged to receiving water without interfering with its proper use. The solids which are removed are mostly organic but may also include inorganic solids. Treatment must also be provided for the solids and liquids which are removed as sludge. Lastly, treatment to control odors, to retard biological activity, or destroy pathogenic organisms may also be needed.

Since there is a lot of devices involve in wastewater treatment and will probably combine physical, chemical and biological methods, they may all be generally grouped under six methods namely:

Preliminary Treatment

Primary Treatment

Secondary Treatment


Sludge Treatment

Tertiary Treatment

The levels of treatment are occasionally indicated by use of the terms primary, secondary and tertiary treatment. access 16.01.2013

1.2.5 Preliminary Treatment put in own words

The preliminary treatment includes simple processes that deal with debris and solid material.

The purpose of preliminary treatment is to remove those easily separable components. This

is usually performed by screening (usually by bar screens) and grit removal. Their removal is

important in order to increase the effectiveness of the later treatment processes and prevent

damages to the pipes, pumps and fittings. Sholzel & Bower,2009, Small Scale wastewater treatment plant project, SOPAC Technical report 288.

To accomplish the objectives of preliminary treatment, the following devices are commonly used:

Screens -- rack, bar or fine

Comminuting devices -- grinders, cutters, shredders

Grit chambers

Pre-aeration tanks

Primary Treatment to check

It is mainly the removal of solids by settlement. Simple settlement of the solid material in sewage can reduce the polluting load by significant amounts. It can reduce BOD by up to 40%.

Sholzel & Bower,2009, Small Scale wastewater treatment plant project, SOPAC Technical report 288.

The goal behind primary treatment is to reduce the rate of the wastewater adequately to allow solids to settle and floatable material to surface. Thus, primary devices include settling tanks, clarifiers or sedimentation tanks. Due to variations in design, operation, and application, settling tanks can be divided into four general groups namely:

Septic tanks

Two story tanks -- Imhoff and several proprietary or patented units

Plain sedimentation tank with mechanical sludge removal

Upward flow clarifiers with mechanical sludge removal

When chemicals are used, other supplementary units are employed. These are:

Chemical feed units

Mixing devices


Secondary Treatment

After having removed about 40 to 60 percent of the suspended solids and 20 to 40 percent of the BOD5 in primary treatment by physical methods, the secondary treatment biologically reduces the organic material that remains in the liquid stream. Normally the microbial processes employed are aerobic that is, the organisms will carry out its activity in the presence of dissolved oxygen. Secondary treatment in fact involves controlling and quickening natural process of waste disposal. Aerobic bacteria in the presence of oxygen convert organic matter to a more stable form such as carbon dioxide, water, nitrates, phosphates and other organic materials. The production of new organic matter is an indirect result of biological treatment processes, and this matter must be removed before the wastewater is discharged into the receiving stream.

The devices used in secondary treatment may be divided into four groups:

Activated sludge

Trickling filters

Rotating Biological contractor

Stabilization ponds

.Karadi, Gabor M., and Huang, Jerry Y.C. 2006 "Sewage Disposal." Redmond, WA: Microsoft Corporation.

Tertiary and Advanced Wastewater Treatment

Importance of sewage treatment

The two important reasons for treating wastewater are to prevent environmental pollution and protecting public health. Thus, protecting the water supplies and prevents waterborne diseases to spread. The safe disposal of human excreta is a pre-requisite for the supply of safe drinking water, since the water supplies can only become contaminated where there is inadequate disposal.

There are many infectious disease transmitted in excreta such as cholera, typhoid and gastro-enteritis. Adequate wastewater treatment is essential to make sure that the outbreaks of waterborne diseases that were so frequent in the eighteenth and nineteenth centuries do no occur again. Untreated wastewater flows into vast oceans and rivers, causing serious problems. Apart from organic enrichment endangering the flora and fauna due to deoxygenation, treated effluents rich in oxidized nitrogen and phosphorus can result in entrophication problems. date access 18.01.13

Health problems among sewage workers

Biological Hazards in wastewater

Biological hazards are organic substances which can cause harm to the human body. Biological hazards include bacteria, viruses, insects, plants, birds, animals, rodents and humans. The risks run from mild skin irritation and to severe allergies and infections.

In a recent study (Guignon and Sandret 2006) it was found that 15% of French workers are involved in Occupations where they are exposed to biological hazards. Out of these 15% which are exposed, 54% of them are exposed to biological hazards from human origin, 8% from animals and 23% in the waste management. Guignon and Sandret,2006,Exposure to biological hazards and the provision of controls against biological hazards in Australian workplaces, National Hazard Exposure Worker Surveillance.

Biological hazards are a common hazard which can be found in the wastewater treatment plant. Some of the most common disease among wastewater workers includes Hepatitis, Typhoid, Cholera, Gastrointestinal diseases, respiratory diseases, Leptospirosis, gastric cancer.



Hepatitis is a health condition where the patient has liver inflammation and inflammatory cells in the tissue of the organ. The main cause of Hepatitis is the exposure to biologically hazardous environment. (World Health Organization ,2012, Hepatitis A).

Hepatitis A

Hepatitis A is a liver disease which is caused by the hepatitis A virus. The virus is primarily spread when an uninfected (and unvaccinated) person ingests food or water that is contaminated with the feces of an infected person. The disease is closely associated poor personal hygiene.

Unlike hepatitis B and C, hepatitis A infection does not cause chronic liver disease and is rarely fatal, but it can cause debilitating symptoms and fulminant hepatitis (acute liver failure), which is associated with high mortality. (World Health Organization 2013, 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 (HAV) infection. In order to ccarry out the study about 600 sewage workers in Singapore were tested for total (IgG and IgM) antibody to HAV by enzyme immunoassay. The study revealed that seroprevalence of sewage workers was 2.2 times higher than that of another non-occupationally exposed population group. The epidemiological data in the study show that sewage workers have an increased occupational risk of acquiring HAV infection and should be protected by active immunization. B. H. Heng, K. T. Goh, S. Doraisingham, and G. H. Quek, 1994, Prevalence of hepatitis A virus infection among sewage workers in Singapore, US National Library of Medicine National Institute of Health.


The risk for transmission of human immunodeficiency virus (HIV) from wastewater is considered unlikely, Johnson RW, Blatchley III ER, Mason DR.1994, HIV and the bloodborne pathogen regulation: implications for the wastewater industry. Water Environ Res. although the virus seems to survive for a limited period in wastewater. Studies have seen that nucleic acids of HIV-1 virus has been detected in some municipal wastewater samples from USA but this does not necessarily equate with the presence of infectious viral particles, Ansari SA, Farrah SR, Chaudry GR.1992, Presence of human immunodeficiency virus nucleic acids in wastewater and their detection by polymerase chainreaction. Appl Environ Microbiol.



Leptospirosis is an occupational disease which affects people who come into contact with animals and their discharges. Rodents usually thrive in underground sewers and are carriers of leptospira. The urine of rodents and other animals present in that area is likely to contaminate these sewers. Leptospira are excreted in the urine of the infected animals. Thus, sewer workers are at a increase risk of leptospirosis. Rajnarayan R. Tiwari,2008, Occupational health hazards in sewage and sanitary workers, Indian J Occup Environ Med.

Ambekar et al made a study among 78 sewer workers from five different municipal wards in Pune to determine the evidence of past infection with leptospira. The prevalence rate was found to be 16.6%. Evidence of leptospiral infection was found to be maximum in sewer workers in the areas of the city that were infested with rodents and stray animals. Ambekar AN, Bharadwaj RS, Joshi SA, Kagal AS, Bal AM.,2004, Sero surveillance of leptospirosis among sewer workers in Pune. Indian J Public Health. De Serres et al. found that sewer workers had a greater prevalence of antibodies against leptospirosis than controls (12% vs. 2%, P = 0.003). De Serres G, Levesque B, Higgins R, Major M, Laliberte D, Boulianne N, et al.1995, Need for vaccination of sewer workers against leptospirosis and hepatitis A. Occup Environ Med.

Helicobacter pylori

Several studies have described that there is 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, Occupational health hazards in sewage and sanitary workers, Indian J Occup Environ Med.

Friis et al studied the occurance of immunoglobulin G (IgG) antibodies against H. pylori in a group of 289 municipal workers. The prevalence of IgG antibodies against H. pylori among sewage workers did not differ from that of the referents. However, an increase in the prevalence of IgG antibodies against H. pylori with increasing age was observed. Friis L, Engstrand L, Edling C.1996, Prevalence of Helicobacter pylori infection among sewage workers. Scand J Work Environ Health.


Legionella pneumophilia is known to be spread by water aerosols, which cause either

pneumonia or a nonpneumonic disease (Pontiac fever). An investigation of American

sewage workers found no increased risk for infection with L pneumophilia. Clark CS, Van Meer GL, Linnemann Jr CC, Bjornson AB, Gartside PS, Schiff

GM, Trimble SE, Alexander D, Cleary EJ, Phair JP.1980, Health effects of

occupational exposure to wastewater. In: Pahren H, Jakubowski W (ed.)

Wastewater aerosols and disease. EPA 600/9-80-028, Cincinnati, OH: United

States Environmental Protection Agency, Health Effects Research Laboratory.

But recently five 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 of the same serogroup as in the infected workers was

cultured from the sludge. Gregersen P, Grunnet K, Uldum SA, Andersen BH, Madsen H. 1999,Pontiac fever at a sewage treatment plant in the food industry. Scand J Work Environ Health


Several studies have been done to study the respiratory function of sewage workers, with all of them reporting that respiratory symptoms are common among this group of workers. Thorn J, Beijer L, Rylander R,2002, Work related symptoms among sewage workers: A nationwide survey in Sweden, Occup Environ Med .The respiratory function studies also discovered abnormal respiratory functions in those sewage workers. These symptoms may arise due to exposure to endotoxins and airborne bacteria by way of bio aerosols. Zuskin et al. reported that sewage workers are exposed to different occupational noxious agents, which may lead to the development of chronic lung function changes. . Zuskin E, Mustajbegovic J, Schachter EN, 1993, Respiratory function in sewage workers. Am J Ind Med.


A significant positive correlation between the finding of protozoa in faeces from sewage workers and the duration of exposure to sewage has been reported, Knobloch J, Bialek R, Hagemann J. Intestinaler Protozoenbefall durchberufsbedingten Abwasserkontakt. Dtsch Med Wochenschr, 1983. and the prevalence of infestation with intestinal parasites decreases with improved compliance with hygienic rules. Schlosser O, Grall D, Laurenceau M-N.1999, Intestinal parasite carriage in workers exposed to sewage. Eur J Epidemiol.

An increased risk for giardiasis has been reported workers in

France and Germany, but not in the USA.48, 49, 51, 52, 53

48 Knobloch J, Bialek R, Hagemann J. Intestinaler Protozoenbefall durch

berufsbedingten Abwasserkontakt. Dtsch Med Wochenschr 1983.

49 Schlosser O, Grall D, Laurenceau M-N.1999, Intestinal parasite carriage in workers

exposed to sewage. Eur J Epidemiol.

51 Doby JM, Duval JM, Beaucournu JC. Amibiase, 1980, maladie profesionelle des

égoutiers? Nouv Presse Med.

52 Clark CS, Linnemann CC, Clark JG, Gartside PS.1984, Enteric parasites in workers

occupationally exposed to sewage. J Occup Med.

53 Sullivan R, Linnemann Jr CC, Clark CS, Walzer PD.1987, Seroepidemiologic study

of giardiasis patients and high-risk groups in a midwestern city in the United

States. Am J Public Health.

An increased prevalence of

Entamoeba histiolytica has been reported in sewage exposed workers in France,

but not in Germany.48, 51

48 Knobloch J, Bialek R, Hagemann J. Intestinaler Protozoenbefall durch

berufsbedingten Abwasserkontakt. Dtsch Med Wochenschr 1983.

51 Doby JM, Duval JM, Beaucournu JC. Amibiase,1980, maladie profesionelle des

Égoutiers. Nouv Presse Med

Another survey was carried out in Sweden to access the risk for work related symptoms among sewage workers. The survey was carried out on sewage workers as well as on other municipal workers not exposed to sewage. The workers not expose to sewage were used as a control. The results showed that there were significantly increased risks for airway symptoms, chronic bronchitis, and toxic pneumonitis, as well as central nervous system symptoms such as headache, unusual tiredness, and concentration difficulties were found among the sewage workers compared with the controls. In addition, an increased risk for non-specific work related gastrointestinal symptoms was found among the sewage workers; an increased risk for joint pains, related to pains in more than four joints but not with loading, was also found. J Thorn, L Beijer, R Rylander,2002, Work related symptoms among sewage workers: A nationwide survey in Sweden,Occup Environ Med.

Chemical Hazard

Wastewater contains a hundred of industrial contaminants an there are dozens or more dangerous combinations that may harm humans who come into contact with sewage.

According to the Pennsylvania DEP, methane and carbon dioxide are common chemical byproducts of wastewater. If caught in a small enclosed space with a quantity of sewage, these gases can crowd out oxygen and asphyxiate anyone trapped in the area. Nellie J.Brown, 1997, Health Hazard Manual: Wastewater Treatment Plant and Sewer Workers, Cornell University ILR School.

Sewage workers are also exposed to gases such as hydrogen disulfide, methane, ammonia and carbon monoxide. Watt et al. carried out a study on 26 sewer workers exposed to smell and he found that 53.8% developed sub-acute symptoms including sore throat, cough, chest tightness, breathlessness, thirst, sweating, irritability and loss of libido. Severity of symptoms seemed to be dose related. Watt MM, Watt SJ, Seaton A. 1997,Episode of toxic gas exposure in sewer workers. Occup Environ Med.

Health & Safety act

OSHA says the employer should give the worker:

Training and education about the hazards of wastewater and sewage

A place onsite with clean water for washing your 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

Clean areas set aside 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, Hazard Alert - Biological Hazards in Sewage and Wastewater Treatment Plants, The Center for Construction Research and Training.

Safety of workers

For work around sewage or wastewater, engineering controls and work practices are the best ways to protect workers from exposures to disease. When engineering controls are not possible, use personal protective equipment (PPE). For some jobs and around some hazards, respiratory protection is required. Anon,2004, Hazard Alert - Biological Hazards in Sewage and Wastewater Treatment Plants, The Center for Construction Research and Training.

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, and 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 should be provided proper PPE, training on how to use it, and hand washing facilities. Workers should wash hands with soap and water immediately after removing PPE. The following PPE is recommended for workers handing human waste or 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 human waste or sewage.

Rubber boots: to prevent exposure to human waste or sewage.

Training for Workers

All workers who handle sewage should receive training. The training should include information on basic hygiene practices; use and disposal of personal protective equipment; proper handling of human waste or sewage; signs and symptoms of the different types of diseases present; and ways in which diseases can be transmitted. Workers must also be advised to immediately seek medical attention if displaying any signs or symptoms such as vomiting, stomach cramps and watery diarrhea.

Vaccination Recommendations for Workers

Vaccination recommendations for workers exposed to sewage or human waste should be developed in consultation with local health authorities. Tetanus vaccinations should be up to date, with consideration also given to the need for polio, typhoid fever, Hepatitis A and Hepatitis B vaccinations.