Background

Sewage

Sewage is the mixture of liquid, faeces, toilet paper and food wastes produced by people. The liquid in sewage includes urine (piss) and wastewater which comes from the toilet, the kitchen, bathroom and laundry. Sewage contains lots of disease-causing germs and parasites. Sewage is treated to get rid of as much of the solid matter as possible. The remaining liquid is called effluent.

Sewage disposal

Getting rid of sewage and effluent is called sewage disposal. If sewage is not disposed of or contained correctly people may come into contact with it and get very sick.

There are different ways to dispose of sewage. Whichever method is used, it is important to make sure that it does not:

cause dangerous conditions which allow people to come into contact with disease-causing germs
cause pollution of a water supply
allow the breeding of insects such as mosquitoes or cockroaches which can carry disease-causing germs inside or on their bodies as a result of eating or walking in sewage
produce bad smells

Disease from sewage

Disease-causing germs can be spread from sewage if it is not disposed of properly or if people do not practise proper toilet hygiene (cleanliness). If a sewage disposal system is not properly maintained it will not be able to get rid of the sewage safely. For a sewage system to be properly maintained, all faulty (blocked, damaged, broken or worn-out) parts must be mended as soon as possible after they stop working correctly.

Viruses, unlike bacteria, require a living host to reproduce. They cannot reproduce outside of a host cell and thus will not grow in wastewater. There have been a number of studies of viral infections in sewage workers. The overall conclusion seems to be that if workers are properly trained and properly protected, then the actual risk of developing viral infections via occupational exposure is very low, according to Clark (1987) and West and Locke (1990).

In sewer systems, HIV is subjected to environmental factors to which it is simply not suited: wrong pH, too low temperature, and the presence of surfactants and other chemicals (Gerardi, M. H., Maczuga, A. P., and Zimmerman, M. C. 1988). However, there are viruses like Norovirus, Coxsackieviruses and Poliovirus in sewers that may cause problems (Forsgren, A., & Brinck, K. 2016).

References

Clark, C. S. (1987). Potential and actual biological related health risks of waste- water industry employment. Journal of the Water Pollution Control Federation, 59, 999–1008.
West, P. A., and Locke, R. (1990). Occupational risks from infectious diseases in the water industry. Water and Environment Journal, 4(6), 520–523.
Gerardi, M. H., Maczuga, A. P., and Zimmerman, M. C. (1988). Operator’s guide to wastewater viruses. Public Works PUWOAH, 119(4), 50.
Forsgren, A., & Brinck, K. (2016). Airborne occupational hazards in sewer systems. CRC Press.

Waterborne & Airborne

A well known waterborne disease is the third outbreak of cholera in London, 1853. John Snow saved the world then. Waterborne diseases, caused by pathogenic micro-organisms, biotoxins, and toxic contaminants that are transmitted in water, lead to devastating illnesses such as cholera, schistosomiasis and other gastrointestinal problems. Outbreaks of waterborne diseases often occur after a severe precipitation event (rainfall, snowfall). A list of diseases caused by sewage or sewage contaminated water that can occur is given at Diseases Involving Sewage.

Climate change-induced flooding and droughts can impact household water and sanitation infrastructure and related health risks. For instance, flooding and/or sewage back-up can disperse faecal contaminants, increasing risks of outbreaks of waterborne diseases such as cholera. In addition, water shortages due to drought can increase risks of diarrhoeal disease. Proper household water and sanitation practices can increase resilience to waterborne disease risks. These measures include sanitary sewage disposal, safe water piping materials and storage, and education on hygienic behaviours. Energy-efficient water infrastructure and water conservation measures can also decrease the burden of waterborne diseases.

The risk of airborne disease transmission from toilets, even from one building to another through the sewerage system, was first demonstrated in 1907. In an experiment in the 1950s a toilet was seeded with bacteria and agar plates used to collect aerosols settling out of the air. This found that the amount of aerosols increased with increasing flush energy and that the bacteria were still in the air eight minutes after the flush.

Research has shown, directly or indirectly, that several types of bacteria and viruses can contaminate the air from a flushing toilet:

E. coli: In the 1970s, it was discovered that aerosols containing E. coli bacteria remained airborne and viable for at least 4-6 hours after flushing. In another experiment, toilets seeded with a bacterium and a virus (MS2 bacteriophage and poliovirus) were not completely free from the microorganisms after seven flushes and attempts to clean the bowl were only minimally effective in eliminating them. (Gerba et al. 1975)
Salmonella: More recently, in 2000, it was found that Salmonella could be cultured from air samples near a toilet bowl after flushing. Salmonella also remained in the bowl water for more than 12 days and in a biofilm below the water line for 50 days after seeding the toilet with the bacteria. This shows that a biofilm may be able to maintain a supply of bacteria that infects the toilet bowl water and the aerosols created on flushing for much longer periods. (Johnson et al. 2013)
Norovirus: The spread of Norovirus on ships, even after attempts to sanitise them after an outbreak, is thought to be a result of the ability of toilets to continue generating contaminated aerosols after multiple flushes and the resistance of Norovirus to cleaning and disinfection. (Johnson et al. 2013)
Influenza: The flu virus may also be spread through the air by toilet flushing. A recent study conducted in healthcare facilities, day care centres, and aircraft found influenza A virus in aerosols of the size that can enter lungs. In the early stages of infection with the H1N1 strain of flu virus, symptoms include diarrhoea and vomiting, which means the virus may be spread by toilet flushing. (Yang et al. 2011)

In apartment blocks the shared sewerage system can lead to the spread of infections between apartments and also by aerial dispersal to other buildings. Following the 2003 SARS outbreak in Hong Kong’s Amoy Gardens apartment complex it was found that the spread of the virus was likely caused by virus-laden aerosols originating in the sanitary system.

The sewerage system was contaminated with SARS coronavirus (SARS-CoV) when an infected person who was suffering from diarrhoea visited one of the apartments and used the toilet. It was concluded that contaminated aerosol was drawn through dry U-tube traps in the bathroom floor drains of other apartments by bathroom exhaust fans. Some aerosol particles may have then have been expelled to the outside of the multistory building and carried upward to other apartments. People in nearby buildings were also infected, thought to be from particles carried by the wind. This could also mean that toilet flushing can generate aerosol particles contaminated with SARS, but it has not been determined experimentally yet.

References

Wan Yang et al. 2011. Concentrations and size distributions of airborne influenza A viruses measured indoors at a health centre, a day-care centre and on aeroplanes. J R Soc Interface. 2011; 8:1176–84.
Johnson DL et al. 2013. Lifting the lid on toilet plume aerosol: A literature review with suggestions for future research. Am J Infect Control. 41(3): 254–258. doi: 10.1016/j.ajic.2012.04.330.
Gerba CP, Wallis C, Melnick JL. 1975. Microbiological hazards of household toilets: droplet production and the fate of residual organisms. Appl Microbiol. 1975;30:229–37.
Hong Kong Special Administrative Unit Department of Health. 2003. Outbreak of severe acute respiratory syndrome (SARS) at Amoy Gardens, Kowloon Bay, Hong Kong: main findings of the investigation.

Diseases Spread Through the Faecal-Oral Route

When the disease spreads through the faecal-oral route, it means that contaminated feces from an infected person are somehow ingested by another person.

Usually, the situation occurs when an infected person might forget to properly wash his hands after using the toilet. Anything he or she touches afterward might be contaminated with microscopic germs that other people may encounter. Proper handwashing seems to be the best defense.

What Happened in Hong Kong, 2003?

The “Faecal Droplet” Route

Reports by the World Health Organization (WHO) have revealed the role sewage plays in spreading the deadly disease known as severe acute respiratory syndrome, or SARS. The issue emerged following a SARS outbreak at the Amoy Garden apartment complex in Hong Kong. According to WHO, ineffective U-trap seals in the drainpipes of Amoy Garden apartments triggered the SARS outbreak. These traps, often called P-traps in the U.S., are designed to hold water at all times. The water acts as a barrier and prevents insects, foul smells and, in this case, viruses and bacteria from backing up through the drains. When the P-trap failed in the Amoy Garden apartment complex in Hong Kong, the plumbing system, in effect, acted as a transportation system for the virus to spread quickly through the building.

The “Faecal Droplet” Route: Droplets originating from virus-rich excreta in a given building’s drainage system re-entered into resident’s apartments via sewage and drainage systems where there were strong upward air flows, inadequate “traps” and non-functional water seals.

In the absence of proper maintenance and without consistent monitoring, reviewing, enforcing and updating of building standards and practices, inadequate plumbing and sewage systems could continue to enhance the potential of SARS and some other diseases to spread. However, it would be relatively easy to interrupt and avoid some diseases, including SARS if it were to return.

References:

WHO Environmental Health Team Reports on Amoy Gardens
The SARS epidemic in Hong Kong: what lessons have we learned? (doi: 10.1258/jrsm.96.8.374).

Plumbing and Drainage in Hong Kong Since Then

Under working and test conditions traps should retain a minimum seal of 25mm of water or equivalent. Self priming type drainage traps or drainage pipe connections which ensure trap priming may be considered, e.g. connection of washbasin discharge to the pipe between the floor drain grating and its U-trap. Care should also be taken to prevent back-flowing at the floor drain.

Where mechanical ventilation in the form of extractor fan is provided, such as in bathrooms and lavatories, care should be taken to ensure that water seals are intact and operate according to the design intent. Consideration should be given to the quality and quantity of air intake, air-flow path and fan capacity.The Environmental Health Team of the World Health Organisation (WHO) has advised that the optimum volume for bathroom ventilation is 2 cfm/sq ft (10.2 l/s per sq. metre). WHO is of the view that a larger volume does not add much on the comfort side and has the hidden risk of building up negative pressure. Designers are advised to provide an opening to bathrooms and lavatories for make-up air, such as an undercut to the door or an opening with a louvre at the door or wall, in order to minimise the build-up of negative pressure where an extractor fan is used for ventilation. The airflow path created should avoid circuiting of the ingress and exhaust air.

How about Ebola?

Source: CDC

Can sanitary sewers be used for the disposal of Ebola-contaminated patient waste?

A sanitary sewer is a system of underground pipes that carries sewage and wastes from homes and other buildings to a wastewater treatment plant for disposal. The World Health Organization (WHO) states sanitary sewers may be used for the safe disposal of waste, such as feces, urine, or vomit, from patients with Ebola.

At this time, there have been no reports of Ebola spreading through sewage. In the United States, wastewater treatment processes are designed to inactivate or remove infectious agents, making it unlikely that Ebola virus could spread through sewers.

Why can sanitary sewers be used for waste disposal from Ebola patients?

In the United States, human waste, blood, and other potentially infectious materials are routinely released into sanitary sewers. Wastewater treatment plant processes are designed to inactivate or remove human disease-causing organisms (pathogens), including bacteria, viruses, protozoa (such as Giardia and Cryptosporidium), and helminthes (parasitic worms).

Workers directly handling sewage pipes and in the prescreening stage of wastewater treatment are at the highest risks for exposure to disease-causing organisms. These workers should follow the guidelines provided in the CDC Interim Guidance for Managers and Workers Handling Untreated Wastewater from Suspected or Confirmed Individuals with Ebola in the U.S. to prevent exposure to Ebola when working with untreated wastewater.

Have enveloped viruses like Ebola been transmitted to wastewater treatment plant workers?

In an enveloped virus, such as Ebola, hepatitis B, hepatitis C, and HIV, the core of the virus is surrounded by a lipoprotein outer layer. This lipoprotein envelope makes enveloped viruses more susceptible to destruction by numerous physical and chemical agents than viruses without a lipoprotein envelope (called non-enveloped viruses, e.g., norovirus, rotavirus, adenovirus, poliovirus).

Several studies have investigated wastewater treatment plant workers for evidence of infection or prevalence of antibodies (antibodies are proteins that are produced by the body’s immune system when it detects harmful substances). The studies looked at both enveloped viruses and enteric non-enveloped viruses that can affect the gastrointestinal tract (stomach).

A few studies evaluated the prevalence of antibodies to hepatitis B, parainfluenza virus, and hepatitis C. Studies found a significantly higher prevalence of anti-hepatitis B virus antibodies in wastewater treatment plant workers, but other risk factors were not taken into account, such as sexual behavior, injection drug use, or possible exposure in the healthcare environment. These factors could have influenced the study results. Other studies reported a significantly higher prevalence of antibodies towards parainfluenza virus type 1. Another study reported two cases of hepatitis C in wastewater treatment plant workers. There have been no other published reports of infections of wastewater treatment plant workers with bloodborne pathogens such as hepatitis B, hepatitis C, or HIV, or other enveloped viruses such as Ebola or influenza.

Will the 2019 Novel Coronavirus Survive in Wastewater?

2019 Novel Coronavirus (2019-nCoV) is a virus (more specifically, a coronavirus) identified as the cause of an outbreak of respiratory illness first detected in Wuhan, China. 2019-nCoV RNA has been detected in a stool specimen collected on day 7 of the patient’s illness, according to a case report published in The New England Journal of Medicine, First Case of 2019 Novel Coronavirus in the United States. ‘However, extrapulmonary detection of viral RNA does not necessarily mean that infectious virus is present, and the clinical significance of the detection of viral RNA outside the respiratory tract is unknown at this time’, the authors stated.

In 2008, a study measured the survival of coronaviruses in water and wastewater and found that: “Coronaviruses die off very rapidly in wastewater, with a 99.9% reduction in 2–3 days. Survival of the coronaviruses in primary wastewater was only slightly longer than secondary wastewater, probably due to the higher level of suspended solids that offer protection from inactivation.”

As a new strain of coronavirus is investigated, the study offers helpful information, demonstrating that transmission of coronaviruses tend to be limited in the aqueous environment due to the fact that they are rapidly inactivated in water and wastewater at ambient temperatures. See the paper Survival of Coronaviruses in Water and Wastewater for more information.

It is hard to tell, at least for now, whether the novel coronavirus will recover from sewage, considering the complexity of the plumbing and drainage systems. An optimistic guess is that it is very unlikely to happen.

References:

Patricia M. Gundy, Charles P. Gerba，Ian L. Pepper. Survival of coronaviruses in water and wastewater. Food Environ Virol,2009,1(1):10–14.

https://www.cdc.gov/coronavirus/2019-ncov/index.html

Zero Sewage Discharge in Zhejiang, China

The Zero Sewage Discharge Project aims to build and/or renovate communities so that over the whole process from sewage collection, transfer to treatment, no untreated discharge or overflow is allowed, the main purpose of which is to ensure surface water quality. Currently, we are working on a sewer system program under such a concept, of which the objectives include performance assessment, quantity and quality modeling, management optimization, and sewer inspection and monitoring technology improvement. Particularly, airflow and air-water interactions in sewer pipelines are of interest, which are likely critical to the virus transmission.

To prevent infection of virus from drainage systems, exposure to raw sewage should be avoided as much as possible. In addition to modern home plumbing systems, the Zero Sewage Discharge Project helps to keep people from contacting with viral materials and reduce the possiblity of infection.

Plumbing Tips for Preventing the Spread of Disease

Push water through floor drains in bathrooms, basements, garages and other areas at least once a month to keep the P-traps filled with water and to prevent insects, air or anything else from passing through pipes.
Run a gallon of water through bathroom drains about once a month, since mopping floors clean - the usual technique in the U.S., as in China - does not allow enough water to fill the P-trap causing it to dry out.
Run a gallon of water at least once a month through lesser-used drains to keep P-trap seals from drying out.
Pour up to a cup of chlorine bleach or other common disinfectants down a drain to kill germs since WHO has determined that they kill most bacteria and viruses, including SARS, within five minutes. But be sure to later flush the drain with water.
Odors that arise from household drains indicate the P-traps are dry and need to be filled with water.
Visit the WHO website to see test results showing how the SARS virus can live for days in human waste.

Let Zero Sewage Discharge Take Care of the Rest

To be updated…

Almost Everything about Urban Drainage

2019-nCoV RNA in Sewage?!