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Reusing Effluents in the Time of COVID-19

Reusing Effluents in the Time of COVID-19

Photo: E.J. Strat/Unsplash

Bengaluru has experienced unprecedented urban growth in recent decades. As the population grew and infrastructure lagged, groundwater became over-exploited and untreated sewage was let into the waterways, resulting in severe pollution of its lakes and waterways.

Against this backdrop of water scarcity and inadequate wastewater treatment, the Karnataka State Pollution Control Board issued a zero liquid discharge order in 2004. It mandates that all buildings with more than 50 residential units or a built-up area of more than 5,000 sq. m in unsewered areas must install on-site sewage treatment plants (STPs) and reuse 100% of the treated water. Complying with this, many apartments have setup decentralized treatment systems and are utilizing treated effluent for non-potable purposes such as landscaping, car-washing and flushing via dual piped systems.

Since the onset of the COVID-19 pandemic, however, residents in high-rise apartments have been increasingly sceptical of reusing treated effluents, driven by fear of contracting an infection. Is this perception scientifically defensible?

Some of the perception of the link between wastewater and COVID-19 comes from media articles discussing the possibility of using sewage to quantify disease burden. The presence of the novel coronavirus’s RNA strands in raw sewage from areas with infection rates is well established. Scientists have shown that monitoring data from STPs can provide useful information about the onset of COVID-19 in an area before it is reported at hospitals. This data can serve as an early warning system, helps with tracing the location of the infected population and set up the control/quarantine measures to curb/prevent the spread of the novel coronavirus.

While particles of the novel coronavirus has been widely reported in raw sewage, none of the studies have reported its presence in treated (especially chlorinated) effluent. Wastewater treatment systems by design are meant to remove all kind of harmful bacteria and viruses present in raw sewage. Even in the pre-COVID times, raw sewage contained various pathogens that were eliminated during the treatment process.

Broadly, wastewater treatment comprises three steps: primary, secondary and tertiary treatment. Primary treatment is designed to remove large suspended particles (organic and inorganic). In the secondary treatment, microorganisms are employed to remove dissolved organic matter. The tertiary treatment process is deployed depending on the end-use. For example, in cases where treated effluent is used for landscaping, tertiary treatment involves disinfection only with the objective to retain nutrients (nitrogen and phosphorus) that are crucial for plant growth, while eliminating harmful pathogens.

When treated effluent is discharged into a water body, like a pond or a lake, it is crucial to use the tertiary treatment process to remove nutrients and pathogens both. The objective here is to prevent eutrophication in the water body.

Nevertheless, whatever the end use is, disinfection is mandatory to eliminate pathogens and prevent the spread of infectious disease. Chlorine in the form of bleaching powder, liquid chlorine gas, or sodium hypochlorite are all highly effective in killing pathogens present in the treated effluent.

The WHO guidelines on wastewater management have not been updated since the start of the COVID-19 pandemic. The document states that the existing guidelines are comprehensive enough to prevent getting COVID-19 via the use of treated effluent. Therefore, ensuring wastewater treatment systems run at their design capacity and treated effluent is disinfected using chlorine is sufficient to prevent the risk of contracting COVID-19 from treated wastewater.

Although the reuse of treated effluent is not considered a risk today, there is some evidence of another possible infection pathway. Some studies, as well as an article in the Times of India, reported fecal aerosols as a potential way to spread the virus. In high-rise buildings, toilets, kitchen sinks and washbasins are usually vertically aligned. The plumbing systems in such buildings act as a conduit for wastewater flow and aerosols within apartment units. The piping systems connecting bathrooms (toilet and hand wash) are potential spaces for aerosol development. These are the spaces where the faeces become aerosolised.

During the SARS outbreak in 2003, a study from Hong Kong reported the spread of infection by aerosols developed and transmitted by faulty plumbing systems. The residents in the apartment vertically aligned to the unit with infected people contracted the virus. Considering the main mode of viral transmission is respiratory droplets, any person in such buildings containing aerosolised faecal matter is at risk of being exposed to potentially infective droplets.

However, the aerosol pathway can be intercepted if the infected person uses a separate bathroom, disinfects the bowl, shuts the bowl and ensures sufficient ventilation, and the residents’ welfare association is informed of which bathrooms are being used by the infected person so that the residents can avoid using washrooms that are vertically aligned with it.

There is a concern regarding the treatment efficiency of an STP if bleaching powder or any disinfectant is added to the plumbing system. In addition to killing pathogens, disinfectants in raw sewage will also kill the heterotrophic bacteria that help remove organic matter. This issue can be fixed by maintaining higher concentrations of heterotrophic bacteria in the reactor, by lowering sludge wastage and maintaining high oxygen supplies in the STP. Though revamping the treatment process will have implications for the operation and maintenance costs of an STP, it is worth investing in prevention and in building a healthier, safer world.

Priyanka Jamwal is a fellow of the Centre for Environment and Development, Ashoka Trust for Research in Ecology and the Environment, Bengaluru.

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