Impact of COVID-19 on Wastewater Reuse
CSEI Insights from before and during the lockdown
by Sahana Balasubramanian and Sneha Singh
During Covid lockdown, with the entire family staying home all day, the domestic water consumption in Bengaluru households had increased by 15%, as per the Bangalore Water Supply and Sewerage Board (BWSSB) by April 2020. Pandemic activities like washing of vegetables and fruits in filtered water, excessive floor cleaning and terrace gardening had all contributed to increased freshwater consumption in homes. The World Health Organisation’s (WHO) recommendation to wash hands frequently to protect ourselves from Covid-19 also led to an increase in water usage.
Interestingly, this happened despite much of the migrant population moving back to their hometowns, leaving many of the units in these apartments unoccupied. One utility that helped to keep the increased water consumption in check, within large multistoried apartments, was the availability of treated wastewater for toilet flushing.
But first, some context on wastewater treatment in apartments
Most multistoried apartments in the city have on-site decentralised sewage treatment plants (STPs) as a result of BWSSB’s notification issued in 2016. This mandate requires the installation of STPs and dual plumbing systems in apartment complexes with over 20 units or built-up area of more than 20,000 sq. ft.
What are these dual plumbing systems?
These are plumbing installations that separately supply freshwater and treated wastewater in different pipelines. Dual plumbing has been installed in Bengaluru’s apartments predominantly to enable toilet flushing. However, in some apartments wastewater is being used beyond this mandate, for cleaning common areas and gardening.
Impact study of dual plumbing systems on water consumption
In this context, we wanted to compare the amount of wastewater that went unused before and during the lockdown period to understand the impact of dual plumbing systems on water consumption.
We conducted telephone interviews with 20 Resident Welfare Associations (RWAs) of multistoried apartments in Bengaluru. The interview focussed on the following aspects:
- Installation of dual plumbing systems
- Purpose of reuse of treated wastewater
- Availability of excess treated wastewater, if any
- Impact of Covid on the usage of treated wastewater
It is worth mentioning here that out of the 20 apartments we interviewed, one did not have an STP installed.
Before the lockdown, on average, 41% of available treated wastewater was being reused for landscaping, toilet flushing and washing common areas. And the excess was being discharged into storm water drains or water bodies. During the lockdown, as the frequency of use of toilet flushes increased, 8 out of 20 apartments were able to reuse all of the available treated wastewater.
Our interviews uncovered that 12 out of 20 apartments had installed dual plumbing systems.
Only 1 out of the 20 apartments is converting wastewater to potable water.
This apartment’s STP is located on the ground level and uses Sequencing Batch Reactor (SBR) technology. It has a capacity of 32 kilo litres per day (KLD) catering to a population of 288 individuals (72 units with an average of 4 persons per unit). 50% of the treated wastewater is reused for purposes like gardening, toilet flushing, car washing and common areas cleaning. The remaining 50% is treated to potable water standards.
Reuse of treated wastewater before and during lockdown
8 out of 20 apartments were able to reuse 100% the treated wastewater during lockdown.
Often the excess treated wastewater is either discharged into nearby lakes or let into storm water drains. This discharge pollutes lakes and keeps them perennially full, preventing them from being natural flood buffers. The excessive buildup of nutrients from wastewater also block sunlight from entering the water, causing the lakes to stink. As a result, plant growth is affected, causing problems further along the food chain.
Impact of COVID on wastewater reuse
Though most of the apartment units were unoccupied, wastewater generation continued to be high. An increase in the quantity of freshwater consumed per household resulting in increased wastewater production could account for this spike.
In the 12 multistoried apartments reusing 100% of their treated wastewater, there were a total of 5783 units. Considering an average of 4 persons per unit, nearly 2500 KLD of freshwater is required per day for a population of 23,132 individuals. With the installation of dual plumbing systems that make it possible to reuse treated wastewater for toilet flushing, nearly 724 KLD of freshwater was saved per day.
By addressing the issue of wastewater, CSEI’s Green Cities initiative hopes to put in place one small piece of the climate change puzzle. Our Grey to Green campaign plans to reuse excess treated wastewater from decentralised STPs in apartments for greening public spaces like parks and medians. Our Grey to Blue campaign plans to improve the water table by using treated wastewater to recharge groundwater.
We would love to hear from you. To collaborate with the Green Cities Initiative, reach out to Green Cities initiative lead, Shreya Nath: shreya.nath@atree.org
