India is adopting advanced sewage wastewater treatment tech, but must choose those that best meet local needs

Subject : Environment

Section: Pollution

Context:

Indian cities currently treat only 28 per cent of the 72,368 million litres of sewage they generate every day, as per the latest data released by the Central Pollution Control Board in December 2022.

Details:

Most sewage treatment plants in the country rely on outdated technologies such as the activated sludge process, planted drying beds, soil biotechnology andupflow anaerobic sludge blanket reactors that have a treatment efficiency of around 65 per cent and are cumbersome to set up and manage.
In recent years, several states have adopted some newer technologies that have treatment efficiency of around 80 to 90 per cent.
Andhra Pradesh and Telangana have opted for sequencing batch reactors (SBRS) and moving bed biofilm reactors (MBBRS).
The sewage treatment plant (STP) at Durgam Cheruvu Lake, Hyderabad and most of the STPs of Bihar, Maharashtra, Goa, Haryana, West Bengal and Uttarakhand have opted for SBRS.
When compared to traditional treatment techniques, these technologies have higher treatment and nutrient removal capacity, are better at handling shock loads (spikes in pollution concentration in wastewater), are more resource-efficient and generate high-quality effluent with greater reuse potential.

Membrane bioreactors:

It has the highest rate of filtration which is achieved by combining biological processes with a membrane.
Working:
- Sewage is first treated inside a bioreactor where microorganisms break down organic matter and eliminate pollutants by converting them into carbon dioxide, water and biomass.
- After this, the wastewater is pressured through a fine-pore membrane to segregate treated effluent from micro-organisms and suspended solids and ensure the production of high-quality, clarified effluent that can be reused without further treatment.
- It also has a small footprint, making it ideal for areas with land scarcity.
- It offers a high level of automation and process control through sensors for real-time control over filtration.
Advantages:
- Highly efficient, and crucial for food processing industries.
Disadvantages:
- Energy-intensive, expensive to set up and operate, requires regular maintenance, skilled human intervention and frequent system downtime to replace the membrane.

Moving Bed Biofilm Reactor (MBBR):

Extensively used for handling municipal sewage.
The process takes place in a bioreactor with plastic carriers on which microorganisms can attach and thrive.
As wastewater flows through the bioreactor, the microorganisms in the biofilm metabolise organic matter and pollutants in the sewage. The biofilm is designed to freely float within the bioreactor, facilitating the distribution of wastewater and oxygen.
Advantages:
- High treatment efficiency, can handle wastewater with different pollutant compositions, produces limited sludge, requires less energy to operate and has negligible downtime.
Disadvantages:
- Limited removal of solids and nutrients, the biofilm carriers within MBBRs can clog up the system if not effectively managed, regular maintenance, and it relies less on automation and focuses on manual adjustments to control parameters like aeration and effluent quality.

Sequencing Batch Reactors:

These combine biological treatment and sedimentation within a single bioreactor and each batch cycle begins with the filling up of the reactor with wastewater.
This is followed by aeration to stimulate microorganisms to metabolise organic matter. Once the biological reaction is complete, aeration is halted, allowing suspended solids to settle at the bioreactor’s bottom.
This results in the formation of a supernatant layer above the settled solids, which is decanted, leaving the settled solids in the reactor.
The treated effluent is typically discharged or further processed.
Advantages:
- A high-efficiency rate, allows high automation and process control, facilitates the removal of nitrogen and phosphorus through specific process stages, and require smaller reactor volumes thus reducing construction costs.
Disadvantages:
- Longer treatment cycles, generate a significant amount of sludge, requiring proper management and disposal strategies.