Treating waste on-site best way to keep Bharat swachh?
August 7, 2017

As the Swacch Bharat Abhiyaan gets underway, ironically, the risk of pollution of water bodies increases manifold, says Rina Mukherjee. More than the convenience and hygiene provided, on-site designs are cheap and easily executed, as compared to the expense involved in laying city sewerage lines, a significant plus-point, she points out

Waste water and solid waste management is a problem of gargantuan proportions in India. More so since the overdrive to build toilets in every town and village under the Swachh Bharat Abhiyaan (a campaign by the Government of India to clean the streets, roads and infrastructure in India’s cities and towns and to focus on sanitation). By 2019, with the successful implementation of the Mission, 30 million septic tanks and pits would have been provided along the Ganga Basin. This, according to the Centre for Science & Environment (CSE), will generate 180 million litres of faecal sludge.

Since the toilets that have come up in most towns and villages are twin-pit types, the pits need to be emptied when they are full. With very few cities equipped with adequate sewerage systems, the human waste ends up being emptied into drains and rivers. Thus, the Swachh Bharat Abhiyaan is at cross-purposes with Namami Gange, which seeks to clean up the Ganga under a time-bound plan. What is true of the Ganga is just as true of the hundreds of rivers flowing across the length and breadth of India.


Baffle reactors and gravel filter with plants outside Bangalore MG.

Limitations of sewerage systems
In the absence of adequate sewerage systems, toilets spell disaster for rivers and drains and, in the event of their contamination, public health. What is more, most toilets and septic tanks installed under the Swachh Bharat Mission do not follow BIS standards mainly because they are installed by local masons unaware of the standards. The level of contamination of water resources in small towns and municipalities is therefore of a high order.

A study conducted by CSE using sewage flow diagrams for 71 Indian cities found that in most cases, 42-78 per cent of the waste generated is disposed of by unsafe means. Even in municipalities like Bansberia in West Bengal, which has a treatment plant to receive the sewage generated within the municipality and from outside, and runs a joint venture project to convert faecal and poultry waste into bio-compost, there is still some faecal sludge that remains untreated, with some liquid waste seeping out into the Hugli River from sludge drying beds.

Besides, laying of sewerage systems poses a huge problem financially and logistically, especially with most urban centres growing at a frenetic pace. Even when sewage treatment plants (STPs) are set up, inadequate pipelines to transport the waste results in STPs not working at full capacity. Consequently, the very purpose of setting up such a plant is defeated.

When municipal solid waste is dumped untreated in landfill sites, it can also result in severe pollution of groundwater, as has been the case in many parts of Madhya Pradesh and Rajasthan, where complaints have had to be dealt with by the National Green Tribunal, and the Central Groundwater Board (CGWB).

1.A typical CAMUS SBT wastewater treatment system using biomimicry and plants
A view of the anaerobic baffle reactors and plant filter beds at Kangeri.

Alternatives to STPs
Mention must be made of a centuries-old system that continues to operate in Kolkata for the treatment of waste water, minus STPs. At the turn of the previous century, the British had got in touch with a zamindar, Bhabanath Sen, who had been growing vegetables on garbage near Patna and Bankipur. In 1879, Bhabanath Sen was allotted a 20-year lease on the Dhapa square mile on the outskirts of Kolkata, which was freed of taxes for perpetuity through a Crown Grant. This saw Sen grow vegetables and cultivate fish using sunlight and human labour to clean waste water and garbage and, in turn, set up the world’s largest natural urban waste recycling system.

The Kolkata Municipal Cor-poration area generates roughly 750 million litres per day of sewage and waste water and more than 2500 tonnes of garbage (1997 figures). The waste water is led by underground sewers to pumping stations, and then pumped into open channels (called dry weather flow channels) of the drainage outfall system. Thereafter, it is drawn into the bheris, or water-bodies, meant for pisciculture (fish farming). Here, the water is held for a few days, and the organic compounds get biologically degraded. A network of channels is used to supply the untreated sewage and to drain out the spent water.

This method reduces biological oxygen demand (BOD) by 80 per cent and coliform bacteria by 99.99 per cent. Sunshine and photosynthesis play an important role in cleaning the waste water, with solar energy being tapped by the dense plankton population in the waters. The plankton, in turn, becomes food for the fish which thrive here. The system is so efficient that a study by the Central Pollution Control Board (CGWB) found it to reduce faecal coliform by 99.7 per cent as compared to a conventional STP which reduces it by 60 per cent, using the activated sludge process.

Dhapa also continues the old practice of growing vegetables on garbage in a modified form, using irrigation with naturally treated waste water from the fisheries segment. However, this huge ecological resource is under threat today, with realtors converting large tracts of this invaluable site. Lack of enough sewage and inclement weather have also been threatening the natural processes used here. This is where on-site decentralised systems can make a huge difference.

On-site waste recycling systems
The decentralised waste water treatment system or DEWATS technology being implemented in many parts of Bangalore and Southern India by the Bremen Overseas Research and Development Association and the Rajiv Gandhi Rural Housing Corporation which run the Centre for Advanced Sanitation Solutions (CASS) is one such on-site recycling system. A DEWATS system can bring down the BOD and chemical oxygen demand (COD) of waste water by 70-90 per cent; besides, the planted gravel filter which is used to clean the waste water is always an aesthete’s delight.

The DEWATS model can be used for underserved communities within urban centres, such as city slums, or for communities outside city limits, such as is being done in the Beedi Workers Colony in Kengeri on the outskirts of Bangalore. Housing societies not served by the municipal sewerage system too can use it to recycle water for flushing and gardening purposes. Since the waste water can also generate biogas, it can help meet the energy needs of communities. For instance, in Kengeri, the biogas generated is used as fuel to serve the cooking needs of the local anganwadi.

The CAMUS SBT (Continuous Aerobic Multistage Unsaturated System – Soil Bio Technology) model is similar to the DEWATS system, but does not yield any biogas. The wastewater is first sent to a settling tank, where flocculent is added. This causes the suspended and dissolved solids to settle down. If the waste water contains a large amount of organic matter, anaerobic digesters may be used. The waste water is then treated in stages, and the final treated water is collected in tanks. The suspended and dissolved solids in the settling tank and anaerobic digesters are then sent through a thickener to be converted into compost.

This simple model can bring down the BOD and COD by as much as 99 per cent, cleaning the water to near-potable levels.

Currently, CAMUS SBT is being used to treat the waste water generated by Lucknow’s Chaudhary Charan Singh International Airport, among other projects.

(The writer is a senior Kolkata-based journalist who specialises in developmental issues. She is the recipient of several national and international fellowships, besides India’s first-ever Laadli Extraordinaire Award (2012-13) for relentlessly fighting gender injustice.)

July – September 2017