Soil Biotechnology for sewage treatment

A viable and cheap alternative for sewage treatment – Soil Biotechnology (SBT) – helps communities tackle water problems in a more cost effective way

An ecological method – Soil Biotechnology (SBT) based STPs – researched for over two decades at IIT-Mumbai, provides clean river quality water at a low cost. Vision Earthcare, incubated in IIT Mumbai, has licensed this method for deployment globally.

STP treats domestic wastewater for disposal. However, apartments and gated communities situated away from the city are totally dependent on bore wells or water tankers. It is mandatory for them to have their own STPs. River water for such communities is a distant dream. Hence, the realities are forcing them to look upon their wastewater output as an abundant new source of water. Some communities have started reusing their treated water for flushing and gardening although there are serious problems with the quality of the treated water. Most STPs in communities are Activated Sludge Process (ASP) based.

Conventional Technologies

In conventional technologies such as ASP, aeration is achieved mechanically, which is very energy intensive. At higher ambient temperatures (like in India) the solubility of oxygen in water is low and therefore, energy requirement increases.

Moreover, air contains only 20% oxygen, the rest being nitrogen that is passed into water wastefully, further adding to process inefficiency. In addition to these inherent limitations of the method, several additional reasons make the reality worse. Treat it somewhat; dump it somewhere is the usual story in most communities.

While interacting with a community in South India, Dr Chandrashekar of Vision Earthcare highlighted several important points that surfaced during the interaction . Some of them were:

1. Conventional STPs are designed for disposal rather than for reuse.
2. They are overloaded, poorly maintained and are prone to frequent breakdowns and are also usually operated by unreliable vendors who employ unskilled labourers as “STP operators”.
3. In addition to a hefty monthly fee, vendors pressurise communities to replace pumps, motors fairly often (to obtain ‘commissions’).
4. There is also significant monthly electricity cost for running STPs.
5. Many communities do not perform an independent quality test of treated water. Vendors usually rig the tests to fake compliance with Karnataka State Pollution Control Board (KSPCB) standards. Foul odour is very common.

Thus, STPs in most communities not only consume large amount of resources but also pollute surface water bodies and eventually our only source, ground water, when partially treated water is dumped onto open lawns or into storm water drains. Vendors pocket large sums and tanker mafias continue to benefit because of increasing demand for water, while communities grapple with water shortage, pollution and flooding.

Soil Biotechnology (SBT) based STPs

SBT is a major paradigm shift in waste processing. Sewage treatment is just one application among many – it can be used for arsenic/iron removal, hospital waste processing, industrial wastewater processing & air purification and so on. Because of its versatility, it revolutionises the way we look at wastewater.

SBT treats water for reuse rather than disposal. Since it reinforces the carbon and nitrogen cycles in nature, the quality of the treated water exceeds KSPCB standards reducing Chemical Oxygen Demand (COD) nitrates to very low levels unlike any other STP method. It is highly scalable and can be designed for houses, apartments, gated layouts, towns or cities. The treated water can be reused in many ways:

• Can be sold to constructions/industries who normally purchase tankers. Plant costs can be recovered within a few years depending on the amount of reuse.
• Can be piped back to homes for flushing toilets, gardening, washing yards, cars which can be almost 50% of daily requirements.
• Can be used to recharge groundwater using rainwater harvesting recharge wells.
• Acts like virtual rain when you want it, where you want it, how much and at the required rate.

Ecologically Safe

SBT is a patented method (US and Indian) developed by Prof HS Shankar, Department of Chemical Engineering, IIT Mumbai. It uses only natural materials, natural agents (bacteria culture, worms) and natural processes (respiration, photosynthesis, nitrogen fixation) – it is ecologically 100% safe.

Unlike a conventional STP or septic tank where periodically the sludge has to be offloaded, everything is consumed within the plant in this SBT based STP. Raw sewage is pumped to a customised media bed for around five hours (dependent on load and capacity) and clean water flows into the collection tank.

It has at most two motors, unlike conventional ASP based STPs with numerous motors, stirrer, blower, reverse flush tank, clarifier, sludge pumps and so on. Hence, it is energy & cost efficient and requires minimal maintenance while being more reliable.

The recurring cost consists of natural materials used as additives and it can be operated by gardeners rather than environmental engineers. Life of the specially constituted filtering media bed is long (tens of years) since with time the natural living agents multiply or shrink to optimal levels based on the actual chemical and biological load in the system. Unlike other ecological STP methods it is far more space and time efficient.

Many communities who have ASP based conventional STPs may hesitate to replace it with a brand new one. Consider these:

1. Your existing STPs are expensive (maintenance, operation) while not providing any water for reuse.
2. Rainwater harvesting investment can be leveraged with SBT for storage, reuse and recharge on a daily basis, all year.
3. If you purchase water tankers for consumption, the yearly cost would pay for a new SBT plant.

In conclusion, the fundamental process accomplished by any STP is taking impurities to the highest oxidised state. Since SBT processes waste on land rather than inside water, it is inherently superior to all the current STP technologies in installation, operation, effectiveness and longevity. For water security, SBT is a must and a blessing.