Monday 29 July 2013

Reusing waste water

Even as the State Government is scrambling to come up with schemes to provide water to a parched Bangalore City and even as it is commissioning several studies, organising seminars, holding meetings and undertaking studies to search for a viable alternative to the Cauvery, the Bangalore Water Supply and Sewerage Board (BWSSB) has come up with a revolutionary idea.
The BWSSB has finally realised that augmenting Bangalore’s water supply should begin at home and it has decided, albeit a little late, to resolve Bangalore’s water woes by reusing water.
Reusing or recycling natural resources has never gained popularity in India and there has not been any serious effort either by the Government or the people to reuse natural resources or recycle waste.
Water is one of the natural resources that can be easily reused. The reused water can be used for non-potable purposes like cleaning, gardening and for toilet purposes. Infact, the technology for reusing water is so good that it can even be used for drinking and  this is what the BWSSB proposes to do.
The BWSSB has drawn up a large-scale plan to reuse water. This, it feels, will not only lessen the dependence on the Cauvery but also replenish ground water levels and provide the authorities with the much needed buffer to rejig the water supply network and also provide better services.
This would perhaps be the first time in India that an urban water supply board is using treated water to augment potable water supply. Ambitiously labelled as the Vrishabhavathi Valley project and this many say is the first of its kind in India, will see 300,000m3/d of sewage effluent undergo stringent secondary treatment. The next step is to treat half of this amount with tertiary treatment before releasing it into the Arkavathy river, where it will mix with fresh water.
This combined flow will be pumped into the Tippegondanahalli (T.G. Halli) reservoir, where the water will be further treated before being distributed to the western parts of Bangalore.
The BWSSB plans to construct a 147,000m3/d ultrafiltration plant at the Tavarekere pumping station. This would be state of art project and would cost at least Rs. 474 crores (USD112 million).
Since the project has been approved under the JNNURM scheme, 50 per cent of the cost will be borne by the Governments- Central Government will bear 35 per cent and state government 15 per cent. The other 50 per cent will be borne by the BWSSB and the water board proposes to raise this amount through loans from financial institutions.
Waste water from the domestic sector or households is also known as sewage and it can generally be divided into two distinct forms:
Blackwater – which is grossly contaminated by faeces or urine; and Greywater - which is not grossly contaminated by faeces or urine.
According to water usage surveys, an average wastewater flow of
586 litres is generated per day per house hold and Grey water represents about 68 per cent of the total waste water stream. When kitchen waste water is also excluded, the percentage of grey water
becomes about 61 per cent. This shows that grey water is a recyclable water resource
The BWSSB says that 80 per cent of the City’s water is met from the Cauvery and the rest from the Arkavathy and borewells. The current water supply is in the region of 870,000m3/d, though demand exceeds 1.2 million m3/d. The shortfall is met by the 3.14 lakhs borewells and this has severely strained the ground water table.
The Board has already signed a memorandum of understanding (MoU) with Singapore Co-operation Enterprise (SCE) and Temasek Foundation (TF), an investment arm of Singapore government, for recycling and reusing treated water.
The Board wants to avail of technical guidance from Singapore as it has adequate expertise in waste water treatment, recycling and re-use.
BWSSB wants to develop a project across the Vrishabhavathi Valley as it already has five sewage treatment plants along the course of the river. The Board will now have to set up a reuse treatment system.
Even the Interim Report of the Expert Committee to Assess Long Term Additional Needs of Water for Bangalore City had recommended this measure among others to ensure that excessive dependence on fresh water is reduced.
The report points out that 1520 MLD of water goes into the Valley after treatment at BWSSB treatment plants. This water could be used to recharge groundwater, supplement inflow to Arkavathy and also be used for non-potable purposes.
It also suggest dual pipelines to transport potable and non-potable water for drinking and other purposes to houses and establishments and this can substantially reduce the burden on fresh water.
Bangalore has 14 secondary sewage treatment plants (STP) and all of them operate much below capacity due to insufficient inflow. They have a collective capacity of treating 873 MLD of water.
Apart from these plants, the BWSSB is installing smaller STPs near several lakes. But, Bangalore uses less than 7 MLDs of treated water. There is thus scope for larger use of recycled water. This is really ironical considering that Bangalore’s first sewage network was developed as early as 1922 but the treatment of waste water started only in 1974.

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