“Review of Proposals for Sewage Treatment in Varanasi” by Swatcha Ganga Campaign
Review of Proposals for Sewage Treatment in Varanasi
In 1997, at the request of the Varanasi Nagar Nigam (VNN), the Sankat Mochan Foundation (SMF) submitted a Project Feasibility Report (PFR) for sewage interception, dispersion and treatment for the city of Varanasi under Ganga Action Plan Phase II. In 1999 the UP Jal Nigam submitted a different PFR for Varanasi under GAP Phase II. Upon receiving this the Varanasi Nagar Nigam requested experts of the stature of Prof. G.D. Agrawal to do a techno-economic appraisal of the two PFRs.
Prof. Agrawal concluded that the VNN-SMF scheme shall be more favourable for Varanasi city due to:
1. Not being dependent on pumping, the interception shall have much less disruptions and shall be more reliable.
2. Treated effluent shall be much lower in coliforms and much better in all other respects.
3. Land costs and acquisition problems shall be much less or absent.
4. Much lower capital costs. (Rs.150 Crores for VNN SMF versus Rs.300 Crores for UPJN – 1997 costs)
5. Pumping energy consumption lower by 6 million units per year.
6. Operation and Maintenance costs lower by Rs.2.50 Crores per year.
As a consequence of this report the Varanasi Nagar Nigam has reiterated its desire for implementation of the VNN-SMF scheme under GAP Phase II. The Varanasi Nagar Nigam has been attempting to assert its rights under the 74th amendment to the Indian Constitution to be recognised as the consenting body for implementation of these works.
Varanasi Nagar Nigam Proposal
Varanasi Nagar Nigam in resolution no. 126 dated 2/5/1997 and resolution 339 dated 22/7/1998 unanimously adopted the Project Feasibility Report (PFR) made by Sankat Mochan Foundation (a Varanasi based NGO), foreign and Indian experts and engineers for implementation under GAP Phase II for Varanasi.
This VNN-SMF PFR details a system to achieve the objective of a complete and fool-proof interception of all polluting waste water reaching Ganga in the Varanasi reach and appropriate treatment and disposal of the diverted wastewater. It utilises a Ghat Interceptor along the river front carrying wastewater under gravity to an Advanced Integrated Wastewater Oxidation Pond System (AIWPS) sewage treatment plant to be located at Sota.
The VNN-SMF system proposes:
– construction of an interceptor sewer along the ghats of Ganga between the last line of buildings and the river. This will collect sewage from all ghat front wastewater outflows and convey this by gravity to a treatment plant at Sota.
– construction of two interceptor sewers along the banks of river Varuna and conveying the collected sewage to the treatment plant at Sota
The interceptor sewer is designed to be completely water proof and is therefore capable of diversion of sewage from the religious bathing areas along River Ganga in Varanasi during both wet and dry seasons.
Advanced Integrated Wastewater Oxidation Pond System (AIWPS)
For the treatment of sewage collected by the interceptor sewers and transported to Sota, construction of an AIWPS of 300 MLD capacity is proposed. The design facility provides for a series of four types of ponds:
1. 6 Advanced Facultative Ponds (AFP)
2. 12 High Rate Ponds (HRP)
3. 24 Algae Settling Ponds (ASP)
4. 3 Maturation Ponds
The Facultative Ponds consist of open ponds containing a methane fermentation pit. Sewage entering the system is injected at the bottom of the methane fermentation pit, where sludge is permanently trapped and consumed by fermentation.
The High Rate Ponds take water from the facultative ponds and aerobic bacteria break down dissolved organic matter. Oxygen is supplied photosynthetically by microalgae. The rapid growth of algae raises the alkalinity of the water, killing pathogens.
In the settling ponds more than half of the algae produced in the high rate ponds settle out. Sufficient algae settle out to meet total suspended solids discharge requirements.
In the maturation ponds treated water is exposed to the suns UV rays and stored for irrigation or disposal.
The treated effluent will produce effluent with a coliform count below the permissible river water standard of MPN 500/100ml, rich in Dissolved Oxygen, odour free and colour free. The dried algal sludge is rich in nitrogen, phosphorus and potash and hence is an excellent fertilizer.
The total area of the system is estimated at 330 hectares. This land will be obtained by reclaiming a part of Sota sandbar by constructing dykes and low embankments. The resulting STP would be above flood level with only the final maturation pond being subject to minor inundation in a 1 in 100 year flood. This land is otherwise useless and is available at only a nominal cost. In addition the embankments proposed would provide two all weather access roads to the mainland for the 25000 inhabitants of Dhab area during the monsoon months.
The UP Jal Nigam PFR involves pumping stations along the ghats, to pump sewage to a sewer main at a higher level. Unlike the VNN-SMF scheme these pumps will be unable to operate during the monsoon when the river level is raised, meaning that sewage will flow into River Ganga along the religious bathing areas at these times.
With more than 6 pumps to be maintained the likelihood of breakdown is much greater. If these pumps breakdown raw sewage is discharged directly into the religious bathing areas. The VNN-SMF proposal involves only one pump. If this pump were to suffer breakdown there is sufficient capacity within the interceptor to allow storage of up to 8 hours sewage, during which time repairs could be made. Should some discharge be possible it would occur only in the river channel downstream from the religious bathing areas.
The UP Jal Nigam scheme proposes to use oxidation ponds of the Duncan Mara design. Operation of these ponds generates sludge which must be disposed of and the digestion produces odours which will disturb surrounding residents. The AIWPS scheme generates no sludge and odours are eliminated due to the presence of an aerobic cap on the Advanced Facultative Ponds.
1. Prof G.D. Agrawal. “Techno-Economic Evaluation of the UPJN and VNN-SMF Proposals for Varanasi under Ganga Action Plan Phase II”. Submitted to Mayor of Varanasi on 28 February 2000.
2. “Feasibility Study of Interceptor Sewers and AIWPS Technology for the Prevention of Pollution of Ganga at Varanasi”. May 1997