21 July 2016, Devanahalli: IMG_0682The Tamil Nadu Urban Sanitation Support Programme team had an exposure visit to Devanahalli which is about 40 km from the city of Bangalore. Here, CDD Society runs a faecal sludge treatment plant (FTSP) along with the Town Panchayat. The Devanahalli FTSP employs gravity-based biological treatment of sludge and has a capacity to handle upto 20-30 million litres per day (mld) of waste.

Priscilla, Suresh, Ananth, Vinitha, and Ramakannan attended the single day event which took them around this facility. Though the group approached the facility with trepidation, they were pleasantly surprised by the complete absence of any foul odour in the surroundings. The plant has 6 sections (Screening Sludge-Liquid Separation -Sludge Stabilization – Dewatering -Disinfection- Liquid Treatment ) of which only the 2 (Screening and dewatering) is visible above the ground. The facility had the look of a well maintained recreational area.

IMG_0699The cycle of treatment follows the process of screening, sedimentation, bio digestion, sludge stabilisation and dewatering, and liquid treatment. In the first stage, a large metal mesh removes macro particles of sludge – plastics, metallic objects, etc. The slurry then passes into a sedimentation tank where the sludge settles to the bottom and the supernatant liquid is siphoned off into the liquid treatment section.

The sludge is then moved to the biodigester where anaerobic bacteria degrade it. A biodigester is a large tank where the sludge is ‘digested’ or degraded with the help of anaerobic bacteria already present in it. This process can take up to two days. Therefore, there are two such biodigesters where the daily incoming sludge is transferred alternately. For further dewatering, the sludge is then transferred to open sludge drying beds which are connected to percolation pits so that the last of the liquid drains out.

An integrated settler with anaerobic baffle reactors is used to treat the liquid from the slurry. From there the liquid flows into planted gravel filters. This process helps bring down level of BOD (biological oxygen demand) to acceptable level. The water is then sent to a collection tank and used for internal gardening and by nearby farms for irrigation.

IMG_0707One of the bye products of degradation is biogas. Currently, the biogas produced in the plant is used by the employees for domestic purposes. Plans for commercial marketing of the gas are being discussed. Plans are also on for the dry sludge to be converted into compost which can then be marketed commercially to farmers in the area.

Funded by the Bill and Melinda Gates Foundation, Keystone’s Tamil Nadu Urban Sanitation Support Programme is discussing details regarding setting up of a similar plant in Periyanaickenpalayam. This FSTP which will not only serve the project areas of Perinaickenpalayam and Narasimhanaickenpalayam, but also other adjoining town panchayats towards North Coimbatore.

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