The concept of a Common Effluent Treatment Plant for tannery wastewaters took root for the first time in the country in Vaniyambadi. Due to limitations of space, time and money, the tanners of Vaniyambadi took the initiative of building upon this unique concept in protecting the environment that would allow them to survive and sustain them through the near millennium at hand.

The initial responsibility of carrying this concept from the drawing board to the field devolved upon the Central Research Institute, Chennai. A survey and feasibility report was prepared in the years 1984 & 1985 and a year later, the detailed project report was finalized. Tenders were floated in 1987 and the works related to the Common Effluent Treatment Plant (CETP) were begun immediately after selection of the contractor. The engineering arm of Batlibol Ltd., Hydraulic & General Engineers, Mumbai were entrusted with the contract and the plant was completed in the year 1991.

The original project cost was Rs; 227 lakhs and this had escalated to Rs. 337 lakhs at which time the plant was completed. It can be seen from the given below that a sum almost equivalent to the revised cost has been spent on further developments and these expenses have been incurred in the last three financial years.

The funding for this wastewater treatment plant has come in the following pattern and these are current figures as on date.

In terms of percentage:

In may 1991, the plant was commission, with member tanneries being gradually connected to the conveyance main of CETP system and has been in operation since such time. It was later, officially inaugurated by the then Chief Minister of Tamil Nadu, Dr. J.Jayalalitha on the 10^th September 1994

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This CETP caters to the wastewater needs of a cluster of 110 tanneries. It is designed to accommodate 290 cubic meters of saline wastes and 2, 832 cubic meters of composite effluents.

The design of the CETP envisage the segregation of tannery wastewaters into two streams-saline wastewater that would be charged in impervious pans and solar evaporated and the composite effluent would undergo a physicals, chemical and biological treatment for the reduction of organic pollution loads in the waste stream.

The segregated wastewaters in the tanneries are carried, by gravity, through underground sever and flow into two pumping stations from whence it is pumped to the site of the Common Effluent Treatment Plant. Where the topography does not permit the flow of wastewater by gravity, tow lift stations are located at vantage points from where they are pumped through a pressure line to the main pumping stations.

In the site, the saline wastewaters are directly charged into impervious pans and allowed to solar evaporate. This CETP has a central solar evaporation facility and has the largest pan area available in the country pertaining to such an application in the leather industry. The total pan area measures about 65, 000 square meters eveuaivalent to nearly 7,00,000 square feet!

The composite effluents are collected in an equalization tank and as the name suggests, the wastewater are thoroughly-mixed and equalized. Equalization is essential as biological treatment systems cannot absorb the swinging chocks of alkalinity and acidity. The effluent is now pumped throu screen chambers that removes coarse particles like hair, fleshings, scraps of skin and other waste. Before the passage through the screens, the volume of waste waster is measured by means of an electromagnetic flow meter and logged onto the computer designed with a specific program to handle this data. The computer provides the operator instantaneous as well as cumulative readings for the day that has transpired.

The wastewater now moves on to the stage where chemical treatment is effected by adding such chemicals that promote the coagulation of suspended solids, thereby aggregating and settling to the bottom of the primary clarifier from where it is under-drawn as primary sludge. This primary sludge is pumped into sludge-drying beds and dried using freely available solar heat.

The supernatant from the primary clarifier flows to the anaerobic lagoon that is designed with a retention time of 10 days and a BOD-reduction efficiency of about 60-65%. The organic waste having been digested to the extent of efficiency of the anaerobic lagoon, now flows into an aerobic lagoon with designed retention time of 5 days equivalent to the total inflow into the CETP. Four fixed surface aerators with a power of 200 HP provide the aerobic bacteria its oxygen requirements. As this aerobic lagoon works in conjunction with the anaerobic lagoon, it is inevitable that sizeable levels of regenerated sulfides flow into the former. Hence, two floating aerators of 15 hp capacity each are placed in the aerobic lagoon and at points that would oxidizes the sulphides into sulphates. It should be noted that the major degradation of organic waste present in tannery wastewater have been cleaned-up at this stage. The aerobic bacteria present in the second aerobic lagoon safely and completely digest that quantum of organic load that has escaped these two lagoons. The chance of organic loads escaping further is very minimal unless there is a major operation and maintenance hitch or failure.

The nearly-clean water flows into the final clarifier where the mixed-liquor suspended solids settle at the bottom and are periodically drawn into the recirculation sump and recycled back into the aerobic lagoons. The treated water flows through an underground pipeline into the branch of the River Palar almost about 500 meters away from the CETP site.

The CETP has an analytical laboratory staffed by competent chemistry graduates and post-graduates. Samples are drawn, and composited, at key points down the treatment system and results are analyzed on daily basis. The results of these findings are graphically represented in a computer program and is available for display and scrutiny and is also used a diagnostic tool.

The treatment effected in this CETP has been meeting standards set by the Tamil Nadu Pollution Control Board, except the case of TDS, Chlorides and sulphates.

While practically operating and maintaining the CETP since the last seven years, the management has learnt invaluable lessons which need to be addressed with little loss of time. The following are some of the schemes that are in mind in order that we have the CETP operating at the best possible efficiency and at the same time, providing results in a consistent and reliable fashion.

• Rotating mechanical screens, positioned prior to the equalization tank would filter out coarse particles and debris in the wastewater, thereby increasing the life of the pump-sets and their efficiencies. COST ; Rs: 18 lakhs
• Primary sludge-drying, using sludge-drying beds and direct solar heat, are fine during the summer months. On the other hands, during the course of the monsoon months primary sludge are very difficult to dry and as a matter of fact, they are wet and difficult to dispose-off. Hence it is proposed to install a mechanical de-watering device for these primary sludge in the shape and form of a plate-and-Frame Filter Press. With such a device in place, it is anticipated that the suspended solids load that would otherwise travel to the anaerobic lagoon could be effectively controlled. The Plate-and-Frames Filter Press would also go a long way in improving the general hygiene in and around the CETP due to less of odor generation that is other wise caused by the septic conditions prevalent in sludge-drying beds. COST: Rs. 60 lakhs
• A pressure-sand filter working in tandem with an activated-carbon filter is proposed to be added after the final clarifier in order that any excess of suspended matter that would otherwise escape, would get trapped in the filters and be periodically back-washed. It is also envisaged that in the event of any low-key process failure, tandem filters would be able to accommodate such shocks and yet, continue to comply with the standards set by the Pollution Control Board, except in the case of TDS, Chlorides and sulphates COST: Rs. 20 lakhs
• For the more constructive use of treated discharge waters, a pilot study under the guidance of the Land Management systems of the National Environmental Engineering Research Institute, Nagpur, has been conducted using species of plants that fall under the agro-forestry category. In this case, the results have been encouraging and the management has proposed to cultivate species like neem, karang, casuarina, eucalyptus, acacia etc. in a land measuring about 10 acres. If this experiment on a larger scale is productive, the CETP system would then contemplate measures that would try and utilize its treated discharge waters for the purpose of converting the area in an afforestation project. COST: Rs. 75 lakhs
• The Company had recently held an Extra ordinary General Meeting of its member-companies with a view to raise additional share capital that would be utilized to develop a temporary but safe and secure land fill in a site with the CETP premise. The Company has written to the Tamil Nadu Pollution Control Board about this proposal and is awaiting its permission in order that work may be started on this front. In this way, it is proposed to dispose-off solid wastes generated by the Company's CETPs as well as that generated by its member-tanneries, in a safe and scientific manner. The design for the construction of this safe and secure land-fill site has come from the National Environment Engineering Research Institute, Nagpur and it is anticipated that it would meticulously followed in order that its full benefits are derived. COST: Rs. 55 lakhs.