TECHNICAL ISSUES IN STABILIZATION OF
THE MULTIPLE STAGE EVAPORATOR (MEE) IN PALLAVARAM CETP
- M/s.RAMKY through their vendor M/s.SSP Pvt. Ltd. installed seven stage (5 Falling film + 2 Forced circulation column) MEE for thermal evaporation, crystallization and recovery of salt from the RO saline reject during mid 2013.
- More than 30 full scale trials with RO reject were made for about 6 months during the second part of 2013 & early 2014.
- As per the common design by increasing the RO reject concentration with 7 columns to the level of 40% the precipitation and separation of salt is expected in the crystallizer.
- However, even after the increase in TDS to 50% level the crystallization has not taken place. SSP Ltd. tried various rearrangements, lab and pilot tests, change in mixing arrangement, etc. the vendor but could not make crystallization in the thickener and reported.
- The slurry type liquor taken for the thickener is taken to centrifuge for salt separation. Here also they could not reduce the moisture content and separate the salt.
- Turnkey contractor reported that crystallization could not be achieved due to low concentration of TDS and chlorides in the effluent (i.e. TDS level in the PTIETC CETP is around 5000 mg/l and which is the lowest in entire Tamilnadu CETPs).
- Large amount (1000 ltrs) of concentrated RO reject were sent to the vendors pilot applied R & D laboratory in Delhi for various trials and options.
- First they tried with alternative to the centrifuge with high speed decanter. But could not succeed in making the salt separation and the outcome was like a paste and it could not be packable for further disposal.
- Finally after exploring various options, they have recommended the option after evaporation is going for ATFD or Spray dryer. As per the proposal, it would take enormous energy and they not in a position to give any guarantee for the material balance and odour control.
- We have cross checked with various expert organizations, they have reported that spray dryer is not suitable for this type of RO reject with low TDS & chlorides and high inert and volatile organic matter.
- The lab and pilot studies made as per the advise of Department of Science and Technology using CSIR-CLRI laboratories could not found any viable solution.
- Turnkey contractor reported that crystallization could not be achieved due to low concentration of TDS and chlorides in the effluent (i.e. TDS level in the PTIETC CETP is around 5000 mg/l and which is the lowest in entire Tamilnadu CETPs) and requested for some alternative option for TDS management which is not under his perview and control.
- Large volume of samples were taken for pilot research field trials by the vendor for salt recovery using decanter instead of centrifuge. They could not succeed in getting baggable salt. Hence, this approach is dropped.
- Pilot studies were entrusted to CSIR-CLRI for reduction of organic matter in the saline reject to achieve salt. The studies made using solvent (i.e. alcohol) could not be adopted in the field in view of high volume of alcohol storage, additional infrastructure requirement for operation and safety aspect, etc.
- Full-scale retrials made in the evaporation system during January 2014 to middle of 2014 by making modifications in the system as suggested by various experts including operators of MEE in other similar CETPs. However, the crystallization and salt recovery could not be achieved even after more than 20 full-scale operation.
- Alternative options such as (ATFD) and Spray dryer were also studied and found not fit for PTIETC CETP condition due to huge energy requirement, odour emission, etc. Turnkey contractor and non of the vendors prepared to give guarantee for the options since it has not been tried for tannery effluent.
- Contractor expressed his inability in making the MEE fully operational in getting crystallization and salt.
- Pallavaram CETP is left with no other option to go in for mixing the treated tannery effluent with domestic wastewater for TDS management.
- Municipal administration of Pallavaram Municipality has given consent to utilize their sewage treatment system for dilution subject to approval of TNPCB.
- Pallavaram CETP request TNPCB to approve the universally followed and viable option of mixing the treated tannery effluent with the domestic sewage system which is currently available in Pallavaram area.
- The Municipal administration has also given consent to utilize the surplus capacity of conveyance and treatment system provided for their municipal sewerage system.
- Currently, the treated effluent is discharge through open canal which is leading to Adyar Backwater and Sea.
- PTIETC CETP request TNPCB to consider the viable option of discharging the treated effluent including colour removal with low TDS in to the existing system which is meeting the backwater / sea discharge standards. We also given undertaking the Pallavaram CETP will not carryout raw to semi-finishing operations which is generally the main cause for the pollutional discharge from the tanning industry.
- Alternatively, so we may be permitted to take the treated effluent along with the sewer line of Pallavaram Municipality which will lead to the Buckingham canal near the permitted discharge point for the treated domestic sewage for the southern part of Chennai city.
- Pallavaram CETP has submitted a proposal to DIPP, Govt. of India for further upgradation of their CETP including the infrastructure required for the alternative disposal of treated tannery effluent such as discharging to the backwater and mixing with treated domestic sewage, etc.
- DIPP has approved the project proposal of Pallavaram CETP for further upgradation at a cost of Rs.14.80crores subject to the consent from TNPCB.
- Kind submission that similar approvals have been accorded to Dindigul CETP and Madhavaram CETP in the leather sector.
- We request TNPCB to accord permission to discharge the treated tannery effluent by meeting sea discharge standards including colour removal.
