Process Description

The Member Tanneries of RANITEC spread over an area of 4-5 Sq.Km has constructed Pre-Treatment Unit (PTU) with Electro Magnetic Flow Metering System in their premises as per the design of CETP to record the flow, which undergoes screening and sedimentation in their PTU before discharging the effluent into the CETP.

The raw effluent discharged from different tanneries are conveyed to the CETP through underground sewer piping system laid about 15 KM with three pumping stations.

The effluent flows through a Mechanized Rake / Bar Screen (which screens solids > 6 mm) to the Receiving Sump, wherein a Submersible mixer is installed for complete mixing before transferred to the pre-settler unit for removal of easily settleable coarse solids.

The overflow from the pre-settler is passed through a rotary fine screen (which screens solids > 3 mm) before discharged into the Equalization Tanks wherein Mix flow systems are installed for homogenous mixing in the tank by injecting pure oxygen generated through Vacuum Swing Adsorption Technology - a latest technology adopted by separating pure oxygen from the atmosphere at onsite by Deployable Oxygen Concentration Systems (DOCS) which removes odour presence in the raw effluent and ensures the homogenous mixing of effluent before fed to the chemical treatment.

The effluent from the Equalization Tank is chemically treated with lime and alum in the flash mixer for coagulation and polyelectrolyte is added in the flocculator to facilitate flocculation of solids and equally distributed to the Primary Clarifier - I & II for the settling of the suspended solids.

The sludge settled in the clarifier is conveyed to the Filter Press for solid-liquid separation by mechanically dewatering. A pH of 8.0 to 8.2 is maintained in the Flash mixer to precipitate the chromium (Cr3+) present in the effluent as chromium hydroxide (Cr(OH)3).

The overflow from the Primary Clarifier-I is conveyed to the Biological Treatment System -I through the Pre-aeration tanks I & II for reducing 50-55% of Hydrogen Sulphide presence in the effluent by using Original Hydrodynamic Reaction (OHR) Aerators, a State-of-Art Technology.

Similarly, the overflow from the Primary Clarifier-II is conveyed to the Biological Treatment System-II in the Balancing tank followed by De-Nitrification to reduce the Ammoniacal Nitrogen into Nitrites and then Nitrates into Nitrogen gas presence in the effluent.

The effluents are further passed through an Extended Aeration Type Activated sludge process in Aeration tanks with the Hydraulic retention time of 1.8 days to maintain a D.O between 2.0 to 2.5 mg/lit and the performance is being monitored closely to ensure consistent COD & BOD reduction across the biological treatment system.

The effluent from the Biological Treatment System-I &II are equally distributed to 4 Nos. of Secondary Clarifier to maintain the Mixed Liquor Suspended Solids level and to further improve the effluent characteristics and colour, the effluent is passed through Pressure Sand Filters for removal of Total Suspended Solids (TSS) after the addition of Alum in the flash mixer and polyelectrolyte in the flocculator for the flocculation in the Tertiary Treatment System.

The secondary treated effluent reaching the RO system is first subjected to softening through lime-soda process in a reactivated clarifier and then neutralized from 8.2 to 7.0 by adding the HCl acid in Neutralization Tank. and fed The softened effluent is further filtered is fed to the Dual Media Filter (DMF) to for reduction of TSS & Turbidity level by using Activated Glass Fiber Media. A very fine filtration is obtained in the Ultra Filtration (UF) system engaging Poly-Vinyledene Flouride (PVDF) UF membranes for removal of TSS & Turbidity in the effluent and the same is collected in the RO feed tank which also reduces the backwash quantity.

The effluent from the RO feed tank is pumped through the Micron Cartridge Filter and fed to Reverse Osmosis (RO) (Spiral Membrane) stage-1 by using a high-pressure pump, the 50 % of permeate is recovered in the stage-1 and reject from the stage-1 is fed to the RO stage-2 by using a high-pressure pump with a turbocharger installed to increase the pressure without using power for the separation of inorganic content and recover 20% permeate from stage-2 RO System.

The entire UF and RO skids are automatically controlled through SCADA The 70% permeate water recovered from stage 1 & 2 are collected in the permeate tank and reject is collected in the HPRO Feed tank for neutralizing by adding HCl to reduce the PH from 7.5 to 6.5.

The neutralized effluent from HPRO Feed tank is pumped to 3rd Stage High-Pressure Reverse Osmosis (Disc Membrane) System followed by Nano-Filtration to recover 40% additional Permeate from the Spiral RO Reject and 50 % NaCl recovered from Nano Filtration, thereby the quantity of the Reject fed to the Evaporator has been reduced.

The RO Reject is fed to Multiple Effect Evaporator (MEE)-I having Seven Effect by using 4 stages of Falling Film & 3 stages of Forced Circulation technology. The effluent getting heated by feeding steam from the boiler to the 1st effect Calendria. The evaporated vapour is collected as the condensate and the final concentrated liquor is fed to centrifuge to separate salt and mother liquor. The mother liquor is recycled back to Calendria -6 for evaporation. The salt-laden solid residue is separated in a Pusher Centrifuge.

The Multiple Effect Evaporator (MEE)-II has installed with Seven Effect by using 3 stages of Falling Film & 4 stages of Forced Circulation technology to maintain the efficiency of ZLD System at all times.

The evaporated vapour is collected as the condensate and the final concentrated liquor is fed to centrifuge to separate salt and mother liquor. The mother liquor is passed through Agitated Thin Film Dryer to evaporate and collect the mixed salt. The Condensate is sent through Ammonia flash vessel to reduce the concentration of Ammonia presence in the Condensate.

The condensate from the MEE I & II is passed through the Ammonia Removal Module System by using microporous Hydrophobic Membranes, this system reduces the free Ammonia gas presence in the MEEs condensate.

Finally, the ammonia free Evaporator condensate water is mixed with RO Permeate water and recycled back to member tanneries for re-use in their process of tanning through a recovered water conveyance system with three Over Head Tanks at different locations in the cluster. Around 85-95% of the water is recovered from the Zero Liquid Discharge system.

The 10 to 15% of the recovered water is used in the boiler for generation of steam, cooling tower & chemical preparation purpose.