INTRODUCTION TO THE TREATMENT OF TANNERY EFFLUENTS Introduction to treatment of tannery effluent - Part 1 (of 6) United Nations Industrial Development Organization INTRODUCTION TO THE TREATMENT OF TANNERY EFFLUENTS What every tanner should know about effluent treatment Part II Compiled by J. Buljan, I. Kral United Nations Industrial Development Organization (UNIDO) 1

2. Treatment within tannery compound Introduction to treatment of tannery effluent - Part 2 (of 6) 2. Treatment within tannery compound Pre-treatment for discharge into CETP collection network  Screening Grit & grease chamber Physical-mechanical (primary) treatment for discharge into municipal sewage  Lifting – lifting pumps Equalization – homogenization, ejectors pH adjustment, coagulation, flocculation Primary clarification/flotation Flow-chart of the physical-chemical (primary) treatment Objectives:  To eliminate the coarse material normally present in the raw wastewater that could clog/block pumps, pipes and, possibly, sewer lines To well mix & balance different tannery streams and thus produce homogenised “raw material” that can be treated in a constant way To adjust pH and eliminate toxic substances (sulphides) and/or shock loads that could negatively affect the rather sensitive biological treatment To significantly decrease the BOD/COD load and thus reduce the cost of and simplify the biological treatment phase.   In short: to eliminate the coarse matter, nearly remove Cr and sulphide, remove the major part of Suspended Solids, considerably reduce the BOD and COD content.    Basic steps: 1. Screening (bar, grease and sand trap, self-cleaning, rotary) 2. Pumping/lifting 3. Equalisation &sulphide oxidation 4. Chemical treatment (coagulation, flocculation) 5. Settling 6. Sludge dewatering United Nations Industrial Development Organization (UNIDO)

Introduction to treatment of tannery effluent - Part 2 (of 6) ROUGH BAR SCREEN Introduction to treatment of tannery effluent - Part 2 (of 6) rake Collected solids bar screen CHANNEL The importance of good screening, including its role in protecting the treatment equipment cannot be overemphasised. Raw effluent From TANNERY Screened effluent To TREATMENT United Nations Industrial Development Organization (UNIDO)

Introduction to treatment of tannery effluent - Part 2 (of 6) BAR SCREEN CLEANING Manual Rotary curved 3600 Rotary curved 900 Auto chain Continuous chain raked The level of mechanization – automation at this stage obviously mainly depends on the size – plant capacity and labour and electricity costs. United Nations Industrial Development Organization (UNIDO)

NON-AERATED GRIT AND FLOATING MATTER REMOVAL CHAMBER Introduction to treatment of tannery effluent - Part 2 (of 6) NON-AERATED GRIT AND FLOATING MATTER REMOVAL CHAMBER Periodically to the sludge disposal site Screen 20 mm Screen 10 mm Screen 6 mm SLUDGE SCUM Removal of sand, grit and oil is essential to avoid difficulties like clogging, excessive wear and tear of equipment, inadequate aeration etc. at subsequent stages of the process. United Nations Industrial Development Organization (UNIDO)

SELF-CLEANING SCREEN PARKWOOD TYPE Introduction to treatment of tannery effluent - Part 2 (of 6) SELF-CLEANING SCREEN PARKWOOD TYPE Effluent inflow Ready to install factory made Parkwood type screen. Many small tanneries have self-made units. United Nations Industrial Development Organization (UNIDO)

SUBMERSIBLE PUMP FOR EFFLUENT LIFTING Introduction to treatment of tannery effluent - Part 2 (of 6) SUBMERSIBLE PUMP FOR EFFLUENT LIFTING Pump maintenance Lifting chain The pump can be brought to the ground inspection/maintenance/repair without emptying the tank/pit. For that purpose essential is good functioning of the special arrangement (not quite visible in this sketch) for easy decoupling and re-coupling of the pump. Pump Water inlet United Nations Industrial Development Organization (UNIDO)

ROTARY DRUM SCREEN KONICA TYPE – outer flow Introduction to treatment of tannery effluent - Part 2 (of 6) ROTARY DRUM SCREEN KONICA TYPE – outer flow WASTWATER INLET WITH SUSPENDED SOLIDS Filtering gap Trapezoidal shaped bars As a rule, fine screening is the next step after effluent lifting. Drum design should ensure avoidance of clogging and easy washing. SOLIDS RECOVERY FILTERED WATER DISCHARGE United Nations Industrial Development Organization (UNIDO)

Rotary fine screen (inner flow) Introduction to treatment of tannery effluent - Part 2 (of 6) Brush Raw effluent Solids Internal screw A different flow principle but again the drum design should ensure avoidance of clogging and easy washing. Filtering panel Filtered effluent United Nations Industrial Development Organization (UNIDO)

ROTARY DRUM SCREEN In some cases a different design with solids lifted/transported by the screw can be preferred.

Screw (Archimedes) type pump for effluent lifting Effluent intake The principle Driving mechanism A different effluent lifting concept, robust and reliable, suitable for large volumes.

Screw (Archimedes) type pump for effluent lifting Introduction to treatment of tannery effluent - Part 2 (of 6) Screw (Archimedes) type pump for effluent lifting A typical installation and modus operandi of Archimedes screw pump. United Nations Industrial Development Organization (UNIDO)

Equalization – homogenization tank Schematic view Introduction to treatment of tannery effluent - Part 2 (of 6) Equalization – homogenization tank Schematic view Continuous level measuring Pump dry protection level Bypass TO SUCCESSIVE TREATMENT High level alarm EFFLUENT INFLOW Free board Well homogenized, uniform effluent is a precondition for successful subsequent treatment. Its volume usually corresponds to one day effluent discharge. Here the robust, Venturi type ejectors keep the remaining particles in suspension and provide the necessary aeration to prevent bad smell – reversal to sulphide. United Nations Industrial Development Organization (UNIDO)

Coagulation and flocculation (scheme) Introduction to treatment of tannery effluent - Part 2 (of 6) Service water POLY- ELECTROLYTE ALUM LIME Dosing pump Dosing pump Dosing pump DRAIN WASTEWATER INLET In order to improve and accelerate the settling of suspended solids, especially of the fine and colloidal matter coagulants such as industrial alum (Aluminium Sulphate Al2(SO4)3.18H2O) and flocculants - polyelectrolytes are added before sedimentators. The coagulants destabilize the colloids by neutralizing the forces that keep them apart resulting in creation of floc whereas flocculants bind them into large agglomerates or clumps. Usual dosage, industrial purity, in g/m3: manganese sulphate 30, aluminium sulphate (alum) 300, hydrated lime 300, anionic polyelectrolyte 1 g/m3 Proper dissolving essential. Note the difference in mixing speed in coagulation and flocculation tank, retention times differ as well. WASTEWATER OUTLET COAGULATION TANK FLOCCULATION TANK United Nations Industrial Development Organization (UNIDO)

Ejector for mixing and aeration Introduction to treatment of tannery effluent - Part 2 (of 6) Air inlet Wastewater Submersible pump Here we can better see in operation the Venturi type ejector mentioned earlier – providing both mixing and aeration effect. Air-wastewater mixture outlet Ejector Wastewater inlet United Nations Industrial Development Organization (UNIDO)

Type of sedimentation tanks Rectangular horizontal flow Sometimes, mainly for space and construction reasons rectangular shape for the sedimentator is preferred.

Type of sedimentation tanks Circular, radial-flow Circular, radial flow is possibly the preferred type of sedimentator in the tanning industry. Please note that here “feeding” is from the bottom to the surface and then radially, at calculated velocity to the edge and overflow. The slowly rotating arms scrape the sludge towards the collecting trough. Two main parameters are surface load in terms of effluent volume per surface area of the tank (m3/m2 of tank surface per hour or m/h, typically 1 - 2 m3/m2 per hour) and retention time, i.e. the total time effluent spends in the tank.

Type of sedimentation tanks Hopper-bottomed, upward-flow The advantage of sloped bottom sedimentation tank is that a rotating sludge scraper is not required.

Typical sedimentation tank Scraper bridge Scraper Here we can better see the overflow and the scraper bridge of the circular, up-flow sedimentator shown earlier.

Typical sedimentation tank Introduction to treatment of tannery effluent - Part 2 (of 6) Schematic cross-section view Drive Skimmer Scum trough Effluent Influent well Scum draw off In this circular sedimentator the influent flows through the pipe into influent well, particles/sludge accumulating at the bottom and being drawn away; cleaner effluent leaves via overflow/pipe, the scum is collected by the skimmer drawn at the opposite side. Scraper Influent Sludge concentrator Sludge draw-off United Nations Industrial Development Organization (UNIDO)

Rectangular sedimentation tank with travelling bridge Introduction to treatment of tannery effluent - Part 2 (of 6) Rectangular sedimentation tank with travelling bridge Scum trough TRAVELLING BRIDGE TRAVELLING BRIDGE Rail INFLUENT EFLUENT SLUDGE DRAWOFF Screw cross collector Here we can see the rectangular type of tank in operation: influent enters sidewise, particles/sludge accumulate at the bottom and are being drawn away; cleaner effluent leaves at the right hand side, the bridge slowly travels to and fro and pushes the sludge at the bottom and the scum (removed at the top). Sludge hopper United Nations Industrial Development Organization (UNIDO)

Dissolved air flotation unit (DAF) Introduction to treatment of tannery effluent - Part 2 (of 6) Floated sludge skimmer TREATED EFFLUENT RAW EFFLUENT Pressure release valve FLOTATED SLUDGE DRAWOFF AIR SETTLED SLUDGE PRESSURED RECYLE WTH DISSOLVED AIR Air saturation tank Due to characteristics of suspended solids and space reasons, instead of sedimentation the "opposite" process, flotation, is selected: air bubbles attached to particles lift them to surface to be subsequently skimmed, removed and dewatered. RECYCLE FLOW Recycle pump United Nations Industrial Development Organization (UNIDO)

Introduction to treatment of tannery effluent - Part 2 (of 6) Purification efficiency of the treatment stages referred to raw effluent Parameter Physical-chemical Biological Reduction Approx. value Reduction* % mg/l SS 80 – 90 300 – 600 95 – 98 20 – 50 BOD5 50 – 65 750 –1500 97 – 99 20 – 30 COD 1500 – 3000 87 – 93 250 – 400 TKN 40 – 50 250 – 300 60 – 70 100 – 200 Cr 92 – 97 5 – 10 99 – 99.5 < 1 S2- 10 – 20 TDS mainly Cl- and (SO4)2 No reduction It can be seen here that the best removal rates in the course of physical-chemical (primary) treatment are for Chromium, Suspended Solids and sulphide, i.e. 92-97 %, 80-90 % and 80-90 % respectively. *Approximately at the load level of 0.30 kg BOD5/kg MLSS, oxygen requirement of 2.0 kg O2/kg BOD5 and MLSS 3300 g/m3. United Nations Industrial Development Organization (UNIDO)