Presentation on theme: "INTRODUCTION TO THE TREATMENT OF TANNERY EFFLUENTS every tanner What every tanner should know about effluent treatment Part IV J. Buljan, I. Kral Compiled."— Presentation transcript:
INTRODUCTION TO THE TREATMENT OF TANNERY EFFLUENTS every tanner What every tanner should know about effluent treatment Part IV J. Buljan, I. Kral Compiled by J. Buljan, I. Kral U nited N ations I ndustrial D evelopment O rganization
4. Biological (secondary) treatment Activated sludge process – principle, parameters Aeration devices Oxidation ditch Flow-chart of the biological (secondary) treatment Flow-chart of the fully-fledged treatment
Activated sludge process AERATION TANK CLARIFIER Influent Effluent Sludge recirculation pump Sludge return Excess of sludge Q Air R Q+R
Activated sludge process Total Influent Volume, Q: Volume of the treated effluent [m 3/ day] Tank Volume, V: Aeration tank volume [m 3 ] Organic Loading, F: The total BOD 5 applied [kg/day] F = (f * Q)/1000 where f – the BOD 5 of the influent [mg/l] Mixed Liquor Suspended Solids, M: M = (MLSS * V)/1000 where MLSS - is the concentration of SS in Mixed Liquor in the aeration tank [mg/l] Loading factor, F/M: BOD 5 kg per day per kg of Mixed Liquor Suspended Solids (MLSS) in the aeration tank [mg/l]. Hydraulic retention time, T: T = (V/Q) * 24 where V – aeration tank volume [m 3 ]
Typical food to microorganisms (F/M) and oxygen to food ratios Process Extended aeration Conventional High rate Food to microorganisms F/M Oxygen to food kg O 2 /kg BOD
Other operational parameters Dissolved Oxygen, DO: The content of molecular oxygen in the aeration tank [mg O 2 /l]. Usually DO = mg O 2 /l. pH: The optimum pH range for aerobic process is Temperature: Affects the metabolic and growth rates of the organisms. Optimum: o C. Nutrients, desirable ratio: BOD : N : P = 100 : 5 : 1 Sludge Volume Index, SVI: Volume of 1 g of activated sludge after settling the aerated mixed liquor in a 1000 ml graduated cylinder or Imhoff cone for 30 min. Desired value < 100 ml/g.
Aeration devices 1.Surface aerators a)Radial flow, low speed, rpm b)Axial flow, high speed, rpm c)Brush rotor (oxidation ditch) 2.Submerged turbines 3.Diffused air a)Bubblers – porous and nonporous diffusers b)Tubular c)Jets (developed from Venturi ejectors) There are many types and subtypes of aerators, models being continuously improved. Here is an arbitrary classification of types frequently installed in tannery ETPs.
Classification of mechanical aerators
Surface (floating) aerators
Bubble bottom diffusers
Bottom diffusers in the oxidation ditch
Submersed turbine aerators in the oxidation ditch
Purification efficiency of the treatment stages referred to raw effluent Parameter Physical-chemicalBiological Reduction Approx. value Reduction* Approx. value %mg/l% SS BOD COD TKN Cr < 1 S < 1 TDS, mainly Cl - and (SO 4 ) 2- No reduction * Approximately at the load level of 0.30 kg BOD 5 /kg MLSS, oxygen requirement of 2.0 kg O 2 /kg BOD 5 and MLSS 3300 g/m 3.
FLOW MEASUREMENT CHANNEL END FLOW MEASURING WITH FLOW SUMMARISING TREATED EFFLUENT FOR DISCHARGE CHAMBER FILTER PRESS G SLUDGE THICKENER SLUDGE DRYING BEDS (optional) SECONDARY SLUDGE PUMPING STATION Biological treatment stage Biological treatment stage Simplified flow-chart SECONDARY SETTLING TANK BLOWER AIR Submersible pump Pump Motor Gate valve PRIMARY TREATED EFFLUENT AERATION TANK 1 AERATION TANK 2 (DIFFUSED AERATION SYSTEM)
MIXED EFFLUENT SERVICE WATER Drain CATALYST MnSO 4 ALUM LIME POLYELECTROLYTE EQUALIZATION TANK WITH PUMPING STATION (WITH EJECTORS FOR MIXING AND AERATION) COAGULATION TANK FLOCCULATION TANK PRIMARY SETTLING TANK FLOW MEASUREMENT CHANNEL END FLOW MEASURING WITH FLOW SUMMARISING TREATED EFFLUENT FOR DISCHARGE CHAMBER FILTER PRESS G SLUDGE THICKENER PRIMARY SLUDGE PUMPING STATION INLET PUMPING STATION FINE SCREEN AUTOMATIC COARSE SCREEN SECONDARY SETTLING TANK AERATION TANK 1 AERATION TANK 2 (DIFFUSED AERATION SYSTEM) BLOWER AIR SECONDARY SLUDGE PUMPING STATION Submersible pump Dosing pump Motor Ball valve Gate valve Agitator Pump Fully-fledged treatment system SLUDGE DRYING BEDS (optional)