INTRODUCTION TO T HE T REATMENT OF TANNERY EFFLUENTS

1. INTRODUCTIONTOTHE TREATMENTOF TANNERY EFFLUENTS What every tanner should knowabout effluent treatment United NationsIndustrialDevelopmentOrganization Part V Compiled byJ. Buljan, I. Kral

2. 5. Occupational Safety and Health (OSH), [Common] Effluent Treatment Plant ([C]ETP) Costing and Management • Monitoring • Occupational safety and health at work • CETP collection network • CETP costing, cost distribution • Flow-chart of the fully-fledged treatment

3. Poisoning effectsof hydrogen sulphide gas (H2S) Mixing of liming and tanning streams results in:  • Obnoxious smell typical for poorly managed tanneries • Much worse: lethally poisonous gas hydrogen sulphide (H2S), the most frequent killer in tannery accidents(mainly in inadequately ventilated spaces, pits and channels) Hydrogen sulphide (H2S): • extremely toxic and irritating gas • strong odour of rotten eggs • paradoxically, it is felt only at lower concentrations. This explains the numerous accidents despite the well known fact about its toxicity.

4. Poisoning effectsof hydrogen sulphide gas (H2S) ppm = parts per million

5. Recent changes of the recommended chronic exposure limits to H2S In view of new toxicological data, some countries have started reducing the recommended chronic exposure limits to hydrogen sulphide.

6. Instrumentsmeasuring H2S presence • Fixed • Portable • Personal detectors Due to nearly permanent life threatening hazard: • H2S meters have to be permanently positioned at critical pointsand/or carried by staff • Entering pits only in presence of skilled supervisor, the worker equipped with safety harness.

7. general and specific measures concerning equipment and chemicals also apply to ETPs(protection from moving parts, fences, storing and handling of chemicals etc.) Otherwise,

8. Structure of the average total treatment costsin selected CETPs in India in 2005 The highest component ispower; sludge handling and disposal costs comparatively low. If the reverse osmosis (RO) stage for desalination is installed, the cost of energy escalates even further.

9. Distribution of average total costsin Italian CETPs In industrialized countries the largest cost component is dewatering and safe disposal of solids (sludge).

10. Computation and distributionof (C)ETP running costs • In an individual tannery itis quite straightforward. • Computation, and in particular, distribution of CETP running (operation) costs among individual tanneries is quite complex. The key parameters typically used forcomputation/distribution of CETP costs • Water consumption, m3/day • Production capacity, tonnes of wet salted hides/day • Actual pollution load in terms of COD (even better CODdestroyed!), suspended solids, sulphide and chromium • Production output, m2/day of wet blue, crust or finished leather

11. Computation & distribution of running costs in one CETP in India • Electromagnetic Flow Metering System installed in each operational tannery monitors the quantity of the effluent discharged. • The actual expenditure for the month is divided by the total flow to arrive at the unit cost for the month. • O & M costs of the CETP plant are covered by monthly contributions by the tannery members according to the quantity of effluent discharged.

12. Management Nowadays it is taken for granted that in a well managed tannery there is a person of appropriate background and seniority dealing only with increasingly complex environmental issues and the ETP in particular; in some countries it is a legal requirement.

13. Example of the CETPmanagement set up

14. General summary on treatment of tannery effluents • Treatment of tannery effluents is now a well established technology. • Modular type common effluent treatment plants CETPs to service traditional tannery clusters or newly set leather industry zones considered optimum solution. • ETPs for individual tanneries require a separate organizational unit lead by a well qualified person, preferably an environmental engineer. • Similarly, a CETP is run by an autonomous establishment – company supervised by a board comprising representatives of tanners association(s), EPA, NGO, residents etc. • Investment and operation costs vary a lot; as a rule the largest components is the biological treatment.

15. Main outstandingissues – challenges(I) High TDS (salinity) content, unaffected by treatment, especially where: • raw material input are hides and skins preserved by salting, • no scope for mixing with domestic sewage, • discharge into sea is not feasible, • relocation of the tanning industry to the sea side not feasible. Desalination of treated effluent by reverse osmosis (RO) is energy intensive and thus very expensive.

16. Main outstandingissues – challenges(II) Utilization or safe disposal of sludge At the moment this is the toughest problem in industrialized countries, increasingly difficult in developing countries too. A genuine breakthrough badly needed (modified gasification, vitrification, biodegradation?).

17. Submersible pump Dosing pump SERVICE WATER Pump POLYELECTROLYTE LIME ALUM CATALYST MnSO4 Motor Ball valve AIR Gate valve Agitator Drain Drain Drain Drain MIXED EFFLUENT BLOWER Fully-fledged treatment system AUTOMATIC COARSE SCREEN FINE SCREEN INLET PUMPING STATION EQUALIZATION TANKWITH PUMPING STATION (WITH EJECTORS FOR MIXING AND AERATION) AERATION TANK 1 AERATION TANK 2 (DIFFUSED AERATION SYSTEM) SECONDARY SETTLING TANK AIR AIR PRIMARY SETTLING TANK END FLOW MEASURING WITH FLOW SUMMARISING TREATED EFFLUENT FOR DISCHARGE FLOCCULATION TANK COAGULATION TANK FLOW MEASUREMENT CHANNEL G SLUDGE DRYING BEDS (optional) CHAMBER FILTER PRESS SECONDARY SLUDGE PUMPING STATION SLUDGE THICKENER PRIMARY SLUDGE PUMPING STATION