INTRODUCTION TO THE TREATMENT OF TANNERY EFFLUENTS every tanner What every tanner should know about effluent treatment U nited N ations I ndustrial D evelopment O rganization Part V J. Buljan, I. Kral Compiled by J. Buljan, I. Kral

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

Poisoning effects of hydrogen sulphide gas (H 2 S) Mixing of liming and tanning streams results in: Obnoxious smell typical for poorly managed tanneries Much worse: lethally poisonous gas hydrogen sulphide (H 2 S), the most frequent killer in tannery accidents (mainly in inadequately ventilated spaces, pits and channels) Hydrogen sulphide (H 2 S): 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.

Poisoning effects of hydrogen sulphide gas (H 2 S) Exposure [ppm]Time Impact on unprotected person 0.03 No time limitNo effect 0.08 – 2.0 No time limit(Mal)odour threshold 10 Up to 8 hoursNo effect 15 Up to 15 minutesThreshold limit value Up to 15 minutesHeadache, nausea, general weakness, pain in legs minuteIrritation of nose & throat, vertigo, blurring of vision, loss of consciousness lasting a few minutes minuteProfound coma, convulsions, disorientation after recovery > minuteInstant coma and death ppm = parts per million

Recent changes of the recommended chronic exposure limits to H 2 S In view of new toxicological data, some countries have started reducing the recommended chronic exposure limits to hydrogen sulphide. Threshold Limit Value (TLV-TWA 8 ) 8 hour time weighted average From 10 ppm → to 1 ppm Short Term Exposure Limit (TLV-STEL) From 15 ppm → to 5 ppm

Instruments measuring H 2 S presence  Fixed  Portable  Personal detectors Due to nearly permanent life threatening hazard: H 2 S meters have to be permanently positioned at critical points and/or carried by staff Entering pits only in presence of skilled supervisor, the worker equipped with safety harness.

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

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

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

Computation and distribution of (C)ETP running costs In an individual tannery it is quite straightforward. Computation, and in particular, distribution of CETP running (operation) costs among individual tanneries is quite complex. The key parameters typically used for computation/distribution of CETP costs Water consumption, m 3 /day Production capacity, tonnes of wet salted hides/day Actual pollution load in terms of COD (even better COD destroyed!), suspended solids, sulphide and chromium Production output, m 2 /day of wet blue, crust or finished leather In developing countries Typically based solely on effluent volume and type of tanning In Italy Very sophisticated, primarily based on pollution load parameters

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.

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.

Example of the CETP management set up

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.

Main outstanding issues – 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. energy intensive Desalination of treated effluent by reverse osmosis (RO) is energy intensive and thus very expensive.

Main outstanding issues – 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?).

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)