I List of contents Content Page List of contents I Acknowledgment VI Abstract in English VII Abstract in Arabic IX List of tables XI List of figures XIII Nomenclature XVI Abbreviations and Acronyms XVII Chapter one 1 1. Introduction 1 1.1. General Background 1 1.2. Afrotan Tannery Company 4 1.3. The objectives 7 1.3.1. General objectives 7 1.3.2. Specific objectives 7 2. Chapter two 8 2.1. General information on the structure of the leather industry 8 2.2. Hides and skins 9 2.3. Leather Manufacturing Process 9 2.3.1. Process of tanning 9 2.3.1.1 Pre-tanning operations 10 2.3.1.1.1. Raw hides/skins 10 2.3.1.1.2. Sorting 11 2.3.1.1.3. Trimming 11 II 2.3.1.1.4. Curing and storing 11 2.3.1.1.5. Soaking 11 2.3.1.1.6. Liming 12 2.3.1.1.7. Fleshing 13 2.3.1.1.8. De–liming 14 2.3.1.1.9. Pickling 14 2.3.1.2 Tanning operations 14 2.3.1.2.1. Chrome tanning 14 2.3.1.2.2. Vegetable tanning 15 2.3.1.3 Post-tanning operations 15 2.4. Tannery waste water and effluents 15 2.4.1. Input Vs output in the tannery process 16 2.4.2 Parameters control in tannery waste Water 17 2.4.4. Environmental effects of the main constituents of tannery effluents 18 2.4.4.1. Solids 18 2.4.4.1.1. Suspended solids 18 2.4.4.1.1.1. Solids with a rapid settling rate (settle able solids) 19 2.4.4.1.1.2. Semi-colloidal solids 19 2.4.4.1.2. Gross solids 19 2.4.4.2. Oxygen demand 20 2.4.4.2.1. Biochemical oxygen demand (BOD5) 21 2.4.4.2.2. Chemical oxygen demand (COD) 21 2.4.4.3. Nitrogen 22 2.4.4.3.1. Total Kjeldahl nitrogen (TKN) 22 2.4.4.4. Sulphides (S2-) 23 III 2.4.4.5. Neutral salts 23 2.4.4.5.1. Sulphates (SO4)2- 24 2.4.4.5.2. Chlorides (Cl-) 24 2.4.4.6. Oils and grease 25 2.4.4.7. pH value 26 2.4.4.8. Chromium compounds 26 2.4.4.8.1. Chrome 3+ (trivalent chrome, chrome III) 26 2.4.4.8.2. Chrome 6+ (hexavalent chrome, chrome VI) 27 2.5. Treatment of tannery waste water 27 2.5.1. Preliminary treatment 29 2.5.2. Physical-chemical treatment (primary) 29 2.5.3. Biological treatment (secondary) 29 2.5.4. Advanced (tertiary) treatment 30 2.5.5. Chromium treatment 30 2.5.5.1. Chromium removal 31 2.5.5.2. Direct chrome recycling 31 2.5.5.2.1. Recycling Techniques 31 2.5.5.3. Chrome recovery 34 2.5.5.3.1. Recovery/reuse techniques 34 2.5.5.4. Recovery/reuse efficiency 38 2.5.6. Sludge from tannery waste water treatment plants 39 2.5.6.1. Land filling of sludge 40 2.5.6.2. Land filling with pretreatment 41 Chapter three 43 3. Materials and Methods 43 3.1. General waste water treatment unit 43 IV 3.1.1. Equipment and chemicals in general waste water treatment unit 44 3.1.2. Process description in general waste water treatment unit 44 3.1.3. Measurement and analysis in general waste water treatment unit 45 3.2. Liming recovery unit 46 3.2.1. Equipment used in liming recovery unit: 46 3.2.2. Process description in liming liquor recovery unit 46 3.2.3. Measurements and analysis in liming recovery unit 46 3.3. Chromium recovery unit 46 3.3.1. Equipment and chemicals in chromium recovery unit 47 3.3.2. Process description in chrome recovery unit 47 3.3.3. Measurements and analysis in chrome recovery unit 47 3.4. Sludge treatment and dewatering unit 48 3.5. Environmental impacts of Afrotan tannery effluents 50 3.5.1. Afrotan tannery drinking water wells 50 3.5.2. Chromium in soil 54 Chapter four 55 Results and discussions 55 3.1. Results 55 4.1.1. General waste water treatment unit 55 4.1.2. Liming recovery unit 59 4.1.3. Chromium recovery unit 64 4.1.4. Sludge treatment and dewatering unit 68 4.1.5. Tannery effluents in tannery drinking water wells 73 V 4.1.5.1. Anions in the tannery drinking water 74 4.1.5.2. Cations in the tannery drinking water 75 4.1.6. Detection of chromium in soil 76 4.2. Discussions 77 4.2.1. In general waste water treatment unit 77 4.2.2. 4.2.2. Liming recovery unit 80 4.2.3. 4.2.3. Chromium recovery unit 81 4.2.4. 4.2.4. Sludge treatment and dewatering unit 82 4.2.5. 4.2.5. Detection of the tannery effluents in tannery drinking water wells 84 4.2.6. 4.2.6. Chromium in soil 88 Chapter five 89 5. Conclusion and Recommendations 89 5.1. Conclusion 89 5.2. Recommendations 92 References 93 Appendices, Papers published from this thesis 101 VI Acknowledgement Many thanks to Afrotan Tannery Company, Construction and Environmental laboratories and Khartoum State Water Corporation for kind support and their cooperating during the experimental procedures. Thanks are also due to Prof Gurashi and Dr Abdalsalaam for their help and support. Also thanks to any person for helping me. VII ABSTRACT Afrotan tannery was established in 1983, in Albagair Area- AlGazira State - Sudan. It tans about 20000 hide per day. It has four units of wastewater treatment. The wastewater of soaking, deliming, fleshing (washing water) and cleaning processes is treated in general waste water treatment unit. The wastewater of un hairing and liming processes is treated in liming recovery unit. The wastewater of tanning processes is treated in chromium recovery unit. The sludge precipitated in sedimentation tanks of these units is treated in sludge treatment and dewatering unit. The objective of this study is to evaluate the efficiency of the methods of treatment and recycling applied in these four units and to assess the environmental impact for these units. The analysis was carried out by using the standards methods for the Examination of Water and Waste Water, Edition 20, (1998). The results showed that, the general wastewater treatment unit receives 1000 m3/day of wastewater. 300 m3/day of this quantity is precipitated as sludge in sedimentation tanks. 700 m3/day is the amount of treated water. 280 m3/day of this treated water is reused in production line and the remaining (420 m3/day) is ditched in land. The removal rates of deliming process substances and chlorides are very low. The removal of deliming process substances in biological oxidation tank increases the treatment cost. The study recommended that waste water of deliming process should be separated, treated and recycled directly. The liming recovery unit receives 300 m3/day of spent liming liquor. 140 m3/day of the quantity is floated and precipitated as sludge. 60 VIII m3/day of this sludge is directly burred in landfills contaminating the soil with sulphide. 160 m3/day of the quantity is the amount of treated liming liquor which is mixed with fresh makeup solution and recycled. The study recommended that further studies to reduce organic loads should be conducted and all sludge should be sent to the sludge treatment unit. The results showed that the chromium recovery unit receives 40 m3/day of spent chromium liquor. Just 1.2 m3 /day of the quantity is recovered and converted to basic chromium sulphate which is reusable. The remaining 38.8 m3/day is supernatant which is sent to general waste water treatment unit and the chromium is precipitated with sludge in sedimentation tanks. For proper chrome treatment, it is recommended that chrome recovery method must be replaced by the direct chrome recycling method. The sludge treatment unit receives 380m3/day of slurry sludge. After treatment and dewatering, 80m3/day of sludge is burred in landfills which it contains chrome, sulphides, chloride and others. The study recommended that sludge should not burred in landfills and also further studies should be conducted to utilize this sludge as fertilizer or in any other purposes. The results showed that there is no contamination by tannery wastewater in the tannery drinking water wells. The study recommended that periodic tests for tannery drinking water must be regularly run and the samples should be taken directly from the well. IX المستخلص تدبغ السودان. –ولاية الجزيرة -بمنطقة الباقير 3891فروتان عام مدبغة ا أنشأت الجتع مياة العادمة.الالمدبغة اربعة وحدات لمعالجة بجلد فى اليوم. 02222المدبغة والنظافة )مياه الغسيل( البلل، ازالة الجير، التلحيممن عمليات المياه العادمة الناتجة الة از اتمن عمليالمياه العادمة الناتجة تعالج فى وحدة معالجة المياه العادمة العامة. مليات من عالمياه العادمة الناتجة تعالجالشعر و التجيير فى وحدة استرجاع الجير. ب لهذه اوعية الترسي فىالحمأه المترسبة تعالج الدباغة فى وحدة استرجاع الكروم. الحمأه. وتجفيف الوحدات فى وحدة معالجة ذه التدوير المتبعة فى ه عادةإطرق المعالجة و كفاءة الدراسة هو تقييممن هدفال . وحداتالاثر البيئى لهذه ال وتقييمالاربعة الوحدات نسخة جريت التحاليل بواسطة الطرق القياسية لاختبارات المياة والمياة العادمة الإ .3889العشرين لسنة أوضحت النتائج ان وحدة معالجة المياه العادمة العامة تستقبل 3222م1 فى اليوم من المياه العادمة. يترسب 122م1 فى اليوم من هذه الكمية كحمأه فى اوعية الترسيب. 022م1 فى اليوم هى كميه المياه المعالجة. يعاد استخدام 092م1 فى اليوم من هذه المياة المعالجة فى خط الانتاج، والباقى )002م1 فى اليوم( يطرح فى الارض. ان ملية مواد ع التخلص من .والكلوريدات منخفضة رمواد عملية ازالة الجيمعدلات ازالة سه وصت الدراأازالة الجير فى وعاء الاكسدة الحيوى تزيد من تكاليف المعالجة. ها.استخدام التدويرالمباشر لمعالجتها ومياه عملية ازالة الجير العادمة وفصل ب تستقبل وحدة استرجاع الجير 122م1 فى اليوم من محلول الجير المستعمل. يطفو ويترسب كحمأه 302م1 فى اليوم من الكميه. 02 م1 فى اليوم من هذه الحمأه تدفن فى الارض مباشرة وتلوث التربة بالكبريتيد. تبلغ كميه محلول الجير المعالجة 302م1 فى .تدويرهاويعاد الطازج حضرستالم المحلولوالتى تخلط مع اليوم لانقاص الاحمال العضوية وارسال كل اضافية باجراء دراسات وصت الدراسهأ الحمأه الى وحدة معالجة الحمأه. تستقبل وحدة استرجاع الكروم 02 م1 فى اليوم من محلول الكروم المستعمل. X فقط 3.0 م1 فى اليوم من الكمية يسترد ويتحول الى كبريتات الكروم و يعاد استخدامه. الباقى 19.9م1 فى اليوم هو الطاف )السوبرنيت( الذى يرسل الى وحدة روم مع الحمأه فى اوعية الترسيب.معالجة المياه العادمة العادمة ويترسب الك م استرجاع الكرو طريقةوجوب إستبدال اوصت الدراسة بلمعالجة ناجعة للكروم المباشر للكروم. أعادة التدويرطريقة ب تستقبل وحدة معالجة الحماه 192 م1 فى اليوم من الحمأه المائع. بعد المعالجة وازالة الماء، يدفن 92م1 فى اليوم من الحماه وهى تحتوى على الكروم والكبريتيد بمنع دفن الحمأة فى الارض الدراسة وصتأ . فى الارضوالكلوريدات وغيرها اى اغراض اخرى. فى او كسماد الحمأة ستخداملإدراسات اخرى ءجراإوب . المدبغةمياه الشرب المبنية ببار لأ تلوث مياه الدباغة العادمة وضحت النتائج عدمأ نتظامبإ يجب ان تجرى غةدورية لمياه الشرب بالمدبالختبارات أن الاوصت الدراسة بأ مباشرة. بئرن يتم اخذ العينات من الأو XI List of tables Content Page Table 2.1: Composition of tannery waste water 18 Table2.2. Effluent treatment methods used by tanneries 28 Table.3.1. Equipment of general waste water treatment unit 44 Table.3.2. Chemicals of general waste water treatment unit 44 Table.3.3. Equipment in liming liquor recovery unit 46 Table 3.4. Equipment in chrome recovery unit 47 Table.3.5. Chemicals in chromium recovery unit 47 Table.3.6. Parameters measurement and samples points in chrome recovery unit 48 Table. 4.1. Results of parameters measured from primary sediment tank outlet 57 Table.4.2. Results of parameters measured from biological tank outlet 57 Table.4.3. Results of parameters measured from tertiary sediment tank outlet 57 Table.4.4. Quantity of waste water and consumption of chemicals in general waste water treatment unit 59 Table.4.5. Inlet versus outlet in liming recovery unit 64 Table.4.6. Analysis of spent chromium liquor from tanning drums outlet 66 Table.4.7. Analysis of liquor in neutralization and acidification tanks 66 Table.4.8. Inlet vs. outlet in chromium recovery unit 68 Table.4.9. Results of TVS, Cl, Al and NH4 measured in slurry 70 XII sludge (before treatment) and in dewatered sludge (after treatment) Table.4.10. Results of chemicals consumption and inlets vs. outlets in sludge dewatering unit 72 Table.4.11. Results of physical parameters measured in the tannery drinking water wells 73 XIII List of figures Content Page Figure 2.1 tanning process flow sheet 10 Figure 2.2 Input vs. Output in the Tanneries 17 Figure 2.3. Recycling of spent tanning float to pickling 32 Figure 2.4.Separate recycling of spent pickling and tanning floats 32 Figure 2.5. Recycling of tanning floats to pre-tanning and tanning 32 Figure 2.6. Separate recycling of spent tanning floats and samm water 33 Figure 2.7. Flow Diagram of chrome recovery by precipitation with sodium hydroxide/carbonate 35 Figure 2.8. Flow diagram of chrome recovery by precipitation with magnesium oxide 36 Figure 4.1. Flow diagram of general waste water treatment unit (inputs vs. outputs) 56 Figure 4.2. Values of pH and TSS (mg/l) at primary (series 1), biological oxidation (series 2) and tertiary (series 3) sedimentation tanks outlet. 58 Figure 4.3. Values of COD, Cl and SO4 in (mg/l) at primary (series 1), biological oxidation (series 2) and tertiary (series 3) sedimentation tanks outlet. 58 Figure 4.4. Values of NH4 (series 1) and NO3 (series 2) in (mg/l) at primary (1), biological oxidation (2) and tertiary (3) sedimentation tanks outlet. 58 XIV Figure.4.5. Flow diagram of liming liquor recovery unit (inputs vs. outputs m3) 60 Figure 4.6. pH of liming liquor before (1) and after (2) treatment 61 Figure 4.7. Concentration of TSS (1), Cl (2) in mg/l in liming liquor before (series 1) and after (series 2) treatment 61 Figure 4.8. Concentration of NH4 in mg/l in liming liquor before (1) and after (2) treatment 62 Figure 4.9. Concentration of COD in mg/l in liming liquor before (1) and after (2) treatment 62 Figure 4.10. Concentration of sulfides in mg/l in liming liquor after treatment (series 1) 63 Figure 4.11. Amount of treated liming liquor and sludge in liming recovery unit 63 Figure 4.12. Flow diagram of chrome recovery unit (inlets vs. outlets) 65 Figure 4.13. pH of spent chromium liquor during recovery processes 67 Figure 4.14. Inlet vs. outlet in chrome recovery unit 67 Figure.4.15. Flow diagram of sludge dewatering unit (inlets vs. outlet ) 69 Figure4.16. BOD (1) & COD (2) mg/l in slurry sludge (series 1) and dewatered sludge (series 2). 70 Figure 4.17. NH3 (1) and NO3 (2) mg/kg in slurry sludge (series 1) and dewatered sludge (series 2) 70 Figure4.18. SO3 (1) & SO4 (2) % in slurry sludge (series 1) and dewatered sludge (series 2) 71 Figure 4.19. Fe (1), Ca (2), Na (3), K (4), and Cr (5) mg/l in slurry sludge (series 1) and dewatered sludge (series 2) 71 XV Figure4.20. Al (1), Cr (2), Mn (3) and Fe (4) mg/l in the tannery drinking water (series 1) and the permissible level of Sudanese Standard Specifications of above anions for drinking water (series 2) 74 Figure 4.21. K (1), Na (2), Mg (3) and Ca (4) mg/l in the tannery drinking water (series 1) and the permissible level of Sudanese Standard Specifications of above anions for drinking water (series 2). 74 Figure 4.22. NO3 (1), SO4 (2) and Cl (3) mg/l in the tannery drinking water (series 1) and the permissible level of Sudanese Standard Specifications of above cations for drinking water (series 2) 75 Figure4.23. NO2 (1), F (2) and PO4 (3) mg/l in the tannery drinking water (series 1) and the permissible level of Sudanese Standard Specifications for drinking water (series 2) 75 Figure 4.24. Cr (mg/l) in soil in depth 0.5 m (series 1), depth 1.5 m (series2) and depth 3 m (series3) 76 XVI Nomenclature Afrotan Tannery Company It is one of the big tanneries in Sudan. It was established in 1983 in ELgazira State – Giad Industrial Area in Albageer City. It tans about 20000 skins per day (13000 sheep & 7000 goat). It consumes high quantity of fresh water and produces high quantity of waste water. Beside the tannery there are four units for waste water treatment. General waste water The waste water generated from soaking, deliming, bating, general cleaning and fleshing washing wastewater processes. General waste water unit The unit for treatment of general waste water. Liming liquor (solution) The waste water generated from un hairing and liming processes. Liming recovery unit The unit for treatment of liming liquor (solution). Chrome liquor (solution) The waste water generated from pickling and chrome tanning and re tanning processes. Chrome recovery unit The unit for treatment of liming liquor (solution). Tannery sludge Sludge generated from the bottoms of the sedimentation tanks of general waste water treatment and liming recovery units. Sludge treatment and dewatering unit The unit for treatment and dewatering of sedimentation tanks sludge. XVII Abbreviations Al2 (SO4)3 Aluminum sulphates APHA American public health association BAT Best available technique BOD Biochemical oxygen demand CCP Cleaner Production program CETPs Common effluent treatment plants COD Chemical oxygen demand CCME Canadian Council of Ministers of the Environment Cl- Chlorides CO2 Carbon dioxide Cr Chromium Cr2 (SO4)3 Chromium sulphate EC European Commission EPA Environmental Protection Agency IPCC Intergovernmental Panel on Climate Change IPCS International Program on Chemical Safety IPPC Integrated Pollution Prevention and Control Kg Kilogram MOEF Ministry of Environment and Forest NH4 Ammonia NEQS National Environmental Quality Standards NO3 Nitrates XVIII NTU Nephelometric Turbidity Unit PPM Part per million SO3 2- Sulfites SO4 Sulfates SSMO Sudanese Standards & Metrology Organization pH Hydrogen ions TCU True Color Unit TDS Total dissolved solids TSS Total suspended solids TVS Total volatile solids WHO World Health Organization