The Leather Sector... Environmental Report

Transcription

1 . The Leather Sector Environmental Report DRAFT i

2 Table of Contents Preface i Executive Summary 1 1. The Environmental Technology Programme for Industry Demonstration Project 2 2. The Leather Industry A Profile Raw Materials and Chemicals Raw Materials Processing Chemicals Water Process and Operation In-House Environmental Conditions 4 3. Waste Generation Wastewater Source Quantity Characteristics Solid Waste Types of Solid Waste Characteristics of Solid Waste Disposal of Solid Waste Air Emission Emissions from Generators and Boilers Emissions from Process Activities 9 4. Environmental Impacts of Tannery Wastes Pollutants of Tanneries and their Impacts ph Biochemical Oxygen Demand Chemical Oxygen Demand Sulphide Chromium Suspended Solids Salts Solvent Vapours Remedial Measures General Measures Environmentally Clean Technologies Review of Cleaner Technologies Reuse of Chrome Wastewater Treatment Technologies Primary Treatment Secondary Treatment Feasible Technology Design Data Assumptions Components of the Plant Land Requirements Final Effluent Quality Estimation of Capital and O&M Costs Wastewater Treatment for Processing Raw Hides to Finished Leather Design Data Assumptions Land Requirements Components of the Treatment Plant Final Effluent Quality Estimation of Capital and O&M Costs 19 List of Tables Table 2.1: Number of Tanneries in Different Cities of Pakistan Table 3.1: Process-wise Water Consumption and Wastewater Generation of a Tannery Table 3.2: Quantity of Wastewater Discharge from Tanneries Table 3.3: Characteristics of Sludge Wastewater (Process-Wise) Table 3.4a: Characteristics of Composite Wastewater of a Tannery Table 3.4b: Characteristics of Composite Wastewater of a Tannery Table 3.5: Characteristics of Sludge in Composite Wastewater of Tannery-A Table 3.6: Estimated Quantities of Solid Waste and Disposal Practices Table 3.7: Characteristics of Solid Waste Table 5.1: A Brief Review of Cleaner Technologies Table 5.2: Summary of Cost-Benefit Analysis for CRRP Table 6.1: Estimated Daily Pollution Loads of Tannery A and B Table 6.2: Load of Aeration Tank Table 6.3: Land Requirement (m 2 ) Table 6.4: Final Effluent Quality Table 6.5: Estimated Investment Cost of a Treatment Plant for (Wet) Finishing Tannery Process Table 6.6 Daily Pollution Load Table 6.7: Load of Aeration Tank Table 6.8: Land Requirement (m 2 ) Table 6.9: Effluent Quality of Treatment Plant Table 6.10: Estimated Capital Cost of a Treatment Plant with the Present Hydraulic Load of a Tannery List of Figures 6. Wastewater Treatment System: Preliminary Designing and Cost Estimation Wastewater Treatment for Wet Finishing Processes 14 Figure 2.1: Figure 3.1: Figure 4.1: General Processes Flow Diagram Drying Characteristics of Sludge Environmental Input of a Tanner ii

3 List of Figures Annexures Figure 5.1: Figure 6.1: Figure 6.2: Figure 6.3: Chrome Recovery and Reuse Plant Preliminary Layout of the Treatment Plant for a Medium Size Segmented Tannery with a Mechanical Dewatering System Preliminary Layout of the Treatment Plant with Mechanical Dewatering System Preliminary Layout of the Treatment Plant without Mechanical Dewatering System Annexure 1: List of Chemical Used in the Tanning Process Annexure 2: National Environmental Quality Standards (NEQS) Annexure 3A: Preliminary Design of a Treatment Plant Annexure 3B: Preliminary Design of a Treatment Plant iii

4 Preface This report has been prepared as part of the ETPI demonstration project component - collaborative efforts between the industry and FPCCI - and aims to address the environmental pollution problems in the leather manufacturing sector. This report has been prepared on the basis of the findings of environmental audits of four tanneries conducted by ETPI. The purpose of the environmental audits was to assess the nature and extent of the environmental problems and to develop solution for the tanning industry. Audits have established the basis of the demonstration project. Findings and recommendation of audits are being implemented in the selected unit and disseminated to the sector as a whole. Industrial unit level information remains confidential with ETPI. However, this program, at each stage shares the progress of the work with all its stakeholder. This report gives an overview about the environmental aspects of tanneries along with the possible investment required to abate these problems to meet the present and future environmental legislation. It is hoped that this effort will help to enable the local tanneries to initiate the efforts to combat the present and future environmental problems and to produce an environmentally clean product. Further, this study may contribute to the efforts which are being made by local research, education, policy making and monitoring institutions. The environmental audits of four tanneries were conducted jointly by two consulting firms of ETPI consortium, hired by Federation of Pakistan Chamber of Pakistan (FPCCI) to execute the program. These firms are National Environmental Consulting (NEC) Private Limited and HASKONING of the Netherlands. The general report has been prepared by the core team of ETPI. This report was first prepared in April 1997 on the basis of three audits and now it is being revised by adding more information obtained from the fourth audit conducted in this sector. Further, more details have been given on environmental technologies. We acknowledge the co-operation of Pakistan Tanners Association (PTA) and Tanneries who participated in the program and extended their co-operation in all the aspects of study. Consulting Team: Mr. Mohammad Iqbal Mr. Izhar-ul-Haque Mr. J. A. S. Berns Co-ordinator Technology; ETPI National Environmental Consulting (Pvt.) Ltd. (NEC), Pakistan HASKONING, The Netherlands April 1998 iv

5 Executive Summary The Federation of Pakistan Chambers of Commerce & Industry (FPPCI) being the apex body representing all the business, trade and industrial organisations of the country, has launched a comprehensive five year program, called Environmental Technology Program for Industry (ETPI), with technical assistance from the Netherlands Government. The major objective of ETPI is to initiate measures to combat the existing and the expected industrial pollution problems which will also enable the industry to comply with the National Environmental Quality Standards (NEQS) and the forthcoming ISO The program is under implementation with the involvement of progressive industrial units. These units have willingly participated in the program for the implementation of the demonstration project. Pakistan s leather and leather products industry is one of the major foreign exchange earners amongst the manufacturing goods sector. At present, about 90 % of the leather is exported in the finished form. There are presently over 595 tanneries in the formal sector and an equally large number of tanneries exist in the informal sector. The major cluster of tanneries are located in Karachi, Kasur, Lahore, Sheikhupura, Gujranwala, Multan, Sialkot and Jahangria. For leather production, locally available raw material ( hides and skins) and predominantly imported chemicals are used. In the leather sector a variety of finished leather is prepared which includes upper, lining, and garment etc., from salted raw skins/hides. The chrome tanning method is widely applied for preparation of finished leather. However, vegetable tanning method and a combination of chrome and vegetable tanning method is also used. Most of the chemicals are used to prepare the skins or hides for the tanning purpose. After performing their functions these chemicals find their way into the environment. The tanneries generate all the three categories of waste, i.e., liquid, air and solid wastes. The sources of air pollution in tannery are of two types; one is from the stack of generators and boiler and the other from the process. The emission here is below the NEQS standard. Hydrogen Sulphide and Ammonia generated from different sources such as washing of drums with ammonia, effluent of de-liming processes and mixing of tanning and de-liming effluent. Although, the emissions are intermittent they are nevertheless hazardous for the health of the workers. The major solid wastes generated are dusted curing salt, wet trimmings, dry trimmings, wet shavings, buffings, raw material packing, etc. Except dust salt other solid waste has a great attraction in local market. Poultry feed manufacturers due to the protein content of fleshing, raw trimmings, chrome shavings, dry trimmings, buffing dust, etc. collect this material from the tannery. The main problem associated with some of these wastes is their chrome content. End use of chrome containing solid waste varies in different parts of the country. In Punjab it is used for making leather board whereas in Karachi it is used for making poultry feed. During the process trivalent chromium (contained in the solid waste) is changed into hexavalent chromium (carcinogenic). Wet processes of the tannery are the main source for generating the wastewater. Water consumption per kg of raw hides varies from tannery to tannery. Consumption of water should not go beyond the normal requirement i.e., 50 litre/kg. However, it was found that tanneries are generally consuming more water as compared to the normal required quantity. During the peak season, the production and wastewater generation doubles. Despite the seasonal fluctuation, daily fluctuation in wastewater generation also exists due to variation in the quantity of raw material processed daily. The characteristics of wastewater shows that it is highly polluted with Biochemical Oxygen Demand (BOD 5 ), Chemical Oxygen Demand (COD), suspended solids, settleable solids, total Kjedhal Nitrogen, Sulphate and Chromium, Chloride, etc. A considerable quantity of Sludge is also present in the wastewater. Values of these parameters vary from tannery to tannery due to different processes and raw material utilisation. Due to the high pollution level in wastewater, very severe environmental impacts are associated with its discharge into the environment without applying any measures. Recommended remedial measures for the various environmental problems are training of the workers, provision of safety items, improvement in the drainage system to avoid formation of hydrogen sulphide gas, installation of boards and notices about safety and health regulations at working places of the tannery and a proper arrangement to stop the use of tanned solid waste for the preparation of poultry feed. Implementation of cleaner technologies such as water conservation, use of environment friendly chemicals, green fleshing of hides, application of hair saving methods, recycling of sulphide liquor, Lime splitting and trimming and chrome recovery and reuse can provide economical benefits and will help the local tannery to combat the environmental problems. Approximately 30% discharge of the unused chrome compound is a financial loss for a tannery. This can easily be recovered from the spent tanning effluent and this can then be reused without compromising the quality of leather. Cost benefit analysis for chrome recovery and reuse plant has also been carried out which gives a payback period of 6-7 months. A wastewater treatment system is inevitable and different technologies are available in this regard. Two stage of treatment are suggested i.e., primary (physio-chemicals) 1

6 and secondary (biological). The characteristics of wastewater permit low loaded activated sludge system for biological treatment to bring down the level of BOD 5, COD, suspended solids, chrome, sulphide and ph. For the removal of salt, in-house improvement is suggested. An estimated investment cost for such a treatment system for a tannery processing about kg of hides per day is approximately 44 million with a cost of about 7-9 million rupees for operation and maintenance. The wastewater generated from tanneries involved in segmented production i.e., producing finished leather by using wet blue also contains significant pollution level which also needs to be treated before discharge into the local environment. The cost of a treatment system (primary and secondary) was estimated for two tanneries, the tannery processing ,000 kg of wet blue per day would cost about Rs.10 million and for a tannery processing kg of wet blue per day, the cost would approximately be Rs.3 million. 1. The Environmental Technology Program for Industry The Environmental Technology Program for Industry (ETPI) is a joint project of the Federation of Pakistan Chambers of Commerce and Industry (FPCCI) and the Government of The Netherlands. The primary objective of ETPI is to promote the use of environmentally safe technologies for the production of environmentally safe products by Pakistan's manufacturing/ industrial sector. The FPPCI, with the assistance of the Dutch government, has hired a consortium of local and foreign consulting firms to provide the required technical expertise and support. The members of the consortium are: National Environmental Consulting (NEC) (Pvt.). Ltd., Karachi-Pakistan; the lead consultant; HASKONING Royal Dutch Consulting Engineering and Architects, The Netherlands; KRACHWERKTUIGEN (KWT), The Netherlands; Management for Development Foundation (MDF), The Netherlands; and Hagler Baily, Pakistan. This five-year project began in 1996 and works with Pakistani industries and their associations in identifying the most economical pollution prevention and abatement technologies and in implementing these solutions. The five components of the program include the development of a user-friendly database of relevant information, institutional networking within and between key industrial institutions of the country, dissemination and communication to promote cleaner industrial production, institutional support and training to create in-house environmental capacity within Chambers and Industrial Associations, and Demonstration Projects in 20 selected industrial sub sectors to demonstrate the economic feasibility and environmental efficacy of environmental technologies. Three representative industrial units were selected in each sub-sector for preliminary environmental audits to assess the extent and nature of the environmental problems. Based on the results of these audits, a general sub sector report is prepared in consultation with industry experts. The sub sector report highlights the key environmental issues in that industrial sector, lists possible solutions for major environmental problems in that sub sector, and recommends the technologies that are most economically feasible and environmentally appropriate to Pakistan's industrial conditions. 1.1 Demonstration Project Each component of ETPI has been given a specific definition and carries its own objective, scope of the work and methodology. The present study is dealing with the demonstration project component. Hence, in this report, this component will be discussed in detail. Physical interventions in the form of demonstration projects are an integral part of the ETPI. A demonstration project is defined as a project under which those environmental technologies will be implemented which qualify both the technology and financial feasibility criteria and at the same time are relevant to the local industrialists. Improvement in processing practices will also be an essential part of the demonstration projects. Objectives of the demonstration project include: To establish live examples in the major industrial sectors of Pakistan for the direct dissemination of environmental technologies in the country. To prepare a representative database in the shape of industry specific Environmental Audit for establishing the environmental policy implication, financial and institutional support requirements. To create more awareness and committed constituencies amongst industrialists for making environmental investment. To identify industry sector specific research and development areas in the discipline of environment and industry for local and international research institutions. For the implementation of the demonstration project, a comprehensive procedure for the selection of industries in each sub sector has been developed. According to this procedure, three industries will be selected for an Environmental Audit from each sub sector. Subsequently one of these three will be selected for the demonstration project. In the sub sector of leather manufacturing, instead of three Environmental audits, 4 have been carried out. The findings of these audits have been compiled in the present report. During the environmental audit work, it was mentioned that the environmental audit report of the individual tannery will be a confidential document and that document must not be made accessible to every body. 2

7 It was therefore decided to prepare a general report by taking the inferences from these audits. However, it is difficult to generalize the information obtained from environmental audits for the whole sector. To overcome this short coming help has been taken from secondary information. This report has been prepared with an aim that it will provide a general scenario about the environmental problems of local tanneries. 2. The Leather Industry 2.1 A Profile Pakistan s leather and leather products industry is one of the major foreign exchange earners amongst the manufactured goods sector. At present about 90 % of the leather is exported in finished form. During the year export earnings from leather and leather goods amounted to US $ 648 million. About 40 million skins and hides were processed during this year. There are presently over 596 tanneries in the formal sector and equally large number tanneries exist in the informal sector. Major clusters of tanneries are located in Karachi, Kasur, Lahore, Sheikhupura, Gujranwala, Multan, Sialkot, and Jahangria. For leather production locally available raw material (hides and skins) and imported process chemicals are used predominantly. Table 2.1: Number of Tanneries in Different Cities of Pakistan Cities No. of Tanneries Percentage Karachi Multan Kasur Sheikhupira Sialkot Gujranwala Total Source: NEC Survey. 2.2 Raw Material and Chemicals Raw Materials In the leather sector, sheep/goat skins and cow buffalo hides (salted) are used as raw material for the production of leather. Most of the raw material is obtained from the Punjab and Sindh provinces. However, imported raw material is also used. During the peak season, which starts every year after Eidul-Azha and extends up to two on three months, the processing in leather sector reaches to a level of about double the normal production. Normal production also varies from day to day depending on many conditions including the availability of the raw skins and hides. Fluctuation in the use of raw material directly effects waste generation Processing Chemicals A variety of chemicals, from common salt (sodium chloride) to the very fine finishing chemicals, are used in Leather sector. About 130 different type of chemicals are applied in leather manufacturing, depending on the type of raw material and the end product of the industry. These chemicals are divided into four major classes, described below, as per their use. The list of chemical is given in annexure 1. Pre-tanning Chemicals: These chemicals are used to clean and to prepare the skins for the tanning processes. These chemicals do not react with the skins fibre, therefore are not retained by the skins. These chemicals after performing their respective functions are discharged with the wastewater. Tanning Chemicals: These tanning chemicals react with the collagen fibres of the skin and convert them into leather. As these chemicals react with the fibre, therefore, a considerable quantity is retained by the fibre. Nevertheless, a significant amount remains unused and is discharged with the wastewater. Basic chrome sulphate is the tanning chemical, which most widely used in local tanneries. This is an expensive chemical and also poses a serious environmental threat. Besides environmental problems, its discharge into wastewater is also a financial loss. Vegetable tanning materials are also used in local tanneries but their use is not common as compared to chromium. (Wet) Finishing Chemicals: These chemicals are used to impart certain properties, e.g. appearance, softness, flexibility, colour, strength, etc. as per the requirement of the finished product. These chemicals also react with the collagen fibres of the tanned leather and again a maximum quantity of the applied chemicals is retained by the skins. Whereas un-reacted or residual chemical is discharged with the wastewater of the process. Finishing Chemicals: Finishing chemicals are applied as surface coating material to impart the desired surface finish to the leather. Most of the applied quantity is retained by the surface of the leather. However, due to limitations of the application procedure some quantity does go into the waste Water An extensive quantity of water is used in the leather sector. The data shows that litre of water is used for the conversion of one kg of raw skin into leather. Tannery wet processes are the major consumers of water. The water in the wet processes and operations is used as a carrier to facilitate all chemical reactions involved in leather processing. After completion of the process and operation, the water leaves the system as wastewater in the same quantity as added to the system. Groundwater is used as a major source of the processing water in Leather sector. 2.3 Process and Operation In the leather sector a variety of finished leather is prepared including upper, lining, and garments from salted raw skins/hides. The Chrome tanning method is 3

8 widely used for the preparation of finished leather. However, vegetable tanning method and a combination of chrome and vegetable tanning method is also being applied. The three tanneries selected for the audit under the Environmental Technology Program for Industry (ETPI) apply chrome tanning process for the production of finished leather. A series of processes and operations are involved for the production of leather. These are described as follows. The flow diagram of processes and operations is given in figure 2.1. Figure 2.1: General Processes Flow Diagram RAW MATERIAL (RAW SKINS/HIDES) PRE SOAK SOAKING SOAK WASH UNHAIRING & LIMING FLESHING DELIMING WASHINGS BATING DEGREASING PICKLING CHROME TANNING WET BLUE STORAGE *SPLITTING OF WET BLUE SORTING OF WET BLUE SHAVING OF WET BLUE WET BACK + NEUTRALIZATION + RETANNING WASHING FAT LIQUORING & DYEING WASHING SAMMYING/SETTING VACUUM DRYING AIR DRYING/STEAM DRYING STACKING HORIZONTAL TOGGLING DRY SHAVING TRIMMING BUFFING SPRAYING/COATING/DRYING GLAZING/POLISHING IRONING MEASURING SELECTION PACKING Hide processing Wet Processes 2.4 In-House Environmental Conditions In-house environmental condition and practices vary from tannery to tannery. However, the findings of the audited tanneries reflect the following facts. Ventilation system is poor to fair. Practices are conventional. All processing chemicals are handled carelessly. Use of gloves, aprons, goggles, and masks during chemical handling is not common. Even if these items are provided by the tannery, workers do not pay much attention. The un-usage of these accessories during work may be due to the and ignorance and un-awareness of the workers. Information boards about safety and health regulations are not installed in the tanneries. Loading and unloading of the skins/hides during processing is normally carried out manually without using gloves and proper clothes for protection. Consequently the cloths of the workers become completely wet with the float of the different tanning processes. 4

9 3. Waste Generation All the three categories of waste, i.e. liquid, air and solid, are generated by the tanneries. Following section describes the source, disposal, characterisation and quantification of these wastes. 3.1 Wastewater Source Wet processes of the tannery are the main source of the wastewater generation. Some mechanical operations also contribute small quantities of wastewater. Canteen, toilets, prayer hall or mosque also contribute a minor quantity of wastewater. Wet processes are highlighted in the flow diagram (Fig. 2.1). In the tannery processes, water is used as a chemical carrier to render the cleaning of raw hides and skins as well as to penetrate the chemicals facilitating reaction of chemical with collagen fibre of the skins. The process water, after completion of the process, is drained out as wastewater in the same quantity as it is added in the processes. The wastewater is disposed off without any treatment into the local environment Quantity Water consumption per kilogram of raw hides varies from tannery to tannery. Generally water consumption should not go beyond the normal requirement i.e., 50 Table 3.1: Process-wise Water Consumption and Wastewater Generation of a Tannery Processes Percentage of Water Used for Process Average Wastewater Generation (m 3 / day) (12,000 kg/day) (A) Processes = Raw - Wet Blue: Pre-soak wash Soaking Soak wash Liming & Un-hairing De-liming Washing-1 Washing Bating Degreasing Washing -1 Washing -2 Washing -3 Washing litre /Kg. However, it was found that the tanneries are generally consuming more water as compared to the normal required quantity. In some cases water consumption reaches to a level which is three time higher to the normal, i.e., 150 litre /kg of raw hides. Water consumption at each processing stage, for a tannery processing sheep and goat skins, has been summarised in Table 3.1. During peak season the processing of raw skins/hides doubles, which directly effects the quantity of wastewater generation. Despite the seasonal fluctuation, daily fluctuation in wastewater generation also exists due to the variation in quantity of raw skins/hides processed daily. The wastewater discharge is also intermittent and needs to be equalised before treatment. The quantity of wastewater discharged from different tanneries is given in Table Characteristics Tannery wastewater is highly polluted in terms of biochemical oxygen demand (BOD), chemical oxygen demand (COD), suspended solids, settleable solids, total kjeldhal nitrogen, conductivity, sulphate, sulphide and chromium. The values of these parameters are very high as compared to the values mentioned in the National Environmental Quality Standards (NEQS) set by the Government of Pakistan (see annexure 2). Pollutant values of different tanneries are given in Table 3.3 and 3.4. Pickling/Tannin Water Consumption from raw to wet blue stage (B) Processes = Wet Back - Finished Leather: Same weight ( 10,000 kg) of the wet blue skins is processed daily throughout the year for onward wet finishing processes Wet back Neutralisation Re-tanning Washing Fat liquoring / dying Washing Water Consumption in wet finishing 108 Total Water Consumption (A+B) = Total Wastewater Generation 574 Source: ETPI Survey - calculated on the basis of water recipe provided by the tannery

10 Wastewater from each tannery process contains different types of pollutants. ph varies considerably from 3.3 to Similarly, a large variation exists in parameters like BOD, COD, Chloride, Sulphate, TDS, TSS, settleable matter, etc. In addition to these parameters, results clearly show that the wastewater carries considerable quantities of chromium. The discharge of these chemicals into wastewater is not only hazardous but also a financial loss. A considerable quantity of sludge was also present in composite wastewater. The settleable matter is responsible for the sludge generation. This sludge content is presented in Table 3.5 and represented in figure 3.1 Table 3.2: Quantity of Wastewater Discharge From Tanneries S. No. Parameters Values 1. Solid content % 2. Volatile matter Inorganic matter 51-74% 4. Chromium (Cr) Figure 3.1: Drying Characteristics of Sludge Moisture Removed (wt %) Drying Time (1x15Minute) Series1 Series2 Table 3.5: Characteristics of Sludge in Composite Wastewater of Tannery-A Tanneries Wastewater Quantity /Kg of Hides or Skins Tannery-A (Sheep & Goat Skins) Raw to finished 48 litre/kg skins upper and lining leather (12000 kg/day) Wet blue to finished upper 11 litre /kg wet blue and lining leather (10000 kg/day) Tannery -B (Sheep and goat skins) Wet Blue to finished Leather ( kg/day) Tannery -C (Calf Hides) (Raw calf hides to finished leather) (12000 kg/day) * As per recipe ** Measured at drain 3.2 Solid Waste *11 litre/kg wet blue **21 litre/kg wet blue *32.5 litre/kg raw hides **150 litre kg/raw hides day The major solid wastes generated by the tanneries are dusted curing salt, wet trimmings, dry trimmings, wet shavings, dry shavings, buffing, raw material packing, etc.. Most of the solid wastes generated are separated at the source. In order to quantify the solid waste being generated from individual process/operation, some data was available with the management of tanneries. However, in case of non-availability of the data, known number of skins/hides were weighed before and after the process/operation and the net difference was taken as the amount of solid waste. In this way, total amount of solid waste was estimated for peak and average seasons. Table 3.6 lists the details of solid waste quantity and their disposal methods. Following is the brief discussion on solid wastes, their types and their generation. Table 3.3: Characteristics Of Wastewater (Process-wise) Parameter * Pre-Tanning Process Tanning and Wet Finishing Process Soaking Liming De-liming Tanning Neutralization Re-tanning Fat Top Dyeing Liquoring Ph T. Solid 52,255 52,966 19,926 91,878 11,181 22,305 22,397 10,645 Total Dissolve 51,251 40,943 19,780 91,710 10,579 20,677 21,578 9,560 Solids Suspended , , Solid Settleable Matter Sulfates 1,100 2,300 12,600 32,000 2,332 4,660 7, Sulfides 120 1, Total Kjeldhal 112 3,080 2, ,216 Nitrogen Phosphate Chlorides 34,490 11,497 1,500 28,991 5,998 4,998 2,499 2,499 BOD (F) 5,800 6,600 1, ,770 2,640 2,400 3,375 COD (F) 30,000 37,600 5,200 2,080 5,000 8,400 6,000 5,800 Chromium All values are in m/l. except ph. 6

11 Table 3.4a: Characteristics Of Composite Wastewater Of A Tannery Processing Raw Skins (Sheep & Goat) to Finished Leather Parameters Quantity = Kg/day; Volume of wastewater = 574 m 3 /day Values in Range mg/l Pollution Load kg/day Pollution kg/kg raw material ph BOD 5 (Unfiltered) at 0 time settling BOD 5 (Unfiltered) at 30 minutes settling BOD 5 (Unfiltered) at 60 minutes settling COD ( Unfiltered) at 0 time settling COD (Unfiltered) at 30 minutes settling COD (Unfiltered) at 60 minutes settling Suspended Solid at 0 time settling Suspended Solids after 30 minutes settling Suspended Solids after 60 minutes settling Settleable matter after 30 min. settling (m 3 /day ) (m 3 /kg) Settleable matter after 60 min. settling (m 3 /day) (m 3 /kg) T. Phosphate at 0 time settling Total Kjeldhal Nitrogen at 0 time settling Conductivity 0 time Sulphate as SO 4 at 0 time settling Sulphide as (S) at 0 time settling Chromium (Cr) at 0 time settling * * Estimated on the basis of chrome content in chrome tanning effluent (6132 mg/l.) Table 3.4b: Characteristics Of Composite Wastewater Of A Tannery Parameters Processing Raw Hides (Calf) to Finished Leather Quantity = 5419 kg/day; Volume of wastewater = 814m 3 /day Values in Range mg/l Pollution Load kg/day Pollution kg/kg raw material ph BOD 5 (Unfiltered) at 0 time settling BOD 5 (Unfiltered) at 30 minutes settling BOD 5 (Unfiltered) at 60 minutes settling COD ( Unfiltered) at 0 time settling COD (Unfiltered) at 30 minutes settling COD (Unfiltered) at 60 minutes settling Suspended Solid at 0 time settling Suspended Solids after 30 minutes settling Suspended Solids after 60 minutes settling Settleable matter after 30 min. settling Settleable matter after 60 min. settling T. Phosphate at 0 time settling Total Kjeldhal Nitrogen at 0 time settling Conductivity 0 time Sulphate as SO 4 at 0 time settling Sulphide as (S) at 0 time settling < 1gm Chromium (Cr) at 0 time settling * Estimated on the basis of chrome content in chrome tanning effluent (6132 mg/l.) 7

12 Table 3.6: Estimated Quantities of Solid Waste and Disposal Practice Solid Waste Type Waste Generation Rate Average Quantity (Kg/day) Disposal Dusted salt 0.1 kg/skin 1000 Thrown Fleshing 0.25 kg/skin 2500 Sold to soap and poultry feed makers Raw trimming kg/skin 240 Sold to poultry feed makers Wet shaving kg/skin 1160 Collected from the tannery by secondary users Dry trimming kg/skin 240 Dry shaving kg/skin 340 Buffing dust kg/skin 20 Total 5500 Cartons, bags, drums, No consistent quantity Sold Miscellaneous refuse Source: Data supplied by Tannery. Note: These quantities are based on the average figures (10,000 kgs./day) Types of Solid Waste Curing Salt: During the handling of raw skins, adhered dusted salt, which is contaminated with blood, hair, dirt and certain type of bacteria is removed from the skins and obtained as solid waste. This salt is partly reused in the curing process and the remaining is indiscriminately dumped in the undeveloped land near the tannery. Raw Trimmings: Raw trimmings are cuttings from the edges of raw skins. The skins are trimmed specially at the legs, belly, neck, and tail parts in order to give a smooth shape to the skins. Fleshing: This is the flesh removed from the limed skins and is generated during the fleshing operation which is carried out after liming and un-hairing processes. Splitting of Wet Blue: This operation is carried out in hides tanneries processing hides. After chrome tanning, the hide s thickness ranges from 6-8 mm. Therefore, to get proper thickness the wet blue of the hide is sliced into two layers. Upper layer, which is having grain, is used for preparation of finished leather. Whereas, the lower layer is treated as a by-product. However, it is further processed and is used for manufacturing low grade shoe upper leather and as such is not considered as solid waste. Chrome Wet Shaving: After chrome tanning, skins or split hides are shaved to proper thickness by the shaving machine. This operation produces chrome containing solid waste usually called shaving. Buffing Dust, Trimming and Dry Shaving: Buffing, adjustment of the thickness of leather and trimming operations are responsible for the generation of buffing dust, cuttings (trimmings) and shavings, respectively. Tanneries mostly have a good buffing dust collection system that does not allow the dust to spread out around the working area. The dust is collected via the suction machine in cloth bags Characteristics of Solid Waste Besides quantification of solid waste, characterisation of solid waste was also carried out. Four samples, each of one kilogram, were taken from major types of solid wastes being generated, i.e. salt dusting, fleshing, wet shaving and trimming, dry shaving, trimming and buffing. This exercise was conducted to determine the major constituents such as moisture, salt, lime, chromium, total and volatile solids, sulphide fats and proteins. Table 3.7 lists the characterisation of solid wastes of tannery processes. Table 3.7: Characteristics of Solid Wastes Constituents Dusted Salts Type of Solid Waste Fleshing Wet Trimming & Shaving Dry Trimming, Shaving & Buffing Mositure Proteins Fats Cr 2O Volatile Matter Salt Lime Sulphide Source: Laboratory Analysis. Note: All values are in gm /Kg. unless otherwise specified Disposal of Solid Waste With the exception of dusted salt, all other solid waste is consumed within the local market. Empty drums, cartons, chemical bags etc. have demand in the retail market. Contractors purchase these materials in bulk from the tannery and sell these in the retail market at a profit. Therefore, it has become a source of income for these people. Poultry feed manufacturers, due to the protein content of some of the solid waste like. fleshing, raw trimming, chrome shaving, dry trimming, buffing dust, etc., collect these materials from the tannery. The main problem associated with some of these wastes is their chrome content. The chrome content in these wastes ranges from gm/kg. The chrome-tanned waste contains chromium in trivalent form, which is less toxic as compared to the hexavalent form of chromium, which is carcinogenic. End use of chrome containing solid waste varies in different parts of the country. In Punjab this solid waste is used for making leather board whereas in Karachi this is used for making poultry feed. 8

13 Recently, a study of solid waste management was carried out in Sector 7-A of Korangi Industrial Area under the PTA (Pakistan Tanners Association) Environmental Management Program. According to the study, poultry feed mixed tannery solid waste was collected and analysed. The results showed that the poultry feed, besides trivalent chromium, also contained hexavalent chromium. It seems that during the poultry feed preparation, trivalent chromium is being changed into its hexavalent form. The mixing of heavy metal in poultry feed in such a high quantity could produce severe health problems for human beings. 3.3 Air Emission Sources of air pollution in tanneries are of two types. One is from stack of generators and boiler and the other from the processes Emissions from Generators and Boilers The generators, in the tanneries that were audited, are used only during power failures, which is mostly less then two hours a day, on an average. Generators are usually diesel based. The boiler is kept operational for approximately 12 hours /day. Samples of emission from the boiler stack were collected and analysed Emission from Process Activities Hydrogen sulphide and ammonia are the major gases emitted during the washing of the drum with ammonia, effluent of de-liming processes where ammonium sulphate is used as a de-liming agent, and mixing of tanning and de-liming effluent. For these reasons, samples of air were collected from the liming section and tanyard/ dyeing section. Laboratory results show very low values as compared to the NEQS permissible limits. Therefore, apparently no environmental impacts are associated with the air emissions of the generator and boiler. In the dyeing and tanyard section of a tannery, ammonia emission were traced in a quantity of 4.1 mg / Nm 3, which is a health hazard to the workers. 4. Environmental Impacts of Tannery Wastes As discussed in the previous Chapter, three types of wastes are generated during the leather manufacturing processes. These are liquid, solid and gaseous emissions. It was observed that air emission values are very low as compared to the limits laid down in the NEQS. Solid waste is being collected by contractors for preparation of poultry feed. As far as liquid waste is concerned, tanneries are disposing off their un-treated wastewater into storm-water drains which finally find their way into natural water bodies such as rivers and sea. Therefore, major environmental problems are generally associated with the wastewater of the tanneries. In this chapter, the general environmental impacts are discussed. Further, the pollutants of tannery wastewater have been compared with the pollutants of sewage ( source: KWSB). 4.1 Pollutants of Tannery and their Impacts ph The ph of directly discharged tannery effluent varies from 3.5 to Water with a low ph is corrosive to water-carrying systems and in unfavourable circumstances, can lead to the dissolution of heavy metals in the wastewater. The high ph in tannery wastewater is produced by lime because it is used in excess quantities and this causes scaling in sewers. Whereas, low ph of wastewater is caused by use of acids in different tannery processes. A large fluctuation in ph exerts stress on aquatic environment which may kill some sensitive species of plants and animals living there. The NEQS recommends a value of ph in the range of Biochemical Oxygen Demand (BOD 5 ) Large quantities of proteins and their degraded products form the largest single constituent group in the effluent. They effect the environment which can be expressed by two composite parameters; Biochemical Oxygen Demand (BOD 5 ) and suspended solids. BOD is a measure of the oxygen consuming capacity of water containing organic matter. Organic matter by itself does not cause direct harm to aquatic environment, but it exerts an indirect effect there by depressing the dissolved oxygen content of the water. The oxygen content is an essential water quality parameter and its reduction causes stress on the ecosystem. As an extreme example, a total lack of dissolved oxygen as a result of high BOD can kill all natural life in an effected area. Tanneries discharge wastewater containing BOD value in the range of mg/l. Whereas the NEQS recommends a BOD value of 80 mg/l. Therefore, tannery wastewater is carrying about times higher value of BOD as compared to the NEQS limit. Further, the BOD value of tannery wastewater is 4-20 times higher as compared to the BOD value ( mg/l) of sewage Chemical Oxygen Demand (COD) The Chemical Oxygen Demand (COD) is a measure of oxygen equivalent to that portion of the organic matter in a sample which is susceptible to oxidation by a strong chemical oxidant. It is an important, rapidly measured parameter for stream and industrial waste studies and for control of waste treatment plants. Along with the organic compounds immediately available to the stream organism, it also determines biological compounds that are not a part of immediate biochemical load on the oxygen assets of the receiving water. With certain wastes containing toxic substances, this test or total organic carbon determination may be the only method for determining the organic load. Where wastes contain only readily available organic bacterial food and no toxic matter, the results can be used to approximate the ultimate carbonaceous BOD values. Composite wastewater of tanneries carries a COD value in a range 9

14 of mg/l. Whereas according to the NEQS, a value of 150 mg/l has been recommended for COD. Hence, tannery wastewater is carrying about times more pollution load in terms of COD. Sewage water usually contains 1000 mg/l COD Sulphide Due to sulphide discharged from the unhairing process, hydrogen sulphide is released at a ph value lower than 8.5. This gas has an unpleasant smell even in trace quantities and is highly toxic to many forms of life. In higher concentrations, fish mortality may occur at a sulphide concentration of 10 mg/l. Sulphide in public sewer can pose structural problems due to corrosion by sulphuric acid produced as a result of microbial action. Sewage contains sulphide in the range of mg/l and composite tannery wastewater contains 290 mg/l, whereas, the NEQS recommends a value of 1.0 mg/l Chromium Trivalent chromium is released from the chrome tanning process. This is much less toxic than hexavalent chromium. For plant and animal life, the toxicity of chromium salts is variable. The toxicity is a function of the species itself. Algae have been shown to be particularly sensitive. Estuarine molluscs, although apparently unaffected in their own metabolism, accumulate trivalent chromium. At present, tanneries are discharging chromium (133 mg/l) in composite wastewater and in sludge ( gm/kg). It can be seen that wastewater of chrome tanning process, which is about 2 % of the total wastewater of the tannery, contains mg/l of chromium (Cr). The sewage of Karachi contains 0.1 to 0.5 mg/l of chromium, whereas the NEQS recommends a value of 1.0 mg/l Suspended Solids Suspended solids, apart from being societal nuisance, have their main effect when they settle. The layer so formed on the bottom of the watercourse, covers the natural fauna on which aquatic life depends. This can lead to a localised depletion of oxygen supplies in the bottom waters. A further secondary effect is the reduced light penetration and consequent reduction in photosynthesis due to the increased turbidity of water. Tanneries discharge wastewater containing mg/l of suspended solids. The Karachi sewage contains mg/l suspended solids, whereas the NEQS recommends a value of 150 mg/l Salts The sodium chloride used in the tannery produces no effect when discharged into estuaries or the sea, but effects fresh water life when its concentration in a stream or lake becomes too high. There is no economically viable way of removing salt from the effluent. A similar problem also exists for sulphate used as the chrome tanning salt. Sulphate in addition causes corrosion to concrete structures. The Chloride content of tanneries composite wastewater ranges from 5820 to and the sulphate content varies from 860 to 1814 mg/l Solvent Vapours Finishing chemicals like acetic acid, formaldehyde, ethylene glycol, etc. are used in the tannery processes. The vapours of these chemicals are very dangerous and can affect the health of workers severely. Figure 4.1: Environmental Input of a Tannery ( Raw Skins to Finished Leather) RAW SKINS KG WASTEWATER (600 M 3 /day) BOD 5 = COD = Suspended Solids = 2790 Chromium = 80 Sulphide = 173 Sludge = 3280 All values in Kg/day SOLID WASTE AND BY- PRODUCTS UNTANNED Dusted Salt = 1000 Raw trimming = 240 Fleshing= 2500 TANNED Shaving = 1500 Trimming = 240 Buffing = 20 Total = 5500 All values are in Kg./day LEATHER 1400 Kg 5. Remedial Measures 5.1 General Measures As tanneries do not have an environmental management system, therefore, this system must be developed in tanneries, specially in the large and medium sized ones. Environmental management should be a responsibility of the personnel in addition to their routine duties. Short-term training on occupational health and safety aspects, modern practices for the handling of hazardous chemicals, etc. is required for the staff. 10

15 Installation of information boards on safety and health regulations at the work places of the tannery are needed. Provision of safety gears like face protective shield for acid work specially in the pickling process, acid resistant gloves and aprons etc. Face masks to avoid inhalation of fumes of finishing chemicals, toxic gases, etc. The use of the safety gear should be implemented strictly. Proper arrangements to stop the use of tanned solid waste for the preparation of poultry feed. Simple disposal to the landfill site may not be a proper solution to stop this practice, as the poultry feed makers can get this material from these sites. Tanned solid waste materials can be used in leather board manufacturing, but in Karachi, a leather board factory does not exist. In the absence of a permanent solution to this problem at present, it is suggested that this material can be disposed off after mixing with other wastes, like circulation water of spray plant that caries unused finishing material. Other waste that can be mixed with tanned solid waste is curing salt. After mixing with this waste, tanned solid waste will become contaminated and will not be useful for poultry feed makers. Improvement in drainage system in order to avoid formation of hydrogen sulphide gas inside the tannery. 5.2 Environmentally Clean Technologies A number of cleaner technologies can be applied for the manufacturing of finished leather. The implementation of cleaner production processes and pollution prevention measures can provide both economic and environmental benefits. However, the applicability of these technologies vary from tannery to tannery due to the varying nature of raw material, processing conditions and the type of finished leather Review of Cleaner Technologies Some of the cleaner technologies have been described in Table 5.1 Table 5.1: A Brief Review on Cleaner Technologies Cleaner Technologies Benefits Water Conservation The use of pit or paddle for soaking operations results in a higher consumption of water, mainly for washing phase which are much less efficient than when using drums. Even for drums it is recommended to operate the sequential washing instead of continuous washing which leads to the savings of enormous amount of water at each stage. Low float technologies would also reduce the water quantity. Although such conservation do not reduce the pollution load, however, they can lead to the reduction in the size of the effluent treatment plant. Use of Environment Friendly Enzymatic product are considered to be less toxic and can be a good replacement of Chemicals sulphide. Surfactants, if used, should be selected with respect to their biodegradability. Use of Penta Chloro Phenol (PCP) must be avoided. Replacement of ammonium sulphate with weak acids (organic). Degreasing with surfactants instead of organic solvent. Use of trivalent chromium for tanning purpose instead of hexavalent chromium (carcinogenic). Metal complex dyes, which contain restricted heavy metals and benzidine based dyes must be replaced. The chlorinated fatliquoring agents and retanning products should be replaced with the easily biodegradable products. Green Fleshing of Hides Green fleshing just after deep soaking is a suitable procedure to obtain by-product at ph close to neutral, which can then easily be processed to recover fats and proteins with good marketing possibilities and to save liming and unhairing chemicals. Further green fleshing also improves the penetration of the chemicals and hence improves the quality of finished leather. Hair savings Methods Hair saving system use smaller quantities of sulphide as compared to hair destruction system, and allows easy separation of the protein constituted by the undissolved hair and hence imply less pollution than the hair dissolving process. The procedure results in a significant reduction of COD, BOD 5, nitrogen, sulphide, total and suspended solids in the wastewater, besides a decrease of sulphide consumption. The hair saving would decrease the organic load for treatment plant. Recycling Liming Liquor Some of the liming unhairing techniques permit a direct reuse of the spent liquors after decantation and/or filtration. The procedure permits savings of water, sulphide, and lime. Recycling of Un-hairing Liquors By reuse of un-hairing liquors after separation of insoluble substances by sedimentation important savings are claimed including 50 % sulphide, 40% lime and 60% of process water. Lime Splitting and Trimming Splitting and trimming is usually carried out after tanning which results in a by-product of low quality containing chromium in it. If these operations are carried out with the pelt, the produced by-product can be sold easily in the market than those resulting from splitting and trimming of wet blue (tanned hides/skins). The un-tanned solid waste will be a good raw material for manufacturing of gelatin or animal feed. This will also results in a reduction in the quantities of chemicals used for deliming, pickling, tanning and consequently the load of the pollutants in wastewater will be considerably reduced. Application of Weak Acids in Deliming Process deliming process. Application of weak acids (organic) can eliminate the discharge of ammonium salt from Chrome Reuse in the Tanning See Section Process Source: Introduction of Cleaner Technologies in Tannery Cluster of Punjab 11

16 5.2.2 Reuse of Chrome Quite a few options are available for the reuse of the chrome discharged in the tanning effluent. These technologies do not completely eliminate the chromium being discharged through the effluent or sludge. However, it can be seen as apart of a general environmental plan of the tannery, since it reduces the necessary amount of chromium being discharged into the environment, thus facilitating the treatment and disposal of a small amounts of chromium containing sludge. Chrome reuse option also provides financial benefits. Figure 5.1: Chrome Recovery & Reuse Plant Direct Recycling of Chrome Tanning Float: This is the easiest method of chrome reuse. In this method after collection and sufficiently fine screening, the float is controlled and the chromium amounts used in the previous cycle are replaced by fresh chromium salts. Depending on the tanning technology in use, the degree of exhaustion reached for each cycle may vary. The recycling method may be repeated several times on the same float. However, it is limited by the occurrence of quality problems with delicate hides and by the need to control residual float. This technology is suitable for small tanneries. Recycling Of Chrome After Precipitation: This allows collection of the tanning float with the rinses, that sometimes occur at the end of the tanning and the effluent from various post-tanning stages (washing, dripping, sammying, etc). After collection, screening and storage, the floats are precipitated with different types of alkalies and bases including sodium hydroxide, sodium carbonate, magnesium oxide and even with lime. The reuse of sludge after simple settling and acidification has been experimented and practised. Schematic diagram of a typical chrome recovery and reuse plant is shown in figure 5.1. Large plants have operated under this scheme for many years in Germany, Itally, South America and France. In Pakistan four chrome recovery plants have been installed under the same process. Table 5.2: Summary of Cost Benefits Analysis for CRRP Cost-Benefit Analysis of a Chrome Recovery and Reuse Plant (CRRP): For the estimation of a total quantity of basic chromium sulphate (BCS) in the tanning effluent the maximum quantity of tanning effluent and minimum value of chrome quantity has been considered. Cost benefit analysis is given in the following table. These cost are approximate costs and given only for a general idea about the investment and pay back period of the chrome recovery project. Tanning Products that Improve the Exhaustion Rate: For the past few years, tanning and basification products have been available in the market which enable a tanning cycle to produce only small quantities of chromium waste. These products are developed with the aim of bringing about the complete fixation of the chrome onto the protein fibres so that the exhausted chrome tanning float contains little or no chrome. Chrome take up of over 90 % with exhaust of less that 1 gm per litre is possible. This reduces the initial chrome oxide offer to about 1.8 % on the fleshed weight and still obtains the same quantity of chrome fixed on the fibres. 1. Basic Data - Raw goat Skins 3000 kg/day - Quantity of tanning float % of a - Total volume of float (a*b/100) litre - Basic Chromium Sulphate (BCS) applied in tanning process 7-8 % of a - Total BCS applied per day ( d*a/100) kg/day - Chromium (Cr) in Tanning Effluent mg/l - Total BCS in Tanning Effluent (c*f/170000) kilo/day - ph Description Amount Unit 2. Capital Cost 683,000 Rs. 3. Operation and Maintenance Cost: A: Annual Operating Cost - Manpower - Electricity - Chemicals - Maintenance 5% of Capital Cost ) - 5% of Capital Cost) B: Depreciation Cost (@ 5% of Capital Cost) 60,000 9, ,000 17,000 34,000 34,000 Rs./year Rs./ year Rs./ year Rs./ year Rs./ year Rs. Year TOTAL O & M Cost 314,600 Rs./ year 4. Benefits: - Total Recovered Chromium/day* - Total Recovered Chromium/annum (300 days) - Value of Recovered Rs. 36/kg ,339,200 kg/day. Kg/year. Rs/year. Net Profit = 3-2 1,024,600 Rs/year 5. Pay Back Period 7-8 months *: Calculated on the basis of 95% recovery. 12

17 5.3 Wastewater Treatment Technologies Two levels of treatment are normally required for treatment of the effluent from the tanneries. These are primary and secondary treatment Primary Treatment Primary treatment system comprises of mechanical screening, ph equalisation (collection of effluent of different processes in a common tank), coagulation and flocculation and sedimentation. Mechanical Screening: Removal of coarse, particulate flesh and hair is achieved by means of perforated screens. The contribution of screening in reducing the BOD load is high, but the primary purpose is to prevent the blockage of pumps and sewers required for further treatment of the effluent. ph Equalization: The wide fluctuation in the effluent s ph value as a result of different requirements of the tannery processes can be reduced by means of an equalization tank. This procedure can reduce the amplitude of ph fluctuation from down to approximately , as observed during the sampling programme. Due to the equalization tank, the flow and composition of the effluent is also maintained more constantly for further treatment. Physio-Chemical Processes: Coagulation and flocculation are applied to the tannery wastewater in order to remove the suspended solid of the wastewater. This is carried out by the addition of coagulating and flocculating to the wastewater Secondary Treatment In secondary treatment, biological processes are used to remove most of the organic matter from the wastewater. This is achieved by using micro-organisms to convert the organic matter into different gases and into cell tissues. Cell tissues have a specific gravity slightly greater than that of the water, the resulting tissue is removed from the treated liquid by gravity settling. For secondary or biological treatment of tannery effluent, the most widely used processes are aerobic. However, anaerobic process is also used for this purpose. On the basis of these two processes, following major treatment technologies are available: Activated Sludge Aerated Lagoon Facultative Ponds Anaerobic Lagoon Trickling Filter UASB (Upflow Anaerobic Sludge Blanket) The selection of the technology depends on many factors like capital cost, availability of land, operation and maintenance cost, efficiency of the process etc. In the following sections, technical viability as per the available tannery data, along with a brief process description of these technologies has been discussed. Activated Sludge: During a biological treatment by activated sludge, the wastewater to be treated is introduced into a tank aerated by mechanical stirring or by compressed air. Here it mixes with the mass of bacterial floc maintained constantly in suspension. After sufficient contact time, the mixture is clarified in a settling pond and sludge is recycled in the aeration tank. The excess sludge from the system is treated with primary sludge. This is a proven technology for the treatment of tannery wastewater and widely used all over the world. Modified forms of this technology are available. Aerated Lagoons: An aerated lagoon is an earthen basin in which the oxygen required by the process is supplied by surface aerators. In an aerobic lagoon, all the solids are maintained as suspension. To meet the secondary treatment standards, this technology can safely be used for the treatment of tannery effluent. However, it requires a large area of land as compared to other technologies. For the present study, this technology is not being considered due to insufficient area of land available. Facultative Ponds: Ponds in which the stabilization of waste is brought about by a combination of aerobic, anaerobic and facultative bacteria, are known as Facultative (anaerobic-aerobic) Stabilization Ponds. Three zones exist in a Facultative Pond: a surface zone where aerobic bacteria and algae exist in a symbiotic relationship; an anaerobic bottom zone in which accumulated solids are decomposed by anaerobic bacteria; and an intermediate zone that is partly anaerobic, in which the decomposition of organic waste is carried out by facultative bacteria. Conventional facultative ponds are earthen basins filled with wastewater. In this pond, large solids settle out to form an anaerobic sludge layer. Soluble and colloidal organic materials are oxidized by aerobic and facultative bacteria, using bacteria produced by algae growing near the surface. Carbon dioxide produced in organic oxidation serves as carbon source for the algae. Anaerobic breakdown of the solids in the sludge layer results in the production of dissolved organic compounds and gases such as carbon dioxide, hydrogen sulphide and methane, which are either oxidized by the aerobic bacteria or vented to the atmosphere. In practice, oxygen is maintained in the upper layer of the facultative lagoon by the presence of algae and by surface aeration. In some cases, surface aerators have also been used. If a surface aerator is used, algae is not required. Like an aerobic lagoon, this type of lagoon also requires a large area of land. In addition, odour is also a problem. Therefore, this technology also does not look feasible for the treatment of wastewater for the tanneries under study. Anaerobic Lagoon: Typically, an anaerobic lagoon is a deep earthen pond with appropriate inlet and outlet piping to conserve heat energy and to maintain an anaerobic condition. Anaerobic lagoons are constructed with depths of up to 30 ft. The waste that is added in the lagoon settles down at the bottom. The partially clarified effluent is usually discharged to another process for further treatment. Usually, these ponds are anaerobic throughout the depth, except for an extremely shallow surface zone. Stabilization is brought about by the combination of 13

18 precipitation and the anaerobic conversion of organic waste into carbon dioxide, methane, other gaseous end products, organic acids and cell tissues. Conversion efficiencies of BOD up to 70% can be achieved. High sulphate concentration in the tanneries would cause the production of hydrogen sulphide gas and which can adversely effect the surrounding areas. This technology also requires a large land area, therefore, it is also not feasible for treatment of wastewater of the tanneries under study. Trickling Filter: The working principle of the trickling filter is by percolating the water to be treated through a mass of porous or cavernous material, which serves as support for micro-organisms. The necessary oxygen required for maintaining an aerobic state for fixing the biomass to the support is generally supplied by natural ventilation. Due to natural ventilation, aeration cost is not required. This technology is being used in Pakistan for the treatment of domestic wastewater. This has not been tested for treatment of tannery wastewater on a large-scale. Due to a heavy load of pollution in tannery wastewater, it s performance is doubtful. Tanneries are discharging wastewater containing 40 times more BOD value as compared to domestic wastewater. Nitrification is possible in this type of technology whereas denitrification of wastewater is not possible. Therefore, it is not possible to apply this technology for the treatment of wastewater of tanneries. However, it is a very simple technology and operation and maintenance cost is also very low as compared to the activated sludge technology. A small land area is required for this technology. Upflow Anaerobic Sludge Blanket (UASB) Technology: As it is evident from its name, this is an anaerobic process based technology. This treatment system is based on the upward flow of wastewater through a sludge layer of active anaerobic microorganisms. The wastewater is evenly distributed at the bottom of the reactor, and after a suitable hydraulic retention time in the reactor it leaves from the system from top of the reactor. The contact between the microorganisms of the wastewater is enhanced by the production of biogas, due to the rising bubbles which provide gentle mixing. There is no need for mechanical mixing. This simplifies the design of the reactor. After passing through the sludge bed, a mixture of biogas, sludge and water enters a three phase separator. The biogas is separated in a gas collector, whilst the sludgewater mixture enters a settling compartment, thus providing effective sludge retention in the reactor. The effluent is discharged from the top of the reactor via an overflow weir. The excess sludge is discharged from the bottom of the reactor at the regular intervals onto a drying bed. This technology has been successfully applied for the treatment of tannery wastewater diluted with domestic wastewater in India. On the basis of the same principle, a UASB treatment plant is also being installed in Karachi, for the treatment of tannery wastewater for a cluster of more than 160 tanneries, situated in sector 7 - A of Korangi Industrial Area. Besides other toxic waste present in the tannery wastewater for anaerobic process, sulphate concentration is one of the more important factors. In the presence of sulphate, an anaerobic process starts the generation of hydrogen sulphide gas and at the same time the production of Methane gas is badly effected. Wastewater of tanneries under study contains sulphate (SO 4 ) in the range of 860-3,146 mg/l. To overcome the problems of this technology, the tannery wastewater is treated after dilution with domestic wastewater in a ratio of 1:3. Due to this large quantities of domestic wastewater would be required. The tanneries under study cannot arrange this large quantity of domestic wastewater, therefore, this technology cannot be considered for the treatment of wastewater for individual tanneries Feasible Technology On the basis of the above discussions and the organic and hydraulic load of the tanneries, it is concluded that the Activated Sludge System can be selected for the treatment of the wastewater of individual tanneries In order to take advantage of the local climatic conditions, it would be better to consider the low loaded system of the activated sludge process. Under this system, given local climatic conditions, it would be possible to treat secondary sludge in the same biological reactor. 6. Wastewater Treatment System: Preliminary Designing and Cost Estimation Two types of tanneries participated in the ETPI program. One type of tannery was invloved in segmented production by using wet blue as raw material to prepare finished leather. The processes they conduct are usually referred to as Wet Finishing Processes. The other type of tannery was a complete tannery, processing raw hides to prepare finshed leather. The wastewater treatment system for both the type of tanneries has been described in the following sections. 6.1 Wastewater Treatment for Wet Finishing Processes Tanneries under study manufacture finished leather by taking wet blue as raw material. Wet blue is either prepared in a separate unit of the same tannery or it is purchased from another tannery. The processes employed to prepare finished leather from wet blue are called wet finishing processes. This designing is carried out to assess the total investment cost alongwith the operation and maintenance cost of the wastewater treatment plant the for two tanneries A and B employing (wet) finishing process. The production of these tanneries is as follows. Tannery A processing 8000 kg to of kg skins (wet blue) per day. Tannery B processing 600 kg to 1500 kg of skins (wet blue) per day. 14

19 The suggested treatment plant comprises of a primary and secondary level treatment system Design Data Water Quantities (Volumes): The daily liquid volumes of wastewater fluctuates between the values given below depending on the quantity of raw material processed daily: Tannery A m 3 /day Tannery B m 3 /day Daily Pollution Loads: The maximum values of water quantities 120 and 40 m 3 /day of tanneries A and B, respectively, have been taken to cover the maximum fluctuation of the wastewater. Daily pollution loads are summarized in Table 6.1 below: Table 6.1: Estimated Daily Pollution Loads of Tannery A and B Description Tannery A 120 m 3 /day Ave.Conc. (mg/l) Load (kg/d) Tannery B 40 m 3 /day Ave. Conc. (mg/l) Load Kg/day PH BOD 5 (20 C) total BOD 5 (20 C) settleable solid COD (total) COD settleable solid Tot. suspended solids Tot. Kj Nitrogen Sulphate Sulphide Nil Nil Phosphate Note: BOD suspended solids are based on the difference of BOD at 0 time and BOD after 60 minutes settling. Source: Laboratory Analysis Assumptions The following assumptions have been made for the preliminary design: Wastewater quantity of the peak season has been taken into consideration, maximum flow which means a higher capacity, especially in aeration tanks and hydraulic capacity; The liquid effluent will be lifted (pumped) only once for the required water level in the plant; The removal efficiencies of the primary sedimentation tank are summarized in Table 6.2; The design of the aeration tank is based on a low loaded activated sludge system (including sludge stabilization); and Mechanical dewatering is taken into consideration as relatively high amounts of sludge are generated daily. Table 6.2: Load of Aeration Tank Tannery -A Description BOD 5 Susp.solids Kj-N Sulphide Tannery - B Description BOD 5 Susp. Solids Kj-N Input to Primary Treatment kg/d Nil Input to Primary Treatment (Kg/d) Efficiency of Primary Treatment (%) Efficiency of Primary Treatment (%) Output of Primary Treatment* (kg/d) Nil Output of Primary Treatment* (kg/d) Sludge (kg/d) 309 Sludg e (kg/d) 0 * Considered loads to the aeration tank for design of volume and capacity Components of the Plant The treatment plant will consist of the following: Water Handling Collecting pit, including a pumping station; Equalization tank (with mixers for stirring to prevent settling). Addition of chemicals like lime and polyelectrolyte will also be carried out at this stage; Primary sedimentation tank; Aeration tank (aeration by surface aerators); and Final sedimentation tank (including return sludge facilities). Sludge Handling Primary sludge pumps (for pumping of primary sludge from the sedimentation tank to the sludge thickener); Excess sludge pumps (for pumping of excess sludge from the return sludge pit to the sludge thickener); Sludge thickener (to increase dry sludge concentration i.e reduction of the sludge volume);and Drying beds and belt filter press Land Requirement Preliminary layout of the treatment plant is presented in Figure Land requirement with and without a mechanical dewatering system is shown in Table 6.3 below: Final Effluent Quality Designing has been carried out to produce effleunt to meet the NEQS level. Table 6.4 shows the final effluent quality after treatment: Table 6.3: Land Requirement ( m 2 ) Tannery A Tannery B With Mechanical Dewatering Without Mechanical Dewatering With Mechanical Dewatering Without Mechanical Dewatering

20 Figure 6.1: Preliminary Layout of the Treatment Plant for a medium size segmented tannery with a Mechanical DeWatering System Table 6.4: Final Efffluent Quality Description Influent Concentration of Treatment Plant (mg/l) PH BOD 5 (20 C) total COD (total) Tot. suspended solids Tot. Kj Nitrogen Sulphate Tannery A Nil Tanney B Effluent Concentration of Treatment Plant (mg/l) Nil Estimation of Capital and O&M Costs Estimated capital and operation and maintenance cost are summarised in Tables 6.5. The process design is given in annexure 3 and 4 Table 6.5: Estimated Investment Cost of Treatment Plant for (Wet) Finishing Tannery Process Description Tannery -A Tannery B A: Civil Works Grit chamber Equalization tank Primary sedimentation tank. Aeration tank Final settling tank Complete sludge thickner Sludge drying bed Control/Service room Sub Total B: Mechanical Equipments Mixer Pumps Scraper, skimmer, bridge etc Surface aerator Belt filter press Sub Total Total A + B Electrical/ mechanical work ( 20 % total A+B) Contingencies (20% of total A+B) Total Cost of Treatment Plant (million Rs) Estimated Annual Operation and Maintenance Cost 15-20% of the total (million Rs) Land Area Requirement (m 2 )