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Table of Contents

1.1 Demonstration Project 2

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2.1 A Profile 3 2.2 Raw Materials and Chemicals 3

- 2.2.1 Raw Materials 3 2.2.2 Processing Chemicals 3 2.2.3 Water 3

2.3 Process and Operation 3 2.4 In-House Enviromnental Conditions 4 -.

3.1 Wastewater 5 3.1.1 Source 5 3.1.2 Quantity 5 3.1.3 Characteristics 5

3.2 Solid Waste 6 3.2.1 Types of Solid Waste 8 3.2.2 Characteristics of Solid Waste 8 3.2.3 DisposaI of Solid Waste 8

3.3 Air Emission 9 3.3.lEmissions t?om Generators and Boilers 9 3.3.2 Emissions from ProcessActivities 9

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4.1 Pollutants of Tamteries and their Impacts 9 4.1.1 pH 9 4.1.2 Biochemical Oxygen Demand 9 4.1.3 Chemical Oxygen Demand 9 4.1.4 Sulphide 10 4.1.5 Chromium 10 4.1.6 Suspended Solids 10 4.1.7 Salts 10 4.1.8 Solvent Vapours

5.1 General Measures 10 5.2 Environmentally Clean Technologies Il

5.2.1 Review of CleanerTechnologies ll 5.2.2 Reuse of Chrome 12

5.3 Wastewater Treatment Technologies 13 5.3.1 Primary Treatment 13 5.3.2 Secondary Treatment 13 5.3.3 Feasible Technology 14

6.1.1 Design Data 6.1.2 Assumptions 6.1.3 Components of the Plant 6.1.4 Land Requirements 6.1.5 Final Effluent Quality 6.1.6 Estimation of Capital and

15 15 15 15 1.5

O&M Costs 17 6.2 Wastewater Treatment for Processing

Raw Hides to Finished Leather 6.2.1 Design Data 6.2.2 Assumptions 6.2.3 Land Requirements 6.2.4 Components of the Treatment

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17 17 18 18

6.2.5 Final Eflluent Quality 6.2.6 Estimation of Capital and

O&M Costs

19 19

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Table 2.1:

Table 3.1:

Table 3.2:

Table 3.3:

Table 3.4a:

Table 3.4b:

Table 3.5:

Table 3.6:

Table 3.7: Table 5.1: Table 5.2:

Table 6.1:

Table 6.2: Table 6.3: Table 6.4: Table 6.5:

Table 6.6 Table 6.7: Table 6.8: Table 6.9: Table 6.10:

Number of Tanneries in Different Cities of Pakistan Process-wise Water Consumption and Wastewater Generation of a Tannery Quantity of Wastewater Discharge from Tanneries Characteristics of Sludge Wastewater (Process-Wise) Characteristics of Composite Wastewater of a Tamrery Characteristics of Composite Wastewater of a Tannery Characteristics of Sludge in Composite Wastewater of Tamrery-A Estimated Quantities of Solid Waste and Disposal Practices Characteristics of Solid Waste A Brief Revkw of Clermer Technologies Summary of Cost-Benefit Analysis for CRRP Estimated Daily Pollution Loads of Tannery A and B Load of Aeration Tank Land Requirement (n?) Final EfIluent Quality Estimated Investment Cost of a Treatment Plant for (Wet) Finishing Tannery Process Daily Pollution Load Load of Aeration Tank Land Requirement (m) Eflluent Quality of Treatment Plant Estimated Capital Cbst of a Treatment Plant with the Present Hydraulic Load of a Tannery

Figure 2.1: General Processes Flow Diagram Figure 3.1: Dtying Characteristics of Sludge Figure 4.1: Environmental lnput of a Tanner

6.1 Wastewater Tmatment for Wet Finishing Processes 14

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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 ofthe Treatment Plant with Mechanical Dewatering System Preliminary Layout of the Treatment Plant without MechanicalDewatering System

Annexure 1: List of Chemical Used in the Tamring Process

Annexure 2: National Environmental Quality Standards (NEQS)

Annexure 3A: Preliminary Design of a Treatment Plant Annexure 3B: Preliminary Design of a Treatment Plant

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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 lindings of enviromnental audits of four tanneries conducted by ETPI. Tbe purpose of the enviromnental audits was to assess the nature and extent of the environmental problems and to develop solution for the tamting 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 leve1 information remains confidential with ETPI. However, this program, at each stage shares the progress of the work withall its stakeholder. This report gives an overview about the environmental aspe& of tamreries along with the possible investment required to abate these problems to meet the present and Mure environmental legislation. It is hoped that this effort will help to enable tbe local tanneries to initiate the efforts to combat the present and tüture 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 tamreries were conducted jointly by two consulting lirms of ETPI consortium, hired by Federation of Pakistan Chamber of Pakistan (FPCCI) to execute the program. These fms are National Environmental Consulting (NEC) Private Limited and HASKONING of the Netherlands. The general report has been prepared by the core teamof ETPI.

This report was IIrst prepared in April 1997 on the basis of three audits and now it is being revised by adding more information obtained 6om the fourth audit conducted in this sector. Further, more details have been given on environmental technologies.

We acknowledge the co-operation of Pakistan Tamrers Association (PTA) and Tamreries who participated in the program and extended their co-operation in al1 the aspects of study.

Mr. Mohammad Iqbal Co-ordinator Technology; ETPI Mr. Izhar-ul-Haque National Environmental Consulting (Pvt.) Ltd. (NEC), Pakistan Mr. J. A. S. Berns HASKONING, The Netherlands

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April1998

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The Federation of Pakistan Chambers of Commerce & Industry (FPPCI) being the apex body representing al1 the business, trade and industrial organisations of the country, has launched a comprehensive five year program, called “Enviromnental Technology Program for Industry (ETPI)“, with technical assistance from the Netherlands Govemment. 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 Enviromnental Quality Standards (NEQS) and the forthcoming ISO 14000. The program is under implementation witb 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 leatber 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 fmished form. There are presently over 595 tanneries in the formal sector and an equally large number of tanneries exist in the mfomtal sector. The major cluster of tamreries are located in Karachi, Kasur, Lahore, Sheikhupura, Gujranwala, Multan, Sialkot and Jahangria. For leather production, locally available raw material ( hides and skins) and predominantly hnported chemicals are used.

In the leather sector a variety of fmished leather is prepared which mcludes upper, lining, and garment etc., tiom salted raw skins/hides. The chrometanning method is widely applied for preparation of tinished leather. However, vegetable tanning method and a combination of chrome and vegetable tamring method is also used. Most of the chemicals are used to prepare the skins or hides for the tanning purpose. After performing their fimctions these chemicals fmd their way mto the environment.

The tanneries generate al1 the three categories of waste, ie., liquid, ah and solid wastes. Tbe 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, eftluent 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 curmg Salt, wet trimmings, dry trimmings, wet shavings, bufftngs, raw material packing, etc. Except dust salt other solid waste has a great attraction in local market. Poultry feed manufacturers due to tbe protem content of fleshmg, raw

trimmmgs, chrome shavings, dry trimmings, buffmg 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 par& of the country. In Punjab it is used for makmg leather board whereas in Karachi it is used for making poultry feed. During the process trivalent chromium (contained in tbe solid waste) is changed into hexavalent chromium (carcinogenic).

Wet processes of the tamrery are the main source for generating the wastewater. Water consumption per kg of raw hides varies from tamrety to tannery. Consumption of water should not go beyond the normal requirement i.e., 50 litrekg. However, it was found that tanneries are generally consuming more water as compared to the normal required quantity. Durmgthe 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 Bio- chemical Oxygen Demand (BOD), 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 tamrery to tannery due to different processes and raw material utilisation.

Due to the high pollution leve1 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 am 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.

lmplementation of cleaner technologies such as water conservation, use of environment fiiendly 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 benetits and will help the local tannery to combat the enviromnental problems.

Approximately 30% discharge of the unused chrome compound is a fmancial loss for a tamtery. This can easily be recovered from the spent tamring eftluent and this can then be reused without compromismg the quality of leather. Cost benefit analysis for chrome recovery and reuse plant has also been carried out which gives apay- back period of 6-7 months.

A wastewater treatment system is inevitableand different technologies are available in this regard. Two stage of treatment are suggested i.e., primary physio-chemicals)

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and secondary (biological). The characteristics of wastewater permit low loaded activated sludge system for biological treatment to bring downtbe leve1 of BOQ, COD, suspended solids, chrome, sulphide and pH. For the

The wastewater generated fìom tamteries involved in segmented production i.e., producing fmished leather by using wet blue also contains significant pollution level which also needs to be treated before discharge into the local enviromnent. The cosí of a treatment system

removal of Salt, in-house improvement is suggested. An (primary and secondary) was estimated for two tanneries, estimated investment cost for such a treatment system for the tannety processing SOOO- 10,000 kg of wet blue per a tannery processing about 12000 kg of hides per day is day would cost about Rs.10 million and for a tamtery

approximately 44 million with a cost of about 7-9 million processing 600 - 1500 kg of wet blue per day, the cost

rupees for operation and maintenance. would approximately be Rs.3 million.

1. The Environmabntal Tedtnology ProgPam faar Industry The Environmental Tecbnology Program for Industry (ETPI) is a joint project of the Federation of Pakistan Chambers of Commerce and Industty (FPCCI) and the Government of The Netherlands. The primary objective of ETPI is to promote the use of environmentallysafe technologies for the production of enviromnentally safe products by Pakistan’smanufacturing/ industrial sector.

The FPPCI, with the assistance of the Dutch govemment, has hired a consortium of local and foreign consulting tirms to provide the required technical expertise and support. The members of the consortium are:

l National Environmental Consulting (NEC) (F’vl..).

Ltd., Karachi-Pakistan; the lead consultant; 0 HASKONING Roya1 Dutch Consulting Engineering

and Architects, The Netherlands; 0 KRACHWERKTlJlGEN (KWT), The Netherlands; l Management for Development Foundation (MDF),

The Netherlands; and 0 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.T’he 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 enviromental 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.

Each component of ETPI has been given a specitic defmition 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 defmed as a “praject under which those environmental technologies will be implemented which qualfi both the technologv and jìnancial feasibility criteria and at the same time are relevan1 to the local industrialists. Improvement in processing practices will also be an essentialpart of the demonstrationprojects. ”

Objectives of the demonstration project include:

. To establish live examples in the major industrial sectors of Pakistan for the direct dissemination of enviromnental technologies in the country.

. To prepare a representative database in the shape of indusuy specific Environmental Audit for establishing the environmental policy implication, financia1 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 intemational 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 fiom each sub sector. Subsequently one of these three will be selected for the demonstration project.

ln the sub sector of leather manufacturing, instead of three Environmental audits, 4 have been carried out. The tindings of these audits have been compiled in the present report. During the enviromnental audit work, it was mentioned that the enviromnental audit report of the individual tamrery will be a contidential document and that document must not be made accessible to every body.

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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 tiorn enviromnental audits for thewhole sector. To overcome

Pakistan’s leather and leather products industry is one of the major foreign exchange eamers amongst the manufactured goods sector. At present about 90 % of the leather is exported in tinished form. During the year 1994-95 export eamings 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 materia1 (hides and skins) and imported process chemicals are used predominantly.

~~~~~~~~~:~~~~~~~ ., ,_> ii I<_ ,, 1 <__,!, I

g&~ 1~~~~~~~~~~~~~~; j ;&#fj (,$Q ;j; 2.i jii ::_: ? f1 ” 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 afieEid- ul-Azha and extends up to two on three montbs, the processing in leather sector reaches to a leve1 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.

~:~~~~~~~~~~~~,all~~~!~~~~!:,~~~~.]:Í~~::~ !i,l’l $6 li s I ,; i il”r $g /_ :;p\‘$ ),${ yjj $j

A variety of chemicals, fiom common salt (sodium chloride) to the very fine fmishing chemicals, are used in Leather sector. About 130 different type of chemicals am applied in leather manufacturing, depending on the type of raw material and the end product of tbe industry. These chemicals are divided into four major classes, described

this short coming help has been taken from secondaty information. This report has been prepared with an aim that it will provide a general scenario about the environmental problems of local tamreries.

below, as per their use. The list of chemical is given in amiexure 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 aher perfotming their respective functions are discharged with the wastewater.

Tanning Chemicals: These tanning chemicals react with the collagen tibres 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 witb 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 fmancial 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 tibres 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 linish 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.

i&i@ ~~~~~~~~~~~~~~ pJ&&

An extensive quantity of water is used in the leather sector. The data shows that 50 -150 litre of water is used for the conversion of one kg of raw skin into leather. Tannety 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.

Jn the leather sector a variety of fmished leather is prepared including upper, lining, and garments from salted raw skinsihides. The Chrome tanning method is

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widely used for the preparation of finished leather. (ETPI) apply chrome tanning process for the production However, vegetable tarming method and a combination of of fmished leather. A series ofprocesses and operations are chrome and vegetable tanning method is also being involved for the production of leather. These are described applied. The three tanneries selected for the audit under as follows. The flow diagram of processes and operations is the Environmental Technology Program for lndustry given in figure 2.1.

1 RAW MATERIAL (RAW SKINS/HIDEQ 1 1

1 FLESHING

.l

WET BLUE STORAGE 3.

l SPLIlTING OF WET BLUE 1

SORTING 0°F WET BLUE 1

SHAVING 0; WET BLUE 1

Hide processing

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

1 1 SAMMYINGISE’TTING 1

1 VACUUM DRYING

5 AIR DRYINGISTEAM DRYING

d

1 STACKING HORIZONTAL J

I TOGGLING J

l DRY SHAVING 1

1 TRIMMING 1

BUFFING J .L

1 SPRAYING/COATlNG/DRYlNG 1

GlAZING/POLISHlNG L

IRONING 1

MEASURING I 1

SELECTION 1

PACKING

items are provided by the tamrery, workers do not pay much attention. The un-usage of these accessories during work may be due tothe and ignorarme andun-awareness of the workers. Information boards about safety and heabh regulations are not installed in the tatmeries. 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.

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All the three categories of waste, i.e. liquid, air and solid, are generated by tbe tanneries. Following section describes the source, disposal, characterisation and quantification of these wastes.

3.1 Wastewater

3.1 .l 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 minar quantity of wastewater. Wet processes are highlighted in the flow diagram @Tg. 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 tibre of the skins. The process water, afier 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 hito the local enviromnent.

3.1.2 Quantity Water consumption per kilogram of raw hides varies frorn tannery to tannery. Generally water consumption should not go beyond the normal requirement i.e., 50

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 skms/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 6om different tatmeries is given in Table 3.2.

3.1.3 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 Govemment of Pakistan (see annexure 2). Pollutant values of different tanneries are given in Table 3.3 and 3.4.

Processes Percentage of Water Used for Avera e Wastewater Generation Process (m’l day) (12,000 kg/day)

(A) Processes = Raw - Wet Blue: Pre-soak wash 500 60 Soaking 500 60 Soak wash 500 60 Liming & Un-hairing 500 60 De-liming 200 24 Washing-l 200 24 Washing-2 200 24 Bating 200 24 Degreasing 200 24 Washing - 1 200 24 Washing -2 200 24 Washing -3 200 24 Washing -4 200 24

PicklingfTannin 80 9.6 Water Consumption from raw to wet blue stage 465.6 (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 fmishing processes Wet back 300 36 Neutralisation Re-tanning Washing 200 24 Fat liquoring / dying 200 24

Washing 200 24 Water Consumption in wet fmishing 108 Total Water Consumption (A+B) 574 = Total Wastewater Generation

Source: ETPI Survey - calculated on the basis of water recipe provided by the tannery

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Wastewater from each tannery process contains different types of pollutants. pH varies considerably from 3.3 to 12.6. Similarty, a large variation exists in parameters hke 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 mese chemicals into wastewater is not only hazardous but also a financial loss.

A considerable quantity of sludge was also present in composite wastewater. The setdeable matter is responsible for the sludge generation. This sludge content is presented in Table 3.5 and represented in figure 3.1

rmo 900

.$ am g 700 y 820 e 5aO

; 420 B 330 g 2.20

lao

QO

1 2 3 4 5 6 7 6 9 10 ll 12 13 14 15 16 17 16

auhs-ww -+s&sl 1.. .=&&2

Tannerv-A (Sheen & Goat SkinsJ

Wel blue to fmished upper and lining leather (10000 Wday)

I 1 litre ikg wet blue

Wet Blue to finished * 11 litreikg wet blue Leather f700- 1740 kddav) **21 litre/ke wet blue

(Raw calf hides to finished leather) (12000 kgday)

* As per recipe * * Measured at drain

*32.5 litrekg raw hides **150 litre kg!raw hides day

The major solid wastes generated by the tarmeries nre dusted curing Salt, wet trimmings, dry trimmings, wet shavings, dry shavings, buffmg, raw material packing, etc.. Most of the solid wastes generated are separated at the source.

In order to quantify the solid waste being generated fiom individual process/operation, some data was available with the management of tanneries. However, in caseof non-availability of the data, known number of skinshides were weighed before and aher 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 sohd wastes, their types and their generation.

Total Dissolve 51,251 40,943 19,780 91,710 10,579 20,677 21.578 9,560 Solids

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* Estimated on the basis of chrome content in chrome tanning effluent (6132 mgll.)

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Dusted salt 0.1 ka/skin

Raw trimming 0.024 kg&in 240 Sold to poultry feed makers

Cartons, bags, drums, Miscellaneous refuse

No consistent quantity Sold

Source: Data supplied by Tannery. Note: These quantities are based on the average figures (10,000 kgsiday)

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dusted Salt, which is contaminated with blood, hair, dirt and certain type of bacteria is removed hom 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 6om the limed skins and is generated during the fleshingoperation which is carried out after liming and un-hairing processes.

Splitting of Wet Blue: This operation is carried out in hides tanneries processing hides. Afier 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 u:sed for preparation of finished leather. Whereas, the lower layer is treated as a by-product. However, it is fiuther processed and is used for manufacturinglow grade shoe upper leather and as such is not considered as solid waste.

Chrome Wet Shaving:AAer 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: Buffmg, adjustment of the thickness of leather and trimming operations are responsible for the generation of butling 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 ~10th bags.

solid waste was also carried out. Four samples, each of one kilogram, were taken hom major types of solid wastes being generated, i.e. salt dusting, fleshing, wet

shaving and trimming, dty shaving, trimming and bufting. 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.

Salt && ‘: ;~’ gt 1;: 2% f ;;i:r’!lrltli~~li!‘$illt ,I;kiltl:R::lli,iii!i’; :

Sulphide - 1.96 -

Source: Laboratory Analysis. Note: Al1 values are in gm /Kg. unless otherwise specifíed.

##@ #j& With the exception of dusted Salt, al1 other solid waste is consumed within the local market. Empty drums, cartons, chemical bags etc. have demand in the retail market. Contracton purchase these materials in bulk fiom the tamrety and se11 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, dty trimming, butling dust, etc., collect these materials fi-om the tannery. The main problem associated with some of these wastes is their chrome content. The chrome content in these wastes ranges from 14 -26 gm/kg. The chrome-tanned waste contains chromium in tr-ivalent forrn, 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. ln Punjab this solid waste is used for making leather board whereas in Karachi this is used for making poultty feed.

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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 inpoultiy feed in such a high quantity could produce severe health problems for human beings.

Sources of air pollution in tanneries are of two types. One is fiom stack of generators and boiler and the other tiom the processes.

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.

~~~~~:~~~~~~~~~~~~ j ~~~~~~~~~~~~~ Hydrogen sulphide and ammonia are the major gases emitted during the washiug 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 / Nr& which is a health hazard to the workers.

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 tbe NEQS.Solid waste is being collected by contractors for preparation of poultry feed. As far as liquid waste is concemed, 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 enviromnental impacts are discussed. Furtber, the pollutants of tannery wastewater have been compared with the pollutants of sewage( source: KWSB).

fiorn-3.5 to 13.5. 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 sewcrs. Whereas, low pH of wastewater is caused by use of acids in different tanuery processes. A large fluctuation in pH exerts stress on aquatic environment which may kill some sensitive species of plants and animals Iiving there. The NEQS recommends a value of pH in the muge of 6 - 10.

~~~~~~~~~ # prote& ‘and tbeir degraded products

form the largest single constituent group in the emuent. They effect the environment which can be expressed by tW0 composite parameters; Biochemical Oxygen Demand (BOB) 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 1740 - 11050 mg/l. Whereas the NEQS recommends a BOD value of 80 mgil. Therefore, tannery wastewater is canying about 20 -140 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 (375 - 525 mg/l) of sewage.

oxygen equivalent to that portionof 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 stndies 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 bacteria1 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

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of 3800 - 41300 mg/l. Whereas according to the NEQS, a value of 150 mg/l has been mcommended for COD. Hence, tannety wastewater is carrying about 25 - 1175 times more pollution load in terms of COD. Sewage water usually contains 1000 mg/l COD.

Due to sulphide discharged kom theunhairing 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 15-20 mg/I and composite tannery wastewater contains 290 mgI, whereas, the NEQS recommends a value of 1 .O mg/l.

process. This is much less toxic than hexavaleni chromium. For plant and animal life, the toxicity of chromium salts is variable. Tbe toxicity is a fimction of the species itself. Algae have been shown to be particularly sensitive. Estuarine molluscs, although apparently unaffected iu their own metabolism, accumulate trivalent chromium.

At present, tamreries are discharging chromium (133 mg/l) in composite wastewater and in sludge (3 - 17.5 gmkg). It can be seen that wastewater of chrome tanning process, which is about 2 % of the total wastewater of the tannery, contains 6000 - 7000 mg/l of chromium Cr).

The sewage of Karachi contains 0.1 to 0.5 mgil of

chromium, whereas the NEQS recommends a value of 1.0 mg/l.

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 Iürther secondary effect is the reduced light penetration and consequent reduction in photosynthesis due to the increased turbidity of water.

Tamreries discharge wastewater containing440 - 890 mg/I of suspended solids. The Karachi sewage contains 500-900 mg/l suspended solids, whereas the NEQS recommends a value of 150 mg/l.

effect when discharged into estuaries or the sea, but effects fkesh water life when its concentration in a stream or lake becomes too high. Tbere is no economically viable way of removing salt from the efkent. 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 fiom 5820 to 14 160 and the sulphate content varies from 860 to 18 14 mg/l.

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.

1 RAW SKINS 12000 KG 1

? 1 WASTEWATER (600 M?davb

BODs = 13680 COD = 34200 Suspended Solids = 2790 Chromium = 80 Sulphide = 173 Sludge = 3280

411 values in Ke/dav

1 LEATHER 14OOKe J

. As tanneries do not have an environmental management system. therefore, this system must be developed in tamreries, specially in the large and

. SOLID WASTE AND BY- PRODUCTS

UNTANNED Dusted Salt = 1000 Raw trimming = 240 Fleshing= 2500

TANNED Shaving = 1500 Trimming = 240 Bufling = 20

Total = 5500 All values are in Ke/dav

medium sized ones. Environmental management should be a responsibility of the persormel in addition to their routine duties.

. Short-term training on occupational health and safety aspects , modem practices for the handling of hazardous chemicals, etc. is required for the staff.

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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 pickhng process, acid resistant gloves and aprons etc. Face masks to avoid inhalation of fumes of finishing chemicals, toxic gases, etc. ?he use of the safety gear should be implemented strictly. Proper mangements 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 afier mixing with other wastes, like circulation watcr of spray plant that caries unused fmishing material. Other waste that can be mixed witb tanned solid waste is

curing Salt. AAer 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.

A number of cleaner technologies can be applied for the manufacturing of fmished 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 tinished leather.

Some of the cleaner technologies have been described Table 5.1

Water Conservation The use of pit or paddle for soaking operations res& in a higher consumption of water, mainly for washing phase which are much less efflcient than when using drums. Even for drums it is recommended to operate the sequential washing instead of continuous washing which leads to tbe savings of enormous amount of water at each stage. Low float technologies would also reduce the water quantity. Although such conservatioldo not reduce the pollution load, however, they can lead to the reduction in the size of the efluent treatment plant.

Green Fleshing of Hides Green fleshing jusl. afier deep soaking is a suitable pmcedure to obtain by-product at pH close to neutral, which can then easily be processed to recover fats and pmteins with good marketing possibilities and to save liming andunhairing chemicals. Further green fleshing also improves the penetration of the chemicals and hence improves the quality of finished leather.

1~~~~~~~~~ ‘:’ ‘SY & i, ; _i , $j!],;r ,;r;, , ,.

fi!/;j;:)<;i;,;,: “ii< :i;!;!jL jljfj

z >, ,)/&i,j:’ il, ” y ‘1 ;;;

_’ _’ (?j!l ,:;;jt_ ; i!i_ : _:‘> ,*j,, $lL

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 savinns of water, sulphide. and lime.

1 .ime Splitting and Trimming Splitting and trimming is usually carried out afier tanning which results in a by-product of low quahty containing chromium in it. If these operations are carried out with the pelt, the produced by-prodoct can be sold easily in the market than those resulting from splitting and trimming of wet blue (tanned hides/skins). Tham-tanned solid waste will be a good raw material for nianufacturing ofgelatin or animal feed. This will also resulta in a reduction in the quantities of chemicals used fordeliming, pickling, tanning and conseauentlv the load of the oollutants in wastewater will be considerablv reduced.

Chrome Reuse in the Tanning Process

See Section 5.2.1.

Source: “lntroduction of Cleaner Technologies in Tannery Cluster of Punjab”

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chrome disch&ged in the tanning eflluent. 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 necessluy amount of chromium being discharged into the enviromnent, thus facilitating the treabnent and disposal of a small amounts of chromium containing sludge. Chrome reuse option also provides fmancial benetits.

Direct Recycling of Chrome Tanning Float: This is the easiest method of chrome reuse. III this method after collection and sufficiently fme screening, the float is controlled and the chromium amounts used in the previous cycle are replaced by fresh chromium salts. Depending on the tarming technology in use, the degree of exhaustion reached for each cycle may vary. The recycling method may be repeated severa1 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 tatmeries.

Recycling Of Chrome After Precipitstion: Ibis allows collection of the tanning float with the rinses, that sometimes occur at the end of the tanning and the effluent fiom various post-tanning stages (washing, dripping. sammying, etc). Afier 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.

Cos+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 tatming eftluent and minimum value of chrome quantity has been considered. Cost benefit analysis is given in the following table. Bese 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 andbasification 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 L8 % on the fleshed weight and still obtains the same quantity of chrome tixed on the fibres.

fqr:$#$RP : 7 :i!Ilri ii;& ;_: ,_,_i $1 "'il//( ;g]& I _>_& _I_ ';; " :'@$ :'ii i;

q$$* Bnfticgf& :'::$ 'II $: : y;iíl f;i __ “,irii, _> j_ I'] ',‘,:':: t ;<' 1,': ;Il:i: < $,; __' I : Et;, ; 3n&~:' ;> ;;_ )I' S')_</I' I j I L j[(Q" 'jji II : ; 'xy ,jfiH '; _i_ ;_

- Raw goat Skins 3000 kg/day - Quantity of tanning float 80-100 % of “a” - Total volume of float (a*b/lOO) 2400 - 3000 litre - Basic Chromium Sulphate (BCS) applied in tanning process 7-8 % of “a” - Total BCS applied per day ( d*a/lOO) 2 10 - 240 kglday - Chromium (Cr) in Tanning Effluent 7000 - 7500 mgA - Total BCS in Tanning Effluent (c*ff 170000) 123.5 kilo/day - PH 3.46 - 3.66

*f;!:j “%l,Í_ g)q&@&)&n 9, : i <’ $_ ‘_ ,: b*u#gt ’ <j i,;: s p&&:, (4; 2. Capital Co.9 683,000 Rs.

TOTAL 0 & M (:ost 314,600 Rs.i year

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Two levels of treatment are normally required for treatment of the effluent tiom the tanneries. These are primary and secondary treatment.

screening, pH equalisation (collection of effluent of different processes in a common tank). coagulation and flocculation and sedimentation.

Mechanical Screening: Removal of coarse, particulate Besh 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 fiuther treatment of the eftluent.

pH Equalization:The wide fluctuation in the efluent‘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 tbe amplitude of pH fluctuation &om 3.5 - 13 down to approximately 8.5-10, as observed during the sampling programme.

Due to the equalization tank, the flow and composition of the eftluent is also maintained more constantly for türther treatment.

Physio-Chemical Processes: Coagulation and flocculation are applied to the tannety 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.

B In secondary treatment, biological processes are used to remove most of the organic matter fiom the wastewater. This is achieved by usingmicro-organisms to convert the organic matter into different gases and into ce11 tissues. Ce11 tissues have a specific gravity slightly greater tban that of the water; the resulting tissue is removed 6om 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, efftciency 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 bacteria1 floc maintained constantly in suspension. Atter 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 tannety wastewater and widely used al1 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 processis supplied by surface aerators. In an aerobic lagoon, al1 the solids are maintained as suspension. To meet the secondaty treatment standards, this technology can safely be used for the treatment of tannery eftluent. 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 areoxidized 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 presente 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. Tbe partially clarified effluent is usually discharged to another process for türther treatment.

Usually, these ponds are anaerobic throughout the depth, except for an extremely shallow surface zone. Stabilization is brought about by the combination of

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precipitation and the anaerobic conversion of organic waste into carbon dioxide, methane, other gaseous end products, organic acids and ce11 tissues. Conversion efficiencies of BOD up to 70% can be achieved.

High sulphate concentration in tbe 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 principie of the trickling filter is by percolating the water to be treated through a mass of porous or cavemous material, which serves as support for micro-organisms. 7he necessary oxygen required for maintaining an aerobic state for tixing Ihe biomass to tbe 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 dischargiug wastewater containing 40 times more BOD value as compared to domestic wastewater. Nitrification is possible in tbis type of technology whereas denitrification of wastewater is not possible. Therefore, it is not possible to apply tbis 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 micro- organisms. The wastewater is evenly distributed at the bottom of the reactor, and aRer a suitable hydraulic retention time in the reactor it leaves from the system from top of the reactor. The contact between themicro- organisms of the wastewater is enbanced by ihe 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. AAer

passing through the sludge bed, a mixture ofbiogas, sludge and water enters a three phase separator. The biogas is separated in a gas collector, whilst the sludge- water mixture enters a settling compartment, thus providing effective sludge retention in the reactor. The effluent is discharged fiom the top of the reactor via an overflow weir. The excess sludge is discharged fiom 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 principie, 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 presente 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 (SO4) in the range of 860 - 3,146 mg/¡.

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

~~h~8,~~d~n~~~ti;b~~~,~~ $l~jj~ jjl 2,: yj’: ’ Í‘i& iji;,,f”‘j’i On the ba.& 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 tbis 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 tatmeries participated in the ETPI program. One type of tannery was invloved in segmented production by using wet blue as raw material to prepare finisbed leather. The processes they conduct are usually referred to as “Wet Finishing Processes”. The other type of tannety was a complete tannery, processing raw hides to prep;ìre finshed leather. Tbe wastewater treatment system for both the type of tanneries has been described in the following sections.

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 tiom another tannety. The processes employed to prepare finished leather from wet blue are called wet fmishing 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) linishing process. The production of tbese tanneries is as follows.

Tannery “A” processing 8000 kg to 10000 of kg skins (wet blue) per day. Tannery “B” processing 600 kg to 1500 kg of skins (wet blue) per day.

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Tbe suggested tmatment plant comprises of a primary and secondary leve1 treatment system.

of wastewater fluctuates between the vahres’given below depcnding on the quantity of raw material processed dail y:

Tannery “A” 80 -120 nhday Tannery “B” 30 - 40 m?day

Daily Pollution Loads: Tbe maximum values of water quantities 120 and 40 d /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:

Ave.Conc. Load (md0 Wd)

BODs (20 C) 1985 238 1468 58.72 total

COD (total) 5755 691 6380 255..33

Tot. suspended 5295 515 1042 42

sulphate 5980 717 ~~~~‘~~ÍÍ~~~;Í~~ p@gg; 2 “:;,:g@ Bj& $[;&g i$ ~:$& Phosphate 25.5 3 3.5 0.14

Note: BOD suspended solids are based on the difference of BOD at 0 time and BOD afier 60 minutes settling. Source: Laboratory Analysis.

:&j.&,, ~~~~~~~~ ríc, ;$ ~Qj! ‘%:$ ,{’ I jic_ : <__ :j ’ ’ The following assumptions have bcen made for the preliminary design: . Wastewater quantity of the peak season has been taken

into consideration, maximum flow which means a higher capacity, especiahy in aeration tanks and hydraulic capacity;

. Tbe liquid effluent will be lified (pumped) only once for the required water leve1 in the plant;

. Tbe removal efftciencies 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 stabihzation); and

. Mechanical dewatering is taken into consideration as relatively high amounts of sludge are generated daily.

JIescripfion Inputto Efficiency outpt of Shdge Primary of Primary Ptilllary (k’d) Treatment Treatment Treatment*

(%) (ke/d)

Taonery - B

BODs 58.12 40 35 susp. 42 60 17 25 Solids 1056 10 10 Kj-N 0.016 0 0.016

* Considered loads to the aeration tank for design of volume and capacity.

Water Handhng . Collecting pit, including a pumping station; . Equalization tank (witb mixers for stirring to prevent

setthng). Addition of chemicals like lime and polyelectrolyte will also be carried out at this stage;

. Primaty sedimentation tank;

. Aeration tank (aeration by surface aerators); and

. Final sedimentation tank (including retum sludge facifies). Sludge Handling . Primary sludge pumps (for pumping of primary sludge

tiorn the sedientation tank to the sludge thickener); . Excess sludge pumps (for pumping of excess sludge

fìom the return sludge pit to the sludge thickener); . Sludge thickener (to increase dry sludge concentratin

i.e reduction of the sludge volume);aud l Ihying beds and belt fiher press.

Pteliminary layout of the treatment plant is presented ~YI Figure. 6.1. Land requirement with and without a mechanical dewatering systcm is shown in Table 6.3 below:

Designing has been carried out to produce effleunt to meet the NEQS level. Table 6.4 shows the final effluent quality afier treabnent:

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~rt:ro~~~r~~~~~~~~~~~~ $; ::_ Estimated capital and operation and maintenancecost are summarised in Tables 6.5. The process design is given in annexure 3 and 4

A: Civil Works

Sub Total 3702200 1430000 B; Me~l&oal~~ ,:i_j "I $1 ,,$$i SII $ ! '>: $$ I _,

Mixer 100000 50000 Pumps 700000 350000 Scraper, skimmer, bridge etc 50000 _________

Surface aerator 150000 200000 Belt fílter press 2500000 --------

'aíhT&alii ;; ~;z$@@oo Mzaooa‘j_~>& Total A + B 7202200 2030000

2. Contingencies (20% of total A+B)

1440440 406000

Estimated Annual Operation and Maintenance Cost 15- 20% of thc total (million Rs)

1.5-2 0.4-0.6

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Tannery processing calf hides to produce tinished shoe upper leather am consideted here. On an average 1.000 hides (approximately 12000 kg/day) are processed daily in a normal production period. The quantity of raw hides reaches upto 2000 hides /day in the peak season.

wastewater tluctuates in between the values given bdow, depending on the quantity of raw material. processed daily: . 1836 m3/day on an average (wbole year); . 3672 m3/day in peak season (about 2 months).

Daily Pollution Loack Daily polhttion load has been calculated on the basis of average and peak flows. Daily pollution loads are summarized in Table 6.6. Whereas, average values of each parameter is taken for designing wwe.

BOD5 (20 C) total 1740 3195 62390 BODs (20 C) 560 1028 2056 setdable solid 1327 2436 4872 Tot suspended solids 25 459 918 Tot Kj Nitrogen 2 3.7 7.4 Sutphate 6 II 22

Note: BOQ suspended solids are based on the difference of B0D5 at 0 time and BOQ atter 60 minutes settbng.

:g; ‘.;$ $11 j[; i_I ;ir;;:: t&; ~~;;i@“; ! ; iij $_! The following assumptions have been applied for the preliminary design:

As peak season is only two months per year, the design

capacity will be based on the average flow, a design for a maximum flow means a high capacity, especially aeration tanks and hydraulic capacity;

The Iiquids effluent will be litbed (pumped) only once

for the tequired water level in the plant; Tbe removal efficiencies of the primary sedimentation

tank ate summarized in Table 6.7; Tbe design of the aeration tank is based on a low

loaded activated sludge system (including sludge stabilization); and

Due to the availabihty of the land, drying bed has been

suggested.

BOD, 3195 30 1218 susp solids 2436 70 398 Kj-N 459 10 225 1705 SUlphide 37 0 37

Phosphate ll ll . Considered loads to the aeration tank for design of

volume and capa+.

Preliminar-y layout of the treatment plant is presented in Figure 6.2 & 6.3. Land requirement with and without a mechanical dewatering system is shown in Table 6.8 below:

7838 13834

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Water Handling . Collecting pi< includmg a pumping station; . Equalization tank (with mixers for stining to prevent

sealing); . Rimary sedimentation tank; . Aeration tank (aeration by surtace aerators); and . Final sedimentation tank (mcluding retum sludge

facilities).

Sludge Handling . Primaty sludge pumps (for the pumping of primary

sludge tiom the sedientation tank to the sludge thickener);

. Excess sludge pumps (for the pumping of excess sludge t?om the retum sludge pit to the sludge thickener);

. Sluldge thickener (to increase the dry sludge concentration and reduction of the sludge volume); and

. Sludge drying beds and a mechanical de-watering option for sludge drying.

&.P5: ;~Ftq& q&::“,&;j’ ‘,-‘::,,i$ ;:_, Designing has been carried out to produce effluent to meet the NEQS leve1 Table 6.9 to show the final effluent quality atter treatment.

PH 7.66 7.5-8 BODI 1740 80 COD 2670 150 Suspended Soild 1323 150 T.Kjeldhal Nitrogen 25 1.25 Sulphide 2 Ni1

chromium* 3 co.25

&f&g Estímg#a;sl:,~;~~~ji~~~~~~~~~~ :; ,:y

The estimated total cost of a treatment plant is given in table 6.10. Process design in detail is given in annexure 5.

19

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