As of estimates made in 2002, India had more than 3000 tanneries with a total capacity of 700000 tonnes of hides and skins per year. The annual income from leather trade in India was about Rs 20000 crores. More than 90% of the tanneries were small or medium with a processing capacity of less then 2 to 3 tonnes of hides/skins per day. Most of the tanneries are located near river banks. The highest concentration of tanneries in India is on the banks of Ganga river (Kanpur, Unnao) in North India and the Palar river system in Tamilnadu.

Leather Production Technology and Pollution:

An animal skin consists of about 61% water, 34% fibrous proteins, 1% globular proteins, 2% lipids, 1% natural salts and some other ingredients including pigments. Out of three layers, the epidermis, dermis and the hypodermis it is the dermis which is later transformed into leather. The epidermis primarily composed of keratin has hair which is removed and the hypodermis has flesh and blood vessels which is also removed. In leather processing, the basic operations revolve round cleaning the skin of unwanted inter fibrillary material through a set of pre-tanning operations in the Beam House, processing the leather permanently by means of tanning and adding aesthetic value during the post tanning process. The starting material in most cases is raw hide or skin which has been preserved temporarily by the addition of common salt.

1. The Beam House process involves the removal of salt, dirt and hair  in the following processes:

(a)   Desalting and Soaking the hides to remove salt and other foreign material such as dirt and also to remove the moisture content.  This process uses a large amount of water about 20 m³ per ton of hide and generates conspicuous pollution. Soaking generates about 6-9 m³ per ton of effluents with a BOD from 1100 to 2500 mg/l, a COD of 3000-6000 mg/L, very high total solids and suspended solids, 15000 to 30000 mg/l of chlorides and 800-1500 mg/l of sulphates.

(b)   Unhairing and Liming – The process yields one of the most polluting effluent streams from tanneries. Liming opens up the collagen structure by removing interstitial material, fleshing removes excess tissue from the interior of the hide.  Unhairing is done by treating soaked hides in a bath containing sodium sulphide / Hydrogen sulphide and lime. About 3 to 5 m³ of effluent per tonne of hide/skin is expected to be discharged with a high pH of 10.0 to 12.8, a BOD of 5000 to 10000 mg/l and COD of 10000 – 25000 mg/l. The concentration of sulphides ranges from 200 to 500 mg/l, the total solids (24000 to 48000 mg/l) and sulphates (600-1200 mg/L) are also high.

(c)    Deliming and bating: A bath of ammonium salts and proteolytic enzymes is used to process the pelt. About 1.5 m³ of effluents are generated in the process at a pH of 7 to 9. The pollutants from the process include Calcium salts, Sulphide residues (30 to 60 mg/l), degraded proteins, residual proteolytic enzymatic agents, Chloride (1000 to 2000 mg/l), Sulphates (2000 to 4000 mg/l), BOD (1000 – 3000 mg/l) and COD (2500 to 7000 mg/l). Nitrogen based deliming agents are considered a long term environmental threat because of their impact on soil NOx values.

Sulphates are an important content of pretanning waste waters. They readily get reduced to sulphide under anaerobic conditions in waste water treatment plants like anaerobic lagoons, contact filters or up flow anaerobic sludge blanket reactors. A build up of sulphides makes the biomethanation of organic materials less effective apart from adding to the COD load. Ammonia is also given off as an air pollutant in the process.

Carbon Activation
Activated carbon is made from any substance with a high carbon content, and activation refers to the development of the property of adsorption. Activated carbon is important in purification processes, in which molecules of various contaminants are concentrated on and adhere to the solid surface of the carbon. Activated carbon is generally nonpolar, and because of this it adsorbs other nonpolar, mainly organic, substances. Extensive porosity (pore volume) and large available internal surface area of the pores are responsible for adsorption.

Any inexpensive material with a high carbon content and a low inorganic content can be used as potential
raw material in producing activated carbons. The most often used raw materials for manufacturing activated carbons include wood, peat, bituminous coal, lignite, coconut shell, nutshells, lignin, and others.
Activated carbons can be manufactured by either a physical or a chemical activation process. The physical activation process generally is used to manufacture activated carbon in a two-step activation process—the carbonization of raw materials in the absence of O2 followed by the activation of carbonized products. Steam and carbon dioxide (CO2) are the activating reagents most commonly used in physical activation, significantly influencing the porosity of the activated carbons.  The chemical activation process is used to manufacture activated carbons usually in a single step, using zinc chloride, phosphoric acid, and potassium hydroxide as the activating reagents.The carbonaceous materials are converted into activated carbons depending upon the nature of the raw materials, the nature of the activating reagent, and the conditions of the activation process.Furthermore, activated carbon can be impregnated with sulfur (S), chloride, or iodine to increase its adsorptive capacity, making the impregnated activated carbon much more effective than un-impregnated activated carbon for removing gaseous mercury (Hg) from flue gases at low temperatures.

Utility of Activated Carbon
Waste Treatment
Activated carbon may be used to treat a number of contaminants in liquid wastes including Non-biodegradable organic compounds (COD), Adsorbable Organic Halogens (AOX), Toxicity ,Colour compounds and dyestuffs ,Inhibitory compounds for biological treatment systems ,Aromatic compound including phenol and bis-phenol A (BPA),Chlorinated/halogenated organic compounds ,Pesticides and a host of toxic substances.

Air Pollution Control
In the context of air pollution control, Volatile Organic Compounds (VOCs) from air and other gases can be removed to below the detection limit.Noxious compounds such as hydrogen sulphide and mercaptans are readily trapped through adsorption and help to prevent odours. Incinerators dealing with Municipal Solid Waste (MSW), hazardous industrial waste, medical waste, sewerage sludge and crematoria results in the formation of a flue gas containing a range of pollutants. Dioxins and heavy metals such as mercury and cadmium are not normally removed to low enough concentrations by conventional treatment.
A range of industrial inorganic compounds and materials can be removed from gas streams, before venting to the atmosphere, using specialised impregnated or catalytic (Centaur) carbons.

In the Food and Beverage Industry
Activated carbons can be used in the Food and Beverage industry to decolourise,dechlorinate,deozonate,decaffeinate,debitter,deodorise a number of food products.

In the Pharmaceutical Industry
In the Pharmaceutical industry activated carbons are used to provide superior removal of colour compounds, odour compounds, proteins and other contaminants that could be present in the raw materials or that form during production.

As a Catalyst
With its large surface area, purity and relative hardness, activated carbon is an ideal carrier for catalytic metals or  a catalyst by itself.Activated carbons  have been successfully used as a catalyst in the manufacture of dry cell batteries, production of biodegradable herbicides like cyanuric chloride glyphosate, mercaptan removal in petroleum distillates and in the production and destruction of phosgene.

In the production of natural gas
Activated carbons have also been used for removal of mercury from natural gas for the production of L.N.G. , the removal of mercury from liquid hydrocarbons and  the removal of mercaptans/thiols , hydrogen sulphide and amine solutions  from natural gas and natural gas scrubbing.

In the brewing industry
Industrial uses of activated carbon also include its use for the purification of  hydrocarbon contaminated Carbon Dioxide generated from the conversion of sugars to alcohol and its reuse for carbonation in the brewing Industry  thereby eliminating the need from purchasing Carbon Dioxide from outside sources.

For the storage of gases
It can also be used to remove trace lubrication oils from waste streams and in fruit storage for gas storage(under pressurised condition the extensively developed carbon porosity provides for greatly enhanced volume storage of either a pure gas, such as carbon dioxide or nitrogen, or a gas mixture such as air) and delivery and also in applications that provide alternatives to greenhouse gas emissions.

In the Caustic soda Industry
Caustic Soda is used extensively in, and is also a by-product from, the chloralkali industry. Mercury cells are used for production of chlorine, hydrogen, and sodium (in a few plants potassium) hydroxides by electrolysis of a brine solution, and this can cause contamination.  Steam activated and impregnated carbons  are proven for this application.

For the purification of Electroplating Chemicals
Electroplating chemicals that become contaminated with organics and metal finishing residues can be purified by the use of steam activated carbon and the chemicals can be recycled for reuse.Chromium can be recovered from electroplating solutions.

In Gold recovery applications
Coconut shell based granular activated carbons are used in gold recovery applications employing the Carbon in Leach (CIL) or Carbon in Pulp (CIP) processes.

In Process Water treatment
In process water treatment, activated carbons are used to remove tastes and odors ,disinfection byproducts like chloramines, free and combined chlorine,trihalomethanes and halocarbons, for pH and alkalinity control,condensate recovery and treatment systems in steam generating operations,personal and collective protective masks against toxic gases includind Industrial and military respirators.

Other Applications
Other applications include within air filtration systems in archives and museums,ozone management in ponds and aquaria,treatment of swimming pool water for removal of organic matter, chloroform ,ozone,chloramine and other bonded chlorine and in cigarette filters,filters for treating cabin air in automobiles.

Recycling of spent activated carbon
Once granular carbon is saturated or the treatment objective is reached, it can be recycled, by thermal reactivation, for reuse. Reactivation involves treating the spent carbon in a high temperature reactivation furnace to over 800°C. During this treatment process, the undesirable organics on the carbon are thermally destroyed. Recycling by thermal reactivation is a highly skilled process, to ensure that spent carbon is returned to a reusable quality.  Recycling activated carbon by thermal reactivation meets the environmental need to minimise waste, reducing CO2 emissions and limiting the use of the world’s resources.

From Walnut shells
Walnut shells serve as an alternative source of  Activated Carbon. Adsorption capacity increased with increase in activation temperature but beyond 400 degrees celsius resulted in thermal decomposition. Activation longer than one hour at 375 degrees celcius resulted in a destruction of the micropore size.Activation with ZnCl2 was better than that with CaCl2 and increased with increasing concentrations upto a certain limit beyond which increasing concentrations inhibited activation.Applicability of the activated carbon from walnut shells, as adsorbent  for synthetic copper wastewater, was better for Copper Ions as compared to  carbon from coconut shell.

From Rosa canina seeds
“An activated carbon has been developed from Rosa canina sp. seeds, characterized and used for the removal of methylene blue (basic dye) from aqueous solutions.”

From Corn Cobs
A new absorbent material  made from the remains of corn cob is being used to store natural gas. A nanaporous carbon material is produced from the waste corn which is referred to as the “sponge for natural gas”,where the methane uptake is 120v/v or more. Other materials used to make this adsorbent material , olive pits and coconut shell, are more expensive to produce.Flat low pressure high capacity natural gas tanks for vehicles holding no greater than 500psi of methane have been developed.This  reduced the effects in the event of an explosion because of lower pressure of the storage tank and allowed for more trunk space in cars.

Corn cob dried and crushed is mixed with phosphoric acid (H3PO4),where it serves as an activating agent.Excess phosphoric acid is removed and the mixture is carbonized at 450-650oC in a reactor, after which it is evaporated at 160oC for 3 hours.It is washed with hot water to bring the pH to a neutral point.The washed activated carbon is dried at 110oC and grinded and sieved to a particle size of 40 mesh.Using a hydraulic press and a die the powder and a small quantity of binding agent is pressed into monoliths or briquettes to obtain the highest density .These briquettes are used for storage of natural gas at a targetted capacity of 150v/v .The applications include use in gas based vehicles,transportation of natural gas and adsorption of gas from land fills.

From Oil Palm wastes,cork powder and other agricultural wastes
Adsorption of Sulfur Dioxide on Activated Carbon from Oil-Palm Waste and use of cork powder as source of activated carbon has also been studied.Agricultural wastes could be considered as suitable raw materials for the production of activated carbon.activated carbon was produced by chemical activation with phosphoric acid of agricultural wastes such as bagasse, hard shells of apricot stones, almond, walnut and hazelnut shells,activated carbon from the hard shells of apricot stones have the best adsorption properties and the highest surface  area. This activated carbon could be used in the separation of metal ions from wastewaters.

From pyrolysis of sewage sludges
Activated carbons can also be produced by the chemical activation and pyrolisis of sewage. The adsorbents produced from sewage sludges were able to adsorb dyes from coloured waste waters like saffranine and methylene blue.Methylene blue absorption was faster than that for Saffranine.

From Waste newsprint
Waste paper activated carbon has been  prepared from waste newsprint paper and its adsorption capacities were almost the same as ordinary activated carbon on the market.

From Waste Tyres
Technology is available to burn tires in order to seperate and recover carbides.Some parts of the carbides are active and can be used as active carbon. Water (steam) is added to the system for activation.Steel and generated steam can be recovered seperately.

Methods for treating waste tires include retreading,stockpiling, landfilling, recycling, pulverization, fueling, incineration,and pyrolysis. The simplest means of treating waste tires are landfilling and stockpiling. However,wastetires are not easily biodegradable in landfills and, when stockpiled, the accumulation of water in waste tires provides an ideal breeding ground for disease-carrying mosquitoes and rodents. Moreover, uncontrolled fires have broken out in piles of waste tires, and the emission of gaseous air pollutants during open burning has threatened human health and the safety of nearby communities.Waste tires contain more than 90% organic materialsand have a heat value of 32.6 mJ/kg (14,000 Btu/lb),compared with that for coal of 18.6–27.9 mJ/kg (8000–12,000 Btu/lb). Several attempts have been made to convert waste tires to auxiliary fuel. Among them, pyrolysis is a favorable choice for treating waste tires from environmentaland economic perspectives. Pyrolysis is a typical thermal treatment process in the absence of oxygen (O2),which decomposes waste tires into carbon black, combustible gas, and pyrolysis oil.The combustible gas can be recovered as an auxiliary fuel, while the pyrolysis oil, with a composition similar to that of diesel, can be further distilled as supplemental fuel. Furthermore, waste tires or carbon black could be activated into powdered or granular activated carbon for air pollution control and wastewater treatment.

Rubber separated from waste tires was first carbonized at 500 °C in N2 atmosphere. Next, the obtained chars were activated with steam at 850 °C. As a result, fairly mesoporous activated carbons  were obtained. To further improve the porous properties of the activated carbons, the char was treated with I M HCl at room temperature for 1 day prior to steam activation. This treatment increased mesopore volumes , Furthermore, adsorption characteristics of phenol and a dye, Black 5, on the activated carbon prepared via acid treatment were compared with those of a commercial activated carbon in the liquid phase. Although the prepared carbon had a larger micropore volume than the commercial carbon, it showed a slightly lower phenol adsorption capacity. On the other hand, the prepared carbon showed an obviously larger dye adsorption capacity than the commercial carbon, because of its larger mesopore volume.

From Waste Wood
Activated carbons have been produced from waste wood and have the added advantage of  better utilization of resources and reduction of carbon dioxide generation from waste incineration.Specific surface area and adsorption performance of activated carbons from waste wood were found to be nearly equal to those of commercial activated carbons which could be used for humidity-control in houses and leachate treatment in landfill. Waste wood activated carbon also demonstrated equivalent or superior performance to commercial activated carbons.

From Waste Tea
Activated carbons were prepared by phosphoric acid activation with and without microwave treatment and carbonisation of  waste tea under nitrogen atmosphere at various temperatures and different phosphoric acid/precursor impregnation ratios.

From spent activated carbon from water filters
Spent activated carbon from water purifier (Aqua Guard, India) for the removal of atrazine (2 chloro-4 ethylamino-6-isopropylamino-1, 3, 5 triazine) from wastewaters has also been tried successfully.

From Beer Lees
Activated carbon was successfully produced from beer lees which are the main waste material from a beer-production process, when KOH and CO2 were used as oxidizing agents in activation process.

From combustion ash from low Nox boilers
Coal fired plants now use low NOX boilers to reduce emissions. These burners reduce the NOX but increase the unburnt carbon left after combustion and power plants are left with fly ash and unburnt carbon.This impacts the recycle and reuse of fly ash.One use of combustion waste is as activated carbon.While both anthracite and unburned carbon can produce acceptable activated carbon, unburned carbon is probably less expensive and better for the environment. Unburned carbon, separated from fly ash, does not need cleaning or crushing, nor does it need heating to remove volatile components. Also, while anthracite sells for about $50 a ton, the waste from power plants can be separated for $10 to $15 per ton, and the fly ash could be sold to cement manufacturers.

From Chicken Waste
Preparation of low cost activated carbon from chicken waste is a promising way to produce a useful adsorbent for Hg removal. The activated carbon from chicken waste has the same mercury  capacity as commercial activated carbon.

From Broiler Excreta
Ammonia (NH3) pollution from broiler excreta is a primary concern for broiler industry viability.Activated carbon made from broiler litter is effective for NH3 adsorption originating from litterand provides  an opportunity to not only reuse the manure, but also treat the emissions from or within broiler houses.
The BAC is a much cheaper alternative than commercially produced activated carbons and can be applied directly tohe litter if health of birds are the concern or via a filtration system if air pollution concerns demand compliance to standards.

From Urban Waste
The organic fraction of urban waste is converted to active carbon via an improved pyrolytic process. The active carbon produced has a low ash content, high pore volume and hardnessand the active carbon of the present invention possesses superior characteristics. The urban waste referred to herein includes various types of waste produced in the urban environment. For the purpose of this invention urban waste is defined as waste which includes domestic waste and commercial waste but does not include industrial waste. In this context, domestic waste includes waste produced in an average normal household which comprises food waste, paper products and packaging, plastic products, wood, glass and metal. Commercial waste is the waste produced by the commercial sector. Much of the commercial waste is generated by food establishments, markets, grocery stores and the like.

In the initial stage the waste is sorted for the removal of foreign materials. The waste is then shredded to particle size of about 2cm x 2cm x 2cm, and then dried at a temperature of about 110°C. The dried particulate waste is then transferred to the pyrolysis vessel wherein the pyrolysis is a two stage process conducted at a temperature, preferably, in the range of 1400C to 500°C, in which primary pyrolysis takes place at about 160°C and in the second stage the temperature reaches 3900C. The pyrolysis stage takes about 2 hours. Optionally, matter made of polymeric materials, typically, plastics and rubbers, are removed prior to and/or subsequent to any one of the pyrolysis stages. The charcoal produced in the pyrolysis is crushed to a mean particle size up to about 0.01mm. This charcoal produced in the pyrolysis stage has an ash content of 9-20%. This charcoal is granulated in an extruder with a charcoal: water: oil ratio of about 1: 0.7: 0.15. The subsequent carbonization is carried out at a temperature, preferably, in the range of 110oC to 600°C. The granulated carbon is then carbonized at about 180°C under anaerobic conditions. The subsequent activation is carried out at about 790OC in the presence of steam and combustion gases. The combustion gases used in this stage are mixed with gases from the drying process.

The final purifying of the activated carbon is done by rinsing with an aqueous acidic solution, preferably, 5%-20% HCl solution, until the ash content is 2%-5% followed by washing in water until the water extracts have a pH of 3.5-5. The rinsed activated carbon is finally dried at about 100oC to a final water content in the range of 4%-8%.

The activated carbon obtained by the process of the present invention has an ash content of 2%-5%, a mean pore volume in the range of 0.95-1.2 ml/g  and a hardness in the range 85-95.

From Chlorella Vulgaris and Rice Husk
Chlorella vulgaris and rice husk were selected from microorganisms and agricultural waste, respectively, to create new gold-eluteable adsorbents for adsorption of gold-thiourea complex, and compared with activated carbon.  Although heated-immobilised C. vulgaris had the highest eluteability, it adsorbed less gold. Therefore, heated rice husk could be used as an alternative adsorbent for gold-thiourea pre-concentration.

Activated carbon (AC) of high quality has been produced from rice husk. The production involves two (2) main steps: (1) carbonization of raw material at temperature below 800oC in the absence of air using fixed bed reactor (furnace); (2) activation of resulting char with an alkali. The high-quality activated carbons produced have surface areas of 2,896-3,287 m2/g, methylene blue values of 999-1,050 mg/g and benzene gas adsorption of 167-212%.
References

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2.Abe Ikuo,Maruyama Jun,   Fukuhara Tomoko,Iwasaki Satoshi ,Production of Activated Carbon from Waste Wood by Air-Based Activation Method. Science and Industry VOL.74;NO.9;PAGE.442-447,2000

3.F. Rozadaa, L. F. Calvoa, A. I. Garcíaa, J. Martín-Villacortab and M. Otero,Dye adsorption by sewage sludge-based activated carbons in batch and fixed-bed systems  , Bioresource Technology ,Volume 87, Issue 3, May 2003, Pages 221-230

4.A. Gürsesa,  Ç. Dogarb, S. Karacac, M. Açikyildiza and R. Bayraka ,Production of granular activated carbon from waste Rosa canina sp. seeds and its adsorption characteristics for dye ,Journal of Hazardous Materials, Volume 131, Issues 1-3, 17 April 2006, Pages 254-259.

5.The Properties of Activated Carbon Made from Waste Newsprint Paper ,Journal of Porous Materials, Volume 6, Number 3 , May, 1999 ,Pages 191-196

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7.Emine Yagmura, Meryem Ozmaka and Zeki Aktas,A novel method for production of activated carbon from waste tea by chemical activation with microwave energy ,Fuel,Volume 87, Issues 15-16, November 2008, Pages 3278-3285

8.Pranab Kumar Ghosh and Ligy Philip, Performance Evaluation of Waste Activated Carbon on Atrazine Removal from Contaminated Water,Journal of Environmental Science and Health, Part B, Volume 40, Issue 3 May 2005 , pages 425 – 441

9.Hyoung-Ho LEE, Yuki HIRANO, Norihiro MURAYAMA, Shigeno MATSUMOTO and Junji SHIBATA, Adsorption Properties of Activated Carbon Prepared from Waste Beer Lees by KOH Activation and CO2 Activation, Department of Chemical Engineering, Kansai University and Asada Iron Works Co. Ltd.  February 1, 2007

10.Aik Chong Lua,  and Jia Guo, Journal of Environmental Engineering, Vol. 127, No. 10, October 2001, pp. 895-901,

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12.Masahiro Shimada1, Takahiko Iida1, Kensuke Kawarada1, Yoshifumi Chiba, Toshihiro Mamoto and Takayuki Okayama
Porous structure of activated carbon prepared from waste newspaper ,Journal of Material Cycles and Waste Management
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14.Yaji Huang, Baosheng Jin, Zhaoping Zhong, Wenqi Zhong, Rui Xiao ,Characteristic and mercury adsorption of activated carbon produced by CO2 of chicken waste.J Environ Sci (China). 2008 ;20 (3):291-6

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Activated  Carbon From Agricultural Wastes ,The Ghana Engineer, May 1999.

Green waste is biodegradable waste, usually from gardens and parks, and includes grass, hedge trimmings, leaves and tree trunks. It can be used to produce energy in biomass power stations and receives a renewable energy subsidy in Germany. It can also be recycled as compost, which reduces the extraction of peat – an important sink for CO2. However, composting does not receive financial support in Germany. The EU is currently developing policy to encourage composting and develop standards for composting across the EU1.

The research compared the environmental benefits of energy recovery from green waste and of recycling green waste using 81 samples. It analysed the CO2 balance of each system by estimating the release and savings of CO2 at the different stages of the process chain. For energy recovery this included the transport, shredding, incineration and the CO2 saved from the renewable energy produced. For recycling this included stages such as transport, composting and CO2 saved by replacing peat. Four different types of green waste were considered that differed in their amount of wood, herbaceous/grassy material and soil.

The results demonstrated that waste with a high percentage of wood produced the most CO2 savings for both composting and energy recovery whilst those with only herbaceous and soil components produced the least savings. The CO2 savings from energy recovery varied from 126 to 1040kg of CO2 saved per tonne of green waste, depending on the type of waste and its composition. The CO2 savings from recycling varied from 259 to 1193kg of CO2 per tonne of green waste, again depending on the type of waste. This indicates that the environmental gains, in terms of CO2 savings, were similar for both energy recovery and recycling of green waste.

Notably, green waste with a high percentage of herbaceous/grassy content and soil content had twice the CO2 savings from recycling as from energy recovery. This is probably because this type of waste has low heating values, due to high water and ash content, and is therefore better for composting purposes.

The researchers suggested that energy recovery and recycling of green waste should be judged as complementary systems. It is unlikely that one method on its own will achieve the desired reduction in CO2 levels and a combination is more likely to lead to a significant decrease in greenhouse gas emissions. As such they recommend that recycling of green waste be awarded equivalent financial support as the use of green waste to produce renewable energy.