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Table of Contents
List of Acronyms
1.2.1 General Objectives
1.2.2 Specific Objectives
2. Waste in Leather Industry
2.1 Solid Waste
2.3 Harmful Effects of Pollutant Present in Tannery Waste
2.3.4 Suspended Mater
3. Tanning of Leather
3.1 Origin and Properties of Tanning Material
3.1.2Washing and Soaking
3.1.5 Deliming and Bating
3.1.7 Chrome Tanning
4. Waste Stabilization Ponds
4.1 Application of Waste Stabilization Pond Systems
4.2 Types of waste stabilization pond
4.2.1 Aerobic Ponds
4.2.2 Facultative Pond
4.2.3 Maturation ponds
5. Anaerobic Ponds
5.1 Description of Anaerobic Pond
5.3 Advantages and Disadvantages of Anaerobic Ponds
6. General Material Balance
6.1 Summary of the Material Balance
7. Pond Design
7.1 Flow Chart for the Treatment of Tanning Waste Water
7.2 Screen Design
7.3 Anaerobic Pond Design
7.4 Facultative Pond
7.5 Maturation Pond
7.6 Detail Design of Anaerobic Pond
7.7 Inlet outlet structure of anaerobic pond
8. Pond Layout
8.1 Pond Geometry
8.2 Inlet and Outlet Structure
8.3 Inlet Outlet Structure of Anaerobic Pond
9. Chrome Removal in Anaerobic Pond
9.1 Site Selection
10. Cost Analysis
11. Conclusion and Recommendation
Appendix A: Percentage of effluents obtained in various processes (Calculated on total waste water in normal working method) (Pocket Book for the Leather Technologist, 1997)
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Waste is the most horrible thing to our environment especially a waste from tannery industries. Kombolcha tannery since it is part of these industries it is affecting the people and brings drastic chance to the environment. Since this is the fact those treatment techniques are necessary to the factory like the one mentioned. In this study an aerobic pond is designed for tannery waste. It is possible to make suitable to our environment by treating it as per the type of the waste and degree of toxicity and hazard. This will be practiced only when the industrialists put themselves in to the boundaries of the industrial legislation otherwise good things will not happen unless the bad situation are developed. For the treatment techniques the one which has lower installation cost and lower running cost were used.
Key Words: Anaerobic pond, Tannery waste , Hazard
Domestic wastewater and most industrial wastewaters contain a mixture of various waste compounds of which the organic matter is an important part. In case of discharge of untreated wastewater into the environment, the organic matter is used in bacterial metabolism. This is called waste degradation or stabilization. In case of discharge of untreated wastewater into the environment, the organic matter is used in bacterial metabolism. This is called waste degradation or stabilization. Stabilization refers to the fact that after the organic matter has been degraded by bacteria, the bacterial activity based on the rest product is low. The material has become stable. Waste stabilization ponds are typically man-made basins surrounded by an earthen embankment. The waste is confined to the basin for a certain time span, such that bacteria that are present in the waste or added to it can stabilize the waste by degrading the organic fraction (Metcalf et al., 2003).
The advantages of waste stabilization ponds result from their simplicity. Ponds require relatively low capital investment when flat land is available at reasonable price. Ponds are easily maintained, can absorb shock loads, produce stabilized sludge that can periodically be removed and used in agriculture, whereas mechanical equipment to aerate or mix the sewage is hardly required. The consequent low operation and maintenance requirements, plus their potential to be easily scaled down to small scale application make them particularly attractive for remote towns and villages. All these features plus the ability to markedly reduce BOD, nutrients and pathogen concentrations have made waste stabilization ponds a very attractive treatment method (Jorge Jaramillo, 2003).
The most appropriate wastewater treatment is that which will produce an effluent meeting the recommended microbiological and chemical quality guidelines both at low cost and with minimal operational and maintenance requirements, Adopting as low a level of treatment as possible is especially desirable in developing countries, not only from the point of view of cost but also in acknowledgement of the difficulty of operating complex systems reliably. In many locations it will be better to design the reuse system to accept a low-grade of effluent rather than to rely on advanced treatment processes producing a reclaimed effluent which continuously meets a stringent quality standard (Metcalf et al., 2003).
Waste Stabilization Ponds are now regarded as the method of first choice for the treatment of wastewater in many parts of the world. Waste stabilization ponds are mainly shallow man-made basins comprising a single or several series of anaerobic, facultative or maturation ponds. The primary treatment takes place in the anaerobic pond, which is mainly designed for removing suspended solids, and some of the soluble element of organic matter (BOD5). During the secondary stage in the facultative pond most of the remaining BOD5 is removed through the coordinated activity of algae and heterotrophic bacteria. The main function of the tertiary treatment in the maturation pond is the removal of pathogens and nutrients (especially nitrogen). Waste stabilization pond technology is the most cost-effective wastewater treatment technology for the removal of pathogenic micro-organisms. The treatment is achieved through natural disinfection mechanisms. It is particularly well suited for tropical and subtropical countries because the intensity of the sunlight and temperature are key factors for the efficiency of the removal processes (Jeffrey P.J. et al., 1997).
The general objective of this project is to design anaerobic pond for Kombolcha tannery.
- To characterize and determine the wastewater flow from Kombolcha tannery.
- To design waste stabilization pond
- To intend detail design of anaerobic pond
Waste from leather industry consists of different kind of chemicals, tanned and untanned solid wastes (Prof. Dr. E. Heidemann, 1993).
This includes cutting of untanned hides with hair, cutting of limed, shaved hair, flashing and cuttings. Some of the untanned solid wastes used for glue production factories for further processing and sometimes it is dumped on special dumps (K. Bienkiewicz et al., 1983).
The composition of the effluent from leather factories is very complex and varies depending on the manufacturing procedure using in the factory concerned and all the starting materials .The particular characteristics of effluents from leather factories which start with row skin or hide are sulfide from the liming, high alkalinity, a very high proportion of dissolved organic compounds and in case of chrome leather factories chromium compounds. The effluent also contains certain amount of organic and inorganic suspended solids which from as a result of natural precipitation when the effluent from various processing stages are mixed. Official regulations that vary from country to country require that before any effluent is discharged to public water. It must be purified sufficiently to insure that there is no risk of biological equilibrium being disturbed where effluent is to be treated in public purification which might impair the functioning of this plants must first be removed (K. Bienkiewicz et al., 1983).
- Corrosion effect in the initial tract
- Toxic dose for man
- Destructive of fish i.e. lethal limit to a stickle
- Toxic in 30min, for gold fish
- Toxic value for brume trout
- Impairment of photosynthesis of algae
- Distraction of microorganisms
- Toxic threshold effect in protozoa (Gerberei-Ing. Gerhard John, 1997).
- It is a most difficult martial in that it is highly toxic and has an obnoxious odor.
- Cause corrosion and may also release poisonous gas in the low parts of the sewer.
- Fatal to sensitive fish even in alkaline water (Gerberei-Ing. Gerhard John, 1997).
- Imposition high oxygen content
- Anthrax (T. C. Thorstensen,1976)
- Detraction fish food bottom found and spawning grounds of fish
- Choking sewer (T. C. Thorstensen, 1976).
- Fishes are either killed or seriously handicapped
- Distraction to concrete structure (T. C. Thorstensen, 1976).
Leather is a seldom used in its natural state as it’s effected by variations in temperature (hard and stiff at low temperature, soft and limp at high temperature) liable to set. The purpose of tanning is to eliminate these problems with special vegetable, animal and synthetic substances. In preparing leather the process involved are used to remove the skin. In the process of removing undesired constituents of the skin the process used are named as bellow. These are curing, soaking, liming, fleshing, and deliming, bating, pickling, tanning. All these processes are done in order to get wet blue which is called semi-processed leather (Pocket Book for the Leather Technologist, 1997).
Tanning process is a slow process and in modern leather production involves a series of chemically inter dependent steps. Tanning is not only preserves the hide or skin but also make the leather resistance to cracking from flexing and the densile properties of leather depends on use (Pocket Book for the Leather Technologist, 1997).
This is a process used to remove undesired part of the skin. This is part of solid waste in the tannery (J. H. Sharphouse, 1972).
Hide or skins when received by the tanning are usually in a condition of preservation based on dehydration. These skins may dried, as in the case with most goat skin and same tropical cattle hides or they may dehydrated by means of salt (J. H. Sharphouse, 1972).
Hair, dirty insecticide, blood and non-fibrous protein of the skin are removed and the moisture lost during preservation and storage is restored. Consequently the effluents are voluminous consists of a high percentage of solid, BOD and volatile solids with the PH usually being 7-8 (J. H. Sharphouse, 1972).
This process is accomplished by the use of lime with sodium sulfide thus effluents contain hair, high percentage of sulfide and high PH. This process is used to loosen the hair, remove the epidermis, and emulsify the skin grease and to bring about a more or less marked plumbing of the fibber structure (T. C. Thorstensen, 1976).
The lined skin is fleshed mechanically or by hand to remove epidemic resides the effluents from this process contain a high percentage of solids and to other processes water (Prof. Dr. E. Heidemann, 1993).
After the operation deliming and bating are done to reduce the swelling, peptize the fiber and remove the protein degradation product thus making the skin reading for tanning as ammonium salts are used for bating and protein degradation. These two steps are further steps in the purification of the hide collagen network. Deliming is the removal of alkali and adjustment of the PH for bating. Bating is the enzymatic actions for the removal of unwanted hide complaints product are squeezed effluents of this process contain high volatile BOD and volatile solids(Prof. Dr. E. Heidemann, 1993).
This process is necessary for chrome tanning to prevent the chances of chrome salt precipitation during tanning as the bates skins are treated with salt of this process that contain very high solid concentration and low PH of 3.0 (T. C. Thorstensen, 1976).
During this process only 68.74 % for is utilized by the skins consequently a large amount of chrome surface rainout to the effluents color green while the PH lies in the range 2.5-2.8 (T. C. Thorstensen, 1976).
Waste Stabilization Ponds are large, shallow basins in which raw sewage is treated entirely by natural processes involving both algae and bacteria. They are used for sewage treatment in temperate and tropical climates, and represent one of the most cost-effective, reliable and easily-operated methods for treating domestic and industrial wastewater. Waste stabilization ponds are very effective in the removal of faecal coliform bacteria. Sunlight energy is the only requirement for its operation. Further, it requires minimum supervision for daily operation, by simply cleaning the outlets and inlet works. The temperature and duration of sunlight in tropical countries offer an excellent opportunity for high efficiency and satisfactory performance for this type of water-cleaning system. They are well-suited for low-income tropical countries where conventional wastewater treatment cannot be achieved due to the lack of a reliable energy source. Further, the advantage of these systems, in terms of removal of pathogens, is one of the most important reasons for its use (Young et al., 1991).
Waste stabilization pond can be classified in respect to the type(s) of biological activity occurring in a pond. Three types are distinguished: anaerobic, facultative and maturation ponds. Usually a waste stabilization pond system comprises a single series of the aforementioned three ponds types or several such series in parallel. In essence, anaerobic and facultative ponds are designed for BOD removal (Biological Oxidation Demand) and maturation ponds for pathogen removal, although some BOD removal occurs in maturation ponds and some pathogen removal in anaerobic and facultative ponds. In many instances only anaerobic and facultative ponds are required. In general, maturation ponds are required only when stronger wastewaters (BOD > 150 mg/l) are to be treated prior to surface water discharge and when the treated wastewater is to be used for unrestricted irrigation (irrigation for vegetable crops). Generally, in waste stabilization pond systems, effluent flows from the anaerobic pond to the facultative pond and finally, if necessary, to the maturation pond. However, for better results wastewater flowing into an anaerobic pond shall be preliminary treated in order to remove coarse solids and other large materials often found in raw wastewater. Preliminary treatment operations typically include coarse screening, grit removal and, in some cases, comminution of large objects (Williams et al., 1998).
An aerobic stabilization pond contains bacteria and algae in suspension; aerobic conditions (the presence of dissolved oxygen) prevail throughout its depth. There are two types of aerobic ponds: shallow ponds and aerated ponds (Stenstrom et al., 1983).
Shallow oxidation ponds obtain their dissolved oxygen via two phenomena: oxygen transfer between air and water surface, and oxygen produced by photosynthetic algae. Although the efficiency of soluble biochemical oxygen demand removal can be as high as 95 percent, the pond effluent will contain a large amount of algae which will contribute to the measured total biochemical oxygen demand of the effluent. To achieve removal of both soluble and insoluble biochemical oxygen demand, the suspended algae and microorganisms have to be separated from the pond effluent (Satyanarayan et al., 1987).
An aerated pond is similar to an oxidation pond except that it is deeper and mechanical aeration devices are used to transfer oxygen into the wastewater. The aeration devices also mix the wastewater and bacteria. The main advantage of aerated ponds is that they require less area than oxidation ponds. The disadvantage is that the mechanical aeration devices require maintenance and use energy. Aerated ponds can be further classified as either complete-mix or partial-mix systems. A complete-mix pond has enough mixing energy input to keep all of the bacterial solids in the pond in suspension. On the other hand, a partial-mix pond contains a lesser amount of horsepower which is sufficient only to provide the oxygen required to oxidize the biochemical oxygen demand entering the pond (Satyanarayan et al., 1987).
Facultative pond is a combination of both aerobic and anaerobic pond. That is, in its top zone it is aerobic whereas it is anaerobic at its lower zone. Most of the stabilization pond constructed fall into the category of Facultative pond. Facultative ponds are of two types-primary facultative ponds and the secondary Facultative ponds. The primary facultative pond is one that receives raw wastewater whereas the secondary Facultative pond is one that receives the settled wastewater from the first stage. These ponds reduce BOD that helps in the production of algae that will further generate the oxygen needed to remove soluble BOD5. The population of algae in any optimally performing facultative pond rest on organic load and temperature (Rosenwinkel et al., 1999).
Three zones exist in facultative pond. They are the following:
(1) A surface zone where aerobic bacteria and algae exist in a symbiotic relationship;
(2) An anaerobic bottom zone in which accumulated solids are actively decomposed by anaerobic bacteria; and
(3) An intermediate zone that is partly aerobic and partly anaerobic in which the decomposition of organic wastes is carried out by facultative bacteria. Because of this, these ponds are often referred to as facultative ponds. In these ponds, the suspended solids in the wastewater are allowed to settle to the bottom. As a result, the presence of algae is not required. The maintenance of the aerobic zone serves to minimize odor problems because many of the liquid and gaseous anaerobic decomposition products, carried to the surface by mixing currents, are utilized by the aerobic organisms (Rosenwinkel et al., 1999).
The amount of oxygen present in the pond depends upon the following factors:
- Organic loading
- Sunlight (Rosenwinkel et al., 1999).
These ponds are of two types: primary facultative ponds receive raw wastewater, and secondary facultative ponds receive the settled wastewater from the first stage (usually the effluent from anaerobic ponds). Facultative ponds are designed for BOD5 removal on the basis of a low organic surface load to permit the development of an active algal population. This way, algae generate the oxygen needed to remove soluble BOD5. Healthy algae populations give water a dark green color but occasionally they can turn red or pink due to the presence of purple sulphide-oxidizing photosynthetic activity. This ecological change occurs due to a slight overload. Thus, the change of coloring in facultative ponds is a qualitative indicator of an optimally performing removal process. The concentration of algae in an optimally performing facultative pond depends on organic load and temperature, but is usually in the range 500 to 2000 μg chlorophyll per liter. The photosynthetic activity of the algae results in a diurnal variation in the concentration of dissolved oxygen and pH values. Variables such as wind velocity have an important effect on the behavior of facultative ponds, as they generate the mixing of the pond liquid a good degree of mixing ensures a uniform distribution of BOD5, dissolved oxygen, bacteria and algae, and hence better wastewater stabilization (Rajeshwari et al., 2000).
Maturation ponds are the ponds that receive effluent from a facultative pond. They are shallow, with less vertical stratification and are well oxygenated. The algae population of the maturation pond is much more diverse than that of facultative ponds. This clearly shows that the diversity of algae increases from pond to pond along the series. It is the Algae that cause the removal of pathogens and faecal coliforms. Though these ponds reduce small amount of BOD5 but they play significant role in phosphorus and nitrogen removal (Annachhatre et al., 1996).
The main removal mechanisms especially of pathogens and faecal coliforms are ruled by algal activity in synergy with photo-oxidation. On the other hand, maturation ponds only achieve a small removal of BOD5, but their contribution to nitrogen and phosphorus removal is more significant. A total nitrogen removal of 80% in all waste stabilization pond systems corresponds to 95% ammonia removal. It should be emphasized that most ammonia and nitrogen is removed in maturation ponds. However, the total phosphorus removal in WSP systems is low, usually less than 50% (Delgenes et al., 2003.
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