Introduction
Waste is generated as a result of a lot of physical, chemical, and biological processes. Dumping it at some appropriate place is one option. However, ecological effects of throwing away waste products are becoming a serious concern these days. In order to minimize waste, the best strategy is to transform it into valuable products . Plenty of research studies have been carried out to utilize waste effectively. The aim of this report is analysis of the proposed methods for the utilization of common forms of wastes for useful purposes. We also recommend better alternatives to help create a lesser negative impact on the environment as compared to the existing methods employed in industrial setups today. Some basic forms of waste and their conversion methods will be provided.
Field of waste processing keeps on evolving, and new strategies for their conversion to useful products are formulated. Plenty of research work has been carried out in recent times, considering their growing demand. Waste processing and recycling is important due to a number of factors like economics, limited resources, legislation, environmental impact, and problems of disposing waste in bulk . Our research methodology will comprise discussion about the production of the following waste sources and their transformation techniques employed in the literature.
Wastes generated from metal processing and related operations
Wastes produced by burning large volumes of coal in power plants
Electrical and electronic waste that could be transformed into useful finite energy resources, and thus reducing potential damaging effects to environment
Wastes produced from food items that has catastrophic effects on environment
Waste from Metal Processing
Metals are used for a huge number of applications in virtually every industry of the world. However, it is very difficult to find the desired metals naturally on Earth and you need to carryout various electrolytic, hydrometallurgical, and Pyrometallurgical methods for extracting metal from the ore . These processes produce a lot of waste, varying in chemical composition and properties. We will discuss processing of steel metal waste in the form of slag and sludge. These are produced as a result of industrial processes in Blast Furnace (BF) and Basic Oxygen Furnace (BOF).
Slag is produced during the blast furnace stage of extracting metals from their ores. It is used for building applications in the European Union (EU). The utilization of slag has become an interesting area of research and plenty of studies have been carried out in this regard (Das, 2007). Some of the common applications include slag as asphalt and concrete mixtures, road construction industry (Khan, 2002), charge in blast furnaces, blended cement and tiles.
Sludge could be recycled in the sinter plant for feed of blast furnaces (Singh, 2011). Sludge may be mixed with some other kinds of solid waste for manufacturing iron pellets that are further used in blast furnaces. It is also possible to separate metallic iron from sludge and then agglomerate it for recycling in steel making (Gomez, 2012).
Aluminum metal is produced via complex extraction process that generates a lot of waste. Through Bayer process, Alumina is produced that is utilized in Hall-Heroult process to form Aluminum. During these processes, waste of Red mud, Dross, Salt Cake, and Spent pot-lining are produced. Red mud finds applications in construction of buildings and ceramics, Gas scrubbing and catalysis, water treatment, and as a soil additive. Dross could be used in cements and refractory materials, metal casting and production, catalysts and chemicals. Salt cake is quite hazardous. It could be treated for recovering salt and metal. Heating Spent pot-lining with Silica produced Silicon Carbide that serves the purpose of abrasive and refractory materials. It is also used in Pig iron manufacturing.
Copper slag is employed for stabilizing expansive clay soils that create road problems. It is also quite useful as a fill material for land reclamation. Nickel slag is effectively utilized with BF slag and sand for preparing glass ceramics. Lead extraction slag finds usage in cement mortar and Zinc processing slag is used in concrete mixtures.
Coal Combustion Waste Utilization
Coal is by far the most important source of energy on Earth. Around 40% of the world’s power generation is contributed by Coal combustion that could be performed by various methods such as Pulverizing. During power generation from coal combustion, solid byproducts are produced termed as Fly ash and Bottom ash. Their applications are numerous in cement industry. The largest applications of fly ash are in concrete, grout, and cement. Fly ash contributes towards strength and durability of structure materials. It is also used as ingredient in Portland cement clinker and for soil stabilization and solidification. Geo-polymers of fly ash are demonstrated to be useful to stabilize hazardous materials in electric arc furnace dust (Luna, 2009). The applications are fly ash find their span in mining and agriculture also.
Electrical and Electronic Equipment Waste Utilization
It is a fast growing waste material as the world is moving more and more towards smart technology and electrical equipments for virtually every purpose. This waste causes particular concern for environment and especially for human health since they are composed for hazardous and toxic material. Therefore, reprocessing of electrical and electronic equipment waste is vital to reduce environmental contamination. Most of the attention is given to recovery of high-valued materials like metals, plastics, and ferrous materials.
The stream of waste generated by electrical and electronic equipment is quite diverse. Take examples of mobile phones and refrigerators that are quite different from each other. The recovered materials are also unique in nature. You can recover precious metals and batteries by using special methods practiced in Belgium, Germany, Canada, Japan, etc. Ferrous materials are very important in these wastes since these are used in most of the electrical products such as refrigerators, washing machines, and air conditioners. Ferrous materials could be easily separated from waste using magnetic methods. These materials find applications in metal smelters for producing more steel and iron. Similarly, Aluminum is precious from various aspects and it can be recovered by heating electrical waste at high temperatures around 800oC. Moreover, the aluminum is such waste could be combined with scrap from some other sources for achieving the required alloy composition.
Another potential use of electrical waste is in the form of plastics. These can be used as valuable energy sources (Menad, 1998). However, when plastics are burnt, some more toxic compounds such as dioxins and furans will be produced that are catastrophic for environment. So, combustion of plastics should be carefully controlled to minimize waste. The plastics in electrical waste also find potential application in aggregate for concrete.
Utilization of Food Waste
Every year, billions of tons of edible human food is wasted. Such as huge amount of waste, requires special attention for best utilization. We have to minimize the waste as well as extract useful material from it. Most of the food waste applications include low value consumption based on nutrients or energy. Recently, bio-refining is used for getting high value products from food waste materials.
The major problem with utilization of food waste is that it cannot be used as food again for animals and humans. The food items containing olive oil, cheese, and coffee are highly important from their uses point of view. Therefore, recycling and recovering are the only feasible options available. Their objective is to enhance the value of nutrients present in waste material for making effective use of the resource. Recycling is a better option as compared to recovering as it generates higher value products.
Recycling of food waste is performed in a sort of treatment process for production of valuable material that could be useful as soil amendments or for extraction of useful chemicals. Food waste could be spread as fertilizer on land to utilize nutrients and it could also be burnt to get energy.
Olive oil waste is also a huge problem in the countries like Spain, Greece, Italy, and Portugal. The potential applications of Olive oil waste are their conversion to useful organic products since these oil wastes cannot be directly spread to land (Arvanitoyannis, 2007). Olive waste has its best utilization in production of polymerin that is quite precious in bio-filters, bio-integrators, or in agricultural amendment. The three-phase extraction of olive waste is the source of pharmaceuticals, and food preservatives. The waste can also be employed for microorganism and mushroom cultivation.
Biowaste generated by the food industry could be employed as a chemical feedstock for producing low-volume, high-valued products that are used in cosmetic additives, industrial chemicals, and gelling agents. The fishery wastes such as crab and shrimp shells contain high chitin contents that are quite valuable. These are widely used as coagulants. For extracting the chitin in required quality, the sea-food waste must be de-mineralized and de-proteinized using strong bases and acids. However, waste disposal problems may also result in this case (Wang, 2011).
Cheese-whey, a liquid by-product from cheese making material, can be concentrated by using the method of reverse osmosis. It may be used as why power after concentrating it for facilitating transportation for using as animal feed. Protein may also be separated from whey using filtration process. These products find applications in pharmacological and food products.
The by-products of coffee productions could also be recycled (Murthy, 2012). The major by-products are peel, coffee husk, and pulp. The coffee husks and hulls may be used in production of particle board, and as absorbent for treatment of waste water. Unfortunately, coffee pulp cannot be used in high quantities in animal feed due to the presence of high tannin. Detoxification using fermentation process of coffee waste is a better idea.
Apart from extracting useful material from food waste, you can also get useful energy by directly burning it. It is quite useful to burn all the food waste and get as much energy as possible. Incineration is the process to produce energy from waste materials. We can minimize the waste substantially by using this method. The countries that have scarce land resources, prefer to incinerate all the available food waste.
Secondary Processes for Waste Utilization
Waste materials could prove to be huge resources of catalysis. They may also be used as resources from which useful material can be extracted for application as materials. However, this large-scale waste source cannot fulfill the demand of catalysts since high-volumes of waste are not always available.
The utilization of waste in terms of energy is a popular concept. You can extract energy in the form of fuel using physical processes, heat energy using thermal processes, and bacterial processes that yield fuel from fermentation of organic products.
Wastes could be added directly to soil for the purposes of supplying nutrients, adjustment of pH, and improvement of physical characteristics. Traditional trends show that slurries and manures were used to be recycled to the soil (Chambers, 2001). The valuable nutrients of nitrogen, phosphorus, and potassium are utilized. As discussed previously, most of the food waste is directly applied to the soil for extracting useful nutrients.
Wastes also find potential application in environmental water (Gupta, 2009) and soil cleanup (Gadepalle, 2007). Prime focus is towards removal of heavy metals from water and soil. The effectiveness of waste material in getting rid of contaminants will be based on three processes: adsorption, ion exchange, and chelation. It happens very rarely that the waste material is applied n its original form to the soil. They are normally crushed before applying to increase their surface area.
Recommendations
As we discussed in the report, waste could be easily minimized if it is utilized properly and converted into a useful form. Plenty of waste categories exist and their potential applications are never ending. It is recommended for future research that transformation of waste into energy in power production should be improved using sophisticated technology to solve energy problems of the world. Moreover, different forms of waste should be thoroughly processed to extract all the available useful materials in them. Secondary processing of waste shouldn’t generate waste by itself.
Conclusion
Waste is undesired stuff produced as a result of many physical, chemical, biological and other types of processes. Treatment of waste is very important to reduce its environmental impact and for recycling important materials from it. This report reviewed different types of waste and their best utilization in the world of today. First of all, waste generated during metal production and extraction is studied. Different forms of metal waste are useful and their potential applications are discussed briefly. Coal is another huge source of waste that needs to be taken care of. The concept of direct utilization of coal in power plants is discussed. The next category of waste under consideration was related to electrical and electronic equipment. This kind of waste is extremely hazardous due to usage of toxic substances in manufacturing of electronic products. They are mostly reprocessed for extracting useful materials from the waste. The food waste includes useful materials that are further applied at suitable places. The food waste reprocessing is carried out in developing as well as developed countries.
Then, we considered the secondary utilization of wastes in general without specifically discussing waste of a single category. At the end, we provided some recommendations and opened some avenues for further research.
References
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