Disposal of Industrial Waste and Treatment of Organic Impurities.
Waste is produced in all countries. The amount of wastes to be managed is enormous. Broadly speaking wastes are of two kinds. The one is that generated from municipal (including domestic) wastes and the other that is generated from various industrial process. Industrial processes generate a variety of waste products, which are generally discharged into water bodies or even on land.
The nature of industrial wastes depends on the industrial process in which they originate. In general, the industrial wastes contain organic or mineral matter along with other corrosive, poisonous and other harmful substances, which are injurious to health. The organic matter of the wastes are destroyed slowly by the bacteria.
A common practice that is followed in some industries is storing or lagooning wastes. Air is passed through the wastes. By this process the organic wastes are degraded. Also if the waste contains acid as well as basic wastes, it reduces the cost of neutralization. This process also decreases the suspended matter and also results in the reduction of biochemical oxygen demand BOD.
It is advantageous to treat the wastes at the source with a view to recover valuable by products. Fermented wastes after evaporation and drying are used as animal food. Metals like chromium from electroplating industries can be recovered by the use of ion exchangers.
Types of Industrial Wastes:
Industrial wastes are classified into a number of types. These include process wastes and chemical wastes. In the process wastes, every industry produces its own waste. These arise from different operations such as washing of the raw materials purification of the intermediates and final products. The process wastes are of two types:
Inorganic process wastes: Such wastes emerge from inorganic chemical manufacturing industries, metallurgical industries, petroleum industries. The inorganic wastes do not pose many biological problems provided the toxic metals are not present.
Organic process wastes: Such wastes arise from food processing industries, dairies, breweries, distilleries, paper mills, textile mills and organic chemicals manufacturing industries.
Chemical wastes arise from industries manufacturing acids, bases, detergents, explosives, dyes, agro chemicals. Some chemical waste require biological oxidation treatment methods, such as trickling filters, activated sludge or lagooning.
Treatment of Wastes or Effluents with Inorganic Impurities
Such wastes are subjected to chemical treatment. The pH of the effluents is maintained between 6.0 and 9.0. The treatment depends on whether the effluents are acidic or alkaline. If acidic, the wastes are neutralized by lime (CaO). The alkaline water (as from tanneries, textiles and chemical industries) are normally treated with H2SO4. After neutralization, the effluents may be discharged into water bodies.
In case the effluents contain heavy metals, there may be precipitated by using suitable precipitating agents. Certain waste water may contain cyanide such wastes are subjected to chlorination under alkaline conditions (chemical oxidation) or with ozone.
Treatment of Wastes or Effluents with Organic Impurities
Such wastes are subjected to conventional biological treatments. Before these treatments, the wastes are neutralised, waste matter is removed by aeration. Suspended organic pollutants and colloidal impurities are coagulated by adding FeSO4 or alum or some other flocculating agent. After the primary treatment the effluents may be subjected to biological treatment such as activated sludge and trickling filter treatments. In case the number of microorganisms in the effluents are less, requisite amount of microorganisms have to be added.
Special types of problems arise when we deal with Hazardous wastes. There have been several practices for managing such wastes. Some of such practices are:
- Production of less waste.
- Conversion of hazardous substances into less hazardous ones.
- Safe and proper disposal of wastes.
Reduction in the amounts of waste:
It is safest and the least expensive option. The amount of hazardous waste generated by manufacturing and other processes can be reduced by changes in the chemical processes involved, equipment used, raw materials used, etc. Recycling and reuse also eliminates hazardous waste. For example, certain solvents and acids can be recovered and recycled.
This practice yields economic benefits both in terms of reducing cost of starting materials and costs involved in the handling of hazardous waste, Also certain industries can mutually benefit by taking wastes from one industry and using it by another industry as raw materials.The waste produced in practically all industries can be prevented or at least minimized to a bare minimum by following the Principles of green chemistry.
Conversion to less Hazardous Substances:
The toxicity or hazardous characteristics can be reduced by physical, chemical or biological methods.
Such as absorption on charcoal or resin filters for absorbing toxins can be used. Distillation is also useful at times. Precipitation and immobilization are also helpful in making wastes suitable for long-term storage.
Such as neutralization, oxidation, reduction, ion exchange, etc., detoxify the waste.
Biological methods involve the use of bacteria, soil micro organisms and other species in reducing the hazardous characteristics of the waste. Biodegradation can be accomplished by aerobic and anaerobic methods.
Incineration is a physical method of treatment. It is very important and has many advantages. It involves heating of the waste to 1200°C for quite sometime to complete destruction. The volume of the waste is reduced by at least 90 per cent and the resulting waste is safer to store in a landfill or other storage site. Incineration removes volatile, combustible and mobile organic matter from the wastes by converting them to CO2 water and other gases. It is a quick, easy and permanent solution for many hazardous wastes and can be used for even mixture of wastes.
The final and ultimate step in the management of hazardous wastes is its permanent storage. But after storing it, we should be able to regularly monitor its safe placement by drawing the samples. The two important methods of disposal are secure landfills and deep well disposal.
Land filling has been a very common and popular option for disposal of hazardous waste. But, the landfills should be secure. The modern secure landfills are specially designed for safe disposal of the waste. Such a landfill is shown in Figure below. The bottom of the ‘secure landfill’ is lined with compacted clay followed by a layer of gravel. A thick polythene liner is then placed over the ground layer. The hazardous wastes are packed in drums and put into the landfill. The filled landfill is then finally covered with clay, plastic and soil.
Deep Well Disposal.
It involves injection of waste into deep wells. The waste in injected into a permeable rock layer several thousand meters below the surface, in geologic basins topped by relatively impervious, fracture resistant rock. The method requires careful monitoring after disposal.Although oceans dumping was used for disposal of hazardous wastes but due of the consequences of marine pollution, this practice has been stopped.
It comprises of used needles, syringes, blood bags, urine bags, glucose bottles, surgical gloves, bandages, chemicals, body parts and radioactive substances. Such a kind of waste is generated in hospital, nursing homes, pathological labs and research institutions. The biomedical wastes possess special problems of spreading disease such as AIDS, hepatitis, fevers, septicemia and other infections.
It has a potential danger for workers, public and the environment. The biomedical waste (Handling and Management) rules, 1998 prescribe the segregation of waste at source, color coding of waste bags, incineration of infectious waste, careful disposal of waste and shedding of plastics to prevent their reuse.
According to the handling and management rules, the treatment of biomedical waste involves processes such as incineration, autoclaving, microclaving, hydroclaving and shredding.
Incineration is a controlled combustion process where waste is completely oxidised and harmful microorganisms present in it are destroyed or denatured by high temperature.
Autoclaving is a low-heat thermal process where steam is brought into direct contact with waste in a controlled manner for sufficient duration to disinfect the waste.
In microclaving, microbial inactivation is done by thermal effects of electromagnetic radiation having frequency between 300 and 3,00,000 MHz.
Hydroclaving is similar to autoclaving except that the waste is subjected to indirect heating by application of steam in the outer jacket.Shredding cuts the waste into smaller pieces to make the waste unrecognizable. It prevents its reuse and signifies that the waste has been disinfected and can be disposed off.