Associate Professor

Department Of Chemistry

R. B. S. College

 Agra, U.P., India 

Abstract

Particularly in the last few decades, there has been a sharp expansion in the number of chemical industries in India. These companies regularly release hazardous and poisonous waste into the sky, contributing to a serious problem of environmental degradation that poses a serious threat to all species of animals, plants, and other living things. The unique qualities of hazardous wastes, such as their toxicity, corrosivity, and reactivity, have helped to characterise them. Hazardous waste is any waste that contains specific chemicals, metals, or infectious organisms. These present a major risk to human health and, even at low quantities, can harm the ecosystem. These threats could be immediate or in the future. As an illustration, short-term and acute toxicity are frequently brought on by ingestion, inhalation, skin contact, or the threat of fire or explosion in a group of individuals. Future risks include chronic toxicity brought on by repeated exposure, cancer development, genetic harm, and the potential to contaminate groundwater or surface waterways. To ensure that the hazardous components of the wastes are rendered harmless by appropriate treatment technologies and safe disposal techniques, it is vital to take precautions. Therefore, in this regard, research has been done on various waste types, and strategies for the removal of hazardous trash have been suggested.

Introduction

The chemical industry, one of India's oldest domestic industries, has significantly aided the country's industrial and economic growth since it attained independence in 1947. In India, a closed economy, the domestic chemical industry was safeguarded by varied import duties on chemical raw materials and finished products until 1993. The creation of chemicals was heavily restricted by licencing rules. Over the past 20 years, the Indian chemicals sector has developed from manufacturing basic chemicals in a highly regulated market to maturing as a company in a liberalised economy. The chemical industry is one of the industries in India that is expanding the fastest. Businesses emit a variety of toxic and hazardous wastes into the atmosphere daily. Due to an increase in product rate and a variety of chemical reactions, there are ever more risks associated with toxic wastes for people and the environment. There are numerous artificial, managerial, marketable, sanitarium, and other sources of hazardous waste.

Sources of Wastes

Hazardous wastes may be an industrial activity's byproduct. The primary waste streams generated by businesses include corrosive wastes, wasted acids, and alkaline materials used in the chemical, metal-finishing, and petroleum-refining industries. They can also be created in homes when commercially dumped goods including paint thinners, oil and gasoline additives, grease and rust solvents, herbicides, insecticides, drain openers, oven cleaners, wood and metal cleaners, and medications are used. These waste streams are hazardous because heavy metals are present in many of them. The manufacturing industry, as well as several equipment maintenance industries that produce used cleaning and degreasing products, both produce significant amounts of solvent waste. The primary producers of reactive waste are the chemical and metal finishing industries.

Table 1: The various industries release different hazardous wastes into the environment.

Major Polluting Industries
INDUSTRIES	Key Environmental Aspects
Aluminium	Red mud, bauxite tailings, and other hazardous waste disposal, as well as significant energy usage.
Caustic	chlorine emissions, mercury waste, and brine mud discharge all contribute to water contamination.
Cement	Energy use; air emissions from stacks and fugitive dust emissions from material handling.
Copper	Smelter slag disposal; water contamination from electrolytic bath and other procedures; emissions of sulphur dioxide and particles;
Dyes	Hazardous azo dyes, highly organic coloured pigments, and phenolic compounds cause water pollution.
Fertilizer	Heavy metal, ammonia and fluoride-bearing effluent, ammonia emission, and fluoride-bearing effluent all contribute to water contamination.
Leather	Water pollution, notably due to salt runoff and hexavalent chromium.
Pesticide	Particulate and volatile organic compound pollution, as well as pesticide-containing wastewater.
Petrochemicals	Effluent containing phenol and benzene causes water contamination, as do fugitive emissions of hazardous and cancer-causing volatile organic chemicals.
Pulp and paper	Black liquor contains a lot of organic and inorganic substances, chlorinated compounds, and highly odorous emissions of reduced sulphur compounds, which pollute the water.
Refinery	Pollution of water from effluent comprising oil, solvent, organic and inorganic debris, as well as particle matter, sulphur dioxide, and "benzene, toluene, and xylene."

 Effects of Hazardous Waste on Health and Environment

Hazardous waste produced by several industrial sectors can have negative effects on human health and the environment. For instance, numerous hazardous waste components, including benzene and chromium VI, have been classified as occupational carcinogens. Kidney and nervous system problems, as well as neurological dysfunction in adults and children, can be brought on by lead in metal sludges.

Table : Impacts of Industrial Hazardous Waste on Health and Environment

Hazardous Waste	Health /Environmental impact	Industrial sector
Cadmium	1. Leads to cancer 2. Kidney injury 3. Bone tissue decalcification	Iron and steel, wood preservatives, textiles, leather, inorganic chemical industries, colours and pigments
Chromium VI	1. Leads to cancer 2. Chronic respiratory tract irritation	manufacturing of chemicals, paper printing, tanning steel, leather, fur, textiles, and metal finishing
Arsenic	1. May lead to cancer 2. Respiratory, ocular, and skin irritations	Inorganic compounds, wood preservatives, paints, pigments, and lead metallurgy
Cyanide	1. Toxic, capable of causing sudden death from respiratory arrest 2. Injures the retina and optic nerves. 3. Has an impact on the nervous system.	Colorants, metal finishing, and coating

Waste Management Hierarchy

There is a hierarchy for decision-making when determining the optimum way to manage any waste, and it takes into account factors like sustainability, cleaner production, health, safety, and environmental preservation. It is used to examine and test procedures that are already in place or that are being considered, starting at the top of the hierarchy

For hazardous waste, the hierarchy is as follows:

1. Lessen the amount of hazardous trash produced.

2. Use techniques to lessen the quantity or hazard when reduction is not an option.

3. Recycle, repurpose, or recover waste to reduce the amount that needs to be disposed of. Included in this is the potential energy recovery from waste.

4. Use waste treatment to immobilise, confine, stabilise, or eliminate harmful qualities.

5. Dispose of residues with the least possible impact on the environment.

6. Properly contain, isolate, and store hazardous material for which there are no currently feasible options for acceptable treatment or disposal.

Source Reduction

Reducing hazardous waste at the source, typically within a process, is what source reduction entails. Process changes, feedstock substitutes, feedstock purity improvements, changes in housekeeping and management practises, equipment efficiency gains, and recycling within a process are all examples of source reduction strategies.

Recycling

This involves using hazardous waste as a reliable replacement for a commercial product or as a component or feedstock in a manufacturing process. It also involves the removal of pollutants from waste materials to enable their reuse or the recovery of usable constituent fractions within waste materials.          

Treatment

Any method, technique, or process that modifies a hazardous waste's physical, chemical, or biological characteristics to neutralise the waste, recover energy or resources from the waste, or make the waste less dangerous, safer to handle, amenable to recovery and storage, or smaller in volume, is referred to as this.              

Disposal

For the waste or any of its elements to reach the air or be released into any water, including groundwater, it must be discharged, deposited, injected, dumped, spilt, or placed on any land or body of water.  

Hazardous Waste Treatment Technologies

Hazardous waste must be transformed into non-hazardous chemicals or stabilised or encapsulated to prevent migration and hazard when released into the environment. For inorganic wastes, such as those containing dangerous heavy metals, stabilisation or encapsulation procedures are especially important. There will still be a significant amount of hazardous waste that needs to be treated and disposed of, even after an aggressive programme to reduce it. The different types of treatment methods fall under the headings of physical, chemical, biological, thermal, or stabilization/fixation.

Physical Processes

Processes used in physical treatment include carbon adsorption, air and steam stripping of volatiles from liquid wastes, phase change systems, and gravity separation.

Chemical Processes

Chemical treatment transforms trash into less hazardous substances using procedures including pH neutralization, oxidation or reduction, and precipitation. In biological treatment, microorganisms are used to degrade organic waste stream constituents.

Thermal Destruction

Pyrolysis, which is the chemical disintegration of waste brought about by heating the substance in the absence of oxygen, and incineration are two thermal destruction methods that are increasingly favoured options for the treatment of hazardous wastes.

Stabilation

The surplus water from waste is removed during stabilisation procedures, and the liquid that is left over is either vitrified to create glass or combined with a stabilising agent, such as Portland cement.

The majority of treatment plans incorporate both chemical and physical elements. The most effective hazardous waste treatment method must be selected based on the type of waste. The type of physical treatment to be applied to the wastes will be greatly influenced by the physical properties of the material to be treated, including its state of matter, solubility in water and organic solvents, density, volatility, boiling temperature, and melting point.

Adsorption

Adsorption is a powerful and adaptable approach for eliminating heavy metals, especially when used in conjunction with the proper regeneration procedures. This solves the sludge disposal issues and makes the system profitable, especially when cheap adsorbents are utilised. Adsorbate atoms or ions flow from the fluid phase to the surface of a solid (adsorbent) during the adsorption process, where they are either chemically bonded or kept in place by weak intermolecular interactions. Adsorption is used in many significant industrial applications, and it is currently being employed more frequently on a large scale as an affordable and effective separation approach for the removal of metal ions from wastewater.

Sedimentation

Physically, sedimentation is the process by which particles suspended in a liquid gravitationally settle. The basic components of the majority of sedimentation processes are:

1. a basin or container large enough to keep the liquid to be treated in a relatively still state for a predetermined amount of time

2. a method of physically removing the settled particles from the liquid;

3. a method of directing the liquid to be treated into the above basin in a way that promotes settling.

There are two types of sedimentation processes: batch and continuous. The majority of operations are continuous, especially when handling big amounts of liquid. This method has been widely used to remove heavy metals from wastewater from the iron and steel industry, fluoride from wastewater from the aluminium production process, wastewater from the copper smelting and metal finishing industries, and wastewater streams from organic compounds.

Electrodialysis

An aqueous stream that is depleted of electrolytes and a stream that is more electrolyte-concentrated than the original are separated during electrodialysis. The effectiveness of the procedure depends on specialised synthetic membranes, typically built from ion exchange resins and permeable to only one kind of ion. Only positively charged ions can travel through cation exchange membranes when they are subject to an electric field, whereas only negatively charged ions can pass through anion exchange membranes.

Reverse Osmosis

The most popular method uses a membrane that is permeable to solvent but impenetrable to the majority of dissolved species, both organic and inorganic. The contaminated water is forced against the semi-permeable membrane by these devices using pressure. Water can be forced through the holes of the membrane's filter while bigger molecules that need to be removed are unable to travel through.

Solvent Extraction

The process of separating the components of a liquid solution through contact with another immiscible liquid is known as solvent extraction. A certain amount of separation will ensue if the components of the original solution distribute themselves differentially across the two liquid phases, and this may be exacerbated by the use of several contacts. The main use of solvent extraction in waste treatment has been to remove phenol from by-product water from phenol-containing processes such as chemical synthesis, petroleum refining, and coal coking.

Distillation

Distillation is costly and energy-intensive, and it is probably only warranted in situations where it is possible to extract value products. The application of this method to the management of diluted hazardous aqueous wastes is somewhat limited.

Evaporation

Among many other uses, the evaporation process is used to treat hazardous waste such as radioactive liquids and sludges, concentrate plating waste, and paint solvent waste. It can handle organic and inorganic liquids, slurries, and occasionally sludges that comprise suspended or dissolved solids or dissolved liquids and at least one essentially non-volatile component. High energy consumption and high capital and operating costs are the main drawbacks of evaporation.

Filtration

The full-scale treatment of various industrial wastewater and waste sludges uses a well-developed, cost-effective filtering technique. The operational parameters are established, and the energy requirements are not excessive. Although it is frequently employed in conjunction with precipitation, flocculation, and sedimentation to remove these materials, it is not a major treatment method.

Coagulation

Two sequential mechanisms can be used to organise the numerous flocculation events.

1.     Chemically induced destabilisation of force particles that recipes from surfaces, allowing them to adhere to one another when they come in contact;

2.     The non-repellent particles become physically and chemically entangled, allowing for the production of bigger particles.

Alum, lime, ferric chloride, ferrous sulphate, and poly electrolytes are some of the chemicals utilised in flocculation.

Conclusion

The consequences of the challenges in managing hazardous waste are one of the significant difficulties in the majority of developing nations. The transitioning countries, who are putting all of their efforts into achieving rapid industrial expansion, should take particular note of this. These countries produce a diverse variety of wastes in various quantities, the fate of which is little understood. These locations have been completely poisoned as a result of disposal into the environment, and the ecology has suffered both immediate and long-term effects. Environmental regulations and laws, as well as a variety of treatment technologies, have all been studied for the removal of hazardous waste from the chemical industries. Now that the regulations and processes have been established, it is up to the authorities to properly regulate hazardous waste.