Hazardous Waste Management Notes

Hazardous Waste

  • Defined as waste that poses a significant hazard to human health and the environment due to its quantity, concentration, or physical, chemical, or infectious characteristics when improperly handled (treated, stored, transported, or disposed of).

Harmful Chemicals in the Home

  • A variety of household products contain harmful chemicals:

    • Cleaning products: Disinfectants, drain, toilet, and window cleaners, spot removers.

    • Gardening products: Pesticides, weed killers, flea powders, ant and rodent killers, septic tank cleaners.

    • Paint products: Paints, stains, varnishes, lacquers, paint thinners, solvents, strippers, wood preservatives, artist paints, and inks.

    • Automotive products: Gasoline, used motor oil, antifreeze, battery acid, brake and transmission fluid.

    • General: Dry-cell batteries (containing mercury and cadmium), glues and cements.

Characteristics of Hazardous Substances

  • Reactivity:

    • Unstable wastes that can cause explosive reactions or release toxic fumes, gases, and vapors under normal conditions.

    • Reacts violently when mixed with water.

    • Examples: Sodium and potassium metal, dry picric acid, cyanide plating operations.

  • Ignitability:

    • Wastes that ignite easily and burn vigorously at temperatures ≤ 60^\circ C.

    • Examples: Volatile liquids like solvents (acetone, toluene, methanol, ethers), rubber, glue, paint thinners.

  • Corrosivity:

    • Liquid wastes with a pH less than 2 or greater than 12.5.

    • Substances capable of corroding metal containers.

    • Examples: Acids, lime, battery acid, drain cleaners.

  • Toxicity:

    • Harmful or fatal when inhaled, ingested, or absorbed.

    • Wastes releasing toxic materials upon leaching in excess of permissible concentrations.

    • Types of toxicity:

      • Acute: Resulting from one massive dose; may be fatal.

      • Chronic: Resulting from long-term exposure to small doses; causes chronic diseases.

Classes of Hazardous Waste

  • Radioactive waste

  • Biomedical wastes

  • Chemical wastes

Radioactive Waste

  • Sources:

    • Discharges from nuclear reactions (contain radionuclides emitting harmful radiation).

    • Use of radioactive materials in nuclear weapons.

    • Mining and processing of ores to produce radioisotopes.

    • Radioactive fallout from nuclear bombs.

    • Emissions from industrial use of nuclear energy.

    • Leakage from underground nuclear detonations.

    • Use of radioisotopes in medicine, industry, agriculture, and research.

Radiation Shielding

  • Different types of radiation require different shielding materials:

    • Alpha particles: Paper

    • Beta particles: Aluminium

    • Gamma rays, X-rays: Lead

    • Neutrons: Concrete

Effects of Radiation

  • Somatic damage:

    • Damage to the living organism itself, resulting in sickness and death.

    • Delayed or chronic effects: potential for cancer and cataract development.

    • Acute effects: skin burns, vomiting, hair loss, temporary sterility in men, blood changes.

  • Genetic damage:

    • Damage passed from one generation to another through radiation damage to reproductive cells.

    • Risks for genetic effects are considered smaller than somatic effects.

Disposal of Radioactive Waste

  • Geological dumping:

    • Disposal in tunnels, vaults, or silos in particular geological formations, at least a few hundred meters below ground level.

    • Suitable for high-level radioactive waste (HLW), including spent fuels.

    • Waste kept buried for 13-15 years and potentially disposed of in the sea.

    • Salt is a radiation absorber; wastes can be disposed of in salt heaps in mines.

  • Deep geological deposits:

    • Geological repository at depths of 250m to 1000m.

    • Implemented in the USA for military waste.

  • Ocean dumping:

    • Dumping or placing of material in the ocean, often on the continental shelf.

    • Hazardous and nuclear waste disposal is highly dangerous for aquatic and human life.

    • Banned by most developed countries due to the detrimental effects on ocean and marine life.

Biomedical Waste

  • Types:

    • Human anatomical waste: Tissues, organs, or body parts (excluding teeth, hair, and nails).

    • Animal waste: Tissues, organs, body parts, fluid blood and blood products, items saturated or dripping with blood, body fluids contaminated with blood, and body fluids removed for diagnosis or during surgery.

    • Microbiology laboratory waste: Laboratory cultures, stocks for specimens of microorganisms, live or attenuated vaccines, human or animal cell cultures used in research.

    • Waste sharps: Clinical and laboratory materials consisting of needles, syringes, blades, or laboratory glass capable of causing punctures or cuts.

Effects of Biomedical Waste

  • Improper handling and disposal can cause the spread of deadly infections like HIV, AIDS, Hepatitis A and B, along with respiratory and gastrointestinal infections.

  • Infectious agents can enter a healthy body through punctures, abrasions, cuts in the skin, mucous membranes, inhalation, or ingestion.

Chemical Wastes

  • Types:

    • Acids and alkalis.

    • Non-degradable toxic heavy metals: Lead, mercury, arsenic.

    • Organic compounds: Solvents, VOCs (benzene, toluene), pesticides, PCBs, dioxins.

Hazardous Waste Treatment Technologies

  • Physical processes

  • Chemical processes

  • Biological processes

  • Incineration

  • Land disposal

Chemical Processes

  • Neutralization:

    • Converts hazardous substances to less hazardous ones by changing their pH.

    • Acidic wastes neutralized with Ca(OH)_2 with continuous stirring; pH is monitored.

    • Alkaline wastes neutralized by adding acid directly or by bubbling CO_2.

    • Simultaneous alkaline and acidic neutralization can be implemented in the same vessel.

  • Chemical Precipitation:

    • Adjusting the pH of wastewater decreases the solubility of toxic metals, forming a precipitate that can be removed by settling and filtration.

    • For example, M^{2+} can be converted into its insoluble hydroxide using lime: M^{2+} + Ca(OH)2 \rightarrow M(OH)2 + Ca^{2+}.

    • Metal hydroxides are generally insoluble in basic solutions; each metal has its own pH at which its solubility is minimum.

    • If the waste contains several metals, multiple stages of precipitation may be required to control the removal of different hazardous substances by using different pH values.

    • At very low concentrations, metals can be precipitated as sulfides due to their lower solubilities than metal hydroxides, although this carries the risk of forming toxic H_2S gas if alkalinity is not properly maintained. Some metals like Pb, Cd, and Ni precipitate as carbonates.

  • Oxidation-Reduction Process:

    • Converts substances to less toxic oxidation states.

    • Reduction of Cr^{6+} to Cr^{3+} (non-toxic) using SO_2:

    3SO2 + 3H2O \rightarrow 3H2SO3

    2CrO3 + 3H2SO3 \rightarrow Cr2(SO4)3 + 3H_2O

    • Cyanide wastes are treated using alkaline chlorination:

    NaCN + Cl2 + NaOH \rightarrow NaCNO + NaCl + H2O

    • Further chlorination oxidizes cyanate to CO2 and N2:

    2NaCNO + 3Cl2 + 4NaOH \rightarrow 2CO2 + N2 + 6NaCl + 2H2O

    • Wastes treated using redox oxidation: benzene, toluene, phenols, cyanide, arsenic ions, iron, and manganese.

    • Wastes treated using redox reduction: chromium (VI), mercury, lead, silver, and chlorinated organics.

Biological Processes

  • Use microorganisms (bacteria, fungi) to oxidize organic matter to CO2 and H2O.

  • Microorganisms require nutrients such as nitrogen, phosphorus, and a carbon and energy source.

  • Microorganisms obtain carbon and energy from the organics they consume.

  • Biological treatment stages utilize processes similar to those in municipal wastewater treatment plants (trickling filters, activated sludge process).

  • Bioremediation:

    • Employs bacteria and enzymes to destroy toxic or hazardous substances or convert them to harmless compounds.

  • Phytoremediation:

    • Uses natural or genetically engineered plants to absorb, filter, and remove contaminants from polluted soil and water.

  • In-situ biodegradation:

    • Uses bacteria to degrade organic compounds in the soil and groundwater on-site, reducing risks associated with hazardous waste transportation.

    • Used to treat wastes containing gasoline, diesel, chlorinated solvents (trichloroethylene, tetrachloroethylene), and heavy metals.

    • Two approaches:

      • Increase the population of existing microorganisms by supplying nutrients such as ammonium sulfate, magnesium sulfate, and sodium carbonate. Oxygen can be supplied by injecting an oxidant such as H2O2 or by forcing air.

      • Alter the underground population of microorganisms by seeding with new microorganisms proven effective at decomposing the hazardous wastes under consideration based on laboratory studies.

Incineration

  • Subjects wastes to combustion, converting them into residue and gaseous products.

  • Reduces waste volume to 70-80% of the original volume.

  • Useful materials and energy can be recovered if the process is done in properly equipped incinerators.

  • Pollution control technologies for treatment of emissions:

    • Scrubbers: Use a liquid spray to neutralize acid gases.

    • Filters: Remove tiny fly ash particles from smoke.

Land Disposal

  • Methods: Landfills, surface impoundments, underground injection wells.

  • Conventional, inexpensive method that has led to tragic incidents due to poorly monitored sites.

  • Resources Conservation and Recovery Act (RCRA) has banned land disposal of some hazardous substances.

  • Hazardous waste landfill:

    • Liquid and solid hazardous wastes can be put into drums or other containers and buried in carefully designed and monitored secure landfills.

    • A double liner system is placed beneath the wastes to stop leakage.

    • The upper liner must be a flexible membrane lining (PVC, HDPE, or rubber).

    • The lower lining can be re-compacted clay (at least three feet thick), often with flexible plastic membranes.

    • Collected leachate undergoes further treatment.

    • The site must include monitoring facilities to check for contamination from soil.

  • Surface Impoundments:

    • Ponds, pits, or lagoons in which wastes are stored.

    • May have liners to contain the waste.

    • Eventually, all impoundment liners are likely to leak and could contaminate groundwater.

  • Underground Injections or deep- well disposal:

    • Liquid hazardous wastes are pumped under pressure into dry, porous rock formations far beneath aquifers.

    • Low cost and wastes can often be retrieved if problems develop.

    • Problems: Wastes can leak into groundwater from the well shaft or migrate unexpectedly.

Case Study: Dumping of Radioactive Material in Delhi’s Mayapuri (February 2010)

  • A Gamma Irradiator was bought in 1968 from Canada for professor B.K.Sharma’s research on the "effect of Gamma rays on compressed cyanide".

  • The Cobalt-60 was in a "Gamma Irradiator" at Delhi University, not in use since 1985.

  • Cobalt-60 is a radioactive isotope (hard, lustrous, grey metal).

  • It was bought by scrap dealers in Mayapuri through an auction in Feb 2010.

  • The scrap dealers dismantled the equipment, peeling off the lead covering, leading to radiation exposure and casualties.

  • Panic triggered after news of a radiation leak; five persons fell ill, and one person died after contact with a "mysterious shining object" in a scrap shop.

Electronic Waste (E-waste)

  • Describes discarded electrical or electronic devices.

  • "Waste" refers to the residue or material dumped by the buyer rather than recycled, including residue from reuse and recycling operations.

  • E-waste contains significant quantities of toxic metals and chemicals.

  • Many elements contain poisonous substances such as Lead, Tin, Mercury, Cadmium, and Barium, which cause severe diseases like cancer, birth defects, neurological and respiratory disorders.

E-waste Treatment & Disposal Methods

  • Land filling

  • Incineration

  • Recycling

  • Re-use

E-Waste Recycling

  • Out of one ton of computer waste, 99% is used for recovery of precious metals, and 1% for safe land filling.

  • Formal recyclers have permission to establish a recycling plant and consent to export metals to approved smelters globally.

E-Waste Collection Centers

  • Delhi (NCR)

  • Kolkata

  • Pune

  • Bangalore