Dead Zones and Bioremediation

• Dead Zones
  • Dead zones are areas in the ocean with very low oxygen concentration (hypoxic conditions)
  • They emerge when the influx of excess chemical nutrients spurs algae growth (algal blooms)
  • Usually occur 200-800 meters below the surface (in the saltwater layer)
  • Hypoxic zones can occur naturally due to the upwelling of excess nutrients
  • They can be created or enhanced by human activity
  • Dead zones are detrimental to animal life and most of the animal life either dies or migrates from the zone

How Dead Zones Form

• Fertilizers, sewage, and nutrients from farming flow down rivers into the water

• Nutrients stimulate massive growth of algae blooms

• Plankton and algae die, sink to the bottom, and decompose using up oxygen in the water

• Area becomes starved of oxygen; fish avoid the area

• Bioremediation

  • Uses microorganisms (bacteria and fungi) to degrade environmental contaminants into less toxic forms
  • Microorganisms can be specifically designed for bioremediation using genetic engineering techniques
  • Can be performed in situ (at the site) or ex situ (involves the removal of contaminated material to be treated elsewhere)

In Situ Bioremediation

• Bioventing: Supply of nutrients through wells to contaminated soil to stimulate the growth of bacteria
• Biosparging: Injection of air under pressure below the water table to increase groundwater oxygen concentrations and enhance the rate of biological degradation of contaminants by bacteria
• Bioaugmentation: Microorganisms are imported to a contaminated site to enhance the degradation process

Ex Situ Bioremediation

• Land farming: Contaminated soil is excavated and spread over a prepared bed, and periodically tilled until pollutants are degraded to stimulate indigenous biodegradative microorganisms and facilitate their aerobic degradation of contaminants

• Bioreactors: These involve the processing of contaminated solid material (soil, sediment, sludge) or water through an engineered containment system

• Composting: a process using nature’s recycling of decomposed organic materials into a soil known as compost

• Air Pollution

  • Refers to undesirable changes in the physical and chemical constituents of air due to human activities

Air Pollutants Based on Source

• Primary: Direct emission into the atmosphere
• Examples: CO, SO₂, NOx, PM
• Secondary: Reaction with atmospheric pollutants
• Examples: Ozone, PAN

Air Pollutants Based on Mode of Release

• Indoor
• Examples: Cooking, smoking, air conditioning
• Examples of pollutants: CO, CO₂, VOCs
• Outdoor: Industrial processes, transportation
• Examples of pollutants: PM, CO, VOCs

Air Pollutants Based on Chemical Composition

• Particulate Matter: Solid or liquid aerosols
• Examples: PM2.5, PM10
• Gaseous: Miscible with air in vaporous form
• Examples: SOx, Ozone, NOx, CO

Air Pollutants Based on Persistence

• Primary Pollutants: Persist in the form in which they are added to the environment
• Examples: DDT, plastic
• Secondary Pollutants: Formed by interaction among the primary pollutants
• PAN (Peroxyacetyl Nitrate, formed by interaction of Nitrogen Oxides and Hydrocarbons)

Air Pollutants Based on Existence in Nature

• Quantitative Pollutants: Occur in nature and become pollutants when concentration reaches beyond a threshold level
• Examples: Carbon Dioxide, Nitrogen Oxide
• Qualitative Pollutants: Man-made, do not occur in nature
• Examples: Fungicides, herbicides, DDT

Air Pollutants Based on Biodegradability

• Biodegradable Pollutants: Waste products degraded by natural process of microbial action
• Example: sewage
• Non-Biodegradable Pollutants: Pollutants which don't decompose naturally or decompose slowly
• Examples: plastics, polythene bags, DDT

Air Pollutants Based on Origin

• Natural: Released during natural processes
• Examples: volcanic eruptions, forest fires, grass fires
• Anthropogenic: Released during anthropogenic activities
• Examples: CO₂ emissions from the burning of fossil fuels

Sources of Air Pollution

• Natural Sources: Ash from burning volcanoes, dust from storms, forest fires, pollen grains from flowers in air

• Human Sources: Power stations using coal or crude oil release CO₂, furnaces using coal, cattle dung cakes, firewood, kerosene. Steam engines such as railways, steamers, motor vehicles give out CO₂

  • Also include motor and internal combustion engines, vegetable oils, and pesticide residues

• Particulate Pollutants

  • Matter suspended in air such as dust and soot
  • Major sources are from industries, vehicles, power plants, construction activities, oil refineries, railway yards, marketplaces
  • PM10: Inhalable particles with diameters generally 10 micrometers and smaller derived from dust stirred up from construction sites, pollen, emissions from vehicles and industrial processes
  • PM2.5: Fine inhalable particles, with diameters generally 2.5 micrometers and smaller derived from combustion processes

Fly Ash

• End product of combustion during power generation in coal-based thermal power plants
• Composed of silica, alumina, oxides of iron, calcium, magnesium, and toxic heavy metals
• Used in manufacturing of Portland Cement, bricks/blocks/tiles, road embankment construction and low-lying area development

Fluorides

• From sources such as aluminum, steel and electrochemical plants, blast furnaces, brick kilns, coal combustion, tile and glass etching factories.
• Volcanoes also release fluorides
• Impact: Fluoride particles settle on vegetation, burn tips of leaves and when cattle eat the vegetation they suffer from fluorosis resulting in loss of teeth, weight, and lameness

Water Pollutants

• Pathogens: Sewage, human and animal wastes leading to depletion of dissolved oxygen in water
• Organic pollutants: Oil & grease, pesticides/weedicides, plastics, detergents disrupt marine life and are sometimes toxic
• Inorganic pollutants: Fertilizers like phosphates and nitrates that lead to eutrophication; Acids and alkalies from mine drainage that kill freshwater organisms
• Radioactive materials: Can lead to cancer and genetic defects
• Heat: Decreases oxygen solubility
• Sediments: affects water quality

Water Pollution Control Measures

• When wastewater is dumped off into rivers, treatment is carried out by sedimentation, coagulation and filtration, known as primary treatment.
• When water is needed for drinking, it undergoes further treatments named as secondary and tertiary treatments.

Primary Treatment

• Sedimentation: Polluted water sits to settle silt, clay and other matter.
• Coagulation: Combines fine particles and colloidal suspensions into large particles called coagulation using coagulants such as potash alum.
• Filtration: Filters suspended particles, flocculants, bacteria, and other organisms. Impurities collected are called sludge.

Secondary Treatment

• Calcium and magnesium cations are removed from hard waters.
• Soft water is exposed to air to encourage bacterial decomposition into harmless products.

Tertiary Treatment

• Chlorine is used as a disinfectant, using methods such as ultraviolet radiation or ozone gas treatment

Sources of Water Pollution

• Community Waste Water: Includes discharges from houses, commercial and industrial establishments, consisting of human excreta, food residues, cleaning agents, detergents and other wastes
• Industrial Waste: Discharges several inorganic and organic pollutants

Types of Industries/Pollutants

• Example Mine Wastes: Chlorides, various metals, ferrous sulphate, sulphuric acid, hydrogen sulphide, ferric hydroxide, surface wash offs, suspended solids, chlorides and heavy metals
• Example Soap and Detergent: Tertiary ammonium compounds alkalies
• Paper and Pulp: Sulphides, bleaching liquors

Oil Spills

• Refers to any uncontrolled release of crude oil, gasoline, fuel or other oil by products into the atmosphere causing major environment harm
• Oil toxicity components may cause serious health problem like heart damage
• To clean Oil spills, floating barriers are used to prevent it dispersing.

Agricultural Sources of Water Pollution

• Fertilizers
• Pesticides
• Animal Excreta
• Excess nitrate in drinking water reacting to form a non-functional compound impairing oxygen transport, know as mathemoglobinemia or blue baby syndrome
• Thermal Pollution reduces the amount of dissolved oxygen
• Marine Pollution caused by cities and navigational discharge

Heavy Metals (Ions) In the Water

• Copper pollutants can come from fertilizers
• Zinc pollutants can come from solders and cosmetics
• Chromium pollutants can come from the leather industry
• Mercury pollutants can come from coal combustion
• Lead pollutants can come from PVC pipes