Characteristics of Water

Characteristics of Water

• Physical characteristics: solids, temperature, color, odor, turbidity, oil and grease, conductivity
• Chemical characteristics: organics (proteins, carbohydrates, lipids, surfactants, phenols, pesticides, emerging organics), inorganics (pH, chlorides, alkalinity, nitrogen, phosphorus, heavy metals), gases (oxygen, hydrogen sulfide, methane)
• Aggregate organics: BOD, COD, TOC
• Biological characteristics: pathogens, indicators, viruses, invertebrates

Sources of Water Pollution

• Point sources: single large sources
• Non-point sources: diffuse source of pollution that cannot be attributed to a clearly identifiable, specific physical location or a defined discharge channel
• Measurements: Amm.N., Inorg.N., Kjeldahl N., Org.N

Physico-chemical Characteristics

• Phosphorus: aqueous forms (orthophosphates, polyphosphate, and organic phosphates), importance as nutrient
• Sulphur: aqueous form (sulphate), reduced to sulphide and further to hydrogen sulfide, formation of sulphuric acid and pipe corrosion
• Metallic constituents: priority pollutants (Cd, Cr, Cu, Fe, Pb, Mn, Hg, Ni, and Zn), micronutrients/toxicants, measurable forms (dissolved, suspended, acid extractable)

Wastewater Treatment

• Primary treatment: removes solids, physical operations (screening, sedimentation)
• Secondary treatment: removes organics, biological and chemical operations
• Tertiary treatment: removes nutrients, biological and chemical operations

Typical Unit Operations of a Wastewater Treatment Plant

Primary and Secondary Sewage Treatment (using Suspended Growth process)

Screen

• First unit operation
• Objective: removal of coarse and fine objects, which may get entangled in mechanical equipment (e.g., grit chambers, sedimentation tanks, etc.)
• Examples: general runoff of sediments, pesticide spraying, fertilizers from farms

Point and Non-Point Sources of Water Pollution

Major Water Pollutants and Their Sources

Contaminants Affecting Water Bodies

• Biodegradable organic matter
• Suspended, colloidal, and dissolved solids
• Nutrients
• Pathogens
• Acidic, basic, and ionic species
• Soaps and detergents
• Pesticides
• Colour and odour causing substances
• Volatile organics
• Recalcitrant and refractory organics
• Thermal/Radioactive material

Categories of Pollutants

• Fund pollutants: those for which the environment has some absorptive capacity
  • Degradable: organic residuals broken down by bacteria
  • Thermal: injection of heat into water source
  • Eutrophic: excessive nutrients leading to too much aquatic plant growth
  • Persistent pollutants: inorganic/synthetic chemicals partially broken down
  • Bacteria, viruses, artificial hormones: from domestic and animal wastes
• Stock pollutants: those for which the environment has little or no absorptive capacity
  • Minerals and inorganic/organic chemicals not removed by natural processes (e.g., lead, cadmium, mercury, some agrochemicals, persistent synthetic chemicals, non-biodegradable plastics, and heavy metals)

Nature and Characteristics of Wastewater

Dissolved Oxygen (DO)

• Important measure of water quality
• Oxygen is marginally soluble in water and inversely proportional to temperature
• Maximum DO at water temperature of 16°C is 10 mg/L
• DO analysis measures the amount of gaseous oxygen (O2) dissolved in an aqueous solution
• Oxygen gets into water by diffusion from the surrounding air, by aeration, and as a product of photosynthesis