Water Pollution: Sources and Characteristics

• Water pollution is defined as the loss of beneficial uses of water caused by changes in its composition due to human activity
• Water pollution results from introducing contaminants into the natural environment at excess concentrations
• Water bodies that can be affected include lakes, rivers, aquifers, and groundwater

Water Quality Characteristics

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

Sources of Water Pollution

• Point sources are single, large, identifiable sources
• Non-point sources are diffuse sources of pollution that cannot be attributed to a specific location or discharge channel
• Non-point sources include runoff of sediments, pesticide spraying, and fertilizers from farms

Major Water Pollutants and Their Sources

• Infectious agents (pathogens) from human and animal wastes cause diseases (bacteria, viruses, protozoa, parasites)
• Oxygen-demanding wastes deplete dissolved oxygen needed by aquatic species (biodegradable animal wastes and plant debris)
• Plant nutrients cause excessive algae growth (nitrates and phosphates)
• Organic chemicals add toxins to aquatic systems (oil, gasoline, plastics, pesticides, cleaning solvents)
• Inorganic chemicals add toxins to aquatic systems (acids, bases, salts, metal compounds)
• Sediments disrupt photosynthesis, food webs, and other processes (soil, silt)
• Heavy metals cause cancer, disrupt immune and endocrine systems (lead, mercury, arsenic)
• Thermal pollution makes some species vulnerable to disease (heat)

Contaminants Affecting Water Bodies

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

Categories of Fund Pollutants

• Degradable: Organic residuals broken down by bacteria
• Thermal: Injection of heat into a water source
• Eutrophic: Excessive nutrients (nitrogen, phosphorous) leading to excessive aquatic plant growth
• Persistent pollutants: Inorganic/synthetic chemicals that are partially broken down
• Bacteria, viruses, artificial hormones: From domestic and animal wastes
• Stock pollutants: Minerals and inorganic/organic chemicals that cannot be naturally removed

Dissolved Oxygen

• An important measure of water quality
• It is marginally soluble in water and inversely proportional to temperature
• Maximum DO at 16 degrees C is 10 mg/L
• Oxygen gets into water by diffusion, aeration, and photosynthesis
• When dissolved oxygen drops below 5 mg/l, aquatic life is under stress

Physico-chemical Characteristics

• Aggregate organics: Total Organic Carbon (TOC), Chemical Oxygen Demand (COD), Biochemical Oxygen Demand (BOD)
• Chemical: Organics, Inorganics, Gases
• Physical: Solids, temperature, color, odor, turbidity, oil and grease, conductivity
• Sampling: Grab, composite & flow weighted composite

Chemical Oxygen Demand (COD)

• Measures the pollution potential of organic matter
• It does not differentiate between biologically degradable & non-biodegradable organic matter
• COD is the amount of oxidant that reacts with an the water sample under controlled conditions
• Can be calculated using: COD(mg/l as O2) = ((B – S) × M × 8000)/(ml of sample used)
• B = Volume of FAS (Ferrous Ammonium Sulphate) used in the blank sample
• S = Volume of FAS used in the original sample
• M = Molarity of FAS
• 8000 = Milli-equivalent weight of oxygen = (8) x 1000 mL/L

Biochemical Oxygen Demand (BOD)

• Test to establish concentration of organic matter in wastewater samples
• Based on the principle that aerobic biological decomposition will continue until all organic matter is consumed if sufficient oxygen is available
• Known as "BOD5" because it is based on a 5-day period
• The sample is held in dark, incubated conditions (20°C or 68°F)
• Can be defined by: BODt = (DOi – DOt) *D
• DOi = initial dissolved oxygen in the sample bottle DOt = final dissolved oxygen in the sample bottle D = Dilution Factor
• BOD is not a measure of any specific pollutant
• Measuring the amount of oxygen required by microorganisms engaged in stabilizing decomposable organic matter
• Oxidation of biochemical oxygen demanding substances is an exponential decay curve
• COD values are higher than BOD values, since COD includes both degradable and non-biodegradable substances
• A greater BOD to COD ratio equals a higher efficiency of organic treatment by biological methods

Total Organic Carbon (TOC)

• Used to express the pollution load in terms of carbon content
• Measured directly using a TOC analyzer
• A theoretical calculation can be done if the chemical formula of the given compound is known

Physical Parameters of Solids

• Total Solids (TS): Residue remaining after wastewater sample has been evaporated and dried at a specific temperature (103 – 105 deg. C)
• Total Volatile Solids (TVS): Solids that burn off when TS is ignited to 500 deg. C
• Total Fixed Solids (TFS): Solids left after the ignition of TS
• Total Suspended Solids (TSS): Portion of TS retained in filter of 2micro-m and measured after drying the filter paper at 105 deg. C
• Total Dissolved Solids (TDS): Solids that passed through 2micro-m, comprises of colloidal and dissolved solids
• Volatile Suspended Solids (VSS): Solids that burn off when TSS is ignited to 500 deg.C
• Fixed Suspended Solids (FSS): Residue after TSS ignition
• Total Volatile Dissolved Solids (TVDS): Solids that burn off when TDS is ignited to 500 deg.C
• Fixed Dissolved Solids (FDS): The residue of the TVDS
• Settle able solids: Suspended solids that settle over time

Turbidity

• Measure of light transmitting properties of water
• Measurement is based on comparison of intensity of light scattered by sample vs that of standard (formazin solution)
• Analytical Techniques – Nephelometry
• Units – Nephelometric Turbidity Units (NTU)

Physical Parameters: Colour, Temperature, Electrical Conductivity

• Colour: Measured by Spectrophotometer and Units are Platinum Cobalt Units (PCU)
• Temperature: An important parameter as it affects the chemical and biochemical reactions and the rates of these reactions
• Electrical Conductivity: A measure of the ability of solution to electric current EC is surrogate measure of TDS [TDS mg/L = EC x 0.55 to 0.70] Units are MilliSiemens/meter

Chemical Parameters

• Aggregate organics
• Physical
• Chemical
• Alkalinity: Hydroxides, carbonates, and bicarbonates
• Common – Ca & Mg bicarbonates
• Importance – Biological treatment
• Nitrogen: Importance- Nutrient, Forms – NH3, NH4+, NO2– and NO3– & Org. N
• Measurements- Amm. N., Inorg. N., Kjeldahl N., Org. N
• Phosphorous: Aqueous forms – Orthophosphates, polyphosphate & 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 & Zn, Micronutrients / Toxicants, Measurable forms – dissolved, suspended, acid extractable

Wastewater Treatment

• Primary: Removes Solids via Physical Operations - Screening, Sedimentation
• Secondary: Removes Organics via Biological and Chemical Operations
• Tertiary: Removes Nutrients via Biological and Chemical Operations

Primary Treatment

• Screening: First unit operation to remove coarse and fine objects, which may get entangled in mechanical equipment etc, protect pump impellers, and remove rocks, leaves, paper, plastic rags, & other materials.
• Coarse Screens: Bar screen with large openings of 25 mm
• Medium Screens: Clear openings of 12 mm
• Fine Screens: Clear openings of 5 mm
• Sedimentation: Separate solids that can settle by gravity, remove organic and residual inorganic solids, and chemical flocs from chemical coagulation
• 60-65% of suspended solids and 30-35% of BOD are removed

Biological Treatment

• Fundamentals of biological treatment involve microbial growth
• Enzymatic reactions involve redox reactions i.e. addition/removal of oxygen/hydrogen
• Temperature
• Psychrophilic (-10 to 30 deg.C) opt. 12–18 °C
• Mesophilic (20 to 50 deg.C) opt. 25-40 °C
• Thermophilic (35 to 75 deg.C) opt. 55-65 °C
• Facultative

Activated Sludge Processes (ASPs)

• Aerobic, continuous flow, treatment system that uses sludge with microorganisms to breakdown organic matter
• Activated sludge is a flocculated mass of microbes
• The organic load from primary treatment enters the reactor where the active microbial population (activated sludge) is present.
• The reactor is continuously aerated
• The mixture then passes to a secondary settling tank where the cells are settled
• Cells are recycled in order to maintain sufficient biomass to degrade the organic quickly

Trickling Filters

• Aerobic attached growth type wastewater treatment that biodegrades organic matter and achieves nitrification
• Wastewater trickles through a circular bed of coarse stones or plastic material evenly distributed from above
• Microorganisms attach themselves to the bed (filter media) and are covered with bacteria
• Bacteria break down organic waste and remove pollutants

Anaerobic Fluidized Bed Process

• A combination of suspended growth and attached growth process
• Anaerobic microbes grow on the surface of the medium, expanding the apparent volume of the medium; leading to the name "expanded bed reactor"

Disinfection

• Partial destruction of disease causing organisms
• Characteristics of an ideal disinfectant
• Availability
• Deodorizing ability
• Homogeneity
• Extraneous material interaction
• Non-corrosive and non-staining
• Toxic to microbes
• Penetration
• Solubility and stability
• Disinfection methods include chemical (Halogens, Ozone), physical (Heating, Solar insolation), mechanical (Chemical precipitators), and radiation (Gamma rad.)
• Disinfectants cause:
• Damage to cell wall and disturbance in cell permeability
• Damage to protoplasm and cell molecules i.e. - Radiation Chlorine and other halogens
• Factors that influence action include contact time, concentration, intensity, temperature, and nature of organisms