Environmental Health

WATER CONTAMINATION AND DISEASES

Body water Facts
��Body composition 65% water; −Water loss: 1% thirst; 5% hallucinations; 15% death��Basic requirements for safe water−Drinking: 2–3 liters/day−Minimum acceptable standard for living (WHO) 20–50 liters/capita/day for cooking and basic hygiene.Water Consumption increases with Population Growth Rate

Global Total Water resources:

Oceans 96.5%. Fresh water reserves 3.5%. fresh water includes: Glaciers and permanent snow cover 68.7%. Groundwater29.9% Rivers, lakes, 0.34% Other 0.97%

Sources of ground water contamination

Major Causes of Stream and River Pollution
Nonpointsources65% 17% Municipal sources 9% Industrial sources 6% Dredge and landfill l3% Unknown

Surface Water Contamination: point and non point contamination

Classes of Water Pollutants
Oxygen-demanding → wastes Plant and animal Infectious agents → Bacteria, viruses, protozoaPlant Fertilizers → nitrates, phosphatesOrganic chemicals → Pesticides, detergentsInorganic chemicals → Acids from coal mine drainageSediment from land erosion → Clay silt on stream bedsRadioactive substances → mining and processingHeat from industry → generation of electricity.


Water Purification
Goals−Provides safe source of water that meets quality objectives− to provide potable water with Reasonable cost

Typical contaminants found in raw water that need to be removed to meet specific water quality criteria
Bulky materials; None(in ground W) Branches, leaves, algal mats, soil particles in surface water. Colloidal materials; Microorganisms, trace organic and inorganic material(in ground W) Clay, silt, organic materials, pathogenic organisms, algae, other microorganisms (in surf. W)

More Typical Contaminants Found in Raw Water

Dissolved materials: Fe, Mn, hardness ions, inorganic salts, trace organic compounds(in G.W); Organic compounds, tannic acids, inorganic salts (in S.W) Dissolved gases: Carbon dioxide, hydrogen sulfide; Immiscible liquids: Oils and greases; (None in GW)

Simplified Flowchart of Drinking Water Treatment

RAW WATER COAGULATION, THEN FLOCCULATION Chemical treatment to form floc, which is allowed to settle from water SEDIMENTATION FILTRATION To remove remaining solids DISINFECTION Chlorine to kill microorganisms DISTRIBUTION SYSTEM

Water Disinfection Requirements

Must destroy bacteria, viruses, and amebic cysts in water within a reasonable time. Must not be toxic for humans and animals, and palatable. Must be reasonable in cost and safe and easy to store, transport. Residual concentration in the treated water must be easily and automatically determinable. Must be sufficiently persistent so that the disappearance of the residual would be a warning of contamination

Chlorine

Chlorine is the favored disinfectant for water: Chlorine kills microorganisms.Chlorine reacts with ammonia and other substances Remaining chlorine, termed “free,” is available to disinfect any new input of microorganisms. Microbial inactivation by chlorine (99.9% of organisms killed)

DIS ADVANTAGES: Chlorine does not kill protozoan cysts and some resistant viruses Chlorination has the potential of reacting with some organic compounds present in the water to create trihalomethanes(THM; chloroform) Surface water supplies, high in dissolved natural organic material (humics), are especially vulnerable to THM formation THM levels are generally higher in communities using rivers and streams water than in communities using wells THMs are potentially carcinogenic


WASTEWATER
Wastewater Components of Concern , BOD*, Nutrients(N and P), Suspended solids, Pathogens, Toxic chemicals,

Some Primary Constituents of Municipal Sewage

Effects in water
Potential sources
Constituents
Consumes dissolved O2

human feces

Oxygen-demanding substances

Cause disease

Human waste
Pathogens
Algal nutrients
Detergents
Nutrients
Toxicity
Industrial waste
Toxic chemicals
Interferes with disinfection
Silt
Suspended solids


Biological Oxygen Demand
��Organic decomposition requires oxygen��BOD is defined as the amount of oxygen used by MO in a body of water to carry out decomposition��CH2O + O2 → H2O + CO2 bacteria

Biological Oxygen Demand

When bacteria act upon organic matter in sewage, large amounts of dissolved oxygen are rapidly used up; → fish kills and drastic alterations of the aquatic environment. BOD is an indication of how good the water is. water with low BOD indicating good water quality, and high BOD reflecting polluted conditions

Why Are Nitrates and Phosphates Pollutants?

��Eutrophication−Premature aging of an aquatic system−Excessive nutrient level and subsequent excessive growth of algae eventually a lake transforms it into a marsh.��Source−Domestic sewage and animal sewage, fertilizer runoff, detergent (P)��Effect :−Fish kills

Simplified Flowchart of Wastewater Treatment

Wastewater Pretreatment Physical methods to remove solid materials Sedimentation, Suspended solids allowed to settle Biological treatment,uses microorganisms to digest soluble substances SEDIMENTATION Specialized treatment, removes phosphorus and nitrogen DISINFECTION DISCHARGE OF EFFLUENTS TO RECEIVING STREAM

Municipal Sewage Treatment

The aim of sewage treatment is to improve the quality of wastewater to the point that it can be discharged into a waterway without seriously disrupting the aquatic environment or causing human health problems in the form of waterborne disease.