Quality of Drinking Water Flashcards
Description of corrosion and impact on water quality
Corrosion is a complex series of reactions between the water and metal surfaces and materials in which the water is stored or transported. The primary health concern is the potential release of toxic metals such as lead, copper and nickel in the water. The source of:
- Lead includes the use of lead pipes and lead lined tanks
- Copper is related to the leaching from household piping used to convey the water throughout the home
- Nickel is related to the corrosion of chromium plated taps/valves, in house and its geological origin in groundwater
Health effects:
- Lead is a toxic metal that is harmful to human health and there is no safe level for lead exposure. High levels of lead contamination in a child result in convulsions, major neurological damage, organ failure, coma, and ultimately death.
- Chronic copper exposure can damage the liver and kidneys.
Description of disinfection processes and ideal disinfectant properties
Disinfection: any process to destroy or prevent the growth of microbes, inactivate the microbes by altering or destroying essential structures or functions within the microbe
Inactivation processes include denaturation of proteins, nucleic acids, lipids
Properties of an Ideal Disinfectant:
- broad spectrum (active against all microbes)
- fast acting (produces rapid inactivation)
- effective in the presence of organic matter, suspended solids and other matrix or sample constituents
- nontoxic; soluble; non-flammable; non-explosive
- compatible with various materials/surfaces
- stable or persistent for the intended exposure period
- provides a residual (sometimes this is undesirable)
- easy to generate and apply
- economical
Disinfection and microbial inactivation laws
Different microbes have different resistance to chemical disinfectants.
From least to most resistance:
vegetative bacteria -> bacterial spores -> fungal spores -> protozoan pores
Problems related to the presence of micropollutants in natural waters
Aliphatic ethers
- Origin: fuel additive (replacing lead)
- Concerns: high solubility, persistent to degradation, contamination of ground and surface waters, bad smell and taste
Microcystins
- Small natural peptides (>70 structures known)
- Origin: intracellular metabolite of cyanobacteria, can be released in the water (extracellular)
- Concerns: high solubility, contamination of surface water from algae bloom, hepatotoxicity
- Toxicity: many cases worldwide of mammalian’s death
Xeno-oestrogens
- Compounds interfering with human and animal controlled hormonal processes
- Origin: human steroid hormones released in waste water, organic chemicals released in waste water from every day’s life, some metals, organochlorine pesticides
- Concerns: sexual organs (malformation or accelerated maturation), reproduction (fertility decrease), growth disturbance, cancer promotion
- Environmental & health impact: proven for fishes, amphibians, reptiles, birds, uncertain for humans
Pharmaceuticals
- Origin: about 3000 to 4000 active compounds authorized, human and veterinary use, released in waster water from human use, released to surface & groundwaters from veterinary use
- Environmental & health impacts: suspected for aquatic organisms, very questionable for humans
Description of biofilm and impact on water quality
Biofilm is a community of microorganisms attached to a surface: bacteria, protozoa, algae and EPS secreted by microorganisms
Concerns:
- Contamination of water
- Habitat for pathogenic organisms
- Increased resistance against disinfectant
- Increased disinfectant demand.
- Formation of bad smell and odor
- Contribution to corrosion
Factors affecting the biofilm growth:
- Concentration of microorganisms in water
- Temperature (>5 degrees and <70 degrees)
- Nutrients (C, N, P)
- Material surface
Disinfectant:
- Biofilm will protect against disinfection - disinfectant is consumed by EPS or corrosion deposits, increasing disinfectant demand
- Less reactive disinfectant (with organic material or corrosion deposits) can penetrate the biofilm (chlorine, chloramine)
Control of biofilm in drinking water
- Reduce corrosion deposits (reduce cavities hosting biofilm)
- Choose non favorable materials (stainless steel)
- Reduce nutrients: Most biofilms can be limited by organic carbon. Removal of organic carbon: ozone- activated carbon, membranes
What impacts corrosion?
Nearly all metals will corrode to some degree. The rate and extent of the corrosion depend on the degree of dissimilarity of the metals and the physical and chemical characteristics of the media, metal, and environment. In water that is soft, corrosion occurs because of the lack of dissolved cations, such as calcium and magnesium. Corrosion is also accelerated by:
- Low pH (acidic water) and high pH (alkaline water)
- High flow rate within the piping can cause physical corrosion
- High water temperature can increase biological rate of growth and chemical corrosion
- Oxygen and dissolved CO2 can induce corrosion
- High dissolved solids, such as salts and sulfates, can include chemicals or bio-chemical corrosion
- Corrosion related bacteria and electrochemical corrosion can result in pinhole leaks and isolated corrosion
- Presence of suspended solids, such as sand sediment, corrosion by-products, and rust can aid in physical corrosion and facilitate chemical and biochemical corrosion
Strategies to mitigate corrosion
Lead: strategies to reduce solubility include water softening, ortho-phosphate salts, lead pipe replacement
Give examples of common disinfectants and their byproducts
Chlorine (Cl2)
- persistent chemical: used locally and for transport across long distance
- more than 500 by-products identified, most are halogenated (Cl, Br, I) organics
Monochloramine (NH2Cl)
- persistent chemical – used for transport across long distance
- nearly no halogenated organic by-products formed
- some halogenated organic by-products formed with trace of chlorine or chlorine in excess
- negligible reaction with organic matter, expect halogen transfer to nitrogen amines
Chlorine Dioxide (ClO2)
- Less persistent chemical – used locally and for transport across long distances
- Nearly no halogenated organic by-products
- Some halogenated organic by-products formed with excess of chlorine used for chlorine formed in-situ
- Significant reaction with organic matter leading to no halogen transfer
Ozone (O3)
- Non persistent chemical: used locally at production plant
- Nearly no halogenated organic by-products
- Some halogenated by-products formed with excess of chlorine used or chlorine formed in-situ
- Main organic by-products: aldehydes, ketones, acids
- Main halogen by-products: bromate
- Significant reaction with organic matter leading to no halogen transfer
