Safe Drinking Water Flashcards
Drinking Water Management Considerations
-Surface water
-Ground water
-Treatment Process
-Storage of clean, treated water
-Distribution/Conveyance to the consumer
-Industrial
-Commercial
-Residential
7 Steps for treating drinking water
-Screening
-Coagulation and Flocculation
-Sedimentation
-Filtration
-Chlorination
-Supplementary Treatment
Screening
-To protect the main units of a treatment plant, screens are used to remove large floating and suspended solids present in the inflow
-This includes leaves, twigs, paper, rags, and other debris that could obstruct flow through the plant or damage equipment
Coagulation
-Coagulationremoves the fine particles less than 1 µm in size) suspended in the water.
-A chemical such as Aluminum Sulfate known as a coagulantwith a positive charge is added to the water, which neutralizes the fine particles’ negative electrical charge.
Flocculation
-occurs as the water is stirred by paddles in a basin, and the flocs join with each other to form larger flocs
-the __ basin has compartments with decreasing speeds that allows increasingly large flocs to form and settle
Sedimentation
when the large flocs settle out in a process calledsedimentation(as floc falls to the floor of a settling tank). The material is called sludge; and is removed for disposal
Filtration
-The process where solids are separated from a liquid using filters made of Sand, Coal, Gravel, or Activated Carbon (GAC)
-When the filters are full of trapped solids, they are back-washed using clean water and air pumped back up the filter to dislodge the trapped impurities
Chlorination
when the water isdisinfectedto eliminate any remaining pathogenic micro-organisms. The most commonly used disinfectant is chlorine in liquid or gas form
contact time
When chlorine is added to water, it reacts with any pollutants present, including micro-organisms, over a given period of time, referred to as the __
residual chlorine
-The amount of chlorine left after this is called __ and stays in the water through the distribution system, protecting it from any micro-organisms that might enter it until the water reaches the consumers
Regulatory requirements for disinfection
EPA requires systems using surface water to:
-disinfect their water
-Filter their water so that the following contaminants are controlled at the following levels
Cryptosporidium - 99 percent (2-log10) removal
Giardia lamblia - 99.9 percent (3-log10) removal/inactivation
Viruses - 99.99 percent (4-log10) removal and inactivation
% inactivation
the disinfection efficiency
ex- 90%= 90 out of 100 microorganisms are killed while 10 out of 100 would survive
-For many microorganisms, the same disinfection efficiency can be achieved by treating a water with any combination of C (disinfectant concentration, in mg/L) and T (contact time, in min) that gives the same CT value
Supplementary Treatment
-this may be required to:
-Adjust water pH to improve taste and to reduce corrosion (breakdown) of pipes
-A pH less than 7 is acidic and can be corrosive causing pipes with metals such as Pb an Cu to leach into the water and cause health problems.
-Orthophosphate is added to the system to create a coating on the inside of lead service lines, creating a barrier between the Pb and Cu pipes and the water. This is called “corrosion control”.
-pH greater than 7 indicates alkalinity and tends to affect the taste of the water.
-Sulfuric acid and sodium hydroxide (caustic) are most used for neutralizingacidsor bases.
-Fluoride addition helps keep teeth strong and reduces cavities
Lead Leaching in DC water supply
-In 2000 the water treatment system for D.C., changed from chlorine to chloramine to reduce disinfectant byproducts
-This change unexpectedly reduced decades of protective mineral coating — or scaling — from the lead service lines
-This allowed lead to leach into the water, and cause lead levels to rise in the drinking water in the city
-DC didn’t use orthophosphate initially, and that caused lead to leach from the pipe
Storage
-After treatment, various structures hold filtered and treated water that is ready to be sent to consumers
-Some cites use above ground tanks, underground chambers and uncovered storage
Baltimore City Drinking water system
-The system delivers treated water to Baltimore area consumers
-The service area is 560 square miles and provides potable water to about 1.8 million people.
-Contains 4,500 miles of mains in the distribution system.
-Supplies drinking water to Baltimore City, Baltimore Howard, and Anne Arundel Counties
Distribution
-this system delivers treated water to consumers in the service area
-distributes water through a network of water mains ranging in size from 3 inches to 12 feet in diameter
-a series of mains connect a series of pumping stations, and elevated storage tanks, which supply the water to consumers
-Finished drinking water is distributed by gravity or by pumping stations and the Second and Third Zones by pumping
Chlorine disinfectant residual; three purposes for it
-PWS supplied by surface water must maintain this chemical for water that is delivered to customers through a distribution system.
-serves three purposes:
1-Protect against microbial contaminants
2-Act as an indicator of distribution problems
3-Limit growth of heterotrophic bacteria and Legionella within the distribution system
Chloramines
a chlorine residual that at higher levels can form disinfection byproducts (DBPs) that are linked to many health issues, including:Cancer, Skin irritation, Respiratory irritation, Kidney damage
