Chapter 6 –Drinking Water Purification(Hwk#6- pp.179 2,4,6,8)•water source – Coliform count up to 5000/100 mL and turbidity of up to 10 units is good. Over 20,000/100 mL and turbidities that exceed 250 units is very poor for treating to potable water.

Chapter 6 –Drinking Water Purification•Surface Water Treatment-Clarification and disinfection. (Clarification –coagulation-flocculation, sedimentation, and filtration; Disinfection –chlorination)•SDWA- Safe Drinking Water Act(1974)-protect surface water quality for people consumption•1996 revision included: stricter controls on microbial contaminants,and by-products of chlorination, water utilities notify public of water saftey violations within 24hrs, and EPA certification for water system operators

Lehigh Valley Water Supply Tourhttp://www.lvwater.org/tour/frame_tour.htm

Chapter 6 –Drinking Water Purification Primary Standards (Drinking Water) -set maximum permissible levels of potentially harmful substances •MCLs- Maximum Contaminant Levels•MCLGs- Maximum Contaminant Level Goals [this level is not expected to cause any health effects; it is not enforceable;zero for carcinogens]

•primary contaminants includes organic and inorganic chemicals, microorganism, turbidity, radionuclides•See table 6.1 & 6.2 in text pp.150 & 151

Secondary Standards (Drinking Water) –are guidelines that apply to the esthetic qualities of drinking water (i.e. color and odor) see Table 6.3

Chapter 6 –Drinking Water PurificationSampling Procedures•Sampling Frequency•Points or Location of Sampling (for representative sample- fully flushed sample for most contaminants, except lead and copper which would be the first draw)• Type and Size of Containers(i.e. 100ml for coliform to 1L for radionuclide)•Temperature/Air Space – VOCs should not allow for any air space•Time for Chain of Custody – Coliform must be delivered within 24 hrs. and radionuclides within a yearRecord Keeping and Reporting•SDWA requires that public water systems submits reports for the public and a monthly report for local regulatory agency•The State must be notified within 48 hrs. of a Violation of a primary MCL

Sedimentation [sedimentation tank, settling tank, or a clarifier]•particles settles to the bottom under quiescent conditions (when flow velocities and turbulence are minimal)•sludge – is the accumulated solids on the bottom•Depends on density, size, drag, buoyancy, temperature and viscosity of water•discrete settling – occurs at lower concentrations, no interference from other particles•hindered settling – interference from other particles due to high concentrationsDetention Time

Chapter 6 –Drinking Water Purification Note: Zone of stream pollution on page 122 &123

tan

( )

D

D

VT

Q

where T dententiontime

V volumeof water in k

Q average flowrate volume per unit time

Overflow Rate – is the average upflow velocity of water in the settling tank, where particles that settle faster than Vo reach the sludge layer.

Chapter 6 –Drinking Water Purification

tan ( )

oS

o

s

Overflow Rate or Surface loading

QV

A

V overflowrate

Q average flowrate

A k surface area top view

SuspendedSolids

EffluentChannel

ClearWater

SWD- side water depth is the actual depth of the water in a settling tank. see p.157 - fig. 6.6Freeboard – it serves to prevent splashing of water over the tank sides.Short-circuiting – Time to flow out of the settling tank exceeds the detention time for settling the particlesWeir loading rate – The flow rate per foot that should be less than the specified maximum value.(should keep particles from flowing over the weir)

Chapter 6 –Drinking Water PurificationSettling Tank Design

Chapter 6 –Drinking Water Purification

http://www.h2o4u.org/story/index.html#contents

2. The floc settles on these plates and eventually falls to the bottom of the basin, leaving clear water on the top! Then, an underwater vacuum cleaner travels along the bottom of the basin and sucks up all the sediment.

1.As the water flows into this basin, it is forced to flow uphill between hundreds of flat 'plates.' As the water flows over the top of these plates, the floc gets stuck on the surface and collects there.

Chapter 6 –Drinking Water PurificationCoagulation and Flocculation Coagulants- causes colloids to stick together by neutralizing their charge.Flocs – are larger clumps of colloids that can settle out. Coagulation – Is considered the combined process of flash-mix of coagulant and the slow mix allowing for sedimentation.Weir loading rate – The flow rate per foot that should be less than the specified maximum value.(should keep particles from flowing over the weir)

Rapid Filters .vs. Slow Sand Filters – rapid filters have water flowing 30 times faster through them than Slow Sand Filter and includes a backwashing system (see P. 161 in Text)

Filtration (sand filtering system)

Chapter 6 –Drinking Water Purification

1.Water flows into these filter beds and slowly flows through layers of anthracite coal, sand and gravel, which collect fine particles and micro-organisms.

2.These controls monitor the level of water in the filter beds to make sure it is evenly distributed among all the filters.

Chapter 6 –Drinking Water Purification

Disinfection THM (TriHaloMethanes) – A carcinogenic compound produced by the decay of an organic substance such as vegetation in Chlorine. (i.e. Chloroform)Note: The lower the pH the more effective the chlorine disinfection.

Chapter 6 –Drinking Water PurificationDisinfection

Chloramines – a compound form from the reaction of ammonia and chlorine (or combined chlorine). (used in swimming pools)• It is a slower disinfectant but last longer.•It has an objectionable taste and odorFree available Chlorine – The radicals HOCL (hypochlorous acid) and OCL- (hypochlorite radical). It is a faster disinfectantBreakpoint Chlorination- is when enough chlorine is added to satisfy the chlorine demand and to react with all the dissolved ammonia.

Chapter 6 –Drinking Water PurificationMethod of Disinfection

•#1 Chlorine Residual - After filtration, extra chlorine travels with the water through the underground pipes that bring the water to your home. If there is any bacteria in the pipes, it will be killed by the remaining chlorine •We monitor the chlorine residual to make sure it's high enough to kill any bacteria it encounters on the way to your home, but low enough to be safe and to reduce odor and taste problems.

Chapter 6 –Drinking Water PurificationMethod of Disinfection

•#2 Turbidimeter - This meter displays numbers which tell us the 'turbidity' level of the water. 'Turbidity' is a measure of the cloudiness of the water. At this stage of the treatment process, the water should be very clear and clean!

Chapter 6 –Drinking Water PurificationMethod of Disinfection

•#3 Particle Counter - As the water passes through this test, the equipment counts the number of particles that pass through it. It also measures the size of the particles. The information generated by this equipment helps us to refine our filtering process.

Chapter 6 –Drinking Water PurificationMethod of DisinfectionOzone (O3) – a gaseous disinfectant •It has been used for greater than 90yrs in Europe•Produced by passing very high electric current into the air (very expensive to produce)•It is very unstable and cannot be stored•It leaves no measurable residual in water, so that some chlorine must be used as a precaution•It does not produce THM (carcinogen)•It is stronger than Chlorine•It can assist as a coagulant when used with alum (aluminum sulfate-a coagulant), reducing the amount of chemicals needed to adjust pH•It also aids in the filtration process as a coagulant •Read the Milwaukee Case study - Text 171•Also oxidizes and precipitates iron, sulfur, and manganese so they can be filtered out of solution.  •Ozone treatment creates its own byproduct that can be harmful to health if they are not controlled (e.g., formaldehyde and bromate).  •Ozone will oxidize and break down many organic chemicals as well

Chapter 6 –Drinking Water PurificationMethod of Disinfection

Ultraviolet Radiation (UV) – an electromagnetic radiation just beyond the blue end of the light spectrum.•It is absorbed by genetic material in micro-organisms interfering with their reproduction•Mercury Lamps are best suited for large fractions of UV energy that is needed for disinfection•It is very unstable and cannot be stored•It does not involve any chemical handling•It leaves no residual in water

Chapter 6 –Drinking Water PurificationGround Water Pollution

http://www.timesunion.com/news/special/water/graphics/ground.stmhttp://www.cyber-nook.com/water/contrisks.htm#sources

Chapter 6 –Drinking Water PurificationMethod of Disinfection

1Leakage from landfill. 2Chemical application to parks and lawns. 3Road salt. 4Irrigation. 5Industrial emission.6Municipal sewage discharge.

7Underground mining. 8Water table reduced by heavily pumped well. 9Sewer and pipeline leaks. 10Storm water runoff. 11Underground storage tanks. 12Fresh water aquifer. 13Municipal water supply well. 14Pesticides and fertilizers from agricultural land. 15Private well. 16Leaks from oil storage tanks. 17Leakage from septic tanks. 18Saturated zone.

Chapter 6 –Drinking Water Purification

19Water table.20Livestock waste. 21Marine waste. 22River water contaminated with urban, industrial and agricultural pollutants. 23Brine from oil injection well. 24Leaks from waste lagoon.25Deep-well hazardous waste disposal. 26Water-bearing sandstone.27Limestone.

Chapter 6 –Drinking Water Purification

Aluminum Sulfate

Chapter 6 –Drinking Water Purification

A Treatment Plant1. Intake: Water is taken from the source. Logs, fish and plants are screened out at the intake and then the water is drawn into the treatment plant. If the source is groundwater, the "screening" is done by the soil as the water travels under the earth's surface. Sometimes very little treatment is required for groundwater. 2. Chemical Addition: Aluminum sulfate (alum) polymers and/or chlorine are added to the water. These kill germs, improve taste and odor, and they help settle solids still in the water. The water and these chemicals are then mixed together. 3. Coagulation and Flocculation: Here, the alum and other chemicals from the chemical addition step cling to particles in the water. This is called coagulation. It causes the particles to stick together and form larger particles called floc.

Chapter 6 –Drinking Water Purification

4. Sedimentation: The water and the floc particles flow into a sedimentation basin. Here the floc settles to the bottom and is removed from the water. 5. Filtration: From the sedimentation basin, the water flows through filters. Filters are made of layers of sand and gravel. The filters are used to remove any remaining particles left in the water. 6. Disinfection: A small amount of chlorine, or other disinfecting chemicals, is added. This is used to kill any remaining germs and to keep the water safe as it travels to the public. In some water systems, especially those with groundwater sources, this is the only treatment provided.

Chapter 6 –Drinking Water Purification

7. Storage: The water is placed in a closed tank or reservoir called a clear well. This allows time for the chlorine to mix throughout the water in order for disinfection to take place. The water then flows into the distribution system.

The water is sampled and tested throughtout the treatment plant. Sampling is performed to make sure the processes are working and that the water is safe before it leaves the plant. In North America, governments have set standards for drinking water. When water leaves a treatment plant, it is as clean or cleaner than required by these standards.

LECTURE #6Chapter 6 –Drinking Water Purification

Municipal Water Treatment (GAC)

                                                                                                                                                                                                                                 

                                              City of Oulu (Finland) –

municipal water treatment plant