Water Treatment Exam Review
Chloramines (as Cl2) - MRDL
4.0 mg/l
Chlorine (as Cl2) - MRDL
4.0 mg/l --> minimum is 0.5 mg/l throughout the distribution system.
What is the Average ground water pH level?
5.8
What is the Average surface water pH level?
6.8
List the three types of control equipment typically required when operating Rapid Sand and Multimedia Filters.
1. Rate-of-flow controller 2. Loss-of-Head indicator 3. Online Turbidimeters
List three major factors that determine backwash frequency, in order of importance.
1. increasing effluent turbidity or particle counts. 2. head loss approaching terminality (approaching Terminal Head Loss) 3. UFRV approaching unreasonable limits. *The turbidity should never be allowed to reach 0.3 NTU before backwashing.*
Chlorite - MCL
1.0 mg/l
Nitrite (measured as Nitrogen) - MCL
1.0 mg/l
Copper - Action Level
1.3 mg/l
Nitrate (measured as Nitrogen) - MCL
10.0 mg/l
What is the Secondary MCL for color?
15 color units
What is the Secondary MCL for odor?
3 TON (threshold odor number)
What is the most typical Gate Valve application for water treatment?
Most gate valves used in treatment and distribution exist to isolate portions of the system or plant, control pressure and flow, shut off water in a targeted manner and protect pumps and pipelines.
Lead - Action Level
.0015 mg/l (15 ppb)
Benzene - MCL
.005 mg/l
Tetrachloroethylene - MCL
.005 mg/l (dry cleaning chemical)
Bromate - MCL
.010 mg/l
Haloacetic acids (HAA5) - MCL
0.060 mg/l **(No individual MCL for TTHM and HAA5 constituents)
Total Trihalomethanes (TTHMs) - MCL
0.080 mg/l **(No individual MCL for TTHM and HAA5 constituents)
Chlorine dioxide (as ClO2) - MRDL
0.8 mg/l
Describe a Butterfly Valve...
A butterfly valve has a disk that is rotated on a shaft. When in the open position the disk is parallel with flow, and when closed, it seals against a rubber or synthetic flange. They operate easily and quickly because only 1/4 turn is required to open or close them.
What is ferrous sulfate?
A coagulant chemical that is less pH-dependent than Alum and so can be utilized in situations where ideal pH adjustment my not be practical or able to be done. Fe2(SO4)3 * 7H2O
Define short circuiting and explain its significance.
A hydraulic condition in a basin in which the actual flow time of water through the basin is less than the actual design flow time. If a basin is not properly designed, water bypasses the normal flow path through the basin and reaches the outlet in less than normal time. In serious occurrences, it can cause floc to be carried out of the basin as a result of shortened sedimentation time. The major cause is poor inlet baffling. A perforated baffle can successfully distribute water without causing strong currents. If short circuiting is suspected, tracer studies are the best method of determining the extent of the problem.
What is a Peristaltic Pump?
A type of positive displacement pump used for pumping a variety of fluids. The fluid is contained within a flexible tube fitted inside a circular pump casing (though linear peristaltic pumps have been made). A rotor with a number of "rollers", "shoes", "wipers", or "lobes" attached to the external circumference of the rotor compresses the flexible tube. As the rotor turns, the part of the tube under compression is pinched closed (or "occludes") thus forcing the fluid to be pumped to move through the tube. Additionally, as the tube opens to its natural state after the passing of the cam ("restitution" or "resilience") fluid flow is induced to the pump. This process is called peristalsis and is used in many biological systems such as the gastrointestinal tract. Typically, there will be two or more rollers, or wipers, occluding the tube, trapping between them a body of fluid. The body of fluid is then transported, at ambient pressure, toward the pump outlet. Peristaltic pumps may run continuously, or they may be indexed through partial revolutions to deliver smaller amounts of fluid. In simpler terms, the peristaltic pump works by squeezing a flexible tube that is filled with liquid so that the liquid squirts out of the open end of the tube. Summary - In water treatment, peristaltic pumps are used mainly to inject chemical treatment agents into pressurized water lines. They are commonly used to inject chlorine, soda ash, polyphosphates
What is Alum, and what is its' most effective pH range?
Aluminum sulfate, the most common coagulant used for conventional treatment methods. It is positively charged and helps create Van der Waals force to assist in creation of floc by neutralizing the negatively charged particles of color or turbidity. The coagulation process occurs within a few seconds after alum is added to the water, provided there is rapid, thorough mixing, a pH range of 5.8 - 8.5 Colder temperatures require more mixing. Al2(SO4)3 * 14(H2O)
Iron and Manganese Threshold levels
Both are 0.3mg/l each - combined, threshold is 0.5 mg/l
What are Check Valves and Foot Valves?
Check valves are designed to allow flow in one direction only. They are most commonly used on discharge pipes to prevent backflow when a pump is shut down. A foot valve is a special type of check valve installed at the bottom of a pump suction so the pump will not lose its prime when the power is shut off.
What is a Secondary MCL (SMCL)?
EPA has established National Secondary Drinking Water Regulations (NSDWRs) that set NON-MANDATORY water quality standards for 15 contaminants. EPA does not enforce these "secondary maximum contaminant levels" (SMCLs). They are established only as guidelines to assist public water systems in managing their drinking water for aesthetic considerations, such as taste, color, and odor. These contaminants are not considered to present a risk to human health at the SMCL.
Explain the maximum allowable Turbidity levels.
Generally speaking, less than 5 NTU - In CT - For systems that use conventional or direct filtration, at no time can turbidity go higher than 1 Nephelometric Turbidity Unit (NTU), and samples for turbidity must be less than or equal to 0.3 NTUs in at least 95 percent of the samples in any month. Systems that use filtration other than the conventional or direct filtration (slow sand) the turbidity level of representative samples of a system's combined filtered water shall be less than or equal to one (1) NTU in all of the measurements taken each month.
Explain what activated silica is, and what it is used for.
It has been used as a coagulant aid since the 1930's and is still used today. When used in the proper dosage, it will increase the rate of coagulation, reduce the coagulant dose needed and also widen the pH range for effective coagulation.The chemical delivered to the plant is actually sodium silicate( Na2SiO3), and it must be "activated" by the operator by adding an acid, typically hypochlorous acid, to reduce the alkalinity. The chief advantage of activated silica is that is strengthens the floc making it less likely to break apart during sedimentation or filtration. The floc formed will be larger, denser and will settle rapidly. Activated silica is typically added after the coagulant, but can also be added before provided the water is already low in turbidity. **It should never be added directly with the Alum because they react with each other.**
What is a Curb Stop?
It is the valve commonly installed as the main shutoff for a particular service connection - older installations used inverted plug style valves, newer installations use ball valves.
Explain the primary uses of potassium permanganate.
KMnO4 - It is an oxidant that is effective for controlling tastes and odors, as well as TTHM control. It is frequently used as the initial chemnical fed into surface water systems because it controls many taste and odor causing substances in raw water. In particular, it will eliminate a number of taste and odor conditions that would not be controlled, or may even be accentuated, by chlorine. It works well in removing hydrogen sulfide, iron and manganese. If it is not completely successful in removing tastes and odors, it can be used along with activated carbon. When added to water permanganate turns the water purple, and so it should be fed as early in the treatment process as possible to to allow completion of the oxidation process before water enters the distribution system. In addition to being a great oxidizer of iron and manganese (used by many groundwater systems), it is also effective at controlling zebra mussels and algae in reservoirs.
Testing for Total Coliforms (including fecal coliform and E. Coli)
No more than 5.0% samples total coliform-positive (TC-positive) in a month. (For water systems that collect fewer than 40 routine samples per month, no more than one sample can be total coliform-positive per month.) Every sample that has total coliform must be analyzed for either fecal coliforms or E. coli if two consecutive TC-positive samples, and one is also positive for E.coli fecal coliforms, system has an acute MCL violaton.
Define and explain UFRV.
Unit Filter Run Value - the amount (gallons) of water produced per square foot of filter surface area. A properly designed and operated filter should be able to produce a minimum UFRV of 5000. The goal of filter operations is to produce low-turbidity water during an acceptable UFRV period of operation. Operators typically want to produce a UFRV between 5,000 and 10,000 - Higher UFRV's are dangerous and may lead to catastrophic floc breakthrough. UFRV is one of the main factors that must be monitored to aid in determining backwash frequency.
Define Terminal Head Loss.
Where Head loss is so high that the filter no longer produces water at the desired rate, and may risk air binding.
Giardia lamblia - MCL
Zero - At least 99.9 percent (3-LOG) removal and/or inactivation of Giardia lamblia cysts between a point where the raw water is not subject to re-contamination by surface water runoff and a point downstream before or at the first customer;
Cryptosporidium - MCL
Zero - For systems serving 10,000 or more persons, and for systems serving fewer than 10,000 persons, at least 99 percent (2-log) removal of cryptosporidium between a point where the raw water is not subject to re-contamination by surface water runoff and a point downstream before or at the first customer.
What is Heterotrophic plate count (HPC)?
an analytic method used to measure the variety of bacteria that are common in water. The lower the concentration of bacteria in drinking water, the better maintained the water system is.
The Fluoride level should be...
maintained between 0.8 mg/l and 1.2 mg/l - the MCL is 4.0 as overexposure can cause health issues (teeth mottling, fluorosis).
What is the standard and acceptable Drinking Water pH level in distribution system?
pH between 6.5 - 8.5