Water Treatment and Distribution Fundamentals

Water Quality Regulations and Treatment Standards

• Safe Drinking Water Act (SDWA) Definitions

  • A public water system is defined as a supply of piped water for human consumption that has at least $15$ service connections or serves $25$ or more persons for at least $60$ or more days each year.

• Surface Water Treatment Rule (SWTR) Requirements

  • Water systems must achieve at least $4\text{-log}$ removal and/or inactivation of viruses between the point where raw water is not subject to recontamination by surface runoff and a point before or at the first customer.
  • Continuous chlorine residual monitoring is required where water enters the distribution system when the population served is greater than $3300$ people.
  • Regulations require that surface water systems maintain specific $C \times T$ values (concentration times contact time) before treated water reaches the first customer.
  • Chloramine disinfection is a treatment technology that is not specifically specified by the Surface Water Treatment Rule.

• Total Coliform Rule (TCR)

  • This rule directly guards against the presence of Escherichia coli in the water supply.
  • For systems collecting at least $40$ samples per month, they remain in compliance with the Maximum Contaminant Level (MCL) if no more than $5\%$ of the total coliform samples are positive.

• Disinfection Byproducts (DBP) and Total Organic Carbon (TOC)

  • The Stage 1 Disinfectants and Disinfection Byproducts Rule (DBPR) established an MCL for Total Trihalomethanes (TTHM) at $0.08\,mg/L$.
  • The Stage 1 DBPR established an MCL for Haloacetic Acids (HAA5) at $0.06\,mg/L$.
  • Under enhanced coagulation requirements of the DBPR, treatment plants must remove specific percentages of Total Organic Carbon (TOC) based on source water TOC and alkalinity levels.
  • Public water systems can comply with TOC removal requirements if the source water TOC level, calculated quarterly as a running annual average, is less than $2.0\,mg/L$.
  • A system using conventional filtration does not have to use enhanced coagulation if the treated water quarterly running average TOC is less than $2.0\,mg/L$.

• Public Notification and Reporting

  • A regulated organic contaminant concentration that exceeds the MCL is categorized as a Tier 2 violation, requiring public notification within $30$ days.
  • Community water systems serving more than $100,000$ people must post their Consumer Confidence Report (CCR) on a publicly accessible website.

• Maximum Contaminant Level Goals (MCLG)

  • The MCLG for substances that are expected carcinogens is set at zero.

Microbiological and Chemical Sampling and Analysis

• Sampling Protocols and Locations

  • Sampling points for regulated organics (excluding THMs) in a community water system are located at the entry points to the distribution system.
  • Sampling points for natural radionuclides are located at each entry point to the system.
  • Turbidity sampling points are located where water enters the distribution system, including all filter effluents of a surface water treatment plant.
  • Disinfection residuals must be collected at the same locations in the distribution system as coliform samples.

• Laboratory Methods for Coliforms

  • A grab sample should always be collected when determining the presence of coliform bacteria.
  • Sodium Thiosulfate ($Na_2S_2O_3$) is the chemical element used to remove chlorine from water samples.
  • The Three steps involved in the Multi-Tube Fermentation (MTF) method are the Presumptive, Confirmed, and Completed tests.
  • In the MTF method, Green Lactose Bile Broth is used as the culture media for the confirmed test.
  • For the Presence-Absence (P-A) test, all positive samples must be confirmed using Brilliant Green Bile tubes.
  • A typical coliform colony in the membrane filter method appears pink to dark red with a green metallic sheen.

• Inorganic and Heavy Metal Analysis

  • Water to be analyzed for inorganic metals should be acidified with concentrated nitric acid ($HNO_3$).
  • An Atomic Absorption Spectrophotometer is the special photometer used to analyze for heavy metals in water.
  • Dissolved solids at a level of $4000\,mg/L$ are considered the first level unfit for human consumption.

Disinfection and Corrosion Control Chemicals

• Disinfection Efficacy

  • Ozone is the disinfectant that works best against Cryptosporidium.
  • Operators must balance satisfying regulations for chlorinated organic compounds while meeting disinfection limits.

• Water Softening and Stabilization

  • When water high in calcium bicarbonate ($Ca(HCO_3)_2$) is softened by ion exchange, sodium bicarbonate ($NaHCO_3$) remains in the product water.
  • The Langelier Index indicates water is scale-forming if the pH of the water sample is greater than the pH of saturation ($pH_s$).
  • The saturation point of Calcium Carbonate ($CaCO_3$) primarily depends upon pH.
  • Lime (Unslaked lime or Quicklime) is commonly used for corrosion control because it adjusts both pH and alkalinity. It is the most common chemical for this purpose because it is available, inexpensive, and easy to feed.
  • Lime increases pH, hardness, and alkalinity.

• Corrosion and Chemical Side Effects

  • Tuberculation refers to the buildup of corrosion products or uncontrolled scale deposits that reduce pipeline capacity and increase flow resistance.
  • Zinc is the metal most likely to corrode compared to tin or aluminum.
  • The principal source of excessive lead and copper in customer water is the corrosion of household plumbing.
  • The action level for copper is $1.3\,mg/L$.
  • Polyphosphate, used for stabilization, acts as a bacterial nutrient.
  • Wastewater discharge requirements could be exceeded if Hexametaphosphate is used for corrosion control in the water system.

Distribution System Management and Pipe Infrastructure

• Valves and Meters

  • A bypass valve is typically used in conjunction with a gate valve.
  • A pinch valve is particularly useful for throttling the flow of corrosive liquids.
  • Water meter pits are usually employed in cold climates.
  • In areas where ground frost is expected, riser pipes in a meter pit should be at least $1-2\,inches$ away from any wall of the meter box to prevent freezing.

• Piping and Joints

  • A Ball and Socket Joint is available in both bolted and boltless flexible pipe joint designs.
  • A push-on joint permits flexible pipe alignment, is inexpensive to manufacture, and is easy to assemble.
  • New Polyvinyl Chloride (PVC) pipe has a C-value of approximately $150+$.
  • Polyethylene pipe is subject to permeation by fuel oil.

Coagulation, Flocculation, and Sedimentation Processes

• Chemical Treatment Selection

  • Factors to consider when selecting treatment chemicals include pH, temperature, alkalinity, TOC, and color.
  • The optimal pH range for removing particulate matter when using alum as a coagulant is $6.5$ to $7.2$.
  • Ferric sulfate has the advantage over alum of producing a more dense floc.
  • Low turbidity levels make it more difficult to form proper floc.
  • Water temperatures approaching the freezing point slow down coagulation and flocculation because floc settles slower and the water is denser.

• Process Dynamics

  • Van der Waals forces pull particles together once they have been destabilized during coagulation.
  • Jar tests are used to determine coagulant effectiveness and are typically expressed in units of $mg/L$.
  • A common mistake in the flocculation process is allowing for excessive flocculation time.
  • The multi-barrier approach (coagulation, flocculation, sedimentation, and filtration) is the probable solution if enteric disease-causing protozoans are found in plant effluent.

• Sedimentation Basin Operation

  • Components of a rectangular sedimentation basin include baffles, adjustable weirs, a sludge pump, and a collector drive.
  • Poor inlet baffling is the major cause of short-circuiting in a sedimentation basin.
  • Conventional sedimentation provides less than $0.5\text{-log}$ removal of Cryptosporidium oocysts.
  • Dissolved air flotation is particularly effective for removing algae.
  • The maximum weir loading for light alum floc in solids contact basins is $10\,gpm/ft$.
  • Turbidity is the primary test used to indicate poor sedimentation.
  • Lime sludge cannot be discharged to a sanitary sewer because its deposits may build up and block the sewers.

Water Utility Operations and Hydraulics

• Hydraulic Definitions

  • Head Loss: The energy used by water when moving from point to point.
  • Static Suction Lift: The difference in water placement.
  • Power: Work done in a given time.
  • Conductivity: A measure of the ability of an aqueous solution to carry an electrical current.
  • pH: A measure of the hydrogen ion concentration in water.

• Pump and System Performance

  • A P-Q curve shows the relationship between power and capacity in pump operation.
  • For populations greater than $3300$, the disinfection residual entering the distribution system must not fall below $0.2\,mg/L$ for more than $4\,hours$.

• Operational Calculations

  • For an ion exchange softener treating a flow rate of $125\,gpm$ with a capacity of $297,000\,gallons$, the operating time is calculation as follows:     $Operating\,Time = \frac{297,000\,gallons}{125\,gpm \times 60\,min/hr} = 39.6\,hr$

Water Calculations and Chemical Formulas

• Chemical Concepts

  • Carbon Dioxide ($CO_2$) is colorless, odorless, and occurs naturally in all water.
  • Molarity: The number of moles of solute per liter of solution.
  • Normality: The number of equivalent weights of solute per liter of solution.
  • A solution consists of a solvent and a solute.
  • The molecular weight must be determined as the first step in calculating the percent by weight of an element in a compound.

• Atomic Counts

  • The chemical formula for Calcium Carbonate is $CaCO_3$.
  • In the formula for Calcium Bicarbonate, $Ca(HCO_3)_2$, there are $6$ atoms of oxygen.

Legal Doctrines and Watershed Management

• Water Rights Doctrines

  • Riparian Doctrine: The rule of reasonable sharing of water.
  • Absolute Ownership: The rule that landowners can capture all the water under their land.
  • Reasonable Use: The rule that a landowner has the right to groundwater as long as it does not harm a neighbor.
  • Appropriation-Permit Systems: Systems where water rights are based on priority and who has used the water for the longest time.

• Source Water Challenges

  • If algae are clogging filters at a water plant, the probable solution is to control nutrients in the source water.
  • For conventional plants in agricultural areas dealing with high nitrates, the best long-term course of action is to manage the watershed to prevent nitrates from entering the water system.

Questions & Discussion

• Q: Benchmarking example?

  • A: Determining the lowest monthly average during a $12$-month monitoring period of Giardia and virus inactivation is an example of benchmarking.

• Q: Scale forming indicator?

  • A: If the pH is higher than the $pH_s$, the Langelier Index indicates the water is scale-forming.

• Q: Chlorine removal chemical?

  • A: Sodium Thiosulfate ($Na_2S_2O_3$) is used to remove chlorine for sampling purposes.

• Q: Filter backwash recycle rule application?

  • A: The Filter Backwash Recycle Rule applies to systems of all sizes.