Comprehensive Study Guide to Municipal Water Quality Control and Hazardous Waste Management

Fundamental Objectives of Municipal Water Quality Control

• The Primary Goal: The central objective of municipal water and wastewater management is to break the carrier-feces-water-victim sequence. This intervention is essential to prevent waterborne disease outbreaks.
• The Dual-System Approach: This goal is achieved through two distinct systems that function in tandem:
  • System 1 (Drinking Water System): tasked with collecting and treating raw water from the environment to ensure it is safe for distribution to homes and businesses.
  • System 2 (Wastewater System): tasked with collecting dirty water after usage, cleansing it of pollutants, and safely releasing it back into natural water bodies.

The Safe Drinking Water Act (SDWA)

• Core Purpose: This legislation ensures the protection of drinking water quality according to specific national standards in the United States.
• Applicability: The SDWA applies to all public water systems serving 15 or more outlets and more than 25 customers. This scope covers approximately 90% of the U.S. population.
• Regulatory Oversight (EPA): System operators must continuously monitor and treat water to comply with Environmental Protection Agency (EPA) standards.
• Legislative Amendments:
  • 1986 Amendment: Mandated that all systems using surface water must perform filtration and disinfection. It also implemented a ban on lead in plumbing; current standards require solder to contain less than or equal to $0.2\%$ lead.
  • 1996 Amendment: Required water systems to provide customers with an annual water quality report. It also introduced a requirement for the EPA to perform cost-benefit analyses to determine if the health benefits of new rules justify their financial costs.
  • 2002 Amendment: Incorporated security measures designed to protect water supplies from intentional attacks or tampering.

Drinking Water Standards

• Primary Standards: These are health-related criteria that are enforceable by law. They target contaminants that can cause adverse health effects.
  • Microbiological Contaminants: Contaminants caused by pathogenic microorganisms, such as bacteria, inhabiting the water supply.
  • Maximum Contaminant Level (MCL): The highest concentration of a chemical allowed in drinking water. For example, the Arsenic Limit is set at $0.010\,mg/L$.
  • Treatment Technique (TT): A mandatory treatment step used when a pollutant is too difficult or expensive to measure directly. For instance, instead of counting exact virus numbers, the law mandates filtration.
  • Maximum Contaminant Level Goal (MCLG): Non-enforceable goals set at levels where no known or anticipated health effects occur, including a margin of safety. These are set regardless of cost or technological feasibility. For carcinogens (cancer-causing chemicals), the MCLG is always set to zero.
• Secondary Standards: These are non-enforceable guidelines regarding the aesthetic and non-aesthetic qualities of water.
  • Aesthetic Characteristics: Includes taste, odor, and color.
  • Non-Aesthetic Characteristics: Includes properties such as corrosivity and hardness.

Chemical and Radical Contaminants

• Inorganic Chemicals: Includes highly toxic metals. Excessive levels can lead to conditions such as methemoglobinemia, also known as "blue-baby syndrome."
• Fluoride: While added intentionally to water to prevent dental caries (cavities), excessive exposure can result in the mottling of teeth.
• Organic Chemical Contaminants:
  • Synthetic Organic Chemicals (SOCs): Man-made compounds used in agriculture and industry, primarily as insecticides and herbicides.
  • Volatile Organic Chemicals (VOCs): Synthetic chemicals that evaporate easily at room temperature. Examples include glues, paint thinners, and industrial degreasers.
  • Disinfectant Byproducts (DBPs): Toxic products formed when disinfectants react with other chemicals naturally present in the water.
• Radionuclides (Radiation):
  • Natural Sources: Substances like radium-266 and radon, which are commonly found in groundwater.
  • Man-made Sources: Substances like strontium from nuclear testing fallouts.
  • Radon Specifics: A colorless, odorless gas found in groundwater; it poses a significant risk when it escapes into the air, as inhalation can cause lung cancer.

The Clean Water Act (CWA) and Wastewater Standards

• The Clean Water Act: The primary law governing wastewater disposal, regulating how treated wastewater is discharged into rivers, lakes, and coastal waters to protect aquatic ecosystems.
• Biochemical Oxygen Demand (BOD) Issues: If wastewater contains excessive organic matter, microbes will consume the dissolved oxygen in the water to break it down. This depletion of oxygen can suffocate fish and damage aquatic life.
• NPDES Permit: The National Pollutant Discharge Elimination System forces dischargers to monitor water and meet strict cleanliness limits.
• Indicator Organisms: Testing for every pathogen is too expensive. Instead, scientists use Coliform Bacteria as an indicator.
  • Coliforms: Harmless bacteria found in massive quantities in human and animal feces. Their presence in drinking water indicates the likely presence of dangerous pathogens.
  • Large System Sampling: No more than $5\%$ of monthly samples may test positive for coliforms.
• Limitations of Coliform Testing:
  • Survival: Non-bacterial pathogens like Giardia and Cryptosporidium survive longer in nature than coliforms.
  • Disinfection Resistance: Chlorine easily kills coliforms, but some viruses and protozoa are tougher. A sample may have zero coliforms but still contain active pathogens.
• EPA Log-Removal Rules:
  • Enteric Viruses: Requirement of 99.99% (4-log) removal.
  • Giardia: Requirement of 99.9% (3-log) removal.
  • Cryptosporidium: Requirement of 99% (2-log) removal.

Sewer Systems and Industrial Wastewater

• Industrial Wastewater Options: Industries must either clean water themselves before direct release or provide "pretreatment" (partial cleansing) to remove toxins before sending it to city sewers.
• Combined Sewer Systems (Older Cities): Rainwater and household sewage share the same pipes. During heavy rain, the system can overflow, releasing raw sewage directly into local waterways (Combined Sewer Overflow). Cities may build massive underground reservoirs to hold storm water until it can be pumped to a treatment plant.
• Separated Sewer Systems (Newer Cities): Prevents treatment plant flooding but leaves street runoff untreated.
  • Sanitary Sewers: Carry toilet and sink water to the treatment plant.
  • Storm Sewers: Carry rainwater, oil, metals, and trash directly to local rivers.

Water Treatment Processes

• Sources of Drinking Water:
  • Surface Water: Rivers, lakes, and reservoirs. High in sediments, organic matter, and microbes. Used primarily by large cities.
  • Groundwater: Underground wells. High in dissolved minerals (calcium, iron, manganese). Used primarily by small towns and rural areas.
• Typical Surface Water Treatment Steps:
  1. Primary Sedimentation: Heavier particles sink.
  2. Rapid Mixing and Coagulation: Chemicals are added to help small particles stick.
  3. Flocculation: Gentle mixing to form large clumps (flocs).
  4. Secondary Sedimentation: Flocs settle out.
  5. Filtration: Removes fine particles.
  6. Sludge Processing: Disposal of collected solids.
  7. Disinfection: Kills microorganisms.
• Typical Groundwater Treatment Steps:
  1. Aeration: Removes objectionable gases.
  2. Flocculation: Particles are clumped together.
  3. Sedimentation: Solids settle.
  4. Recarbonation: Adjusts pH and hardness.
  5. Filtration: Final particle removal.
  6. Disinfection: Microbiological safeguard.
  7. Solid Processing: Solids removal.

Engineering Principles in Treatment

• Sedimentation: Uses gravity tanks (clarifiers) to remove floating and settling solids.
  • Governed by Stokes' Law involving Drag Force and Critical Settling Velocity.
• Coagulation and Flocculation: Neutralization of electrical charges on Colloids (fine particles with net negative charges that repel each other).
• Variables: Mixing Intensity ($s^{-1}$), Floc Volume Fraction, and Flocculation Rate Constant.
• Filtration: Water passes through sand, gravel, or coal. It relies on adsorption rather than just physical straining because filter openings are often larger than the particles.
• Disinfection Objectives:
  • Primary Disinfection: Kills pathogens currently in the water.
  • Secondary Disinfection: Prevents the regrowth of pathogens in the distribution system.
• Hardness and Alkalinity: Adjusted to manage multivalent cations like calcium and magnesium.

Wastewater Treatment Phases

• Primary Treatment (Physical):
  • Utilizes screening (bars spaced $2-7\,cm$ apart), skimming, and sedimentation.
  • Removes approx. $35\%$ of BOD and $60\%$ of suspended solids.
  • Does not remove nutrients, leading to potential Eutrophication (excessive algae growth from nutrient enrichment).
• Secondary Treatment (Biological):
  • Removes approx. $90\%$ of BOD and suspended solids.
  • Suspended Growth Treatment: Microbes are suspended in water.
    • Activated Sludge: Mixture of wastewater and biological sludge aerated in tanks and then settled in a secondary clarifier.
    • Membrane Bioreactors: Submerged hollow fiber membranes replace the secondary clarifier.
    • Aerated Lagoons/Oxidation Ponds: Use mechanical aerators or natural photosynthesis; ponds are typically $1\text{ to }2\,m$ deep.
  • Attached Growth Treatment: Microbes grow on stationary surfaces.
    • Trickling Filters: Wastewater sprays over rocks or plastic from a rotating arm.
    • Rotating Biological Contactors (RBC): Series of circular plastic disks (approx. $3.6\,m$ diameter) on a rotating shaft.
• Sludge Treatment: Focuses on reducing volume and stabilizing organic matter before disposal.

Nutrient Removal and Microbial Kinetics

• Nitrogen Removal:
  • Nitrification: Aerobic process converting ammonia to nitrate. Nitrosomonas converts ammonia to nitrite; Nitrobacter oxidizes nitrite to nitrate.
  • Denitrification: Nitrate is converted to nitrogen gas ($N_2$) in an environment without oxygen (anaerobic/anoxic).
• Phosphorus Removal: Necessary to prevent eutrophication in receiving waters.
• Microbial Kinetics: Measures the rate at which microorganisms consume the Substrate (organic matter).
  • Measured using Volatile Suspended Solids (VSS), determined by the mass difference after drying at $105^{\circ}C$ and burning at $500^{\circ}C$.
  • Key formulas include the Monod Equation and substrate utilization rates.

Hazardous Waste Management

• Definitions:
  • Hazardous Waste: Materials that increase the risk of death, illness, or environmental hazard.
  • Hazardous Substance: Materials that still have value and can be reused or processed (e.g., stored solvents).
• Major Disasters:
  • Love Canal, NY: Chemicals leaked into homes from an abandoned site.
  • Times Beach, MO: Dioxin-contaminated oil sprayed on roads; led to town evacuation.
• Legislation:
  • CERCLA (1980): Also known as Superfund, it manages the cleanup of old contaminated sites and holds parties accountable.
  • TSCA: Regulates individual chemicals throughout their lifecycle.
  • RCRA (1976): Establishes Cradle-to-Grave Management for hazardous waste handling.
  • HSWA (1984): Strengthened RCRA by banning untreated hazardous waste from landfills and requiring double-liner systems and underground tank monitoring.
• EPA Classifications:
  • Listed Wastes: Explicitly named by the EPA.
  • Characteristic Wastes: Defined by properties: Ignitability (flash point $\le 60^{\circ}C$), Corrosivity ($pH < 2$ or $> 12.5$), Reactivity (unstable/explosive), and Toxicity (harmful substances like lead/mercury).

Waste Treatment Technologies

• Management Priorities: 1. Eliminate, 2. Reduce, 3. Recycle/Reuse, 4. Treatment, 5. Disposal.
• Brownfields Initiative (1995): Encourages redevelopment of abandoned, contaminated properties.
• Treatment Categories:
  • Physical: Sedimentation, Aeration (Air Stripping), and Monitored Natural Attenuation (MNA).
  • Chemical: Neutralization, Precipitation (Metal or Sulfide), and Redox (Oxidation/Reduction).
  • Waste Incineration: Controlled burning via Liquid Injection or Rotary Kilns.
  • Land Disposal: Includes Surface Impoundments and Underground Injection (disposing waste into deep, isolated wells with pressure gauges and sealing packoffs).