Wastewater Treatment iCollege (3)

Chapter 6 Study Questions

• EPA Requirements for BOD and SS

  • Must be less than or equal to 30 mg/L BOD and 30 mg/L SS leaving secondary treatment facilities.

• Path of Wastewater through Treatment Plant

  • Preliminary Treatment: Screening of large solids, grit removal.

  • Primary Treatment: Settling of materials, removal of primary sludge.

  • Secondary Treatment: Biological processes to reduce organic matter.

  • Tertiary Treatment: Further purification and nutrient removal.

  • Disinfection: Final treatment before effluent release.

• Treatment Processes

  • Preliminary Treatment: Removal of trash, grit.

  • Primary Treatment: Settling, initial reduction of BOD and SS.

  • Secondary Treatment: Biological processes (activated sludge, trickling filters).

  • Tertiary Treatment: Advanced filtration, nutrient removal.

  • Disinfection: Ensures pathogen removal, importance for health.

• Comparing Trickling Filters and Activated Sludge

  • Trickling Filters:

    • Advantages: Less sludge, cost-effective, adaptable.

    • Disadvantages: More land required, odor issues.

  • Activated Sludge:

    • Advantages: Higher removal efficiency, less land needed.

    • Disadvantages: More secondary sludge, higher operational costs.

  • Situational Preference:

    • Trickling filters preferred in land-abundant areas.

    • Activated sludge preferred in compact urban settings.

• Biological vs. Chemical Processes

  • Biological: Secondary treatment, nitrogen removal.

  • Chemical: Phosphorus removal, disinfection.

• Difference Between Primary and Activated Sludge

  • Primary sludge: Material settled during primary treatment.

  • Activated sludge: Mixed microorganisms in secondary treatment.

• Fate of Sludge

  • Stabilization through anaerobic digestion, potential reuse as fertilizer.

• Effluent Post-Treatment

  • Released into water bodies after meeting quality standards.

• Nitrogen Removal in Tertiary Treatment

  • Biological (nitrification/dentrification) and chemical processes (ammonia stripping).

• Phosphorus Removal Techniques

  • Chemical precipitation, ion exchange, reverse osmosis.

• Disinfection Methods

  • Uses chlorine, UV radiation, or ozone; critical for removing pathogens.

• Unconventional Sewage Treatment Strategies

  • Examples: Constructed wetlands, eco-engineering systems like the WaterHub at Emory University.

The Clean Water Act (CWA)

• Overview: Establishes regulations on pollutant discharges into US waters.

• Requires secondary treatment in municipal plants, potential for tertiary treatment.

Wastewater Treatment Plant Overview

• Components:

  • Secondary clarifiers, bioreactors, pump stations.

  • UV disinfection and nutrient recovery facilities.

  • Primary clarifiers and anaerobic digesters for sludge treatment.

Average Concentrations in Wastewater Components**

• Reports average concentrations of contaminants in urban runoff, raw sewage, and rainfall:

  • SS: Urban runoff (227 mg/L), Raw Sewage (200 mg/L), Rainfall (13 mg/L)

  • COD: Urban runoff (111 mg/L), Raw Sewage (350 mg/L), Rainfall (16 mg/L)

  • BOD: Urban runoff (17 mg/L), Raw Sewage (200 mg/L)

  • Total N: Urban runoff (3.1 mg/L), Raw Sewage (40 mg/L)

  • Total P: Urban runoff (0.36 mg/L), Raw Sewage (10 mg/L)

Wastewater Treatment Basics

• Define Wastewater Treatment: Accelerates natural purification processes using physical, biological, and chemical means.

Conventional Wastewater Treatment Process

• Involves:

  • Preliminary, Primary, Secondary, and Tertiary Treatments.

  • Regulatory standards for discharge to surface waters.

Treatment Process Components**

• Preliminary Treatment: Large solids removal via screens.

• Primary Treatment: Settling tanks to separate solids from wastewater.

• Secondary Treatment: Aerobic processes to reduce BOD and SS.

• Tertiary Treatment: Further filtration and disinfection processes.

Trickling Filters vs. Activated Sludge**

• Trickling Filters Dynamics:

  • Utilizes inert substrate for microbial growth and oxidation of organic waste.

• Activated Sludge Dynamics:

  • Continuous flow with aeration creating conditions favorable for microorganisms, producing flocculent aggregates.

Phosphorus and Nitrogen Removal**

• Phosphorus: Chemical precipitation techniques.

• Nitrogen: Removal techniques include ammonia stripping and biological processes transforming ammonium to nitrogen gas.

Sludge Treatment Process**

• Critical methods for sludge treatment such as anaerobic digesters reducing volume and treating organic material.

• Overall goal: Decrease putrescibility and enable disposal or reuse.

Non-Traditional Water Treatment Strategies**

• Constructed Wetlands: Environmental benefits through natural treatment processes and habitats.

• WaterHub at Emory University: On-site recycling system for wastewater treatment, emphasizing sustainability and reducing municipal water use.