Wastewater Sludge & Biological Waste Treatment Methods

Wastewater Sludge Treatment: Chemical Processes

Types of Sludge in a Wastewater Treatment Plant (WWTP)

• Primary (Decanting)
• Secondary
• Mixed

Other Sludge in a WWTP

• Fats and Oils
• Separator-Flotation
• Precipitation
• Trickling Filters

Sludge Treatment Goals

• Decrease water content
• Removal of organic matter to the solid phase for easy evacuation from the WWTP

Treatments Used

• Thickening

  • Gravity
  • Flotation

• Stabilization

  • Biological
  • Chemical

• Dehydration

  • Centrifugation
  • Filtration

Thickening Objectives

Reducing the volume of water to be treated in subsequent treatments.

Stabilization Objectives

Elimination of biodegradable organic matter present in the sludge, so that no subsequent decompositions generate odors at the final destination.

Dehydration Objectives

Achieving a suitable dryness in the sludge, which is in the solid phase, which involves the ability to evacuate the sewage plant by truck.

Types of Chemical Processes

• Coagulation and Flocculation

  Chemical treatment is the reaction that occurs by the addition of products to produce a destabilization of colloids by neutralizing the electric charges.

• Neutralization

  Neutralize the wastewater containing acids or alkalis that must be eliminated or adjusted to its pH value before any biological treatment.

• Precipitation

  The solubility product of the salt formed must be as low as possible, at a low cost, and easy to get on the market.

• Redox

Biological Waste Treatments: Anaerobic Processes

Uses

Wastewater with high Biochemical Oxygen Demand (BOD) loads.

Justification

This implies a very high energy consumption and operating costs, as well as impact on installation levels.

Objectives

Disposal of biodegradable organic matter to obtain energy for heating the process.

Fundamentals of Anaerobic Digestion

Anaerobic Digestion Stages

• Hydrolysis: Organic compounds in a solid-state are transformed.
• Acidogenesis: Organic compounds are transformed into CO2.
• Acetogenesis: Acetic acid production.
• Methanogenesis: Methane is obtained from acetic acid.

Factors Affecting the Anaerobic Process

• Temperature
• Time
• Hydraulic Load
• Retention of Volatile Suspended Solids (VSS)
• Gas Generation
• pH
• Presence of Toxic Compounds
• Inhibitors

Types of Digesters

• Plug Flow Digesters

  Its great advantage is its simplicity and functionality, although with low yields. It is a treatment used for livestock waste.

• Mixed Digesters

  They are the easiest to use on a large scale.

• Anaerobic Contact Digesters

• Sludge Bed Digesters

• Anaerobic Filter or Fixed Bed Digesters

  The cell retention time is higher than the hydraulic residence time.

• Expanded or Fluidized Bed Digesters

General Design Rules

Equipment Used in Anaerobic Processes

• Digesters and Mechanical Agitation
• Recirculation Gas
• Recirculation Water
• Energy Recovery from Gases

Other General Design Rules