Lecture 5_ Waste water Treatment

Pollution Sources and Management

  • Topics Covered:

    • Pollution sources

    • Management of liquid and solid waste

    • Focus on wastewater treatment

Characteristics of Domestic Wastewater

Physical Characteristics

  1. Odour

    • Fresh, aerobic domestic wastewater has a kerosene or freshly turned earth smell.

    • Aged, septic sewage has a pungent rotten-egg smell due to hydrogen sulfide and mercaptans.

  2. Color

    • Fresh sewage: Gray

    • Septic sewage: Black

  3. Temperature

    • Ranges between 10 to 20 °C, usually higher than the supply water.

Weight and Solids

  1. 1 m³ of wastewater weighs approximately 1,000,000 grams, containing about 500 grams of solids.

    • Half of these solids are dissolved solids (e.g., calcium, sodium).

    • 250 grams are insoluble, 125 grams settle in 30 minutes, 125 grams remain suspended, contributing to high turbidity.

Chemical Characteristics of Domestic Wastewater

  1. Complexity

    • Wastewater contains numerous chemical compounds.

  2. COD vs BOD

    • The COD test measures organic matter oxidizable by strong chemical agents, revealing that COD is higher than BOD5.

  3. Total Kjeldahl Nitrogen (TKN)

    • Measures total organic and ammonia nitrogen, indicating nitrogen availability for cell building and oxygen demand.

  4. Phosphorus Forms

    • Phosphorus presents as orthophosphates, polyphosphates, and organic phosphate, grouped as Total Phosphorus.

  5. pH Levels

    • Typical range: 6.5 to 8.5, generally slightly alkaline.

Characteristics of Industrial Wastewater

  1. Variability

    • Industrial settings generate diverse wastewater pollutants that vary significantly by industry.

  2. Pollutant Categories

    • EPA groups pollutants into three categories: conventional, nonconventional, and priority pollutants.

Municipal Wastewater Treatment Systems

Treatment Categories

  1. Primary Treatment

    • Includes bar racks, grit chambers, equalization basins.

    • Removes pollutants that settle or float; about 60% suspended solids and 35% BOD5 are removed.

  2. Secondary Treatment

    • Achieves further removal of soluble BOD5 and suspended solids, utilizing biological processes to enhance natural reactions for degradation.

    • May remove over 85% of BOD5 and suspended solids but is inadequate for nitrogen, phosphorus, or heavy metals.

  3. Advanced Wastewater Treatment (AWT)

    • Applied when secondary treatment is insufficient, involving chemical treatment and filtration, with the potential to remove 99% of many pollutants.

Unit Operations of Pretreatment

Bar Racks

  1. Purpose

    • Remove large objects that harm WWTP equipment.

  2. Process

    • Mechanically cleaned, solid materials transferred to landfills.

Grit Chambers

  1. Definition

    • Removes dense materials like sand and silt to prevent damage.

  2. Types

    • Velocity-controlled, aerated, and constant-level sedimentation.

Equalization

  1. Purpose

    • Enhances the effectiveness of subsequent treatments by regulating flow rates at WWTPs.

  2. Method

    • Large basins collect wastewater, ensuring constant flow to treatment plant.

Primary Treatment

  1. Description

    • Sedimentation tanks remove light organic solids, producing raw sludge.

    • Skimmers remove floating materials like grease.

Unit Processes of Secondary Treatment

  1. Objective

    • Remove soluble BOD and further reduce suspended solids using various biological approaches such as activated sludge and trickling filters.

Wastewater Microbiology

Role of Microorganisms

  1. Stabilization of Organic Matter

    • Microorganisms convert organic matter into gas and protoplasm.

    • Protoplasm must be removed to achieve complete treatment.

Classification by Energy and Carbon Source

  1. Heterotrophic vs Autotrophic

    • Heterotrophs use organic material for carbon and energy, while autotrophs use CO2.

    • Phototrophs and chemotrophs defined by their energy source.

Microbial Classification by Oxygen Use

  1. Aerobes

    • Require oxygen; processes are aerobic.

  2. Anaerobes

    • Cannot survive with oxygen (decompose in absence) and include facultative types that adapt to oxygen presence or absence.

Microbes of Interest in Wastewater Treatment

  1. Bacteria

    • Most abundant microorganisms; favored conditions for chemoheterotrophs.

  2. Fungi

    • Multicellular, nonphotosynthetic; thrive in nitrogen-deficient environments.

  3. Algae

    • Produce dissolved oxygen during photosynthesis; important for overall oxygen balance.

  4. Protozoa

    • Bacteria consumers, beneficial for maintaining effluent quality.

  5. Rotifers and Crustaceans

    • Indicators of high dissolved oxygen and low organic matter.

Bacterial Biochemistry

  1. Metabolism

    • Comprises catabolism (energy release) and anabolism (cell synthesis).

  2. Decomposition Types

    • Defined by available electron acceptors: aerobic, anoxic, and anaerobic.

Aerobic Decomposition

  1. Condtions

    • Requires molecular oxygen; produces CO2, water, and new cells.

    • Efficient for dilute wastewater (BOD5 < 500 mg/L) due to rapid decomposition.

Anoxic Decomposition

  1. Process

    • Uses nitrate as an acceptor, producing nitrogen gas and influencing nitrogen removal in treatment processes.

Anaerobic Decomposition

  1. Conditions

    • BOD5 > 1,000 mg/L suited for anaerobic digestion; stabilizes sludge with minimal biomass production.

Representative End Products

  • Differentiation between aerobic, anoxic, and anaerobic processes results in varying end products such as ammonia, methane, and CO2.

Population Dynamics

  1. Definition

    • Refers to species competition and success rates in treatment systems, expressed through microorganism mass.

Activated Sludge Process

  1. Overview

    • A biological technique involving mixing wastewater with sludge in an aeration process to grow microorganisms.

  2. Functionality

    • Microorganisms clump to form activated sludge for effective waste degradation.