Chapter 9 Industrial Pollution (1)

Module 9: Industrial Pollution

Learning Outcomes

• After viewing this lecture you should be able to:

  • List the major problems associated with industrial wastewater.

  • Explain what the oxygen sag is, what causes it, and why it is problematic for aquatic communities.

  • List general strategies to reduce or eliminate the oxygen sag.

Problems Associated with Industrial Wastewater

• Key issues include:

  • High Biochemical Oxygen Demand (BOD): Measure of the amount of oxygen required to decompose organic matter in water.

  • High Concentration of Suspended Solids (SS): Particles that do not dissolve in water and can cause turbidity.

  • Presence of Toxic Substances: Chemicals that can harm aquatic life and ecosystems.

Sources and Sinks of Dissolved Oxygen (DO) in Rivers

• Sources of DO:

  • Reaeration from the atmosphere

  • Photosynthesis by aquatic plants

  • DO from incoming tributaries or effluents

• Sinks of DO:

  • Oxidation of organic matter and sediments (BOD)

  • Chemical oxidation of organic and inorganic materials (COD)

  • Respiration by aquatic organisms

Biochemical Oxygen Demand & The Oxygen Sag

• Some industrial wastewater (e.g., from:

  • Pulp & Paper

  • Sugar Refineries

  • Food Processing Plants

  • Textiles)

  • Can have exceedingly high BOD levels, leading to a drop in oxygen concentration downstream from discharge sites.

The Oxygen Sag

• Defined as the characteristic decline followed by a rise in oxygen concentration downstream from high BOD discharges.

Oxygen Sag Causes

• Results in changes in aquatic species composition:

  • Clean Zone: Presence of sensitive species (e.g., trout, perch).

  • Decomposition Zone: Increase in rough fish and leeches as oxygen drops.

  • Septic Zone: Further decrease in oxygen leading to absence of fish.

  • Recovery Zone: Oxygen levels improve, allowing sensitive species to return.

Effects of Oxygen Sag on Anoxia

• Oxygen sag may lead to anoxia (depletion of oxygen) from:

  • A single large BOD discharge or a series of smaller discharges in close succession.

Oxygen Demand from Wastewater

• Comparison of oxygen demand of industrial vs municipal wastewater over time.

  • BOD5 for industrial wastewater can be significantly higher.

Solutions to the Oxygen Sag Problem

• Strategies to combat oxygen sag:

  • Oxidize organic matter before discharge, common in sewage treatment plants.

  • Remove suspended solids (SS).

  • Challenges: High BOD and SS may make treatment costs prohibitive, and conventional methods may not adequately remove toxic substances.

  • Aim to minimize waste through less toxic chemicals and improved recycling.

EPA Goals

• Objectives to achieve:

  • Reduction of waste and efficient resource use.

  • Prevention of human and ecosystem exposure to hazardous chemicals.

  • Management of waste and cleanup of chemical releases in an environmentally safe manner.

Case Study: Hawaiian Sugar Industry

• Explore sugarcane growing and processing:

  • Discuss water use at different stages, pollution challenges, and strategies to mitigate pollution.

Key Stages in Sugar Cane Production

1. Field Preparation: Loosening soil, using disease-resistant varieties.

2. Planting & Irrigation: Efficient drip irrigation methods based on monitoring.

3. Crop Maintenance: Manage weeds using limited herbicides.

4. Ripening: Controlled reduction of water and nutrients to increase sugar content.

Water Pollution from Sugar Production

• Pollution problems associated with sugar production observed in tailwater and stormwater runoff:

  • Constituent Concentrations:

    • Fecal coliforms: 1934/100 mL

    • Suspended solids: 843 ppm

    • Settleable solids: 576 ppm

    • COD: 91 ppm

    • Total Nitrogen: 10 ppm

    • Total Phosphorus: 5.5 ppm

Harvesting Effects on Wastewater

• Harvesting processes can contribute undesirable wastewater characteristics due to contamination during loading.

Historical Pollution Issues in Sugar Industry (1966-1968 EPA Studies)

• Observed issues include:

  • Sediment plumes and high total coliform counts.

  • Navigation hazards due to cane trash and bagasse.

  • Sludge affecting benthic communities and corals.

  • Oxygen levels remained adequate despite BOD and COD issues.

Recommendations and Responses for Sugar Industry Pollution

• Recommendations include:

  • No discharge of cane trash/bagasse.

  • Minimize runoff through ponds and reuse strategies.

  • Treat all wastewater before ocean discharge.

Case Study: Pulp and Paper Industry

• Learning Outcomes:

  • Overview of paper production steps and associated water pollution issues.

  • Comparison of pulping processes and their environmental impacts, with focus on kraft vs sulfite processes.

Paper Production Steps:

1. Debarking and Chipping.

2. Pulp Production via mechanical or chemical breakdown.

3. Pulp Treatment (bleaching, additives).

4. Formation and Drying of Paper.

Pulping Methods Impact on Wastewater Quality

• Mechanical vs Chemical pulping:

  • Mechanical produces high yield, lower quality pulp.

  • Chemical methods (sulfite/kraft) produce better quality pulp but generate significant waste.

Effluent Characteristics from Pulp and Paper Mills

• Key issues include:

  • Suspended Solids: Can clog fish gills and disrupt ecosystems.

  • Dissolved Organics: Lead to high BOD, foam, and discoloration.

  • Toxic Chemicals: Result from chemical processes, requiring careful management.

Treatment Solutions for Pulp and Paper Effluents

• Wastewater management includes:

  • Pretreatment to remove grit and adjust pH.

  • Primary treatment via settling.

  • Secondary treatment to reduce BOD and toxicity (with biooxidation lagoons recommended).

  • Tertiary treatment to address dissolved organics, color, and odor.

Additional Solutions

• Shift to oxygen-based bleaching and increased recycling, recognizing limits to recycling efficiency.