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.