Water Pollution Control and Wastewater Treatment

Control of Water Pollution

• Measures to control water pollution include minimizing water requirements, reusing water with or without treatment, and maximizing water recycling after treatment.
• Minimizing waste water discharge is also crucial.
• Modern measuring devices are essential for tracking water usage, though currently, an estimated 30% of global water isn't tracked. Many existing systems are outdated and rely on manual meter readings.

Waste Water Treatment

• Surface water and groundwater are often critical for human use, especially in cities for households, industries, and firefighting.
• Often, large quantities of water are used for drinking, and it's important to consider if using this high-quality water for other purposes like irrigation is efficient.
• Dual water supply systems are being considered. One high-quality supply for drinking and personal use, and another lower-quality supply for things like irrigation, firefighting.

Wastewater Treatment Processes

• Pretreatment: Aeration helps release gases (like hydrogen sulfide), and physical methods remove solid materials (like grit).
• Sedimentation: Suspended solids settle out. This produces "Primary sludge."
• Biological Treatment: Microorganisms digest organic material in wastewater producing "Secondary sludge".
• Sedimentation: The microorganisms settle out.
• Specialized Treatment: May be used to remove remaining contaminants like phosphorus or nitrogen.
• Disinfection: Removes contaminants, and prepares for discharge into receiving water

The Sludge

• Wastewater treatment discharges solids into a watercourse as a byproduct—"sludge."
• Sludge is primarily suspended solids (SS) not completely removed during primary treatment.
• Typically, about 60% of SS becomes raw primary sludge.
• Raw primary sludge is usually about 96% water and contains pathogenic organisms.

Sludge Disposal Classifications (EPA Standards)

• "A" sludge: Completely disinfected and has low metal content.
• "B" sludge: Treated to a pathogen level reached after approximately 30 days of anaerobic digestion
• "C" sludge: Untreated.

Sludge Treatment

• Sludge treatment and disposal accounts for over 50% of treatment costs in secondary plants, making it vital for efficient wastewater plants.
• Sludge disposal is difficult because it is visually unappealing, potentially harmful, and has a high water content. Improved disposal methods could save money and reduce environmental issues.

Wastewater Treatment Process Flow

• Wastewater goes through a primary treatment stage using screens, grit removal, and primary clarifiers.
• Secondary treatment using aeration and clarifiers follows.
• Then, tertiary treatment and disinfection occur.
• Finally, discharge goes to surface water.

Thermal Pollution

• Thermal pollution is defined as adding excessive and undesirable heat to water, which harms humans, animals, and aquatic life, and disrupts aquatic community activities.

Sources of Thermal Pollution

• Nuclear power plants
• Coal-fired power plants
• Industrial effluents
• Domestic sewage
• Hydroelectric power

Nuclear Power Plant Impacts

• Emissions from nuclear reactors and processing cause increased water temperatures.
• Nuclear processing is a primary contributor to heat in aquatic environments.
• Radioactive materials (H-3, C-14, Fe-59, Co-60) and corrosion products are in the liquid radioactive water.
• Accidental leaks in nuclear reactors raises water temperatures which hurts aquatic flora and fauna.
• Heated effluents are discharged at 10°C higher than the natural temperature in receiving waters.

Coal Fired Power Plant Impacts

• Condenser cooling uses nearby water (lake or river), which then raises the temperature of the water by about 15°C.
• The heated water reduces dissolved oxygen content and kills fish and other marine organisms.

Industrial Effluent Impacts

• Industries like textiles, paper, pulp, and sugar release heat into the water
• Cooling water used in steam-electric power plants using turbo generators has higher temperatures from 6°C to 9°C than the receiving water.

Domestic Sewage Impacts

• Domestic sewage is commonly discharged into waterways (rivers, lakes, canals, streams), often without treatment.
• Municipal sewage discharge has a higher temperature than natural water temperatures.
• Increased temperatures of receiving water reduces the dissolved oxygen level which negatively impacts aquatic life, and releases foul-smelling gases.

Hydroelectric Power Impacts

• Hydroelectricity uses flowing water to generate electricity.
• Hydroelectric power may cause negative thermal loading in water systems.
• Other industries that use cooling also contribute to thermal loading.

Thermal Pollution Impacts:

• Reduction in Dissolved Oxygen (DO): Higher temperatures reduce the amount of dissolved oxygen in water.
• Change in Water Properties: Temperature affects water's viscosity, vapour pressure, and solubility of gases, which impacts aquatic organisms, food supply, and the settling speed of solid particles.
• Interference with Biological Activities: Temperatures disrupt metabolic rates, respiration, digestion, excretion, and overall development in aquatic organisms. Reproduction in fish (nest building, spawning, hatching) is also disrupted, with excess heat killing eggs laid.
• Increased Vulnerability to Disease: Higher temperatures speed up the growth/activity of disease-causing microorganisms, making aquatic organisms more vulnerable.

Controlling Thermal Pollution

• Cooling Towers: Transfer heat from cooling water to the atmosphere via evaporation.
• Cooling Ponds: These are simpler, dissipating heat to the atmosphere while minimizing water volume.
• Artificial Lakes: Heated water is discharged into a lake, and water is withdrawn at the other end to be cooled. These require continuous rejuvenation to maintain useful temperature.