Thermal Pollution of Water

Thermal pollution refers to degradation of water quality caused by changes to the ambient water temperature. Common causes include the discharge of cooling water by power plants and factories as well as urban stormwater runoff from paved surfaces. Thermal pollution impacts aquatic organisms by exceeding temperature thresholds beyond which physiological processes breakdown.

Sources of Thermal Pollution

The primary sources of thermal pollution are:

• Power Plants – Cooling water discharged from electricity generating stations elevates temperatures of receiving waters.
• Manufacturing – Many industrial processes utilize cooling systems that cycle water back into natural water bodies at temperatures up to 110°F.
• Urban Runoff – Rainwater that flows over hot paved surfaces before entering lakes/streams via storm drains absorbs heat that can stress aquatic life.

Ecological Impacts

Thermal pollution has several damaging ecological effects:

• Thermal Shock – When power plants temporarily shut down, aquatic organisms accustomed to specific temperature ranges can be killed by sudden water temperature changes.
• Metabolic Disruption – Most aquatic organisms including fish, macroinvertebrates and algae thrive in relatively narrow temperature ranges. Exceeding thresholds impairs cell processes.
• Lowered Oxygen Levels – Warmer water cannot hold as much dissolved oxygen, resulting in oxygen deficiency which makes it harder for aquatic animals to breathe.
• Toxicity – Some pollutants become more toxic to aquatic life when water temperature is elevated due to synergistic effects.
• Altered Ecosystems – Increases in tolerated exotic species can outcompete native organisms adapted to historic temperature regimes.

Recovery Factors

Recovery from thermal pollution depends on key factors:

• Rate of Change – Gradual temperature changes allow for better adaptation than sudden shifts.
• Water Body Type – Fast flowing streams dissipate heat quicker while lakes/ponds allow heat accumulation.
• Climate Conditions – Colder regions are more sensitive as species live closer to survival thresholds.

Mitigation Strategies

Methods to control thermal pollution include:

• Cooling Towers – Partial reuse of warmed water for plant cooling to reduce discharged volumes.
• Constructed Wetlands – Engineered wetland systems to naturally cool effluent prior to aquatic release through vegetation transpiration.
• Seasonal Shutdowns – Ceasing plant activity during warmer summer months when potential damage is higher.

Legal Framework

• In India, thermal pollution is mainly regulated under the Water (Prevention and Control of Pollution) Act of 1974 which aims to maintain and restore the wholesomeness of water. The associated Central Pollution Control Board (CPCB) has set industry-specific standards for the discharge of effluents.
• Additionally, the Environment Protection Act of 1986 contains provisions to manage environmental pollution including thermal pollution. Other regulations such as the Coastal Regulation Zone Notification also have implications for thermal discharges.

Regulatory Standards

• The CPCB has laid out temperature increase limits for the discharge of cooling water from power plants and other industries based on the temperature sensitivity of aquatic life in different inland and marine water bodies.
• For example, the standard for rivers, streams and canals less than 10 kilometers from mixing zone in tidal waters is that the temperature should not exceed 5°C over and above the ambient temperature of receiving water bodies.

Compliance Monitoring

The respective State Pollution Control Boards conduct water quality monitoring of receiving water bodies near major thermal point source discharges. Parameters like temperature, pH, oil/grease, ammonia and residual chlorine are analysed on a monthly or quarterly basis. High temperature readings can trigger plant inspections, show cause notices and directions for remedial action. Violations may also involve court cases and financial penalties.